Bioorganic & Medicinal Chemistry Letters 25 (2015) 1692–1699

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Bioorganic & Medicinal Chemistry Letters

journal homepage: www.elsevier .com/ locate/bmcl

Synthesis and broad-spectrum antiproliferative activity ofdiarylamides and diarylureas possessing 1,3,4-oxadiazole derivatives

http://dx.doi.org/10.1016/j.bmcl.2015.03.0010960-894X/� 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +82 2 958 5160; fax: +82 2 958 5308.E-mail address: choh@kist.re.kr (C.-H. Oh).

Mahmoud M. Gamal El-Din a,b,c, Mohammed I. El-Gamal d, Mohammed S. Abdel-Maksoud a,b,c,Kyung Ho Yoo e, Chang-Hyun Oh a,b,⇑a Center for Biomaterials, Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul 130-650, Republic of Koreab Department of Biomolecular Science, University of Science and Technology, 113 Gwahangno, Yuseong-gu, Daejeon 305-333, Republic of Koreac Pharmaceutical and Drug Industries Research Division, National Research Centre, Dokki-Giza 12622, Egyptd Department of Medicinal Chemistry, Faculty of Pharmacy, University of Mansoura, Mansoura 35516, Egypte Chemical Kinomics Research Center, Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul 130-650, Republic of Korea

a r t i c l e i n f o

Article history:Received 12 January 2015Revised 25 February 2015Accepted 2 March 2015Available online 7 March 2015

Keywords:Antiproliferative activityDiarylamidesDiarylureas1,3,4-Oxadiazole

a b s t r a c t

A series of diarylamides and diarylureas possessing 1,3,4-oxadiazole scaffold was designed and synthe-sized. Their in vitro antiproliferative activities were tested against a panel of 58 cell lines of nine differentcancer types at the NCI, and compared with Sorafenib as a reference compound. Most of the compoundsshowed strong and broad-spectrum antiproliferative activities. The diarylurea compound 2g possessing4-chloro-3-(trifluoromethyl)phenyl terminal moiety showed the highest mean % inhibition value ofabout 100% over the 58-cell line panel at 10 lM concentration. Also compounds 2h, 2l, 2m exhibitedmean % inhibition over 90% at 10 lM concentration. The IC50 value of compound 2b over SNB-75 CNScancer cell line was 0.65 lM. Compound 2h also exerted submicromolar IC50 values of 0.67, 0.80, and0.87 lM against PC-3 prostate cancer cell line, HCT-116 colon cancer cell line, and ACHN renal cancer cellline, respectively. Compound 2h showed comparable efficacy to Sorafenib.

� 2015 Elsevier Ltd. All rights reserved.

Cancer is a one of the most serious diseases which is consideredthe second major leading cause of death all over the world aftercardiovascular diseases. In 2012 in the USA only, 577,190 cancerpatients died and more than 1.6 million new cancer cases wereidentified according to the American Cancer Society Report.1

More than 70% of all cancer deaths have occurred in low and mid-dle-income countries. According to the WHO (World HealthOrganization) report,2 more than 13 million deaths from cancerworldwide are expected to occur in 2030. Despite of exerting somuch efforts and investment in this field research, the con-temporary medicinal chemistry still faces major challenges forcontrol and treatment of human cancers. That is why there is stillan urgent need for searching for and development of more poten-tial anticancer agents with minimal side effects.

Many research articles have recently reported the potentialantiproliferative activity of diarylureas and diarylamides againsta variety of cancer cell lines.3–23 Sorafenib (Nexavar�, Fig. 1) is anexample of anticancer diarylureas that has been approved by theU.S. Food and Drug Administration (FDA) for treatment ofadvanced renal cancer and also subjected to clinical trials for

treatment of other cancer types such as metastatic colorectal, ovar-ian, brain, esophageal/gastroesophageal, leukemia, glioblastoma,Hodgkin’s lymphoma, metastatic breast, advanced gastric, hep-atocellular carcinoma (HCC), thyroid, non-small cell lung cancer(NSCLC), pancreatic, prostate, bladder, skin/ocular melanoma andneuroendocrine cancers.24,25 Regorafenib (BAY73-4506, Stivarga�,Fig. 1) is the fluoro analogue of Sorafenib (Fig. 1) that was approvedby the FDA in 2012 for treatment of metastatic colorectal cancer.26

