Evidence for the induction of protease activity on cultured tumour cells as a consequence of implantation into nude mice.

We have studied the enzymic status of a tumour associated protease on human colonic tumour cells cultured in vitro and grown in vivo in nude mice. The cultured tumour cells lack this protease. The cells of the tumour colonies in the mice possess active enzyme although the tissue contains an inhibitor capable of inactivating this tumour cell protease. The evidence indicates that the induction of this protease on the tumour cells is a consequence of implantation of the cultured cells into the nude mouse.