Effect of Corynebacterium parvum on the response to irradiation of a C3H fibrosarcoma.

A methylcholanthrene-induced fibrosarcoma of C3H mice has been used as 5th- to 6th-generation syngeneic transplant in an investigation of the role of Corynebacterium parvum as an adjuvant to the therapeutic effect of local irradiation of established tumors. The most effective route for administration of C. parvum in this tumor system was i.v., and the greatest effect of the C. parvum-mediated tumor graft rejection was observed for tumor growing intracutaneously or s.c. An intermediate level of effectiveness was obtained for tumor growing i.m. The combined C. parvum and local irradiation studies were performed using tumors growing in the leg muscle and measuring 8 mm in diameter at the time of local irradiation. Several routes of administration of C. parvum, dose levels of C. parvum, and time relationships between administration of C. parvum and irradiation were investigated. The outstanding finding was that very low doses of radiation were quite effective when administered to tumors growing in animals pretreated with C. parvum. This was true for radiation administered as a single or fractionated dose (10 equal doses spread over 18 days). For single-dose irradiation the effect was relatively dose independent over the range of 200 to 3000 rads. Some indication was obtained that local irradiation may impair the tumor graft rejection reaction. No evidence was obtained of an enhanced growth of tumor. Regression of tumor following irradiation was not modified by pretreatment with C. parvum. The mice that were unsuccessfully treated by radiation and C. parvum had a lower incidence of metastatic disease in the lung than did the mice treated unsuccessfully with radiation alone.