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Updated: Jun 23, 2026
Kinase Inhibitor Screening In Self-assembled Human Protein Microarrays
Published on: October 23, 2019
Pharmacological inhibitors to identify roles of cathepsin K in cell-based studies: a comparison of available tools
Sylvie Desmarais1, Frédéric Massé, M David Percival
1Department of Discovery Biology, Merck Frosst Center for Therapeutic Research, Kirkland, Quebec, Canada.
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.
Insights
Evaluating Cathepsin K inhibitors for osteoporosis research is crucial. L-873724 and odanacatib show high selectivity and cell permeability, making them valuable tools for studying Cathepsin K
Area of Science:
- Biochemistry
- Pharmacology
- Cell Biology
Background:
- Cathepsin K (Cat K) is a key enzyme in bone resorption and a therapeutic target for osteoporosis.
- Emerging research suggests additional roles for Cat K, often investigated using selective inhibitors in cell-based assays.
Purpose of the Study:
- To evaluate the selectivity and cell permeability of twelve Cathepsin K inhibitors.
- To determine the suitability of these inhibitors as research tools for studying Cat K in human cell-based systems.
Main Methods:
- Profiling twelve Cat K inhibitors against purified human, rat, and mouse cysteine cathepsins.
- Assessing inhibitor activity against Cat K, B, and L in cell-based enzyme occupancy assays.
- Investigating the cellular accumulation and properties of specific inhibitors, such as balicatib.
Main Results:
- Ten of the twelve inhibitors exhibited limited Cat K selectivity or poor cell penetration.
- L-873724 and odanacatib demonstrated over 100-fold selectivity for human Cat K and consistent cellular activity.
- Balicatib displayed unexpected cellular potency, attributed to lysosomotropic properties.
Conclusions:
- L-873724 and odanacatib are recommended as reliable tools for investigating novel Cat K functions in human cell-based studies.
- Caution is advised when interpreting results from studies using other evaluated Cat K inhibitors due to selectivity or cell penetration issues.
