Inhibition of radiation-induced transformation of C3H/10T1/2 cells by carboxypeptidase inhibitor 1 and inhibitor II from potatoes

In the current study, the ability of four protease inhibitorsto suppress radiation-induced transformation of C3H/10T1/2 cellswas investigated. The inhibitors tested included: (i) aprotinin(a serine protease inhibitor), (ii) N-acetyl-L-tyrosine ethylester (a chymotrypsin substrate and competitive inhibitor ofprotein degradation), (iii) carboxypeptidase inhibitor (a metallo-exopeptidaseinhibitor) and (iv) Inhibitor II (a chymotrypsin/trypsin inhibitor).While none of the inhibitors were toxic to the cells at theconcentrations employed, only carboxypeptidase inhibitor andInhibitor II are internalized radiation-induced transformationin a statistically significant manner. Utilizing fluorescentlabeled inhibitors, we found that carboxypeptidase inhibitorsand Inhibitor II are internalized by the cells. Fluorescent-labeledinhibitor could be observed in the cells within 15 min of incubationand is present in distinct intercellular vacuoles within 1 h.These results indicate that carboxypeptidase inhibitor and InhibitorII are internalized by C3H/10T1/2 cells and thus would be ableto inhibit intracellular proteases (or other enzymes) involvedin the conversion of a cell to the malignant state.