Cathepsin B-like activity in viable tumor cells isolated from rodent tumors

The cathepsin B-like cysteine proteinase activity which has been implicated in tumor malignancy has been attributed to several cellular sources, including viable tumor cells, necrotic tumor cells, and host-inflammatory cells. We have isolated subpopulations of cells from eight rodent tumors of five histological types, using centrifugal elutriation, and verified the cellular composition of the subpopulations cytologically. Ninety-two % or greater of the cathepsin B-like activity was associated with the isolated fractions containing greater than or equal to 95% tumor cells of 86 +/- 2% (SE) viability (beta fractions). The isolated fractions consisting of necrotic tumor cells and inflammatory cells (alpha fraction) apparently contain a cysteine proteinase inhibitor, since both cathepsin B-like and cathepsin H activities in the beta fraction of B16 amelanotic melanomas could be inhibited by addition of the alpha fraction.