The activity of ketoconazole and other azoles against Trypanosoma cruzi: biochemistry and chemotherapeutic action in vitro.

Trypanosoma cruzi epimastigotes in culture medium, and amastigotes and trypomastigotes in cultured human diploid lung cells were exposed to the antimycotic agent ketoconazole and their growth and/or sterol biosynthesis observed. Propagation of epimastigotes and amastigotes was impaired by concentrations of ketoconazole achievable in human serum, and amastigotes were more sensitive than were epimastigotes. Epimastigotes and trypomastigotes (non-dividing stage) displayed changes in their membrane sterol content such that the amounts of normal, end-product sterols (ergosterol, ergosta-5,7-dien-3 beta-ol, 24-ethylcholesta-5,7,22-trien-3 beta-ol, 24-ethylcholesta-5,7-dien-3 beta-ol) were notably decreased and the amounts of 14 alpha-methyl sterol precursors of these sterols (24-methylenedihydrolanosterol, obtusifoliol, lanosterol) were increased. Other azole drugs, itraconazole and fluconazole, when tested on epimastigotes, evoked the same qualitative pattern of changes in free sterols. Itraconazole was nearly as potent as ketoconazole, but fluconazole was significantly less potent. The nature of the sterols found in T. cruzi and the actions of azole drugs on their biosynthesis were similar in many respects to those observed in fungi and in Leishmania species. By analogy, it would seem that the primary mechanism of action of azole drugs on T. cruzi life-cycle stages is the impairment of the cytochrome P-450 sterol 14 alpha-demethylase. The consequent loss of normal sterols and accumulation of 14 alpha-methyl sterols may be responsible for the coincident retardation or cessation of growth.