title: A novel approach to inhibit bone resorption: exosite inhibitors against cathepsin K.
abstract: OBJECTIVE
  Cathepsin K (CatK) is a major drug target for the treatment of osteoporosis. Potent active site-directed inhibitors have been developed and showed variable success in clinical trials. These inhibitors block the entire activity of CatK and thus may interfere with other pathways. The present study investigates the antiresorptive effect of an exosite inhibitor that selectively inhibits only the therapeutically relevant collagenase activity of CatK.
  
  
  METHODS
  Human osteoclasts and fibroblasts were used to analyse the effect of the exosite inhibitor, ortho-dihydrotanshinone (DHT1), and the active site inhibitor, odanacatib (ODN), on bone resorption and TGF-ß1 degradation. Cell cultures, Western blot, light and scanning electron microscopy as well as energy dispersive X-ray spectroscopy, molecular modelling and enzymatic assays were used to evaluate the inhibitors.
  
  
  RESULTS
  DHT1 selectively inhibited the collagenase activity of CatK, without affecting the viability of osteoclasts. Both inhibitors abolished the formation of resorption trenches, with DHT1 having a slightly higher IC50 value than ODN. Maximal reductions of other resorption parameters by DHT1 and ODN were comparable, respectively 41% and 33% for total resorption surface, 46% and 48% for resorption depths, and 83% and 61% for C-terminal telopetide fragment (CTX) release. DHT1 did not affect the turnover of fibrosis-associated TGF-ß1 in fibroblasts, whereas 500 nM ODN was inhibitory.
  
  
  CONCLUSIONS
  Our study shows that an exosite inhibitor of CatK can specifically block bone resorption without interfering with other pathways.
authors.affiliation: Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada.|Center for Blood Research, Vancouver, BC, Canada.|Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark, Vejle, Denmark.
authors.forename: Preety
authors.initials: P
authors.lastname: Panwar
authors.affiliation: Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark, Vejle, Denmark.
authors.forename: Kent
authors.initials: K
authors.lastname: Søe
authors.affiliation: Laboratório de Química Medicinal e Computacional, Centro de Inovação em Biodiversidade e Fármacos, Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, Brazil.
authors.forename: Rafael Vc
authors.initials: RV
authors.lastname: Guido
authors.affiliation: Laboratório de Química Medicinal e Computacional, Centro de Inovação em Biodiversidade e Fármacos, Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, Brazil.
authors.forename: Renata V C
authors.initials: RV
authors.lastname: Bueno
authors.affiliation: Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark, Vejle, Denmark.
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Delaisse
authors.affiliation: Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada.|Center for Blood Research, Vancouver, BC, Canada.|Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Dieter
authors.initials: D
authors.lastname: Brömme
mesh_terms: D045784:Abietanes / Q000378:metabolism* / Q000494:pharmacology / Q000627:therapeutic use; D000818:Animals; D001713:Biphenyl Compounds / Q000378:metabolism* / Q000494:pharmacology / Q000627:therapeutic use; D001862:Bone Resorption / Q000188:drug therapy / Q000378:metabolism*; D056657:Cathepsin K / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism; D017434:Protein Structure, Tertiary
chemical_list: D045784:Abietanes; D001713:Biphenyl Compounds; C021751:tanshinone; D056657:Cathepsin K; C527128:odanacatib