Objectives: This study was performed to investigate the activity of tamoxifen, an antioestrogen widely used in the treatment of breast cancer, against Leishmania.
Methods: Drug activity was assessed in vitro against axenically grown promastigotes and amastigotes through cell counting or by measuring the cleavage of MTT, and against intracellular amastigotes by treating infected macrophage cultures and evaluating the number of intracellular parasites. Intravacuolar pH changes induced inside parasitophorous vacuoles of Leishmania (Leishmania) amazonensis-infected macrophages were evaluated using the fluorescent probes SNAFL-calcein and Acridine Orange.
Results: Tamoxifen killed L. (L.) amazonensis promastigotes and amastigotes with 50% inhibitory concentrations (IC50) of 16.4 +/- 0.2 and 11.1 +/- 0.2 microM, respectively. The drug was also effective against Leishmania (Viannia) braziliensis, Leishmania (Leishmania) major, Leishmania (Leishmania) chagasi and Leishmania (Leishmania) donovani with IC(50) values ranging from 9.0 to 20.2 microM. Tamoxifen induced a rapid and long-lasting alkalinization of the vacuolar environment. We also provide evidence that tamoxifen is more effective against promastigotes and amastigotes at pH 7.5 when compared with cultures at pH 4.5.
Conclusions: Tamoxifen effectively kills several Leishmania species and its activity against the parasite is increased by a modulation of the host cell intravacuolar pH induced by the drug.