title: DNA repair rate and etoposide (VP16) resistance of tumor cell subpopulations derived from a single human small cell lung cancer.
abstract: Two human small cell lung cancer (SCLC) subpopulations, CPH 54A, and CPH 54B, established from the same patient tumor by in vitro cloning, were investigated. The tumor was classified as intermediate-type SCLC. The cellular sensitivity to ionizing radiation (IR) was previously determined in the two sublines both in vivo and in vitro. Here we measured the etoposide (VP16) sensitivity together with the induction and repair of VP16- and IR-induced DNA double-strand breaks (DSBs). The two subpopulations were found to differ significantly in sensitivity to VP16, with the radioresistant 54B subline also being VP16 resistant. In order to explain the VP16 resistant phenotype several mechanisms where considered. The p53 status, P-glycoprotein, MRP, topoisomerase IIalpha, and Mre11 protein levels, as well as growth kinetics, provided no explanations of the observed VP16 resistance. In contrast, a significant difference in repair of both VP16- and IR-induced DSBs, together with a difference in the levels of the DSB repair proteins DNA-dependent protein kinase (DNA-PK(cs)) and RAD51 was observed. The VP16- and radioresistant 54B subline exhibited a pronounced higher repair rate of DSBs and higher protein levels of both DNA-PK(cs) and RAD51 compared with the sensitive 54A subline. We suggest, that different DSB repair rates among tumor cell subpopulations of individual SCLC tumors may be a major determinant for the variation in clinical treatment effect observed in human SCLC tumors of identical histological subtype.
authors.affiliation: Institute of Molecular Pathology, University of Copenhagen, Frederik V's vej 11, 5 sal, DK-2100 Copenhagen, Denmark. riis@pai.ku.dk
authors.forename: Lasse Tengbjerg
authors.initials: LT
authors.lastname: Hansen
authors.forename: Cecilia
authors.initials: C
authors.lastname: Lundin
authors.forename: Thomas
authors.initials: T
authors.lastname: Helleday
authors.forename: Hans Skovgaard
authors.initials: HS
authors.lastname: Poulsen
authors.forename: Claus Storgaard
authors.initials: CS
authors.lastname: Sørensen
authors.forename: Lone Nørgård
authors.initials: LN
authors.lastname: Petersen
authors.forename: Mogens
authors.initials: M
authors.lastname: Spang-Thomsen
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000235:genetics / Q000378:metabolism; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D018288:Carcinoma, Small Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D004249:DNA Damage / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects*; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism; D004273:DNA, Neoplasm / Q000187:drug effects*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology*; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D051135:Rad51 Recombinase; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D016159:Tumor Suppressor Protein p53; D005047:Etoposide; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; C094191:MRE11 protein, S cerevisiae; D004250:DNA Topoisomerases, Type II