Potential role of odanacatib in the treatment of osteoporosis

Review of Cathepsin K Inhibitor Development and the Potential Role of Phytochemicals

Cathepsin K plays a pivotal role in bone resorption and has emerged as a prominent therapeutic target for treating bone-related diseases such as osteoporosis. Despite significant advances in synthetic inhibitor development, none have achieved FDA approval due to safety and efficacy challenges. This review highlights the potential of phytochemicals as alternative inhibitors, emphasizing their natural origin, structural diversity, and minimal adverse effects. Key phytochemicals, including AC-5-1, Cycloaltilisin 6, Cycloaltilisin 7, Nicolaioidesin C, and Panduratin A, were examined for their inhibitory activities against cathepsin K. While these compounds exhibit varying IC50 values, their docking studies revealed significant interactions within Cathepsin K's active site, particularly involving critical residues such as Cys25 and His162. However, challenges such as lower potency compared to synthetic inhibitors and limited in vivo studies underscore the need for structural optimization and comprehensive preclinical evaluations. This review discusses biological insights, current limitations, and future strategies for advancing phytochemical-based inhibitors toward clinical applications in managing Cathepsin K-associated diseases.

Cortical bone mineral density is increased by the cathepsin K inhibitor ONO-5334, which leads to a robust increase in bone strength: results from a 16-month study in ovariectomised cynomolgus monkeys

This study evaluated the long-term effects of the cathepsin K inhibitor ONO-5334 on bone mass and strength in ovariectomised (OVX) cynomolgus monkeys. Animals were assigned to one of the following six groups: Sham (non-OVX), OVX control treated with vehicle, ONO-5334 1.2, 6 or 30 mg/kg/day, p.o., or alendronate (ALN) 0.05 mg/kg/2 weeks, i.v. for 16 months. Peripheral quantitative computed tomography (pQCT) analysis revealed that ONO-5334 increased not only trabecular bone mineral density (BMD) but also cortical BMD in the distal radius and the lumbar vertebra. ONO-5334 and ALN suppressed the deterioration of trabecular architecture by micro-CT analysis in the distal radius. Assessments of bone strength showed that ONO-5334 increased maximum load at the distal and midshaft radius. The linear regression lines between bone mass and strength in the lumbar vertebra were tended to be shifted towards increasing bone strength in the ONO-5334 6 and 30 mg/kg groups compared with the ALN groups. This indicated that bone strength was higher in the ONO-5334 groups than the ALN group, even though bone mineral content (BMC) and BMD were comparable. Subpopulation analysis revealed that, at similar integral BMC or BMD level, cortical bone mass for ONO-5334 was higher than for ALN; the opposite effects were observed for trabecular bone. In conclusion, ONO-5334 preferentially increased cortical bone, which may provide a greater contribution to bone strength. Since these results support a different mode of action for ONO-5334 compared with that of ALN, ONO-5334 may offer new therapeutic options to patients with osteoporosis.

Biological Activity and Physicochemical Properties of Dipeptidyl Nitrile Derivatives Against Pancreatic Ductal Adenocarcinoma Cells

Background:

Pancreatic cancer is one of the most aggressive types with high mortality in patients. Therefore, studies to discover new drugs based on cellular targets have been developed to treat this disease. Due to the importance of Cysteine Protease (CP) to several cellular processes in cancer cells, CP inhibitors have been studied as novel alternative approaches for pancreatic cancer therapy.

Objective:

The cytostatic potential of new CP inhibitors derived from dipeptidyl nitriles is analyzed in vitro using pancreatic cancer (MIA PaCa-2) cells.

Methods:

The cytotoxic and cytostatic activities were studied using MTT colorimetric assay in 2D and 3D cultures. Colony formation, migration in Boyden chamber and cell cycle analysis were applied to further study the cytostatic activity. The inhibition of cysteine proteases was evaluated with Z-FR-MCA selective substrate, and ROS evaluation was performed with DCFH-DA fluorophore. Permeability was investigated using HPLC-MS to obtain log kw. Combination therapy was also evaluated using the best compound with gemcitabine.

