Cytarabinetriphosphate (Ara-CTP), a competitive inhibitor of DNA synthesis and an active metabolite of Cytarabine, exhibits predictive potential for leukemic blasts' chemosensitivity to Cytarabine through intracellular levels.
Fazarabine, also known as Kymarabine, is an orally-active pyrimidine analogue of an aza-substituted cytidine in which the ribose moiety is replaced by an arabinose sugar. Similar in action to cytarabine, fazarabine is phosphorylated by deoxycytidine kinase to a triphosphate form which competes with thymidine for incorporation into DNA; its incorporation into DNA inhibits DNA synthesis, resulting in tumor cell death and tumor necrosis. The presence of deoxycytidine kinase in a tumor is a determinant of tumor sensitivity to this drug.