Anti tumor effect of Corynebacterium liquefaciens and combined treatment with radiation

Anaerobic Corynebacterium liquefaciens (C. liq.) inhibited growth of a transplanted squamous cell carcinoma that had arisen spontaneously in a C3Hf/He female mouse. This inhibition was most effective when C. liq. was administered 2 - 4 days before transplantation of the tumor cells, and it was also effective even when administered after transplantation. A dose of more than 0.1 mg of C. liq. resulted in intensive inhibition. Repeated injections of C. liq. after a 2.0 mg administration did not show any effect superior to that of a single 2.0 mg administration. The tack of difference between TD50 values in C. liq. treated and not-treated animals negated the cytotoxic effect of C. liq. on the tumor cells. Percent labeled mitosis curves indicated that tumors in C. liq. treated animals had generation times longer than those in not-treated ones. Furthermore, the fraction of tumor cells able to divide at least once more (Fd) decreased after C. liq. administration. Possibly, growth inhibition of C. liq. is caused not by its cytotoxic effect but by its cytostatic action. Combined treatment, e.g., simultaneous administration of a single dose or multi-fractionated doses of γ-rays and C. liq., was found to be additive. (Evans, J.)