Results:

The inhibition of intracellular CP activity by the compounds was confirmed, and the cytostatic effect was established with cell cycle retention in the G1 phase. CP inhibitors were able to reduce cell proliferation by 50% in the clonogenic assay, and the same result was achieved for the migration assay, without any cytotoxic effect. The Neq0554 inhibitor was also efficient to increase the gemcitabine potency in the combination therapy. Physicochemical properties using an artificial membrane model quantified 1.14 ≥ log Kw ≥ 0.75 for all inhibitors (also confirmed using HPLC-MS analysis) along with the identification of intra and extracellular metabolites. Finally, these dipeptidyl nitrile derivatives did not trigger the formation of reactive oxygen species, which is linked to genotoxicity.

Conclusion:

Altogether, these results provide a clear and favorable picture to develop CP inhibitors in pre-clinical assays.

Morning vs evening dosing of the cathepsin K inhibitor ONO-5334: effects on bone resorption in postmenopausal women in a randomized, phase 1 trial

The cathepsin K inhibitor, ONO-5334, improves bone mineral density in postmenopausal women with osteoporosis. The effects of morning versus evening administration of ONO-5334 were investigated by measuring bone turnover marker levels in healthy postmenopausal women. Morning administration of ONO-5334 showed a more consistent suppressive effect on bone resorption than evening administration.

INTRODUCTION

Bone turnover is thought to be subject to circadian variation, and the efficacy of osteoporosis treatments may be optimized by regulating the time of dosing. This study assessed whether evening administration of the cathepsin K inhibitor, ONO-5334, had a differential effect on the bone turnover marker, C-terminal telopeptide of type I collagen (CTX-I), compared with morning administration.

METHODS

This was a single-center, single blind crossover study. Fourteen healthy postmenopausal women were assigned to receive ONO-5334 150 mg once daily for 5 days in each period; they were randomized to receive either evening doses in the first period and morning doses in the second or vice versa. Serum and urinary levels of CTX-I were measured throughout the study.

RESULTS

Both regimens showed similar patterns of reduction in serum and urinary CTX-I; however, CTX-I suppression was more consistently >60% over 24 h following morning administration. Morning administration led to 6% greater suppression of 24-h serum CTX-I area under the effect curve (AUE; 69 vs 63%; P < .05) and 7% greater suppression of urinary CTX-I/creatinine AUE (93 vs 86%; P < .01) than evening administration. Higher plasma ONO-5334 concentrations were observed between 12 and 24 h postdose following morning administration, with mean trough concentrations for the morning and evening regimens at 9.4 and 4.0 ng/mL, respectively. There were no safety findings of concern.

CONCLUSION

Morning dosing of ONO-5334 is more efficacious at reducing markers of bone turnover in healthy postmenopausal women than evening dosing.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01384188 , registered on June 27, 2011 EudraCT: 2008-006284-37.

Development of N-(Functionalized benzoyl)-homocycloleucyl-glycinonitriles as Potent Cathepsin K Inhibitors

Cathepsin K is a major drug target for osteoporosis and related-bone disorders. Using a combination of virtual combinatorial chemistry, QSAR modeling, and molecular docking studies, a series of cathepsin K inhibitors based on N-(functionalized benzoyl)-homocycloleucyl-glycinonitrile scaffold was developed. In order to avoid previous problems of cathepsin K inhibitors associated with lysosomotropism of compounds with basic character that resulted in off-target effects, a weakly- to nonbasic moiety was incorporated into the P3 position. Compounds 5, 6, and 9 were highly selective for cathepsin K when compared with cathepsins L and S, with the Ki values in the 10-30 nM range. The kinetic studies revealed that the new compounds exhibited reversible tight binding to cathepsin K, while the X-ray structural studies showed covalent and noncovalent binding between the nitrile group and the catalytic cysteine (Cys25) site.

Azanitrile Cathepsin K Inhibitors: Effects on Cell Toxicity, Osteoblast-Induced Mineralization and Osteoclast-Mediated Bone Resorption

Aim

The cysteine protease cathepsin K (CatK), abundantly expressed in osteoclasts, is responsible for the degradation of bone matrix proteins, including collagen type 1. Thus, CatK is an attractive target for new anti-resorptive osteoporosis therapies, but the wider effects of CatK inhibitors on bone cells also need to be evaluated to assess their effects on bone. Therefore, we selected, among a series of synthetized isothiosemicarbazides, two molecules which are highly selective CatK inhibitors (CKIs) to test their effects on osteoblasts and osteoclasts.

