Review ArticleCombinatorial Approach to Improve Cancer ImmunotherapyRational Drug Design Strategy to Simultaneously Hit MultipleTargets to Kill Tumor Cells and to Activate the Immune System

Shweta Joshi 1 and Donald L Durden12

1Division of Pediatric Hematology-Oncology Department of Pediatrics Moores Cancer Center University of CaliforniaSan Diego CA USA2SignalRx Pharmaceuticals Inc San Diego CA USA

Correspondence should be addressed to Shweta Joshi shjoshiucsdedu

Received 24 September 2018 Revised 15 December 2018 Accepted 1 January 2019 Published 3 February 2019

Academic Editor Reza Izadpanah

Copyright copy 2019 Shweta Joshi and Donald L Durden This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Cancer immunotherapy including immune checkpoint blockade and adoptive CAR T-cell therapy has clearly established itself asan importantmodality to treat melanoma and other malignancies Despite the tremendous clinical success of immunotherapy overother cancer treatments this approach has shown substantial benefit to only some of the patients while the rest of the patientshave not responded due to immune evasion In recent years a combination of cancer immunotherapy together with existinganticancer treatments has gained significant attention and has been extensively investigated in preclinical or clinical studies Inthis review we discuss the therapeutic potential of novel regimens combining immune checkpoint inhibitors with therapeuticinterventions that (1) increase tumor immunogenicity such as chemotherapy radiotherapy and epigenetic therapy (2) reversetumor immunosuppression such as TAMs MDSCs and Tregs targeted therapy and (3) reduce tumor burden and increase theimmune effector response with rationally designed dual or triple inhibitory chemotypes

1 Introduction

The ultimate aim of immunotherapy is to boost the bodyrsquosimmune system to destroy tumor cells and to provide adurable antitumor immune response The strategy of usingmonoclonal antibodies against two distinct inhibitory recep-tors on T-cells PD1 and CTLA-4 is a major breakthroughin the field of cancer immunotherapy The efficacy of thisstrategy was first established in patients with metastaticmelanoma based on the antitumor immune response andincreased overall survival rates of patients treated withipilimumab a monoclonal antibody targeting human CTLA-4 [1] The remarkable antitumor activity of PD-1PDL-1 inhi-bition in melanoma renal cell carcinoma and NSCLC leadto regulatory approval of increasing list of anti-PD1PDL1antibodies in hematological malignancies and various othersolid cancers [2 3] Nevertheless the efficacy of PD-1PD-L1pathway inhibition as a monotherapy has provided benefit to

only some of the patients while a significant fraction does notrespond to this therapy

Analysis of clinical trial data suggests three types ofpatients (a) those that do not respond (innate resistance)(b) those that respond initially but fail to respond in laterstages (acquired resistance) and (c) those that respondinitially and continue to respond [4 5] Extensive researchhas been performed in the past few years to understand themechanisms that regulate immune response to cancer butobstacles still exist in the field of cancer immunotherapyMechanisms of innate and acquired resistance to PD1PDL1blockade have been excellently reviewed before [6 7] Inorder to generate an efficient antitumor immune responseactivation and proliferation of antigen experienced T-cellsare required due to inadequate generation and function oftumor-reactive CD8 T-cells patients do not respond to thistherapy [8] Scarcity of suitable neoantigens and impairedprocessing and presentation of neoantigens are other reasons

HindawiJournal of OncologyVolume 2019 Article ID 5245034 18 pageshttpsdoiorg10115520195245034

2 Journal of Oncology

that lead to ineffective activation of tumor-reactive T-cells[5] Additionally variability in cancer type treatment historytumor heterogeneity and the immunosuppressive tumormicroenvironment generated due to tumor-intrinsic andtumor-extrinsic factors lead to a failure in response toimmune checkpoint inhibitor therapy [4] The identificationof biomarkers including mutationalneoantigen load [9] andthe PDL1 expression on tumor and immune cells [10] mightpredict the responders who would benefit from this therapybut in most of the studies these markers did not showany correlation with the anti-PD1 response [11] Hence theconcept of combination therapies that can modulate theimmunogenicity of tumor cells or can block immunosup-pressive TME or target other inhibitory receptors on T-cells comes in place to improve the therapeutic efficiency ofcheckpoint inhibitors

The dual checkpoint blockade using anti-PD1 and anti-CTLA-4 antibodies was considered a first combinatorialapproach in cancer immunotherapy [23 24]The outstandingsuccess of the combination of nivolumab (anti-PD1mAb) andipilimumab (anti-CTLA-4 mAb) in eliciting an antitumorresponse in various clinical trials opened the concept of com-bining immunotherapy with other therapeutic approachesAs a result various combination immunotherapeutic clinicaltrials are being conducted nationwide and the outcomes ofthese studies suggest that these strategies hold the potentialto increase the number of patients that might benefit fromimmunotherapy Besides CTLA-4 and PD-1 T cells expressseveral inhibitory coreceptors namely TIM3 TIGIT andLAG3 that function as immune checkpoint regulators andcan be targeted to activate antitumor immune responseTim 3 is a negative coinhibitory receptor which negativelyregulates T cell responses Coexpression of TIM3 and PD1symbols exhausted T cells which leads to loss of functionof CD8+ T cells [25 26] and hence Tim 3 antagonistsare suggested as excellent partners for PD1PDL1 blockadeAnother inhibitory receptor expressed on activated CD4 andCD8 T cells is LAG-3 and various studies have suggestedthat anti-LAG-3 and anti PD-1 treatment cured mice withestablished colon adenocarcinoma and fibrosarcoma tumors[27] TIGIT is found on subsets of activated T cells andNK cells are an emerging target in preclinical developmentActivation of costimulatory receptors namely CD27 4-1BBOX40 and GITR is an alternative approach to activateantitumor immune responses and has recently gained muchattention [28] In addition to inhibitory and costimulatoryreceptors on T cells various therapeutic combinations havebeen emerged which include pairing checkpoint inhibitorswith (1) tumor vaccines (2) IDO inhibitors (3) oncolyticviruses (4) inducers of immunogenic cell death and (5)targeted therapy and various other therapies Various reviewsare available which can provide insight into the combinatorialapproaches recently ongoing in clinical trials [29 30] and willnot be discussed here

2 Combinatorial Approaches toEnhance PD1-PDL1 Blockade

In this review we will focus on strategies that induce tumorimmunogenicity and reverse tumor immunosuppression

thus increasing antitumor immune responses (Figure 1) Wealso discuss a novel rational drug design approach to synthe-size chemotypes that hit multiple oncogenic pathways in thetumor and reverse myeloid cell-mediated immunosuppres-sion (Figure 1)

21 Strategies to Increase Tumor Immunogenicity Chemo-therapy and radiotherapy have long been used as conven-tional methods to reduce tumor burden It has been recentlyreported that these therapies activate the immune system byreleasing tumor antigens and subverting immunosuppressivefactors [31ndash33] These facts provide the rationale to exploreradiotherapy and chemotherapy with other immunothera-pies as these strategic combinatorial approaches could boostthe effectiveness of immunotherapy by killing tumor cellsand consequently stimulating the immune system and recruitimmune cells to the affected area In this section we alsodiscuss epigenetic therapy which recently emerged as a newstrategy to increase tumor immunogenicity

211 Chemotherapy Standard chemotherapeutic drugsincluding paclitaxel cyclophosphamide gemcitabine andcisplatin are reported to modulate tumor immunity at lowdoses [34] At their standard dose and schedule these drugsinduce immunogenic cell death (ICD) which involves therelease of tumor antigens and the emission of danger signalsby dying cancer cells known as DAMPs which in turnelicit tumor targeting immune responses [34] These drugscan modulate the immunogenicity of tumor cells throughdifferent mechanisms including (1) increasing the expressionof tumor antigens and enhancing tumor antigen presentation(2) upregulating costimulatory molecules (B7-1) and down-regulating coinhibitory molecules (B7-H1PDL1) expressedon the tumor cell surface which in turn increases effectorT-cell function (3) increasing T-cell mediated lysis of tumorcells through granzyme and perforin-dependent mecha-nisms and (4) reducing the infiltration of MDSCs and Tregsin the tumor microenvironment (Figure 2) Various clinicaltrials of this combination are ongoing to increase the efficacyof immunotherapy and some of which are listed in Table 1

Preclinical and clinical studies have shown that a low doseof cyclophosphamide or doxorubicin or paclitaxel given oneday before vaccination or immunotherapy depleted Tregsincreased IFN gamma secreting CD44+ effector memory T-cells and enhanced antitumor immune responses in end-stage cancer patients [35 36] Likewise several clinicaltrials have shown that patients who received a low dose ofcyclophosphamide given 1-3 days before vaccination showedan increase in effector T-cell function and higher overallsurvival as compared to those who received the vaccine alone[35 37] Based on these reports a phase 2 clinical studyrandomized 68 patients with advanced renal cell carcinoma33 patients received a low dose of cyclophosphamide 3 daysbefore vaccinationwithmultipeptide vaccine IMA901 +GM-CSF adjuvant and 35 patients received vaccination with onlyIMA901 + GM-CSF adjuvant [38] In this trial patientswho received 300 mgm2 cyclophosphamide 3 days prior tovaccination with IMA901 + GM-CSF adjuvant had longer

Journal of Oncology 3

Strategies to reverse immune suppression

Blockade of immune inhibitionpromotes activation of CD8+ T cells better tumor response

anti PD1PDL1CTLA-4mAb +

combination strategies

Combination strategiesanti-PD1PDL1 blockade

PDL1

Exhausted T cell

APC

Tumor cell

PD1

TAM

MDSCT reg

TCR

MHC antigen

MHC antigen

CD28CD8086

CTLA4

Tumor shrinkage activation of adaptiveimmune response improved survival

Effector T cell

NK cell

ImmunostimulatoryM

Strategies to increasetumor immunogenicity

and decrease tumor burden

Chemotherapy

Cyclophosphamide Paclitaxel Doxorubicin Cisplatin 5-fluorouracil

Release of DAMPs promotes anti-tumor CD8+ T cellsabrogates MDSC activity promotes tumor cell lysis enhances cross priming of dendritic cells

Abscopal Radiation

Radiotherapy

Release of DAMPs Apoptosis and necrosis increases antigenexpression

Epigenetic therapy

EpigeneticModulators

Increased expression ofHLA class moleculestumor associated antigensand decreased PDL1expression on tumor cells

Immuno-suppressiveMC TAMMDSC

Strategies to design and synthesize novel dual or triplechemo types to block multiple

signaling pathways

Orthogonally hit multiple pathways to kill cancer cells polarize immunosuppressive myeloid cellsinto Immunostimulatory phenotype promotes

anti-tumor CD8+ T cells improves survival

Rational designing of novel dual triple inhibitors

eg SF2523 or SF1126

PI3K

BRD4PI3Ka

BRD4

Suppress Mycactivation block

tumor metastasisPI3KgBRD4

PI3KgBRD4

Immuno-stimulatory MC

T reg

PI3kd

ActivatedT cell

PI3kd

T reg

CancercellBRD4

Arg VEGFMMP9 TGF beta

IL1 IL6 TNF IFNγImmuno-

suppressive MC

IDO inhibitorsTGF beta inhibitorsCCR4 inhibitors

MDSCTAM T regATRAVitamin DBevacizumabAnti-CXCR2TadalafilCOX-2 inhibitors

Cold tumor Immuno-suppressive

TME

Immuno-stimulatory M

Cytotoxic T cells

Hot tumorImmuno-stimulatory TME

Carlumab

CSF1-RInhibitors

Trabectedin

Anti-CD40

Figure 1 Combination immunotherapy strategies to reduce tumor burden and to activate durable antitumor immune response Leftpanel shows cartoon of strategies to increase tumor immunogenicity including certain chemotherapeutic drugs radiotherapy and epigeneticmodulatorswhich induce immunogenic cell death and release tumor antigens in TME that activate antitumor immune response Lower panelshows cartoon of agents targeting Tregs TAMs and MDSCs to block immunosuppression to skew their polarization to proinflammatorystate and to promote effector T cell function and to convert cold immunosuppressive TME into hot immune-stimulatory type Right panelshows novel strategy of rational designing of dual inhibitory chemotypes eg SF2523 dual PI3KBRD4 inhibitor targeting multiple signalingpathways to kill tumor cells and simultaneously stimulate immune cells to provide durable adaptive immune response Middle panel showscartoon of checkpoint inhibitor therapy and pairing of combination therapies with anti-PD1PDL1 blockade whichmay significantly improveclinical efficacy of cancer immunotherapy

overall survival (OS) as compared to the ones who receivedIMA901 only [38] Very few reports have examined theefficacy of immune checkpoint blockade with low doses ofcyclophosphamide One study in the cervical cancer modelshowed that anti-PD1 in combination with a low dose ofcyclophosphamide induced infiltration of CD8+ T-cells inthe tumor and promoted tumor-free survival [39] In anotherstudy using the lung adenocarcinomamodel authors showedthat the combined use of immunogenic drugs oxaliplatin andcyclophosphamide induced antitumor T-cell immunity andsuccessfully sensitized to checkpoint blockade [40] Thesestudies led to a clinical trial utilizing cyclophosphamide andpembrolizumab (anti-PD1 mAb) in patients with advancedsarcomas and gastrointestinal stromal tumors [13] Only3 out of 50 patients showed clinical benefit in this studyand the infiltration of immunosuppressive macrophages andactivation of the IDO1 pathway were suggested as reasons forresistance to anti-PD1 therapy in this trial

Gemcitabine is another example of standard dosechemotherapy which demonstrates potent immunomodula-tory effects as it induces apoptosis enhances cross-priming ofCD8+ T-cells and reduces infiltration of MDSCs in preclin-ical animal models [41ndash43] Gemcitabine given before vac-cination or a CD40 agonist augmented the survival of micein preclinical models [44] In another study gemcitabineand cisplatin given after immunotherapy with an adenoviral

vector expressing IFN alpha (AdIFN120572) also demonstratedgreat antitumor activity compared to chemotherapy orAdIFN120572 [45] These results led to the design of the Telo-Vac study a Phase 3 trial for patients with advanced ormetastatic pancreatic cancer These studies aimed to studygemcitabine in combination with MHC class 2 telomerasevaccine GV1001 given with GM-CSF adjuvant [14] Therewas a failure in the synergy between immunotherapy andchemotherapy in the Telo-Vac study [14] In addition to thisother trials have also shown that chemotherapy does not syn-ergize with immunotherapy [46] A Phase 2 trial integratedpancreas GVAX with standard adjuvant 5-fluorouracil-basedchemotherapy in stage 2 and 3 pancreatic cancer patientsthat led to failure [46] Contrary to these studies multiplesmall trials have shown that concurrent or standard phasechemotherapy may enhance vaccine-induced immunity invarious cancers [47] Recent reports suggest the efficacyof checkpoint inhibitors combined with gemcitabine in thetreatment of pancreatic cancer [15] In 2017 Phase I andII clinical trials were opened to explore gemcitabine withanti-CD40 antibody APX005M or with anti-PD-1 mAbnivolumab for pancreatic patients (NCT03214250) [15] Inanother clinical trial gemcitabine was paired with ipili-mumab for treating patients with stages 3-4 or recurrentpancreatic cancer that could not be removed by surgery(NCT01473940)

Journal of Oncology 3

Strategies to reverse immune suppression

Blockade of immune inhibitionpromotes activation of CD8+ T cells better tumor response

anti PD1PDL1CTLA-4mAb +

combination strategies

Combination strategiesanti-PD1PDL1 blockade

PDL1

Exhausted T cell

APC

Tumor cell

PD1

TAM

MDSCT reg

TCR

MHC antigen

MHC antigen

CD28CD8086

CTLA4

Tumor shrinkage activation of adaptiveimmune response improved survival

Effector T cell

NK cell

ImmunostimulatoryM

Strategies to increasetumor immunogenicity

and decrease tumor burden

Chemotherapy

Cyclophosphamide Paclitaxel Doxorubicin Cisplatin 5-fluorouracil

Release of DAMPs promotes anti-tumor CD8+ T cellsabrogates MDSC activity promotes tumor cell lysis enhances cross priming of dendritic cells

Abscopal Radiation

Radiotherapy

Release of DAMPs Apoptosis and necrosis increases antigenexpression

Epigenetic therapy

EpigeneticModulators

Increased expression ofHLA class moleculestumor associated antigensand decreased PDL1expression on tumor cells

Immuno-suppressiveMC TAMMDSC

Strategies to design and synthesize novel dual or triplechemo types to block multiple

signaling pathways

Orthogonally hit multiple pathways to kill cancer cells polarize immunosuppressive myeloid cellsinto Immunostimulatory phenotype promotes

anti-tumor CD8+ T cells improves survival

Rational designing of novel dual triple inhibitors

eg SF2523 or SF1126

PI3K

BRD4PI3Ka

BRD4

Suppress Mycactivation block

tumor metastasisPI3KgBRD4

PI3KgBRD4

Immuno-stimulatory MC

T reg

PI3kd

ActivatedT cell

PI3kd

T reg

CancercellBRD4

Arg VEGFMMP9 TGF beta

IL1 IL6 TNF IFNγImmuno-

suppressive MC

IDO inhibitorsTGF beta inhibitorsCCR4 inhibitors

MDSCTAM T regATRAVitamin DBevacizumabAnti-CXCR2TadalafilCOX-2 inhibitors

Cold tumor Immuno-suppressive

TME

Immuno-stimulatory M

Cytotoxic T cells

Hot tumorImmuno-stimulatory TME

Carlumab

CSF1-RInhibitors

Trabectedin

Anti-CD40

Figure 1 Combination immunotherapy strategies to reduce tumor burden and to activate durable antitumor immune response Leftpanel shows cartoon of strategies to increase tumor immunogenicity including certain chemotherapeutic drugs radiotherapy and epigeneticmodulatorswhich induce immunogenic cell death and release tumor antigens in TME that activate antitumor immune response Lower panelshows cartoon of agents targeting Tregs TAMs and MDSCs to block immunosuppression to skew their polarization to proinflammatorystate and to promote effector T cell function and to convert cold immunosuppressive TME into hot immune-stimulatory type Right panelshows novel strategy of rational designing of dual inhibitory chemotypes eg SF2523 dual PI3KBRD4 inhibitor targeting multiple signalingpathways to kill tumor cells and simultaneously stimulate immune cells to provide durable adaptive immune response Middle panel showscartoon of checkpoint inhibitor therapy and pairing of combination therapies with anti-PD1PDL1 blockade whichmay significantly improveclinical efficacy of cancer immunotherapy

overall survival (OS) as compared to the ones who receivedIMA901 only [38] Very few reports have examined theefficacy of immune checkpoint blockade with low doses ofcyclophosphamide One study in the cervical cancer modelshowed that anti-PD1 in combination with a low dose ofcyclophosphamide induced infiltration of CD8+ T-cells inthe tumor and promoted tumor-free survival [39] In anotherstudy using the lung adenocarcinomamodel authors showedthat the combined use of immunogenic drugs oxaliplatin andcyclophosphamide induced antitumor T-cell immunity andsuccessfully sensitized to checkpoint blockade [40] Thesestudies led to a clinical trial utilizing cyclophosphamide andpembrolizumab (anti-PD1 mAb) in patients with advancedsarcomas and gastrointestinal stromal tumors [13] Only3 out of 50 patients showed clinical benefit in this studyand the infiltration of immunosuppressive macrophages andactivation of the IDO1 pathway were suggested as reasons forresistance to anti-PD1 therapy in this trial

