Anticarcinogenic action of protease inhibitors.
Protease inhibitors are synthesized in biological systems and play a critical role in controlling a number of diverse physiological functions. They participate in blood clotting and lysis of clots, in growth processes by modulation of proteolytic digestion of proteins and thus availability of amino acids, and in the induction of selective DNA amplification. When incorporated into the diet, protease inhibitors appear to suppress many types of cancer. In vitro, they suppress neoplastic transformation caused by chemical carcinogens, ionizing radiation, and oncogenes. These observations offer the hope that judiciously applied protease inhibitors in small concentrations may prevent a wide range of human cancers. This hope is further supported by epidemiological studies which show that populations consuming relatively large amounts of protease inhibitors have a lower occurrence of cancer. The tasks remaining are to determine the kind and the level of protease inhibitors that are most effective in preventing cancer without also having toxic side effects and to incorporate them into our diet. Perhaps the most encouraging investigations are those using small nontoxic protease inhibitors available in pure form (epsilon-aminocaproic acid, a trypsin plasminogen activator inhibitor, and nicotinamide, a chymotrypsin inhibitor and known vitamin). Both agents have been shown to be preventive agents of cancer in animals and in vitro models. Further studies with natural protease inhibitors may yield even more effective agents which when incorporated into our diet will prevent the development of many types of cancer.