[Combined effect of the topical administration of OK-432 with radiation on the C3H mouse fibrosarcoma (NFSa)--TCD50 and the mechanism of action].

Optimal timing of topical administration of OK-432 and TCD50 were studied using weakly immunogenic and radioresistant C3H mouse fibrosarcoma (NFSa). The mechanism of action of this combined therapy was examined histologically and electron microscopically. Topical administration of OK-432 was performed from 2 days before irradiation to 7 days after irradiation and tumor volumes on the 20th day after irradiation were compared with a control group given radiation alone. Significant difference was observed only in the group which was given OK-432 just after irradiation. The TCD50 of the combined therapy of radiation with topical administration of OK-432, 4 KE which was given just after irradiation was 64.5 Gy and that of radiation alone was 83.5 Gy. Combined therapy shifted the TCD50 curve about 20Gy to the left. Histological examination of the tumor on the 6th day after combined therapy showed marked degeneration and necrosis of tumor cells with marked infiltration of lymphocytes. These lymphocytes were electron microscopically seen surrounding not only damaged cells, but also apparently active tumor cells. We postulate the latter cells had a tendency to be degenerative. This phenomenon suggests that lymphocytes recognize as foreign these tumor cells which are apparently active but some what damaged by radiation.