hdac inhibitors for the treatment of cutaneous t-cell lymphomas

471ISSN 1756-8919Future Med. Chem. (2012) 4(4), 471–48610.4155/FMC.12.6 © 2012 Future Science Ltd

Review

Special FocuS: TaRgeTed oncology

Cutaneous T-cell lymphomaCutaneous T-cell lymphoma (CTCL) is a het-erogeneous group of extranodal non-Hodgkin’s lymphomas that is characterized by clonal prolif-eration of mature T cells that localize to the skin. In the USA, the overall age-adjusted incidence of CTCL has been approximated to 6.4 cases per million people [1].

Mycosis fungoides (MF), the most common subtype of CTCL, represents a predominance of mature effector memory T cells in the skin [2]. Clinically, it presents as indolent skin lesions in sun-shielded areas that usually begin as patches or plaques and may progress to become tumors or erythroderma (covering ~80% body surface area) [3]. Often, MF is not diagnosed for several years due to indefinite clinical and histopatho-logical findings. To diagnose early disease, his-tology must demonstrate atypical and epidermo-tropic lymphocytes with supportive features such as evidence of clonality or elevated CD4+:CD8+ ratios [4]. Sézary syndrome (SS) is an aggressive leukemic variant of CTCL that can arise de novo or evolve from long-standing MF. SS patients present with a triad of generalized erythro-derma, lymphadenopathy and malignant central memory T cells in the peripheral blood (>1000 malignant T cells/µl) known as Sézary cells [2–4]. Other features include colonization with Staphylococcus aureus and keratoderma associ-ated with tinea infections [4,5]. Severe and recal-citrant pruritus is a frequent symptom of CTCL, particularly erythrodermic MF and SS, which can cause significant morbidity and a decline

in patients’ quality of life [6,7]. The pathophysi-ologic basis for the pruritus is not totally clear, but likely results from the cutaneous inflamma-tion induced by the disease. CTCL is generally considered advanced when the patient has eryth-roderma, tumors or nodal involvement (stage 2B or higher). We have previously shown that the median overall survival in patients with eryth-rodermic CTCL is 5.1 years, with the strongest predictive factors being elevated serum lactate dehydrogenase, advanced age and the absolute Sézary cell count [8].

The fact that CTCL is associated with increased Class II HLA-DR5 and DQB*03 alleles suggests that the disease may be linked to antigen stimulation or genetic predisposition, as seen with other autoimmune skin diseases [9]. Mutations in T cells may promote both T-cell accumulation via defects in the Fas/Fas ligand death pathway [10] and attraction to the skin via mutations in skin-homing molecules [4]. Although a number of infectious and environ-mental triggers have been hypothesized, stud-ies have failed to identify a consistent antigen stimulant [11,12]. Additionally, Pautrier’s micro-abscesses, a clustering of malignant CD4+ T cells around Langerhans cells, may be observed in the epidermis of MF lesions. These epidermal dendritic cells are thought to present antigens and activate T cells to clonally expand, and may thereby explain the presence of both tumor cells and an inflammatory infiltrate in early MF lesions [13,14]. Malignant T cells in SS typically have a CD4+CD26- phenotype and exhibit

HDAC inhibitors for the treatment of cutaneous T-cell lymphomas

Epigenetic modification by small-molecule histone deacetylase inhibitors (HDAC-Is) has been a promising new antineoplastic approach for various solid and hematological malignancies, particularly for cutaneous T-cell lymphoma (CTCL). Vorinostat, a pan-HDAC-I and, most recently, romidepsin, a bicyclic pan-HDAC-I, have been US FDA approved for treatment of relapsed or refractory CTCL. However, because many patients do not reach the 50% partial response mark and response is not always sustainable, overcoming HDAC-I resistance by adding other agents or finding more selective molecules is an important clinical problem in realizing the full clinical potential of HDAC-Is. In this review, we discuss the molecular basis for HDAC-I function in cancer, the clinical response and side-effect profile experienced by CTCL patients, and the progress made in attempting to identify biomarkers of response and resistance, as well as synergistic combination therapies.

Sophia Rangwala, Chunlei Zhang & Madeleine Duvic*Department of Dermatology, Box 1452, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA *Author for correspondence: Tel.: +1 713 745 4615 Fax: +1 713 745 3597 E-mail: [email protected]

For reprint orders, please contact [email protected]

Review | Rangwala, Zhang & Duvic

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dysfunctional apoptotic mechanisms, such as loss of Fas and expression of bcl-2, which result in the loss of activation-induced cell death and prolonged lifespan [15]. Progression of disease is marked by the dominance of a Th2 cytokine profile among tumor cells and the loss of CD8+ cytotoxic T cells, thus further depressing cellular immunity and allowing the accumulation of malignant clones [16].

Current treatment optionsUS FDA-approved therapeutic modalities for CTCL are limited. At this time, the options include intravenous (iv.) denileukin diftitox (approved in 1999), topical and oral bexarotene (2000), oral vorinostat (2006), iv. depsipeptide (2009) and extracorporeal photopheresis (2009) [3,7,17,18]. Many nonapproved agents, such as topi-cal steroids, topical mustargen, phototherapy, interferons and chemotherapy, are commonly used as a standard of care and may be more effec-tive than approved therapies (Table 1) [3]. Despite the treatment options available, CTCL rarely undergoes complete remission and no specific agent has been correlated with improved sur-vival. Refractory or transformed disease is often associated with poor prognosis [3].

A combination of topical therapies and sys-temic biological response modifiers are often used for patients refractory to first-line skin-directed treatments who have less than 10% involvement of body surface area (stage IA), for patients with more than 10% involvement (stage IB), or those with lymphadenopathy (stage 2A). Most common combinations include photo-therapy plus retinoids (bexarotene, acitretin or isotretinoin) or interferon, or mustargen plus topical steroids. Thick plaque lesions or fol-liculotropic MF lesions are usually more recal-citrant and are treated with psoralen plus UVA plus interferon, an oral retinoid, and/or localized radiation. Total body skin electron-beam radia-tion is suggested for those who fail to respond to other therapies and need palliation due to extensive skin involvement. This therapy should be followed by long-term maintenance therapy, such as mustargen, phototherapy, oral bexaro-tene, or if the patient is young and healthy, an allogeneic stem cell transplant [19].