Research Design and Methods

Cell viability upon treatment of CKIs were was assayed on human osteoblast-like Saos-2, mouse monocyte cell line RAW 264.7 and mature mouse osteoclasts differentiated from bone marrow. Osteoblast-induced mineralization in Saos-2 cells and in mouse primary osteoblasts from calvaria, with or without CKIs,; were was monitored by Alizarin Red staining and alkaline phosphatase activity, while osteoclast-induced bone resorption was performed on bovine slices.

Results

Treatments with two CKIs, CKI-8 and CKI-13 in human osteoblast-like Saos-2, murine RAW 264.7 macrophages stimulated with RANKL and mouse osteoclasts differentiated from bone marrow stimulated with RANKL and MCSF were found not to be toxic at doses of up to 100 nM. As probed by Alizarin Red staining, CKI-8 did not inhibit osteoblast-induced mineralization in mouse primary osteoblasts as well as in osteoblast-like Saos-2 cells. However, CKI-13 led to a reduction in mineralization of around 40% at 10–100 nM concentrations in osteoblast-like Saos-2 cells while it did not in primary cells. After a 48-hour incubation, both CKI-8 and CKI-13 decreased bone resorption on bovine bone slices. CKI-13 was more efficient than the commercial inhibitor E-64 in inhibiting bone resorption induced by osteoclasts on bovine bone slices. Both CKI-8 and CKI-13 created smaller bone resorption pits on bovine bone slices, suggesting that the mobility of osteoclasts was slowed down by the addition of CKI-8 and CKI-13.

Conclusion

CKI-8 and CKI-13 screened here show promise as antiresorptive osteoporosis therapeutics but some off target effects on osteoblasts were found with CKI-13.

New antiresorptive therapies for postmenopausal osteoporosis

Osteoporosis is a systemic skeletal disease whose risk increases with age and it is common among postmenopausal women. Currently, almost all pharmacological agents for osteoporosis target the bone resorption component of bone remodeling activity. Current antiresorptive agents are effective, but the effectiveness of some agents is limited by real or perceived intolerance, longterm adverse events (AEs), coexisting comorbidities, and inadequate long-term adherence. New antiresorptive therapies that may expand options for the prevention and treatment of osteoporosis include denosumab, combination of conjugated estrogen/bazedoxifene and cathepsin K inhibitors. However, the long-term efficacy and AEs of these antiresorptive therapies need to be confirmed in studies with a longer follow-up period.

Effect of odanacatib on BMD and fractures: estimates from Bayesian univariate and bivariate meta-analyses

CONTEXT

Odanacatib (ODN), a selective cathepsin-K inhibitor, was found to increase bone mineral density (BMD); the effect on fractures is based on adverse event reports.

OBJECTIVE

To estimate current effects and predict future effects of ODN on BMD and fractures.

DATA SOURCES

Electronic databases (Medline, EMBASE, Cochrane Library), conference proceedings, and bibliographies.

STUDY SELECTION

Trials that compared ODN 50 mg/wk to placebo for at least 1 year and reported changes in BMD or fractures. Meta-analysis: Two bone outcomes were pooled as independent and as joint outcomes in Bayesian univariate and bivariate random-effects models.

DATA SYNTHESIS

Of 32 potentially eligible articles, six citations describing four trials (993 patients) were included. ODN for 3 years increased mean BMD at the lumbar spine by 5.0% (95% credible interval [CrI], 2.7, 7.5), total hip by 3.6% (95% CrI, 1.6, 5.9), and femoral neck (FN) by 3.6% (95% CrI, 1.6, 5.7). In a future trial of 3-year duration, the predicted mean increase in BMD, adjusted for the effect on fractures, was 4.9% for lumbar spine (95% CrI, 2.5, 7.4), 3.4% for total hip (95% CrI, 1.7, 5.2), and 3.5% for FN (95% CrI, 1.8, 5.3). After accounting for the effect on FN BMD, ODN for 3 years was associated with a population odds ratio of 0.38 (95% CrI, 0.1, 0.8). In a future trial, the odds ratio was 0.41 (95% CrI, 0.1, 1.1). The probability of benefit on fractures was 96-99%. The estimates remained robust in sensitivity analyses.

