title: The influence of inhibitors on the repair of benzo[a]pyrene-damaged DNA in hamster tracheal epithelial cells.
abstract: We investigated, in a cloned hamster tracheal epithelial cell line HTE-B, the effects of inhibitors of DNA topoisomerase, novobiocin and nalidixic acid; of DNA polymerase, 1-beta-arabinofuranosylcytosine (ara-C) and 2',3'-dideoxythymidine; of ribonucleotide reductase, hydroxyurea; and of poly(ADP-ribose)synthetase, 3-aminobenzamide, upon the removal of benzo[a]pyrene adducted to DNA [B[a]P--DNA]. A substantial reduction in the rate of removal of the polycyclic hydrocarbon-adducts occurred when nalidixic acid was added to the HTE-B cells that had been previously incubated with B[a]P for 8 h. Novobiocin produced a similar, but less marked, effect. The rate of disappearance of the individual B[a]P--DNA adducts was measured by analysis of the h.p.l.c. profiles. Of the 5 major adducts observed under the h.p.l.c. conditions, 4 were reduced in control cells to 30% of the original levels by 24 h after removal of the B[a]P from the medium; adduct 5 was almost completely removed. In the presence of nalidixic acid, during the 24 h repair period, only the removal of adduct 5 was unimpaired; the removal of the other 4 adducts was significantly retarded. On the other hand, 3-aminobenzamide addition did not affect the rate of removal of B[a]P--DNA adducts from the HTE-B cells. We employed the combinations of ara-C and dideoxythymidine or ara-C and hydroxyurea to allow the accumulation of single strand breaks after incubation of the HTE-B cells with B[a]P. These breaks were assayed by alkaline elution analysis. Inclusion of these inhibitors during the 2 h after removal of the B[a]P from the medium resulted in the accumulation of 4-5 single strand breaks/10(10) daltons of HTE-B DNA. This compares with a minimum estimate of the number of adducts removed during this period of 3 adducts/10(7) daltons. This discrepancy may indicate that the majority of lesions are not repaired by a pathway sensitive to polymerase inhibitors. In the presence of 3-aminobenzamide, we routinely observed a 10% increase in the alkaline elution of the DNA obtained from B[a]P-treated cells (1-2 breaks/10(10) daltons). Our results indicate that an excision repair process may be involved in the removal of at least some of the B[a]P-induced damage to DNA. However, the repair of the multiple adducts is complex and may involve pathways other than classical excision repair.
mesh_terms: D000818:Animals; D001549:Benzamides / Q000633:toxicity*; D001564:Benzo(a)pyrene; D001580:Benzopyrenes / Q000633:toxicity*; D002273:Carcinogens / Q000633:toxicity*; D002460:Cell Line; D002999:Clone Cells; D006224:Cricetinae; D003561:Cytarabine / Q000633:toxicity*; D004260:DNA Repair / Q000187:drug effects*; D004261:DNA Replication / Q000187:drug effects*; D004848:Epithelium / Q000378:metabolism; D006918:Hydroxyurea / Q000633:toxicity*; D007700:Kinetics; D009268:Nalidixic Acid / Q000633:toxicity*; D009675:Novobiocin / Q000633:toxicity*; D014132:Trachea / Q000378:metabolism*
chemical_list: D001549:Benzamides; D001580:Benzopyrenes; D002273:Carcinogens; D003561:Cytarabine; D009675:Novobiocin; D001564:Benzo(a)pyrene; D009268:Nalidixic Acid; C025160:3-aminobenzamide; D006918:Hydroxyurea