In 2013, the FDA approved its use for treatment of patients withgastrointestinal stromal tumors (GIST).27 Moreover, many clinicaltrials have been conducted for Regorafenib against NSCLC, renalcell carcinoma (RCC), HCC (in combination with Sorafenib), angio-sarcoma, biliary tract carcinoma, liposarcoma, osteogenic sarcoma,and Ewing/Ewing-like sarcomas.28 Imatinib (Gleevec�, Fig. 1) is anexample of diarylamides used for treatment of chronic myeloidleukemia (CML) with diminished side effects.29 It has been studiedin clinical trials for treatment of GIST, thyroid cancer, breast cancer,meningioma, ovarian cancer, and NSCLC in combination with otherdrugs.30

Much attention has been paid to the chemistry and biologicalactivities of 1,3,4-oxadiazole nucleus. Several compounds possess-ing 1,3,4-oxadiazole scaffold have been recently reported as poten-tial antiproliferative agents.31–40 Apart from anticancer activity,

NNH

H3CO

O

NH

NH

OCl

CF3

X = H, SorafenibX = F, Regorafenib

X

N

O

N O

F

NH

R1

R2

O

The target compounds 1a-l and 2a-mR1 = H, Cl, OMeR2 = Ar, ArNH

Imatinib

N NN

HN

HNO

N N CH3

Figure 1. Structures of Imatinib, Sorafenib, Regorafenib, the previously reported oxadiazole sulfonamide derivative, and the target compounds 1a–l and 2a–m.

M. M. Gamal El-Din et al. / Bioorg. Med. Chem. Lett. 25 (2015) 1692–1699 1693

other biological activities have been reported for 1,3,4-oxadiazolederivatives such as antidiabetic,41 antitubercular,42 antifungal,43

antiinflammatory,44 and antibacterial activities.45

In the present study, we report synthesis of a new series ofdiarylamide and diarylurea analogues possessing 1,3,4-oxadiazolenucleus (Fig. 1). Their in vitro antiproliferative activities againstNCI-58 cancer cell line panel of nine different cancer types weretested and reported.

Synthesis of the target compounds 1a–l and 2a–m was achievedthrough the pathway illustrated in Scheme 1. Refluxing the ben-zoate esters 3a–c with hydrazine monohydrate in ethanol pro-duced the corresponding benzohydrazide derivatives 4a–c.28

Cyclization to 2-(chloromethyl)-5-aryl-1,3,4-oxadiazole analogues(5a–c) was done through refluxing the hydrazides 4a–c with chlor-oacetic acid in phosphorus oxychloride.29 Nucleophilic substitutionof chloro group of compounds 5a–c with 2-fluoro-4-nitrophenolwas done by reflux in acetonitrile in the presence of potassium car-bonate to obtain the ether derivatives 6a–c. The nitro group ofcompounds 6a–c was reduced to amino using Raney nickel inhydrogen atmosphere.40 Treatment of the aniline derivatives7a–c with the appropriate alkyl or aryl carbonyl chloride deriva-tives in presence of pyridine as a base afforded the target amidederivatives 1a–l. Reaction of the aniline derivatives 7a–c with theappropriate aryl isocyanates resulted in the corresponding diary-lurea derivatives 2a–m. The structures of the target compounds,their yield percentages, and their melting points are shown inTables 1 and 2. The target compounds were characterized by IR,1H NMR, 13C NMR, and MS analysis (Supplementary file).

R1

d

NN

O

R1

O

F

NH2

a b

e

O

NN

5a-c

7a-c

R1

O

O

3a-cR1

O

NH2HN

4a-c

3-7 : a: R1 = H; b: R1 = Cl; c: R1 = OCH3

f

Scheme 1. Reagents and conditions: (a) hydrazine monohydrate, EtOH, reflux, overnight(5b), 72.5% (5c); (c) 2-fluoro-4-nitrophenol, K2CO3, acetonitrile, reflux, 36 h, 61.2% (6a), 4(7b), 93.2% (7c); (e) appropriate alkyl or aryl acid chloride, C5H5N, CH2Cl2, rt, overnight,

