Odanacatib: a review of its potential in the management of osteoporosis in postmenopausal women

Emerging nano-scale delivery systems for the treatment of osteoporosis

Osteoporosis is a pathological condition characterized by an accelerated bone resorption rate, resulting in decreased bone density and increased susceptibility to fractures, particularly among the elderly population. While conventional treatments for osteoporosis have shown efficacy, they are associated with certain limitations, including limited drug bioavailability, non-specific administration, and the occurrence of adverse effects. In recent years, nanoparticle-based drug delivery systems have emerged as a promising approach for managing osteoporosis. Nanoparticles possess unique physicochemical properties, such as a small size, large surface area-to-volume ratio, and tunable surface characteristics, which enable them to overcome the limitations of conventional therapies. These nanoparticles offer several advantages, including enhanced drug stability, controlled release kinetics, targeted bone tissue delivery, and improved drug bioavailability. This comprehensive review aims to provide insights into the recent advancements in nanoparticle-based therapy for osteoporosis. It elucidates the various types of nanoparticles employed in this context, including silica, polymeric, solid lipid, and metallic nanoparticles, along with their specific processing techniques and inherent properties that render them suitable as potential drug carriers for osteoporosis treatment. Furthermore, this review discusses the challenges and future suggestions associated with the development and translation of nanoparticle drug delivery systems for clinical use. These challenges encompass issues such as scalability, safety assessment, and regulatory considerations. However, despite these challenges, the utilization of nanoparticle-based drug delivery systems holds immense promise in revolutionizing the field of osteoporosis management by enabling more effective and targeted therapies, ultimately leading to improved patient outcomes.

Cysteine Cathepsins as Therapeutic Targets in Immune Regulation and Immune Disorders

Cysteine cathepsins, as the most abundant proteases found in the lysosomes, play a vital role in several processes-such as protein degradation, changes in cell signaling, cell morphology, migration and proliferation, and energy metabolism. In addition to their lysosomal function, they are also secreted and may remain functional in the extracellular space. Upregulation of cathepsin expression is associated with several pathological conditions including cancer, neurodegeneration, and immune-system dysregulation. In this review, we present an overview of cysteine-cathepsin involvement and possible targeting options for mitigation of aberrant function in immune disorders such as inflammation, autoimmune diseases, and immune response in cancer.

Discovery of selective covalent cathepsin K inhibitors containing novel 4-cyanopyrimidine warhead based on quantum chemical calculations and binding mode analysis

Cathepsin K (Cat K), mainly expressed by osteoclasts, plays an important role in bone resorption. Covalent Cat K inhibitors will show great potential in the future treatment of osteoporosis. It has been reported that the selectivity of covalent cathepsin K inhibitors was related to the drug's safety. The type of warhead has a crucial influence on the enzyme bioactivity and selectivity of covalent inhibitors. In order to develop novel covalent inhibitors with the selective new warhead, quantum chemical calculations were performed to estimate the reactivity of the nitrile warheads. Moreover, binding mode analysis between ligands and high homology Cat K, S and B revealed differences in non-covalent interactions. Novel covalent Cat K inhibitors containing 4-cyanopyrimidine warhead (11) were determined for the first time. Among them, compound 34 significantly inhibited Cat K (IC50 = 61.9 nM) with excellent selectivity compared to Cat S (>810-fold) and Cat B (>1620-fold), respectively. Binding mode analysis of Cat K-34 complex provided the basis for further optimization. Compound 34 could be a valuable lead compound for further research on safe and effective Cat K inhibitors.

Osteoporosis therapies and their mechanisms of action (Review)

Osteoporosis is a common disease that affects millions of patients worldwide and is most common in menopausal women. The main characteristics of osteoporosis are low bone density and increased risk of fractures due to deterioration of the bone architecture. Osteoporosis is a chronic disease that is difficult to treat; thus, investigations into novel effective therapeutic methods are required. A number of studies have focused on determining the most effective treatment options for this disease. There are several treatment options for osteoporosis that differ depending on the characteristics of the disease, and these include both well-established and newly developed drugs. The present review focuses on the various drugs available for osteoporosis, the associated mechanisms of action and the methods of administration.

Duration-Dependent Increase of Human Bone Matrix Mineralization in Long-Term Bisphosphonate Users with Atypical Femur Fracture

Bisphosphonates (BPs) are the most widely used drugs for the treatment of osteoporosis but prolonged use of BPs might increase the risk of atypical femur fracture (AFF). There are only a few studies that address the bone material quality in patients on long-term BP treatment with or without AFFs. We analyzed 52 trans-iliac bone biopsies from patients on long-term BP therapy with (n = 26) and without (n = 26) AFF. At the microscopic level, the degree of mineralization of bone (DMB) was assessed on whole bone by X-ray digitized microradiography while microhardness by Vickers microindentation, and bone matrix characteristics by Fourier transform infrared microspectroscopy (FTIRM) (mineral/organic ratio, mineral maturity and crystallinity, and collagen maturity) were measured at random focal areas. The AFF patients were treated longer than non-AFF patients (9.7 ± 3.3 years versus 7.9 ± 2.7 years). As expected, bone remodeling was low in both groups, without difference between them. The AFF group had significantly higher DMB in cortical bone (+2.9%, p = .001), which remained so after adjusting for treatment duration (p = .007), and showed a trend in cancellous bone (+1.6%, p = .05). Consistent with higher DMB, heterogeneity index (HI) was lower in the AFF than in the non-AFF group, illustrating lower heterogeneity of mineralization in the AFF group. A significant positive correlation between the duration of treatment and DMB in cortical bone was found in AFF, and not in the non-AFF group. Microhardness and bone matrix characteristics were similar between groups. We conclude that the AFF group had a duration-dependent increase in DMB leading to a significantly higher DMB than the non-AFF. Because BPs have high affinity to bone mineral and lining the walls of the osteocyte lacunae, the accumulation of matrix-bound BPs in AFF could lead to inhibition of the osteocyte cytoskeleton blunting their response to mechanical strains, a hypothesis to be further investigated. © 2021 American Society for Bone and Mineral Research (ASBMR).