Gemcitabine is another example of standard dosechemotherapy which demonstrates potent immunomodula-tory effects as it induces apoptosis enhances cross-priming ofCD8+ T-cells and reduces infiltration of MDSCs in preclin-ical animal models [41ndash43] Gemcitabine given before vac-cination or a CD40 agonist augmented the survival of micein preclinical models [44] In another study gemcitabineand cisplatin given after immunotherapy with an adenoviral

vector expressing IFN alpha (AdIFN120572) also demonstratedgreat antitumor activity compared to chemotherapy orAdIFN120572 [45] These results led to the design of the Telo-Vac study a Phase 3 trial for patients with advanced ormetastatic pancreatic cancer These studies aimed to studygemcitabine in combination with MHC class 2 telomerasevaccine GV1001 given with GM-CSF adjuvant [14] Therewas a failure in the synergy between immunotherapy andchemotherapy in the Telo-Vac study [14] In addition to thisother trials have also shown that chemotherapy does not syn-ergize with immunotherapy [46] A Phase 2 trial integratedpancreas GVAX with standard adjuvant 5-fluorouracil-basedchemotherapy in stage 2 and 3 pancreatic cancer patientsthat led to failure [46] Contrary to these studies multiplesmall trials have shown that concurrent or standard phasechemotherapy may enhance vaccine-induced immunity invarious cancers [47] Recent reports suggest the efficacyof checkpoint inhibitors combined with gemcitabine in thetreatment of pancreatic cancer [15] In 2017 Phase I andII clinical trials were opened to explore gemcitabine withanti-CD40 antibody APX005M or with anti-PD-1 mAbnivolumab for pancreatic patients (NCT03214250) [15] Inanother clinical trial gemcitabine was paired with ipili-mumab for treating patients with stages 3-4 or recurrentpancreatic cancer that could not be removed by surgery(NCT01473940)

4 Journal of Oncology

Dying tumor cell

HGMB 1

ATP

Immature dendritic cell

Mature and activateddendritic cell

gemcitabine

TLR4

P2RX7CRT

CRTR NRLP3

IL1

NRLP3

IL1

Tumor antigenspecific T cells

CD4+T cell

CD8+T cell

1) Promote anti-tumor CD4+ T cell phenotype2) Abrogate MDSC activity3) Enhances cross priming

Enhances cross-priming of T cellsriming

MDSCT reg

PDL1

MHC I

MDSC Activated T cell

Activated T cell

TCRMHC antigen

TCRMHC

TCR Antigenuptake

Antigenpresentation

Activated T cell

PD1

BRD4i

T reg

BRD4i

Convert immunosuppressive Mac to immunostimulatory phenotype

BRD4i

Immuno-stimulatory MTAM

Chem

othe

rapy

Radi

othe

rapy

Epig

enet

ic

ther

apy

Radiation

Dyingtumor cell HGMB 1

ATPDAMPs

Immature dendritic cell

Activation of dendritic cell

Co-stimulation

Activated T cell

Translocation of calreticulin

Endocytosis of tumor antigen

MHC

MHC TCR

PDL1

TAM polarization from M1 to M2

T regproliferation

Hypoxic tumor inductionof TGF beta MDSC

accumulation

1) Promote anti-tumor

CD4+ T cell phenotype

2) Increases DC activation

3) Promotes lysis of tumor cells

4) Decrease T reg activity

cyclophosphamide

Doxorubicinpaclitaxel

1) Abrogate MDSC activity

CD4+ T cell phenotype

2) promote anti-tumor CD8+

T cell phenotype3) Promotes tumor cell lysis

Epigenetic drugs

DNMTi amp HDACi

Increase recognition

of cancer antigenBRD4i

Figure 2 Mechanisms of inducing immunogenic tumor cell death and decreasing tumor burden by chemotherapy radiotherapy andepigenetic therapyUpper panel shows how chemotherapeutic drugs induce immunogenic death through release of tumor antigens secretionof danger associated signals HGMB1 and ATP and translocation of calreticulin to cell surface These death-associated molecules bind toTL4R P2RX7 receptors and calreticulin receptors which leads to activation of NRLP3 inflammasome and activation of dendritic cells toinduce tumor antigen specific T-cell responses Some chemotherapeutic drugs decrease infiltration and accumulation of Tregs and MDSCsin the TME leading to activation of adaptive immune responses Middle panel shows the immunogenic cell death induced by radiotherapyFigure also shows that radiation induces increased transcription of HIF 1120572 and activation of latent TGF beta which leads to increased Tregproliferation and polarization of M1 macrophages to M2macrophages leading to activation of immunosuppressive TME Lower panel showshow epigenetic therapy promotes antitumor responses by upregulating tumor-associated antigens and downregulating PDL1 expressionBRD4 inhibitors block accumulation of MDSCs in TME and reduce immunosuppression by promoting the polarization of macrophages intoimmunostimulatory phenotypes

Journal of Oncology 5Ta

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Pembrolizum

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vanced

sarcom

asandgastr

ointestin

altumors

(NCT

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6781)[13]

Gem

citabine

GV1001

vaccineg

iven

with

GMCS

Fadjuvant

InPh

ase3

Telo-Vac

clinicalstu

dyin

pancreaticcancer

[14]

Anti-C

D40

antib

odyAPX

005M

orwith

nivolumab

PhaseI

andIIclinicaltrialfor

pancreatic

patie

nts(NCT

03214250)[15]

Ipilimum

abPh

aseI

clinicaltrialfor

PancreaticCancer

(NCT

01473940)

Melp

halanandDactin

omycin

Ipilimum

abPh

ase2

trialinadvanced

melanom

a(N

CT01323517)

Dacarbazine

Ipilimum

abPh

ase3

clinicaltrialinadvanced

melanom

a(NCT

00324155)[16]

Paclita

xeland

Carbo

platin

Ipilimum

ab

Phase2

clinicaltrialfor

nonndash

smallcell

lung

cancer

(NSC

LC)(NCT

00527735)a

ndsm

all-c

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(NCT

00527735)

[1718]

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etrexed

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a(NCT

01970527)prostrate

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00323882)a

ndlung

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(NCT

02239900)

Highdo

seIL-2

Kidn

eyandskin

cancer

(NCT

01896271)

[19]

Pembrolizum

abandnivolumab

PhaseI

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radiation

with

inNSC

LC(N

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[20]

Nivolum

abGlio

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NCT

02617589)triple

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ebreastcancer

(NCT

02499367)

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abmetastatic

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03386357)

Durvalumab

andtre

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Locally

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enet

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(DNMTinhibitor)

Ipilimum

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a(NCT

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Pembrolizum

abAd

vanced

sarcom

asandgastr

ointestin

altumors

(NCT

0240

6781)[13]

Gem

citabine

GV1001

vaccineg

iven

with

GMCS

Fadjuvant

InPh

ase3

Telo-Vac

clinicalstu

dyin

pancreaticcancer

[14]

Anti-C

D40

antib

odyAPX

005M

orwith

nivolumab

PhaseI

andIIclinicaltrialfor

pancreatic

patie

nts(NCT

03214250)[15]

Ipilimum

abPh

aseI

clinicaltrialfor

PancreaticCancer

(NCT

01473940)

Melp

halanandDactin

omycin

Ipilimum

abPh

ase2

trialinadvanced

melanom

a(N

CT01323517)

Dacarbazine

Ipilimum

abPh

ase3

clinicaltrialinadvanced

melanom

a(NCT

00324155)[16]

Paclita

xeland

Carbo

platin

Ipilimum

ab

Phase2

clinicaltrialfor

nonndash

smallcell

lung

cancer

(NSC

LC)(NCT

00527735)a

ndsm

all-c

elllun

gcancer

(NCT

00527735)

[1718]

Paclita

xelCarbo

platin

and

Prem

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Pembrolizum

abPh

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clinicaltrialfor

lung

cancer

(NCT

02039674)

Paclita

xelCarbo

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Nivolum

abPh

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Ipilimum

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a(NCT

01970527)prostrate

(NCT

00323882)a

ndlung

cancer

(NCT

02239900)

Highdo

seIL-2

Kidn

eyandskin

cancer

(NCT

01896271)

[19]

Pembrolizum

abandnivolumab

PhaseI

andIIclinicaltrialsof

radiation

with

inNSC

LC(N

CT3148327)

[20]

Nivolum

abGlio

blastoma(

NCT

02617589)triple

negativ

ebreastcancer

(NCT

02499367)

Pembrolizum

abmetastatic

Headandneck

squamou

scarcinom

a(NCT

03386357)

Durvalumab

andtre

melim

umab

Locally

advanced

Headandneck

squamou

scarcino

maN

CT03426657

Epig

enet

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erap

y

SGI-110

(DNMTinhibitor)

Ipilimum

abMelanom

a(NCT

0260

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Vorin

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Pembrolizum

abRe

nalcellcarcino

ma

(NCT

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Nivolum

abNSC

LC(N

CT01928576)

6 Journal of Oncology

Table1Con

tinued

Com

bina

torialapproa

chCom

bina

tion

Therap

yampDrug

Used

Can

cerV

accine

orIm

mun

otherapy

Drug

Used

Tumor

Type

ampRe

ference

Stra

tegi

esto

reve

rset

umor

imm

unos

uppr

essio

n

Mac

roph

ageT

arge

ted

Ther

apy

Blocking

recruitm

entof

macrophages

Carlumab

(hum

ananti-CCL

2IgG

1120581mAb

(CNTO

888)

Prostratec

ancer[21]a

ndadvanced

cancer

patie

nts[22]

PF-04136309

(CCL

2-CCR

2axisinh

ibito

r)

PF-04136309p

lusF

OLF

IRIN

OXshow

bette

rtreatmentrespo

nseinpatie

ntsw

ithlocally

advanceP

DAC

(NCT

01413022)

Redu

ctionofTA

Msb

ydepletingT

AMso

rits

precursor

RG7155

(anti-C

SF1R

neutralizing

antib

odies)

RG7155

demon

strated

therapeutic

efficacy

inpatie

ntsw

ithdiffu

se-ty

pegiantcell

tumor

Plexifo

rmNeurofib

romas

Neurofib

romatosis

(NCT

02390752)

PLX3

397(pexidartin

ib)(CS

F-1R

inhibitor)

Urvalum

abAd

vanced

Pancreaticandcolorectalcancer

(NCT

02777710)

Pembrolizum

abMelanom

aand

solid

tumors

(NCT

02452424)

BLZ9

45(C

SFIR

inhibitor)

PDR0

01(anti-P

D1)

PhaseIII

clinicaltrialinadvanced

solid

tumors(NCT

02829723)

Trabectedin

PhaseIIIstu

dyshow

edtrabectedinplus

PLDim

proves

overallsurvivalthanPL

Dalon

einovariancancer

PhaseIIItrialinlocally

advanced

ormetastatic

liposarcoma(N

CT01692678)

Reprogrammingo

fmacrophagesinto

anti-tumor

phenotype

IPI-549

Pembrolizum

abSolid

tumors

(NCT

02637531)

RO7009789

(AgonistCD

40Ab

)Nab-paclitaxelandgemcitabine

Pancreaticadenocarcino

ma

(NCT

02588443)

Atezolizum

abMetastatic

solid

tumors

(NCT

02304393)

TLRagonists

DV821(TLR

9agonist)

Anti-P

D1ab

PhaseI

NSC

LCNCT

03326752

Poly-IC-

LC(TLR

3)Pembrolizum

abColon

cancer

(NCT

028340

52)

MD

SCTa

rget

edth

erap

y

Redu

ctionin

accumulation

ofMDSC

s

ATRA

Ipilimum

abStageIVmelanom

a(N

CT02403778)

Bevacizumabentinostat

Atezolizum

abAd

vanced

renalcellcarcino

ma

(NCT

03024437)

Blockade

orrecruitm

entof

MDSC

s

SX-682

Pembrolizum

abMelanom

a(N

CT03161431)

RTA-

408

Ipilimum

abNivolum

abMelanom

a(N

CT02259231)

Journal of Oncology 7

Table1Con

tinued

Com

bina

torialapproa

chCom

bina

tion

Therap

yampDrug

Used

Can

cerV

accine

orIm

mun

otherapy

Drug

Used

Tumor

Type

ampRe

ference

Treg

targ

eted

ther

apy

CCR

4inhibitor

Pembrolizum

abPh

ase1

and2forsolid

tumors

(NCT

02178722)

Epacadostat(ID

Oinhibitor)

Durvalumab

Advanced

solid

tumors

(NCT

02318277)

Atezolizum

abNSC

LC(N

CT02298153)

galunisertib

(TGFbetainhibitor)

Durvalumab

ornivolumab

Pancreaticcancer

(NCT

02423343)

Stra

tegi

esto

desig

nan

dsy

nthe

sizen

ovel

dual

ortr

iple

inhibi

tory

chem

otyp

esth

atca

nbl

ock

mul

tiple

pathw

ays

SF112

6

Solid

tumors(NCT

00907205)

Recurrento

rprogressiv

eSCCH

Ntumors

(NCT

0264

4122)

Neuroblastoma

(NCT

02337309)

Nivolum

abHepatocellularc

arcino

ma(

NCT

03059147)

8 Journal of Oncology

In addition to cyclophosphamide and gemcitabine otherstandard chemotherapeutic drugs such as paclitaxel car-boplatin and dactinomycin have also been combined withimmune checkpoint inhibitors for treatment of melanomaNSCLC and SCLC [17 18 48] In a recent study the combi-nation of local chemotherapy (melphalan and dactinomycin)and ipilimumab showed better response rates in patientswith advanced melanoma [16] A Phase 3 trial utilizingthe combination of ipilimumab and dacarbazine showedbetter overall survival response in patients compared to theones treated with dacarbazine alone [48] In addition ipili-mumab paired with paclitaxel and carboplatin was evaluatedfor the treatment of non-small-cell lung cancer (NSCLC)and small-cell lung cancer [17 18] For NSCLC standardprogression-free survival (PFS) was observed when patientsreceived phased treatment with chemotherapy followed byipilimumab Alternatively for SCLC for the same phasedtreatment immune-related responses were improved butno standard PFS was observed Some of the other clinicaltrials combining chemotherapy with checkpoint blockade arediscussed in Table 1 These trials have shown great promisefor treatment of some cancers however further investigationof the dosage and schedule of chemotherapeutic drugsis essential for effective translation of these combinatorialapproaches in the clinic

212 Radiotherapy Radiotherapy has been known to killtumors via DNA damage-induced apoptosis or programmedcell death but recent pieces of evidence suggest that itstimulates tumor antigen release and promotes an immune-mediated antitumor response [49ndash52] Contrary to initiatingan antitumor immune response radiation therapy can alsopromote the generation of immunosuppressive factors thathinder the activation of dendritic cells and impair thefunction of effector T-cells [53 54] Radiotherapy has beenreported to promote immunosuppressive tumor microen-vironment by (1) increasing transcription of HIF 1 alphawhich induces Treg proliferation MDSC accumulation andM2 polarization of TAMs and (2) activating latent TGF-beta in the tumor that polarizes TAMs into M2 phenotypeand converting CD4+ T-cells into Tregs (Figure 2) [53 54]Hence combining radiotherapy with immune modulatorsmight provide increased benefit to radiation monotherapy

Radiotherapy is mostly used in combination with surgeryor chemotherapy and combination regimens involving radio-therapy and immunotherapies are now emerging treat-ment regimens [55ndash58] These studies suggest that combin-ing radiotherapy with immunotherapy will boost abscopalresponse rates and will extend the use of radiotherapy intreatment for both local and metastatic disease The absco-pal effect is defined as a phenomenon in the treatmentof metastatic cancer whereby localized radiation eradicatesdistant metastasis and activates systemic antitumor effectsVarious preclinical studies have been conducted to explorethe role of radiation in combination with immune checkpointinhibitors [59 60] Deng et al have shown that radiationin combination with a PD-L1 checkpoint blockade reducesthe infiltration of MDSC in the MC38 colon carcinoma

mousemodel [59] In another study anti-CTLA-4 antibodiescombined with radiation showed an abscopal antitumorresponse in the metastatic 4T1 breast cancer model [60] Inpreclinical intracranial glioma models the combination ofradiation and anti-PD1 showed robust systemic immunologicmemory in surviving mice and long-term survival in treatedmice [61] Based on the results of these preclinical studiesseveral clinical trials have been initiated to assess the efficacyof combining radiation therapy with checkpoint inhibitors

Reports by Postow et al and Hiniker et al have shownthat melanoma patients treated with the combined regimenof ipilimumab and radiation showed a systemic completeresponse [62 63] In a case report for a patient with NSCLCconcurrent treatment with radiation and ipilimumab led toan abscopal response [64] In another Phase III clinical studySolvin and his colleagues found that ipilimumab and radi-ation induced a great response in patients with metastaticcastration-resistant prostate cancer [65] In a small cohort ofpatients with skin and kidney cancer stereotactic body radio-therapy with high dose IL2 showed better tumor responserates over that of IL2 alone [19] There are several Phase Iand 2 clinical trials ongoing in patients with NSCLC for eval-uation of radiotherapy with PD-PDL1 immune checkpointinhibitors pembrolizumab and nivolumab [20] outlined inTable 1