Structures of the synthesized target compounds were submit-ted to National Cancer Institute (NCI), Bethesda, Maryland, USA,46

and the 22 compounds shown in Figure 2 were selected on thebasis of degree of structural variation and computer modelingtechniques for evaluation of their antineoplastic activity. Theselected compounds were subjected to in vitro anticancer assayagainst tumor cells in a full panel of 58 cell lines taken from ninedifferent tissues (blood, lung, colon, CNS, skin, ovary, kidney, pros-tate, and breast). The compounds were tested at a single-dose con-centration of 10 lM, and the percentages of growth inhibition overthe 58 tested cell lines were determined. The mean % inhibitionresults exerted by the tested compounds against the NCI-58 cancercell line panel are illustrated in Figure 2.

Upon comparing the activities of amide and urea derivatives, itwas found that urea derivatives 2a, 2b, 2e–g, and 2k exhibitedhigher activity than the corresponding amide ones 1b, 1c, 1f–h,and 1l. This may be rationalized that the longer spacer, urea moi-ety, may geometrically allow appropriate fitting of the moleculeat the receptor site. Or the terminal NH group of the urea moietymay form additional hydrogen bond(s) at the receptor site. Anyor both of these effects would enable optimal drug–receptor inter-action, and hence higher antiproliferative activity. So the urea moi-ety is the most appropriate spacer for this series of compounds.

For the amide series, the influences of aliphatic and aromaticterminal moieties on activity were studied. The aromatic deriva-tives were found generally more active than aliphatic analogues(compounds 1e–h and 1j–l showed higher mean % inhibition than1d and 1i). For both amide and urea derivatives, more lipophilic

NN

O

R1

ClO

F

NO2

NN

O

R1

O

F

NH

c

6a-c

1a-l

NNO

R1

O

F

NH

2a-m

R2

O

NH

O

R3

, 70% (4a), 82.4% (4b), 87% (4c); (b) ClCH2COOH, POCl3, reflux, 6 h, 63.5% (5a), 71.3%7.3% (6b), 55.6% (6c); (d) Raney Ni, H2, THF/MeOH (2:1 v/v), rt, 24 h, 85% (7a), 89%28–45%; (f) appropriate aryl isocyanate, THF, rt, 24 h, 27–46%.

Table 1Structures of the target amide compounds 1a–l, their yield %, and melting points

NN

O

R1

O

F

NH

1a-l

R2

O

Compound No. R1 R2 Yield (%) Melting point (�C)

1a H Ph 32 148–50

1b HCl

Cl31 174–6

1c HCF3

45 152–3

1d Cl C2H5 43 165–71e Cl Ph 35 172–4

1f ClCl

Cl25 199–201

1g ClCF3

30 164–5

1h ClCl

CF3

28 173–5

1i OMe C2H5 35 149–511j OMe Ph 37 155–7

1k OMeCl

Cl38 187–9

1l OMeCF3

35 175–7

Table 2Structures of the target diarylurea compounds 2a–m, their yield %, and melting points

NNO

R1

O

F

NH

2a-m

NH

O

R3

Compound No. R1 R3 Yield (%) Melting point (�C)

2a HCl

Cl46 200–2

2b HCF3

44 217–9

2c HCl

CF3

35 195–7

2d H

CF3

CF3

35 181–3

1694 M. M. Gamal El-Din et al. / Bioorg. Med. Chem. Lett. 25 (2015) 1692–1699

Table 2 (continued)

Compound No. R1 R3 Yield (%) Melting point (�C)

2e ClCl

Cl35 209–11

2f ClCF3

33 215–7

2g ClCl

CF3

27 200–2

2h Cl

CF3

CF3

31 168–70

2i OMe Ph 30 167–9

2j OMeCl

Cl31 214–6

2k OMeCF3

34 180–2

2l OMeCl

CF3

30 181–3

2m OMe

CF3

CF3

38 170–2

Mean % Inhibition

-20.00%

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

1a 1b 1c 1d 1e 1f 1g 1h 1i 1j 1k 1l 2a 2b 2c 2e 2f 2g 2h 2k 2l 2m

Compound No.