Covalent Small Molecule Immunomodulators Targeting the Protease Active Site

Cells of the immune system utilize multiple proteases to regulate cell functions and orchestrate innate and adaptive immune responses. Dysregulated protease activities are implicated in many immune-related disorders; thus, protease inhibitors have been actively investigated for pharmaceutical development. Although historically considered challenging with concerns about toxicity, compounds that covalently modify the protease active site represent an important class of agents, emerging not only as chemical probes but also as approved drugs. Here, we provide an overview of technologies useful for the study of proteases with the focus on recent advances in chemoproteomic methods and screening platforms. By highlighting covalent inhibitors that have been designed to target immunomodulatory proteases, we identify opportunities for the development of small molecule immunomodulators.

Dopamine D1 receptor stimulates cathepsin K-dependent degradation and resorption of collagen I in lung fibroblasts

Matrix resorption is essential to the clearance of the extracellular matrix (ECM) after normal wound healing. A disruption in these processes constitutes a main component of fibrotic diseases, characterized by excess deposition and diminished clearance of fibrillar ECM proteins, such as collagen type I. The mechanisms and stimuli regulating ECM resorption in the lung remain poorly understood. Recently, agonism of dopamine receptor D1 (DRD1), which is predominantly expressed on fibroblasts in the lung, has been shown to accelerate tissue repair and clearance of ECM following bleomycin injury in mice. Therefore, we investigated whether DRD1 receptor signaling promotes the degradation of collagen type I by lung fibroblasts. For cultured fibroblasts, we found that DRD1 agonism enhances extracellular cleavage, internalization and lysosomal degradation of collagen I mediated by cathepsin K, which results in reduced stiffness of cell-derived matrices, as measured by atomic force microscopy. In vivo agonism of DRD1 similarly enhanced fibrillar collagen degradation by fibroblasts, as assessed by tissue labeling with a collagen-hybridizing peptide. Together, these results implicate DRD1 agonism in fibroblast-mediated collagen clearance, suggesting an important role for this mechanism in fibrosis resolution.This article has an associated First Person interview with the first author of the paper.

Recent advances in seafood bioactive peptides and their potential for managing osteoporosis

Marine biodiversity provides a range of diverse biological resources, including seafoods that are rich in protein and a well-balanced amino acid composition. Previous studies have shown that peptides can improve bone formation and/or inhibit bone resorption, suggesting the potential for seafood bioactive peptides (SBPs) in development of food and pharmaceuticals for management of osteoporosis. In this review, we provided an up-to-date overview of the anti-osteoporosis activity of SBPs and describe their underlying molecular mechanisms. We focus on SBPs' development, broadening the scope and depth of research, as well as strengthening in vivo and clinical research. In vitro cell cultures and in vivo animal osteoporosis models have demonstrated the potential for seafood-derived SBPs, including fish, mollusks, crustaceans, seaweed and microalgae, in preventing osteoporosis. These peptides may act by activating the signaling pathways, such as BMP/Smads, MAPK, OPG/RANKL/RANK, and NF-κB, which are associated with modulation bone health.

The Potential Role of Cathepsin K in Non-Small Cell Lung Cancer

(1) Background: Cathepsin K has been found overexpressed in several malignant tumors. However, there is little information regarding the involvement of Cathepsin K in non-small cell lung cancer (NSCLC). (2) Methods: Cathepsin K expression was tested in human NSCLC cell lines A549 and human embryo lung fibroblast MRC-5 cells using Western blot and immunofluorescence assay. Cathepsin K was transiently overexpressed or knocked down using transfection with a recombinant plasmid and siRNA, respectively, to test the effects on cell proliferation, migration, invasion, and on the mammalian target of rapamycin (mTOR) signaling pathway. (3) Results: Expression of Cathepsin K was increased significantly in A549 cells and diffused within the cytoplasm compared to the MRC-5 cells used as control. Cathepsin K overexpression promoted the proliferation, migration, and invasion of A549 cells, accompanied by mTOR activation. Cathepsin K knockdown reversed the above malignant behavior and inhibited the mTOR signaling activation, suggesting that Cathepsin K may promote the progression of NSCLC by activating the mTOR signaling pathway. (4) Conclusion: Cathepsin K may potentially represent a viable drug target for NSCLC treatment.

