Discovery of tri(indolyl)methanes as potent and selective inhibitors against human carboxylesterase 2

Human carboxylesterase 2A (CES2A) plays a crucial role in the hydrolysis and metabolic activation of esters and amides. There is increasing evidence that development of CES2A inhibitors to modulate the hydrolysis of ester drugs will increase the potency of these drugs or reduce their side effects. In this study, three sets of indole analogues (4a-j, 5a-k, 6a-e) were designed and synthesized. Moreover, the inhibitory effects of these compounds on CES2A and CES1A were investigated using two sets of optical substrates. The results showed that tri(indolyl)methane 6a, 6b, 6c and 6e, and all of them exhibited strong inhibition for CES2A and good selectivity over CES1A and other five serine hydrolases. In addition, molecular docking results revealed that probe substrate and these inhibitors were significantly different from their interacting amino acid residues in the CES2A active cavity, which may be an important reason why these inhibitors did not show competitive inhibition. Further studies showed that these tri(indolyl)methanes had negligible cytotoxicity, and 6b and 6c significantly dose-dependent inhibited CES2A activity in HepG2 and Caco2 cells. Collectively, tri(indolyl)methane is a potent and selective inhibitor of CES2A, which can be served as lead compounds for the development of more efficacious and selective indole-type CES2A inhibitors.