Figure 2. Mean inhibition percentages observed with the final compounds in single-dose (10 lM) 58-cancer cell line screening. Mean % inhibition represents the meaninhibition percentages over the 58 cell lines. The inhibition percentages were calculated by subtracting the growth percentages from 100.

M. M. Gamal El-Din et al. / Bioorg. Med. Chem. Lett. 25 (2015) 1692–1699 1695

substitutions on the aromatic tail gave stronger activity.Compounds 1h among the amide derivatives and 2g among theurea derivatives possessing 3-trifluoromethyl-4-chlorophenyl tailshowed the highest mean % inhibition (compounds 1h, 2c, 2g,and 2l exhibited more antiproliferative activities than compounds2a, 2b, 2e, 2f, 2h, and 2k). This may attributed to stronger affinitydue to stronger hydrophobic interaction at the receptor site and/or increased penetration into the cell lines influenced by thisincreased lipophilicity. For comparing the effect of aryl ring directlyattached to 1,3,4-oxadiazole ring on activity, it was found that com-pounds possessing p-chlorophenyl and p-methoxyphenyl weremore active than the compounds with phenyl ring. Compounds2g with urea linker containing p-chlorophenyl showed higherantiproliferative activity than the corresponding p-methoxyphenylanalogues 2l, and 2l exerted higher activity than 2c with unsubsti-tuted phenyl ring. So it can be concluded that p-chlorophenyl is the

most optimum and unsubstituted phenyl is the least optimum foractivity of both series of compounds. This can be attributed to stericand/or electronic differences between chloro, methoxy, and hydro-gen groups. At 10 lM concentration, compound 2g showed 99.64%(mean % inhibition) over 58 cell lines. It exerted broad-spectrumcytotoxicities over all the nine tested cancer types. Also compounds2h, 2l, and 2m exhibited mean % inhibition values exceeding 90% at10 lM concentration and they showed % inhibition of more than100% inhibition over many cancer cell lines for instance, compound2h exhibited 184.74%, 137.94% and 129.59% against COLO-205, SK-MEL-2, and SK-MEL-5 cancer cell lines. Other compounds showedalso % inhibition more than 100% inhibition against different cancercell lines as shown in Figure 3.

Compounds 2b, 2c, 2e, 2g, 2h, 2l and 2m with promising resultsin single-dose testing were further tested in a five-dose testingmode, in order to determine their IC50 values over the 58 cancer

%inhibi�on 2g

020406080

100120140160180200

CC

RF-

CEM

HL-

60(T

B)

K-5

62

MO

LT-4

RPM

I-822

6

SR

A54

9/A

TCC

HO

P-62

HO

P92

NC

I-H22

6

NC

I-H23

NC

I-H46

0

NC

I-H52

2

CO

LO 2

05

HC

C-2

998

HC

T-11

6

HC

T-15

HT2

9

KM

12

SW-6

20

SF-2

68

SF-2

95

SF-5

39

SNB

-75

U25

1

LOX

IMVI

M14

MD

A-M

B-

435

SK-M

EL-2

SK-M

EL-

28SK

-MEL

-5

UA

CC

-257

OVC

AR

-3

OVC

AR

-4

OVC

AR

-5

OVC

AR

-8N

CI/A

DR

-R

ESSK

-OV-

3

786-

0

A49

8

AC

HN

CA

KI-1

TK-1

0

PC-3

DU

-145

MC

F7

HS

578T

BT-

549

T-47

DM

DA

-MB

-46

8

Leukemia Non-Small Cell Lung Cancer Colon Cancer CNS Cancer Melanoma Renal Cancer ProstateCancer

Breast Cancer

%Inhibi�on 2h

0

20

40

60

80

100

120

140

160

180

200

CC

RF-

CEM

HL-

60(T

B)

