title: Lysosomotropism of basic cathepsin K inhibitors contributes to increased cellular potencies against off-target cathepsins and reduced functional selectivity.
abstract: The lysosomal cysteine protease cathepsin K is a target for osteoporosis therapy. The aryl-piperazine-containing cathepsin K inhibitor CRA-013783/L-006235 (1) displays greater than 4000-fold selectivity against the lysosomal/endosomal antitargets cathepsin B, L, and S. However, 1 and other aryl-piperazine-containing analogues, including balicatib (10), are approximately 10-100-fold more potent in cell-based enzyme occupancy assays than against each purified enzyme. This phenomenon arises from their basic, lipophilic nature, which results in lysosomal trapping. Consistent with its lysosomotropic nature, 1 accumulates in cells and in rat tissues of high lysosome content. In contrast, nonbasic aryl-morpholino-containing analogues do not exhibit lysosomotropic properties. Increased off-target activities of basic cathepsin K inhibitors were observed in a cell-based cathepsin S antigen presentation assay. No potency increases of basic inhibitors in a functional cathepsin K bone resorption whole cell assay were detected. Therefore, basic cathepsin K inhibitors, such as 1, suffer from reduced functional selectivities compared to those predicted using purified enzyme assays.
authors.affiliation: Department of Biochemistry, Merck Frosst Centre for Therapeutic Research, Kirkland, Quebec, Canada.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Falgueyret
authors.forename: Sylvie
authors.initials: S
authors.lastname: Desmarais
authors.forename: Renata
authors.initials: R
authors.lastname: Oballa
authors.forename: W Cameron
authors.initials: WC
authors.lastname: Black
authors.forename: Wanda
authors.initials: W
authors.lastname: Cromlish
authors.forename: Karine
authors.initials: K
authors.lastname: Khougaz
authors.forename: Sonia
authors.initials: S
authors.lastname: Lamontagne
authors.forename: Frederic
authors.initials: F
authors.lastname: Massé
authors.forename: Denis
authors.initials: D
authors.lastname: Riendeau
authors.forename: Sylvie
authors.initials: S
authors.lastname: Toulmond
authors.forename: M David
authors.initials: MD
authors.lastname: Percival
mesh_terms: D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects; D001345:Autoradiography; D001549:Benzamides / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology*; D050071:Bone Density Conservation Agents / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology; D002401:Cathepsin B / Q000037:antagonists & inhibitors; D056657:Cathepsin K; D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors*; D002460:Cell Line; D003546:Cysteine Endopeptidases; D005260:Female; D006801:Humans; D008247:Lysosomes / Q000187:drug effects* / Q000201:enzymology; D051379:Mice; D008810:Mice, Inbred C57BL; D009025:Morpholines / Q000737:chemistry / Q000494:pharmacology*; D010879:Piperazines / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats; D013329:Structure-Activity Relationship; D013844:Thiazoles / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology*; D014018:Tissue Distribution
chemical_list: D001549:Benzamides; D050071:Bone Density Conservation Agents; C507712:CRA 013783; D009025:Morpholines; D010879:Piperazines; D013844:Thiazoles; C529767:balicatib; D002403:Cathepsins; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; C534281:CTSL protein, human; D056668:Cathepsin L; C534278:Ctsl protein, mouse; C534280:Ctsl protein, rat; C028217:cathepsin S; C534130:CTSK protein, human; D056657:Cathepsin K; C534132:Ctsk protein, mouse; C534133:Ctsk protein, rat