[Background] Recently, chemoradiotherapy has been reported to show more effective outcome than chemotherapy alone in the treatment of gastrointestinal cancer patients, however, few scientific evidence to support the effectiveness of chemoradiotherapy have been clarified at present. [Purpose] In the study, we are to clarify the antitumor activity by combination with chemotherapeutic agents and radiation, using in vitro system of gastric cancer cell lines. [Materials and Methods] 1) Human gastric cancer cell lines, MKN-45/MKN-74/TMK-1, were utilized in order to investigate the combination effect by chemoradiation using cisplatin (CDDP) or 5-fluorouracil (5-FU). The cell lines were exposed with various concentrations of CDDP / 5-FU for 24 hour followed by radiation (0-12Gy). Cell counting was triplicated to evaluate antitumor activity, analyzing synergistic/antagonistic combination effect with the chemotherapeutic agents and radiation using isobologram. 2) Apoptotic inductions after exposure of radiation 0/4 Gy followed by exposure of CDDP 3 μg/ml/5-FU 2 μg/ml were evaluated in MKN-45 by photometric enzyme immunoassay for the quantitative in vitro determination of cytoplasmic histone-associated DNA fragments (Cell Death Detection ELISA PLUS, Roche Applied Science, Mannheim, Germany). [Results] 1) a) In MKN-45, Inhibition rates (IRs) of CDDP 0/3/10 μg/ml without/with radiation were 0/43/65% (0 Gy), 35/60/74% (2 Gy), 43/78/91% (6Gy), respectively, evaluated as synergistic effect. IRs of 5-FU 0/1/3 μg/ml without/with radiation were 0/61/78% (0 Gy), 18/64/88% (2 Gy), 82/91/93 % (6 Gy), evaluated as synergistic effect. b) In MKN-74, IRs of CDDP 0/3/10 μg/ml without/with radiation were 0/56/78% (0 Gy), 51/73/83% (2 Gy), 72/89/92% (6 Gy), evaluated as synergistic effect. IRs of 5-FU 0/3/10 μg/ml without/with radiation were 0/45/63% (0 Gy), 24/56/71% (2 Gy), 57/72/73 % (6 Gy), evaluated as additive effect. c) In TMK-1, IRs of CDDP 0/1/3 μg/ml without/with radiation were 0/46/74% (0 Gy), 20/75/82% (2 Gy), 57/89/95% (6 Gy), evaluated as synergistic. IRs of 5-FU 0/10/30 μg/ml without/with radiation were 0/61/70% (0 Gy), 36/74/85% (6 Gy), 70/82/90 % (10 Gy), evaluated as synergistic. 2) Apoptosis Enrichment Factors by radiation 0/4 Gy without/with drug were 1/1.16 (without drug), 0.92/1.24 (with CDDP 3 μg/ml), 0.95/1.51 (with 5-FU 2 μg/ml), suggesting that apoptosis was induced by additional radiation to chemotherapeutic agents, while chemotherapeutic agent alone did not showed apoptosis at the concentration. [Conclusion] Radiation will be an effective tool, enhancing antitumor activity of chemotherapeutic agents against gastric cancer cell lines in vitro. In addition, apoptotic induction was observed by means of additional radiation to chemotherapy, suggesting one of mechanism of synergy in antitumor activity by chemoradiation.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]