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Updated: Oct 7, 2026

The Importance of Correct Protein Concentration for Kinetics and Affinity Determination in Structure-function Analysis
Published on: March 18, 2010
In vivo inhibition of cathepsin B by peptidyl (acyloxy)methyl ketones
B M Wagner1, R A Smith, P J Coles
1Department of Lipid and Protease Biochemistry, Syntex Research, Palo Alto, California 94304.
Abstract:
Peptidyl (acyloxy)methyl ketones, previously established as potent irreversible inhibitors of the cysteine proteinase cathepsin B in vitro, were investigated and optimized for their inhibitory activity in vivo. Incorporation of polar or charged functional groups in the inhibitor structure afforded effective cathepsin B inhibition, following dosing to rats. The most effective inhibitor, Z-Phe-Lys-CH2OCO-(2,4,6-Me3)Ph (8), was found to give ED50 values of 18 mg/kg po (orally) and 5.0 mg/kg ip (intraperitoneally) at 4-5 h postdose, and 2.4 mg/kg sc (subcutaneously) at 24 h postdose, for liver cathepsin B inhibition (measured ex vivo). The subcutaneous route of administration of (acyloxy)methyl ketone 8 also provided potent cathepsin B inhibition in certain peripheral tissues (e.g., ED50 1.0 mg/kg for skeletal muscle, 0.1 mg/kg for heart). These investigations demonstrate that peptidyl (acyloxy)methyl ketones such as 8 have promise as tools for the characterization of in vivo biochemical processes and as therapeutic agents.
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