Effects of C. parvum on radiation response of murine tumors.

The effects of intravenous C. parvum (CP) on the efficacy of fractionated gamma-irradiation in treating a fairly immunogenic fibrosarcoma (FSa) and a weakly immunogenic mammary carcinoma (MDAH-MCa-4) were studied in C3Hf/Bu mice. Tumors were 8 mm in diameter at the start of irradiation. The FSa was exposed to 500 and the MDAH-MCa-4 to 750 rads daily for 3.6 or 10 days. The administration of 0.25 mg CP varied from 4 days before to 14 days after the start of irradiation. CP greatly augmented radiocurability of FSa, especially when applied before irradiation. The effect was evidenced by the increase in the cure rate, and, in mice not cured, by the tumor growth retardation, reduction of pulmonary metastasis incidence and prolongation in survival of mice. This effect of i.v. CP on FSa radiocurability was not further increased by intralesional CP, or by systemic injections of vitamin A or the hypoxic tumor cell radiosensitizer Ro-07-0582. CP was less effective in augmenting radiation response of the MDAH-MCa-4. Here, CP slowed the growth of irradiated tumors and prolonged the survival of mice.