Inhibition of radiation-induced transformation of C3H/10T1/2 cells by chymotrypsin inhibitor 1 from potatoes.

In this report, we have investigated whether a protease inhibitor obtained from potatoes (chymotrypsin inhibitor 1; CI-1) will inhibit carcinogen-induced transformation of C3H/10T1/2 cells. CI-1 was as effective as the soybean-derived Bowman Birk inhibitor at suppressing radiation-induced transformation of C3H/10T1/2 cells, at a concentration of 10 micrograms/ml. The inhibitor was not toxic to the cells at concentrations of 0.1-10 micrograms/ml, the concentrations of CI-1 employed in the transformation experiments. To investigate the interaction of this inhibitor with the target cells, binding studies were carried out. 125I-labelled CI-1 could not be displaced from C3H/10T1/2 cells by co-incubation of the cells with a 5000-fold excess of unlabelled inhibitor. These results suggest that this inhibitor does not reversibly bind to specific receptor proteins on the surface of these cells.