title: 2-Chloro-2'-deoxyadenosine inhibits DNA repair synthesis and potentiates UVC cytotoxicity in chronic lymphocytic leukemia B lymphocytes.
abstract: 2-Chloro-2'-deoxyadenosine (CdA) is a deoxyadenosine analogue which targets enzymes involved in DNA synthesis, and hence might interfere with the resynthesis step of DNA repair. We tested this hypothesis in resting B cell chronic lymphocytic leukemia (B-CLL) lymphocytes, after firstly characterizing unscheduled DNA synthesis occurring in these cells. We observed that the spontaneous incorporation of [methyl-3H]thymidine (dThd) into DNA of B-CLL cells was not completely inhibitable by hydroxyurea (HU) which blocks DNA replication. In addition, in the presence of HU, dThd incorporation could be upregulated by UVC radiation or DNA alkylation, without re-entry of the cells into S phase. CdA was found to inhibit both spontaneous and upregulated DNA synthesis in B-CLL cells. Phosphorylation of CdA was essential to exert this effect. We finally observed a strong synergistic cytotoxicity between UV light and CdA, which was correlated with activation of caspase-3 and high molecular weight DNA fragmentation, two markers of apoptosis. Taken together, these observations indicate that in B-CLL cells CdA inhibits unscheduled DNA synthesis which represents the polymerizing step of a repair process responsive to DNA aggression. Inhibition of this process by CdA, together with a combined activation of the apoptotic proteolytic cascade by CdA and UV, may explain their synergistic cytotoxicity.
authors.affiliation: Laboratory of Physiological Chemistry, Christian de Duve Institute of Cellular Pathology (ICP), Brussels, Belgium.
authors.forename: E
authors.initials: E
authors.lastname: Van Den Neste
authors.forename: S
authors.initials: S
authors.lastname: Cardoen
authors.forename: B
authors.initials: B
authors.lastname: Husson
authors.forename: J-F
authors.initials: JF
authors.lastname: Rosier
authors.forename: A
authors.initials: A
authors.lastname: Delacauw
authors.forename: A
authors.initials: A
authors.lastname: Ferrant
authors.forename: G
authors.initials: G
authors.lastname: Van den Berghe
authors.forename: F
authors.initials: F
authors.lastname: Bontemps
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology; D000478:Alkylation; D000964:Antimetabolites, Antineoplastic / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D001402:B-Lymphocytes / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D053148:Caspase 3; D020169:Caspases / Q000032:analysis; D017338:Cladribine / Q000378:metabolism / Q000494:pharmacology*; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D004261:DNA Replication / Q000187:drug effects*; D004273:DNA, Neoplasm / Q000096:biosynthesis / Q000187:drug effects / Q000528:radiation effects; D003864:Depression, Chemical; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000473:pathology*; D009363:Neoplasm Proteins / Q000032:analysis; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D010766:Phosphorylation; D011355:Prodrugs / Q000378:metabolism / Q000494:pharmacology*; D011836:Radiation Tolerance; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013936:Thymidine / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D000477:Alkylating Agents; D000964:Antimetabolites, Antineoplastic; D004273:DNA, Neoplasm; D009363:Neoplasm Proteins; D011355:Prodrugs; D011838:Radiation-Sensitizing Agents; D017338:Cladribine; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D013936:Thymidine; D006918:Hydroxyurea