In head and neck cancer the application of anti-PD1therapies has shown promising results and during thelast two years several clinical trials have been initiatedto combine immunotherapy with radiation [66] some ofwhich are listed in Table 1 In a randomized Phase 2 clinicaltrial opened in 2018 pembrolizumab and radiation havebeen combined for metastatic head and neck squamouscell carcinoma (HNSCC) (NCT03386357) In 2018 anotherPhase 2 clinical trial was opened to treat locally advancedHNSCC with double checkpoint blockade (durvalumab andtremelimumab) and radiotherapy dependent on intratumoralCD8+ T-cell infiltration (NCT03426657)

213 Epigenetic erapy The epigenetic mechanisms inimmune responses have recently gained significant atten-tion because of their potential as therapeutic targets [67ndash69] Epigenetic modulators such as histone deacetylase andDNAmethyltransferase (DNMT) inhibitors increase expres-sion of tumor-associated antigens that lead to improvedimmunologic recognition of cancer cells and enhanced anti-tumor response in various tumor models (Figures 1 and2) HDAC inhibitors vorinostat and panobinostat showedrobust antitumor activity in colon adenocarcinoma andleukemia model by inducing signs of ICD [70] HDACinhibitors are also known to increase expression of HLAclass molecules in cancer cells [71] and promote recog-nition and lysis of cancer cells by activated NK cells[72] Likewise DNMT inhibitors are known to promoteantitumor responses by upregulating expression of HLAclass molecules [73] and tumor-associated antigens [74]in different tumor models Various studies highlight thecombinatorial approach of epigenetic therapy with immunecheckpoint blockade in mouse models and human patients

Journal of Oncology 9

as discussed in this review [75] Epigenetic modulatorsin combination with checkpoint inhibitors are known (1)to increase T-cell infiltration in TME (2) to reduce MDSCinfiltration in TME and (3) to enhance surface expressionof immune checkpoints [75] Recently other epigeneticmodulators such as bromodomain inhibitors and histonedemethylase inhibitors have also been reported to increaseantitumor response JQ1 is a selective BETbromodomaininhibitor that is reported to block the interaction betweenmultiple BET proteins (BRD234) and acetylated histones[76] Recently JQ1 was reported to suppress PD-L1 expressionin ovarian cancer cells leading to enhancing cytotoxic T-cellresponses [77] Another report by Wang et al also showedthat JQ1 increases the immunogenicity of lymphoma cellsby increasing expression of PDL1 [78] JQ1 has additionallybeen reported to enhance T-cell persistence and functionin various models [79] JQ1 in combination with anti-PD1therapy increased antitumor response in a murine model oflung cancer [80] There are several ongoing clinical trialscombining immune checkpoint inhibitors with epigeneticmodulators some of them are shown in Table 1

22 Strategies to Reverse Tumor Immunosuppression Thecomposition of stromal cells in the tumor microenviron-ment plays an important role in predicting the responseof cancer immunotherapy agents It is now clearly estab-lished that tumor-associated macrophages (TAMs) myeloid-derived suppressor cells (MDSCs) and regulatory T-cells(Tregs) are the major mediators of tumor-induced immuno-suppression and play a major role in suppressing normalfunctions of effector T-cells Hence they serve as hurdlesthat limit the therapeutic potential of cancer immunothera-pies [81] These immunosuppressive immune cells limit theactivation of CD8+ T-cells through various mechanisms suchas (1) blocking T-cell function by the production of anti-inflammatory cytokines (2) depleting metabolites needed forT-cell proliferation and (3) engaging with T-cell inhibitoryreceptors to block cytotoxic T-cell activity Hence targetingthese immunosuppressive immune cells will increase theefficacy of checkpoint inhibitors

221Macrophage-Targetederapy TAMs aremajor orches-trators of cancer-related inflammation as they promote tumorgrowth angiogenesis metastasis tissue remodeling andimmunosuppression A detailed description of macrophagephenotypes and their function can be found in other reviews[82 83] TAM-targeting therapy has recently emerged as apromising novel strategy for the treatment of cancer [84]as these cells possess poor antigen presentation capabilitiesand suppress the immune response of T-cells by releasing thefollowing factors arginase TGF-120573 and IL10 To overcomethe immunosuppressive and protumoral functions of TAMscurrent therapies are majorly focused on three aspects (a)the blockade of macrophage recruitment (b) the depletionof existing macrophages and (c) the reprogramming ofmacrophages into antitumor phenotypes In this section wealso discuss toll-like receptor agonists in clinical trials andtheir potential pairing with checkpoint inhibitors

(a) Blockade of Recruitment of Macrophages in the TumorMicroenvironment Chemokines have long been knownto promote the infiltration of myeloid cells in the tumormicroenvironment [85] Chemokine-cytokine mediatedinfiltration of macrophages can be blocked by targetingCCR2 receptors that bind to ligands CCL2 CCL8 andCCL16 Inhibition of CCL2 with specific antibodies reducedtumor growth in different experimental models such asprostrate melanoma breast liver and lung cancer [86ndash88]In the Phase I clinical trial administration of anti-CCL2IgG1120581 mAb carlumab (CNTO 888) was well tolerated andshowed greater efficacy in patients with solid tumors whilethere was no response of this antibody in the Phase II clinicaltrial that involved patients with castration-resistant prostatecancer [21 22] Few preclinical studies demonstrate enhancedantitumor responses when carlumab was administered incombination with chemotherapeutic drugs [86] howevercombining carlumab with a chemotherapy regimen didnot show the significant antitumor immune response in aclinical trial conducted on patients with solid tumors [89]By contrast the combination of novel CCR2 antagonistPF-04136309 with cytotoxic cocktail FOLFIRINOX showedan improved antitumor response in a clinical trial conductedon pancreatic adenocarcinoma patients (NCT01413022) [90]There is only one report illustrating that the blockade ofCCL2 enhanced the immunotherapeutic effect of anti-PD1in lung cancer [91] However therapeutic efficacy of thiscombination has yet to be tested in clinical trials

(b) Reduction of TAMs by Depleting TAMs oreir PrecursorsCSF-1 receptor is expressed by most of the cells of themonocytic lineage and is a direct target to block monocyticprecursors directly and indirectly CSF-1 commonly knownas MCSF is used as a differentiation factor for cells ofmonocyte or macrophage lineages Antagonists or antibod-ies to CSF1R have been developed and tested in variouspreclinical models (eg cervical cancer pancreatic can-cer and glioblastoma) in combination with chemotherapyradiation therapy and checkpoint inhibitors whereby theydepleted immunosuppressive macrophages and increased theCD8CD4 ratio in the tumors [92] Clinical trials combiningthe use of CSF1-R inhibitors and chemotherapy have beeninitiated for the treatment of various cancers based on initialpreclinical data inmouse breast cancermodelswhere aCSF1Rblockade increased the efficiency of paclitaxel [93] RG7155(Emactuzumab) is a humanized monoclonal antibody thatblocks CSF1R activation A Phase I clinical trial of RG7155in patients with diffuse-type giant cell tumors (Dt-GCT)showedmeasurable clinical responses with the disintegrationof tumor mass in one patient This data is also correlatedwith the depletion of TAMs from tumor biopsies and asubstantial increase in CD8+ T-cell infiltration [94] Pexidar-tinib an inhibitor of CSF-1R augmented antitumor immuneresponses when combined with radiotherapy in glioblastomamodels [95] BLZ 945 another potent and selective inhibitorof CSF-1R blocked recruitment of bone marrow-derivedmacrophages and tumor progression in glioma models [96]Currently there are several ongoing clinical trials to combine

10 Journal of Oncology

these CSF1-R inhibitors with PD-1PD-L1 inhibitors as listedin Table 1

Trabectedin which was originally recognized for itsability to induce cell cycle arrest and death was foundto cause a partial depletion of circulating monocytes andTAMs in cancer patients [97] Trabectedin-induced TAMreduction was associated with decreased angiogenesis inmurine tumors and human sarcomas [98] Based on the effi-ciency of trabectedin in the selective killing of mononuclearphagocytes from tumors in preclinical mouse models it hasbeen translated to numerous clinical trials either as a singleagent or in combination with other drugs to study safetyand efficacy in human tumors To date two Phase III clinicaltrials mentioned in Table 1 have confirmed the therapeuticadvantage of trabectedin These observations open up theoption to combine trabectedin with checkpoint blockadeinhibitors

(c) Reprogramming of Macrophages into Antitumor Pheno-type Macrophages are highly plastic cells and can changetheir phenotype in accordance with environmental cues Inresponse to various signals produced by tumor and stromalcells proinflammatory macrophages shift to an immunosup-pressive phenotype that blocks antitumor immunity [99]Hence targeting the molecular pathwayssignaling nodesin the macrophages that regulate the transition of pro-tumorigenic MΘs into antitumorigenic MΘs will activatethe immune response in cancer [100] Various preclinicalstudies identified signaling pathways or key genes such asthe jumonji domain containing proteins (JMJD3) STAT3STAT6 Myc Rac2 PI3K120574 Btk etc which play a crucialrole in stimulating alternative activation of macrophagesand promoting tumor growth [101ndash105] Recent studies haveprovided evidence that targeting PI3K120574 in macrophages canpolarize macrophages into immunostimulatory phenotypespromote CD8+ T-cell cytotoxicity and augment the tumorsuppressive effects of anti-PD1 antibody in mouse models[101 103 106] These studies have led to the clinical trialof PI3K120574 inhibitor IPI549 in combination with nivolumabfor advanced solid tumors [106 107] In another preclin-ical study in pancreatic cancer model Brutonrsquos tyrosinekinase (BTK) inhibitor ibrutinib repolarized macrophagesinto the M1 phenotype and promoted cytotoxic CD8+ T-cell activity [108] This strategy is under consideration forthe opening of a clinical trial to study ibrutinib in com-bination with checkpoint inhibitors for pancreatic cancers[108]

Another example of macrophage targeting comes fromthe administration of the anti-CD40 antibody in a preclinicalmodel of pancreatic cancer This study showed that use ofthe anti-CD40 antibody repolarized M2-like macrophagesinto an M1-like phenotype leading to a reduction in tumorgrowth [109] This preclinical data lead to the clinical trialof human CD40 agonist with gemcitabine in advanced pan-creatic cancer patients which showed partial responses [109]RO7009789 is another CD40 agonist which has been testedin combination with chemotherapy and immunotherapy insolid tumors and are listed in Table 1

(d) Toll-Like Receptor Agonists Toll-like receptors (TLRs) asthe most important pattern-recognition receptors in innateimmunity play a critical role in the defense against infectionand disease including cancer TLRs are expressed in a widerange of immune cells including monocytes macrophagesand dendritic cells Certain TLRs have been shown toenhance DC maturation and antigen presentation leadingto effective antitumor effects Thus the agonists of TLRsignaling are explored as anticancer agents or vaccines toinduce effective immune reactions against tumor antigens Astudy by Bald et al has shown that TLR-3 activation inducestype I interferon and synergizes with anti-PD1 therapy inthe melanoma model [110] Poly-IC-LC a TLR 3 ligandhas been used in combination with pembrolizumab for thetreatment of colon cancer (NCT02834052) FurthermoreTLR9 agonists are reported to increase T-cell infiltrationand to induce CD4 and CD8 T-cell antitumor immunity invarious mouse models [111] In a lymphoma mouse model aTLR9 agonist (intratumoral CpG) in combination with anti-OX40 and anti-CTLA-4 cured large and systemic lymphomatumors without the need for chemotherapy [112] A recentreport by Sato-Kaneko et al suggests that TLR7 and TLR9agonists in combination with anti-PD1 mAb increased M1to M2 macrophage ratio and increased infiltration of IFNgamma secreting CD8+ T-cells in head and neck cancermodels [113] There are several ongoing clinical trials to testthe combination of TLR9 agonist with anti-PD1 therapy invarious cancers DV281 a TLR9 agonist has been used incombination with anti-PD1 antibody in Phase I clinical trialincluding NSCLC patients (NCT03326752)

222 MDSCs Targeted erapy Myeloid-derived suppressorcells are immature myeloid cells that expand in patho-physiological conditions like inflammation and cancer andsuppress T-cell activity [114 115] They play an importantrole in mediating immunosuppression and are considereda promising target to be paired with check point blockadeSimilar to macrophage targeted therapy MDSC targetedtherapy can also be divided into three sections based on thestrategies to block its accumulation recruitment and reversalof MDSC-mediated immunosuppression

(a) BlockingAccumulation ofMDSCs andeirDifferentiationinto Macrophages or Dendritic Cells In order to reduce theaccumulation of MDSCs the process of myelopoiesis has tobe normalized and the strategies to differentiate them intonormal macrophages or dendritic cells has to be stimulatedVarious studies have suggested that a blockade of retinoicacid signal transduction by all-trans-retinoic acid (ATRA)promotes the differentiation of MDSCs into macrophagesand dendritic cells inmouse and human samples [116] ATRAis a vitamin A derivative and is an FDA approved drug forthe treatment of acute promyelocytic leukemia (APL) [117]ATRA has been applied to two clinical trials in combinationwith immunotherapy to target MDSCs in cancer patientsThe first clinical trial was in patients with metastatic renalcancer [118] and the second trial was in patients with smalllung cancer [119] Both trials resulted in reductions of MDSC

Journal of Oncology 11

accumulation and improved patient survival In anotherPhase 2 clinical trial ATRA was combined with ipilimumabto treat stage IV melanoma patients (NCT02403778) Similarto ATRA vitamin D3 differentiates immature MDSCs intomacrophages and dendritic cells A small clinical studyinvolving 17 HNSCC patients showed that treatment withvitamin D3 reduced the number of infiltrating MDSCsincreased the number of mature tumor-infiltrating dendriticcells and an improved antitumor immune response [120]

Recent studies have shown that anti-VEGF antibodybevacizumabmdashwhich is used to treat VEGF-mediated angio-genesis can also be used to decrease circulating immaturemyeloid cells in cancer patients VEGF is a key mediatorof tumor-induced angiogenesis [121] and plays an importantrole in inhibiting the maturation of myeloid cells [122] Asmall clinical trial involving 19 metastatic colorectal patientsshowed that bevacizumab decreased immature MDSCs andimproved the stimulatory capacity of DCs isolated fromtreated patients [123] Based on this clinical trial Phase I and2 clinical trials enrolled 62 patients with advanced renal cellcarcinoma for treatment with bevacizumab entinostat andatezolizumab

(b) Blockade of Recruitment of MDSCs MDSCs are recruitedin the tumor site to promote immunosuppression andthis process is mediated by chemokines that have beensecreted by chemokine receptors found on MDSCs in thetumor microenvironment The roles of CCL2 CCL5 CCL7and CXCL8 and their receptors CCR2 and CCR4 in therecruitment of MDSCs are well described [124] A studyby Highfill et al has shown that anti-CXCR2 plus anti-PD-1 mAb blocked MDSC recruitment and enhanced anti-PD1 efficacy [124] In another study the combination of aCCR1 inhibitor (CCX9588) andPD-L1 inhibitor increased theantitumor effects in a murine model of breast cancer [125]Yet another clinical trial in melanoma patients is utilizingthe combination of pembrolizumab with MDSC targetingby SX-682 a small molecule dual inhibitor of C-X-C-motifchemokine ligands 1 and 2 (NCT03161431) RTA-408 ananti-inflammatory drug is also explored within melanomapatients

(c) Reversal of MDSC Mediated Immunosuppression Phos-phodiesterase-5 inhibitors are known to inhibit the immuno-suppressive function of MDSCs by decreasing IL-4120572 expres-sion There are three PDE-5 inhibitors in clinical trialssildenafil tadalafil and vardenafil In preclinical mousemodels sildenafil has reduced tumor growth by blockingthe immunosuppressive function of MDSCs and enhancedthe activation and infiltration of T-cells [126 127] Tadalafilhas been applied to patients with head and neck squamouscarcinoma and melanoma where it showed improved clinicaloutcome due to a reduction in tumor-infiltrating MDSCs[128 129]

Recent studies have shown that PI3K120574 plays an importantrole in the trafficking ofMDSCs and their polarization into animmunosuppressive phenotype [101 130] PI3K120575120574 inhibitorIPI-145 in combination with anti-PDL1 antibodies resulted

in the inhibition of MDSC activity increased CD8+ T-cellinfiltration and improved survival in head and neck tumormodels [131]

223 Treg Targeted erapy Tregs are highly immunosup-pressive fractions of CD4+ T-cells and are known to play amajor role in maintaining self-tolerance Treg cells exhibittheir suppressive activity via several mechanisms includinginhibition of APC maturation through the CTLA-4 pathwaysecretion of inhibitory cytokines such as IL10 TGF betaand IL35 and expression of granzyme and perforin whichkills effector T-cells There are several potential therapiesthat target Treg cell suppression either directly or indi-rectly including candidates targeting CD25 CTLA-4 OX-40 GITR and CCR4 In this section we will discuss IDOinhibitors and TGF beta inhibitors

(a) CCR4 Inhibitors It has been previously reported thattumor cells and macrophages produce CCL22 which chemo-tracts Treg cells expressing the CCR4 receptor This antibodyis reported to deplete CD25+ Tregs and promote antitumorimmune responses in human patients [132] Hence anti-CCR4 is an attractive target to combine with checkpointinhibitors Currently the anti-CCR4 antibody is being testedin combination with nivolumab (NCT02705105) or dur-valumab (NCT02301130) in patients with advanced solidtumors

(b) IDO Inhibitors IDO is a metabolic enzyme which cat-alyzes the cleavage of L-tryptophan to its metabolites result-ing in the generation of Kynurenine [133] IDO is expressedby tumor cells and MDSCs in response to interferon gamma[134] Recent studies have provided evidence that IDOactivity is critical to support the activity of FoxP3 Tregs [135]and MDSCs [136] leading to suppression of the activity of T-cells andNK cells [137] IDO has been reported to promote T-cell resistance to anti-CTLA 4 therapy in murine melanomamodels [138] Recent reports have shown that combinedinhibition of IDOand immune checkpoint inhibitors (CTLA-4 PD1 and PD-L1) synergize in melanoma mouse modelsBased on the impressive preclinical data in melanomamodelseveral IDO inhibitors are explored in combination withCTLA-4 and PD-1 inhibition [139] There are several IDOinhibitors in a clinical trial with epacadostat (INCB024360)which has been explored in clinical trials mostly in combi-nation with immune checkpoint inhibitors A Phase I trialcombining epacadostat and ipilimumab (anti-CTLA-4) waswell tolerated in patients of metastatic melanoma [140]Pembrolizumab and the epacadostat were recently reportedto show promising response rates in NSCLC and melanomawhich lead to a Phase III clinical trial of this combinationin melanoma patients [141] Very recently this Phase III trialhas been expanded to NSCLC head and neck cancer andrenal and bladder cancers [142] Indoximod is another IDOinhibitor in clinical trials [143] A Phase 2 study combiningindoximod with ipilimumab or anti-PD1 (pembrolizumab ornivolumab) is currently ongoing (NCT02073123)

