Molecular target of the antileishmanial action of sinefungin

Sinefungin, a natural nucleoside isolated from cultures of Streptomyces incarnatus and S. griseolus, is structurally related to S-adenosylhomocysteine and S-adenosylmethionine. Sinefungin has been shown to inhibit the development of various fungi and viruses, but its major attraction to date resides in its potent antiparasitic activity. This compound has been reported to display antiparasitic activity against malarial, trypanosomal, and leishmanial species. Very little is known about the antiparasitic mode of action of sinefungin. We found that S-adenosylmethionine was capable of reversing the inhibitory growth effects of sinefungin in Leishmania mexicana and that dATP was capable of reversing inhibitory effects of the drug on DNA polymerase activity when pyrophosphate release was measured. However, when incorporation of [3H]dTTP was used to measure DNA polymerase activity, no inhibition could be observed. Inhibition of DNA polymerase activity by sinefungin occurred only during the initial stages of purification of this enzyme, and inhibition by aphidicolin, a known DNA polymerase inhibitor, paralleled the inhibition by sinefungin. Neither sinefungin nor aphidicolin inhibited partially purified DNA polymerase. S-Adenosylmethionine synthetase was partially purified, and sinefungin, at levels active in vitro, had no significant effect. Sinefungin was significantly suppressive against both L. donovani and L. braziliensis panamensis infections in hamsters when compared with meglumine antimonate (Glucantime).