K-5

62

MO

LT-4

RPM

I-822

6SR

A54

9/A

TCC

HO

P-62

HO

P92

NC

I-H22

6N

CI-H

23N

CI-

H32

2MN

CI-H

460

NC

I-H52

2

CO

LO 2

05H

CC

-299

8H

CT-

116

HC

T-15

HT2

9K

M12

SW-6

20SF

-268

SF-2

95SF

-539

SNB

-19

SNB

-75

U25

1LO

X IM

VIM

ALM

E-3M

M14

MD

A-M

B-

435

SK-M

EL-2

SK-M

EL-

28SK

-MEL

-5U

AC

C-2

57U

AC

C-6

2IG

RO

V1

OVC

AR

-3O

VCA

R-4

OVC

AR

-5O

VCA

R-8

NC

I/AD

R-

RES

SK-O

V-3

786-

0A

498

AC

HN

CA

KI-1

SN12

C

TK-1

0U

O-3

1PC

-3D

U-1

45M

CF7

MD

A-M

B-

231/

ATC

CH

S 57

8T

BT-

549

T-47

D

Leukemia Non-Small Cell LungCancer

Colon Cancer CNS Cancer Melanoma Ovarian Cancer Renal Cancer ProstateCancer

Breast Cancer

%Inhibi�on 2l

020406080100120140160180

CC

RF-

CEM

HL-

60(T

B)

K-5

62

MO

LT-4

RPM

I-822

6 SR

A54

9/A

TCC

HO

P-62

HO

P92

NC

I-H22

6

NC

I-H23

NC

I-H

322M

NC

I-H46

0

NC

I-H52

2

CO

LO 2

05

HC

C-2

998

HC

T-11

6

HC

T-15

HT2

9

KM

12

SW-6

20

SF-2

68

SF-2

95

SF-5

39

SNB

-19

SNB

-75

U25

1

LOX

IMVI

MA

LME-

3M M14

MD

A-M

B-

435

SK-M

EL-2

SK-M

EL-

28SK

-MEL

-5

UA

CC

-257

UA

CC

-62

IGR

OV1

OVC

AR

-3

OVC

AR

-4

OVC

AR

-5

OVC

AR

-8N

CI/A

DR

-R

ESSK

-OV-

3

786-

0

A49

8

AC

HN

CA

KI-1

SN12

C

TK-1

0

UO

-31

PC-3

DU

-145

MC

F7M

DA

-MB

-23

1/A

TCC

HS

578T

BT-

549

T-47

D

Leukemia Non-Small Cell Lung Cancer Colon Cancer CNS Cancer Melanoma Ovarian Cancer Renal Cancer ProstateCancer

Breast Cancer

%Inhibi�on 2m

020406080100120140160

CC

RF-

CEM

HL-

60(T

B)

K-5

62M

OLT

-4R

PMI-8

226 SR

A54

9/A

TCC

HO

P-62

HO

P92

NC

I-H22

6N

CI-H

23N

CI-

H32

2MN

CI-H

460

NC

I-H52

2C

OLO

205

HC

C-2

998

HC

T-11

6H

CT-

15H

T29

KM

12SW

-620

SF-2

68SF

-295

SF-5

39SN

B-1

9SN

B-7

5U

251

LOX

IMVI

MA

LME-

3M M14

MD

A-M

B-

435

SK-M

EL-2

SK-M

EL-

28SK

-MEL

-5U

AC

C-2

57U

AC

C-6

2IG

RO

V1O

VCA

R-3

OVC

AR

-4O

VCA

R-5

OVC

AR

-8N

CI/A

DR

-R

ESSK

-OV-

378

6-0

A49

8A

CH

NC

AK

I-1R

XF-3

93SN

12C

TK-1

0U

O-3

1PC

-3D

U-1

45M

CF7

MD

A-M

B-

231/

ATC

CH

S 57

8T

BT-

549

T-47

DM

DA

-MB

-46

8

Leukemia Non-Small Cell LungCancer

Colon Cancer CNS Cancer Melanoma Ovarian Cancer Renal Cancer ProstateCancer

Breast Cancer

Figure 3. % Inhibition expressed by compounds 2e (a), 2h (b), 2j (c), and 2m (d) at a single-dose concentration of 10 lM over all cell lines of the NCI cancer cell line panel ofnine different cancer types.

1696 M. M. Gamal El-Din et al. / Bioorg. Med. Chem. Lett. 25 (2015) 1692–1699

cell lines. The mean IC50 values of these seven compounds over thenine cancer types are shown in Table 3. Compound 2c with40-chloro-30-(trifluoromethyl)phenyl terminal ring was generallymore potent than compound 2b possessing 30-(trifluo-romethyl)phenyl terminal moiety. Compound 2h containing 30,

50-bis(trifluoromethyl)phenyl terminal ring and p-chlorophenylring directly attached to the 1,3,4-oxadiazole scaffold showedhigher potency than Sorafenib against eight different cancer types.These findings reinforce the assumption that the higher thelipophilicity, the higher the potency.

