No abstract

Parasitic illnesses are major causes of human disease and misery worldwide. Among them, both amebiasis and Chagas disease, caused by the protozoan parasites, Entamoeba histolytica and Trypanosoma cruzi, are responsible for thousands of annual deaths. The lack of safe and effective chemotherapy and/or the appearance of current drug resistance make the development of novel pharmacological tools for their treatment relevant. In this sense, within the framework of the medicinal inorganic chemistry, metal-based drugs appear to be a good alternative to find a pharmacological answer to parasitic diseases. In this work, novel ruthenium complexes [RuCl2(HL)(HPTA)2]Cl2 with HL=bioactive 5-nitrofuryl containing thiosemicarbazones and PTA=1,3,5-triaza-7-phosphaadamantane have been synthesized and fully characterized. PTA was included as co-ligand in order to modulate complexes aqueous solubility. In fact, obtained complexes were water soluble. Their activity against T. cruzi and E. histolytica was evaluated in vitro. [RuCl2(HL4)(HPTA)2]Cl2 complex, with HL4=N-phenyl-5-nitrofuryl-thiosemicarbazone, was the most active compound against both parasites. In particular, it showed an excellent activity against E. histolytica (half maximal inhibitory concentration (IC50)=5.2 μM), even higher than that of the reference drug metronidazole. In addition, this complex turns out to be selective for E. histolytica (selectivity index (SI)>38). The potential mechanism of antiparasitic action of the obtained ruthenium complexes could involve oxidative stress for both parasites. Additionally, complexes could interact with DNA as second potential target by an intercalative-like mode. Obtained results could be considered a contribution in the search for metal compounds that could be active against multiple parasites.

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is a major health problem worldwide. In this work, we report the development of palladium and platinum metal complexes with 5‐nitrofuryl‐containing thiosemicarbazones (L) as bioactive ligands against T. cruzi and PTA (1,3,5‐triaza‐7‐phosphaadamantane) as co‐ligand. Eight new complexes of the formula [MCl(L)(PTA)] with M = Pd or Pt were synthesized and fully characterized. Most complexes showed similar activities against T. cruzi to those of the corresponding free thiosemicarbazone ligands. No significant differences between palladium and platinum complexes were observed. Metal compounds with the phenylthiosemicarbazone derivative were the most active ones (IC50 = 9.84 ± 0.32 and 4.94 ± 0.24 μM for Pd2+ and Pt2+, respectively). The prepared complexes were not toxic on mammalian cells, showing selective indexes of more than 10–20. The ability of the complexes to be reduced in the parasite, which leads to toxic free radical species, was confirmed by the detection of OH· and nitroanion free radical species by ESR spectroscopy experiments. Gel electrophoresis and fluorescence experiments were consistent with an intercalating‐like mode of DNA interaction for the complexes, but DNA interaction does not seem to be the main mechanism of anti T. cruzi action for these compounds. The results obtained show that complexation of the bioactive ligands with the selected metals is a valid strategy to obtain improved metal‐based antiparasitic compounds.