Abstract 3848: Functionalized small-molecule thiosemicarbazones as inhibitors of cathepsin K-mediated collagenase activity (2018)

Abstract The metastatic spread of malignant cells from a primary tumor remains the major cause of death in cancer patients. Metastasis also contributes significantly to the debilitating side effects and pain associated with the disease. For example, patients with advanced breast cancer have a high rate of skeletal metastases that can result in intractable bone pain, nerve compression syndrome-associated paralysis, pathologic bone fractures and hypercalcemia. Clearly, the prevention and management of bone metastases has significant potential to improve the quality of life and survival of breast cancer patients. Recently, CatK was found to be overexpressed in various types of cancers, including highly metastatic breast, prostate, osteosarcoma melanoma and glioma cancers. In bone remodeling, the degradation of type I collagen, the major component of the organic matrix in bone, as well as other proteins is largely accomplished by cathepsin K (CatK) with a contribution by neutral matrix metalloproteinases. CatK is a powerful proteolytic enzyme that is synthesized as a proenzyme and is abundantly expressed by osteoclasts, multinucleated cells that form a specialized sealing zone within which their ruffled border secretes acid to dissolve the mineral component, and proteinases to degrade the organic component of bone. Procathepsin K (proCatK) is autocatalytically activated under acidic conditions, and can also be cleaved to its active form by other proteolytic enzymes. It is the major cysteine proteinase of osteoclast lysosomes. While CatK quickly loses activity after cleavage of its proenzyme in vitro, additional studies have shown that the enzyme is greatly stabilized by complex formation with the glycosaminoglycan chondroitin sulfate. Small-molecule thiosemicarbazones have received special attention due to their antibacterial, antiviral, antifungal and antineoplastic effects. Recent studies have also confirmed that thiosemicarbazones have the ability to inhibit human and parasitic cathepsin L like-cysteine proteases and the mammalian cathepsin L. This work reports the investigation of a library of thiosemicarbazones synthesized to test their efficiency to inhibit human cathepsin K. Nine thiosemicarbazone (TSC) compounds had IC50 values of less than 50 nM against CatK using a fluorogenic assay with Z-L-Phe-L-Arg-AMC. Kinetics of their inhibition demonstrated that they were time-dependent but slowly reversible enzyme inhibitors. One of these compounds was shown to inhibit the activity of CatK against collagen. This compound also inhibited the cleavage of the proenzyme to its mature form. The activity of CatK was greatly stabilized by the inclusion of chondroitin sulfate in the reaction mixture, but inhibition of the enzyme was not affected. These data indicate that potent, small-molecule TSC CatK inhibitors may be useful to prevent the metastatic spread of cancer to bone. Citation Format: Mary Lynn Trawick, Kevin G. Pinney. Functionalized small-molecule thiosemicarbazones as inhibitors of cathepsin K-mediated collagenase activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3848.