Patients with advanced CTCL may respond to localized radiation, denileukin diftitox, or histone deacetylase inhibitors (HDAC-Is) [20]. Chemotherapies, including nucleoside analogues (gemcitabine and pentostatin) or PEGylated liposomal doxorubicin, are reserved for patients

with refractory tumors or nodal disease [20]. Although combined chemotherapies are often effective for a short duration, they subject the patient to further immunosuppression, leading to line-induced sepsis and other opportunistic infections. Because patients can experience con-siderable morbidity from progression of disease and cumulative adverse effects from multiple treatments, development of novel therapies with better therapeutic indices and more dura-ble remissions is critical. HDAC-Is have yielded clinical benefit for various hematological malig-nancies, most particularly for CTCL. This is evi-denced by the FDA approval of the HDAC-Is, vorinostat and romidepsin [7,18,21], for relapsed or refractory CTCL. Ongoing clinical trials with these and several other HDAC-Is demonstrate the clinical potential of this novel targeted ther-apy towards the treatment of advanced CTCL (Table 2).

The mechanistic profile of histone deacetylase inhibitorsEpigenetic modifications involve changes in gene or protein expression not secondary to direct DNA mutations. Examples are miRNA silencing, DNA methylation and DNA histone acetylation. The addition and removal of acetyl groups to positively charged lysine tails of core nucleosomal histones play an important role in transcriptional regulation. This is a dynamic process of chromatin remodeling that depends on the opposing activities of histone acetyl-transferases and HDACs [22]. Histone acetyla-tion by histone acetyltransferases unfolds chro-matin by neutralizing the lysine tails, thereby reducing the affinity of the histones to the negatively charged DNA phosphate backbone. Acetylation thus promotes binding of transcrip-tion factor complexes to facilitate gene tran-scription. In contrast, histone deacetylation by HDACs condenses chromatin and thereby pro-hibits transcription. HDAC-Is, by reversibly or irreversibly blocking the active sites of HDACs, allow the unopposed acetylation of histones and other nonhistone proteins. These small-mole-cule agents are relevant to cancer therapeutics because they may restore the expression of tumor suppressor genes that are abnormally repressed in malignant T cells, such as those involved in cell-cycle arrest, differentiation, apoptosis and angiogenesis [23].

In humans, 18 HDACs have been identi-fied and can be subdivided into five groups (Table 3): Class I (HDAC1, HDAC2, HDAC3

Key Terms

Cutaneous T-cell lymphoma: Extranodal non-Hodgkin’s lymphomas with clonal proliferation of skin‑homing mature T cells.

Mycosis fungoides: Most common and indolent form of CTCL that typically presents as patches and plaques that may progress to tumors, erythroderma, or nodal lymphoma.

Sézary syndrome: Aggressive leukemic variant of CTCL with generalized erythroderma, lymphadenopathy, and malignant T cells in the peripheral blood.

Histone deacetylases: Class of enzymes that remove acetyl groups from the lysine tails of DNA histones and other proteins to induce chromatin compaction and thus gene silencing.

Epigenetics: Changes in phenotype or gene expression that are not secondary to direct DNA mutations (e.g., DNA methylation, DNA acetylation, or microRNA silencing).

Histone acetyltransferases: A class of enzymes that add acetyl groups to the lysine tails of DNA histones to induce chromatin expansion and thus gene expression.

HDAC inhibitors for the treatment of cutaneous T-cell lymphomas | Review

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and HDAC8), Class IIa (HDAC4, HDAC5, HDAC7 and HDAC9), Class IIb (HDAC6 and HDAC10), Class III (SIRT 1–7) and Class IV (HDAC11) [22]. Class I, II and IV enzymes are zinc dependent, while Class III enzymes are nicotinamide adenine dinucleotide-dependent enzymes. Class I HDACs primarily localize to the nucleus and are small, expressed ubiquitously and generally involved in cell proliferation and differentiation. Class II HDACs are larger, act in association with tissue-specific transcription fac-tors and have both histone and nonhistone tar-gets. Class IIa enzymes are shuttled to and from the nucleus, whereas Class IIb enzymes primar-ily localize to the cytoplasm. Class III HDACs are homologues of yeast Sir2 and are insensi-tive to inhibition by Class I and II HDAC-Is due to nonhomologous catalytic sites. Because the primarily nuclear HDAC11 is homologous to both Class I and II HDACs, it has been categorized separately as a Class IV enzyme (Table 3) . Knocking out individual HDAC isotypes in mouse models have demonstrated the physio logical importance of these enzymes. Interestingly, deleting Class I HDACs are lethal in the embryonic and perinatal stages, while deleting Class II HDACs usually produces viable mice with significant developmental defects [24].

Aberrant overexpression, function, and recruitment of Class I and II HDACs are associ-ated with malignancies including T-cell lympho-mas [22,25]. Notably, increased expression of par-ticularly Class I HDAC1, HDAC2, and HDAC3 has been shown to be essential for cancer cell proliferation and survival [26]. Additionally, Class I HDAC expression in both solid and

hematological malignancies tends to correlate with a worse prognosis [26], with high expres-sion of HDAC2 being seen with more aggressive forms of CTCL [25]. Alternatively, the expression of Class II HDACs 4, 5, 6, 7 and 10 tends to be associated with a better prognosis, especially in CTCL (HDAC6) and non-small-cell lung cancer [25,26]. The reasons for these correlations are not yet understood but, nevertheless, suggest that selective inhibition of Class I HDACs may be a more effective therapeutic strategy.

HDAC-Is have demonstrated anti-tumor activity in solid and hematological malignan-cies, particularly in T-cell lymphomas and, most remarkably, in CTCL. The rationale for the anti-tumor activity of HDAC-I involves a compli-cated and poorly understood range of pleiotropic effects. Gene expression profiling of T-cell lym-phoblastic cell lines incubated with HDAC-Is vorinostat and romidepsin demonstrated up to 22% of the genome being affected within 16 h of treatment [27]. In several tumors and cell lines, HDAC-I treatment has been shown to induce accumulation of acetylated histones as well as the acetylation of nonhistone protein substrates, such as transcriptional co-activators (RB and MSL-3), transcription factors (e.g., p53, c-myc, E2F, bcl-6, GATA, NF-kB, CREB and IRF), signaling mediators (STAT-3, IRS-1), steroid receptors (e.g., androgen, estrogen and glucocorticoid), DNA repair enzymes (e.g., KU70, FEN1 and WRN), cytoskeletal compo-nents (e.g., a-tubulin), molecular chaperones (e.g., heat shock protein-90) and nuclear import factors [27–30]. Unregulated acetylation of these proteins leads to alterations in transcription,

Table 1. Approved and nonapproved therapies available for cutaneous T-cell lymphoma.

