title: Pharmacological inhibitors to identify roles of cathepsin K in cell-based studies: a comparison of available tools.
abstract: Cathepsin K (Cat K) degrades bone type I collagen and is a target for the pharmacological treatment of osteoporosis. Further roles for Cat K have been recently described, some of which are supported by the use of purportedly selective Cat K inhibitors in human and rodent cell-based assays. Twelve commercial and non-commercial Cat K inhibitors were profiled against a panel of purified human, rat, and mouse cysteine cathepsins and in two cell-based enzyme occupancy assays for activity against Cat K, B, and L. Ten inhibitors, including the carbohydrazide Cat K inhibitor II (Boc-Phe-Leu-NHNH-CO-NHNH-Leu-Z), the non-covalent K4b, and the epoxide NC-2300, have either little Cat K selectivity, or appear poorly cell penetrant. The amino-acetonitrile-containing inhibitors L-873724 and odanacatib show greater than 100-fold human Cat K enzyme selectivity and have similar IC(50) values against each cathepsin in cell-based and enzyme assays. The basic inhibitor balicatib has greater cellular potencies than expected on the basis of purified enzyme assays. The accumulation of [(14)C]-balicatib in fibroblasts is blocked by prior treatment of the cells with NH(4)Cl, consistent with balicatib having lysosomotropic properties. These results support the use of L-873724 and odanacatib as tools to identify novel roles for Cat K using human cell-based systems, but suggest using caution in the interpretation of studies employing the other compounds.
authors.affiliation: Department of Discovery Biology, Merck Frosst Center for Therapeutic Research, Kirkland, Quebec, Canada.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Desmarais
authors.forename: Frédéric
authors.initials: F
authors.lastname: Massé
authors.forename: M David
authors.initials: MD
authors.lastname: Percival
mesh_terms: D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D001713:Biphenyl Compounds / Q000494:pharmacology; D056657:Cathepsin K; D002403:Cathepsins / Q000037:antagonists & inhibitors*; D002460:Cell Line; D045744:Cell Line, Tumor; D004852:Epoxy Compounds / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects*; D006801:Humans; D006834:Hydrazines / Q000494:pharmacology; D051379:Mice; D015394:Molecular Structure; D010879:Piperazines / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats
chemical_list: D001549:Benzamides; D001713:Biphenyl Compounds; D004852:Epoxy Compounds; D006834:Hydrazines; C527129:L-873724; D010879:Piperazines; D011480:Protease Inhibitors; C529767:balicatib; D002403:Cathepsins; C534130:CTSK protein, human; D056657:Cathepsin K; C534132:Ctsk protein, mouse; C534133:Ctsk protein, rat; C527128:odanacatib; C019289:carbohydrazide