12 Journal of Oncology

(c) TGF120573 Inhibitors Transforming growth factor-120573 (TGF120573)is a cytokine that plays a crucial role in mediating immuno-suppression in the tumor microenvironment by stimulat-ing Tregs [144] A study in preclinical melanoma mod-els (BRAFV600EPTENminusminus) has shown synergy combin-ing TGF-120573 receptor kinase inhibitor I with anti-CTLA-4antibodies [145] Recently clinical trials have been ongo-ing to test the combination of TGF-120573 inhibitor (galu-nisertib) [146] and PD-1L1 checkpoint blockade (durval-umab or nivolumab) in patients with pancreatic cancer(NCT02734160) and hepatocellular carcinoma NSCLC andglioblastoma (NCT02423343)

23 Strategies to Design and Synthesize Novel Dual or TripleInhibitory Chemotypes at Can Block Multiple PathwaysConcomitant inhibition of multiple pathways required fortumor progression has recently been established as aninnovative strategy to improve targeted therapies in can-cer [147ndash151] The ldquodual- or triple-targeted single agentrdquostrategy could provide similar benefits as multiple combi-nation therapies do with minimal convolutions observedin combination approach including drug toxicities lengthyclinical investigations and high treatment costs SF1126 isthe first PI3KBRD4 inhibitor reported by SignalRx Pharma-ceuticals Inc blocking tumor growth in various preclinicalmouse models [152ndash155] SF1126 blocked tumor angiogenesisand metastasis as well as increasing the M1 to M2 ratioin various preclinical mouse models [101] Based on thepromising preclinical results various clinical trials of SF1126were opened A Phase I clinical trial of SF1126 enrolled44 patients with advanced solid tumors and B cell malig-nancies at 9 dose levels (90-1110 mgm2day) (155) SF1126was well tolerated in patients with stable disease (SD) asthe best response in patients with advanced malignanciesBased on this convincing data Phase 1 clinical trials ofSF1126 were opened for patients with relapsed or refrac-tory neuroblastoma (NCT02337309) or those with advancedhepatocellular carcinoma (NCT03059147) The combinationof SF1126 with anti-PD1PDL1 inhibitors is in the planningstages for treating advanced solid tumors In addition toSF1126 various other multikinase inhibitors such as BI-2536(clinical PLK1) and TG-101348 (JAK2FLT3 kinase inhibitor)are reported to have BRD4 activity and are suggested asdual kinasebromodomain inhibitors [156] Another reportby Weinstock et al has demonstrated the selective dualinhibition of cancer-related deubiquitinating proteases USP7and USP47 and has shown in vivo activity against multiplemyeloma and B cell leukemia [149]

Morales et al have recently reported the synthesis of a5-morpholino-7H-thieno [32-b] pyran-7-one (TP scaffold)system to design novel inhibitors having improved potencytowards PI-3K [157] SF2523 is a dual PI3KBRD4 inhibitorgenerated from the TP series which orthogonally hit PI3Kand BRD4 to block expression activation and stabilizationof Myc leading to reduced tumor growth and metastasisin various preclinical models [158ndash160] Unpublished resultsby Joshi et al suggest that SF2523 is an immunoonco-logical inhibitor that hits tumor cells increases the ratio

of M1 to M2 and increases the infiltration of cytotoxicCD8+ T-cells in various tumor models This moleculehas PI3K120572 and BRD4 activity which blocks tumor growthby inducing apoptosis and cell cycle arrest suppressingPDL1 expression on tumor cells and simultaneously thismolecule blocks myeloid cell-derived immunosuppressionand provides a durable antitumor immune response invarious tumor models due to its potent PI3K120574 and PI3K120575activity Using this TP scaffold and computational meth-ods novel dual or triple PI3KBRD4CDK46 PI3KPARPPI3KBRD4HDAC PI3KMEK and PI3KIDO inhibitorychemotypes are engineered by SignalRx Pharmaceuticals[161] These rationally designed chemotypes are highly selec-tive and potent against their targets SRX3177 is a ldquofirstin classrdquo triple PI3K-BRD4-CDK46 inhibitor for combi-natorial inhibition of three oncogenes promoting cancercell growth phosphatidylinositol-3 kinase (PI3K) cyclin-dependent kinases 4 and 6 (CDK46) and the epigeneticregulator BRD4 [162] in a single molecule This chemotypeshowed potent in vitro and in vivo activity in mantle celllymphoma neuroblastoma and hepatocellular carcinomatumor models [162] Another report suggests the develop-ment of rationally designed pazopanib based HDAC andVEGFR dual inhibitors that target cancer epigenetics andangiogenesis simultaneously and this chemotype has shownantitumor efficacy in human colorectal carcinoma models[150] This rational drug design strategy has recently gainedsignificant attention resulting in a number of dual or tripleinhibitory chemotypes for the treatment of cancer Thisstrategy of rationally designing novel dual or triple chemo-types which can effectively kill tumor cells and at the sametime activate immune cells will be an effective combinationregimen to explore with immunotherapy Although most ofthese chemotypes are not yet explored in clinical trials thereis strong hope that these rationally designed chemotypes willshow a durable antitumor immune response when combinedwith immunotherapy

3 Conclusions

In summary the durable antitumor response generated by theapplication of checkpoint inhibitors has revolutionized thefield of cancer immunotherapy Very soon it will be realizedthat the clinical benefit obtained from the immune check-point blockade is limited to only a small subset of patientsand that most patients do not respond to this therapy Thecombination of immune checkpoint blockade with severalother anticancer treatments has shown remarkable successin various cancers and provided hope for the patients whodo not respond to checkpoint inhibitor monotherapy Wehave summarized the therapeutic potential of checkpointinhibitors with drugs that increase tumor immunogenicityreduce tumor burden and reverse tumor-mediated immuno-suppression leading to an effective and durable antitumorimmune response In the end we provided a novel approachto rationally design dual or triple inhibitory chemotypes thatcan concomitantly hit several tumor-promoting pathwaysand increase the immune effector response by blocking

Journal of Oncology 13

myeloid cell-mediated tumor immunosuppression Thisnovel approach is early in its development stage but thepromising antitumor results generated so far by use of dualor triple inhibitor chemotypes in different cancer modelsprovide a rationale to continue exploring these agents withimmune checkpoint inhibitors

Conflicts of Interest

Donald L Durden is an employee of Signal Rx Pharmaceuti-cals and has financial conflicts of interest regarding novel dualor triple inhibitors described in this review

Acknowledgments

This work was supported in part by NIHGrant R01 FD04385(to Donald L Durden) The authors thank Stellar Chang forformatting the manuscript

References

[1] F S Hodi S J OrsquoDay D F McDermott et al ldquoImproved sur-vival with ipilimumab in patients with metastatic melanomardquoe New England Journal of Medicine vol 363 no 8 pp 711ndash723 2010

[2] S L Topalian F S Hodi J R Brahmer et al ldquoSafety activityand immune correlates of anti-PD-1 antibody in cancerrdquo eNew England Journal of Medicine vol 366 no 26 pp 2443ndash2454 2012

[3] J R Brahmer S S Tykodi L Q M Chow et al ldquoSafetyand activity of anti-PD-L1 antibody in patients with advancedcancerrdquoe New England Journal of Medicine vol 366 no 26pp 2455ndash2465 2012

[4] JM Pitt MVetizou R Daillere et al ldquoResistanceMechanismsto Immune-Checkpoint Blockade in Cancer Tumor-Intrinsicand -Extrinsic Factorsrdquo Immunity vol 44 no 6 pp 1255ndash12692016

[5] J S OrsquoDonnell G V Long R A Scolyer MW Teng andM JSmyth ldquoResistance to PD1PDL1 checkpoint inhibitionrdquoCancerTreatment Reviews vol 52 pp 71ndash81 2017

[6] R W Jenkins D A Barbie and K T Flaherty ldquoMechanisms ofresistance to immune checkpoint inhibitorsrdquo British Journal ofCancer vol 118 no 1 pp 9ndash16 2018

[7] P Sharma SHu-Lieskovan JAWargo andARibas ldquoPrimaryAdaptive and Acquired Resistance to Cancer ImmunotherapyrdquoCell vol 168 no 4 pp 707ndash723 2017

[8] F M Marincola E M Jaffee D J Hicklin and S FerroneldquoEscape of human solid tumors from T-cell recognition molec-ular mechanisms and functional significancerdquo Advances inImmunology vol 74 pp 181ndash273 2000

[9] N A Rizvi M D Hellmann A Snyder et al ldquoMutationallandscape determines sensitivity to PD-1 blockade in non-smallcell lung cancerrdquo Science vol 348 no 6230 pp 124ndash128 2015

[10] E B Garon N A Rizvi R Hui et al ldquoPembrolizumab forthe treatment of non-small-cell lung cancerrdquoe New EnglandJournal of Medicine vol 372 no 21 pp 2018ndash2028 2015

[11] L Carbognin S Pilotto andMMilella ldquoDifferential activity ofnivolumab pembrolizumab and MPDL3280A according to thetumor expression of programmed death-ligand-1 (PD-L1) sen-sitivity analysis of trials in melanoma lung and genitourinarycancersrdquo PLoS ONE vol 10 no 6 Article ID e0130142 2015

[12] M Murahashi Y Hijikata K Yamada et al ldquoPhase I clinicaltrial of a five-peptide cancer vaccine combined with cyclophos-phamide in advanced solid tumorsrdquo Clinical Immunology vol166-167 pp 48ndash58 2016

[13] M Toulmonde N Penel J Adam et al ldquoCombination of pem-brolizumab and metronomic cyclophosphamide in patientswith advanced sarcomas and GIST A French Sarcoma Groupphase II trialrdquo Journal of Clinical Oncology vol 35 no 15 supplpp 11053-11053 2017

[14] G Middleton P Silcocks T Cox et al ldquoGemcitabine andcapecitabine with or without telomerase peptide vaccineGV1001 in patients with locally advanced or metastatic pancre-atic cancer (TeloVac) an open-label randomised phase 3 trialrdquoe Lancet Oncology vol 15 no 8 pp 829ndash840 2014

[15] Immunotherapy PIfC ldquoEvaluating the Safety and Efficacyof a CD40 Antibody Anti-PD-1 Checkpoint Inhibitor andChemotherapy in Combination Pancreatic Cancer ClinicalTrial Combining Immunotherapy and Chemotherapy 2017rdquohttpswwwparkericiorgresearch projectcd40-pancreatic-cancer-clinical-trial-immunotherapy-and-chemotherapy

[16] C E Ariyan M S Brady R H Siegelbaum et al ldquoRobust anti-tumor responses result from local chemotherapy and CTLA-4Blockaderdquo Cancer Immunology Research vol 6 no 2 pp 189ndash200 2018

[17] T J Lynch I Bondarenko A Luft et al ldquoIpilimumab in com-bination with paclitaxel and carboplatin as first-line treatmentin stage IIIBIV non-small-cell lung cancer results from arandomized double-blind multicenter phase II studyrdquo Journalof Clinical Oncology vol 30 no 17 pp 2046ndash2054 2012

[18] M Reck I Bondarenko A Luft et al ldquoIpilimumab in com-bination with paclitaxel and carboplatin as first-line therapyin extensivedisease-small-cell lungcancer Results from a ran-domized double-blind multicenter phase 2 trialrdquo Annals ofOncology vol 24 no 1 Article ID mds213 pp 75ndash83 2013

[19] S K Seung B D Curti M Crittenden et al ldquoPhase 1 studyof stereotactic body radiotherapy and interleukin-2 Tumor andimmunological responsesrdquo Science Translational Medicine vol4 no 137 Article ID 137ra74 2012

[20] G G Hanna and T Illidge ldquoRadiotherapy and ImmunotherapyCombinations in Non-small Cell Lung Cancer A PromisingFuturerdquo Clinical Oncology vol 28 no 11 pp 726ndash731 2016

[21] K J Pienta J-P Machiels D Schrijvers et al ldquoPhase 2 study ofcarlumab (CNTO 888) a human monoclonal antibody againstCC-chemokine ligand 2 (CCL2) in metastatic castration-resistant prostate cancerrdquo Investigational New Drugs vol 31 no3 pp 760ndash768 2013

[22] S K Sandhu K Papadopoulos P C Fong et al ldquoA first-in-human first-in-class phase i study of carlumab (CNTO 888)a human monoclonal antibody against CC-chemokine ligand2 in patients with solid tumorsrdquo Cancer Chemotherapy andPharmacology vol 71 no 4 pp 1041ndash1050 2013

[23] J D Wolchok H Kluger and M K Callahan ldquoNivolumab plusIpilimumab in advanced melanomardquoe New England Journalof Medicine vol 369 no 2 pp 122ndash133 2013

[24] M A Curran W Montalvo H Yagita and J P Allison ldquoPD-1 and CTLA-4 combination blockade expands infiltrating Tcells and reduces regulatory T and myeloid cells within B16melanoma tumorsrdquo Proceedings of the National Acadamy ofSciences of the United States of America vol 107 no 9 pp 4275ndash4280 2010

[25] Q Zhou M E Munger R G Veenstra et al ldquoCoexpression ofTim-3 and PD-1 identifies a CD8+ T-cell exhaustion phenotype

14 Journal of Oncology

inmice with disseminated acutemyelogenous leukemiardquoBloodvol 117 no 17 pp 4501ndash4510 2011

[26] J Fourcade Z Sun andM Benallaoua ldquoUpregulation of Tim-3and PD-1 expression is associated with tumor antigen-specificCD8+ T cell dysfunction in melanoma patientsrdquoe Journal ofExperimental Medicine vol 207 no 10 pp 2175ndash2186 2010

[27] S-R Woo M E Turnis M V Goldberg et al ldquoImmuneinhibitory molecules LAG-3 and PD-1 synergistically regulateT-cell function to promote tumoral immune escaperdquo CancerResearch vol 72 no 4 pp 917ndash927 2012

[28] L Chen and D B Flies ldquoMolecular mechanisms of T cell co-stimulation and co-inhibitionrdquo Nature Reviews Immunologyvol 13 no 4 pp 227ndash242 2013

[29] A E Vilgelm D B Johnson andA Richmond ldquoCombinatorialapproach to cancer immunotherapy Strength in numbersrdquoJournal of Leukocyte Biology vol 100 no 2 pp 275ndash290 2016

[30] P A Ott F S Hodi H L Kaufman J M Wigginton and J DWolchok ldquoCombination immunotherapy A roadmaprdquo Journalfor Immunoerapy of Cancer vol 5 p 16 2016

[31] L Bracci G Schiavoni A Sistigu and F Belardelli ldquoImmune-based mechanisms of cytotoxic chemotherapy implications forthe design of novel and rationale-based combined treatmentsagainst cancerrdquo Cell Death amp Differentiation vol 21 no 1 pp15ndash25 2014

[32] L Zitvogel O Kepp and G Kroemer ldquoImmune parametersaffecting the efficacy of chemotherapeutic regimensrdquo NatureReviews Clinical Oncology vol 8 no 3 pp 151ndash160 2011

[33] T Takeshima K Chamoto D Wakita et al ldquoLocal radiationtherapy inhibits tumor growth through the generation oftumor-specific CTL Its potentiation by combination with TH1cell therapyrdquoCancer Research vol 70 no 7 pp 2697ndash2706 2010

[34] L A Emens and G Middleton ldquoThe interplay of immunother-apy and chemotherapy harnessing potential synergiesrdquo CancerImmunology Research vol 3 no 5 pp 436ndash443 2015

[35] F Ghiringhelli C Menard P E Puig et al ldquoMetronomiccyclophosphamide regimen selectively depletes CD4+CD25+regulatory T cells and restores T and NK effector functions inend stage cancer patientsrdquo Cancer Immunology Immunother-apy vol 56 no 5 pp 641ndash648 2007

[36] J-P H Machiels R T Todd Reilly L A Emens et alldquoCyclophosphamide doxorubicin and paclitaxel enhance theantitumor immune response of granulocytemacrophage-colony stimulating factor-secreting whole-cell vaccines inHER-2neu tolerized micerdquo Cancer Research vol 61 no 9 pp3689ndash3697 2001

[37] L A Emens and E M Jaffee ldquoEnhancement of an AllogeneicGM-CSF-Secreting Breast Cancer Vaccine by Immunomodu-latory Doses of Cyclophosphamide and Doxorubicinrdquo DefenseTechnical Information Center 2003

[38] S Walter T Weinschenk A Stenzl R Zdrojowy A Pluzanskaand C Szczylik ldquoMultipeptide immune response to cancervaccine IMA901 after single-dose cyclophosphamide associateswith longer patient survivalrdquoNature Medicine vol 18 no 8 pp1254-61 Aug 2012

[39] M Mkrtichyan Y G Najjar E C Raulfs et al ldquoAnti-PD-1synergizes with cyclophosphamide to induce potent anti-tumorvaccine effects through novelmechanismsrdquo European Journal ofImmunology vol 41 no 10 pp 2977ndash2986 2011

[40] C Pfirschke C Engblom S Rickelt et al ldquoImmunogenicChemotherapy Sensitizes Tumors to Checkpoint BlockadeTherapyrdquo Immunity vol 44 no 2 pp 343ndash354 2016

[41] A K Nowak R A Lake A L Marzo et al ldquoInduction oftumor cell apoptosis in vivo increases tumor antigen cross-presentation cross-priming rather than cross-tolerizing hosttumor-specific CD8 T cellsrdquo e Journal of Immunology vol170 no 10 pp 4905ndash4913 2003

[42] E Suzuki V Kapoor A S Jassar L R Kaiser and SM Albelda ldquoGemcitabine selectively eliminates splenic Gr-1+CD11b+ myeloid suppressor cells in tumor-bearing animalsand enhances antitumor immune activityrdquo Clinical CancerResearch vol 11 no 18 pp 6713ndash6721 2005

[43] T Ghansah N Vohra K Kinney et al ldquoDendritic cellimmunotherapy combined with gemcitabine chemotherapyenhances survival in a murine model of pancreatic carcinomardquoCancer Immunology Immunotherapy vol 62 no 6 pp 1083ndash1091 2013