Stage Features First-line treatment Second-line treatment

1A Limited patch/plaque (<10% BSA)

Skin-directed treatment (topical steroids [class III-IV], topical mustargen, topical retinoids [bexarotene† and tazarotene], phototherapy [UVB and PUVA] and electron beam radiation)

Adjunctive skin-directed treatmentAdjunctive biologic agent (oral retinoids [bexarotene†, acitretin and isotretinoin], interferons)

1B, 2A Extensive patch/plaque (>10% BSA) ± lymphadenopathy

Skin-directed treatment ± biologic agent Adjunctive biologic agent

2B Tumors ± lymphadenopathy

Skin-directed treatment (PUVA and electron beam radiation) ± biologic agent (denileukin† diftitox†, vorinostat†, romidepsin† and alemtuzumab)

Adjunctive biologic agent or chemotherapy (pralatrexate, methotrexate, pegylated doxorubicin and gemcitabine)Allogeneic stem cell transplantation

3 Erythroderma ± lymphadenopathy

ECP† ± skin-directed treatment or biologic agentMultimodality systemic treatment

Multimodality systemic treatmentAllogeneic stem cell transplantation

4A, 4B Nodal or visceral metastasis

ChemotherapyMultimodality systemic treatment

Salvage chemotherapyAllogeneic stem cell transplantation

†US FDA approved.BSA: Body surface area; ECP: Extracorporeal photopheresis; PUVA: Psoralen plus ultraviolet A; UVB: Ultraviolet B.



mitosis and protein stability, with downstream effects on tumor proliferation, survival and maintenance.

HDAC-Is can repress tumor proliferation by inducing cell-cycle arrest at the G1/S and G2/M timepoints. By repressing cyclin D and cyclin A and upregulating p27, p16 and, particularly, p21, HDAC-Is reduce activity of CDK4 and CDK2 and interrupt T-cell-cycle progression at the G1/S checkpoint [27,30–32]. Also, for reasons that are still elusive, HDAC-Is preferentially activate intrinsic and extrinsic apoptosis in malignant T cells at low concentrations for which healthy cells are relatively resistant [33–35].

The intrinsic pathway involves mitochondrial permeabilization in response to internal cellular triggers. This in turn induces release of cyto-chrome c, which activates the caspase cascade via caspase-9. HDAC-Is affect the intrinsic pathway via repression of anti-apoptotic pro-teins (bcl-2, bcl-xL and XIAP) and activation of pro-apoptotic proteins (bim and bax). In fact, overexpression of bcl-2 and occasionally bcl-xL has been shown to protect lymphoma cells from HDAC-I-induced death [36–38]. The extrin-sic pathway is activated by receptors respond-ing to extracellular stimuli. The subsequent induction of the downstream death-inducing signaling complex activates the caspase cascade via caspase-8. HDAC-Is have been shown to increase gene expression for both death recep-tors (e.g., Fas and TRAIL receptors DR4/DR5) and their ligands, and to decrease expression of extrinsic pathway inhibitors (e.g., c-FLIP, cIAP2 and X1AP) [39]. Moreover, HDAC-I induction of autophagy has been consistently demonstrated, and was first suggested when HDAC-I-treated cancer cells were found to undergo cell death despite inhibition of caspase-mediated apoptotic cascades [38,40].

In addition to disrupting cell cycle and survival pathways, HDAC-Is also appear to inhibit angiogenesis by upregulating anti-angio-genic proteins (e.g., thrombospondin-1, Von-Hippel-Landau factor and neurofibromin-2) and downregulating pro-angiogenic proteins (e.g., VEGF and hypoxia-induced protein-1a) [7,41,42]. Finally, HDAC-Is may repress inflammation via inhibition of pro-inflammatory cytokines and upregulation of anti-inflammatory cytokines; and its use in inflammatory and autoimmune conditions is currently being investigated [43].

Many structurally variable subclasses of HDAC-Is have been studied, including hydroxamic acids, cyclic peptides, benzamides,

short-chain fatty acids and electrophilic ketones [30]. These HDAC-Is can either act as pan-inhibitors that target zinc-containing HDAC isoforms of at least classes I and II, or selective inhibitors that target particular isoforms or sub-classes of HDACs. However, there is so far no data that indicate inhibiting a particular HDAC isoform is correlated with increased efficacy, or that selective HDAC-Is are correlated with decreased adverse events.

The biological basis for why CTCL is espe-cially sensitive to HDAC-Is remains uncertain. Several HDAC-Is are currently under going extensive clinical evaluation in CTCL (Table 2) [23]. In addition to the FDA-approved agents vorinostat and romidepsin [7,18,21], panobino-stat (LBH589) and belinostat (PXD101) have achieved partial and complete responses in CTCL patients with refractory disease [44,45]. Herein, we present preclinical and clinical data supporting the use of particular HDAC-Is for treating refractory CTCL.

CTCL clinical trials of histone deacetylase inhibitors � Vorinostat

Vorinostat (suberoylanilide hydroxamic acid, SAHA, Zolinza®) and is an orally administered HDAC-I (t

½ = 2 h) approved for treatment

of CTCL in October 2006 [46]. It has been shown to reversibly inhibit Class I HDACs and Class IIb HDAC6, and weakly inhibit Class IIa HDACs [47,48]. We discuss the mechanistic understanding of vorinostat in CTCL below and then describe the CTCL clinical trials that led to its FDA approval.

Preclinical studiesSelective induction of apoptosisVorinostat has been shown to inhibit the cell viability of several malignant T-cell lines and human tumor xenografts in mice at concentra-tions to which normal cells stay relatively unaf-fected [49]. We have previously demonstrated that clinically relevant doses (1–2 µM) of vori-2 µM) of vori-nostat induce apoptosis in both CTCL cell lines and primary malignant T cells but not normal T cells from healthy donors [7,33]. However, this difference in sensitivity to vorinostat-induced apoptosis is unlikely secondary to differing lev-els of HDAC inhibition because both tumor and normal cells had a similar accumulation of acetylated histones. Rather, transformed cells treated with vorinostat may be exclusively sen-sitive to reactive oxygen species accumulation



and caspase activation [50], or may be unable to recover from vorinostat-induced DNA double-strand breaks [51].

Accumulation of acetylated histonesHistone acetylation after HDAC-I treatment has been shown to correlate with drug activity in both normal and transformed cells [30]. For this

reason, acetylated histones have been measured as an intermediary marker in Phase I clinical tri-als, such as with vorinostat [52]. Vorinostat results in increased protein levels of acetylated histones (H2B, H3 and H4) in both sensitive and resis-tant CTCL cell lines in vitro [33]. Furthermore, MF lesions had unexpectedly high H4 acetyla-tion in keratinocyte and T-cell nuclei at baseline,

Table 2. Ongoing clinical trials of various histone deacetylase-inhibitors in cutaneous T-cell lymphoma.

