Analysis of antitumor effects of OK-432 against syngeneic mouse fibrosarcoma: combination effect of OK-432 and recombinant lymphokines.

OK-432, a streptococcal preparation with potent biological response modifying activities, had the ability to cure mice bearing BAMC-1 (fibrosarcoma) ascites when it was injected intraperitoneally five times, 2, 4, 6, 8, and 10 days after the tumor inoculation. Previously, it was shown that the OK-432 injection on day 2 was indispensable since only a minimal antitumor effect was obtained when an inflammation-inducing agent such as thioglycolate instead of OK-432 was injected on day 2, followed by four OK-432 injections on days 4, 6, 8 and 10. In the present study, the injection of OK-432 on day 2 and a subsequent injection of either IL-2 or IFN-gamma on day 4 or 6 showed a significant antitumor effect, achieving a complete cure in approximately 50% of mice treated, although none of the mice could be cured by a single injection of either OK-432, IL-2, or IFN-gamma on day 2. Interestingly, however, the mice treated with an injection of a lymphokine (IL-2 or IFN-gamma) on day 2 followed by OK-432 on day 4 were not cured either. Peritoneal cells on day 12 in mice treated with OK-432 and either of the lymphokines contained pantropic killer cells, which were Thy-1+ and asialo GM1+ (AsGM1+). Moreover, the antitumor effect of the combined treatment was abolished when mice were pre-treated with anti-AsGM1. No significant antitumor effect was observed in athymic nu/nu mice. Together with our previous findings, these results indicate that lymphokines induced by OK-432 administration may account for some of its therapeutic effects and that these lymphokines may also facilitate the subsequent induction of specific killer cells. These results warrant further investigation on possible effective therapeutic protocols with the combined use of OK-432 and lymphokines.