[Background] Recently, radiotherapy with combination chemotherapy is reported to show more effective outcome than chemotherapy alone, objecting esophageal, gastric, rectal cancer, however, few scientific evidence to support the effectiveness with chemotherapy and radiation have been clarified at the present. [Purpose] In the study, we are to clarify significant role of radiation in controlling cell resistance to chemotherapy, using in vitro system with establishment of resistant gastric cancer cells to CDDP. [Materials and Methods] Human gastric cancer cells, MKN-45, is studied to establish chemo-resistant cell line in vitro, evaluating the efficacy of radiation in the resistant cells to CDDP. Each cell line was exposed with each IC50 value of CDDP for 24h followed by incubation with control medium for 48h. The treated cell (MKN-45/CDDP) showed suppressed growth with resistance to CDDP. Utilizing the model in vitro, efficacy by radiation (0-12Gy) was evaluated. Cell proliferation assay was triplicated with cell count or MTT method. In addition, several molecules were monitored with immunocytochemistry, using mouse anti-human PCNA, cyclin D1, or β-catenin antibody, to observe cell characteristics during the experiments. [Results] Inhibition rates (IRs) of 4, 8 and 12 Gy of Radiation alone were 48.2, 64.3, 98.7 %, respectively, and 4 and 8 Gy were settled for irradiated dose of the experiment. Combination with radiation with CDDP showed additive effect with 4 Gy and synergistic effect with 8 Gy on MKN-45 cells ; IRs of CDDP 3 and 10 μg/ml with 8 Gy of radiation were 77.1 and 91.5%, while IRs of CDDP 3 , 10 μg/ml alone and 8 Gy radiation alone were 44, 66.1, 45.8%. On the other hand, in the establishment of resistant cell of MKN-45/CDDP, IC50 of MKN-45 and MKN-45/CDDP is 2.39 and 21.3 μg/ml, showing 10 times of IC50 was obtained in the resistant cell compared with the wild typed cell. Immunocytochemistry showed that the wild MKN-45 cell expressed all of PCNA, cyclin D1, and β-catenin, but the MKN-45/CDDP cell showed no expression of PCNA, cyclin D1, and β-catenin, suggesting that characteristics of the MKN-45/CDDP cell will be non-proliferating and non-differentiated type, causing resistance to CDDP. Under the treatment by radiation, cytotoxic effect was observed on MKN-45/CDDP cells effectively; 0, 3, 10, 30 μg/ml of CDDP with 8 Gy of radiation showed 40.4, 77, 81.4, 100% of IRs on the MKN-45/CDDP cells, while 0, 3, 10, 30 μg/ml of CDDP alone showed 0, 0, 11, 77 % of IRs on the cell, showing significant synergistic effect on the resistant cell by the additional radiation. [Conclusion] Although radiation therapy shows a potential to add anticancer effect to chemotherapy, more significant role of radiation will be in the potent ability to control resistant cell to a chemotherapeutic agent, especially when the cells do not show proliferating potency, which is necessary to show anticancer potentials by chemotherapy alone.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]