Treatment with endotoxins of peritoneal carcinomatosis induced by colon tumor cells in the rat.

Peritoneal carcinomatosis, a common spreading of human colon carcinoma, can be obtained by intraperitoneal injection of colon tumor cells in rats. When BDIX rats are injected with 10(6) syngeneic tumor cells, isolated and cloned from a chemically induced colon carcinoma, they die within 2-3 months with solid peritoneal tumors and hemorrhagic ascites. Repeated intraperitoneal injections of 20 micrograms endotoxins (Escherichia coli W0128:B12) from day 3 after tumor cell challenge inhibited tumor growth. This effect was long-lasting since 7 out of 10 treated rats were still alive and tumor-free 6 months after tumor cell challenge. When the endotoxins were administered from day 15 after the tumor cell challenge, in rats with established tumors visible with the naked eye, the survival times were significantly increased, and 6 out of 30 treated rats were still alive and tumor-free 6 months after tumor cell challenge. The optimum effect was obtained with 5 repeated injections. The different frequencies of injection tested, i.e. 1, 3 or 5 days apart were equally effective. Endotoxins were ineffective when administered intravenously. No side effect was observed.