Antifungal Azoles: Structural Insights into Undesired Tight Binding to Cholesterol-Metabolizing CYP46A1

Abstract

Although there are currently three generations of antifungal azoles on the market, even the third-generation agents show undesirable interactions with human cytochrome P450 (P450) enzymes. CYP46A1 is a cholesterol-metabolizing P450 in the brain that tightly binds a number of structurally distinct azoles. Previously, we determined the crystal structures of CYP46A1 in complex with voriconazole and clotrimazole, and in the present work we cocrystallized the P450 with posaconazole at 2.5 Å resolution. This long antifungal drug coordinates the P450 heme iron with the nitrogen atom of its terminal azole ring and adopts a linear configuration occupying the whole length of the substrate access channel and extending beyond the protein surface. Numerous drug-protein interactions determine the submicromolar K d of posaconazole for CYP46A1. We compared the crystal structure of posaconazole-bound CYP46A1 with those of the P450 in complex with other drugs, including the antifungal voriconazole and clotrimazole. We also analyzed the accommodation of posaconazole in the active site of the target enzymes, CYPs 51, from several pathogenic species. These and the solution studies with different marketed azoles, collectively, allowed us to identify the determinants of tight azole binding to CYP46A1 and generate an overall picture of azole binding to this important P450. The data obtained suggest that development of CYP51-specific antifungal agents will continue to be a challenge. Therefore, structural understanding of the azole binding not only to CYPs 51 from the pathogenic species but also to different human P450s is required to deal efficiently with this challenge.

Pharmacologic Stimulation of Cytochrome P450 46A1 and Cerebral Cholesterol Turnover in Mice

“…Our previous crystallographic studies showed that when the substrate (cholesterol sulfate) is present, there is no space in the CYP46A1 active site for a second molecule the size of EFV (14). Also, only one drug molecule was found in the substrate-binding cavity in all seven CYP46A1-drug complexes crystallized so far (15,16,20,50). Furthermore, in all ligand-bound CYP46A1 crystal structures, the P450 active site undergoes conformational changes to better fit the ligand.…”

Complexes of Trypanosoma cruzi Sterol 14α-Demethylase (CYP51) with Two Pyridine-based Drug Candidates for Chagas Disease

“…To date, within this type of P450 inhibitor, azoles have certainly remained the most potent, with 1,3-imidazole and 1,2,4-triazole derivatives serving as clinical antifungal drugs and agricultural fungicides (CYP51 inhibition), and yet, especially within the last decade, becoming quite notorious for their off-target activity (particularly, their inhibition of other human CYPs (48,(52)(53)(54)(55)(56)(57) and relatively high propensity to induce resistance (58,59)). Although several heterocyclic compounds other than azoles have been identified as T. cruzi CYP51 inhibitors, their inhibitory effects on the enzyme activity in vitro are much weaker, e.g.…”

Marketed Drugs Can Inhibit Cytochrome P450 27A1, a Potential New Target for Breast Cancer Adjuvant Therapy

“…These structures share at least two common features. One is conformational flexibility, a feature indicated by crystal structures of bicalutamide cocomplexes with the androgen receptor and CYP46A1 (Bohl et al, 2005;Mast et al, 2013c), and posaconazole cocomplexes with CYP46A1 and CYP51s from different pathogenic species (Chen et al, 2010;Lepesheva et al, 2010;Mast et al, 2013b). These crystal structures reveal protein-specific drug conformations and demonstrate how bicalutamide and posaconazole can adopt different conformations and fit the shape of the active site of very different proteins.…”