Antitumor effect of the streptococcal preparation OK-432 in a murine model of ovarian cancer.

The antitumor effects of the streptococcal preparation OK-432 were analyzed in a murine ovarian teratocarcinoma (MOT) model. Administration of OK-432 i.p. prevented tumor outgrowth in 75% of mice challenged with 10(3) MOT cells i.p. 24 h previously. Treatment was less successful in mice challenged with 10(4) or 10(5) cells, preventing tumor growth in 25% of the former and only 5% of the latter group. Tumor-challenged mice cured by injections of OK-432 were not rendered resistant to a subsequent challenge with 10(3) MOT cells 75 days after initial treatment. Only the i.p. route of administration was effective as i.v. OK-432 did not prolong survival of tumor-challenged mice. An antitumor response was detected as early as 24 h after i.p. treatment. This correlated temporally with an influx of neutrophils into the peritoneal cavity. Peritoneal cells obtained between 6 and 24 h after treatment were capable of lysing MOT targets in vitro. A single cell cytotoxicity assay demonstrated that peritoneal neutrophils, elicited by i.p. injection of OK-432, could bind to and lyse MOT targets. These data indicate that OK-432 is effective against small tumor cell inocula in this murine model of ovarian cancer and, furthermore, that the neutrophilic response into the peritoneal cavity plays a role in tumor rejection.