Cell growth-inhibitory action of SAGP, an antitumor glycoprotein from Streptococcus pyogenes (Su strain)

An antitumor acidic glycoprotein (SAGP) from Streptococcus pyogenes (Su strain) inhibited the growth of BALB/3T3 cells in culture in a dose-dependent manner (0.03-10.0 micrograms/ml). This effect of SAGP was abolished by washing the cells, suggesting that SAGP weakly binds to the cell membrane. The ability of the cells to form colonies was unaffected by three days exposure to SAGP. Cell cycle analysis by flow cytometry revealed an accumulation of SAGP-treated cells in the S-phase. SAGP (3 micrograms/ml) reduced the incorporation of 3H-thymidine into the cells to approximately half of the control level. These results suggest that SAGP inhibits the growth of target cells by acting on their surface membrane and decreasing the rate of DNA synthesis.