Drug Structure HDACs inhibited Trial number Phase Aim

Vorinostat

O

O

OHNH

HN

Class I, Class IIb (HDAC6) > Class IIa

NCT00958074 II Vorinostat for CTCL patients with history of no prior systemic therapy

NCT01386398 III Vorinostat and bortezomib for refractory or recurrent stage IIB, stage III, or stage IV CTCL

NCT00992446 II Vorinostat and bortezomib for non-Hodgkin lymphoma after an autologous stem cell transplant.

NCT00837174 II Vorinostat and bortezomib for relapsed/refractory non-Hodgkin lymphoma

NCT00691210 I Vorinostat, etoposide, and niacinamide for relapsed lymphoid malignancies

NCT01187446 I/II Vorinostat and low-dose total-skin-electron-beam therapy for mycosis fungoides

Romidepsin

S

S O

O

OO

OO

NH

NH

NH

NH

Class I > Class II NCT00477698 I Topical romidepsin for stage I/II CTCL

Belinostat

NH

O OS

O

OHNH

Class I, Class II NCT00274651 II Belinostat for relapsed/refractory T-cell lymphoma

PanobinostatOH

O

NH

NH

NH

Class I, Class II and Class IV

NCT00425555 I/III Panobinostat for refractory CTCL

NCT00918333 I/II Panobinostat and everolimus for recurrent multiple myeloma or lymphoma

NCT00962507 I Panobinostat and everolimus for relapsed/recurrent lymphoma/multiple myeloma

NCT01261247 II Panobinostat for relapsed/refractory non-Hodgkin lymphoma

CTCL: Cutaneous T-cell lymphoma; HDAC: Histone deacetylase; HDAC-I:Histone deacetylase inhibitor.



the significance of which is unknown [7]. Because vorinostat treatment significantly decreased the lymphocyte infiltrate in MF tissue, the effect of this HDAC-I on histone acetylation was difficult to assess. Based on these data, it seems that the degree of histone acetylation is not predictive of response in CTCL.

Upregulation of the intrinsic apoptosis pathwayThe cyclin-dependent kinase inhibitor p21 (WAF1/CIP1) is one of the most commonly reported genes to be upregulated by vorino-stat and other HDAC-Is [33,53], and results in downstream induction of G2 cell-cycle arrest and apoptosis. Although upregulation of p21 occurred in response to vorinostat in CTCL cell lines, immunoblot ana lysis showed that this effect was independent of the tumor suppres-sor p53 [33]. In addition, the balance between protein expression of the anti-apoptotic bcl-2 and the pro-apoptotic bax is critical in control-ling the activation of caspases by regulating the release of cytochrome C from mitochondria [54]. Of interest, vorinostat treatment of three CTCL cell lines and patient-derived primary Sézary cells in vitro did not change bcl-2, but increased bax, activated caspase-3 and cleaved poly (ADP-ribose) polymerase [33].

Modulation of STAT signalingCTCL cells have been shown to constitutively express STAT proteins, which dimerize and become phosphorylated after growth factor stimulation to induce gene transcription and promote cell proliferation [55,56]. Vorinostat did not decrease protein expression of STAT-3 and phospho-STAT-3 but did decrease STAT-6 and phospho-STAT-6 in CTCL cell lines, and pri-mary Sézary cells [33]. Interestingly, following vorinostat treatment, phospho-STAT-3 protein immunostaining changed from a predominantly nuclear to cytoplasmic location in skin lesions of

responders [7]. Nuclear accumulation of STAT-1 and high levels of nuclear phospho-STAT-3 were present in malignant T cells in CTCL skin lesions and correlated with a lack of clini-cal response to vorinostat (Table 4) [56]. Thus, deregulation of STAT activity is likely to play a key role in vorinostat response and resistance in CTCL.

Cytokine modulationVorinostat may also have immunomodulatory effects, by shifting the immune milieu away from the Th2-dominant profile of malignant CTCL cells. A recent study found selective downregulation of the Th2 cytokine IL-10 to be likely mediated by the STAT3 pathway in both CTCL cell lines and primary Sézary cells [57]. This effect was seen to a lesser extent in the expression of IL-4. Additionally, vorinostat enhanced expression of the Th1 cytokine IFN-g and mildly decreased expression of the T-cell growth-stimulating cytokine IL-2.

Inhibition of angiogenesisAngiogenesis is a key process during tumor development and metastasis that is tightly con-trolled by the balance between positive and negative environmental signals that induce and inhibit angiogenesis, respectively [58]. We found that treatment with vorinostat decreases the expression of the pro-angiogenic protein VEGF in CTCL [7]. In addition, thrombospondin-1, a potent inhibitor of angiogenesis, was increased eightfold in a cDNA microarray analysis of vorinostat-treated CTCL cells [7]. We confirmed this finding by demonstrating that in CTCL patients’ paired skin lesions, treatment with vori-nostat (2 h, 4 weeks and 8 weeks) often induced a significant decrease in microvascular density and an increase in dermal thrombospondin-1 in responders, when compared with baseline [7] (Table 4). Thus, inhibition of angiogenesis and

Table 3. Human histone deacetylases.

Class Class I Class IIa Class IIb Class III Class IV

Members HDAC 1, 2, 3 and 8 HDAC4, 5, 7 and 9 HDAC6, 10 SIRT1–7 HDAC11MW 22–25 kDa 120–135 kDa 120–135 kDa 40–50 kDa 120–135 kDaLocalizationNuclear + + + + +

Cytoplasmic + + + +

Binding site Zn++ Zn++ Zn++ AD+ Zn++Homology with yeast RPD3 deacetylase Zn++ Zn++ AD+ Zn++HDAC: Histone deacetylase. Reprinted with permission from [93].



upregulation of thrombospondin-1 by vorinostat may participate in inhibiting CTCL growth.

Potential biomarkersHR23B, a candidate biomarker identified in a genome-wide loss-of-function screen for HDAC-I-induced apoptosis, has an important role in shuttling ubiquitinated cargo proteins to the proteasome [59]. Interestingly, HR23B controls the sensitivity of CTCL cells to vorinostat [60]. Moreover, proteasome activity is deregulated in vorinostat-treated CTCL cells through a mecha-nism dependent on HR23B and vorinostat sensi-tizes CTCL cells to the effects of the proteasome inhibitor bortezomib. Of interest, an ana lysis of HR23B levels in CTCL skin lesions taken from our Phase II trial of vorinostat [7] showed a positive correlation between HR23B expression and clinical efficacy of vorinostat (Table 4) [60].