Microbial lipases and their industrial applications: a comprehensive review

Lipases are very versatile enzymes, and produced the attention of the several industrial processes. Lipase can be achieved from several sources, animal, vegetable, and microbiological. The uses of microbial lipase market is estimated to be USD 425.0 Million in 2018 and it is projected to reach USD 590.2 Million by 2023, growing at a CAGR of 6.8% from 2018. Microbial lipases (EC 3.1.1.3) catalyze the hydrolysis of long chain triglycerides. The microbial origins of lipase enzymes are logically dynamic and proficient also have an extensive range of industrial uses with the manufacturing of altered molecules. The unique lipase (triacylglycerol acyl hydrolase) enzymes catalyzed the hydrolysis, esterification and alcoholysis reactions. Immobilization has made the use of microbial lipases accomplish its best performance and hence suitable for several reactions and need to enhance aroma to the immobilization processes. Immobilized enzymes depend on the immobilization technique and the carrier type. The choice of the carrier concerns usually the biocompatibility, chemical and thermal stability, and insolubility under reaction conditions, capability of easy rejuvenation and reusability, as well as cost proficiency. Bacillus spp., Achromobacter spp., Alcaligenes spp., Arthrobacter spp., Pseudomonos spp., of bacteria and Penicillium spp., Fusarium spp., Aspergillus spp., of fungi are screened large scale for lipase production. Lipases as multipurpose biological catalyst has given a favorable vision in meeting the needs for several industries such as biodiesel, foods and drinks, leather, textile, detergents, pharmaceuticals and medicals. This review represents a discussion on microbial sources of lipases, immobilization methods increased productivity at market profitability and reduce logistical liability on the environment and user.

Leading the invasion: The role of Cathepsin S in the tumour microenvironment

Elevated expression of the cysteine protease Cathepsin S has been correlated with a number of different cancer types in recent years. As tools have been developed to enable more accurate examination of individual cathepsin species, our knowledge and appreciation of the role that this protease plays in facilitating cancer has increased exponentially. This review focuses on our current understanding of the role of Cathepsin S within tumours and the surrounding microenvironment. While various publications have shown that Cathepsin S can be derived from tumour cells themselves, a plethora of more recent studies have identified that Cathepsin S can also be derived from other cell types within the tumour microenvironment including endothelial cells, macrophages and T cells. Furthermore, specific proteolytic substrates cleaved by Cathepsin S have also been identified which have reinforced our hypothesis that this protease facilitates key steps within tumours leading to their invasion, angiogenesis and metastasis.

Targeting fundamental aging mechanisms to treat osteoporosis

Introduction: Osteoporotic fractures represent a growing burden of mortality, morbidity and socioeconomic cost to health-care systems worldwide. Osteoporosis is a disease uniquely associated with aging, therefore, an understanding of the physiological mechanisms underpinning its development as we age may open new avenues for therapeutic exploitation. Novel treatments, as well as refinement of the current approaches, are vital in the effort to sustain healthy, independent patients across the lifespan.Areas covered: This review covers the anabolic and catabolic pathways seen in bone maintenance, highlighting how they are changed with age, leading to osteoporosis. It will also discuss how these changes may be targeted therapeutically, in the development of new therapies, and the refinement of those already in use.Expert opinion: New effective and safe treatments for osteoporosis are still needed. Bone anabolics seem to be the most appropriate therapeutic approach to osteoporosis in older persons. Considering that bone and muscle mass synchronically decline with aging thus predisposing older persons to falls and fractures, combined therapeutic approaches to osteosarcopenia with a dual anabolic effect on muscle and bone will be a major advance in the treatment of these devastating conditions in the future.

Applications of fluorine-containing amino acids for drug design

Fluorine-containing amino acids are becoming increasingly prominent in new drugs due to two general trends in the modern pharmaceutical industry. Firstly, the growing acceptance of peptides and modified peptides as drugs; and secondly, fluorine editing has become a prevalent protocol in drug-candidate optimization. Accordingly, fluorine-containing amino acids represent one of the more promising and rapidly developing areas of research in organic, bio-organic and medicinal chemistry. The goal of this Review article is to highlight the current state-of-the-art in this area by profiling 42 selected compounds that combine fluorine and amino acid structural elements. The compounds under discussion represent pharmaceutical drugs currently on the market, or in clinical trials as well as examples of drug-candidates that although withdrawn from development had a significant impact on the progress of medicinal chemistry and/or provided a deeper understanding of the nature and mechanism of biological action. For each compound, we present features of biological activity, a brief history of the design principles and the development of the synthetic approach, focusing on the source of tailor-made amino acid structures and fluorination methods. General aspects of the medicinal chemistry of fluorine-containing amino acids and synthetic methodology are briefly discussed.

Opportunities and challenges for the development of covalent chemical immunomodulators

Compounds that react irreversibly with cysteines have reemerged as potent and selective tools for altering protein function, serving as chemical probes and even clinically approved drugs. The exquisite sensitivity of human immune cell signaling pathways to oxidative stress indicates the likely, yet still underexploited, general utility of covalent probes for selective chemical immunomodulation. Here, we provide an overview of immunomodulatory cysteines, including identification of electrophilic compounds available to label these residues. We focus our discussion on three protein classes essential for cell signaling, which span the 'druggability' spectrum from amenable to chemical probes (kinases), somewhat druggable (proteases), to inaccessible (phosphatases). Using existing inhibitors as a guide, we identify general strategies to guide the development of covalent probes for selected undruggable classes of proteins and propose the application of such compounds to alter immune cell functions.

