Role of deoxycytidine kinase in the inhibitory activity of 5-substituted 2'-deoxycytidines and cytosine arabinosides on tumor cell growth.

A number of 5-substituted derivatives of dCyd and 1-beta-D-arabinofuranosylcytosine (araC) have been evaluated for their inhibitory effects on the growth of three murine leukemia cell lines (L1210/0, L1210/BdUrd, and L1210/araC). The L1210/BdUrd and L1210/araC cell lines were selected from the parental L1210/0 cell line by their ability to grow at high concentrations of 5-bromo-2'-deoxyuridine and araC, respectively; the L1210/BdUrd cell line was deficient in dThd kinase activity, whereas the L1210/araC cell was deficient in dCyd kinase activity. The most effective inhibitors of L1210/0 cell proliferation were 5-fluoro-dCyd, araC, and 5-fluoro-araC. Their 50% inhibitory dose fell within the 0.001-0.015 micrograms/ml range. The 5-substituted araC analogues were much less inhibitory for L1210/araC cells but equally inhibitory for L1210/BdUrd as for the parental L1210/0 cell line. The role of dCyd kinase in the antitumor activity of the dCyd and araC analogues was further assessed by kinetic studies with dCyd kinase extracted from L1210/0 cells. All dCyd and araC analogues caused a competitive inhibition of dCyd kinase, the most potent inhibitor being 5-fluoro-dCyd (Ki/Km value 0.24). The Km of dCyd kinase from L1210/0 cells for dCyd was 23.1 microM as compared with 50 microM for araC. These values were increased to 53 and 182 microM, respectively, for the dCyd kinase isolated from L1210/araC cells.