CONCLUSIONS

Our analyses suggest that ODN will increase BMD and decrease all fractures in the fracture outcome trial; however, direct demonstration of this antifracture efficacy is needed.

The role of small molecules in bone regeneration

Although several methods have been used in bone regeneration medicine, current methods still have many limitations. The tissue used for autogenous bone graft is limited and allograft has weak osteoinductive activity. Tissue engineering provides a good choice for bone regeneration. However, the growth factors needed have a high price and short half-life. Recently, a number of small molecules have been confirmed to have osteoinductive activity and some have been clinically used. Natural small molecules including decalpenic acid, flavonoids, quinones can be extracted from plants and others can be synthesized according to the structure designed or mimicking the structure of natural small molecules. Small molecules can act as co-activator of BMP2 pathway or activate Wnt pathway; others can be the inhibitors of NF-κB signaling pathway. This review gives an overview on the small molecules with osteoinductive activity and discusses the mechanism of the small molecules.

New therapeutics for osteoporosis

Two new approaches for the treatment of osteoporosis are summarized, each having arisen out of important new discoveries in bone biology. Odanacatib (ODN) inhibits the enzyme, cathepsin K, that is essential for the resorbing activity of osteoclasts. It is effective in preventing ovariectomy-induced bone loss in preclinical studies, and a phase II clinical study has shown inhibition of resorption sustained over five years. Outcome of a phase III study is awaited. The finding from mouse and human genetics that Wnt signaling is a powerful inducer of bone formation led to developments aimed at enhancing this pathway. Of the several approaches towards this, the most advanced is with a neutralizing antibody against sclerostin, the osteocyte-derived inhibitor of Wnt signaling. Preclinical studies show a powerful bone anabolic effect, and a clinical phase II study shows dose-dependent increases in bone formation and decreases in bone resorption markers.

Implications of osteoblast-osteoclast interactions in the management of osteoporosis by antiresorptive agents denosumab and odanacatib

Antiresorptive agents, used in the treatment of osteoporosis, inhibit either osteoclast formation or function. However, with these approaches, osteoblast activity is also reduced because of the loss of osteoclast-derived coupling factors that serve to stimulate bone formation. This review discusses how osteoclast inhibition influences osteoblast function, comparing the actions of an inhibitor of osteoclast formation [anti-RANKL/Denosumab (DMAB)] with that of a specific inhibitor of osteoclastic cathepsin K activity [Odanacatib (ODN)]. Denosumab rapidly and profoundly, but reversibly, reduces bone formation. In contrast, preclinical studies and clinical trials of ODN showed that bone formation at some skeletal sites was preserved although resorption was reduced. This preservation of bone formation appears to be due to effects of coupling factors, secreted by osteoclasts and released from demineralized bone matrix. This indicates that bone resorptive activities of osteoclasts are separable from their coupling activities.

Osteoporosis - a current view of pharmacological prevention and treatment

Postmenopausal osteoporosis is the most common bone disease, associated with low bone mineral density (BMD) and pathological fractures which lead to significant morbidity. It is defined clinically by a BMD of 2.5 standard deviations or more below the young female adult mean (T-score =−2.5). Osteoporosis was a huge global problem both socially and economically – in the UK alone, in 2011 £6 million per day was spent on treatment and social care of the 230,000 osteoporotic fracture patients – and therefore viable preventative and therapeutic approaches are key to managing this problem within the aging population of today. One of the main issues surrounding the potential of osteoporosis management is diagnosing patients at risk before they develop a fracture. We discuss the current and future possibilities for identifying susceptible patients, from fracture risk assessment to shape modeling and in relation to the high heritability of osteoporosis now that a plethora of genes have been associated with low BMD and osteoporotic fracture. This review highlights the current therapeutics in clinical use (including bisphosphonates, anti-RANKL [receptor activator of NF-κB ligand], intermittent low dose parathyroid hormone, and strontium ranelate) and some of those in development (anti-sclerostin antibodies and cathepsin K inhibitors). By highlighting the intimate relationship between the activities of bone forming (osteoblasts) and bone-resorbing (osteoclasts) cells, we include an overview and comparison of the molecular mechanisms exploited in each therapy.