Atypical Femur Fractures: Review of Epidemiology, Relationship to Bisphosphonates, Prevention, and Clinical Management

Bisphosphonates (BPs) are highly effective in treating osteoporosis and reducing hip, vertebral, and other fractures by as much as 50% to 70%. However, since 2006, atypical femur fractures (AFFs) emerged as potential side effects of BPs and other treatments. These fractures have unusual radiologic features and occur with little trauma. Public concern has led to a >50% decrease in BP usage. AFFs are rare: for each AFF, >1200 fractures, including 135 hip fractures, are prevented. Case definition criteria were updated by the American Society of Bone and Mineral Research in 2014. Many epidemiologic studies have been reported, and although methodologically challenging, generally support a BP-AFF association. However, the magnitude of the association between BPs and AFFs is uncertain: estimates of relative risk for AFFs among BP users vs nonusers range from 1 to 65 with a meta-analysis estimate of 1.7. Although mechanistic studies have proposed several hypotheses explaining how BPs might decrease bone strength, AFF pathogenesis remains uncertain and cannot explain the paradox of efficacy of reduction of common fractures while increasing risk for rare fractures at one site. There are several consistent risk factors, including Asian race (in North America), femoral bowing, and glucocorticoid use, whereas others remain unclear. Consensus is emerging about strategies to prevent AFFs in BP users (including drug holidays after 5 years' use in some patients). In conclusion, AFFs can be devastating, but even under the most pessimistic assumptions, the benefit/risk ratio is highly positive for BPs, particularly during 3 to 5 years of use. As understanding of AFFs increases, it is becoming increasingly possible to maximize BP benefits while minimizing AFF risk.

Coupling factors involved in preserving bone balance

Coupling during bone remodeling refers to the spatial and temporal coordination of bone resorption with bone formation. Studies have assessed the subtle interactions between osteoclasts and osteoblasts to preserve bone balance. Traditionally, coupling research related to osteoclast function has focused on bone resorption activity causing the release of growth factors embedded in the bone matrix. However, considerable evidence from in vitro, animal, and human studies indicates the importance of the osteoclasts themselves in coupling phenomena, and many osteoclast-derived coupling factors have been identified. These include sphingosine-1-phosphate, vesicular-receptor activator of nuclear factor-κB, collagen triple helix repeat containing 1, and cardiotrophin-1. Interestingly, neuronal guidance molecules, such as slit guidance ligand 3, semaphorin (SEMA) 3A, SEMA4D, and netrin-1, originally identified as instructive cues allowing the navigation of growing axons to their targets, have been shown to be involved in the intercellular cross-talk among bone cells. This review discusses osteoclast-osteoblast coupling signals, including recent advances and the potential roles of these signals as therapeutic targets for osteoporosis and as biomarkers predicting human bone health.

Small molecule nAS-E targeting cAMP response element binding protein (CREB) and CREB-binding protein interaction inhibits breast cancer bone metastasis

Bone is the most common metastatic site for breast cancer. The excessive osteoclast activity in the metastatic bone lesions often produces osteolysis. The cyclic-AMP (cAMP)-response element binding protein (CREB) serves a variety of biological functions including the transformation and immortalization of breast cancer cells. In addition, evidence has shown that CREB plays a key role in osteoclastgenesis and bone resorption. Small organic molecules with good pharmacokinetic properties and specificity, targeting CREB-CBP (CREB-binding protein) interaction to inhibit CREB-mediated gene transcription have attracted more considerations as cancer therapeutics. We recently identified naphthol AS-E (nAS-E) as a cell-permeable inhibitor of CREB-mediated gene transcription through inhibiting CREB-CBP interaction. In this study, we tested the effect of nAS-E on breast cancer cell proliferation, survival, migration as well as osteoclast formation and bone resorption in vitro for the first time. Our results demonstrated that nAS-E inhibited breast cancer cell proliferation, migration, survival and suppressed osteoclast differentiation as well as bone resorption through inhibiting CREB-CBP interaction. In addition, the in vivo effect of nAS-E in protecting against breast cancer-induced osteolysis was evaluated. Our results indicated that nAS-E could reverse bone loss induced by MDA-MB-231 tumour. These results suggest that small molecules targeting CREB-CBP interaction to inhibit CREB-mediated gene transcription might be a potential approach for the treatment of breast cancer bone metastasis.

