Antagonism of the osteoclast vitronectin receptor with an orally active nonpeptide inhibitor prevents cancellous bone loss in the ovariectomized rat

Yeast Hydrolysate and Postmenopausal Osteoporosis

We used an ovariectomy (OVX) rat model to test whether yeast hydrolysate (YH) has therapeutic effects on postmenopausal osteoporosis-induced bone loss. The rats were separated into five treatment groups: the sham group (sham operation); the control group (no treatment after OVX); the estrogen group (estrogen treatment after OVX); YH 0.5% group (drinking water supplementation with 0.5% YH after OVX); and the YH 1% group (drinking water supplementation with 1% YH after OVX). In addition, the YH treatment restored serum testosterone concentration in the OVX rats up to the normal level. Further, YH treatment affected bone markers; a significant increase in serum calcium concentration was observed after adding YH to the diet. The levels of serum alkaline phosphatase, osteocalcin, and cross-linked telopeptides of type I collagen were reduced by YH supplementation, unlike those in the no-treatment control. Although not statistically significant, YH treatment in OVX rats improved trabecular bone microarchitecture parameters. These results show that YH may ameliorate the bone loss caused by postmenopausal osteoporosis because of the normalization of serum testosterone concentration.

Specialized Roles for Actin in Osteoclasts: Unanswered Questions and Therapeutic Opportunities

Osteoclasts are cells of the hematopoietic lineage that are specialized to resorb bone. In osteoclasts, the actin cytoskeleton engages in at least two unusual activities that are required for resorption. First, microfilaments form a dynamic and structurally elaborate actin ring. Second, microfilaments bind vacuolar H⁺-ATPase (V-ATPase) and are involved in forming the V-ATPase-rich ruffled plasma membrane. The current review examines these two specialized functions with emphasis on the identification of new therapeutic opportunities. The actin ring is composed of substructures called podosomes that are interwoven to form a cohesive superstructure. Studies examining the regulation of the formation of actin rings and its constituent proteins are reviewed. Areas where there are gaps in the knowledge are highlighted. Microfilaments directly interact with the V-ATPase through an actin binding site in the B2-subunit of V-ATPase. This binding interaction is required for ruffled membrane formation. Recent studies show that an inhibitor of the interaction blocks bone resorption in pre-clinical animal models, including a model of post-menopausal osteoporosis. Because the unusual actin-based resorption complex is unique to osteoclasts and essential for bone resorption, it is likely that deeper understanding of its underlying mechanisms will lead to new approaches to treat bone disease.

Irisin Mediates Effects on Bone and Fat via αV Integrin Receptors

Irisin is secreted by muscle, increases with exercise, and mediates certain favorable effects of physical activity. In particular, irisin has been shown to have beneficial effects in adipose tissues, brain, and bone. However, the skeletal response to exercise is less clear, and the receptor for irisin has not been identified. Here we show that irisin binds to proteins of the αV class of integrins, and biophysical studies identify interacting surfaces between irisin and αV/β5 integrin. Chemical inhibition of the αV integrins blocks signaling and function by irisin in osteocytes and fat cells. Irisin increases both osteocytic survival and production of sclerostin, a local modulator of bone remodeling. Genetic ablation of FNDC5 (or irisin) completely blocks osteocytic osteolysis induced by ovariectomy, preventing bone loss and supporting an important role of irisin in skeletal remodeling. Identification of the irisin receptor should greatly facilitate our understanding of irisin's function in exercise and human health.

The Cooccurrence of Obesity, Osteoporosis, and Sarcopenia in the Ovariectomized Rat: A Study for Modeling Osteosarcopenic Obesity in Rodents

Background

Obesity, osteoporosis, and sarcopenia may individually occur due to age-related gradual alterations in body composition. This study investigates the cooccurrence of these age-related diseases in female animals with low levels of ovarian hormone in the absence of complex multifactorial process of chronological aging.

Methods

Thirty-six 5- and 10-month-old female rats were chosen to model pre- and postmenopausal women, respectively. Rats were divided into three treatment groups in each age category—sham, ovariectomized (ovx), and ovx + E₂ (17β-estradiol, 10 μg/kg)—and were pair-fed. Volunteer wheel running activity, body composition, bone microstructure, serum C-telopeptides of type I collagen, bone specific alkaline phosphatase, E₂, and gastrocnemius and soleus muscles were analyzed.

Results

The cooccurrence of osteoporosis, sarcopenia, and obesity was observed in the older ovx rats associated with a significant (p < 0.05) increased fat mass (30%), bone loss (9.6%), decreased normalized muscle mass-to-body-weight ratio (10.5%), and a significant decrease in physical activity (57%). The ratio of tibial bone mineral density to combined muscle mass was significantly decreased in both ovx age categories.

Conclusion

Ovariectomized rat could be used as an experimental model to examine the effect of loss of ovarian hormones, while controlling for energy intake and expenditure, to conduct obesity and body composition translational research in females without the confounding effect of genetic background.

