Potent Growth Inhibition of Human Tumor Cells in Culture by Arginine Deiminase Purified from a Culture Medium of a Mycoplasma-infected Cell Line1

Two kinds of growth-inhibitory substances were found in culture of a Rous sarcoma virus-transformed rat liver cell line, RSV-BRL. The two substances were purified from the serum-free culture medium and iden tified as transforming growth factor ß, and Mycoplasma-áerÃ-\edarginine deiminase (EC 3.5.3.6), respectively. The arginine deiminase was an acidlabile but dithiothreitol-resistant protein with a molecular weight of 45,000 and pi 4.7. Its A',,,value for i.-arginine was 0.3 m\i. which is about 30 times lower than that of bovine liver arginase. It was stable and active under culture conditions. When added into cultures, the arginine deimi nase inhibited the growth of various human cancer cell lines at a dose of 5 nu nil or higher by depleting i.-arginine in the culture media. This effective dose was about 1000 times lower than that of bovine liver arginase. These results suggested the possibility of chemotherapeutic use of arginine deiminase for human cancers.