The Antiviral Potential of Host Protease Inhibitors

The replication of numerous pathogenic viruses depends on host proteases, which therefore emerged as potential antiviral drug targets. In some cases, e.g., for influenza viruses, their function during the viral propagation cycle is relatively well understood, where they cleave and activate viral surface glycoproteins. For other viruses, e.g., Ebola virus, the function of host proteases during replication is still not clear. Host proteases may also contribute to the pathogenicity of virus infection by activating proinflammatory cytokines. For some coronaviruses, human proteases can also serve in a nonproteolytical fashion simply as receptors for virus entry. However, blocking of such protein-protein contacts is challenging, because receptor surfaces are often flat and difficult to address with small molecules. In contrast, many proteases possess well-defined binding pockets. Therefore, they can be considered as well-druggable targets, especially, if they are extracellularly active. The number of their experimental crystal structures is steadily increasing, which is an important prerequisite for a rational structure-based inhibitor design using computational chemistry tools in combination with classical medicinal chemistry approaches. Moreover, host proteases can be considered as stable targets, and their inhibition should prevent rapid resistance developments, which is often observed when addressing viral proteins. Otherwise, the inhibition of host proteases can also affect normal physiological processes leading to a higher probability of side effects and a narrow therapeutic window. Therefore, they should be preferably used in combination therapies with additional antiviral drugs. This strategy should provide a stronger antiviral efficacy, allow to use lower drug doses, and minimize side effects. Despite numerous experimental findings on their antiviral activity, no small-molecule inhibitors of host proteases have been approved for the treatment of virus infections, so far.

La(iii) biodistribution profiles from intravenous and oral dosing of two lanthanum complexes, La(dpp)3 and La(XT), and evaluation as treatments for bone resorption disorders

Trivalent lanthanum (La³⁺) has the potential to treat bone resorption disorders (such as osteoporosis) by eliciting a bone-building response in the cells which control skeletal remodelling. Because La³⁺ suffers from extremely poor intestinal absorption, specifically designed chelators are required in order that a biologically active form of lanthanum can be administered orally. Two such chelators, 1,2-dimethyl-3-hydroxy-4-pyridinone (Hdpp) and bis-{[bis(carboxymethyl)amino]methy}phosphinic acid (H₅XT), have previously been the subjects of extensive physical, in vitro, and in vivo testing as the tris- and mono-lanthanum(iii) complexes La(dpp)₃ and La(XT), respectively. In this manuscript, we expand upon those studies to include 4-week intravenous (IV) and oral La³⁺ biodistribution profiles, which show that the metal ion initially accumulates in the liver followed by preferential redistribution and retention by bone. Of the two compounds, La(XT) demonstrates the more favourable in vivo characteristics, therefore dose-dependent oral biodistribution studies were carried out with this complex. These show drug saturation above a dose of 100 mg kg^-1 day^-1, so liver histology was performed in order to assess any potential toxicity. Finally, we improve upon the physical characterization of La(dpp)₃ to include a single crystal X-ray structure, which exhibits an 8-coorindate La³⁺ centre with two bound water molecules, and a disordered exoclathrate-type hydrogen bonded network.

The bone remodelling cycle

The bone remodelling cycle replaces old and damaged bone and is a highly regulated, lifelong process essential for preserving bone integrity and maintaining mineral homeostasis. During the bone remodelling cycle, osteoclastic resorption is tightly coupled to osteoblastic bone formation. The remodelling cycle occurs within the basic multicellular unit and comprises five co-ordinated steps; activation, resorption, reversal, formation and termination. These steps occur simultaneously but asynchronously at multiple different locations within the skeleton. Study of rare human bone disease and animal models have helped to elucidate the cellular and molecular mechanisms that regulate the bone remodelling cycle. The key signalling pathways controlling osteoclastic bone resorption and osteoblastic bone formation are receptor activator of nuclear factor-κB (RANK)/RANK ligand/osteoprotegerin and canonical Wnt signalling. Cytokines, growth factors and prostaglandins act as paracrine regulators of the cycle, whereas endocrine regulators include parathyroid hormone, vitamin D, calcitonin, growth hormone, glucocorticoids, sex hormones, and thyroid hormone. Disruption of the bone remodelling cycle and any resulting imbalance between bone resorption and formation leads to metabolic bone disease, most commonly osteoporosis. The advances in understanding the cellular and molecular mechanisms underlying bone remodelling have also provided targets for pharmacological interventions which include antiresorptive and anabolic therapies. This review will describe the remodelling process and its regulation, discuss osteoporosis and summarize the commonest pharmacological interventions used in its management.

A novel osteoporosis model with ascorbic acid deficiency in Akr1A1 gene knockout mice

The AKR1A1 protein is a member of the aldo-keto reductase superfamily that is responsible for the conversion of D-glucuronate to L-gulonate in the ascorbic acid (vitamin C) synthesis pathway. In a pCAG-eGFP transgenic mouse line that was produced by pronuclear microinjection, the integration of the transgene resulted in a 30-kb genomic DNA deletion, including the Akr1A1 gene, and thus caused the knockout (KO) of the Akr1A1 gene and targeting of the eGFP gene. The Akr1A1 KO mice (Akr1A1eGFP/eGFP) exhibited insufficient serum ascorbic acid levels, abnormal bone development and osteoporosis. Using micro-CT analysis, the results showed that the microarchitecture of the 12-week-old Akr1A1eGFP/eGFP mouse femur was shorter in length and exhibited less cortical bone thickness, enlargement of the bone marrow cavity and a complete loss of the trabecular bone in the distal femur. The femoral head and neck of the proximal femur also showed a severe loss of bone mass. Based on the decreased levels of serum osteocalcin and osteoblast activity in the Akr1A1eGFP/eGFP mice, the osteoporosis might be caused by impaired bone formation. In addition, administration of ascorbic acid to the Akr1A1eGFP/eGFP mice significantly prevented the condition of osteoporotic femurs and increased bone formation. Therefore, through ascorbic acid administration, the Akr1A1 KO mice exhibited controllable osteoporosis and may serve as a novel model for osteoporotic research.

