title: Mechanisms associated with the expression of cisplatin resistance in a human ovarian tumor cell line following exposure to fractionated X-irradiation in vitro.
abstract: Interactions between cisplatin (CDDP) and irradiation are of potential significance for the combined modality treatment of cancer. Previous data have indicated that following in vitro exposure to X-irradiation certain tumour cells expressed resistance to CDDP. To identify parameters associated with this CDDP resistance, the human ovarian carcinoma cell line SK-OV-3/P was pre-exposed to fractionated X-irradiation (total dose: 50 Gy) in vitro. The resultant subline (SK-OV-3/DKR-10) proved 2-fold resistant to CDDP, but not to acute X-irradiation. Consistent with unaltered dihydrofolate reductase and thymidylate synthase activities, SK-OV-3/DXR-10 cells were neither cross-resistant to methotrexate nor to 5-fluorouracil. Verapamil (6.6 microM) significantly (P less than 0.05) enhanced CDDP-induced cytotoxicity in the resistant DXR-10 subline, but not in the parental cells. Total glutathione levels were significantly (P less than 0.01) lower in the resistant subline and BSO pretreatment failed to influence cytotoxicity, whilst related enzyme activities were not consistently modified in the SK-OV-3/DXR-10 cells. Resistance in these cells was associated with significantly decreased cisplatin uptake (P less than 0.002). Immediately following drug exposure the total platination level of the DNA, quantitated immunochemically, was higher (P less than 0.05) in the resistant subline indicative of increased tolerance to DNA damage. After an 18 h post-treatment incubation the parental cell line appeared proficient in the removal of the intrastrand adduct Pt-AG, but deficient in removing the major adduct Pt-GG and the difunctional Pt-(GMP)2 lesion, whilst the DXR-10 resistant subline appeared proficient in removal of all four Pt-DNA adducts. DNA polymerases alpha and beta activities, however, were comparable in both cell lines. These data implicate both enhanced repair and increased tolerance of DNA damage as mechanisms of resistance to CDDP resulting from in vitro exposure of a human ovarian carcinoma cell line to fractionated X-irradiation.
authors.affiliation: Laboratory of Cellular Chemotherapy, Imperial Cancer Research Fund Laboratories, Lincoln's Inn Fields, London, UK.
authors.forename: W C
authors.initials: WC
authors.lastname: Dempke
authors.forename: S A
authors.initials: SA
authors.lastname: Shellard
authors.forename: L K
authors.initials: LK
authors.lastname: Hosking
authors.forename: A M
authors.initials: AM
authors.lastname: Fichtinger-Schepman
authors.forename: B T
authors.initials: BT
authors.lastname: Hill
mesh_terms: D001692:Biological Transport; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000378:metabolism / Q000494:pharmacology*; D002999:Clone Cells; D004260:DNA Repair; D004273:DNA, Neoplasm / Q000032:analysis; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004351:Drug Resistance / Q000528:radiation effects*; D005260:Female; D005978:Glutathione / Q000378:metabolism; D005980:Glutathione Reductase / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism; D009363:Neoplasm Proteins / Q000032:analysis; D010051:Ovarian Neoplasms; D013482:Superoxide Dismutase / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism; D013940:Thymidylate Synthase / Q000378:metabolism; D014965:X-Rays
chemical_list: D004273:DNA, Neoplasm; D009363:Neoplasm Proteins; D013482:Superoxide Dismutase; D013762:Tetrahydrofolate Dehydrogenase; D016660:NAD(P)H Dehydrogenase (Quinone); D005980:Glutathione Reductase; D013940:Thymidylate Synthase; D005982:Glutathione Transferase; D004259:DNA-Directed DNA Polymerase; D005978:Glutathione; D002945:Cisplatin