[44] A K Nowak B W S Robinson and R A Lake ldquoSynergybetween chemotherapy and immunotherapy in the treatmentof established murine solid tumorsrdquo Cancer Research vol 63no 15 pp 4490ndash4496 2003

[45] Z G Fridlender J Sun S Singhal et al ldquoChemotherapydelivered after viral immunogene therapy augments antitumorefficacy via multiple immune-mediated mechanismsrdquo Molecu-larerapy vol 18 no 11 pp 1947ndash1959 2010

[46] L Eric C J Yeo K D Lillemoe et al ldquoA lethally irradiatedallogeneic granulocyte-macrophage colony stimulating factor-secreting tumor vaccine for pancreatic adenocarcinoma Aphase II trial of safety efficacy and immune activationrdquo Annalsof Surgery vol 253 no 2 pp 328ndash335 2011

[47] G Chen and L A Emens ldquoChemoimmunotherapy Reengi-neering tumor immunityrdquo Cancer Immunology Immunother-apy vol 62 no 2 pp 203ndash216 2013

[48] C Robert L Thomas and I Bondarenko ldquoIpilimumab plusdacarbazine for previously untreated metastatic melanomardquoeNew England Journal of Medicine vol 364 no 26 pp 2517ndash2526 2011

[49] G G Hanna V M Coyle and K M Prise ldquoImmune modula-tion in advanced radiotherapies Targeting out-of-field effectsrdquoCancer Letters vol 368 no 2 pp 246ndash251 2015

[50] B Frey Y Rubner R Wunderlich et al ldquoInduction of abscopalanti-tumor immunity and immunogenic tumor cell death byionizing irradiation - Implications for cancer therapiesrdquoCurrentMedicinal Chemistry vol 19 no 12 pp 1751ndash1764 2012

[51] S Demaria B Ng M L Devitt et al ldquoIonizing radiationinhibition of distant untreated tumors (abscopal effect) isimmunemediatedrdquo International Journal of Radiation Oncology∙ Biology ∙ Physics vol 58 no 3 pp 862ndash870 2004

[52] E A Reits J W Hodge C A Herberts et al ldquoRadiation mod-ulates the peptide repertoire enhancesMHC class I expressionand induces successful antitumor immunotherapyrdquoe Journalof Experimental Medicine vol 203 no 5 pp 1259ndash1271 2006

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[56] E J Van Limbergen D K De Ruysscher V O Pimentel et alldquoCombining radiotherapy with immunotherapy The past the

Journal of Oncology 15

present and the futurerdquo British Journal of Radiology vol 90 no1076 2017

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[58] E Chajon J Castelli H Marsiglia and R De CrevoisierldquoThe synergistic effect of radiotherapy and immunotherapyA promising but not simple partnershiprdquo Critical Review inOncologyHematology vol 111 pp 124ndash132 2017

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[65] S F Slovin C S Higano and O Hamid ldquoIpilimumab aloneor in combination with radiotherapy in metastatic castration-resistant prostate cancer results from an open-label multicen-ter phase III studyrdquo Annals of Oncology vol 24 pp 1813ndash18212013

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[67] A C West and R W Johnstone ldquoNew and emerging HDACinhibitors for cancer treatmentrdquoe Journal of Clinical Investi-gation vol 124 no 1 pp 30ndash39 2014

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[69] YHe I Korboukh J Jin and JHuang ldquoTargeting protein lysinemethylation and demethylation in cancersrdquo Acta Biochimica etBiophysica Sinica vol 44 no 1 pp 70ndash79 2012

[70] A C West S R Mattarollo J Shortt et al ldquoAn intact immunesystem is required for the anticancer activities of histonedeacetylase inhibitorsrdquo Cancer Research vol 73 no 24 pp7265ndash7276 2013

[71] W J Magner A L Kazim C Stewart et al ldquoActivation of MHCClass I II and CD40 Gene Expression by Histone DeacetylaseInhibitorsrdquoe Journal of Immunology vol 165 no 12 pp 7017ndash7024 2000

[72] S Armeanu M Bitzer U M Lauer et al ldquoNatural killercell-mediated lysis of hepatoma cells via specific induction ofNKG2D ligands by the histone deacetylase inhibitor sodiumvalproaterdquoCancer Research vol 65 no 14 pp 6321ndash6329 2005

[73] E Fonsatti H J M Nicolay L Sigalotti et al ldquoFunctionalup-regulation of human leukocyte antigen class I antigensexpression by 5-aza-21015840-deoxycytidine in cutaneous melanomaImmunotherapeutic implicationsrdquo Clinical Cancer Researchvol 13 no 11 pp 3333ndash3338 2007

[74] S Coral L Sigalotti M Altomonte et al ldquo5-aza-21015840-deox-ycytidine-induced expression of functional cancer testis anti-gens in human renal cell carcinoma Immunotherapeutic impli-cationsrdquo Clinical Cancer Research vol 8 no 8 pp 2690ndash26952002

[75] J Dunn and S Rao ldquoEpigenetics and immunotherapy Thecurrent state of playrdquo Molecular Immunology vol 87 pp 227ndash239 2017

[76] P Filippakopoulos J Qi S Picaud et al ldquoSelective inhibition ofBET bromodomainsrdquo Nature vol 468 no 7327 pp 1067ndash10732010

[77] H Zhu F Bengsch N Svoronos et al ldquoBET BromodomainInhibition Promotes Anti-tumor Immunity by Suppressing PD-L1 Expressionrdquo Cell Reports vol 16 no 11 pp 2829ndash2837 2016

[78] F C Hongwei Wang J Cheng V Alejandro et al ldquoJQ1 a Selec-tive Bromodomain Inhibitor Augment the Immunogenicity ofMantle Cell Lymphoma By Influencing the Expression of PD-L1rdquo Blood pp 126ndash822 2015

[79] Y Kagoya M Nakatsugawa Y Yamashita et al ldquoBET bro-modomain inhibition enhances T cell persistence and functionin adoptive immunotherapy modelsrdquo e Journal of ClinicalInvestigation vol 126 no 9 pp 3479ndash3494 2016

[80] O A Dennis J F Gordon and K K Wong ldquoBET bromod-omain inhibition synergizes with immune checkpoint blockadeto facilitate anti-tumor response in a murine model of non-small cell lung cancer harboring activating KRAS mutationrdquoe Journal of Immunology vol 196 suppl 1 7410 2016

[81] D Lindau P GielenM Kroesen PWesseling andG J AdemaldquoThe immunosuppressive tumour network myeloid-derivedsuppressor cells regulatory T cells and natural killer T cellsrdquoe Journal of Immunology vol 138 no 2 pp 105ndash115 2013

[82] RNoy and JW Pollard ldquoTumor-associatedmacrophages frommechanisms to therapyrdquo Immunity vol 41 no 1 pp 49ndash61 2014

[83] A Mantovani S Sozzani M Locati P Allavena and A SicaldquoMacrophage polarization tumor-associated macrophages as aparadigm for polarizedM2mononuclear phagocytesrdquoTrends inImmunology vol 23 no 11 pp 549ndash555 2002

[84] M A Cannarile C H Ries S Hoves and D RuttingerldquoTargeting tumor-associated macrophages in cancer therapyand understanding their complexityrdquo OncoImmunology vol 3no 9 article no e955356 2014

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[87] Z G Fridlender V Kapoor G Buchlis et al ldquoMonocytechemoattractant protein-1 blockade inhibits lung cancer tumorgrowth by alteringmacrophage phenotype and activatingCD8+cellsrdquo American Journal of Respiratory Cell and MolecularBiology vol 44 no 2 pp 230ndash237 2011

16 Journal of Oncology

[88] A Mantovani F Marchesi A Malesci L Laghi and PAllavena ldquoTumour-associated macrophages as treatment tar-gets in oncologyrdquo Nature Reviews Clinical Oncology vol 14 no7 pp 399ndash416 2017

[89] I Brana A Calles P M LoRusso et al ldquoCarlumab an anti-C-C chemokine ligand 2 monoclonal antibody in combinationwith four chemotherapy regimens for the treatment of patientswith solid tumors an open-label multicenter phase 1b studyrdquoTargeted Oncology vol 10 no 1 pp 111ndash123 2015

[90] T M Nywening A Wang-Gillam D E Sanford et al ldquoTar-geting tumour-associated macrophages with CCR2 inhibitionin combination with FOLFIRINOX in patients with borderlineresectable and locally advanced pancreatic cancer a single-centre open-label dose-finding non-randomised phase 1btrialrdquoe Lancet Oncology vol 17 no 5 pp 651ndash662 2016

[91] Y Wang X Zhang L Yang J Xue and G Hu ldquoBlockade ofCCL2 enhances immunotherapeutic effect of anti-PD1 in lungcancerrdquo Journal of Bone Oncology vol 11 pp 27ndash32 2018

[92] B Ruffell and L M Coussens ldquoMacrophages and therapeuticresistance in cancerrdquo Cancer Cell vol 27 no 4 pp 462ndash4722015

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[94] C H Ries M A Cannarile S Hoves et al ldquoTargeting tumor-associated macrophages with anti-CSF-1R antibody reveals astrategy for cancer therapyrdquoCancer Cell vol 25 no 6 pp 846ndash859 2014

[95] J H Stafford T Hirai L Deng et al ldquoColony stimulating factor1 receptor inhibition delays recurrence of glioblastoma afterradiation by alteringmyeloid cell recruitment and polarizationrdquoNeuro-Oncology vol 18 no 6 pp 797ndash806 2016

[96] S M Pyonteck L Akkari A J Schuhmacher et al ldquoCSF-1Rinhibition alters macrophage polarization and blocks gliomaprogressionrdquo Nature Medicine vol 19 no 10 pp 1264ndash12722013

[97] G Germano R Frapolli M Simone et al ldquoAntitumor andanti-inflammatory effects of trabectedin on human myxoidliposarcoma cellsrdquo Cancer Research vol 70 no 6 pp 2235ndash2244 2010

[98] G Germano R Frapolli C Belgiovine et al ldquoRole ofmacrophage targeting in the antitumor activity of trabectedinrdquoCancer Cell vol 23 no 2 pp 249ndash262 2013

[99] JW Pollard ldquoTumour-educatedmacrophages promote tumourprogression and metastasisrdquo Nature Reviews Cancer vol 4 no1 pp 71ndash78 2004

[100] F O Martinez and S Gordon ldquoThe M1 and M2 paradigmof macrophage activation time for reassessmentrdquo F1000PrimeReports vol 6 article 13 2014

[101] S Joshi A R Singh M Zulcic and D L Durden ldquoAmacrophage-dominant PI3K isoform controls hypoxia-inducedHIF1120572 andHIF2120572 stability and tumor growth angiogenesis andmetastasisrdquoMolecular Cancer Research vol 12 no 10 pp 1520ndash1531 2014

[102] S Joshi A R Singh M Zulcic et al ldquoRac2 controls tumorgrowth metastasis and M1-M2 macrophage differentiation invivordquo PLoS ONE vol 9 no 4 2014

[103] M M Kaneda K S Messer N Ralainirina et al ldquoPI3K120574 is amolecular switch that controls immune suppressionrdquo Naturevol 539 no 7629 pp 437ndash442 2016

[104] O M Pello M De Pizzol M Mirolo et al ldquoRole of c-MYCin alternative activation of human macrophages and tumor-associated macrophage biologyrdquo Blood vol 119 no 2 pp 411ndash421 2012

[105] S Gordon and F O Martinez ldquoAlternative activation ofmacrophagesmechanism and functionsrdquo Immunity vol 32 no5 pp 593ndash604 2010

[106] O De Henau M Rausch D Winkler et al ldquoOvercomingresistance to checkpoint blockade therapy by targeting PI3K120574in myeloid cellsrdquo Nature vol 539 no 7629 pp 443ndash447 2016

[107] A W Tolcher D S Hong R J Sullivan et al ldquoIPI-549-01-Aphase 11b first in human study of IPI-549 a PI3K-120574 inhibitoras monotherapy and in combination with pembrolizumabin subjects with advanced solid tumorsrdquo Journal of ClinicalOncology vol 34 no 15 suppl pp TPS3111ndashTPS3111 2016

[108] A J Gunderson M M Kaneda T Tsujikawa et al ldquoBrutontyrosine kinasendashDependent immune cell cross-talk drives pan-creas cancerrdquo Cancer Discovery vol 6 no 3 pp 270ndash285 2016

[109] G L Beatty D A Torigian E Gabriela Chiorean et al ldquoA phaseI study of an agonist CD40 monoclonal antibody (CP-870893)in combination with gemcitabine in patients with advancedpancreatic ductal adenocarcinomardquo Clinical Cancer Researchvol 19 no 22 pp 6286ndash6295 2013

[110] T Bald J LandsbergD Lopez-Ramos et al ldquoImmune cell-poormelanomas benefit fromPD-1 blockade after targeted type I IFNactivationrdquo Cancer Discovery vol 4 no 6 pp 674ndash687 2014

[111] Y Shirota H Shirota and D M Klinman ldquoIntratumoral injec-tion of CpG oligonucleotides induces the differentiation andreduces the immunosuppressive activity of myeloid-derivedsuppressor cellsrdquoe Journal of Immunology vol 188 no 4 pp1592ndash1599 2012

[112] R Houot and R Levy ldquoT-cell modulation combined withintratumoral CpG cures lymphoma in a mouse model withoutthe need for chemotherapyrdquo Blood vol 113 no 15 pp 3546ndash3552 2009

[113] F Sato-Kaneko S Yao A Ahmadi et al ldquoCombinationimmunotherapy with TLR agonists and checkpoint inhibitorssuppresses head and neck cancerrdquo JCI Insight vol 2 no 18 2017

[114] D I Gabrilovich and S Nagaraj ldquoMyeloid-derived suppressorcells as regulators of the immune systemrdquo Nature ReviewsImmunology vol 9 no 3 pp 162ndash174 2009

[115] S Ostrand-Rosenberg ldquoMyeloid-derived suppressor cellsmore mechanisms for inhibiting antitumor immunityrdquo CancerImmunology Immunotherapy vol 59 no 10 pp 1593ndash16002010

[116] Y Nefedova M Fishman S Sherman X Wang A A Beg andD I Gabrilovich ldquoMechanism of all-trans retinoic acid effecton tumor-associated myeloid-derived suppressor cellsrdquo CancerResearch vol 67 no 22 pp 11021ndash11028 2007

[117] M E Huang Y C Ye S R Chen et al ldquoUse of all-trans retinoicacid in the treatment of acute promyelocytic leukemiardquo Bloodvol 72 no 2 pp 567ndash572 1988

[118] N Mirza M Fishman I Fricke et al ldquoAll-trans-retinoic acidimproves differentiation of myeloid cells and immune responsein cancer patientsrdquo Cancer Research vol 66 no 18 pp 9299ndash9307 2006

[119] C Iclozan S Antonia A Chiappori D-T Chen and DGabrilovich ldquoTherapeutic regulation of myeloid-derived sup-pressor cells and immune response to cancer vaccine in patientswith extensive stage small cell lung cancerrdquoCancer ImmunologyImmunotherapy vol 62 no 5 pp 909ndash918 2013

Journal of Oncology 17

[120] J E Walsh A Clark T A Day M B Gillespie and MR Young ldquoUse of 12057225-Dihydroxyvitamin D3 treatment tostimulate immune infiltration into head and neck squamouscell carcinomardquoHuman Immunology vol 71 no 7 pp 659ndash6652010

[121] T Veikkola M Karkkainen L Claesson-Welsh and K AlitaloldquoRegulation of angiogenesis via vascular endothelial growthfactor receptorsrdquo Cancer Research vol 60 no 2 pp 203ndash2122000

[122] D I Gabrilovich H L Chen K R Girgis et al ldquoProductionof vascular endothelial growth factor by human tumors inhibitsthe functional maturation of dendritic cellsrdquo Nature Medicinevol 2 no 10 pp 1096ndash1103 1996

[123] T Osada G Chong R Tansik et al ldquoThe effect of anti-VEGFtherapy on immature myeloid cell and dendritic cells in cancerpatientsrdquoCancer Immunology Immunotherapy vol 57 no 8 pp1115ndash1124 2008

[124] S L Highfill Y Cui A J Giles et al ldquoDisruption of CXCR2-mediated MDSC tumor trafficking enhances anti-PD1 efficacyrdquoScience Translational Medicine vol 6 no 237 Article ID237ra67 2014

[125] H Jung A Bischof K Ebsworth et al ldquoAbstract A90 Com-bination therapy of chemokine receptor inhibition plus PDL-1 blockade potentiates anti-tumor effects in a murine modelof breast cancerrdquo Molecular Cancer erapeutics vol 3 p 2272015

[126] P Serafini K Meckel M Kelso et al ldquoPhosphodiesterase-5 inhibition augments endogenous antitumor immunity byreducingmyeloid-derived suppressor cell functionrdquoe Journalof Experimental Medicine vol 203 no 12 pp 2691ndash2702 2006

[127] C Meyera A Sevko M Ramacher et al ldquoChronic inflam-mation promotes myeloid-derived suppressor cell activationblocking antitumor immunity in transgenic mouse melanomamodelrdquo Proceedings of the National Acadamy of Sciences of theUnited States of America vol 108 no 41 pp 17111ndash17116 2011

[128] J A Califano Z Khan K A Noonan et al ldquoTadalafil augmentstumor specific immunity in patients with head and necksquamous cell carcinomardquo Clinical Cancer Research vol 21 no1 pp 30ndash38 2015

[129] J C Hassel H Jiang C Bender et al ldquoTadalafil has bio-logic activity in human melanoma Results of a pilot trialwith Tadalafil in patients with metastatic Melanoma (TaMe)rdquoOncoImmunology vol 6 no 9 article no e1326440 2017

[130] M C Schmid C J Avraamides H C Dippold et al ldquoReceptortyrosine kinases and TLRIL1Rs unexpectedly activate myeloidcell PI3K120574 A single convergent point promoting tumor inflam-mation and progressionrdquo Cancer Cell vol 19 no 6 pp 715ndash7272011

[131] R J Davis E CMoore P E Clavijo et al ldquoAnti-PD-L1 EfficacyCan Be Enhanced by Inhibition ofMyeloid-Derived SuppressorCells with a Selective Inhibitor of PI3K120575120574rdquo Cancer Researchvol 77 no 10 pp 2607ndash2619 2017

