ObjectiveTo investigate the synergistic antitumor effects of ionizing radiation and the cytosine deaminase (CD)/5-flurocytosine (5-FC) system therapy in human pancreatic cancer cell.MethodsThe expression vector containing CD was transfected into the human pancreatic cancer cell line PC3. The clones were picked out after G418 selection. The CD gene integration and expression were confirmed by the RT-PCR. The cytotoxicity to the cells with or without CD and (or) ionizing radiation under the treatment with 5-FC was measured by the MTT assay. The clonogenic assay was used to investigate the radiosensitizing effect of 5-FC on the PC3 cells transfected or untransfected with CD gene.ResultsThe CD gene was stably expressed in the PC3 cells transfected with CD gene. The cytotoxic effect of 5-FC was superior on the PC3 cells transfected than that of untransfected with CD gene (P<0.05) and which were enhanced in combination with the ionizing radiation (P<0.05). The CD/5-FC enhanced the radiosensitivity of PC3 cells transfected with CD gene (P<0.05). The change in the radiosensitivity was quantified by calculating the sensitization enhancement ratio (SER) at the clinically relevant dose of 2 Gy. The SER was 1.5 in the PC3 cells transfected with CD gene by giving ionizing radiation of 2 Gy.ConclusionsCD/5-FC system is a potenial radiosensitizer in PC3 cells transfected with CD gene. Ionizing radiation and CD/5-FC system is more effective for killing effect of PC3 cells than ionizing radiation or CD/5-FC system alone.