Ru(ii) polypyridyl complexes as photocages for bioactive compounds containing nitriles and aromatic heterocycles

Photocaging allows for precise spatiotemporal control over the release of biologically active compounds with light. Most photocaged molecules employ organic photolabile protecting groups; however, biologically active compounds often contain functionalities such as nitriles and aromatic heterocycles that cannot be caged with organic groups. Despite their prevalence, only a few studies have reported successful caging of nitriles and aromatic heterocycles. Recently, Ru(ii)-based photocaging has emerged as a powerful method for the release of bioactive molecules containing these functional groups, in many cases providing high levels of spatial and temporal control over biological activity. This Feature Article discusses recent developments in applying Ru(ii)-based photocaging towards biological problems. Our groups designed and synthesized Ru(ii)-based platforms for the photoinduced delivery of cysteine protease and cytochrome P450 inhibitors in order to achieve selective control over enzyme inhibition. We also reported Ru(ii) photocaging groups derived from higher-denticity ancillary ligands that possess photophysical and photochemical properties distinct from more traditional Ru(ii)-based caging groups. In addition, for the first time, we are able to rapidly synthesize and screen Ru(ii) polypyridyl complexes that elicit desired properties by solid-phase synthesis. Finally, our work also defined steric and orbital mixing effects that are important factors in controlling photoinduced ligand exchange.

Key Triggers of Osteoclast-Related Diseases and Available Strategies for Targeted Therapies: A Review

Osteoclasts, the only cells with bone resorption functions in vivo, maintain the balance of bone metabolism by cooperating with osteoblasts, which are responsible for bone formation. Excessive activity of osteoclasts causes many diseases such as osteoporosis, periprosthetic osteolysis, bone tumors, and Paget's disease. In contrast, osteopetrosis results from osteoclast deficiency. Available strategies for combating over-activated osteoclasts and the subsequently induced diseases can be categorized into three approaches: facilitating osteoclast apoptosis, inhibiting osteoclastogenesis, and impairing bone resorption. Bisphosphonates are representative molecules that function by triggering osteoclast apoptosis. New drugs, such as tumor necrosis factor and receptor activator of nuclear factor kappa-B ligand (RANKL) inhibitors (e.g., denosumab) have been developed for targeting the receptor activator of nuclear factor kappa-B /RANKL/osteoprotegerin system or CSF-1/CSF-1R axis, which play critical roles in osteoclast formation. Furthermore, vacuolar (H⁺)-ATPase inhibitors, cathepsin K inhibitors, and glucagon-like peptide 2 impair different stages of the bone resorption process. Recently, significant achievements have been made in this field. The aim of this review is to provide an updated summary of the current progress in research involving osteoclast-related diseases and of the development of targeted inhibitors of osteoclast formation.

An Ectosteric Inhibitor of Cathepsin K Inhibits Bone Resorption in Ovariectomized Mice

The potent cathepsin K (CatK) inhibitor, Tanshinone IIA sulfonic sodium (T06), was tested for its in vitro and in vivo antiresorptive activities. T06 binds in an ectosteric site of CatK remote from its active site and selectively inhibits collagen degradation with an IC₅₀ value of 2.7 ± 0.2 μM (CatK:T06 molar ratio of 1:5). However, it does not suppress fluorogenic peptide cleavage and gelatinolysis at a 2500-fold molar excess. Contrary to active site-directed CatK inhibitors, such as odanacatib, T06 suppresses bone resorption in both human and mouse osteoclasts equally well (IC₅₀ value for human and mouse osteoclasts: 237 ± 60 nM and 245 ± 55 nM, respectively) and its antiresorptive activity is fully reversible in both cell types. Moreover, T06 affects neither the metabolic activity of osteoclasts nor osteoclastogenesis. In in vivo studies, 40 mg T06/kg/d given to 12-week-old ovariectomized (OVX) mice for 3 months reduced plasma CTx-1 by 20% and increased osteoblast numbers and plasma P1NP by ∼28% when compared with the OVX control. μCT analysis of T06-treated OVX mice showed a 35% increase in bone mineral density and other femoral trabecular bone parameters when compared with OVX animals. T06 did not alter the number of osteoclasts, had no estrogenic effect on the uterus, did not change plasma estradiol levels, and did not inhibit fibroblast-mediated TGF-ß1 processing or degradation and cognitive functions in OVX mice. This study indicates that the ectosteric inhibitor, T06, is a selective antiresorptive CatK inhibitor that may overcome the shortcomings of side effect-prone active site-directed drugs, which all failed in clinical trials. © 2017 American Society for Bone and Mineral Research.

