title: Everolimus suppresses cancellous bone loss, bone resorption, and cathepsin K expression by osteoclasts.
abstract: The proliferation inhibitor of the macrolide class, everolimus, is a drug shown to be effective in the prevention of organ transplant rejection and to have a potential in the treatment of rheumatoid arthritis and certain cancers. As these diseases or their current treatments are associated with bone loss, we examined the effect of everolimus on mouse and human bone cells in vitro and on bone in an ovariectomized (OVX) rat model. Everolimus potently inhibited primary mouse and human osteoclast activity in the pit assay (IC50 values of 0.6-4.0 nM), as well as osteoclast formation, measured as the number of tartrate-resistant acid phosphatase (TRAP) multinucleated cells (IC50 values of 7.7-10.5 nM). Inhibition of osteoblastic differentiation was also observed (IC50 value of 13.5 nM). As expected, everolimus inhibited proliferation of osteoclast precursors and stimulated apoptosis, albeit with insufficient potency and efficacy to explain inhibition of osteoclast activity. Thus, everolimus appeared to directly inhibit bone resorption, which is in accord with the detected inhibition of mRNA and protein expression of cathepsin K; the main collagen-degrading protease in osteoclasts. Despite the in vitro antiproliferative activity of everolimus and the observed inhibition of osteoblast differentiation, no detrimental effects were detected at different skeletal sites in mature OVX rats at doses up to 3 mg/kg/day. This everolimus dose also prevented the OVX-induced loss of cancellous bone by 60%, an effect predominantly associated with decreased osteoclast-mediated bone resorption, resulting in a partial preservation of the cancellous bone network. Everolimus inhibited S6 kinase 1 activity in rat blood cells, skin, and bone, at doses equivalent to those used for efficacy experiments in the OVX rat model, which demonstrated in vivo targeting of the expected molecular pathway. In conclusion, everolimus directly inhibits bone resorption by osteoclasts and thus could at least be neutral or protective for bone in vivo, which would favor its use in disease indications associated with bone loss.
authors.affiliation: Arthritis and Bone Metabolism Disease Area, Novartis Institutes for BioMedical Research Basel, Basel, Switzerland.
authors.forename: Michaela
authors.initials: M
authors.lastname: Kneissel
authors.forename: Ngoc-Hong
authors.initials: NH
authors.lastname: Luong-Nguyen
authors.forename: Myma
authors.initials: M
authors.lastname: Baptist
authors.forename: Reto
authors.initials: R
authors.lastname: Cortesi
authors.forename: Sabine
authors.initials: S
authors.lastname: Zumstein-Mecker
authors.forename: Sophia
authors.initials: S
authors.lastname: Kossida
authors.forename: Terry
authors.initials: T
authors.lastname: O'Reilly
authors.forename: Heidi
authors.initials: H
authors.lastname: Lane
authors.forename: Mira
authors.initials: M
authors.lastname: Susa
mesh_terms: D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D015519:Bone Density / Q000187:drug effects; D001862:Bone Resorption / Q000188:drug therapy*; D001842:Bone and Bones / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D002113:Calcification, Physiologic / Q000187:drug effects; D056657:Cathepsin K; D002403:Cathepsins / Q000235:genetics* / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D000068338:Everolimus; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006131:Growth Inhibitors / Q000494:pharmacology; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010052:Ovariectomy; D011494:Protein Kinases / Q000235:genetics; D051381:Rats; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D006131:Growth Inhibitors; D000068338:Everolimus; D011494:Protein Kinases; D019893:Ribosomal Protein S6 Kinases; D002403:Cathepsins; C534130:CTSK protein, human; D056657:Cathepsin K; C534132:Ctsk protein, mouse; C534133:Ctsk protein, rat; D020123:Sirolimus