Antitumor Effect of Streptococcus pyogenes by Inducing Hydrogen Peroxide Production

The Su strain of Streptococcus pyogenes (S‐coccus)‐derived anticancer preparation, OK‐432, which is immobilized by heating in the presence of penicillin G, is well known to have an immunopotentiating activity through activation of natural killer cells in vivo. In this study, a streptococcal anticancer preparation stronger than OK‐432 was prepared. Live streptococci (S‐cocci) of the Su strain were induced to acquire H(2)O(2)‐producing ability by treatment with serum under aerobic conditions. The resulting preparation no longer possessed hemolytic activity, and was not viable. The serum‐treated S‐coccus preparation activated natural killer cells as well as OK‐432 did, and had stronger antitumor activity than OK‐432 did. These results suggest that the serum‐treated S‐coccus preparation would be a useful tool for chemotherapy, in addition to immunotherapy, for the treatment of cancer.