Cathepsin K Inhibitors for Osteoporosis: Biology, Potential Clinical Utility, and Lessons Learned

Cathepsin K is a cysteine protease member of the cathepsin lysosomal protease family. Although cathepsin K is highly expressed in osteoclasts, lower levels of cathepsin K are also found in a variety of other tissues. Secretion of cathepsin K from the osteoclast into the sealed osteoclast-bone cell interface results in efficient degradation of type I collagen. The absence of cathepsin K activity in humans results in pycnodysostosis, characterized by increased bone mineral density and fractures. Pharmacologic cathepsin K inhibition leads to continuous increases in bone mineral density for ≤5 years of treatment and improves bone strength at the spine and hip. Compared with other antiresorptive agents, cathepsin K inhibition is nearly equally efficacious for reducing biochemical markers of bone resorption but comparatively less active for reducing bone formation markers. Despite multiple efforts to develop cathepsin K inhibitors, potential concerns related to off-target effects of the inhibitors against other cathepsins and cathepsin K inhibition at nonbone sites, including skin and perhaps cardiovascular and cerebrovascular sites, prolonged the regulatory approval process. A large multinational randomized, double-blind phase III study of odanacatib in postmenopausal women with osteoporosis was recently completed. Although that study demonstrated clinically relevant reductions in fractures at multiple sites, odanacatib was ultimately withdrawn from the regulatory approval process after it was found to be associated with an increased risk of cerebrovascular accidents. Nonetheless, the underlying biology and clinical effects of cathepsin K inhibition remain of considerable interest and could guide future therapeutic approaches for osteoporosis.

The Future of Cysteine Cathepsins in Disease Management

Since the discovery of the key role of cathepsin K in bone resorption, cysteine cathepsins have been investigated by pharmaceutical companies as drug targets. The first clinical results from targeting cathepsins by activity-based probes and substrates are paving the way for the next generation of molecular diagnostic imaging, whereas the majority of antibody-drug conjugates currently in clinical trials depend on activation by cathepsins. Finally, cathepsins have emerged as suitable vehicles for targeted drug delivery. It is therefore timely to review the future of cathepsins in drug discovery. We focus here on inflammation-associated diseases because dysregulation of the immune system accompanied by elevated cathepsin activity is a common feature of these conditions.

Inhibition of cathepsin K promotes osseointegration of titanium implants in ovariectomised rats

The bone mineral deficiency in osteoporosis poses a threat to the long-term outcomes of endosseous implants. The inhibitors of cathepsin K (CatK) significantly affect bone turnover, bone mineral density (BMD) and bone strength in the patients with osteoporosis. Therefore, we hypothesised that the application of a CatK inhibitor (CatKI) could increase the osseointegration of endosseous implants under osteoporotic conditions. Odanacatib (ODN), a highly selective CatKI, was chosen as the experimental drug. Sixteen rats were randomised into 4 groups: sham, ovariectomy (OVX) with vehicle, OVX with low-dose ODN (5 mg/kg) and OVX with high-dose ODN (30 mg/kg). Titanium implants were placed into the distal metaphysis of bilateral femurs of each OVX rat. After 8 weeks of gavaging, CatKI treatment increased the removal torque, BMD and bone-to-implant contact (BIC). Moreover, high-dose CatKI exerted a better influence than low-dose CatKI. Furthermore, CatKI treatment not only robustly suppressed CatK gene (CTSK) expression, but also moderately reduced expression of the osteoblast-related genes Runx2, Collagen-1, BSP, Osterix, OPN, SPP1 and ALP. Thus, CatKI could affect the osteoblast-related genes, although the balance of bone turnover was achieved mainly by CatK inhibition. In conclusion, CatKI prevented bone loss and aided endosseous implantation in osteoporotic conditions.

New horizons in treatment of osteoporosis

BACKGROUND

Prevalence of osteoporosis is increasing both in developed and developing countries. Due to rapid growth in the burden and cost of osteoporosis, worldwide, it seems reasonable to focus on the reduction of fractures as the main goal of treatment. Although, efficient pharmacological agents are available for the treatment of osteoporosis, there still remains a need to more specific drugs with less adverse effects.

MAIN BODY

This review article provides a brief update on the pathogenesis, presenting current pharmacological products approved by the US Food and Drug Administration (FDA) or Europe, and also newer therapeutic agents to treat osteoporosis according to the clinical trial data available at PubMed, UpToDate, International Osteoporosis Foundation (IOF), and clinical practice guidelines. As well, the effect of combination therapy and recommendations for future research will be further discussed.

SHORT CONCLUSION

The use of current antiresorptive and anabolic agents alone or in combinations for the treatment of osteoporosis entails several limitations. Mainly, their efficacy on non-vertebral fracture reduction is lower than that observed on vertebral fracture. In addition, they have potential adverse events on long time usage. Development of newer agents such as cathepsin k inhibitor and strontium ranelate not only have increased the available options for treating osteoporosis, but also have opened doors of opportunity to improvements in the effective treatment. However, the high cost of new agents have restricted their usage in selective patients who are at high risk of fracture or whom failed response to first line treatment options. Thus, personalized medicine should be considered for future evaluation of genetic risk score and also for environmental exposure assessment. In addition to permanent attention to early diagnosis of osteoporosis and understanding of the pathophysiology of osteoporosis for novel approach in drug discovery, there seems a need to more well-designed clinical trials with larger sample sizes and longer duration on current as well as on newer agents. Also, continuous research on plant-derived components as the source of discovering new agents, and conducting more clinical trials with combination of two or more synthetic drugs, plants, or drug-plant for the treatment of osteoporosis are recommended. Summary of treatment modalities for osteoporosis.

