Synthesis and Antiproliferative Activity of Some Quinoline and Oxadiazole Derivatives

1Department of Pharmaceutical Chemistry,Maharishi Arvind College of Pharmacy, Ambabari Circle, Jaipur, Rajasthan 302 039, India 2School of Chemical Science, University Sains Malaysia, Penang 118 00, Malaysia 3Department of Pharmaceutical Chemistry, College of Pharmacy, Prince Sattam Bin Abdulaziz University, P.O. Box 11323, Al-Kharj, Saudi Arabia 4Department of Pharmaceutical Chemistry, Birla Institute of Technology, Mesra, Ranchi, Jharkhand 835 215, India


Introduction
Cancer is a genetic disease that is caused by changes to gene that control the way our cell functions.In all types of cancers some of the body's cells begin to divide without stopping and spread into the surrounding tissues.There are more than 100 types of cancer [1].A total of 1,658,370 new cancer cases and 589,430 cancer deaths are projected to occur in the United States in 2015 [2].Despite the availability of improved drugs and targeted cancer therapies, it is expected that the new cases of cancer will jump to 19.3 million worldwide by 2025 [3].The types of cancer treatment include surgery, chemotherapy, radiation therapy, immunotherapy, targeted therapy, and hormonal therapy.The cancer patients are treated either with single therapy or with combinations of more than one therapy depending on the type of cancer's advancement [1].The therapeutic applications of antiproliferative drugs are restricted due to their toxic potentials, resistance, and genotoxicity [4].The demand for relatively more effective and safer agents for the treatment of cancer is today's need.
Heterocyclic quinoline nucleus occurs in nature and biologically active substances displaying broad therapeutic applications [5].Several quinoline analogues were reported as anticancer agents [6][7][8][9][10][11][12][13].The structure of some of the quinoline anticancer drug is shown in Figure 1 [6].The biological potential of quinoline inspired us to explore further the quinoline derivatives.The quinoline derivatives showed promising antiproliferative activity against HeLa (human cervix cancer cell line) and MDA-MB-435 (melanoma) cell lines [6,7,14].Hence we selected HeLa and MDA-MB-435 to test the in vitro antiproliferative activity of quinoline derivatives (5a-j) reported here in the present investigation.Three-dose response parameters (GI 50 , TGI, and LC 50 ) were calculated for each of the experimental agents.Similarly the biological prospects of five member oxadiazoles as anticancer [15,16], antitubercular [17], anticonvulsant [18], antimicrobial [19], anti-HIV [20], and anti-inflammatory [21] inspired us to go on further with the exploration of this moiety.Zibotentan, an endothelin receptor A (ET A ) antagonist, is an anticancer agent which contains 1,3,4-oxadiazole ring [22].A series of oxadiazoles (10a-c) were synthesized and evaluated for their antiproliferative activity against 60 cell lines according to the National Cancer Institute (NCI US) Protocol at 10 M drug concentration and percent growth inhibition (GI) was reported.

Materials and Methods
2.1.General.The chemicals were procured from Merck, Mumbai, and S. D. Fine Chemicals, Mumbai (India).Melting points were determined by open tube capillary method and are uncorrected.The completion of reaction was monitored throughout by thin layer chromatography (TLC) using mobile phase benzene/methanol (1 : 4) and cyclohexane/acetone (1 : 4) and the spots were located under iodine vapours or UV light.IR spectra were obtained on a Shimadzu 8201 PC, FT-IR spectrometer (KBr pellets). 1H NMR spectra were recorded on a Bruker AC 400 MHz spectrometer using TMS as internal standard in DMSOd 6 .Mass spectra were recorded on a Bruker Esquire LCMS using ESI and elemental analyses were performed on Perkin-Elmer 2400 Elemental Analyzer.
Three-dose response parameters (GI 50 , TGI, and LC 50 ) were calculated for each of the experimental agents.Growth inhibition of 50% (GI 50 ) was calculated from 100 × [(  −   )/( −   )] = 50, which was the drug concentration resulting in a 50% reduction in the net protein increase (as measured by sulforhodamine B, SRB staining) in control cells during the drug incubation.The total growth inhibition (TGI) was calculated from   =   , which was the drug concentration resulting in total growth inhibition and signified the cytostatic effect.The LC 50 was calculated from 100×[(  −   )/( −   )] = −50, which was the drug concentration resulting in a net loss of cells following treatment which indicated the concentration of drug resulting in a 50% reduction in the measured protein at the end of the drug treatment as compared to that at the beginning.
Both the analytical and spectral data of the compounds were in full agreement with the proposed structure.