SB-273005, an antagonist of αvβ3 integrin, reduces the production of Th2 cells and cytokine IL-10 in pregnant mice

Pregnancy is associated with complex immunoreactions. In the present study, the effect of SB-273005, an antagonist of αvβ3 integrin, on the alterations of T helper (Th) cells and their derived cytokines that occur during pregnancy was investigated in mice. Five non-pregnant mice were used as a negative control. Mice were impregnated by co-housing females and males at a ratio of 2:1 overnight and pregnancy was confirmed by the appearance of vaginal plugs the following morning. Day 1 (D1) pregnant mice were randomly divided into two groups (n=20) and were administered either dimethylsulfoxide (mock treatment) or SB-273005 (3 mg/kg) by gavage at D3, D4 and D5. At D8, the levels of Th1 and Th2 cells and interleukin (IL)-2 and IL-10 in the spleen and peripheral blood were determined using flow cytometry and enzyme-linked immunosorbent assay. Pregnancy significantly increased the ratio of Th2:Th1 cells in the spleen compared with that in non-pregnant mice (P<0.01). However, this increase was significantly reduced by SB-273005 (P<0.001). Furthermore, whilst pregnancy decreased Th1 cell-produced IL-2 levels and increased Th2 cell-derived IL-10 levels, SB-273005 reversed both processes (P<0.05 for IL-2; P<0.01 for IL-10). The results from the present study demonstrated that pregnancy induces changes in the spleen, including a reduction of IL-2 and an increase in IL-10 production by Th1 and Th2 cells, respectively, as well as an upregulation of the Th2:Th1 ratio in the spleen. These immunological changes are reversed by SB-273005, indicating an important role for αvβ3 integrin in mediating these immunological alterations.

Advances in osteoclast biology: old findings and new insights from mouse models

The maintenance of adequate bone mass is dependent upon the controlled and timely removal of old, damaged bone. This complex process is performed by the highly specialized, multinucleated osteoclast. Over the past 15 years, a detailed picture has emerged describing the origins, differentiation pathways and activation stages that contribute to normal osteoclast function. This information has primarily been obtained by the development and skeletal analysis of genetically modified mouse models. Mice harboring mutations in specific genetic loci exhibit bone defects as a direct result of aberrations in normal osteoclast recruitment, formation or function. These findings include the identification of the RANK-RANKL-OPG system as a primary mediator of osteoclastogenesis, the characterization of ion transport and cellular attachment mechanisms and the recognition that matrix-degrading enzymes are essential components of resorptive activity. This Review focuses on the principal observations in osteoclast biology derived from genetic mouse models, and highlights emerging concepts that describe how the osteoclast is thought to contribute to the maintenance of adequate bone mass and integrity throughout life.

Integrin targeted therapeutics

Integrins are heterodimeric, transmembrane receptors that function as mechanosensors, adhesion molecules and signal transduction platforms in a multitude of biological processes. As such, integrins are central to the etiology and pathology of many disease states. Therefore, pharmacological inhibition of integrins is of great interest for the treatment and prevention of disease. In the last two decades several integrin-targeted drugs have made their way into clinical use, many others are in clinical trials and still more are showing promise as they advance through preclinical development. Herein, this review examines and evaluates the various drugs and compounds targeting integrins and the disease states in which they are implicated.

Mechanisms modulating inflammatory osteolysis: a review with insights into therapeutic targets

Inflammatory osteolysis is a relatively frequent and incapacitating complication of rheumatoid arthritis and multiple other inflammation-associated bone diseases. It is thought to operate through an ultimate common pathway of accelerated osteoclast recruitment and activation under the control of cytokines produced in the inflammatory environment. Over the past decade, there have been major advances in our understanding of the mechanisms of osteoclastogenesis. It is now clear that the interaction of receptor activator NF-kappaB (RANK) and its ligand, RANKL, plays a central role in osteoclast formation and activity. Therefore, understanding osteoclastogenesis offers new pathways for potential therapeutic intervention in inflammatory osteolysis. The success of anti-tumor necrosis factor-alpha and interleukin-1 therapy highlights the central role that these specific cytokines play in this disease. This review outlines our current understanding of the mechanisms mediating inflammatory osteolysis and highlights potential therapeutic strategies.

Antiresorptive agents and osteoclast apoptosis

Antiresorptive agents have proven to be effective therapies for the treatment of bone diseases associated with excessive osteoclast activity. Decreased osteoclast formation, inhibition of osteoclast actions, and reduced osteoclast survival represent mechanisms by which antiresorptive agents could act. The goals of this article are to present the evidence that antiresorptive agents can decrease osteoclast survival through apoptosis, to review the mechanisms by which they are thought to activate the apoptotic process, and to consider whether the actions on apoptosis fully account for the antiresorptive effects. As background, the apoptotic process will be briefly summarized together with the evidence that factors that promote osteoclast survival affect steps in the process. Following this, therapeutic agents that are both antiresorptive and can stimulate osteoclast apoptosis will be discussed. Other bone therapeutic agents that are either antiresorptive or apoptotic, but not both, will be described. Finally, newer antiresorptive compounds that elicit apoptosis and could represent potential therapeutic agents will be noted.

