title: Effect of cathepsin k inhibitor basicity on in vivo off-target activities.
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)-N(2)-{(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, (125)I-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.
authors.affiliation: Department of Biochemistry and Molecular Biology, Merck Frosst Centre for Therapeutic Research, P.O. Box 1005, Pointe-Claire-Dorval, Quebec, Canada.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Desmarais
authors.forename: W Cameron
authors.initials: WC
authors.lastname: Black
authors.forename: Renata
authors.initials: R
authors.lastname: Oballa
authors.forename: Sonia
authors.initials: S
authors.lastname: Lamontagne
authors.forename: Denis
authors.initials: D
authors.lastname: Riendeau
authors.forename: Paul
authors.initials: P
authors.lastname: Tawa
authors.forename: Le Thi
authors.initials: LT
authors.lastname: Duong
authors.forename: Maureen
authors.initials: M
authors.lastname: Pickarski
authors.forename: M David
authors.initials: MD
authors.lastname: Percival
mesh_terms: D000818:Animals; D056657:Cathepsin K; D002403:Cathepsins / Q000037:antagonists & inhibitors*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D051379:Mice
chemical_list: D004791:Enzyme Inhibitors; D002403:Cathepsins; D056657:Cathepsin K; C534132:Ctsk protein, mouse; C534133:Ctsk protein, rat