6-oxopurine phosphoribosyltransferase: a target for the development of antimalarial drugs.

Malaria remains the most serious parasitic diseases affecting humans in the world today, resulting in 1-2 million fatalities each year. Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) are the predominant causative agents. Both are responsible for widespread mortality and morbidity and are a serious socio-economic burden, especially for countries in the developing world. One of the most important defences against malaria has been the use of chemotherapeutic drugs (e.g. chloroquine, artemisinins, pyrimethamine) but these have mainly been found by serendipity. Their mechanisms was not understood at the time of their discovery and, even today, are still not unequivocal. For many of these compounds, the parasite is now resistant and, hence, there is an urgent need to develop new therapeutic drugs directed to validated targets. One metabolic pathway crucial for the survival and replication and survival of the parasite is the synthesis of the purine nucleoside monophosphates essential for the production of DNA/RNA molecules. A key enzyme in this pathway is the 6-oxopurine phosphoribosyltransferase (PRTase). The focus of this review is on the identification and characterization of inhibitors of the enzymes from both Pf and Pv as antimalarial drug leads. The acyclic nucleoside phosphonates (ANPs) appear to be excellent candidates because they are good inhibitors of the two Plasmodium enzymes, can be selective compared to the human enzyme, can arrest parasitemia in cell based assays, have low cytotoxicity to the human host cell and, because of their stable carbon-phosphorous bond, are stable within the cell.