Antitumor and interferon-inducing activities of TH69, a whole bacterial preparation of Streptococcus faecalis, in mice

The antitumor effect of TH69, a lyophilized whole cell preparation of Streptococcus faecalis, was examined in mice using four experimental tumors: Ehrlich carcinoma and sarcoma-180 in DDI mice, MCA tumor in syngeneic C3H mice and Meth-A tumor in syngeneic BALB/c mice. Consecutive intraperitoneal injections of TH69 started one day after the tumor implantation markedly inhibited the growth of the two allogeneic ascites tumors and two syngeneic solid tumors. However, even with the most sensitive Ehrlich ascites tumor, TH69 was ineffective when the tumor cell inoculum was more than 2 X 10(6) cells per mouse. Neither oral nor subcutaneous administrations of TH69 produced significant antitumor effects. After a single intraperitoneal administration of TH69 (300 mg/kg) to mice, interferon was induced in the serum with a titer of 220 U/ml at 14 hr after administration. As TH69 has no direct cytotoxic activity against Ehrlich tumor cells, the antitumor effect of TH69 in mice must be ascribed to some immunopotentiating activity including interferon induction.