Osteoprotegerin as a potential therapy for osteoporosis

Genetics and Epigenetics of Bone Remodeling and Metabolic Bone Diseases

Bone metabolism consists of a balance between bone formation and bone resorption, which is mediated by osteoblast and osteoclast activity, respectively. In order to ensure bone plasticity, the bone remodeling process needs to function properly. Mesenchymal stem cells differentiate into the osteoblast lineage by activating different signaling pathways, including transforming growth factor β (TGF-β)/bone morphogenic protein (BMP) and the Wingless/Int-1 (Wnt)/β-catenin pathways. Recent data indicate that bone remodeling processes are also epigenetically regulated by DNA methylation, histone post-translational modifications, and non-coding RNA expressions, such as micro-RNAs, long non-coding RNAs, and circular RNAs. Mutations and dysfunctions in pathways regulating the osteoblast differentiation might influence the bone remodeling process, ultimately leading to a large variety of metabolic bone diseases. In this review, we aim to summarize and describe the genetics and epigenetics of the bone remodeling process. Moreover, the current findings behind the genetics of metabolic bone diseases are also reported.

Type 2 17-β hydroxysteroid dehydrogenase as a novel target for the treatment of osteoporosis

Low estradiol level in postmenopausal women is implicated in osteoporosis, which occurs because of the high bone resorption rate. Estrogen formation is controlled by 17-β hydroxysteroid dehydrogenase 17-β HSD enzymes, where 17-β HSD type 1 contributes in the formation of estradiol, while type 2 catalyzes its catabolism. Inhibiting 17-β HSD2 can help in increasing estradiol concentration. Several promising 17-β HSD2 inhibitors that can act at low nanomolar range have been identified. However, there are some specific challenges associated with the application of these compounds. Our review provides an up-to-date summary of the current status and recent progress in the production of 17-β HSD2 inhibitors as well as the future challenges in their clinical application.

The role of RANK/RANKL/OPG signalling pathways in osteoclastogenesis in odontogenic keratocysts, radicular cysts, and ameloblastomas

The aim of this study was to evaluate the immunohistochemical expression of molecules involved in osteoclastogenesis, including the receptor activator of nuclear factor kappa B (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG) in odontogenic keratocysts (OKCs), which has been named as a keratocystic odontogenic tumour by the WHO, and compare their expression with radicular cysts and ameloblastomas. RANK is a member of tumour necrosis factor receptor family and it is activated by RANK ligand. OPG binds to RANKL and inactivates it. The imbalance of these factors could cause the differential bone resorption activity in some diseases and tumours. The expression of these molecules was evaluated in ameloblastomas (n = 20), OKCs (n = 20), and radicular cysts (n = 20) by immunohistochemistry. Immunohistochemical reactivity for RANK, RANKL, and OPG was detected in neoplastic and nonneoplastic epithelium and connective tissue cells. RANK showed the greatest expression in OKCs followed by ameloblastomas, with the lowest expression seen in radicular cysts. Expression of RANKL was detected in all lesions and no significant differences were observed between groups. OPG was expressed very low in all groups. In the stroma, the number of RANK positive cells was higher in OKCs when compared with ameloblastomas and radicular cysts but radicular cyst had higher numbers of RANKL positive cells in the stroma than ameloblastomas. The molecular system of RANK/RANKL/OPG is variably expressed in OKCs, radicular cysts, and ameloblastomas and this system may be involved in the osteoclastogenic mechanisms in OKCs and ameloblastomas. Advanced studies could further clarify the role of RANK, RANKL, and OPG in mediating tumour associated bone osteolysis.

