title: Wortmannin potentiates the combined effect of etoposide and cisplatin in human glioma cells.
abstract: The combination of etoposide and cisplatin represents a common modality for treating of glioma patients. These drugs directly and indirectly produce the most lethal DNA double-stand breaks (DSB), which are mainly repaired by non-homologous DNA end joining (NHEJ). Drugs that can specifically inhibit the kinase activity of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), the major component of NHEJ, are of special interest in cancer research. These small molecule inhibitors can effectively enhance the efficacy of current cancer treatments that generate DNA damage. In this study, we investigated the effect of DNA-PKcs inhibitor, wortmannin, on the cytotoxic mechanism of etoposide and cisplatin in MO59K and MO59J human glioblastoma cell lines. These cell lines are proficient and deficient in DNA-PKcs, respectively. Wortmannin synergistically increased the cytotoxicity of cisplatin and etoposide, when combined, in NHEJ-proficient MO59K cells. Surprisingly, wortmannin sensitizing effect was also observed in DNA-PKcs-deficient MO59J cells. These data suggest that wortmannin sensitization to etoposide and cisplatin in human glioma cells is mediated by inhibition of not only DNA-PKcs activity but other enzymes from PI3-K family, e.g. ATM and ATR. A concentration-dependent increase in etoposide and cisplatin-induced DSB levels was potentiated by inhibitor in both cell lines. Moreover, drug-induced accumulation in the G2/M checkpoint and S-phase was increased by wortmannin. Wortmannin significantly inhibited drug-induced DSB repair in MO59 cells and this effect was more pronounced in MO59J cells. We conclude that the mechanism of wortmannin potentiation of etoposide and cisplatin cytotoxicity involves DSBs induction, DSBs repair inhibition, G2/M checkpoint arrest and inhibition of not only DNA-PKcs activity.
authors: Molecular Genetics Laboratory, Medical University of Lodz, Mazowiecka 6/8, 92-215 Lodz, Poland. Electronic address: epastwa@csk.umed.lodz.pl.
authors: Elzbieta
authors: E
authors: Pastwa
authors: Department of Molecular Genetics, Faculty of Biology and Environmental Protection, University of Lodz, Lodz, Poland.
authors: Tomasz
authors: T
authors: Poplawski
authors: Department of Medical Enzymology, Medical University of Lodz, Poland.
authors: Urszula
authors: U
authors: Lewandowska
authors: Windber Research Institute, Windber, PA, USA.
authors: Stella B
authors: SB
authors: Somiari
authors: Department of Molecular Genetics, Faculty of Biology and Environmental Protection, University of Lodz, Lodz, Poland.
authors: Janusz
authors: J
authors: Blasiak
authors: Functional Genomics & Proteomics, ITSI-Biosciences, Johnstown, PA, USA.
authors: Richard I
authors: RI
authors: Somiari
mesh_terms: D000730:Androstadienes / Q000008:administration & dosage*; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000008:administration & dosage; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D004249:DNA Damage / Q000187:drug effects*; D059766:DNA End-Joining Repair / Q000187:drug effects*; D051747:DNA-Activated Protein Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D004357:Drug Synergism; D005047:Etoposide / Q000008:administration & dosage; D005910:Glioma / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D006801:Humans; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D005047:Etoposide; D051747:DNA-Activated Protein Kinase; D002945:Cisplatin; D000077191:Wortmannin
keywords: Chemosensitization; Cisplatin; DNA double-strand breaks; DNA-dependent protein kinase; Etoposide; Human glioma cells; Non-homologous DNA end joining; Wortmannin