Protection against fludarabine neurotoxicity in leukemic mice by the nucleoside transport inhibitor nitrobenzylthioinosine.

Fludarabine phosphate (F-ara-AMP, Fludara) is rapidly converted in the circulation to fludarabine (F-ara-A) and is among the most effective single agents in the treatment of chronic lymphocytic leukemia. Although current treatment protocols are well tolerated, severe neurotoxicity was a consequence of high-dose F-ara-AMP regimens used in early phase I trials against adult acute leukemia. The present study showed that in mice implanted with leukemia L1210, fatal neurotoxicity, which initially manifested as hind-limb paralysis, was a consequence of high-dose F-ara-AMP treatment. However, the incidence of neurotoxicity was reduced by the coadministration of NBMPR-P, the 5'-phosphate of nitrobenzylthioinosine, a potent inhibitor of the es equilibrative nucleoside transport (NT) system. NBTGR-P, the 5'-phosphate of nitrobenzylthioguanosine (also a potent NT inhibitor) similarly prevented F-ara-AMP neurotoxicity in this experimental system. Treatment with F-ara-AMP/NBMPR-P combinations was more effective with respect to the fractional yield of "cured" mice than were the same treatment regimens without NBMPR-P.