Table 3Mean IC50 values (lM) of the tested compounds over in vitro subpanel cancer cell linesa

Subpanel cancer lineb

I II III IV V VI VII VIII IX

No. of cell lines in each subpanel 5 8 7 6 9 7 8 2 6Compound No.2b 3.08 5.28 3.77 4.81 6.25 6.85 7.44 4.04 3.002c 1.75 2.23 2.31 2.27 2.46 3.17 2.02 1.55 2.382e 7.31 4.89 11.02 4.98 7.14 10.86 9.63 5.61 4.312g 2.30 2.21 2.21 2.29 2.43 2.73 2.27 2.16 2.242h 2.20 2.22 1.98 2.32 2.29 2.29 2.33 2.12 1.802l 2.34 3.73 3.05 3.48 3.23 4.84 4.11 2.47 2.692m 2.34 1.82 1.98 2.35 2.44 2.43 2.25 1.57 2.11Sorafenib 2.43 2.25 2.19 2.33 1.87 2.88 2.94 2.58 2.17

The bold figures indicate superior potency than the reference drug, Sorafenib.a Mean IC50 values were calculated by dividing the summation of IC50 values of the compound over cell lines of the same cancer type by the number of cell lines in the

subpanel.b I: leukemia; II: non-small cell lung cancer; III: colon cancer; IV: CNS cancer; V: ovarian cancer; VI: renal cancer; VII: prostate cancer; VIII: breast cancer.

M. M. Gamal El-Din et al. / Bioorg. Med. Chem. Lett. 25 (2015) 1692–1699 1697

The IC50 values of the seven compounds tested in five-dose test-ing mode against the most sensitive cell line of each subpanel aresummarized in Table 4. Due to structural similarity, the resultswere compared with those of Sorafenib as a reference standard.The results of Sorafenib were obtained from NCI data warehouseindex,47 and are depicted in Table 4. Most of the compounds exhib-ited high potency (in micromolar and some in submicromolarscale) over the most sensitive cancer cell lines of the nine cancertypes. Most of the IC50 data were less than 10 lM. Of special inter-est, compound 2h showed higher potencies against all the ninemost sensitive cell lines than Sorafenib. Furthermore, it exhibitedsubmicromolar IC50 values of 0.67, 0.80, and 0.87 lM over PC-3prostate cancer cell line, HCT-116 colon cancer cell line, andACHN renal cancer cell line, respectively. Compound 2b alsoexerted submicromolar IC50 value, 0.65 lM, against SNB-75 CNScancer cell line. Compound 2m results were almost similar orhad higher mean IC50 in comparison to Sorafenib over many sub-panels. From Table 4, it could be found compound 2h was the mostpotent one, and the PC-3 prostate, HCT-116 colon, and ACHN renalcancer cell lines were the most sensitive cell lines for the targetcompounds as their results were in sub-micromolar scale as wasstated before. Also the rest compounds showed higher activitiesthan Sorafenib against many sensitive cancer cell lines as shownin Table 4. Compound 2h showed broad-spectrum antiproliferativeactivities, which can be emphasized from Figure 4.

Table 4IC50 values (lM) of the tested compounds over the most sensitive cell line of each subpan

Compound No. Cance

RPMI-8226a HOP-92b HCT-116c KM12c SNB-75d

2b 1.67 1.77 3.02 2.43 0.652c 1.11 1.78 1.81 1.47 1.642e 10.70 2.39 5.01 16.50 1.722g 1.82 1.46 1.80 1.71 1.442h 1.02 1.14 0.80 1.00 1.322l 1.53 1.87 2.49 2.31 1.482m 1.35 1.50 1.63 1.51 2.02Sorafenib 1.58 1.58 1.58 1.58 3.16

Bold figures indicate superior potency than the reference compound, Sorafenib.a Leukemia cell line.b Non-small cell lung cancer cell line.c Colon cancer cell line.d CNS cancer cell line.e Melanoma cell line.f Ovarian cancer cell line.g Renal cancer cell line.h Prostate cancer cell line.i Breast cancer cell line.

