Experimental chemotherapy of leishmaniasis with adenosine analogue Formycin A, in combination with inhibitor of nucleoside transport, nitrobenzylthioinosinate.

A single dose of the adenosine analogue Formycin A (FoA) (20 mg/kg), combined with nitrobenzyl mercaptopurine ribonucleoside 5'-monophosphate (NBMPR-P) (10 mg/kg), a prodrug of nitrobenzylthioinosine (NBMPR), was effective in reducing the size of the foot pad lesions from 7.4 +/- 0.2 to 3.9 +/- 0.2 of Syrian golden hamsters infected with Leishmania major. There was a statistical difference (p < 0.01) in the size of the foot pad by the fifth day between the infected groups that received treatment and the controls, as well as between the groups that were treated with combined drugs and FoA only. The initial reduction in size of the foot pad noted in the group that received only FoA was transient. The effect of FoA or FoA combined with NBMPR on the in vitro cultured promastigotes was similar, indicating that the transport inhibitor might be manipulating the availability of FoA in the host's macrophages where the leishmania amastigotes are resident. The results further indicate the need to explore the usefulness of combining cytotoxic nucleoside analogues with host protecting nucleoside transport inhibitors in the treatment of protozoan parasitic infections.