Promotion of skin epithelial cell migration and wound healing by a 2-benzazepine derivative

Re-epithelialization is an important event in the healing of skin wounds. We have now shown that a 2-benzazepine derivative, N-(2,2,2-trifluoroethyl)-8-methoxy-4-methyl-2-benzazepin-3-one (compound A), facilitated the migration of human keratinocyte HaCat cells in an in vitro model of wound healing and inhibited the attachment of these cells to a collagen matrix. Topical application of compound A also promoted the healing of skin wounds in mice. Our results suggest that compound A promotes the repair of skin wounds by facilitating epithelial cell migration and that this 2-benzazepine derivative is a potential new drug for the treatment of such wounds.

Involvement of alpha(v)beta3 integrins in osteoclast function

Integrins are heterodimeric adhesion receptors that mediate cell-matrix interaction. Osteoclast exhibits high expression of the alpha(v)beta(3) integrin, which binds to a variety of extracellular matrix proteins including vitronectin, osteopontin, and bone sialoprotein. Arg-Gly-Asp (RGD)-containing peptides, RGD-mimetics, and blocking antibodies to alpha(v)beta(3) integrin were shown to inhibit bone resorption in vitro and in vivo, suggesting that this integrin may play an important role in regulating osteoclast function. Several lines of evidence have demonstrated that a number of signaling molecules are involved in the alpha(v)beta(3) integrin-dependent signaling pathway, including c-Src, Pyk2, c-Cbl, and p130(Cas). In this article, we review the history of "alpha(v)beta(3) integrin and osteoclasts" and discuss the involvement of alpha(v)beta(3) integrins in osteoclast function at tissue, cellular, and molecular levels. A better understanding of the role of alpha(v)beta(3) integrin in osteoclastic bone resorption would provide opportunities for developing new therapeutics to treat human bone diseases, including rheumatoid arthritis, osteoporosis, and periodontal disease.

The cellular and molecular biology of periprosthetic osteolysis

The generation of prosthetic implant wear after total joint arthroplasty is recognized as the major initiating event in development of periprosthetic osteolysis and aseptic loosening, the leading complication of this otherwise successful surgical procedure. We review current concepts of how wear debris causes osteolysis, and report ideas for prevention and treatment. Wear debris primarily targets macrophages and osteoclast precursor cells, although osteoblasts, fibroblasts, and lymphocytes also may be involved. Molecular responses include activation of MAP kinase pathways, transcription factors (including NFkappaB), and suppressors of cytokine signaling. This results in up-regulation of proinflammatory signaling and inhibition of the protective actions of antiosteoclastogenic cytokines such as interferon gamma. Strategies to reduce osteolysis by choosing bearing surface materials with reduced wear properties should be balanced by awareness that reducing particle size may increase biologic activity. There are no approved treatments for osteolysis despite the promise of therapeutic agents against proinflammatory mediators (such as tumor necrosis factor) and osteoclasts (bisphosphonates and molecules blocking receptor activator of NFkappaB ligand [RANKL] signaling) shown in animal models. Considerable efforts are underway to develop such therapies, to identify novel targets for therapeutic intervention, and to develop effective outcome measures.

A selective androgen receptor modulator that reduces prostate tumor size and prevents orchidectomy-induced bone loss in rats

The pharmacological activity of JNJ-26146900 is described. JNJ-26146900 is a nonsteroidal androgen receptor (AR) ligand with tissue-selective activity in rats. The compound was evaluated in in vitro and in vivo models of AR activity. It binds to the rat AR with a K(i) of 400nM and acts as a pure androgen antagonist in an in vitro cell-based assay. Its in vitro profile is similar to the androgen antagonist bicalutamide (Casodex). In intact rats, JNJ-26146900 reduces ventral prostate weight with an oral potency (ED(50)) of 20-30mg/kg, again comparable to that of bicalutamide. JNJ-26146900 prevented prostate tumor growth in the Dunning rat model, maximally inhibiting growth at a dose of 10mg/kg. It slowed tumor growth significantly in a CWR22-LD1 mouse xenograft model of human prostate cancer. It was tested in aged male rats for its ability to prevent bone loss and loss of lean body mass following orchidectomy. After 6 weeks of dosing, bone volume decreased by 33% in orchidectomized versus intact vehicle-treated rats with a probability (P) of less than 0.05, as measured by micro-computerized tomography analysis. At a dose of 30mg/kg, JNJ-26146900 significantly reduced castration-induced tibial bone loss as indicated by the following parameters: bone volume, trabecular connectivity, trabecular number and spacing between trabeculae. Bone mineral density decreased from 229+/-34mg/cm(3) of hydroxyapatite to 166+/-26mg/cm(3) following orchidectomy, and was maintained at 194+/-20mg/cm(3) with JNJ-26146900 treatment (P<0.05 relative to orchidectomy alone). Using magnetic resonance imaging, the compound was found to partially prevent orchidectomy-induced loss of lean body mass. Our data show that selective androgen receptor modulators (SARMs) have the potential for anabolic effects on bone and muscle while maintaining therapeutic efficacy in prostate cancer.

