Biochemical Studies of Cathepsin B and Cruzain Inhibitors Sharing a Thiosemicarbazone Moiety
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Over-expression of cysteine proteases has been implicated in a number of diseases, making them attractive targets for drug design. The cysteine protease, cathepsin B has been implicated in the degradation of the extracellular matrix and thereby facilitates tumor cell metastasis and invasiveness, suggesting that inhibition of cathepsin B may be an important target for anti-cancer treatment. Natural and synthetic inhibitors of cathepsin B have demonstrated selective enzyme inhibition, but many of these compounds exhibit peptidic characteristics, reducing their bioavailability. A separate cysteine protease, cruzain, is essential for the survival of Trypanasoma cruzi, the causative agent of Chagas’ disease and is involved in parasitic nutrition, replication, and evasion of the host immune system. In these studies, a library of small non-peptidic compounds that share a thiosemicarbazone moiety were analyzed against cathepsin B and cruzain. A number of thiosemicarbazone derivatives were found that exhibited IC50 values (the concentration of compound that resulted in fifty percent enzyme inhibition) in the lower micro-molar and nano-molar range against cathepsin B and cruzain respectively. Fluorometric microplate assays were used to determine IC50 values as a measure of effectiveness of the compounds. Advanced kinetic studies were conducted on cathepsin B in order to determine the mechanism of inhibition. Analysis of the structure activity relationships (SAR) of these compounds show promising results for drug design. These studies represent collaborative research between the Trawick (biochemistry) and Pinney (organic synthesis) Laboratories.