Pharmacokinetics of the 5'-triphosphates of arabinosylcytosine and 2',2'-difluorodeoxycytidine in L1210 cells.

The clinical efficacy of ara-C is limited by a rapid elimination of the active triphosphate by target cells. The nucleoside antimetabolite, 2',2'-difluorodeoxycytidine, accumulates in leukemia cells as the respective 5'-triphosphate dFdCTP. In contrast to ara-C triphosphate, dFdCTP is eliminated with biphasic kinetics that exhibit a terminal half-life that approaches the cell cycle time. The cellular pharmacokinetics of dFdCTP may explain the unusual dose schedule and spectrum of efficacy against murine tumors.