Clinical studiesOral vorinostat at a dose of 400 mg/day has a rapid onset of action, and improved nodes, blood burden and itching in heavily pretreated patients [7,21]. A Phase I trial of patients with advanced cancer first noted the clinical efficacy of oral vorinostat for a patient with refractory CTCL who had failed five systemic regimens [52]. The disease stabilized after 4 months of 200-mg oral vorinostat given twice daily.

A single-center Phase II dose-ranging study for oral vorinostat was conducted by our group in 33 patients with refractory or relapsed CTCL who had been unresponsive to a median of five systemic therapies (range 1–15) [7]. Of the enrolled patients, 85% had advanced disease (stage 2B or higher) and 33% had SS. The first cohort received 400 mg vorinostat daily, the sec-ond received 300 mg twice daily for 3 days with a rest for 4 days, and the third received 300 mg twice daily for 14 days with rest for 7 days fol-lowed by 200 mg twice daily. Demographics, such as age and gender, were similar among these three groups. The clinical response for each cohort and suggested dose modification schedule are summarized in Table 5. The first cohort (400 mg daily) had the best response without the significant dose-limiting thrombo-cytopenia seen in the third cohort (300 mg twice daily). The primary end point of the study was to assess the complete response (CR) and partial response (PR) rates. The secondary objectives were to evaluate time to progressive disease, response duration, relief of pruritus and safety. The response to therapy was categorized

according to the Physician’s Global Assessment for CR, PR, stable disease or progressive disease [17]. Skin involvement was assessed as the percent body surface area involvement of patch, plaque or tumor disease. Considering unique patients for an intent-to-treat ana lysis, eight of 33 (24%) patients achieved a documented PR with no CRs. An additional 14 (42%) patients experienced improvement in pruritus, such that a total of 19 of 33 (58%) enrolled patients clinically benefited from treatment. Vorinostat was clinically effec-tive for a variety of CTCL phenotypes, including patients with early-stage refractory MF, advanced tumors with histologic large-cell transformation, and nodal and/or blood involvement. Notably, lymphadenopathy, when present, also improved in responders. The response rates in patients who had received prior bexarotene (23%) or not (27%) were similar. The median time to response was 11.9 weeks, and the median duration of response was 15.1 weeks (range 9.4–19.4 weeks). The median duration of response was lowest in the second cohort, who received intermit-tent dosing (9.4 weeks), and highest in the first cohort, treated with 400 mg daily (16.1 weeks). Overall, oral vorinostat 400 mg daily provided the most favorable risk–benefit profile and the dose of 400 mg/day was selected for evaluation in a pivotal open-label, multicenter Phase IIb trial [21].

The pivotal study supporting FDA approval was a Phase IIb trial of oral vorinostat at 400 mg

Table 4. Potential biomarkers of response to histone deacetylase inhibitors in patients with cutaneous T-cell lymphoma.

HDAC inhibitors

Clinical trial (Phase)

Biomarkers studied Correlation with clinical response

Vorinostat II p-STAT-3 [7] NegativeVEGF [7] NegativeTSP-1 [7] Positive STAT-1 [56] NegativeHR23B [60] Positive

Depsipeptide II Histone 3 acetylation [71]

Positive

HbF [71] PositiveABCB1 [71] None

Panobinostat II Histone 3 acetylation [80]

None

GUCY1A3 [80] Negative?ANGPT1 [80] Negative?NR2F2 [80] Negative?CCND1 [80] Negative?

ANGPT1: Endothelial Tie2/Tek ligands angiopoietiN-1; CCND1: Cyclin D1; GUCY1A3: Guanylate cyclase 1A3; HbF: Fetal haemoglobin; HDAC: Histone deacetylase; NR2F2: Transcription factor COUP-TFII.



daily, which enrolled 74 patients with Stage 1B–4A MF and SS [21]. Two dose modifica-tions were allowed: 300 mg daily or 300 mg daily for 5 days per week. Safety assessments were performed with the National Cancer Institure (NCI) Common Terminology Criteria for Adverse Events version 3.0. Inclusion cri-teria were patients with MF/SS Stage 1B–4B who had progressive, persistent or recurrent disease that was resistant to at least two prior systemic treatments, one of which was bex-arotene. Patients with Eastern Cooperative Oncology Group performance status of 0–2 and adequate hematologic, hepatic and renal function were included. Patients with prior use of HDAC-Is or anti cancer treatment within 3 weeks of study entry were excluded. Unlike the previous Phase II study, skin involvement was assessed with the modified severity weighted assessment tool, which weighed plaque and tumor disease. Of the 82% of patients who had refractory advanced-stage MF/SS (≥Stage 2B), approximately 30% achieved an overall response. The median time to response was less

than 2 months. Median response duration and time to progression in advanced-stage respond-ers were not reached but were estimated to be more than 6.1 and 9.8 months, respectively. Median time to progression in all patients was 4.9 months. Pruritus relief was observed in 32% of study patients, including 25% of those who had not met the criteria for an objective cutaneous response.

Of the 74 patients who participated in the Phase IIb trial, a continuation phase study was implemented for six patients who had received vorinostat for at least 2 years [61]. Upon enrollment, five of the six patients had achieved an objective response, with one patient with facial tumors having experienced a durable com-plete response, and one patient had prolonged stable disease. Of these six patients, one patient discontinued as a result of a serious adverse event and three additional patients discontinued treat-ment because of progressive disease (day 780, 1008 and 1066). One patient discontinued vorinostat (day 803) after relocating, and sub-sequently continued treatment with vorinostat

Table 5. Phase II data on oral vorinostat in patients with cutaneous T-cell lymphoma.

Treatment group

Group 1 Group 2 Group 3

Dosing schedule

400 mg q.d.† 300 mg b.i.d. × 3 days/week × 4 week, then 5 days/week

300 mg b.i.d. × 14 days with 7 days restmaintenance: 200 mg b.i.d.

