Selective anti- Toxoplasma gondii activities of azasterols

Abstract

We report potent and selective inhibitory effects of 22,26-azasterol and 24,25-( R, S)-epiminolanosterol, known inhibitors of Δ 24(25)-sterol methyltranferase (SMT) in fungi and protozoa, on the proliferation of Toxoplasma gondii in LLCMK2 cells. These compounds produced a dose-dependent reduction in parasite proliferation. 22,26-azasterol had an IC 50 of 5.3 μM after 24 h and 4.5 μM after 48 h, while for 24,25-( R, S)-epiminolanosterol the IC 50 values were 1 μM after 24 h and 0.12 μM after 48 h. The rapid reduction of parasite load suggested these compounds have selective cytotoxic effects against T. gondii. However, we were unable to detect 24-alkyl sterols in purified T. gondii tachyzoites using highly sensitive gas–liquid chromatography/mass spectrometry methods, a fact which indicated that the anti-proliferative effects of these azasterols were not mediated by inhibition of SMT. Transmission electron microscopy showed that the mitochondrion was the major target of drugs. Ultrastructural effects on plasma membrane, apicoplast and the formation of autophagosomal structures were also observed.