The Clinical Candidate VT-1161 Is a Highly Potent Inhibitor of Candida albicans CYP51 but Fails To Bind the Human Enzyme

Abstract

The binding and cytochrome P45051 (CYP51) inhibition properties of a novel antifungal compound, VT-1161, against purified recombinant Candida albicans CYP51 (ERG11) and Homo sapiens CYP51 were compared with those of clotrimazole, fluconazole, itraconazole, and voriconazole. VT-1161 produced a type II binding spectrum with Candida albicans CYP51, characteristic of heme iron coordination. The binding affinity of VT-1161 for Candida albicans CYP51 was high (dissociation constant [K d ], <39 nM) and similar to that of the pharmaceutical azole antifungals (K d , <50 nM). In stark contrast, VT-1161 at concentrations up to 86 M did not perturb the spectrum of recombinant human CYP51, whereas all the pharmaceutical azoles bound to human CYP51. In reconstitution assays, VT-1161 inhibited Candida albicans CYP51 activity in a tight-binding fashion with a potency similar to that of the pharmaceutical azoles but failed to inhibit the human enzyme at the highest concentration tested (50 M). In addition, VT-1161 (MIC ‫؍‬ 0.002 g ml ؊1 ) had a more pronounced fungal sterol disruption profile (increased levels of methylated sterols and decreased levels of ergosterol) than the known CYP51 inhibitor voriconazole (MIC ‫؍‬ 0.004 g ml ؊1 ). Furthermore, VT-1161 weakly inhibited human CYP2C9, CYP2C19, and CYP3A4, suggesting a low drug-drug interaction potential. In summary, VT-1161 potently inhibited Candida albicans CYP51 and culture growth but did not inhibit human CYP51, demonstrating a >2,000-fold selectivity. This degree of potency and selectivity strongly supports the potential utility of VT-1161 in the treatment of Candida infections.

Azole Antifungal Agents To Treat the Human Pathogens Acanthamoeba castellanii and Acanthamoeba polyphaga through Inhibition of Sterol 14α-Demethylase (CYP51)

“…The relatively poor performance of itraconazole against Acanthamoeba may be due in part to poor uptake of the drug into the cells, as itraconazole is a bulky molecule with a long hydrophobic tail compared to the relatively compact voriconazole molecule. MIC values achieved with voriconazole against C. albicans were 24-to 375-fold lower (strain dependent) than those for the Acanthamoeba species used in this study (47), suggesting higher doses of triazoles will be required to be clinically effective against Acanthamoeba infections than those presently used to treat C. albicans infections. However, triazoles have relatively low toxicity and fewer side effects in patients than alternatives such as amphotericin B and can be safely tolerated at higher doses, especially in topical applications.…”

Efficacy of the Clinical Agent VT-1161 against Fluconazole-Sensitive and -Resistant Candida albicans in a Murine Model of Vaginal Candidiasis

“…A much larger number of sensitive and resistant clinical isolates are required to fully characterize the in vitro antifungal activity of VT-1161. However, these data coupled with MIC data from other laboratories (16,17) and the biochemical data demonstrating nanomolar potency against the CYP51 target (17) indicate that VT-1161 is one of the most potent CYP51 inhibitors of C. albicans yet described.…”

“…NCT01891305 and NCT01891331, respectively; www.clinicaltrials.gov). It was rationally designed to be highly selective relative to human CYP enzymes while maintaining potent inhibition of the fungal CYP target (16,17). Its intrinsic in vitro antifungal potency against susceptible C. albicans was reproduced in this study where the MIC was at or below the lowest concentration tested of 0.015 g/ml.…”

“…The potency of VT-1161 against C. albicans CYP51 in a cellular assay was Յ0.5 nM compared to in vitro 50% inhibitory concentration (IC 50 ) values of ϳ100 M or greater against human CYP51 and key xenobiotic-metabolizing CYPs present in human liver microsomes (e.g., CYP2C9, CYP2C19, and CYP3A4), and its in vitro MIC value against wild-type fluconazole-sensitive C. albicans was 0.002 g/ml (17). We present here the in vitro MIC potency of VT-1161 against several clinical isolates that have reduced susceptibility or were fully resistant to fluconazole and also the in vivo activity of VT-1161 in a murine model of vaginal candidiasis using fluconazole-sensitive wild-type or select fluconazole-resistant C. albicans isolates.…”

“…We have recently described a novel fungal CYP51 inhibitor, VT-1161, (16) that was designed for greater selectivity relative to off-target human cytochrome P450 (CYP) enzymes while retaining the same or greater potency for the fungal CYP51 target (17). The potency of VT-1161 against C. albicans CYP51 in a cellular assay was Յ0.5 nM compared to in vitro 50% inhibitory concentration (IC 50 ) values of ϳ100 M or greater against human CYP51 and key xenobiotic-metabolizing CYPs present in human liver microsomes (e.g., CYP2C9, CYP2C19, and CYP3A4), and its in vitro MIC value against wild-type fluconazole-sensitive C. albicans was 0.002 g/ml (17).…”