Effect on Tumor Homografts of Treating Hosts with Antiproteolytic Enzyme Compounds.

Two compounds, EACA and SBTI, known suppressors of certain proteolytic enzymes, were administered daily to mice that had been inoculated with a tumor that they normally reject. Nearly half of all the Strain A and C-57Bl mice treated with either agent developed large tumors within 12 days. No tumor growth was seen in any of the untreated control animals. Of the 18 mice given combined doses of both compounds, 15 developed sizable tumors. The tumors always reached a maximum size and then regressed. Therefore, it seems that proteolytic enzymes participate in the rejection of homotransplanted tumors, but that suppressing their effect merely attenuates the immune response, and other mechanisms eventually cause the demise of the tissue.