Design and synthesis of quinoxaline-1,3,4-oxadiazole hybrid derivatives as potent inhibitors of the anti-apoptotic Bcl-2 protein.

Quinoxaline is one of the privileged heterocyclic fragments for drug molecules. Quinoxaline anticancer drug candidates XK469 and CQS exhibit antiproliferative and proapoptotic properties against various cancers. Based on their chemical structures, we therefore synthesized a series of quinoxaline-1,3,4-oxadiazole hybrids and assessed their anticancer potential on human leukemia HL-60 cells. Although these hybrids exerted significant inhibition of HL-60 cell proliferation, they showed high cytotoxicity on human normal cells (WI-38). Utilizing information from molecular modelling of the hybrids to the anti-apoptotic Bcl-2 protein, we added substructures including phenyl, piperazine, piperidine, and morpholine rings to their frameworks. The designed quinoxaline-1,3,4-oxadiazole hybrid derivatives successfully induced apoptotic response on HL-60 cells with low toxicity on WI-38 cells. Furthermore, RT-PCR analysis demonstrated that these derivatives predominantly inhibit Bcl-2 expression. Our findings highlight the great potential for the development of synthetic quinoxaline-1,3,4-oxadiazole hybrid derivatives as proapoptotic anticancer agents.