Cancer metastasis, or the migration of cancer cells from the primary loci is the major cause of death. Matriptase is a large transmembrane serine protease, originally isolated from the extracellular domain of human mammary epithelial cells. Overexpression of this membrane bound protease on cancer cells functions in the degradation of extracellular matrix. Matriptase activates hepatocyte growth factor by a specific proteolytic cleavage. It also activates urokinase-type plasminogen activator, and also the protease activated receptor-2. Based on these biological functions of Matriptase, developing inhibitors to Matriptase may provide therapeutic applications to the prevention of cancer cell invasion and metastasis.
Our aim i n this project is to develop selective inhibitors to Matriptase, as a way of inhibiting the metastatic and oncogenic cell proliferation. Several years ago we discovered that a bicyclic cage-like conformationally restricted, and proteolytically stable cyclopeptide natural product, termed SFTI-1, inhibited the matriptase enzyme, with an impressive Ki of 0.92 nM. To date, we have prepared 17 analogs of these cyclopeptidic protease inhibitors, including redox stable analogs of the disulfide linkage. We have the task to develop selective agents that minimize the deleterious effect of SFTI analogs on other physiologically required trypsin/chymotrypsin family of enzymes. Our collaborators at the Lombardi Cancer Center evaluated SFTI-1 in matriptase expressing tumor bearing mice. Significant survival promoting effect was observed with as little as 10 ug SFTI-1 per day treatment of mice with implanted ovarian tumor cells. Our small drug-like inhibitors may function as metastasis inhibitors. Results may also corroborate the idea that populations which consume substantially more legumes in their diets that contain natural related protease inhibitors, have relatively lower incidences of prostate, colon, breast and skin cancers. Our laboratory has also been interested in developing experimental anti-HIV agents. Integrase is an attractive target because it has no counterpart in mammalian cells; therefore, selective integrase inhibitors should not produce any toxicity. The complex mechanism of integrase function poses a challenging opportunity for enzyme inhibitor design. In this regard, we have identified a tryptophan rich natural product peptide, termed indolicidin, with a sequence of Ile-Leu-Pro-Trp-Lys-Trp-Pro-Trp-Trp-Pro-Trp-Arg-Arg. Robinson's group discovered that this 13 amino acid long peptide showed anti-HIV activity, and suggested a membrane -mediated mechanism for its antiviral activity. We carried out selective modifications of this initial peptide sequence, including construction of covalently linked tetrameric constructs. These efforts produced a 100-fold more potent integrase inhibitory agent with an IC50 of 0.6 microM. These results support the hypothesis that multimeric inhibitory peptides may act as multivalent inhibitors, simultaneously occupying two or four neighboring catalytic sites within the integrase oligomeric complex.
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