TUMOR PROTEASE-ACTIVATED, PORE-FORMING TOXINS FROM A COMBINATORIAL LIBRARY

We describe a library of two-chain molecular complementation mutants o f staphylococcal alpha-hemolysin that features a combinatorial cassett e encoding thousands of protease recognition sites in the central pore -forming domain. The cassette is flanked by a peptide extension that i nactivates the protein. We screened the library to identify alpha-hemo lysins that are highly susceptible to activation by cathepsin B, a pro tease that is secreted by certain metastatic tumor cells. Toxins obtai ned by this procedure should be useful for the permeabilization of mal ignant cells thereby leading directly to cell death or permitting dest ruction of the cells with drugs that are normally membrane impermeant.