Metabolism of Pyrazolo(3,4-d)pyrimidines in Leishmania braziliensis and Leishmania donovani

Leishmania donovani and Leishmania braziliensis grown in culture formed millimolar concentrations of allopurinol ribonucleoside 5’-monophosphate from [6“C]allopurinol. In addition, allopurinol l-ribonucleoside, oxipurinol riboside 5’-monophosphate, and three new metabolites of allopurinol, namely, 4-aminopyrazolo(3,4-d)pyrimidine ribonucleoside V-monophosphate and the corresponding diand triphosphates (lribosyl 4-aminopyrazolo(3,4-d)pyrimidine Q’-diphosphate and 1-ribosyl4-aminopyrazolo(3,4-d)pyrimidine 5’-triphosphate) were identified in the parasitic cells. They were formed via a unique amination reaction from 1-ribosyl allopurinol 5’-phosphate, analogous to the conversion of IMP to AMP. [6-“C]Allopurinol was incorporated into RNA of L. donovani in the form of 4aminopyrazolo(3,4-d)pyrimidine. Adenine reversed the growth inhibition of allopurinol and prevented its metabolism to all of the ribonucleotide metabolites. L. donovani was 2to I-fold more active in its metabolism of allopurinol to ribonucleotides than L. braziliensis. I-Aminopyrazolo(3,4-d)pyrimidine inhibited cell growth and resulted in high intracellular levels of 1-ribosyl allopurinol5’-phosphate and smaller amounts of the 4-aminopyrazolo(3,4-d)pyrimidine ribonucleotides. The metabolism of allopurinol to 4-aminopyrazolo(3,4-d)pyrimidine ribonucleotides and its resultant cytotoxicity occurs in these parasitic protozoans, but not in mammalian cells.