Water soluble cationic trans-platinum complexes which induce programmed cell death in the protozoan parasite Leishmania infantum

Abstract We have evaluated the cytotoxic properties against the protozoan Leishmania infantum of four water soluble cationic trans -Pt(II)Cl 2 compounds containing as inert groups NH 3 and piperazine ( 1 ), 4-picoline and piperazine ( 2 ), n -butylamine and piperazine ( 3 ), and NH 3 and 4-piperidino-piperidine ( 4 ). The leishmanicidal activity of compounds 3 and 4 against promastigotes of the parasite Leishmania infantum was 2.5- and 1.6-times higher than that of the cytotoxic drug cis -diamminedichloroplatinum(II), respectively. Interestingly, compounds 3 and 4 produce in Leishmania infantum promastigotes a higher amount of programmed cell death than cisplatin, which is associated with cell cycle arrest in G2/M. In contrast to cis -diamminedichloroplatinum(II), binding of compounds 3 and 4 to calf thymus DNA induces conformational changes more similar to those of trans -diamminedichloroplatinum(II) that may be attributed to denaturation of the double helix. Similarly to cis -diamminedichloroplatinum(II) and trans -diamminedichloroplatinum(II), the interaction of compounds 3 and 4 with ubiquitin results in an increase of the α-helix content of the protein as observed by circular dichroism spectroscopy. However, fluorescence studies indicate that compounds 3 and 4 produce a decrease in the fluorescence of the tyrosine 59 residue of ubiquitin higher than both cis -diamminedichloroplatinum(II) and trans -diamminedichloroplatinum(II). Altogether, our results suggest that the biochemical mechanism of cytotoxic activity of compounds 3 and 4 against Leishmania infantum must be different from that of cis -diamminedichloroplatinum(II). To the best of our knowledge, compounds 3 and 4 are the first reported trans -platinum complexes that show antiparasitic activity.