title: 1-beta-D-arabinofuranosylcytosine is cytotoxic in quiescent normal lymphocytes undergoing DNA excision repair.
abstract: We have sought to clarify the potential activity of the S-phase-specific antileukemic agent 1-beta-D-arabinofuranosylcytosine (ara-C), an inhibitor of DNA synthesis, in quiescent cells that are substantially non-sensitive to nucleoside analogues. It was hypothesized that the combination of ara-C with DNA damaging agents that initiate DNA repair will expand ara-C cytotoxicity to non-cycling cells. The repair kinetics, which included incision of damaged DNA, gap-filling by DNA synthesis and rejoining by ligation, were evaluated using the single cell gel electrophoresis (Comet) assay and the thymidine incorporation assay. When normal lymphocytes were treated with ultraviolet C or with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), the processes of DNA excision repair were promptly initiated and rapidly completed. When the cells were incubated with ara-C prior to irradiation or BCNU treatment, the steps of DNA synthesis and rejoining in the repair processes were both inhibited. The ara-C-mediated inhibition of the repair processes was concentration-dependent, with the effect peaking at 10 microM. The combination of ara-C with these DNA repair initiators exerted subsequent cytotoxicity, which was proportional to the extent of the repair inhibition in the presence of ara-C. In conclusion, ara-C was cytotoxic in quiescent cells undergoing DNA repair. This might be attributed to unrepaired DNA damage that remained in the cells, thereby inducing lethal cytotoxicity. Alternatively, ara-C might exert its own cytotoxicity by inhibiting DNA synthesis in the repair processes. Such a strategy may be effective against a dormant subpopulation in acute leukemia that survives chemotherapy.
authors.affiliation: First Department of Internal Medicine, Fukui Medical University, Matsuoka, Fukui 910-1193, Japan. tyamauch@fmsrsa.fukui-med.ac.jp
authors.forename: Takahiro
authors.initials: T
authors.lastname: Yamauchi
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Kawai
authors.forename: Takanori
authors.initials: T
authors.lastname: Ueda
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D002330:Carmustine / Q000494:pharmacology; D003561:Cytarabine / Q000494:pharmacology*; D004260:DNA Repair / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008214:Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D000964:Antimetabolites, Antineoplastic; D003561:Cytarabine; D002330:Carmustine