Clinical applications of RANK-ligand inhibition

An enhanced rate of bone remodelling fuelled by osteoclastogenesis mediates diseases such as osteoporosis, arthritic bone destruction, Paget's disease and malignancy-induced bone loss. Thus, the control of osteoclastogenesis is of major clinical importance. The receptor activator of nuclear factor kappa B (RANK); its ligand, RANKL and decoy receptor, osteoprotegerin, are critical determinants of osteoclastogenesis, and increased RANK signalling is involved in several bone diseases, providing the rationale for RANKL inhibition. The effects of RANKL inhibition are being witnessed in clinical trials of neutralizing fully human monoclonal antibodies that target RANKL (e.g. denosumab) and which induce profound and sustained inhibition of bone resorption. The relative efficacy, cost-effectiveness and side-effects of targeted RANKL inhibition compared with conventional antiresorptive drugs (i.e. bisphosphonates) should be resolved by clinical trials in coming years.

Denosumab in osteoporosis and oncology

OBJECTIVE

To review the pharmacology, pharmacokinetics, pharmacodynamics, safety, efficacy, and use of denosumab in osteoporosis, breast cancer, prostate cancer, and multiple myeloma.

DATA SOURCES

Studies and abstracts were identified through MEDLINE and International Pharmaceutical Abstracts (1966-July 2009). Key search terms include denosumab, AMG-162, and receptor activator of nuclear factor-kappaB ligand system. Information available in abstract form was retrieved from major oncology and bone metabolism meetings. Additional data were obtained from the manufacturer.

STUDY SELECTION AND DATA EXTRACTION

All available studies in humans were included except for studies in rheumatoid arthritis and giant cell tumor of the bone.

DATA SYNTHESIS

In patients with osteoporosis, denosumab significantly reduces bone resorption and fractures. Studies of denosumab in the prevention and treatment of osteoporosis have demonstrated significantly increased bone mineral density and reduced bone turnover markers. Studies of denosumab versus placebo in the treatment of osteoporosis have demonstrated reductions in vertebral, hip, and nonvertebral fractures. In oncology, positive results from clinical trials in patients receiving endocrine therapy for breast and prostate cancer demonstrated decreases in bone loss and skeletal-related events. Denosumab seems to be at least as effective in reducing bone turnover markers as intravenous bisphosphonates in the oncology setting. The most common adverse effects in patients with osteoporosis were arthralgia, nasopharyngitis, back pain, and headache. The most common adverse effects in patients with cancer were infection, pain in the extremities, arthralgia, bone pain, fatigue, and pain. Serious adverse effects include infections requiring hospitalization.

CONCLUSIONS

Denosumab has documented efficacy and safety in patients with osteoporosis, breast cancer, and prostate cancer. Additional clinical trial data are needed to more completely establish the effectiveness of denosumab in the treatment of osteoporosis and neoplastic disease as well as its cost-effectiveness and long-term safety.

Recognition and management of treatment-related side effects for breast cancer patients receiving adjuvant endocrine therapy

In postmenopausal women with hormone receptor-positive early-stage breast cancer, the use of aromatase inhibitors (AIs) to suppress estrogen is associated with improved clinical outcomes compared with tamoxifen therapy. Women receiving such endocrine therapy may experience treatment-related side effects that negatively affect health-related quality of life (QoL) and adherence to therapy. In published clinical trials and in clinical practice, adverse events (AEs) constitute the main reason for nonadherence to endocrine treatment. Serious AEs are sometimes resolved by switching to a different agent, whereas other side effects can often be managed to allow patients to remain on therapy without sacrificing QoL. Across all adjuvant endocrine trials, regardless of the treatment received, vasomotor symptoms such as hot flashes are the most common side effects. Other frequently reported side effects, such as vaginal discharge, vaginal dryness, dyspareunia, and arthralgia, vary in prevalence between tamoxifen and AIs. Here we provide an overview of reported AEs of adjuvant endocrine therapy, focusing on those that are amenable to pharmacologic or nonpharmacologic management without treatment discontinuation. Also highlighted are specific management strategies that may improve patient QoL and thereby optimize adherence to therapy, which in turn might improve patient outcomes.