In vitro and in vivo activity of two Pt(IV) salts against leishmania donovani.

The activities of 8 platinum drug complex salts were determined against Leishmania donovani promastigotes. The three most active salts were selected: [PtIVBr6]H2 (pentamidine); [PtIVBr6]H2 (stilbamidine), and [PtIVCl6]H2 (2-piperazinyl(1) ethyl amine), which induced growth-inhibition rates of more than 50% at 24 h of treatment and at the maximum dosage tested. The cytotoxicity assays on the macrophage cell line J-774 showed high cytotoxicity for the salt [PtIVBr6]H2 (stilbamidine) with a percentage of specific 51Cr release of 58.2% at 24 h of incubation and 100 microg/ml. Meanwhile, assays of the other compounds showed practically no cytotoxicity. The salt [PtIVBr6]H2 (pentamidine) notably inhibited the incorporation of 3H-thymidine in the treated parasites. The ultrastructural alterations observed in the flagellates treated with the salts [PtIVCl6]H2 (2-piperazinyl(1)ethyl amine) and [PtIVBr6]H2 (pentamidine) suggest that both act preferentially at the nuclear level and at the kinetoplast-mitochondrion complex. Both compounds showed a high in vivo activity in parasitized Wistar rats.

Haemonchus contortus: cloning and functional expression of a cDNA encoding ornithine decarboxylase and development of a screen for inhibitors.

Polyamines (PA) are essential for viability and replication of all cells; organisms either synthesize PA or acquire them from the environment. How nematodes that parasitize the gut satisfy their PA requirement has not been resolved. The primary regulatory enzyme in PA biosynthesis in most animals is ornithine decarboxylase (ODC). This enzyme has recently been characterized in free-living nematodes and in the parasitic species. Haemonchus contortus. Nematode and mammalian ODC are reported to differ in subcellular localization, kinetics, and sensitivity to inhibitors. We cloned an H. contortus cDNA that encodes a full-length ODC (sequence data from this article have been deposited with the GenBank Data Library under Accession Nos. AF016538 and AF016891). This cDNA was functionally expressed in strains of Escherichia coli and Saccharomyces cerevisiae that lack ODC and are dependent upon exogenous PA for survival. Expression of nematode ODC reversed the PA-dependence phenotype of both microorganisms. The complemented yeast strain was used to develop a nutrient-dependent viability screen for selective inhibitors of nematode ODC. The antiprotozoal drug stilbamidine isethionate was identified as active in this screen, but biochemical characterization revealed that this compound did not inhibit ODC. Instead, like other cationic diamidines, stilbamidine probably inhibits yeast S-adenosylmethionine decarboxylase. Nonetheless, the activity in the screen of the known ODC inhibitor difluoromethylornithine (DFMO) validates the concept that specific recombinant microorganisms can serve as the basis for extremely selective and facile screens.