Dose modification

First dose reduction 350 mg q.d. 250 mg × 3 days/week 200 mg b.i.d.Second dose reduction 300 mg q.d. 200 mg b.i.d. × 3 days/week 200 mg b.i.d. × 5 days/week

Clinical response

Partial response (PR) 31% (4/13) 9% (1/11) 33% (3/9)Median PR duration (range/weeks)

15 (8–24) 16 (8–24) 13 (3–21)

Mean time to PR (weeks) 11 4 11LN regression (at 4 weeks) 78% (7/9) 38% (3/8) 56% (5/9)>50% decreased pruritus 82% (9/11) 67% (8/12) 50% (4/8)

Adverse events (Grade 3/4)

Thrombocytopenia 8% (1/13) 8% (1/12) 42% (5/12)Anemia 8% (1/13) 17% (2/12) 0% (0/0)Deep vein thrombosis 0% (0/0) 25% (3/12) 0% (0/0)Dehydration 8% (1/13) 0% (0/0) 17% (2/12)Pyrexia 0% (0/0) 25% (3/12) 0% (0/0)Hypotension 0% (0/0) 17% (2/12) 0% (0/0)Pulmonary embolism 0% (0/0) 17% (2/12) 0% (0/0)Sepsis 0% (0/0) 8% (1/12) 8% (1/12)†Initial three patients treated with vorinostat 250 mg/m2/day.b.i.d.: Twice a day; q.d.: Once a day.Information extracted and adapted from [7].Reprinted with permission from [93].



by prescription. One patient remained on vorinostat therapy.

Oral vorinostat is generally well tolerated, with side effects being dose-related and reversible upon cessation of therapy. As is often noted with other HDAC-Is, the most common toxicities with oral vorinostat in these studies were fatigue and gastrointestinal symptoms, including diar-rhea, dysgeusia, nausea and dehydration from not eating/drinking (Table 5). In the Phase IIa study, serious grade 3/4 adverse experiences included thrombocytopenia (19%), dehydra-tion (8%), vomiting (8%), anemia (8%), deep vein thrombosis (8%), pyrexia (8%), hypo-tension (5%), pulmonary embolism (5%) and sepsis (5%) [7]. Grade 3/4 thrombocytopenia was most common (42%) in the third cohort who received 300 mg twice daily for 14 days compared with the other cohorts (8%). Notably, thrombo cytopenia was reversible 4–5 days after treatment cessation [62]. In the Phase IIb dose-ranging study, vorinostat at 400 mg daily was generally tolerated well, with less than 15% patients requiring dose reductions due to intol-erability [21]. The most common adverse events, most of which were grade 2 or less, included gas-trointestinal symptoms (diarrhea [49%], nausea [43%], anorexia [26%], dysgeusia, dry mouth, vomiting, constipation and anorexia) or fatigue (46%), thrombocytopenia (22%), weight loss, alopecia, muscle spasms, creatinine elevation, anemia and chills. Grade 3/4 adverse events involved fatigue (5%), deep venous thrombosis/pulmonary embolism (5%), thrombocytopenia (5%)and nausea (4%). Three patients died dur-ing the course of the study. Since five patients

suffered pulmonary embolisms while on these vorinostat trials, there was concern as to whether HDAC-I has pro-coagulant properties. Recent research indicates the events to be likely coin-cidental and more directly related to the pro-coagulability of relapsed cancers, especially SS. Notably, none of the patients in these vorinostat trials experienced grade 3/4 neutropenia and only three had grade 1/2 QTc prolongation but no associated cardiac irregularities. The latter was initially a concern with HDAC-I use, partic-ularly romedepsin, but no clinically significant sequelae has been substantiated.

� RomidepsinRomidepsin (depsipeptide, FK228, Istodax®) is a bicyclic tetrapeptide antibiotic (t

½ = 2.5 h)

extracted from Chromobacterium violaceum that is a potent Class I and weak Class II HDAC-I [63,64]. Romidepsin induces cell differentiation, G1 and G2/M cell-cycle arrest, and apoptosis, even at nanomolar concentrations. In addition to modulating histone acetylation, this HDAC-I inhibits hypoxia-induced angiogenesis, depletes several heat shock protein 90-dependent onco-proteins, upregulates p53, p21, cyclin-E, and hypophosphorylated retinoblastoma protein, and downregulates c-myc and cyclin D1 [32,65]. In CTCL cells, it has also been shown to have anti-Th2 immunomodulatory effects similar to vorinostat [57].

In a Phase I trial for advanced cancer con-ducted by the NCI [66], romidepsin induced a partial response in a patient with extensive tumor-stage MF whose lesions later recurred but responded well to localized radiation [67].

Table 6. Combination studies of histone deacetylase inhibitors in cutaneous T-cell lymphoma.

Combination Model Activity Genes/mechanisms

Vorinostat plus bexarotene Phase I trial (22 CTCL patients) 4/22 OR, 7/22 improved pruritus

Regulation of RXR/RAR [84]

Vorinostat plus bexaroten plus fenofibrate

Case report (one MF patient) One CR Regulation of co-repressors? [86]

Vorinostat plus IFN-g Case report (three SS patients) Three OR T-reg/TGF-b↓? [87]Vorinostat plus IFN-a plus ECP Case report (three MF/SS

patients)Two OR, one SD T-reg/TGF-b↓? [88]

Vorinostat plus JAK inhibitor CTCL cell lines Synergistic p-STAT3/bcl-2/bcl-xL/survivin/mcl-1↓c-Myc/OSM↓ [56]

Vorinostat plus bortezomib CTCL cell lines Synergistic Proteasome activity↓, p21/p27/p-p38↑ [89]Vorinostat plus PI3K inhibitor CTCL cell lines Synergistic GSK3b↑ [91]Vorinostat plus PIM inhibitor CTCL cell lines Additive PIM1/PIM2↑ [91]Vorinostat plus HSP90 inhibitor CTCL cell lines Antagonistic HSP90↓ [91]Panobinostat plus Bcl-2 antagonist CTCL cell lines Synergistic HDAC7/Nur77/Bcl-2/Bcl-xL↓ [79]CR: Complete response; CTCL: Cutaneous T-cell lymphoma; OR: Overall response; PI3K: Phosphoinositide-3 kinase; RXR/RAR: Retinoid receptor; SD: Stable disease; TGF-b: Transforming growth factor-b; T-reg: Regulatory T cell.



Two SS patients in this trial also experienced reduced tumor burden of their skin and circu-lating Sézary cells, but both had to drop out because of a Staphylococcus aureus infection and unremitting pruritus, respectively.

