Metabolism of 9-Beta-D-Arabinofuranosylhypoxanthine and 9-Beta-D-Arabinofuranosyladenine in L5178y Mouse Lymphoma Cells

Abstract

Both 9-β-D-arabinofuranosyladenine (araA) and 9-β-D-arabinofuranosylhypoxanthine (araHx) reduce the proliferation of L5178y mouse lymphoma cells at concentrations of 0.78 and 31.4 μM, respectively, to 50% in dose-response experiments. Simultaneous administration of araA and araHx produces an additive effect, while araHx as well as araA in combination with 9-β-D-arabinofuranosylguanine yield a pronounced antagonism. Intracellularly, 24% of the araA is deaminated to araHx which is subsequently phosphorylated to 9-β-D-arabinofuranosylinosine 5’-triphosphate (araITP). The remaining araA is completely phosphorylated to 9-β-D-arabinofuranosyladenine-triphosphate (araATP). After incubation of the cells with araA or araHx no 9-β-D-arabinofuranosylguanine 5’-monophosphate (araGMP) could be detected intracellularly. Incorporation studies in vivo revealed that thymidine incorporation to DNA is strongly reduced in the presence of araHx, while RNA and protein synthesis are only slightly affected by the compound. In in vitro studies with DNA polymerases from L5178y cells, it was established that aralTP strongly inhibits DNA polymerase α, while DNA polymerase β activity is less sensitively affected. The aralTP-caused inhibition is of the competitive type with respect to deoxyadenosine-triphosphate. From both the in vivo and the in vitro studies we conclude, that after exogenously supplied araA two ultimate active metabolites are formed: araATP and aralTP. We have no indication for a conversion to araGMP.