Future Treatment of Bone Metastases

All bone surfaces are periodically remodeled by the coupled and balanced action of osteoclasts and osteoblasts, of which the activities are regulated by a variety of cytokines and growth factors. Patients with cancer metastatic to the skeleton often develop osteolytic bone lesions, in which the actions of osteoclasts and osteoblasts remain coupled, but become imbalanced in sites adjacent to the tumor. The result is net bone loss. Many cancers secrete osteoclast-stimulating cytokines, which increase bone resorption by osteoclasts. In turn, factors released from the bone matrix during osteolysis can stimulate tumor growth. In this so-called "vicious cycle," there are multiple sites that are targets for new bone-directed therapies. A variety of new agents for the treatment and prevention of osteolytic bone metastasis are currently being developed. These include new agents that inhibit osteoclast differentiation, bone adhesion, and osteoclast function. These new strategies have evolved from a better understanding of the interaction between tumor cells and cells in the bone marrow microenvironment. There is great promise that these new bone-targeted therapies can decrease the frequent skeletal-related events that greatly diminish quality of life of patients with bone metastases.

The central role of wear debris in periprosthetic osteolysis

Periprosthetic osteolysis remains the leading complication of total hip arthroplasty, often resulting in aseptic loosening of the implant, and a requirement for revision surgery. Wear-generated particular debris is the main cause of initiating this destructive process. The purpose of this article is to review recent advances in our understanding of how wear debris causes osteolysis, and emergent strategies for the avoidance and treatment of this disease. The most important cellular target for wear debris is the macrophage, which responds to particle challenge in two distinct ways, both of which contribute to increased bone resorption. First, it is well known that wear debris activates proinflammatory signaling, which leads to increased osteoclast recruitment and activation. More recently, it has been established that wear also inhibits the protective actions of antiosteoclastogenic cytokines such as interferon gamma, thus promoting differentiation of macrophages to bone-resorbing osteoclasts. Osteoblasts, fibroblasts, and possibly lymphocytes may also be involved in responses to wear. At a molecular level, wear particles activate MAP kinase cascades, NFkappaB and other transcription factors, and induce expression of suppressors of cytokine signaling. Strategies to reduce osteolysis by choosing bearing surface materials with reduced wear properties (such as metal-on-metal) should be balanced by awareness that reducing particle size may increase biological activity. Finally, although therapeutic agents against proinflammatory mediators [such as tumor necrosis factor (TNF)] and osteoclasts (bisphosphonates and molecules blocking RANKL signaling) have shown promise in animal models, no approved treatments are yet available to osteolysis patients. Considerable efforts are underway to develop such therapies, and to identify novel targets for therapeutic intervention.

Synthesis of pyrazoles and isoxazoles as potent αvβ3 receptor antagonists

We describe a series of pyrazole and isoxazole analogs as antagonists of the alpha(v)beta3 receptor. Compounds showed low to sub-nanomolar potency against alpha(v)beta3, as well as good selectivity against alpha(IIb)beta3. In HT29 cells, most analogs also demonstrated significant selectivity against alpha(v)beta6. Several compounds showed good pharmacokinetic properties in rats, in addition to anti-angiogenic activity in a mouse corneal micropocket model. Compounds were synthesized in a straightforward manner from readily available glutarate precursors.

Soy moderately improves microstructural properties without affecting bone mass in an ovariectomized rat model of osteoporosis

Soy protein is reported to prevent bone loss in both women and rat models of osteoporosis. However, the role of soy isoflavones on the trabecular microarchitectural properties needs to be explored. In the present study, we examined whether soy protein with graded doses of isoflavones reverses loss of bone mineral density (BMD), bone mineral content (BMC), and trabecular microstructure in an ovariectomized (Ovx) osteopenic rat model. Seventy-eight 9-m old female Sprague-Dawley rats were either sham-operated (Sham; 1 group) or Ovx (5 groups) and fed a semi-purified casein-based diet. After 90 days, the occurrence of bone loss was confirmed using dual energy X-ray absorptiometry. Thereafter, rats were assigned to the following treatments: Sham, Ovx (control), Ovx + 17beta-estradiol (E(2); 10 microg/kg body wt. twice per week), Ovx + soy protein depleted of isoflavones (Soy-; 0.06 mg isoflavones/g protein), Ovx + soy protein with normal isoflavone content (Soy; 3.55 mg isoflavones/g protein), and Ovx + isoflavone-enriched soy protein (Soy+; 7.10 mg isoflavones/g protein). After 125 days of treatment, rats were euthanized, and tibia and lumbar bones were collected for the assessment of BMD, BMC, and trabecular microarchitectural properties using X-ray microcomputed tomography. None of the treatments had an effect on BMD or microarchitectural properties of the lumbar vertebra. However, Soy treatment significantly increased tibial BMC and BMD by 10% and 4.5% compared with Ovx control, but the increase in BMD was not enough to reach the BMD levels of the Sham control group. The Soy+ diet positively affected the tibial architectural properties including trabecular thickness, separation, and number. In summary, our findings suggest that soy protein does not restore bone loss in osteopenic rats; however, higher doses of isoflavones may be required to reverse the loss of tibial microstructural properties.

