Ligand-based virtual screening and ADME-tox guided approach to identify triazolo-quinoxalines as folate cycle inhibitors

In the process of drug discovery the lead-identification phase may be critical due to the likely poor safety profile of the candidates, causing the delay or even the abandonment of a certain project. Nowadays, combining molecular modeling and in vivo cellular evaluation can help to identify compounds with an enhanced safety profile. Previously, two quinoxalines have been identified as inhibitors of the folate-dependent proteins belonging to the Thymidylate Synthase cycle. Unfortunately, cytotoxic activity against a panel of cisplatin(cDDP)-sensitive ovarian carcinoma cell lines and their resistant counterparts was coupled with toxicity to non-tumorigenic Vero cells. Here we describe the application of a ligand-based virtual screening, and several [1,2,4]triazolo[4,3-a]quinoxalines were optimized to improve their ADME-tox profile. The resulting 4-(trifluoromethyl)-1-p-tolyl-[1,2,4]triazolo[4,3-a]quinoxaline (24), which interferes intracellularly with DHFR and TS reducing the protein levels like 5-FU, but without inducing TS ternary complex formation, was 2-times less toxic in vitro than cisplatin and 5-FU.