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 co lorectal adenocarcinoma (LS 174T) growth was examined. On inhibition o f DNA synthesis of LS 174T cells, almost all combined treatments prese nted a synergistic effect, excepting that the additive effects were sh own at the lowest or the highest doses of CAM prior to the gamma-ray ( Cs-137) irradiation. The in vivo antitumor activity of I-131-NCC-CO-41 1 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 resul ts suggest that the efficacy of radioimmunotherapy may be enhanced by combination treatment with CAM. A clinical protocol involving a combin ation treatment with CAM is underway.