Biological activities and modes of action of 9-[alpha]--arabinofuranosyladenine and 9-[alpha]--arabinofuranosyl-8-azaadenine

Abstract

From earlier studies it is known that 9-[alpha]--arabinofuranosyladenine ([alpha]-araA) and 9-[alpha]--arabinofuranosyl-8-azaadenine ([alpha]-ara-8-azaA) bave in vitro antiviral activity, are cytotoxic, and are metabolized in mammalian cells to the triphosphates. This study was designed to compare the in vivo antiviral activities of these compounds and their loci of action with those of 9-[beta]--arabinofura-nosyladenine ([beta]-araA). the latter compound selectively inhibits DNA synthesis in intact cells, and its triphosphate is a known inhibitor of DNA polymerases and ribonucleotide reductase. Whereas [beta]-araA was significantly effective in the treatment of systemic herpes simplex virus type 1 (HSV-1) infections in mice, [alpha]-araA and [alpha]-ara-8-azaA were therapeutically ineffective. [alpha]-AraATP at a concentration of ~1 mM did not inhibit (1) DNA polymerases present in crude extracts of cultured H.Ep.-2 cells; (2) DNA polymerases present in extracts of KB cells; (3) partially purified DNA polymerase-[alpha] from mouse embryo cells; or (4) DNA polymerases induced by HSV-1 and HSV-2. DNA polymerase-[beta] from mouse embryo cells was inhibited to a small extent by 10-4 M [alpha]-araATP. In contrast, all of these enzymes were inhibited by [beta]-araATP at a concentration of 10-5M (as shown in these or in earlier studies). the reductions of CDP and UDP by ribonucleotide reductase from L1210 cells were not inhibited by [alpha]araATP (~10-3M), whereas [beta]-araATP produced 70-80 per cent inhibition at this concentration. In cultured H.Ep.-2 cells, [alpha]-ara-8-azaA inhibited the incorporation of thymidine, uridine, and formate into macromolecules, but it was without effect on the incorporation of adenine and hypoxanthine, and produced marginal inhibition of the incorporation of leucine. [alpha]-Ara-8-azaA produced a dose-dependent inhibition of the accumulation of [14C] formyl-glycinamide ribonucleotide in H.Ep.-2 cells treated with azaserine and [14C] formate. These results indicate that the [alpha]-nucleosides inhibit nucleic acid synthesis by mechanisms different from those of [beta]-araA.