Abstract
Cathepsin K is a lysosomal cysteine protease that is a pharmacological target for the treatment of osteoporosis. Previous studies showed that basic, lipophilic cathepsin K inhibitors are lysosomotropic and have greater activities in cell-based assays against cathepsin K, as well as the physiologically important lysosomal cysteine cathepsins B, L, and S, than expected based on their potencies against these isolated enzymes. Long-term administration of the basic cathepsin K inhibitors N-(1-(((cyanomethyl)amino)carbonyl)cyclohexyl)-4-(2-(4-methyl-piperazin-1-yl)-1,3-thiazol-4-yl)benzamide (L-006235) and balicatib to rats at a supratherapeutic dose of 500 mg/kg/day for 4 weeks resulted in increased tissue protein levels of cathepsin B and L but had no effect on cathepsin B and L message. This is attributed to the inhibitor engagement of these off-target enzymes and their stabilization to proteolytic degradation. No such increase in these tissue cathepsins was detected at the same dose of N-(cyanomethyl)-N2-{(1S)-2,2,2-trifluoro-1-[4'-methylsulfonyl)biphenyl-4-yl]ethyl}-l-leucinamide (L-873724), a potent nonbasic cathepsin K inhibitor with a similar off-target profile, although all three inhibitors provided similar plasma exposures. Using an activity-based probe, 125I-BIL-DMK, in vivo inhibition of cathepsins B, L, and S was detected in tissues of mice given a single oral dose of L-006235 and balicatib, but not in mice given L-873724. In each case, similar tissue levels were achieved by all three compounds, thereby demonstrating the in vivo cathepsin selectivity of L-873724. In conclusion, basic cathepsin K inhibitors demonstrate increased off-target cysteine cathepsin activities than their nonbasic analogs and potentially have a greater risk of adverse effects associated with inhibition of these cathepsins.
Footnotes
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ABBREVIATIONS: Cat, cathepsin; BIL-DMK, biphenyl-leucine-diazomethylketone; E-64, trans-epoxysuccinyl-L-leucylamido(4-guanidino)butane; Ca-074, N-(3-propylcarbamoyloxirane-2-carbonyl)-isoleucyl-proline; CHO, aldehyde; Z-, N-benzyloxycarbonyl; AMC, amino-4-methylcoumarin; Ac-, N-acetyl; EDANS, 5-[(2-aminoethyl)amino]naphthalene-1-sulfonyl; DABCYL, 4-dimethylaminoazobenzene-4′-sulfonyl; MES, 2-(N-morpholino)-ethanesulfonic acid; NAGA, β-N-acetylglucosaminidase; PAGE, polyacrylamide gel electrophoresis; RT, reverse transcription; PCR, polymerase chain reaction; TBST, Tris-buffered saline/0.1% Tween 20; AUC, area under the curve; ABP, activity-based probe; L-873724, N-(cyanomethyl)-N2-{(1S)-2,2,2-trifluoro-1-[4'-methylsulfonyl)biphenyl-4-yl]ethyl}-l-leucinamide.
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↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
- Received June 29, 2007.
- Revision received October 12, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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