Synthesis of 2,5-thiazole butanoic acids as potent and selective αvβ3 integrin receptor antagonists with improved oral pharmacokinetic properties

We describe a series of 2,5 thiazole containing compounds, which are potent antagonists of the integrin alpha(v)beta3 and show selectivity relative to the other integrins, such as alpha(IIb)beta3 and alpha(v)beta6. These analogs were demonstrated to have high bioavailability relative to other relative heterocyclic analogs.

A functional radioreceptor assay of alpha-V-beta-3 (αvβ3) inhibitors in plasma: Application as an ex vivo pharmacodynamic model

Development of alphavbeta3-integrin inhibitors has been hampered by a lack of pharmacodynamic endpoints to identify doses that inhibit alphavbeta3 in vivo. To address this need, we developed an alphavbeta3 radioreceptor assay (RRA) that could be performed in 100% plasma. The RRA was based on 125I-echistatin binding to plate-immobilized alphavbeta3. Small molecule alphavbeta3 inhibitors efficiently competed echistatin binding to alphavbeta3 when the assay was carried out in buffer. However, when carried out in 100% plasma, the RRA revealed a 45 to >3000-fold loss in compound potencies. The losses in potency reflected, in part, the high plasma protein binding by the compounds examined. The RRA was adapted as an ex vivo pharmacodynamic model. Echistatin binding was measured in the presence of plasma harvested at timed intervals from rats dosed with select compounds. Using this pharmacodynamic model, compound and dose selection was optimized for further testing in models of corneal angiogenesis. Moderate anti-angiogenic activity was achieved when rats were dosed sufficient to achieve sustained (>50%) plasma inhibition through the trough interval. Thus, the RRA provided a simple technique to rank order compound potency in plasma, and could find general use as an ex vivo pharmacodynamic assay to select compounds and doses for preclinical and clinical proof-of-principle studies.

Convergent, parallel synthesis of a series of beta-substituted 1,2,4-oxadiazole butanoic acids as potent and selective alpha(v)beta3 receptor antagonists

We describe a series of 1,2,4-oxadiazoles, which are potent antagonists of the integrin alpha(v)beta3 and, in addition, show selectivity relative to the other beta3 integrin alpha(IIb)beta3. In whole cells, the majority of these analogs also demonstrated modest selectivity against other alpha(v) integrins such as alpha(v)beta1 and alpha(v)beta6.

Mitigation of ectopic calcification in osteopontin-deficient mice by exogenous osteopontin

Ectopic calcification is a major cause of bioprosthetic heart valve failure. New therapeutic opportunities are offered by the growing understanding that ectopic calcification is an actively regulated process involving several key gene products. One of these products, osteopontin (OPN), is a glycosylated phosphoprotein previously shown to inhibit apatite crystal formation, induce carbonic anhydrase II, and promote mineral resorption. In this study, OPN-deficient mice (OPN-/-) were utilized as an in vivo model to stimulate the ectopic calcification of glutaraldehyde-fixed bovine pericardium (GFBP) tissue and to examine OPN delivery and structure-function relationships with respect to its anti-calcific activity. Significant calcification of GFBP tissue was obtained within 7 days of subcutaneous implantation in OPN-/- mice. Direct rescue of the calcification phenotype was achieved by the administration of exogenous recombinant rat, histidine-fused OPN (rat His-OPN) to the implant site via soluble injection (up to 72% mitigation achieved) or adsorption onto the implant materials (up to 91% mitigation achieved). Effects were specific, since neither fibronectin nor polyhistidine alone could mitigate calcification of GFBP. The maximum anti-calcific effect was achieved only when rat His-OPN was adequately phosphorylated and contained a functional arginine-glycine-aspartate (RGD) cell adhesive domain. Furthermore, CAII levels in host cells surrounding GFBP were greatest when phosphorylated, RGD-containing rat His-OPN was adsorbed. These data suggest that both physical inhibition, mediated by phosphorylation sites in OPN, as well as the induction of CAII and mineral regression, mediated by the RGD domain, contribute to the unique ability of OPN to mitigate ectopic calcification of bioprosthetic valve tissue.

Nonpeptide αvβ3 antagonists: identification of potent, chain-shortened 7-oxo RGD mimetics

Potent, novel 7-oxo alpha(v)beta3 antagonists have been prepared. These antagonists offer decreased plasma protein binding and excellent pharmacokinetic profiles.

