A novel approach to inhibit bone resorption: exosite inhibitors against cathepsin K

Abstract

BACKGROUND AND PURPOSECathepsin 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. EXPERIMENTAL APPROACHHuman 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. KEY RESULTSDHT1 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 IC 50 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 AND IMPLICATIONSOur study shows that an exosite inhibitor of CatK can specifically block bone resorption without interfering with other pathways. Abbreviations

Osteoimmunology and Beyond

“…OC are multinucleated myeloid cells, specialized to remove mineralized bone matrix through the production of lysosomal enzymes, such as tartrate-resistant acid phosphatase (TRAP) and catepsin k, against which a selective inhibitor (odanacatib) has been recently synthesized to be employed in osteoporotic patients [12]. They derive from a bone marrow precursor which gives rise also to professional antigen presenting cells (APC), i.e.…”

“…Bisphosphonates, drugs used for some time in the therapy of osteoporosis, are potent inhibitors of OC activity both in the primitive and secondary osteoporosis, such as that associated with autoimmune diseases [61,62]. A decreased BMD in the spine and hip and higher prevalence of osteoporosis have been described in RA patients [63]. In early untreated RA, BMD is related to longer symptom duration, the presence of rheumatoid factor (RF) and cyclic citrulinated peptide antibodies (anti-CCP), disease activity score, and the presence and progression of joint damage [1, 19].…”

Suppression of Notch Signaling in Osteoclasts Improves Bone Regeneration and Healing

“…Cortical bone slices (Immunodiagnostic Systems, East Boldon, UK) were purchased for in vitro assessment of osteoclastic bone resorption using pit formation assay as per the procedure described with slight modifications . Bone chips were sterilized under ultraviolet for at least 2 h and then washed with media before placing in 96‐well plates.…”

Cathepsin K osteoporosis trials, pycnodysostosis and mouse deficiency models: Commonalities and differences

“…We have recently demonstrated that an exosite inhibitor of CatK is capable of inhibiting bone resorption in an osteoclast assay indistinguishable from and with only a slightly lesser potency to that of odanacatib. [170] This compound specifically blocks the collagenase activity of CatK by binding in an exosite remote from the active site without interfering with the degradation of cytokines such as TGF-ß1. Here it is of interest that a previously identified pycnodysostosis-causing point mutation (Y283C) is located in the putative exosite.…”