Chagas disease, caused by the eukaryotic (protozoan) parasite Trypanosoma cruzi, is an alarming emerging global health problem with no clinical drugs available to treat the chronic stage. Azole inhibitors of sterol 14α-demethylase (CYP51) were proven effective against Chagas, and antifungal drugs posaconazole and ravuconazole entered clinical trials in Spain, Bolivia and Argentina. Here we present the X-ray structures of T.cruzi CYP51 in complexes with two alternative drug candidates, pyridine derivatives (S)-(4-chlorophenyl)-1-(4-(4-(trifluoromethyl)phenyl)- piperazin-1-yl)-2-(pyridin-3-yl)ethanone (UDO) and N-[4-(trifluoromethyl)phenyl]-N-[1-[5-(trifluoromethyl)-2-pyridyl]-4-piperi-dyl]pyridin-3-amine (UDD). These compounds have been developed by Drugs for Neglected Diseases initiative (DNDi) and are highly promising antichagasic agents, both in cellular and in vivo experiments. Binding parameters and inhibitory effects on sterol 14α-demethylase activity in reconstituted enzyme reactions confirm UDO and UDD as potent and selective T. cruzi CYP51 inhibitors. Comparative analysis of the pyridine- and azole-bound CYP51 structures uncovers the features which make UDO and UDD T. cruzi CYP51 specific. The structures suggest that while precise fit between the shape of the inhibitor molecules and T. cruzi CYP51 active site topology underlies their high inhibitory potency, a longer coordination bond between the catalytic heme iron and the pyridine nitrogen implies weaker influence of pyridines on the iron reduction potential, which may be the basis for the observed selectivity of these compounds towards the target enzyme versus other CYPs, including human drug-metabolizing P450s. The findings might pave the way for the development of novel CYP51-targeted drugs with optimized metabolic properties that are highly needed for treatment of human infections caused by eukaryotic microbial pathogens.
Hargrove, T.Y.; Wawrzak, Z.; Alexander, P.W.; Chaplin, J.H.; Keenan, M.; Charman, S.A.; Perez, C.J.; Waterman, M.R.; Chatelain, E.; Lepesheva, G.I. Complexes of Trypanosoma cruzi Sterol 14 alpha-Demethylase (CYP51) with Two Pyridine-based Drug Candidates for Chagas Disease: Structural basis for pathogen-selectivity. Journal of Biological Chemistry (2013) 288 (44) 31602-31615. [DOI: 10.1074/jbc.M113.497990]