title: Cyclopentenyl cytosine increases gemcitabine radiosensitisation in human pancreatic cancer cells.
abstract: The deoxycytidine analogue 2',2'-difluoro-2'-deoxycytidine (dFdC, gemcitabine) is a potent radiosensitiser, but has limited efficacy in combination with radiotherapy in patients with pancreatic cancer due to acute toxicity. We investigated whether cyclopentenyl cytosine (CPEC), targetting the 'de novo' biosynthesis of cytidine triphosphate (CTP), could increase dFdC cytotoxicity alone or in combination with irradiation in a panel of human pancreatic cancer cells (Panc-1, Miapaca-2, BxPC-3). To investigate the role of deoxycytidine kinase (dCK), the rate-limiting enzyme in the activation of dFdC, human lung cancer cells without (dFdC-resistant SWg) and with an intact dCK gene (dFdC-sensitive SWp) were included. We found that CPEC (100-1000 nmol l(-1)) specifically reduced CTP levels in a dose-dependent manner that lasted up to 72 h in all cell lines. Preincubation with CPEC resulted in a dose-dependent increase in dFdC incorporated into the DNA only in dFdC-sensitive cells. Consequently, CPEC increased the effectiveness of dFdC (300 nmol l(-1) for 4 h) only in dFdC-sensitive cells, which was accompanied by an increase in apoptosis. We also found that CPEC enhanced the radiosensitivity of cells treated with dFdC (30-300 nmol l(-1) for 4 h). These results indicate that CPEC enhances the cytotoxicity of dFdC alone and in combination with irradiation in several human tumour cell lines with an intact dCK gene.
authors: Department of Radiation Oncology, Academic Medical Centre-University of Amsterdam, Laboratory for Experimental Oncology and Radiobiology, Centre for Experimental Molecular Medicine, Amsterdam, The Netherlands. c.vanbree@amc.uva.nl
authors: C
authors: C
authors: van Bree
authors: Hm
authors: H
authors: Rodermond
authors: R
authors: R
authors: Leen
authors: Jp
authors: J
authors: Medema
authors: Abp
authors: A
authors: van Kuilenburg
mesh_terms: D017209:Apoptosis; D045744:Cell Line, Tumor; D002470:Cell Survival; D003562:Cytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D003570:Cytidine Triphosphate / Q000032:analysis; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy; D010190:Pancreatic Neoplasms / Q000532:radiotherapy*; D011836:Radiation Tolerance / Q000187:drug effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D000093542:Gemcitabine
chemical_list: D011838:Radiation-Sensitizing Agents; D003841:Deoxycytidine; D003562:Cytidine; D003570:Cytidine Triphosphate; C045911:cyclopentenyl cytosine; D000093542:Gemcitabine