Antitumor effect in peritoneal carcinomatosis of intraperitoneal administration of a streptococcal preparation, OK-432: I. Experimental study in the rat.

The effect of intraperitoneal OK-432 administration and its mechanism of action were investigated using an experimental rat tumor. On day 4 or 6 of intraperitoneal inoculation of tumor cells, 50 Klinische Einheit (KE)/kg of OK-432 was intraperitoneally administered, and intraperitoneal exudate cells were microscopically examined daily. Distribution of peritoneal exudate cells: A marked increase in neutrophils was noted in ascites at 24 hours after intraperitoneal administration of OK-432, with macrophages and lymphocytes appearing later than neutrophils. A subsequent decrease in neutrophils was accompanied by a gradual increase in tumor cells. Findings of tumor cells: When OK-432 was intraperitoneally administered on day 4 of tumor inoculation, aggregation of neutrophils around tumor cells was observed on day 6, and rosette formations around tumor cells were noted on day 7 or 8. Subsequently tumor cells that formed the centers of the rosettes were destroyed and disappeared. These reactions were not observed when OK-432 was administered on day 6, nor were they observed in untreated cases. These results suggest that cytotoxic effects of intraperitoneally administered OK-432 were displayed mainly by rosette formation by neutrophilic cells, as far as this model was concerned.