Cathepsin V is a lysosomal cysteine peptidase, a member of the papain-like cysteine peptidase family. It is closely related to cathepsin L; however, like cathepsin L it is not ubiquitously expressed while its physiological expression is manly limited to thymus, testis, and corneal epithelium. In pathological processes, it is expressed also in other tissues. It contributes to cancer progression, where its increased expression was observed in colorectal and breast carcinomas, but not in the normal colon or mammary tissue. In addition, cathepsin V plays an important role in immune cells and in antitumor immune response, where it is involved in the activation of cystatin F, which impairs the function of cytotoxic cells. Due to its involvement in cancer progression, targeting this enzyme with selective inhibitors may open new possibilities for improvements in cancer immunotherapy.
For this purpose, we tested compounds obtained from virtual chemical libraries, by their molecular docking into the active site of cathepsin V. Their inhibition of cathepsin V activity and selectivity for cathepsin V compared to cathepsin L was evaluated by using enzyme kinetics and microscale thermophoresis. Compounds 7, 26, and 28 were identified as the most potent inhibitors of cathepsin V. Compounds 7 and 28 are selective inhibitors of cathepsin V while compound 26 is a non-selective inhibitor. Best performing compounds were further tested for their effect on cell viability to determine non-cytotoxic compound concentrations. Compounds 7, 26, and 28 did not have cytotoxic effect on cells at concentrations lower than 5 μM. Moreover, additional compounds were selected form commercially available compound libraries based on the structural properties and evaluated for inhibition and selectivity for cathepsin V using enzyme kinetics. Among them, compounds 43 and 45 were the strongest and most selective inhibitors of cathepsin V.
In our work, as the most potent cathepsin V inhibitor, we identified the piperidine carboxylate derivative, compound 7. This compound has great potential for further development of reversible, selective, and non-toxic cathepsin V inhibitors that could be used as possible antitumor agents.
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