Anti-Leishmania braziliensis activity of 1,10-phenanthroline-5,6-dione and its Cu(II) and Ag(I) complexes

Leishmaniasis, included in the priority list of the WHO, remains as a neglected disease caused by parasites of the Leishmania genus. There is no vaccine available for human leishmaniasis, and the current treatment is based on old drugs that cause serious side effects. Herein, we initially studied the cellular distribution of the virulence factor gp63, the major metallopeptidase, in a virulent strain of Leishmania braziliensis, and then we measured the inhibitory effects of 1,10-phenanthroline-5,6-dione (phendione), and its metal complexes, [Cu(phendione)₃](ClO₄)₂.4H₂O and [Ag(phendione)₂]ClO₄, on both cellular and extracellular metallopeptidases produced by promastigotes. The action of the three compounds on parasite viability and on parasite-macrophage interaction was also determined. Gp63 molecules were detected in several parasite compartments, including the cytoplasm, the membrane lining the cell body and flagellum, and in the flagellar pocket, which explains the presence of gp63 in the culture medium. The test compounds inhibited parasite metallopeptidases in a typical dose-dependent manner, and they also caused a significant and irreversible inhibition of parasite motility. Moreover, the pre-treatment of promastigotes with the test compounds induced a decrease in the association index with macrophages. Collectively, phendione and its Cu(II) and Ag(I) complexes are excellent prototypes for the development of new anti-L. braziliensis drugs.