Highly specific protease inhibitors provide new tools for disease research

Using the serine protease inhibitor ecotin as a scaffold, chemists have engineered protease inhibitors with specificity comparable to that of monoclonal antibodies.

These new tools may rival knock-out gene models and RNA interference for dissecting complex biological pathways and identifying new therapeutics for human disease, co-investigator Dr. Charles S. Craik told Reuters Health. “About 3% of the human genome encodes proteases in general, and of that, approximately half are serine proteases,” Dr. Craik noted. Serine proteases are involved in widely diverse physiological processes, such as blood coagulation, fertility, and host defense, and some have been implicated in cancer and other diseases.Ecotin is a macromolecule highly expressed by Escherichia coli that presents a large protease-inhibitor interface involving four surface loops organized in primary and secondary binding sites, Drs. Craik and A. Allart Stoop, both at the University of California San Francisco, explain in Nature Biotechnology, published online August 17th.Even though previous attempts to re-engineer ecotin to inhibit individual proteases resulted in relatively potent agents, their use was limited by low specificity. The two researchers have developed agents that exert specific inhibition by mutagenizing the four surface loops simultaneously, while avoiding destabilization in the backbone of the ecotin scaffold.So far they have developed ecotin variants specific to three different human serine proteases: plasma kallikrein (Pkal), membrane-type serine protease 1 (MT-SP1), and the coagulation protease Factor XIIa.”Membrane-type serine proteases are a class of enzymes bound to the surface of epithelial cells,” Dr. Craik said. Using their ecotin-based scaffold, the researchers were able to block MT-SP1 at a functional level, and are investigating the role of these proteases in ovarian and prostate cancer development.Pkal, on the other hand, affects adipocyte development. When the Pkal inhibitor was used to treat mice, “the mice gained less weight,” Dr. Craik noted, suggesting an “extremely exciting” development in obesity research.The investigators have filed a patent application for the ecotin scaffold.(Source: Nat Biotechnol online edition August 17, 2003: Reuters Health: Karla Gale: August 21, 2003: Oncolink)