Herbal extract prevents bone loss in ovariectomized rats

This research aims to test a new drug candidate based on a traditional medicinal herb, F1, an herbal extract obtained from Astragalus membranaceus and its main ingredient, 1-monolinolein that may have fewer side effects and less uterine hypertrophy. In vitro experiments, human osteoblast-like cell lines, MG-63 and Saos-2, were analyzed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and an alkaline phosphatase (ALP) assays. Mouse osteoclasts were induced through a calcium-deficient diet and inhibition effects were measured. In vivo experiments were done using ovariectomized (OVX) rats for 9 weeks. At necropsy, uterus weights were measured, trabecular bone area (TBA) of tibia and lumbar vertebra were measured bone histomorphology. In results, cell proliferation and ALP activity in Saos-2 by ether F1 or 1-monolinolein did not increased significantly compared to the control. The F1 inhibited osteoclast development (IC25 = 3.37 x 10(-5) mg/mL) less than 17beta-estradiol. The OVX rats administered F1 (2 mg/kg/day and 10 mg/kg/day) showed an increase in TBA of the tibia significantly (136.3 +/- 4.2% and 138.5 +/- 10.3% of control). In conclusions, the herbal extract, F1 inhibited tibia and lumbar bone loss and did not cause uterine hypertrophy. However, 1-monolinolein, the main ingredient of the herbal extract, did not inhibit bone loss.

Matrix metalloproteinases (MMPs) safeguard osteoblasts from apoptosis during transdifferentiation into osteocytes: MT1-MMP maintains osteocyte viability

Osteoblasts undergo apoptosis or differentiate into either osteocytes or bone-lining cells after termination of bone matrix synthesis. In this study, we investigated the role of matrix metalloproteinases (MMPs) in differentiation of osteoblasts, bone formation, transdifferentiation into osteocytes, and osteocyte apoptosis. This was accomplished by using calvarial sections from the MT1-MMP-deficient mouse and by culture of the mouse osteoblast cell line MC3T3-E1 and primary mouse calvarial osteoblasts. We found that a synthetic matrix metalloprotease inhibitor, GM6001, strongly inhibited bone formation in vitro of both primary osteoblasts and MC3T3 cells by approximately 75%. To further investigate at which level of osteoblast differentiation MMP inhibition was attenuating osteoblast function, we found that neither preosteoblast nor mature osteoblast activity was affected. In contrast, cell survival of osteoblasts forced to transdifferentiate into osteocytes in 3D type I collagen gels were inhibited by more than 50% when exposed to 10 microM GM6001 and to Tissue Inhibitor of Metalloproteinase-2 (TIMP-2), a natural MT1-MMP inhibitor. This shows the importance of MMPs in safeguarding osteoblasts from apoptosis when transdifferentiating into osteocytes. By examination of osteoblasts and osteocytes embedded in calvarial bone in the MT1-MMP deficient mice, we found that MT1-MMP deficient mice had 10-fold higher levels of apoptotic osteocytes than wild-type controls. We have previously shown that MT1-MMP activates latent Transforming Growth Factorbeta (TGF-beta). These findings strongly suggest that MT1-MMP-activated TGF-beta maintains osteoblast survival during transdifferentiation into osteocytes, and maintains mature osteocyte viability. Thus, the interrelationship of MMPs and TGF-beta may play an important role in bone formation and maintenance.

Synthesis of cinnamic acids and related isosteres as potent and selective αvβ3 receptor antagonists

We describe a series of conformationally-restricted cinnamic acid peptidomimetics as well as several cinnamic acid isosteres, including 3-phenylpropionic acids, 2-amino-3-phenylpropionic acids, phenoxyacetic acids and 2-phenylcyclopropylcarboxylic acids. Several analogues demonstrated low to sub-nanomolar potencies against alpha(v)beta(3) and greater than 200-fold selectivity against the other beta(3) integrin alpha(IIb)beta(3). In whole 293 cells, many of these analogues also showed modest selectivity against other alpha(v) integrins such as alpha(v)beta(1) and alpha(v)beta(5). These compounds were synthesized from readily available starting materials using either Heck or Mitsunobu coupling conditions.

An Efficient Synthesis of an αvβ3 Antagonist

A practical preparation of an alpha(v)beta(3) antagonist is reported. The antagonist consists of three key components, a tetrahydronaphthyridine moiety, a beta-alanine moiety, and a central imidazolidone moiety. The tetrahydronaphthyridine component was prepared using two different methods, both of which relied on variations of the Friedländer reaction to establish the desired regiochemistry. The beta-alanine component was prepared using Davies' asymmetric 1,4-addition methodology as the key stereo-defining step. The central imidazolidone portion was created from these two components using an effective three-step cyclization protocol. Thus, a highly convergent process for the drug candidate was defined.

Non-peptide α v β 3 antagonists: Identification of potent, chain-shortened RGD mimetics that incorporate a central pyrrolidinone constraint

Antagonists of the integrin receptor alpha(v)beta(3) are expected to have utility in the treatment of osteoporosis through inhibition of bone resorption. A series of potent, chain-shortened, pyrrolidinone-containing alpha(v)beta(3) receptor antagonists is described. Two sets of diasteromeric pairs of high-affinity antagonists demonstrated marked differences in log P values, which translated into differing dog pharmacokinetic properties. One member of this set was demonstrated to be effective in reducing bone resorption in rats.

