Differences in metabolism and cytotoxicity between 9-beta-D arabinofuranosyladenine and 9-beta-D-arabinofuranosyl-2-fluoroadenine in human leukemic lymphoblasts.

Abstract

We compared the effects of 9-β-d-arabinofuranosyladenine (ara-A) and its 2-fluoro derivative (F-ara-A) on DNA synthesis and viability in human leukemic lymphoblasts (CCRF-CEM). The relative DNA content and cloning capacity of the cells were determined by flow cytometry and growth in methylcellulose, respectively. Incubation with either 1 µm ara-A in the presence of 2′-deoxycoformycin, a potent inhibitor of adenosine deaminase, or 2.5 µm F-ara-A alone for 18 hr stopped the progression of cells through S phase. At higher concentrations, from 2.5 to 20 µm, both arabinonucleosides preferentially produced toxic effects in cells arrested in S phase. The DNA-inhibitory effects and cytotoxicity of F-ara-A, but not ara-A, were prevented by adding deoxycytidine to the growth medium. A CCRF-CEM variant that was unable to phosphorylate deoxycytidine proved to be highly resistant to the inhibitory effects of F-ara-A but was normally sensitive to ara-A. These results indicate that the cytotoxicity of ara-A in both sensitive and resistant cells and of F-ara-A in sensitive cells is probably mediated by the intracellular formation of nucleotides and inhibition of DNA synthesis. By contrast, the reduction in the cloning efficiency of 1-β-d-arabinofuranosylcytosine-resistant cells at high concentrations of F-ara-A may be due to some direct effect of the nucleoside. Finally, the different susceptibility of the mutant CCRF-CEM cells to the toxic effects of ara-A and F-ara-A suggests that alternative pathways phosphorylate these arabinonucleosides, one being associated with deoxycytidine kinase and the other with either deoxyadenosine kinase or, less likely, adenosine kinase.