Cytotoxic and antitumor effect of a fraction from cell-free extract of group A Streptococcus on transplantable tumor cells.

A fraction (60F) which had cytotoxic and antitumor activity could be obtained by precipitating cell-free extract (CFE) of group A streptococcus (Su strain) with a 50% to 60% saturation of ammonium sulfate. 60F exhibited a potent inhibitory effect on the incorporation of 3H-thymidine into various types of transplantable tumor cells. The activity of 60F was reduced by proteases and heating at 45 degrees C, but not by glycosidases and nucleases. Furthermore, 60F showed antitumor activity, such as cure and prolongation of life, in animals bearing EAC, MM-2, and S-180 tumors. These results show that 60F is probably protein and essentially exerts cytotoxic action against every cell line of tumor tested in vitro, and that the antitumor activity of 60F in vivo depends on the transplantability of tumor cells.