The single-agent efficacy of romidepsin in two follow-up Phase II studies enrolling a total of 167 patients with refractory CTCL led to its FDA approval in late 2009 [18,68]. As suggested by the NCI Phase I trial, the dose administered was 14 mg/m2 given as a 4-h iv. infusion on day 1, 8 and 15 for each 28-day cycle. The pivotal, mul-ticenter NCI Phase II trial enrolled 71 CTCL patients who had failed a median of four systemic regimens and who mostly (87%) had advanced disease (stage 2B or higher) [18]. Twenty four patients (34%) experienced a reduction in tumor burden, with four CR and 20 PR. The median time to response was 2 months and the median duration of response was 13.7 months. A second international, multicenter Phase II registration trial (GPI-04–0001) of 96 patients with the same treatment course had similar results [68]. Patients had failed a median of three systemic therapies (range 1–8), 68 (71%) had advanced disease and 19 (20%) had SS. Thirty three (34%) patients reported marked improvement (six CR [6%] and 27 PR [28%]). Notably, 58% of SS patients responded. The median time to response was 2 months and the median dura-tion of response was 14.9 months. Of the 65 (68%) patients with moderate to severe pruritus, this symptom was significantly reduced in 28 (43%) patients, including in enrollees who did not fit the criteria for an objective response. The median duration of pruritus relief was 6 months.

Side effects were similar to other HDAC-Is. The most common were fatigue, nausea, vomit-ing, neutropenia and thrombocytopenia. The latter occurred in 32% patients and was consid-ered grade 3/4 in 5%. Neutropenia was another notable event, occurring as grade 3/4 in 12% patients. Although there was an initial concern for cardiac toxicity due to QTc prolongation [69], only reversible low-grade ECG changes of ST/T wave flattening were seen [66,70]. Though clini-cally meaningful QTc prolongation was not cor-related with romidepsin or other HDAC-I use, the prescribing practitioner should be aware of the possible risk. It is recommended to carefully monitor low K+ and Mg2+ ions in patients on HDAC-Is prior to infusing drug and avoid treat-ing patients who either have a prior history of arrhythmias or are on other medications known to prolong QTc intervals.

Additionally, it is worth comparing the data from the two registration trials of oral vorinostat and iv. romidepsin because both utilized pan-HDAC-Is. Both trials enrolled CTCL patients who had a similar degree of advanced disease (82 vs 71%, respectively) and a similar median number of preceding systemic regimens (3 vs 4, respectively). Approximately a third of patients responded to either of these medications and toxicities were very similar, though the response rate and incidence of gastrointestinal symptoms were slightly higher in the romidepsin trials. Moreover, a small portion of romidepsin-treated patients experienced neutropenia.

Correlative studies showed that histone H3 acetylation and ABCB1 gene expression in peripheral blood mononuclear cells (PBMCs); ABCB1 gene expression in tumor biopsy sam-ples; and blood fetal hemoglobin levels, all of which were increased following romidepsin treatment. Histone acetylation in PBMCs at 24 h was associated with response (p = 0.026) as was the increase in fetal hemoglobin (p = 0.014); this latter association may be due to the lon-ger on-study duration for patients with disease response (Table 4) [71].

� BelinostatBelinostat (PXD101) is a hydroxamide pan-HDAC-I that is administered intravenously (t½ = 3 h). An oral preparation that has better tolerability was recently developed and is still undergoing early-phase studies [72]. Although no preclinical studies specific to CTCL have been published, belinostat has shown pro-apoptotic activity in myeloma, leukemia and lymphoma cell lines, and has inhibited growth of xenografts tumors in mice with no appreciable toxicity to the host [73]. Activation of TGFbR-II with concomi-tant repression of survivin may be significant to the anti-tumor effect of belinostat [74].

Phase I clinical trials evaluating the safety and tolerability of iv. belinostat in advanced solid and hematological malignancies have established the maximum tolerated dose (MTD) to be 1000 mg/m2 administered daily over a 30-min infusion on days 1–5 of a 3-week cycle [75–77]. A recent open-label, multicenter Phase II study found belinostat to be moderately effective for patients with refractory or relapsed CTCL or peripheral T-cell lymphoma (PTCL) who had not responded to at least one systemic regimen [45]. Of the 53 patients enrolled, 29 patients had CTCL (15 MF, seven SS, five non-MF/SS and two unclassified) with a median of three prior



systemic therapies and 55% with stage 4 dis-ease. While 25% of PTCL patients responded, approximately four (14%) of the 29 CTCL patients responded, with a short median time to response of 16 days and a durable response that lasted for a median of 273 days. Of these four patients, two achieved CR (ALCL, MF) and two PR (MF, SS). Furthermore, stable dis-ease was seen in 17 CTCL patients (ten MF, three SS, two non-MF/SS and two unclassi-fied). For the 14 patients with significant base-line pruritus, seven (50%) indicated substantial relief after a median of 16 days of treatment. The treatment had an acceptable safety profile with no grade III prolonged QT intervals reported and minimal hematological toxicity. Grade III and IV adverse events reported were neutrope-nia, thrombo cytopenia, rash/erythema, pruri-tus, edema and adynamic ileus. A clinical trial of this drug for PTCL was recently conducted.

� PanobinostatPanobinostat (LBH589) is a highly potent hydroxamate-derived pan-HDAC-I that is avail-able in both oral and iv. formulations. It inhibits Class I, II and IV HDACs at low nanomolar concentrations, and has a long mean terminal half-life (t

½ = 16 h). The molecule has demon-

strated selective cytotoxicity of malignant T cells in in vitro and in vivo tumor models, and clinical activity in various hematological malignancies [78]. Preclinical studies have shown CTCL cell lines and xenograft mouse models to be highly sensitive to panobinostat [37,79]. This sensitivity was also observed in CTCL cells refractory to vorinostat, possibly due to the ability of pano-binostat to downregulate STAT activation [37]. Additionally, NF-kB was constitutively activated and the anti-apoptotic bcl-2 was significantly upregulated in CTCL cell lines resistant to pano-binostat [37,79]. The anti-tumor activity of pano-binostat appears to be mediated by the intrinsic apoptotic pathway, since drug resistance was reversed when the anti-apoptotic bcl-2/bcl-xL proteins were inhibited, and drug resistance was induced in sensitive cells after knock-down of the pro-apoptotic bax protein [37,79]. Panobinostat activity in CTCL cells has also been associated with the inhibition of HDAC7 and the resul-tant activation of the pro-death nuclear orphan receptors Nur77 and Nor1, which in turn con-verts bcl-2 from an anti-apoptotic to a pro-apoptotic molecule [79]. Additionally, malignant CTCL cells isolated from six patients treated with panobinostat were subjected to microarray

gene-expression profiling. This study indicated that distinct gene expression profiles over time can be observed. In total, 23 genes showed statistical significance, including those involved in angio-genesis, apoptosis and immune regulation. Of these, four genes were validated by quantitative real-time PCR, two angiogenesis related genes (GUCY1A3 and endothelial Tie2/Tek ligands ANGPT1) and two cell-cycle progression genes (the transcription factor COUP-TFII [NR2F2] and CCND1) (Table 4) [80]. In an open-label, multicenter Phase I trial, ten advanced CTCL patients who had progressed despite alternate sys-temic therapy were instructed to take oral cap-sules of 20- (nine patients) or 30-mg (one patient) panobinostat on days 1, 3 and 5 weekly as part of a 28-day cycle [80]. The MTD was identified to be 20 mg. Six of ten patients responded, with two CR (one of which was of the 30-mg cohort) and four PR. Median time to response was 60 days. Notably, the two patients who met the criteria for stable disease both achieved CR 2 and 24 weeks after panobinostat was discontinued. The major grade 3 event was diarrhea, with other grade 3 toxicities being thrombocytopenia, neutropenia, skin infection, atrial fibrillation, eye swelling and anemia.

