The inhibition of ultraviolet radiation-induced DNA repair in human diploid fibroblasts by arabinofuranosyl nucleosides

Abstract

The antiviral compounds 9-β-D-arabinofuranosyladenine (ara-A), 9-β-D-arabinofuranosyl-2-fluoroadenine (FAA), 9-β-D-arabinofuranosylhypoxanthine (ara-Hx), 9-β-D-arabinofuranosylguanine (ara-G), 1-β-D-arabinofuranosylthymine (ara-T), 1-β-D-arabinofuranosyl-2′-fluorocytosine (FAC), 1-β-D-arabinofuranosyl-2′-fluoro-5-iodocytosine (FIAC) and 1-β-D-arabinofuranosyl-2′-fluoro-5-methyluracil (FMAU) were compared to 1-β-D-arabinofuranosyl cytosine (ara-C) in their ability to inhibit ultraviolet (UV) light-induced DNA repair in log phase and confluent human diploid fibroblasts. Inhibition of the polymerization or ligation steps of DNA excision repair manifests itself in the form of DNA single-strand breaks which may be quantitated through velocity sedimentation analysis in alkaline sucrose gradients. In UV-irradiated quiescent, confluent human fibroblast cultures, treatment with any of the aranucleosides leads to accumulation of single-strand breaks but the effective dose for this inhibition varies greatly. The order of their effectiveness in confluent cultures was ara-C and its derivatives >ara-A, FAA, ara-G, ara-Hx > ara-T. In rapidly cycling cells on the other hand, sensitivity to repair inhibition was exhibited only in response to ara-C and FAC. If 2 mM hydroxyurea (HU) was administered with ara-A, FAA or FMAU, however, DNA strand breaks were seen. HU also increased the efficiencies of ara-C and FAC. No significant strand breaks were observed in UV-irradiated log phase cells treated with FIAC, ara-Hx, ara-G or ara-T even in the presence of HU. The efficiencies of inhibition of unscheduled DNA synthesis (UDS) and semiconservative DNA synthesis by the aranucleosides is consistent with their relative efficiencies at producing strand breaks. The ability of the aranucleosides to inhibit DNA repair is discussed with respect to their hypothesized effects on DNA metabolic processes in eucaryotic cells.