Thiazolidinediones in type 2 diabetes mellitus: current clinical evidence

Type 2 diabetes mellitus is characterised by insulin resistance as well as progressive pancreatic beta cell dysfunction. The cornerstone of current oral blood-glucose lowering therapy consists of metformin, which primarily lowers hepatic glucose production, and the sulphonylureas that act by stimulating pancreatic beta-cells to secrete insulin. Recently, a novel class of agents, the thiazolidinediones, has been introduced that favourably influence insulin sensitivity and possibly also pancreatic beta-cell function. The thiazolidinediones are synthetic ligands that bind to the nuclear peroxisome proliferator-activated receptor-gamma and exert their action by activating transcription of genes that, among others, regulate adipocyte differentiation and adipogenesis as well as glucose and lipid metabolism. To date, the precise mechanisms underlying the actions of thiazolidinediones are largely unknown. When given as monotherapy or in combination with sulphonylureas, metformin or insulin in patients with type 2 diabetes, the currently available thiazolidinediones (rosiglitazone and pioglitazone) ameliorate glycaemic control, by lowering fasting and postprandial blood glucose levels, and improve insulin sensitivity in placebo-controlled trials. They seem to have differential effects on dyslipidaemia in patients with type 2 diabetes; rosiglitazone increases total cholesterol as well as high-density lipoprotein (HDL) and low-density lipoprotein cholesterol levels and affects plasma triglyceride levels depending on the baseline values, whereas pioglitazone lowers triglycerides and increases HDL cholesterol levels. The adverse events of both agents that occur with greater frequency than in patients treated with placebo are fluid retention and oedema. As demonstrated, mainly in preclinical studies to date, rosiglitazone and pioglitazone possess beneficial effects on other cardiovascular risk factors associated with the insulin resistance syndrome. Thus, these agents were shown to decrease blood pressure, enhance myocardial function and fibrinolysis, as well as possess anti-inflammatory and other beneficial vascular effects. Long-term efficacy and surveillance of this promising class of drugs in patients, however, still need to be demonstrated in outcome trials.

Design and synthesis of 1,5- and 2,5-substituted tetrahydrobenzazepinones as novel potent and selective integrin alphaVbeta3 antagonists

The design and synthesis of novel integrin alpha(V)beta(3) antagonists based on a 1,5- or 2,5-substituted tetrahydrobenzaezpinone core is described. In vitro activity of respective compounds was determined via alpha(V)beta(3) binding assay, and selected derivatives were submitted to further characterization in functional cellular assays. SAR was obtained by modification of the benzazepinone core, variation of the spacer linking guanidine moiety and core, and modification of the guanidine mimetic. These efforts led to the identification of novel alpha(V)beta(3) inhibitors displaying potency in the subnanomolar range, selectivity versus alpha(IIb)beta(3) and functional efficacy in relevant cellular assays. A method for the preparation of enantiomerically pure derivatives was developed, and respective enantiomers evaluated in vitro. Compounds 31 and 37 were assessed for metabolic stability, resorption in the Caco-2 assay and pharmacokinetics.

Rapid inhibition of thyroxine-induced bone resorption in the rat by an orally active vitronectin receptor antagonist

An excess of thyroid hormone results in increased bone turnover and loss of bone mass in humans. Exogenous administration of thyroid hormone to rats has served as a model of human hyperthyroidism in which antiresorptive therapies have been tested. We have further refined this model of thyroxine (T4)-induced turnover in the rat. Daily administration of T4 to aged rats for as short as 1 week resulted in elevated bone resorption determined by significantly higher urinary deoxypyridinoline (Dpd) compared with vehicle controls or animals receiving T4 plus estradiol. Three weeks of daily administration of T4 led to significantly lower bone mineral density compared with untreated controls or animals receiving T4 plus estradiol. In a follow-up study, a depot formulation of T4 caused an increase in Dpd identical to that achieved with a bolus dose. SB-273005 [(4S)-2,3,4,5-tetrahydro-8-[2-[6-(methylamino)-2-pyridinyl] ethoxy]-3-oxo-2-(2,2,2-trifluoroethyl)-1H-2-benzazepine-4- acetic acid] a potent antagonist of the integrins alpha(v)beta(3) and alpha(v)beta(5), has been shown previously to inhibit bone resorption in cultures of human osteoclasts and to protect bone in ovariectomized rats. The effect of SB-273005 by oral administration was evaluated in this thyroxine-induced turnover model. Dose-dependent inhibition of resorption was seen with SB-273005 after 7 days of dosing using Dpd as a measure of bone resorption. In summary, it has been demonstrated that the antiresorptive activity of a vitronectin receptor antagonist can be measured after only 7 days of treatment in this refined rat model of thyroxine-induced bone turnover. These data suggest that SB-273005 may be useful for the treatment of metabolic bone diseases, including those resulting from hyperthyroidism.