3.2.
In Vitro Antiproliferative Activity.10 compounds (5a-j) were evaluated for antiproliferative activity on HeLa (human cervix cancer cell line) and MDA-MB-435 (melanoma) at four different molar drug concentrations (10 −7 , 10 −6 , 10 −5 , and 10 −4 M) and the growth percent was recorded.The cytotoxic result was less at first three concentrations but 10 −4 M concentration produced strong cytotoxicity ranging between −66.9 and 61.2 percent growth against HeLa and  ).The compound 5j showed maximum cytotoxicity with −66.9 and 0.6 percent growths against HeLa and MDA-MB-435, respectively.The cytotoxicity of compound 5j was found to be higher than the standard drug, adriamycin, at 10 −4 M concentration against HeLa.Further three parameters (GI 50 , TGI, and LC 50 ) were calculated for all the quinoline derivatives.The GI 50 recorded were ranging between 35.1 and >100 M against HeLa, while only the compound 5j registered GI 50 of 60.4 M against MDA-MB-435 and rest of the compounds showed GI 50 of >100 M.
The LC 50 recorded was found to be >100 M for both the cell lines, except for the compound 5j which showed LC 50 of 91.33 M against HeLa.The compounds 5j, 5e, and 5d showed TGI of 63.19, 88.17, and 97.28 M, respectively, against HeLa, while compounds 5e and 5d showed TGI of 63.19 and 88.17 M, respectively, against MDA-MB-435.The GI 50 , TGI, and LC 50 were recorded for the quinoline derivatives (5a-j) and are shown in Table 1.The value of GI 50 was taken into consideration to establish the structure activity relationship (SAR) of the synthesized compounds.The quinoline having 2,4-dimethyl substitution in phenyl ring was found to be more favorable than 4-methyl and 2-methyl substitution, while 2-chloro substitution was found to be more favorable than 4-fluoro and 4-bromo substitutions.The 4-methoxy substitution on phenyl ring showed significant antiproliferative activity.The order of antiproliferative activity followed with substitution on phenyl ring as 4-OCH Further since quinoline derivatives were found to inhibit epidermal growth factor receptor tyrosine kinase (EGFR-TK) [33].A molecular docking study implying epidermal growth factor receptor tyrosine kinase (EGFR-TK) was carried out to observe the binding mode of new quinoline analogues (5a-j) on the active site of EGFR-TK.The molecular docking protocol is the same as reported earlier by our research group [34].Three different binding modes (green, yellow, and grey) were observed by ligands (5a-j) as shown in the Figure 4.The binding mode of compounds 5c, 5d, 5f, 5 h, 5i, and 5j (green ligands) with the active site of EGFR-TK showed interaction with backbone H-bonding of hydroxyl group with Met793 and side chain H-bonding of NH with Asp855 (5f, 5i, and 5j).The binding mode of compounds 5b (yellow ligands) with the active site of EGFR-TK showed backbone H-bonding of hydroxy group with Met793 and side chain Hbonding of terminal amine with Thr854.The binding mode of compounds 5a, 5e, and 5g (grey ligands) with the active site of EGFR-TK showed backbone H-bonding of NH group with Arg841 and side chain H-bonding of hydroxyl and aryl NH group with Asp855 and Asn842, respectively, while showing - stacking with Phe723 (compound 5e), -cationic interaction of substituted phenyl ring with Arg841 (compound 5g).The compound 5j showed hydrophobic interaction with Met793, Leu792, Ala743, Gly796, Met766, Leu788, Leu777, and Lys745, backbone H-bonding of hydroxyl group with Met793, and side chain H-bonding of NH with Asp855.The binding mode of interaction with EGFR-TK is given in Figure 5.
Three compounds (10a-c) were tested for antiproliferative activity on leukemia, melanoma, lung, colon, CNS, ovarian, prostate, and breast cancer cell lines (nearly 60 cell lines) as per the NCI US protocol and carried out at Nation Cancer Institute, USA.The compound 10b showed maximum activity with growth percent (GP) of 94.33 followed by compound 10c (GP = 95.12) and 10a (GP = 96.37).The compound 10a showed maximum selectivity towards HOP-92, MCF7, SNB-75, T-47D, PC-3, and UO-31 with percent GI of 34.14, 21.22, 20.52, 15.39, 14.97, and 13.57, respectively.The compound 10b showed maximum selectivity towards Earlier we have reported the synthesis of oxadiazole derivatives from pyrimidine-2-amine that showed efficiently binding to the active site of EGFR-TK [35].We can conclude here that EGFR-TK could also be target of the oxadiazoles (10a-c) reported here in the present investigation.

Conclusion
All the quinoline (5a-j) and oxadiazole (10a-c) derivatives were synthesized in satisfactory yields.The compound 5j showed antiproliferative activity among quinoline derivatives with GI 50 of 35.1 M against HeLa (cervix cancer cell line) and 60.4 M against MDA-MB-435 (melanoma), respectively.The structure activity relationship established showed that 4-methoxy substitution was found to be more favorable than 2-chloro and 2,4-dimethyl substitution in the phenyl ring.Similarly the compound 10b expressed maximum antiproliferative activity on human cancer cell lines at 10 M concentration.EGFR-TK could be the potential target of the quinoline and oxadiazole derivatives reported here.

Figure 1 :
Figure 1: Some of the quinoline containing anticancer drugs.

ControlFigure 3 :
Figure 3: (a) Images of growth control of MDA-MB-435 cancer cell line by quinoline (5a-j) and adriamycin.(b) Images of growth control of HeLa cancer cell line by quinoline (5a-j) and adriamycin.