[132] D Sugiyama H Nishikawa Y Maeda et al ldquoAnti-CCR4mAb selectively depletes effector-type FoxP3+CD4+ regulatoryT cells evoking antitumor immune responses in humansrdquoProceedings of the National Acadamy of Sciences of the UnitedStates of America vol 110 no 44 pp 17945ndash17950 2013

[133] G C Prendergast C Smith S Thomas et al ldquoIndoleamine23-dioxygenase pathways of pathogenic inflammation andimmune escape in cancerrdquo Cancer Immunology Immunother-apy vol 63 no 7 pp 721ndash735 2014

[134] R Yoshida J Imanishi T Oku T Kishida and O HayaishildquoInduction of pulmonary indoleamine 23-dioxygenase byinterferonrdquo Proceedings of the National Acadamy of Sciences ofthe United States of America vol 78 no 1 pp 129ndash132 1981

[135] F Fallarino U Grohmann K W Hwang et al ldquoModulation oftryptophan catabolism by regulatory T cellsrdquo Nature Immunol-ogy vol 4 no 12 pp 1206ndash1212 2003

[136] C Smith M Y Chang K H Parker et al ldquoIDO is a nodalpathogenic driver of lung cancer and metastasis developmentrdquoCancer Discovery vol 2 no 8 pp 722ndash735 2012

[137] G Frumento R Rotondo M Tonetti G Damonte U Benattiand G B Ferrara ldquoTryptophan-derived catabolites are respon-sible for inhibition of T and natural killer cell proliferationinduced by indoleamine 23-dioxygenaserdquoe Journal of Exper-imental Medicine vol 196 no 4 pp 459ndash468 2002

[138] R B Holmgaard D Zamarin D H Munn J D Wolchokand J P Allison ldquoIndoleamine 23-dioxygenase is a criticalresistance mechanism in antitumor T cell immunotherapytargeting CTLA-4rdquo e Journal of Experimental Medicine vol210 no 7 pp 1389ndash1402 2013

[139] S Spranger H K Koblish B Horton P A Scherle RNewton and T F Gajewski ldquoMechanism of tumor rejectionwith doublets of CTLA-4 PD-1PD-L1 or IDO blockadeinvolves restored IL-2 production and proliferation of CD8+ Tcells directly within the tumor microenvironmentrdquo Journal forImmunoerapy of Cancer vol 2 no 1 2014

[140] G Gibney O Hamid J Lutzky et al ldquo511 Updated results froma phase 12 study of epacadostat (INCB024360) in combinationwith ipilimumab in patients with metastatic melanomardquo Euro-pean Journal of Cancer vol 51 pp S106ndashS107 2015

[141] Merck Ia ldquoIncyte and Merck to Advance ClinicalDevelopment Program Investigating the Combination ofEpacadostat with KEYTRUDA (pembrolizumab)rdquo httpswwwmrknewsroomcomnews-releaseoncology-newsroomincyte-and-merck-advance-clinical-development-program-investigating-c

[142] Incyte ldquoIncyte and Merck Provide Update on Phase 3Study of Epacadostat in Combination with KEYTRUDA(pembrolizumab) in Patients with Unresectable or MetastaticMelanomardquo

[143] H H Soliman S E Minton H S Han et al ldquoA Phase I study ofindoximod in patientswith advancedmalignanciesrdquoOncotarget vol 7 no 16 pp 22928ndash22938 2016

[144] J J Lebrun ldquoThe Dual Role of TGFbeta in Human CancerFrom Tumor Suppression to Cancer Metastasisrdquo MolecularBiology vol 2012 2012

[145] B A Hanks A Holtzhausen K Evans M Heid and G CBlobe ldquo Combinatorial TGF-120573 signaling blockade and anti-CTLA-4 antibody immunotherapy in a murine BRAF rdquo Journalof Clinical Oncology vol 32 no 15 suppl pp 3011-3011 2014

[146] S Herbertz J S Sawyer A J Stauber et al ldquoClinical devel-opment of galunisertib (Ly2157299 monohydrate) a smallmolecule inhibitor of transforming growth factor-beta signalingpathwayrdquo Drug Design Development and erapy vol 9 pp4479ndash4499 2015

[147] Y-C Duan Y-C Ma W-P Qin et al ldquoDesign and synthesisof tranylcypromine derivatives as novel LSD1HDACs dualinhibitors for cancer treatmentrdquo European Journal of MedicinalChemistry vol 140 pp 392ndash402 2017

[148] L Gu H Zhang T Liu et al ldquoDiscovery of Dual Inhibitors ofMDM2 and XIAP for Cancer Treatmentrdquo Cancer Cell vol 30no 4 pp 623ndash636 2016

Journal of Oncology 15

present and the futurerdquo British Journal of Radiology vol 90 no1076 2017

[57] R R Weichselbaum H Liang L Deng and Y-X Fu ldquoRadio-therapy and immunotherapy A beneficial liaisonrdquo NatureReviews Clinical Oncology vol 14 no 6 pp 365ndash379 2017

[58] E Chajon J Castelli H Marsiglia and R De CrevoisierldquoThe synergistic effect of radiotherapy and immunotherapyA promising but not simple partnershiprdquo Critical Review inOncologyHematology vol 111 pp 124ndash132 2017

[59] L Deng H Liang B Burnette et al ldquoIrradiation and antindashPD-L1 treatment synergistically promote antitumor immunity inmicerdquo e Journal of Clinical Investigation vol 124 no 2 pp687ndash695 2014

[60] S Demaria N Kawashima A M Yang et al ldquoImmune-mediated inhibition of metastases after treatment with localradiation and CTLA-4 blockade in a mouse model of breastcancerrdquo Clinical Cancer Research vol 11 pp 728ndash734 2005

[61] J Zeng A P See J Phallen et al ldquoAnti-PD-1 blockadeand stereotactic radiation produce long-term survival in micewith intracranial gliomasrdquo International Journal of RadiationOncology ∙ Biology ∙ Physics vol 86 no 2 pp 343ndash349 2013

[62] S M Hiniker D S Chen S Reddy et al ldquoA Systemiccomplete response of metastatic melanoma to local radiationand immunotherapyrdquo Translational Oncology vol 5 no 6 pp404ndash407 2012

[63] M A PostowM K Callahan C A Barker et al ldquoImmunologiccorrelates of the abscopal effect in a patientwithmelanomardquoeNew England Journal of Medicine vol 366 no 10 pp 925ndash9312012

[64] E B Golden S Demaria P B Schiff A Chachoua and S CFormenti ldquoAn abscopal response to radiation and ipilimumabin a patient with metastatic non-small cell lung cancerrdquo CancerImmunology Research vol 1 no 6 pp 365ndash372 2013

[65] S F Slovin C S Higano and O Hamid ldquoIpilimumab aloneor in combination with radiotherapy in metastatic castration-resistant prostate cancer results from an open-label multicen-ter phase III studyrdquo Annals of Oncology vol 24 pp 1813ndash18212013

[66] D C Ling C J Bakkenist R L Ferris and D A ClumpldquoRole of Immunotherapy in Head and Neck Cancerrdquo Seminarsin Radiation Oncology vol 28 no 1 pp 12ndash16 2018

[67] A C West and R W Johnstone ldquoNew and emerging HDACinhibitors for cancer treatmentrdquoe Journal of Clinical Investi-gation vol 124 no 1 pp 30ndash39 2014

[68] F Crea L Fornaro G Bocci et al ldquoEZH2 inhibition Targetingthe crossroad of tumor invasion and angiogenesisrdquo Cancer andMetastasis Reviews vol 31 no 3-4 pp 753ndash761 2012

[69] YHe I Korboukh J Jin and JHuang ldquoTargeting protein lysinemethylation and demethylation in cancersrdquo Acta Biochimica etBiophysica Sinica vol 44 no 1 pp 70ndash79 2012

[70] A C West S R Mattarollo J Shortt et al ldquoAn intact immunesystem is required for the anticancer activities of histonedeacetylase inhibitorsrdquo Cancer Research vol 73 no 24 pp7265ndash7276 2013

[71] W J Magner A L Kazim C Stewart et al ldquoActivation of MHCClass I II and CD40 Gene Expression by Histone DeacetylaseInhibitorsrdquoe Journal of Immunology vol 165 no 12 pp 7017ndash7024 2000

[72] S Armeanu M Bitzer U M Lauer et al ldquoNatural killercell-mediated lysis of hepatoma cells via specific induction ofNKG2D ligands by the histone deacetylase inhibitor sodiumvalproaterdquoCancer Research vol 65 no 14 pp 6321ndash6329 2005

[73] E Fonsatti H J M Nicolay L Sigalotti et al ldquoFunctionalup-regulation of human leukocyte antigen class I antigensexpression by 5-aza-21015840-deoxycytidine in cutaneous melanomaImmunotherapeutic implicationsrdquo Clinical Cancer Researchvol 13 no 11 pp 3333ndash3338 2007

[74] S Coral L Sigalotti M Altomonte et al ldquo5-aza-21015840-deox-ycytidine-induced expression of functional cancer testis anti-gens in human renal cell carcinoma Immunotherapeutic impli-cationsrdquo Clinical Cancer Research vol 8 no 8 pp 2690ndash26952002

[75] J Dunn and S Rao ldquoEpigenetics and immunotherapy Thecurrent state of playrdquo Molecular Immunology vol 87 pp 227ndash239 2017

[76] P Filippakopoulos J Qi S Picaud et al ldquoSelective inhibition ofBET bromodomainsrdquo Nature vol 468 no 7327 pp 1067ndash10732010

[77] H Zhu F Bengsch N Svoronos et al ldquoBET BromodomainInhibition Promotes Anti-tumor Immunity by Suppressing PD-L1 Expressionrdquo Cell Reports vol 16 no 11 pp 2829ndash2837 2016

[78] F C Hongwei Wang J Cheng V Alejandro et al ldquoJQ1 a Selec-tive Bromodomain Inhibitor Augment the Immunogenicity ofMantle Cell Lymphoma By Influencing the Expression of PD-L1rdquo Blood pp 126ndash822 2015

[79] Y Kagoya M Nakatsugawa Y Yamashita et al ldquoBET bro-modomain inhibition enhances T cell persistence and functionin adoptive immunotherapy modelsrdquo e Journal of ClinicalInvestigation vol 126 no 9 pp 3479ndash3494 2016

[80] O A Dennis J F Gordon and K K Wong ldquoBET bromod-omain inhibition synergizes with immune checkpoint blockadeto facilitate anti-tumor response in a murine model of non-small cell lung cancer harboring activating KRAS mutationrdquoe Journal of Immunology vol 196 suppl 1 7410 2016

[81] D Lindau P GielenM Kroesen PWesseling andG J AdemaldquoThe immunosuppressive tumour network myeloid-derivedsuppressor cells regulatory T cells and natural killer T cellsrdquoe Journal of Immunology vol 138 no 2 pp 105ndash115 2013

[82] RNoy and JW Pollard ldquoTumor-associatedmacrophages frommechanisms to therapyrdquo Immunity vol 41 no 1 pp 49ndash61 2014

[83] A Mantovani S Sozzani M Locati P Allavena and A SicaldquoMacrophage polarization tumor-associated macrophages as aparadigm for polarizedM2mononuclear phagocytesrdquoTrends inImmunology vol 23 no 11 pp 549ndash555 2002

[84] M A Cannarile C H Ries S Hoves and D RuttingerldquoTargeting tumor-associated macrophages in cancer therapyand understanding their complexityrdquo OncoImmunology vol 3no 9 article no e955356 2014

[85] AMantovaniA Sica S Sozzani P Allavena A Vecchi andMLocati ldquoThe chemokine system in diverse forms of macrophageactivation and polarizationrdquo Trends in Immunology vol 25 no12 pp 677ndash686 2004

[86] R D Loberg C Ying M Craig et al ldquoTargeting CCL2 withsystemic delivery of neutralizing antibodies induces prostatecancer tumor regression in vivordquo Cancer Research vol 67 no19 pp 9417ndash9424 2007

[87] Z G Fridlender V Kapoor G Buchlis et al ldquoMonocytechemoattractant protein-1 blockade inhibits lung cancer tumorgrowth by alteringmacrophage phenotype and activatingCD8+cellsrdquo American Journal of Respiratory Cell and MolecularBiology vol 44 no 2 pp 230ndash237 2011

16 Journal of Oncology

[88] A Mantovani F Marchesi A Malesci L Laghi and PAllavena ldquoTumour-associated macrophages as treatment tar-gets in oncologyrdquo Nature Reviews Clinical Oncology vol 14 no7 pp 399ndash416 2017

[89] I Brana A Calles P M LoRusso et al ldquoCarlumab an anti-C-C chemokine ligand 2 monoclonal antibody in combinationwith four chemotherapy regimens for the treatment of patientswith solid tumors an open-label multicenter phase 1b studyrdquoTargeted Oncology vol 10 no 1 pp 111ndash123 2015

[90] T M Nywening A Wang-Gillam D E Sanford et al ldquoTar-geting tumour-associated macrophages with CCR2 inhibitionin combination with FOLFIRINOX in patients with borderlineresectable and locally advanced pancreatic cancer a single-centre open-label dose-finding non-randomised phase 1btrialrdquoe Lancet Oncology vol 17 no 5 pp 651ndash662 2016

[91] Y Wang X Zhang L Yang J Xue and G Hu ldquoBlockade ofCCL2 enhances immunotherapeutic effect of anti-PD1 in lungcancerrdquo Journal of Bone Oncology vol 11 pp 27ndash32 2018

[92] B Ruffell and L M Coussens ldquoMacrophages and therapeuticresistance in cancerrdquo Cancer Cell vol 27 no 4 pp 462ndash4722015

[93] D G DeNardo D J Brennan E Rexhepaj et al ldquoLeukocytecomplexity predicts breast cancer survival and functionallyregulates response to chemotherapyrdquo Cancer Discovery vol 1no 1 pp 54ndash67 2011

[94] C H Ries M A Cannarile S Hoves et al ldquoTargeting tumor-associated macrophages with anti-CSF-1R antibody reveals astrategy for cancer therapyrdquoCancer Cell vol 25 no 6 pp 846ndash859 2014

[95] J H Stafford T Hirai L Deng et al ldquoColony stimulating factor1 receptor inhibition delays recurrence of glioblastoma afterradiation by alteringmyeloid cell recruitment and polarizationrdquoNeuro-Oncology vol 18 no 6 pp 797ndash806 2016

[96] S M Pyonteck L Akkari A J Schuhmacher et al ldquoCSF-1Rinhibition alters macrophage polarization and blocks gliomaprogressionrdquo Nature Medicine vol 19 no 10 pp 1264ndash12722013

[97] G Germano R Frapolli M Simone et al ldquoAntitumor andanti-inflammatory effects of trabectedin on human myxoidliposarcoma cellsrdquo Cancer Research vol 70 no 6 pp 2235ndash2244 2010

[98] G Germano R Frapolli C Belgiovine et al ldquoRole ofmacrophage targeting in the antitumor activity of trabectedinrdquoCancer Cell vol 23 no 2 pp 249ndash262 2013

[99] JW Pollard ldquoTumour-educatedmacrophages promote tumourprogression and metastasisrdquo Nature Reviews Cancer vol 4 no1 pp 71ndash78 2004

[100] F O Martinez and S Gordon ldquoThe M1 and M2 paradigmof macrophage activation time for reassessmentrdquo F1000PrimeReports vol 6 article 13 2014

[101] S Joshi A R Singh M Zulcic and D L Durden ldquoAmacrophage-dominant PI3K isoform controls hypoxia-inducedHIF1120572 andHIF2120572 stability and tumor growth angiogenesis andmetastasisrdquoMolecular Cancer Research vol 12 no 10 pp 1520ndash1531 2014

[102] S Joshi A R Singh M Zulcic et al ldquoRac2 controls tumorgrowth metastasis and M1-M2 macrophage differentiation invivordquo PLoS ONE vol 9 no 4 2014

[103] M M Kaneda K S Messer N Ralainirina et al ldquoPI3K120574 is amolecular switch that controls immune suppressionrdquo Naturevol 539 no 7629 pp 437ndash442 2016

[104] O M Pello M De Pizzol M Mirolo et al ldquoRole of c-MYCin alternative activation of human macrophages and tumor-associated macrophage biologyrdquo Blood vol 119 no 2 pp 411ndash421 2012

[105] S Gordon and F O Martinez ldquoAlternative activation ofmacrophagesmechanism and functionsrdquo Immunity vol 32 no5 pp 593ndash604 2010

[106] O De Henau M Rausch D Winkler et al ldquoOvercomingresistance to checkpoint blockade therapy by targeting PI3K120574in myeloid cellsrdquo Nature vol 539 no 7629 pp 443ndash447 2016

[107] A W Tolcher D S Hong R J Sullivan et al ldquoIPI-549-01-Aphase 11b first in human study of IPI-549 a PI3K-120574 inhibitoras monotherapy and in combination with pembrolizumabin subjects with advanced solid tumorsrdquo Journal of ClinicalOncology vol 34 no 15 suppl pp TPS3111ndashTPS3111 2016

[108] A J Gunderson M M Kaneda T Tsujikawa et al ldquoBrutontyrosine kinasendashDependent immune cell cross-talk drives pan-creas cancerrdquo Cancer Discovery vol 6 no 3 pp 270ndash285 2016

[109] G L Beatty D A Torigian E Gabriela Chiorean et al ldquoA phaseI study of an agonist CD40 monoclonal antibody (CP-870893)in combination with gemcitabine in patients with advancedpancreatic ductal adenocarcinomardquo Clinical Cancer Researchvol 19 no 22 pp 6286ndash6295 2013

[110] T Bald J LandsbergD Lopez-Ramos et al ldquoImmune cell-poormelanomas benefit fromPD-1 blockade after targeted type I IFNactivationrdquo Cancer Discovery vol 4 no 6 pp 674ndash687 2014

[111] Y Shirota H Shirota and D M Klinman ldquoIntratumoral injec-tion of CpG oligonucleotides induces the differentiation andreduces the immunosuppressive activity of myeloid-derivedsuppressor cellsrdquoe Journal of Immunology vol 188 no 4 pp1592ndash1599 2012

[112] R Houot and R Levy ldquoT-cell modulation combined withintratumoral CpG cures lymphoma in a mouse model withoutthe need for chemotherapyrdquo Blood vol 113 no 15 pp 3546ndash3552 2009

