Author Interviews, Osteoporosis, Pharmacology / 30.08.2017
New Approach Could Lead To Osteoporosis Drugs With Fewer Side Effects
MedicalResearch.com Interview with:
Dieter Bromme, Ph.D.
Professor and Canada Research Chair
The University of British Columbia Faculty of Dentistry
Vancouver, BC
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: Every three seconds somebody will fracture a bone because of osteoporosis. Several treatments are available to slow down bone loss but all of them have shortcomings ranging from poor bone quality to various side effects. Thus new treatment strategies and novel drug targets are needed that promise efficacy without significant adverse reactions.
One of the novel promising targets was cathepsin K, a protease solely responsible for the degradation of our organic bone matrix. Major efforts and funds were spent by the pharmaceutical industry to develop potent and selective cathepsin K inhibitors. These inhibitors were highly effective in preserving bone in clinical trials. Despite the good news, cathepsin K inhibitors were never approved because of various non-skeletal side effects. We hypothesized that these side effects are not caused by off-target effects (drugs react with undesired targets) but by on-target effects. Most drugs that target enzymes are active site-directed compounds and thus will stop the entire activity of the target enzyme. If the target is a multifunctional enzyme, safety problems are preprogrammed. Based on our studies to understand the molecular mechanism of collagen degradation by cathepsin K, we developed the concept of ectosteric enzyme inhibition, which allowed us to identify highly selective collagenase inhibitors of this protease.
In our study, we used a red sage-derived small molecule that selectively blocked the collagenase activity of cathepsin K and thus consequently bone degradation in an osteoporosis mouse model without affecting other known functions of the protease. The crucial difference might be that the red sage inhibitor did not block the cathepsin K-mediated degradation of TGF-ß1, a growth factor involved in fibrotic pathologies described in the clinical trials. TGF-ß1 degradation is blocked by these inhibitors and thus accumulates in tissues, causing fibrosis.
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