[Regulation of bone metabolism in osteoporosis : novel drugs for osteoporosis in development]

Bone is continuously regenerated and remodeled as an adaptation to mechanical load. Bone mass and fracture resistance are maintained by a balanced equilibrium between bone formation and bone resorption. Regeneration and response to mechanical load are, however, impaired in osteoporosis and during aging. Bone resorption is enhanced by chronic inflammation while bone formation is altered by rising levels of inhibitors in the aging organism. Core molecular principles of the regulation of bone metabolism in health and disease have been characterized and developed as therapeutic targets. The receptor activator of nuclear factor kappaB ligand (RANKL) and osteoclast-derived protease cathepsin K are important regulators and effectors of osteoclast differentiation and bone resorption. Bone formation is stimulated by bone morphogenetic proteins (BMP) and via the parathyroid hormone receptor and the Wnt signaling pathway. The principles of osteoclast inhibition using bisphosphonates have now been known for almost three decades. Based on more recent knowledge RANKL and cathepsin K have been developed as new therapeutic targets to inhibit bone resorption. While denosumab, a RANKL antibody, has already been introduced into routine treatment strategies, the cathepsin K antagonist odanacatib is currently in the licensing process. Bone formation can also be stimulated by local administration of BMPs, by systemic treatment with the parathyroid hormone fragment teriparatide and by using antibodies targeting the Wnt inhibitor sclerostin. The latter are presently being tested in phase III clinical studies. In the near future a panel of traditional and novel treatment strategies will be available that will enable us to meet the individual clinical needs during aging and for the treatment of osteoporosis.

Medication-Related Osteonecrosis of the Jaw: New Insights into Molecular Mechanisms and Cellular Therapeutic Approaches

In recent years, medication-related osteonecrosis of the jaw (MRONJ) became an arising disease due to the important antiresorptive drug prescriptions to treat oncologic and osteoporotic patients, as well as the use of new antiangiogenic drugs such as VEGF antagonist. So far, MRONJ physiopathogenesis still remains unclear. Aiming to better understand MRONJ physiopathology, the first objective of this review would be to highlight major molecular mechanisms that are known to be involved in bone formation and remodeling. Recent development in MRONJ pharmacological treatments showed good results; however, those treatments are not curative and could have major side effects. In parallel to pharmacological treatments, MSC grafts appeared to be beneficial in the treatment of MRONJ, in multiple aspects: (1) recruitment and stimulation of local or regional endogenous cells to differentiate into osteoblasts and thus bone formation, (2) beneficial impact on bone remodeling, and (3) immune-modulatory properties that decrease inflammation. In this context, the second objective of this manuscript would be to summarize the molecular regulatory events controlling osteogenic differentiation, bone remodeling, and osteoimmunology and potential beneficial effects of MSC related to those aspects, in order to apprehend MRONJ and to develop new therapeutic approaches.

Effects of odanacatib on bone matrix mineralization in rhesus monkeys are similar to those of alendronate

Odanacatib (ODN) is a selective and reversible inhibitor of cathepsin K which is an important enzyme for the degradation of collagen I. Aim of the present work was the head-to-head comparison between the effects of ODN and alendronate (ALN) on bone mineralization density distribution (BMDD), based on quantitative backscattered electron imaging in relation to changes in histomorphometric mineralizing surface per bone surface (MS/BS) in 12–22 years old ovariectomized rhesus monkeys. Trabecular and cortical BMDD derived parameters from vertebrae and proximal tibiae were compared among vehicle (VEH, n = 8), odanacatib low dose (ODN-L, n = 8), odanacatib high dose (ODN-H, n = 8), and alendronate (ALN, n = 6) treated animals. Additionally, data from an intact, non-treated group of animals are shown (INT, n = 8). In trabecular bone from the vertebra and metaphyseal tibia, the BMDD of the ODN and ALN treatment groups was shifted toward higher mineralization densities (p < 0.001) consistent with the significant reduction of MS/BS (p < 0.05 in ODN-H and ALN) compared to VEH. Vertebral trabecular CaMean (average degree of mineralization) was significantly higher in ODN-L (+ 6.5%), ODN-H (+ 6.1%), and ALN (+ 6.7%, all p < 0.001). Tibial osteonal cortical bone revealed also significantly increased CaMean for ODN-L (+ 1.4%, p < 0.05), ODN-H (+ 2.2%, p < 0.05), and ALN (+ 3.4%, p < 0.001) versus VEH, while primary cortical bone (devoid of secondary osteons) did not show any significant differences between the study groups. The percentage of primary bone area in the tibial cross-sections (on average 45 ± 12%) was also not significantly different between the study groups (p = 0.232). No significant differences in any BMDD parameters of all studied skeletal sites between ODN and ALN treatment were found. Correlation analysis revealed that MS/BS was highly predictive for trabecular BMDD in vertebral bone. The higher MS/BS, the lower was CaMean. Our findings are consistent with the inhibition of bone resorption of ODN and ALN in trabecular and osteonal compartments.

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In line with its anti-resorptive action ODN increased trabecular and osteonal bone mineralization in treated rhesus monkeys.

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Both lower and higher dosages of ODN were similarly efficient with respect to bone matrix mineralization outcomes.

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ODN treatment affected bone matrix mineralization in a similar manner compared to ALN.

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ODN treatment did not significantly change the percentage of primary bone area in tibial cross-sections.