Ara-C metabolism: implications for drug resistance and drug interactions.

Clinical studies of resistance to cytosine arabinoside have not produced agreement as to the specific biochemical lesions responsible for altered sensitivity, although experimental and clinical work supports the concept that a decreased ability to generate ara-CTP must be the ultimate effect of this lesion. 3-deazauridine, an inhibitor of CTP synthetase, was found to enhance ara-CTP production in murine tumor cells, and in the present study, was shown to inhibit deamination of ara-C at both the nucleoside and nucleotide level. Enhanced ara-CTP formation was observed in cells lacking cytidine deaminase (L1 210 and HL60), indicating that 3-deazauridine inhibition of deoxycytidylate deaminase may be important in this drug interaction.