[113] F Sato-Kaneko S Yao A Ahmadi et al ldquoCombinationimmunotherapy with TLR agonists and checkpoint inhibitorssuppresses head and neck cancerrdquo JCI Insight vol 2 no 18 2017

[114] D I Gabrilovich and S Nagaraj ldquoMyeloid-derived suppressorcells as regulators of the immune systemrdquo Nature ReviewsImmunology vol 9 no 3 pp 162ndash174 2009

[115] S Ostrand-Rosenberg ldquoMyeloid-derived suppressor cellsmore mechanisms for inhibiting antitumor immunityrdquo CancerImmunology Immunotherapy vol 59 no 10 pp 1593ndash16002010

[116] Y Nefedova M Fishman S Sherman X Wang A A Beg andD I Gabrilovich ldquoMechanism of all-trans retinoic acid effecton tumor-associated myeloid-derived suppressor cellsrdquo CancerResearch vol 67 no 22 pp 11021ndash11028 2007

[117] M E Huang Y C Ye S R Chen et al ldquoUse of all-trans retinoicacid in the treatment of acute promyelocytic leukemiardquo Bloodvol 72 no 2 pp 567ndash572 1988

[118] N Mirza M Fishman I Fricke et al ldquoAll-trans-retinoic acidimproves differentiation of myeloid cells and immune responsein cancer patientsrdquo Cancer Research vol 66 no 18 pp 9299ndash9307 2006

[119] C Iclozan S Antonia A Chiappori D-T Chen and DGabrilovich ldquoTherapeutic regulation of myeloid-derived sup-pressor cells and immune response to cancer vaccine in patientswith extensive stage small cell lung cancerrdquoCancer ImmunologyImmunotherapy vol 62 no 5 pp 909ndash918 2013

Journal of Oncology 17

[120] J E Walsh A Clark T A Day M B Gillespie and MR Young ldquoUse of 12057225-Dihydroxyvitamin D3 treatment tostimulate immune infiltration into head and neck squamouscell carcinomardquoHuman Immunology vol 71 no 7 pp 659ndash6652010

[121] T Veikkola M Karkkainen L Claesson-Welsh and K AlitaloldquoRegulation of angiogenesis via vascular endothelial growthfactor receptorsrdquo Cancer Research vol 60 no 2 pp 203ndash2122000

[122] D I Gabrilovich H L Chen K R Girgis et al ldquoProductionof vascular endothelial growth factor by human tumors inhibitsthe functional maturation of dendritic cellsrdquo Nature Medicinevol 2 no 10 pp 1096ndash1103 1996

[123] T Osada G Chong R Tansik et al ldquoThe effect of anti-VEGFtherapy on immature myeloid cell and dendritic cells in cancerpatientsrdquoCancer Immunology Immunotherapy vol 57 no 8 pp1115ndash1124 2008

[124] S L Highfill Y Cui A J Giles et al ldquoDisruption of CXCR2-mediated MDSC tumor trafficking enhances anti-PD1 efficacyrdquoScience Translational Medicine vol 6 no 237 Article ID237ra67 2014

[125] H Jung A Bischof K Ebsworth et al ldquoAbstract A90 Com-bination therapy of chemokine receptor inhibition plus PDL-1 blockade potentiates anti-tumor effects in a murine modelof breast cancerrdquo Molecular Cancer erapeutics vol 3 p 2272015

[126] P Serafini K Meckel M Kelso et al ldquoPhosphodiesterase-5 inhibition augments endogenous antitumor immunity byreducingmyeloid-derived suppressor cell functionrdquoe Journalof Experimental Medicine vol 203 no 12 pp 2691ndash2702 2006

[127] C Meyera A Sevko M Ramacher et al ldquoChronic inflam-mation promotes myeloid-derived suppressor cell activationblocking antitumor immunity in transgenic mouse melanomamodelrdquo Proceedings of the National Acadamy of Sciences of theUnited States of America vol 108 no 41 pp 17111ndash17116 2011

[128] J A Califano Z Khan K A Noonan et al ldquoTadalafil augmentstumor specific immunity in patients with head and necksquamous cell carcinomardquo Clinical Cancer Research vol 21 no1 pp 30ndash38 2015

[129] J C Hassel H Jiang C Bender et al ldquoTadalafil has bio-logic activity in human melanoma Results of a pilot trialwith Tadalafil in patients with metastatic Melanoma (TaMe)rdquoOncoImmunology vol 6 no 9 article no e1326440 2017

[130] M C Schmid C J Avraamides H C Dippold et al ldquoReceptortyrosine kinases and TLRIL1Rs unexpectedly activate myeloidcell PI3K120574 A single convergent point promoting tumor inflam-mation and progressionrdquo Cancer Cell vol 19 no 6 pp 715ndash7272011

[131] R J Davis E CMoore P E Clavijo et al ldquoAnti-PD-L1 EfficacyCan Be Enhanced by Inhibition ofMyeloid-Derived SuppressorCells with a Selective Inhibitor of PI3K120575120574rdquo Cancer Researchvol 77 no 10 pp 2607ndash2619 2017

[132] D Sugiyama H Nishikawa Y Maeda et al ldquoAnti-CCR4mAb selectively depletes effector-type FoxP3+CD4+ regulatoryT cells evoking antitumor immune responses in humansrdquoProceedings of the National Acadamy of Sciences of the UnitedStates of America vol 110 no 44 pp 17945ndash17950 2013

[133] G C Prendergast C Smith S Thomas et al ldquoIndoleamine23-dioxygenase pathways of pathogenic inflammation andimmune escape in cancerrdquo Cancer Immunology Immunother-apy vol 63 no 7 pp 721ndash735 2014

[134] R Yoshida J Imanishi T Oku T Kishida and O HayaishildquoInduction of pulmonary indoleamine 23-dioxygenase byinterferonrdquo Proceedings of the National Acadamy of Sciences ofthe United States of America vol 78 no 1 pp 129ndash132 1981

[135] F Fallarino U Grohmann K W Hwang et al ldquoModulation oftryptophan catabolism by regulatory T cellsrdquo Nature Immunol-ogy vol 4 no 12 pp 1206ndash1212 2003

[136] C Smith M Y Chang K H Parker et al ldquoIDO is a nodalpathogenic driver of lung cancer and metastasis developmentrdquoCancer Discovery vol 2 no 8 pp 722ndash735 2012

[137] G Frumento R Rotondo M Tonetti G Damonte U Benattiand G B Ferrara ldquoTryptophan-derived catabolites are respon-sible for inhibition of T and natural killer cell proliferationinduced by indoleamine 23-dioxygenaserdquoe Journal of Exper-imental Medicine vol 196 no 4 pp 459ndash468 2002

[138] R B Holmgaard D Zamarin D H Munn J D Wolchokand J P Allison ldquoIndoleamine 23-dioxygenase is a criticalresistance mechanism in antitumor T cell immunotherapytargeting CTLA-4rdquo e Journal of Experimental Medicine vol210 no 7 pp 1389ndash1402 2013

[139] S Spranger H K Koblish B Horton P A Scherle RNewton and T F Gajewski ldquoMechanism of tumor rejectionwith doublets of CTLA-4 PD-1PD-L1 or IDO blockadeinvolves restored IL-2 production and proliferation of CD8+ Tcells directly within the tumor microenvironmentrdquo Journal forImmunoerapy of Cancer vol 2 no 1 2014

[140] G Gibney O Hamid J Lutzky et al ldquo511 Updated results froma phase 12 study of epacadostat (INCB024360) in combinationwith ipilimumab in patients with metastatic melanomardquo Euro-pean Journal of Cancer vol 51 pp S106ndashS107 2015

[141] Merck Ia ldquoIncyte and Merck to Advance ClinicalDevelopment Program Investigating the Combination ofEpacadostat with KEYTRUDA (pembrolizumab)rdquo httpswwwmrknewsroomcomnews-releaseoncology-newsroomincyte-and-merck-advance-clinical-development-program-investigating-c

[142] Incyte ldquoIncyte and Merck Provide Update on Phase 3Study of Epacadostat in Combination with KEYTRUDA(pembrolizumab) in Patients with Unresectable or MetastaticMelanomardquo

[143] H H Soliman S E Minton H S Han et al ldquoA Phase I study ofindoximod in patientswith advancedmalignanciesrdquoOncotarget vol 7 no 16 pp 22928ndash22938 2016

[144] J J Lebrun ldquoThe Dual Role of TGFbeta in Human CancerFrom Tumor Suppression to Cancer Metastasisrdquo MolecularBiology vol 2012 2012

[145] B A Hanks A Holtzhausen K Evans M Heid and G CBlobe ldquo Combinatorial TGF-120573 signaling blockade and anti-CTLA-4 antibody immunotherapy in a murine BRAF rdquo Journalof Clinical Oncology vol 32 no 15 suppl pp 3011-3011 2014

[146] S Herbertz J S Sawyer A J Stauber et al ldquoClinical devel-opment of galunisertib (Ly2157299 monohydrate) a smallmolecule inhibitor of transforming growth factor-beta signalingpathwayrdquo Drug Design Development and erapy vol 9 pp4479ndash4499 2015

[147] Y-C Duan Y-C Ma W-P Qin et al ldquoDesign and synthesisof tranylcypromine derivatives as novel LSD1HDACs dualinhibitors for cancer treatmentrdquo European Journal of MedicinalChemistry vol 140 pp 392ndash402 2017

[148] L Gu H Zhang T Liu et al ldquoDiscovery of Dual Inhibitors ofMDM2 and XIAP for Cancer Treatmentrdquo Cancer Cell vol 30no 4 pp 623ndash636 2016

16 Journal of Oncology

[88] A Mantovani F Marchesi A Malesci L Laghi and PAllavena ldquoTumour-associated macrophages as treatment tar-gets in oncologyrdquo Nature Reviews Clinical Oncology vol 14 no7 pp 399ndash416 2017

[89] I Brana A Calles P M LoRusso et al ldquoCarlumab an anti-C-C chemokine ligand 2 monoclonal antibody in combinationwith four chemotherapy regimens for the treatment of patientswith solid tumors an open-label multicenter phase 1b studyrdquoTargeted Oncology vol 10 no 1 pp 111ndash123 2015

[90] T M Nywening A Wang-Gillam D E Sanford et al ldquoTar-geting tumour-associated macrophages with CCR2 inhibitionin combination with FOLFIRINOX in patients with borderlineresectable and locally advanced pancreatic cancer a single-centre open-label dose-finding non-randomised phase 1btrialrdquoe Lancet Oncology vol 17 no 5 pp 651ndash662 2016

[91] Y Wang X Zhang L Yang J Xue and G Hu ldquoBlockade ofCCL2 enhances immunotherapeutic effect of anti-PD1 in lungcancerrdquo Journal of Bone Oncology vol 11 pp 27ndash32 2018

[92] B Ruffell and L M Coussens ldquoMacrophages and therapeuticresistance in cancerrdquo Cancer Cell vol 27 no 4 pp 462ndash4722015

[93] D G DeNardo D J Brennan E Rexhepaj et al ldquoLeukocytecomplexity predicts breast cancer survival and functionallyregulates response to chemotherapyrdquo Cancer Discovery vol 1no 1 pp 54ndash67 2011

[94] C H Ries M A Cannarile S Hoves et al ldquoTargeting tumor-associated macrophages with anti-CSF-1R antibody reveals astrategy for cancer therapyrdquoCancer Cell vol 25 no 6 pp 846ndash859 2014

[95] J H Stafford T Hirai L Deng et al ldquoColony stimulating factor1 receptor inhibition delays recurrence of glioblastoma afterradiation by alteringmyeloid cell recruitment and polarizationrdquoNeuro-Oncology vol 18 no 6 pp 797ndash806 2016

[96] S M Pyonteck L Akkari A J Schuhmacher et al ldquoCSF-1Rinhibition alters macrophage polarization and blocks gliomaprogressionrdquo Nature Medicine vol 19 no 10 pp 1264ndash12722013

[97] G Germano R Frapolli M Simone et al ldquoAntitumor andanti-inflammatory effects of trabectedin on human myxoidliposarcoma cellsrdquo Cancer Research vol 70 no 6 pp 2235ndash2244 2010

[98] G Germano R Frapolli C Belgiovine et al ldquoRole ofmacrophage targeting in the antitumor activity of trabectedinrdquoCancer Cell vol 23 no 2 pp 249ndash262 2013

[99] JW Pollard ldquoTumour-educatedmacrophages promote tumourprogression and metastasisrdquo Nature Reviews Cancer vol 4 no1 pp 71ndash78 2004

[100] F O Martinez and S Gordon ldquoThe M1 and M2 paradigmof macrophage activation time for reassessmentrdquo F1000PrimeReports vol 6 article 13 2014

[101] S Joshi A R Singh M Zulcic and D L Durden ldquoAmacrophage-dominant PI3K isoform controls hypoxia-inducedHIF1120572 andHIF2120572 stability and tumor growth angiogenesis andmetastasisrdquoMolecular Cancer Research vol 12 no 10 pp 1520ndash1531 2014

[102] S Joshi A R Singh M Zulcic et al ldquoRac2 controls tumorgrowth metastasis and M1-M2 macrophage differentiation invivordquo PLoS ONE vol 9 no 4 2014

[103] M M Kaneda K S Messer N Ralainirina et al ldquoPI3K120574 is amolecular switch that controls immune suppressionrdquo Naturevol 539 no 7629 pp 437ndash442 2016

[104] O M Pello M De Pizzol M Mirolo et al ldquoRole of c-MYCin alternative activation of human macrophages and tumor-associated macrophage biologyrdquo Blood vol 119 no 2 pp 411ndash421 2012

[105] S Gordon and F O Martinez ldquoAlternative activation ofmacrophagesmechanism and functionsrdquo Immunity vol 32 no5 pp 593ndash604 2010

[106] O De Henau M Rausch D Winkler et al ldquoOvercomingresistance to checkpoint blockade therapy by targeting PI3K120574in myeloid cellsrdquo Nature vol 539 no 7629 pp 443ndash447 2016

[107] A W Tolcher D S Hong R J Sullivan et al ldquoIPI-549-01-Aphase 11b first in human study of IPI-549 a PI3K-120574 inhibitoras monotherapy and in combination with pembrolizumabin subjects with advanced solid tumorsrdquo Journal of ClinicalOncology vol 34 no 15 suppl pp TPS3111ndashTPS3111 2016

[108] A J Gunderson M M Kaneda T Tsujikawa et al ldquoBrutontyrosine kinasendashDependent immune cell cross-talk drives pan-creas cancerrdquo Cancer Discovery vol 6 no 3 pp 270ndash285 2016

[109] G L Beatty D A Torigian E Gabriela Chiorean et al ldquoA phaseI study of an agonist CD40 monoclonal antibody (CP-870893)in combination with gemcitabine in patients with advancedpancreatic ductal adenocarcinomardquo Clinical Cancer Researchvol 19 no 22 pp 6286ndash6295 2013

[110] T Bald J LandsbergD Lopez-Ramos et al ldquoImmune cell-poormelanomas benefit fromPD-1 blockade after targeted type I IFNactivationrdquo Cancer Discovery vol 4 no 6 pp 674ndash687 2014

[111] Y Shirota H Shirota and D M Klinman ldquoIntratumoral injec-tion of CpG oligonucleotides induces the differentiation andreduces the immunosuppressive activity of myeloid-derivedsuppressor cellsrdquoe Journal of Immunology vol 188 no 4 pp1592ndash1599 2012

[112] R Houot and R Levy ldquoT-cell modulation combined withintratumoral CpG cures lymphoma in a mouse model withoutthe need for chemotherapyrdquo Blood vol 113 no 15 pp 3546ndash3552 2009

[113] F Sato-Kaneko S Yao A Ahmadi et al ldquoCombinationimmunotherapy with TLR agonists and checkpoint inhibitorssuppresses head and neck cancerrdquo JCI Insight vol 2 no 18 2017

[114] D I Gabrilovich and S Nagaraj ldquoMyeloid-derived suppressorcells as regulators of the immune systemrdquo Nature ReviewsImmunology vol 9 no 3 pp 162ndash174 2009

[115] S Ostrand-Rosenberg ldquoMyeloid-derived suppressor cellsmore mechanisms for inhibiting antitumor immunityrdquo CancerImmunology Immunotherapy vol 59 no 10 pp 1593ndash16002010

[116] Y Nefedova M Fishman S Sherman X Wang A A Beg andD I Gabrilovich ldquoMechanism of all-trans retinoic acid effecton tumor-associated myeloid-derived suppressor cellsrdquo CancerResearch vol 67 no 22 pp 11021ndash11028 2007

[117] M E Huang Y C Ye S R Chen et al ldquoUse of all-trans retinoicacid in the treatment of acute promyelocytic leukemiardquo Bloodvol 72 no 2 pp 567ndash572 1988

[118] N Mirza M Fishman I Fricke et al ldquoAll-trans-retinoic acidimproves differentiation of myeloid cells and immune responsein cancer patientsrdquo Cancer Research vol 66 no 18 pp 9299ndash9307 2006

[119] C Iclozan S Antonia A Chiappori D-T Chen and DGabrilovich ldquoTherapeutic regulation of myeloid-derived sup-pressor cells and immune response to cancer vaccine in patientswith extensive stage small cell lung cancerrdquoCancer ImmunologyImmunotherapy vol 62 no 5 pp 909ndash918 2013

Journal of Oncology 17

[120] J E Walsh A Clark T A Day M B Gillespie and MR Young ldquoUse of 12057225-Dihydroxyvitamin D3 treatment tostimulate immune infiltration into head and neck squamouscell carcinomardquoHuman Immunology vol 71 no 7 pp 659ndash6652010

[121] T Veikkola M Karkkainen L Claesson-Welsh and K AlitaloldquoRegulation of angiogenesis via vascular endothelial growthfactor receptorsrdquo Cancer Research vol 60 no 2 pp 203ndash2122000

[122] D I Gabrilovich H L Chen K R Girgis et al ldquoProductionof vascular endothelial growth factor by human tumors inhibitsthe functional maturation of dendritic cellsrdquo Nature Medicinevol 2 no 10 pp 1096ndash1103 1996

[123] T Osada G Chong R Tansik et al ldquoThe effect of anti-VEGFtherapy on immature myeloid cell and dendritic cells in cancerpatientsrdquoCancer Immunology Immunotherapy vol 57 no 8 pp1115ndash1124 2008