A multicenter Phase II study of CTCL patients (stage 1B–4A) was conducted in which 20-mg panobinostat was administered at the same dosing schedule as the Phase I trial. Ninety-five patients with relapsed/refrac-tory CTCL have been grouped based on prior bexarotene treatment. So far, 15 (16%) have responded to therapy: 11 (18%) of the 62 bex-arotene-treated patients and four (12%) of the 33 bexarotene-naive patients [44].

Potential combination treatmentsBecause long-term remissions are rare in advanced or otherwise refractory CTCL, HDAC-Is are administered as a third-line monotherapy until the patient experiences disease progression or medication intolerance. Unfortunately, only approximately one third of refractory CTCL patients respond to HDAC-I and these patients experience a limited response duration. The development of synergistic combination treat-ments may be more effective for overcoming HDAC-I resistance by promoting increased and more durable response rates. Combined regimens may also allow for lower doses of each individual agent to be used, thereby decreasing the risk of side effects without compromising on efficacy.



Preclinical and clinical studies for several solid and hematologic malignancies have shown tar-geted cytotoxic agents such as anthracyclines [81,82] and all-trans-retinoic acid [83], anti-angio-genesis agents, radiation [84] and other anticancer treatments to enhance the anti-tumor effects of HDAC-Is [30]. For advanced CTCL, a Phase I dose-ranging trial of vorinostat and bexarotene combination therapy was recently conducted [85]. The MTD was established to be lower than each drug individually: vorinostat at 200 mg daily and bexarotene at 300 mg/m2 daily. Of the 22 patients evaluated, four (18%) had an objective response and seven (32%) had relief of pruritus. The most common side effects have been hypothyroidism (35%), fatigue (30%) and hypertriglyceridemia (30%). Additionally, several case reports suggest that vorinostat had better clinical efficacy in CTCL when combined with bexarotene plus fenofibrate [86], IFN-g [87], or IFN-a plus extracorporeal photopheresis [88]. Preclinical studies in T-cell lymphomas have also increased interest in assessing other combination therapies in CTCL patients. For instance, vori-nostat has demonstrated synergy with the prote-asome inhibitor bortezomib in cells derived from CTCL, adult T-cell leukemia/lymphoma and B-cell leukemia/lymphoma patients [30,89,90]. In CTCL cells, the combination upregulates p21

and p27, and activates p38 mitogen-activated protein kinase, an enzyme responsive to stress stimuli [89]. Vorinostat and other HDAC-Is can also exert a synergistic or additive anti-tumor effects when combined with a bcl-2/bcl-xL antagonist [79], a JAK/STAT inhibitor [56], phosphoinositide-3 kinase inhibitors and PIM inhibitors in CTCL cells [91]. These potential combinations are listed in Table 6 and merit further evaluation.

Future perspectiveBoth the clinical efficacy and the minimally immunosuppressive nature of HDAC-I com-pared with traditional chemotherapy make these small molecules appealing for cancer treatment, particularly for CTCL, as immunosuppression is severe in advanced patients. Despite the sig-nificant and sustainable single-agent activity of the pan-HDAC-Is vorinostat and romidepsin in refractory advanced-stage CTCL, clinical hurdles include the need to increase the response rate and address the frequent development of HDAC-I resistance. Since we have only just begun to understand the biological mechanisms by which HDAC-I selectively target tumor cells, the hope is that additional studies can help identify reli-able markers of response and resistance that will allow the personalized selection of patients most

Executive summary

Mechanisms of histone deacetylase inhibitors

� Vorinostat and other histone deacetylase inhibitors (HDAC-Is) have multiple anti-tumor effects in cutaneous T-cell lymphomas (CTCL), such as selective induction of malignant T-cell apoptosis, inhibition of angiogenesis and upregulation of pro-apoptotic proteins.

Clinical trials of HDAC-Is in CTCL

� Oral vorinostat was the first HDAC-I approved to enter the clinical oncology market for treating CTCL patients who have progressive, persistent or recurrent disease after failing two systemic therapies.

� Intravenous romidepsin is a more potent HDAC-I that was recently approved for the treatment of refractory CTCL. Two Phase II clinical trials demonstrated similar clinical response, duration of response and side-effect profile to vorinostat.

� Approximately half of CTCL patients receiving vorinostat or romidepsin experience substantial relief in pruritus and a marked improvement in quality of life.

� Vorinostat and romidepsin are generally well tolerated. Fatigue and gastrointestinal symptoms are the most common side effects at low doses and thrombocytopenia at higher doses. Side effects are dose related and reversible upon cessation of therapy.

� Compared to traditional chemotherapy, vorinostat and romidepsin are minimally immunosuppressive with low risk of neutropenia and infection.

� Belinostat and panobinostat are novel pan-HDAC-Is that have been shown to be clinically effective and well tolerated in patients with refractory CTCL, but have not yet been US FDA approved.

� No single biomarker has emerged as a predictor of clinical response to HDAC-Is although there are several potential biomarkers in CTCL patients.

� Future perspective

� The absence of validated biomarkers of responsive and unresponsive disease remains an important shortcoming in realizing the full clinical potential of vorinostat and other HDAC-Is.

� There is a need to develop hypothesis-driven HDAC-I combination therapies with agents that can be predicted to act additively or synergistically.



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Financial & competing interests disclosureM Duvic received clinical and basic support from Aton/Merck for conducting clinical trials. C Zhang received research support from Merck & Co., Inc. Dermatology Foundation, Ladies Leukemia League Inc., and Novartis Pharmaceuticals. This article was independently commis-sioned and no fee was received for preparation of the manu-script. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.



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hdac inhibitors for the treatment of cutaneous t-cell lymphomas

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