The cLogP values were calculated and summarized in Table 4as a measure of lipophilicity. They are correlated with thecompound potencies against the cell lines. For example, the mostlipophilic compound 2h possessing 4-chlorophenyl and 3,5-bis(trifluoromethyl) phenyl ring moieties showed the highest poten-cies compared with the other tested compounds and Sorafenib.This can be attributed to higher ability to cross the cell membranedue to higher lipophilicity and hence stronger cytotoxic effect.

Apart from potency, the efficacies of the most potent compound2h against the most sensitive cell lines were studied and comparedwith those of Sorafenib (Table 5). The results showed high efficacyof compound 2h almost in the same range with those of Sorafenib.Compound 2h exerted one-digit micromolar TGI values againstnine cell lines, and LC50 values less than 92 lM over ten cell lines.Compound 2h demonstrated superior efficacies to Sorafenibagainst HOP-92, ACHN, and MDA-MB-468 cell lines.

In this study, a series of new 1,3,4-oxadiazole derivativespossessing amide and urea terminal moieties was synthesized.Twenty two target compounds were selected for single-dosein vitro antiproliferative test over NCI-58 cancer cell line panel ofnine different cancer types, and seven compounds with promisingresults in single-dose screening were selected for five-dose testingin order to determine their IC50 values. Among them, compounds2g, 2h, 2l, and 2m with urea linker showed the highest mean %inhibition values of 93.41%, 99.64%, 95.23%, and 95.28%,

el and calculated cLogP values

r cell line cLogP

SK-MEL-5e OVCAR-3f ACHNg PC-3h MDA-MB-468i

5.71 4.23 2.92 2.01 2.57 4.771.74 2.06 1.84 1.30 1.90 5.316.60 10.70 4.95 6.16 2.99 5.732.01 1.70 2.11 1.84 1.80 6.051.51 1.08 0.87 0.67 1.00 6.502.10 3.02 2.55 1.84 2.27 5.381.73 1.50 2.51 1.00 1.55 5.831.58 3.16 2.51 1.99 1.99 5.46

Figure 4. Dose–response curves of compound 2h against the tested 58 cancer cell line panel of nine different cancer types.

Table 5TGI and LC50 data (lM) of compound 2h and Sorafenib

Cell line Compd 2h Sorafenib

TGI LC50 TGI LC50

RPMI-8226 5.30 91.70 3.16 NDa

HOP-92 4.06 34.20 5.01 63.10HCT-116 3.02 10.90 2.51 6.31KM12 5.72 36.20 2.51 7.94SNB-75 5.37 29.00 3.98 7.94SK-MEL-5 2.96 5.77 2.51 5.010VCAR-3 3.92 18.80 3.98 7.94ACHN 9.20 81.20 10.00 100PC-3 11.20 80.40 5.01 100MDA-MB-468 4.17 28.60 5.01 50.12

Bold figures indicate higher efficacy than Sorafenib.a Not determined.

1698 M. M. Gamal El-Din et al. / Bioorg. Med. Chem. Lett. 25 (2015) 1692–1699

respectively, at 10 lM concentration, and compound 2h possessingp-chlorophenyl ring attached to 1,3,4-oxadiazole ring, urea linker,and 30,50-bis(trifluoromethyl)phenyl terminal moiety showed themost promising results at five-dose testing. It exerted high potencyand efficacy, and broad-spectrum antiproliferative activities overmany different cell lines of different cancer types. It was morepotent than Sorafenib against eight different cancer types, andmore potent against the most sensitive cell line of each cancer sub-panel. Furthermore, its IC50 values were in submicromolar scaleagainst ACHN renal cancer cell line, HCT-116 colon cancer cell line,and PC-3 prostate cancer cell line. Upon studying the linker effecton the activity, urea linker was found to be optimal for antipro-liferative activity of this series of compounds.

Acknowledgments

This work was supported by Korea Institute of Science andTechnology (KIST), Seoul, Republic of Korea, KIST Project(2E24680). We would like to thank the National Cancer Institute(NCI), Bethesda, Maryland, USA, for performing the in vitro antic-ancer testing over the cell lines.

Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.bmcl.2015.03.001.

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