Enhancement of the antitumor effect of gamma-ray irradiation in combination with camptothecin against human colorectal adenocarcinoma.

The effect of gamma-ray irradiation and camptothecin (CAM) on human colorectal adenocarcinoma (LS 174T) growth was examined. On inhibition of DNA synthesis of LS 174T cells, almost all combined treatments presented a synergistic effect, excepting that the additive effects were shown at the lowest or the highest doses of CAM prior to the gamma-ray (137Cs) irradiation. The in vivo antitumor activity of 131I-NCC-CO-411 monoclonal antibody against carcinoembryonic antigen in combination with CAM was assessed by a tumor growth rate in LS 174T tumor-bearing nude mice. The tumor growth of the combined group was supra-additively suppressed in comparison with that of the individual group. The results suggest that the efficacy of radioimmunotherapy may be enhanced by combination treatment with CAM. A clinical protocol involving a combination treatment with CAM is underway.