Effect of leupeptin, a protease inhibitor, on the development of spontaneous tumors in strain A mice.

The effect of leupeptin, a protease inhibitor, on the development of spontaneous tumors was studied in strain A mice. Three-week-old mice were divided into two groups: one group was fed on diet containing 0.1% leupeptin and the other was fed on basal diet. The experiment was terminated 480 days after the start of a administration of the leupeptin diet. Almost all animals survived until the end of the experiment. In the group given the leupeptin diet, 15 of 50 mice developed liver tumors (14 of 25 males and 1 of 25 females). In the control group, only male mice developed liver tumors (4 of 23 males). There was a significant difference between the incidences of liver tumors in males fed leupeptin diet and basal diet, but there was not in the case of females.