[124] S L Highfill Y Cui A J Giles et al ldquoDisruption of CXCR2-mediated MDSC tumor trafficking enhances anti-PD1 efficacyrdquoScience Translational Medicine vol 6 no 237 Article ID237ra67 2014

[125] H Jung A Bischof K Ebsworth et al ldquoAbstract A90 Com-bination therapy of chemokine receptor inhibition plus PDL-1 blockade potentiates anti-tumor effects in a murine modelof breast cancerrdquo Molecular Cancer erapeutics vol 3 p 2272015

[126] P Serafini K Meckel M Kelso et al ldquoPhosphodiesterase-5 inhibition augments endogenous antitumor immunity byreducingmyeloid-derived suppressor cell functionrdquoe Journalof Experimental Medicine vol 203 no 12 pp 2691ndash2702 2006

[127] C Meyera A Sevko M Ramacher et al ldquoChronic inflam-mation promotes myeloid-derived suppressor cell activationblocking antitumor immunity in transgenic mouse melanomamodelrdquo Proceedings of the National Acadamy of Sciences of theUnited States of America vol 108 no 41 pp 17111ndash17116 2011

[128] J A Califano Z Khan K A Noonan et al ldquoTadalafil augmentstumor specific immunity in patients with head and necksquamous cell carcinomardquo Clinical Cancer Research vol 21 no1 pp 30ndash38 2015

[129] J C Hassel H Jiang C Bender et al ldquoTadalafil has bio-logic activity in human melanoma Results of a pilot trialwith Tadalafil in patients with metastatic Melanoma (TaMe)rdquoOncoImmunology vol 6 no 9 article no e1326440 2017

[130] M C Schmid C J Avraamides H C Dippold et al ldquoReceptortyrosine kinases and TLRIL1Rs unexpectedly activate myeloidcell PI3K120574 A single convergent point promoting tumor inflam-mation and progressionrdquo Cancer Cell vol 19 no 6 pp 715ndash7272011

[131] R J Davis E CMoore P E Clavijo et al ldquoAnti-PD-L1 EfficacyCan Be Enhanced by Inhibition ofMyeloid-Derived SuppressorCells with a Selective Inhibitor of PI3K120575120574rdquo Cancer Researchvol 77 no 10 pp 2607ndash2619 2017

[132] D Sugiyama H Nishikawa Y Maeda et al ldquoAnti-CCR4mAb selectively depletes effector-type FoxP3+CD4+ regulatoryT cells evoking antitumor immune responses in humansrdquoProceedings of the National Acadamy of Sciences of the UnitedStates of America vol 110 no 44 pp 17945ndash17950 2013

[133] G C Prendergast C Smith S Thomas et al ldquoIndoleamine23-dioxygenase pathways of pathogenic inflammation andimmune escape in cancerrdquo Cancer Immunology Immunother-apy vol 63 no 7 pp 721ndash735 2014

[134] R Yoshida J Imanishi T Oku T Kishida and O HayaishildquoInduction of pulmonary indoleamine 23-dioxygenase byinterferonrdquo Proceedings of the National Acadamy of Sciences ofthe United States of America vol 78 no 1 pp 129ndash132 1981

[135] F Fallarino U Grohmann K W Hwang et al ldquoModulation oftryptophan catabolism by regulatory T cellsrdquo Nature Immunol-ogy vol 4 no 12 pp 1206ndash1212 2003

[136] C Smith M Y Chang K H Parker et al ldquoIDO is a nodalpathogenic driver of lung cancer and metastasis developmentrdquoCancer Discovery vol 2 no 8 pp 722ndash735 2012

[137] G Frumento R Rotondo M Tonetti G Damonte U Benattiand G B Ferrara ldquoTryptophan-derived catabolites are respon-sible for inhibition of T and natural killer cell proliferationinduced by indoleamine 23-dioxygenaserdquoe Journal of Exper-imental Medicine vol 196 no 4 pp 459ndash468 2002

[138] R B Holmgaard D Zamarin D H Munn J D Wolchokand J P Allison ldquoIndoleamine 23-dioxygenase is a criticalresistance mechanism in antitumor T cell immunotherapytargeting CTLA-4rdquo e Journal of Experimental Medicine vol210 no 7 pp 1389ndash1402 2013

[139] S Spranger H K Koblish B Horton P A Scherle RNewton and T F Gajewski ldquoMechanism of tumor rejectionwith doublets of CTLA-4 PD-1PD-L1 or IDO blockadeinvolves restored IL-2 production and proliferation of CD8+ Tcells directly within the tumor microenvironmentrdquo Journal forImmunoerapy of Cancer vol 2 no 1 2014

[140] G Gibney O Hamid J Lutzky et al ldquo511 Updated results froma phase 12 study of epacadostat (INCB024360) in combinationwith ipilimumab in patients with metastatic melanomardquo Euro-pean Journal of Cancer vol 51 pp S106ndashS107 2015

[141] Merck Ia ldquoIncyte and Merck to Advance ClinicalDevelopment Program Investigating the Combination ofEpacadostat with KEYTRUDA (pembrolizumab)rdquo httpswwwmrknewsroomcomnews-releaseoncology-newsroomincyte-and-merck-advance-clinical-development-program-investigating-c

[142] Incyte ldquoIncyte and Merck Provide Update on Phase 3Study of Epacadostat in Combination with KEYTRUDA(pembrolizumab) in Patients with Unresectable or MetastaticMelanomardquo

[143] H H Soliman S E Minton H S Han et al ldquoA Phase I study ofindoximod in patientswith advancedmalignanciesrdquoOncotarget vol 7 no 16 pp 22928ndash22938 2016

[144] J J Lebrun ldquoThe Dual Role of TGFbeta in Human CancerFrom Tumor Suppression to Cancer Metastasisrdquo MolecularBiology vol 2012 2012

[145] B A Hanks A Holtzhausen K Evans M Heid and G CBlobe ldquo Combinatorial TGF-120573 signaling blockade and anti-CTLA-4 antibody immunotherapy in a murine BRAF rdquo Journalof Clinical Oncology vol 32 no 15 suppl pp 3011-3011 2014

[146] S Herbertz J S Sawyer A J Stauber et al ldquoClinical devel-opment of galunisertib (Ly2157299 monohydrate) a smallmolecule inhibitor of transforming growth factor-beta signalingpathwayrdquo Drug Design Development and erapy vol 9 pp4479ndash4499 2015

[147] Y-C Duan Y-C Ma W-P Qin et al ldquoDesign and synthesisof tranylcypromine derivatives as novel LSD1HDACs dualinhibitors for cancer treatmentrdquo European Journal of MedicinalChemistry vol 140 pp 392ndash402 2017

[148] L Gu H Zhang T Liu et al ldquoDiscovery of Dual Inhibitors ofMDM2 and XIAP for Cancer Treatmentrdquo Cancer Cell vol 30no 4 pp 623ndash636 2016

Journal of Oncology 17

[120] J E Walsh A Clark T A Day M B Gillespie and MR Young ldquoUse of 12057225-Dihydroxyvitamin D3 treatment tostimulate immune infiltration into head and neck squamouscell carcinomardquoHuman Immunology vol 71 no 7 pp 659ndash6652010

[121] T Veikkola M Karkkainen L Claesson-Welsh and K AlitaloldquoRegulation of angiogenesis via vascular endothelial growthfactor receptorsrdquo Cancer Research vol 60 no 2 pp 203ndash2122000

[122] D I Gabrilovich H L Chen K R Girgis et al ldquoProductionof vascular endothelial growth factor by human tumors inhibitsthe functional maturation of dendritic cellsrdquo Nature Medicinevol 2 no 10 pp 1096ndash1103 1996

[123] T Osada G Chong R Tansik et al ldquoThe effect of anti-VEGFtherapy on immature myeloid cell and dendritic cells in cancerpatientsrdquoCancer Immunology Immunotherapy vol 57 no 8 pp1115ndash1124 2008

[124] S L Highfill Y Cui A J Giles et al ldquoDisruption of CXCR2-mediated MDSC tumor trafficking enhances anti-PD1 efficacyrdquoScience Translational Medicine vol 6 no 237 Article ID237ra67 2014

[125] H Jung A Bischof K Ebsworth et al ldquoAbstract A90 Com-bination therapy of chemokine receptor inhibition plus PDL-1 blockade potentiates anti-tumor effects in a murine modelof breast cancerrdquo Molecular Cancer erapeutics vol 3 p 2272015

[126] P Serafini K Meckel M Kelso et al ldquoPhosphodiesterase-5 inhibition augments endogenous antitumor immunity byreducingmyeloid-derived suppressor cell functionrdquoe Journalof Experimental Medicine vol 203 no 12 pp 2691ndash2702 2006

[127] C Meyera A Sevko M Ramacher et al ldquoChronic inflam-mation promotes myeloid-derived suppressor cell activationblocking antitumor immunity in transgenic mouse melanomamodelrdquo Proceedings of the National Acadamy of Sciences of theUnited States of America vol 108 no 41 pp 17111ndash17116 2011

[128] J A Califano Z Khan K A Noonan et al ldquoTadalafil augmentstumor specific immunity in patients with head and necksquamous cell carcinomardquo Clinical Cancer Research vol 21 no1 pp 30ndash38 2015

[129] J C Hassel H Jiang C Bender et al ldquoTadalafil has bio-logic activity in human melanoma Results of a pilot trialwith Tadalafil in patients with metastatic Melanoma (TaMe)rdquoOncoImmunology vol 6 no 9 article no e1326440 2017

[130] M C Schmid C J Avraamides H C Dippold et al ldquoReceptortyrosine kinases and TLRIL1Rs unexpectedly activate myeloidcell PI3K120574 A single convergent point promoting tumor inflam-mation and progressionrdquo Cancer Cell vol 19 no 6 pp 715ndash7272011

[131] R J Davis E CMoore P E Clavijo et al ldquoAnti-PD-L1 EfficacyCan Be Enhanced by Inhibition ofMyeloid-Derived SuppressorCells with a Selective Inhibitor of PI3K120575120574rdquo Cancer Researchvol 77 no 10 pp 2607ndash2619 2017

[132] D Sugiyama H Nishikawa Y Maeda et al ldquoAnti-CCR4mAb selectively depletes effector-type FoxP3+CD4+ regulatoryT cells evoking antitumor immune responses in humansrdquoProceedings of the National Acadamy of Sciences of the UnitedStates of America vol 110 no 44 pp 17945ndash17950 2013

[133] G C Prendergast C Smith S Thomas et al ldquoIndoleamine23-dioxygenase pathways of pathogenic inflammation andimmune escape in cancerrdquo Cancer Immunology Immunother-apy vol 63 no 7 pp 721ndash735 2014

[134] R Yoshida J Imanishi T Oku T Kishida and O HayaishildquoInduction of pulmonary indoleamine 23-dioxygenase byinterferonrdquo Proceedings of the National Acadamy of Sciences ofthe United States of America vol 78 no 1 pp 129ndash132 1981

[135] F Fallarino U Grohmann K W Hwang et al ldquoModulation oftryptophan catabolism by regulatory T cellsrdquo Nature Immunol-ogy vol 4 no 12 pp 1206ndash1212 2003

[136] C Smith M Y Chang K H Parker et al ldquoIDO is a nodalpathogenic driver of lung cancer and metastasis developmentrdquoCancer Discovery vol 2 no 8 pp 722ndash735 2012

[137] G Frumento R Rotondo M Tonetti G Damonte U Benattiand G B Ferrara ldquoTryptophan-derived catabolites are respon-sible for inhibition of T and natural killer cell proliferationinduced by indoleamine 23-dioxygenaserdquoe Journal of Exper-imental Medicine vol 196 no 4 pp 459ndash468 2002

[138] R B Holmgaard D Zamarin D H Munn J D Wolchokand J P Allison ldquoIndoleamine 23-dioxygenase is a criticalresistance mechanism in antitumor T cell immunotherapytargeting CTLA-4rdquo e Journal of Experimental Medicine vol210 no 7 pp 1389ndash1402 2013

[139] S Spranger H K Koblish B Horton P A Scherle RNewton and T F Gajewski ldquoMechanism of tumor rejectionwith doublets of CTLA-4 PD-1PD-L1 or IDO blockadeinvolves restored IL-2 production and proliferation of CD8+ Tcells directly within the tumor microenvironmentrdquo Journal forImmunoerapy of Cancer vol 2 no 1 2014

[140] G Gibney O Hamid J Lutzky et al ldquo511 Updated results froma phase 12 study of epacadostat (INCB024360) in combinationwith ipilimumab in patients with metastatic melanomardquo Euro-pean Journal of Cancer vol 51 pp S106ndashS107 2015

[141] Merck Ia ldquoIncyte and Merck to Advance ClinicalDevelopment Program Investigating the Combination ofEpacadostat with KEYTRUDA (pembrolizumab)rdquo httpswwwmrknewsroomcomnews-releaseoncology-newsroomincyte-and-merck-advance-clinical-development-program-investigating-c

[142] Incyte ldquoIncyte and Merck Provide Update on Phase 3Study of Epacadostat in Combination with KEYTRUDA(pembrolizumab) in Patients with Unresectable or MetastaticMelanomardquo

[143] H H Soliman S E Minton H S Han et al ldquoA Phase I study ofindoximod in patientswith advancedmalignanciesrdquoOncotarget vol 7 no 16 pp 22928ndash22938 2016

[144] J J Lebrun ldquoThe Dual Role of TGFbeta in Human CancerFrom Tumor Suppression to Cancer Metastasisrdquo MolecularBiology vol 2012 2012

[145] B A Hanks A Holtzhausen K Evans M Heid and G CBlobe ldquo Combinatorial TGF-120573 signaling blockade and anti-CTLA-4 antibody immunotherapy in a murine BRAF rdquo Journalof Clinical Oncology vol 32 no 15 suppl pp 3011-3011 2014

[146] S Herbertz J S Sawyer A J Stauber et al ldquoClinical devel-opment of galunisertib (Ly2157299 monohydrate) a smallmolecule inhibitor of transforming growth factor-beta signalingpathwayrdquo Drug Design Development and erapy vol 9 pp4479ndash4499 2015

[147] Y-C Duan Y-C Ma W-P Qin et al ldquoDesign and synthesisof tranylcypromine derivatives as novel LSD1HDACs dualinhibitors for cancer treatmentrdquo European Journal of MedicinalChemistry vol 140 pp 392ndash402 2017

[148] L Gu H Zhang T Liu et al ldquoDiscovery of Dual Inhibitors ofMDM2 and XIAP for Cancer Treatmentrdquo Cancer Cell vol 30no 4 pp 623ndash636 2016

18 Journal of Oncology

[149] J Weinstock J Wu P Cao et al ldquoSelective dual inhibitors ofthe cancer-related deubiquitylating proteasesUSP7 andUSP47rdquoACS Medicinal Chemistry Letters vol 3 no 10 pp 789ndash7922012

[150] J Zang X Liang Y Huang et al ldquoDiscovery of NovelPazopanib-BasedHDACandVEGFRDual Inhibitors TargetingCancer Epigenetics and Angiogenesis Simultaneouslyrdquo Journalof Medicinal Chemistry vol 61 no 12 pp 5304ndash5322 2017

[151] S He G Dong S Wu et al ldquoSmall Molecules SimultaneouslyInhibiting p53-Murine Double Minute 2 (MDM2) Interactionand Histone Deacetylases (HDACs) Discovery of Novel Mul-titargeting Antitumor Agentsrdquo Journal of Medicinal Chemistryvol 61 no 16 pp 7245ndash7260 2018

[152] A Erdreich-Epstein A R Singh S Joshi et al ldquoAssociationof high microvessel alphavbeta3 and low PTEN with pooroutcome in stage 3 neuroblastoma rationale for using first inclass dual PI3KBRD4 inhibitor SF1126rdquo Oncotarget vol 8 no32 2017

[153] A R Singh S Joshi A M Burgoyne et al ldquoSingle agentand synergistic activity of the ldquofirst-in-classrdquo dual PI3KBRD4inhibitor SF1126 with sorafenib in hepatocellular carcinomardquoMolecular Cancer erapeutics vol 15 no 11 pp 2553ndash25622016

[154] S Joshi A R Singh and D L Durden ldquoPan-PI-3 kinaseinhibitor SF1126 shows antitumor and antiangiogenic activity inrenal cell carcinomardquoCancer Chemotherapy and Pharmacologyvol 75 no 3 pp 595ndash608 2015

[155] J R Garlich P De N Dey et al ldquoA vascular targeted panphosphoinositide 3-kinase inhibitor prodrug SF1126 with anti-tumor and antiangiogenic activityrdquoCancer Research vol 68 no1 pp 206ndash215 2008

[156] P Ciceri S Muller A OrsquoMahony et al ldquoDual kinase-bromodomain inhibitors for rationally designed polypharma-cologyrdquo Nature Chemical Biology vol 10 no 4 pp 305ndash3122014

[157] G A Morales J R Garlich J Su et al ldquoSynthesis and can-cer stem cell-based activity of substituted 5-morpholino-7H-thieno[32-b]pyran-7-ones designed as next generation PI3Kinhibitorsrdquo Journal of Medicinal Chemistry vol 56 no 5 pp1922ndash1939 2013

[158] F H Andrews A R Singh S Joshi et al ldquoDual-activityPI3KndashBRD4 inhibitor for the orthogonal inhibition of MYC toblock tumor growth andmetastasisrdquo Proceedings of the NationalAcadamy of Sciences of the United States of America vol 114 no7 pp E1072ndashE1080 2017

[159] G Shen M Jiang and J Pu ldquoDual inhibition of BRD4 andPI3K by SF2523 suppresses human prostate cancer cell growthin vitro and in vivordquo Biochemical and Biophysical ResearchCommunications vol 495 no 1 pp 567ndash573 2018

[160] H Zhu J-HMao YWang et al ldquoDual inhibition of BRD4 andPI3K-AKT by SF2523 suppresses human renal cell carcinomacell growthrdquo Oncotarget vol 8 no 58 pp 98471ndash98481 2017

[161] S R Pharmaceuticals httpwwwsignalrxcomsignal-rxproduct-candidatespi3k

[162] AM Burgoyne FMVega A Singh et alAbstract LB-298eNovel Triple PI3K-CDK46-BRD4 Inhibitor SRX3177 HarnessesSynthetic Lethality Relationships to Orthogonally Disrupt CancerCell Signaling AACR Annual Meeting Washington DC USA2017

Stem Cells International

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Disease Markers

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