Leishmania infantum: Stage-specific activity of pentavalent antimony related with the assay conditions

The determination of the intrinsic sensitivity of Leishmania strains to pen tavalent antimonials in clinical trials, before treatment is begun, is esse ntial in order to avoid failures and to allow alternative drugs to be chose n. A comparative study of SbV activity on promastigotes, axenic amastigote- like cells, and intracellular amastigotes of Leishmania infantum, when admi nistered in the form of meglumine antimoniate and free, in hydrochloric sol ution, was performed. Results indicate that the conditions under which the promastigotes were cultured affect the IC50 obtained, although results were homogeneous when the products were assayed on axenic-like and intracellula r amastigotes. The IC50 obtained for SbV in the form of meglumine antimonia te or in hydrochloric solution on promastigotes cultured in Schneider's med ium depends on the growth rate of the culture and therefore could be regula ted by modifying the fetal calf serum concentration in the medium. The pH o f the culture medium strongly affected the activity of meglumine antimoniat e but not that of the SbV hydrochloric solution on promastigotes cultured i n Schneider's medium. This influence of pH was observed to a much lesser ex tent when promastigotes were cultured on M199 or RPMI media. In homogeneous culture conditions, which included the regulation of the promastigote grow th rate through the hear-inactivated fetal calf serum concentration in the medium and the dilution of the meglumine antimoniate with Schneider's mediu m at pH 6.5, the activity of SbV, free or in the form of meglumine antimoni ate, was the same in promastigotes, intracellular amastigotes, and axenic a mastigote-like cells. (C) 2000 Academic Press.