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

Abstract

ABSTRACTIn this study, we investigate the amebicidal activities of the pharmaceutical triazole CYP51 inhibitors fluconazole, itraconazole, and voriconazole againstAcanthamoeba castellaniiandAcanthamoeba polyphagaand assess their potential as therapeutic agents againstAcanthamoebainfections in humans. Amebicidal activities of the triazoles were assessed byin vitrominimum inhibition concentration (MIC) determinations using trophozoites ofA. castellaniiandA. polyphaga. In addition, triazole effectiveness was assessed by ligand binding studies and inhibition of CYP51 activity of purifiedA. castellaniiCYP51 (AcCYP51) that was heterologously expressed inEscherichia coli. Itraconazole and voriconazole bound tightly to AcCYP51 (dissociation constant [Kd] of 10 and 13 nM), whereas fluconazole bound weakly (Kdof 2,137 nM). Both itraconazole and voriconazole were confirmed to be strong inhibitors of AcCYP51 activity (50% inhibitory concentrations [IC50] of 0.23 and 0.39 μM), whereas inhibition by fluconazole was weak (IC50, 30 μM). However, itraconazole was 8- to 16-fold less effective (MIC, 16 mg/liter) at inhibitingA. polyphagaandA. castellaniicell proliferation than voriconazole (MIC, 1 to 2 mg/liter), while fluconazole did not inhibitAcanthamoebacell division (MIC, >64 mg/liter)in vitro. Voriconazole was an effective inhibitor of trophozoite proliferation forA. castellaniiandA. polyphaga; therefore, it should be evaluated in trials versus itraconazole for controllingAcanthamoebainfections.