A potent small molecule, nonpeptide inhibitor of cathepsin K (SB 331750) prevents bone matrix resorption in the ovariectomized rat

Inhibition of the cyteine proteinase, cathepsin K (E.C. 3.4.22.38) has been postulated as a means to control osteoclast-mediated bone resorption. The preferred animal models for evaluation of antiresorptive activity are in the rat. However, the development of compounds that inhibit rat cathepsin K has proven difficult because the human and rat enzymes differ in key residues in the active site. In this study, a potent, nonpeptide inhibitor of rat cathepsin K (K(i) = 4.7 nmol/L), 5-(2-morpholin-4-yl-ethoxy)-benzofuran-2-carboxylic acid ((S)-3-methyl-1-(3-oxo-1-[2-(3-pyridin-2-yl-phenyl)-ethenoyl]-azepan-4-ylcarbanoyl)-butyl)-amide (SB 331750), is described, which is efficacious in rat models of bone resorption. SB 331750 potently inhibited human cathepsin K activity in vitro (K(i) = 0.0048 nmol/L) and was selective for human cathepsin K vs. cathepsins B (K(i) = 100 nmol/L), L (0.48 nmol/L), or S (K(i) = 14.3 nmol/L). In an in situ enzyme assay, SB 331750 inhibited osteoclast-associated cathepsin activity in tissue sections containing human osteoclasts (IC(50) approximately 60 nmol/L) and this translated into potent inhibition of human osteoclast-mediated bone resorption in vitro (IC(50) approximately 30 nmol/L). In vitro, SB 331750 partially, but dose-dependently, prevented the parathyroid hormone-induced hypercalcemia in an acute rat model of bone resorption. To evaluate the ability of SB 331750 to inhibit bone matrix degradation in vivo, it was administered for 4 weeks at 3, 10, or 30 mg/kg, intraperitoneally (i.p.), u.i.d. in the ovariectomized (ovx) rat. Both 10 and 30 mg/kg doses of compound prevented the ovx-induced elevation in urinary deoxypyridinoline and prevented the ovx-induced increase in percent eroded perimeter. Histological evaluation of the bones from compound-treated animals indicated that SB 331750 retarded bone matrix degradation in vivo at all three doses. The inhibition of bone resorption at the 10 and 30 mg/kg doses resulted in prevention of the ovx-induced reduction in percent trabecular area, trabecular number, and increase in trabecular spacing. These effects on bone resorption were also reflected in inhibition of the ovx-induced loss in trabecular bone volume as assessed using microcomputerized tomography (microCT; approximately 60% at 30 mg/kg). Together, these data indicate that the cathepsin K inhibitor, SB 331750, prevented bone resorption in vivo and this inhibition resulted in prevention of ovariectomy-induced loss in trabecular structure.

Synthesis and SAR of N-substituted dibenzazepinone derivatives as novel potent and selective alpha(V)beta(3) antagonists

Synthesis and SARs of new integrin alpha(V)beta(3) antagonists based on an N-substituted dibenzazepinone scaffold are described. Variation of spacer and guanidine mimetic led to potent compounds exhibiting an IC(50) towards alpha(V)beta(3) in the nanomolar range, high selectivity versus integrin alpha(IIb)beta(3) and efficacy in functional cellular assays.

Nonpeptide alpha(v)beta(3) antagonists. Part 2: constrained glycyl amides derived from the RGD tripeptide

Mimetics of the RGD tripeptide are described that are potent, selective antagonists of the integrin receptor, alpha(v)beta(3). The use of the 5,6,7,8-tetrahydro[1,8]naphthyridine group as a potency-enhancing N-terminus is demonstrated. Two 3-substituted-3-amino-propionic acids previously contained in alpha(IIb)beta(3) antagonists were utilized to enhance binding affinity and functional activity for the targeted receptor. Further affinity increases were then achieved through the use of cyclic glycyl amide bond constraints.

Emerging therapies in osteoporosis

The approval of alendronate in 1994 marked a watershed in the treatment of osteoporosis. Before that time there was no therapy for which unequivocal proof of efficacy existed. Since then several more agents, all from the anti-resorptive class, have also been approved for use in the treatment of this disease and the range of indications for alendronate has been extended to include the prevention of osteoporosis in women with lesser degrees of bone loss, the treatment of glucocorticoid-induced osteoporosis and, most recently, the treatment of male osteoporosis. Despite this there are still several areas of unmet medical need in this disease, including the availability of well tolerated and convenient therapies and treatments that will go beyond the levels of efficacy offered by current therapies. An intense effort is now being directed towards meeting these unmet needs with the improvement of existing therapies and the development of novel agents that will provide superior long term benefit. Important and exciting drug targets are yielding novel compounds with anti-resorptive activity or anabolic effects to complement current anti-resorptives. Despite this effort considerable obstacles to the successful development of these compounds remain, not least the stringent safety requirements needed to provide an acceptable risk-to-benefit profile and the increasing difficulties of conducting placebo controlled studies in patients at high risk of fracture.