Denosumab for the treatment of bone metastases in breast cancer: evidence and opinion

Engineering small-molecule and protein drugs for targeting bone tumors

Bone cancer is common and severe. Both primary (e.g., osteosarcoma, Ewing sarcoma) and secondary (e.g., metastatic) bone cancers lead to significant health problems and death. Currently, treatments such as chemotherapy, hormone therapy, and radiation therapy are used to treat bone cancer, but they often only shrink or slow tumor growth and do not eliminate cancer completely. The bone microenvironment contributes unique signals that influence cancer growth, immunogenicity, and metastasis. Traditional cancer therapies have limited effectiveness due to off-target effects and poor distribution on bones. As a result, therapies with improved specificity and efficacy for treating bone tumors are highly needed. One of the most promising strategies involves the targeted delivery of pharmaceutical agents to the site of bone cancer by introduction of bone-targeting moieties, such as bisphosphonates or oligopeptides. These moieties have high affinities to the bone hydroxyapatite matrix, a structure found exclusively in skeletal tissue, and can enhance the targeting ability and efficacy of anticancer drugs when combating bone tumors. This review focuses on the engineering of small molecules and proteins with bone-targeting moieties for the treatment of bone tumors.

Anti-osteoporosis drugs reduce mortality in cancer patients: A national cohort study of elderly with vertebral fractures

Introduction

The most prevalent type of fragility fractures is osteoporotic vertebral fractures (OVFs). However, only a few studies have examined the relationship between anti-osteoporosis treatments and malignancy-related mortality following an OVF. The goal of this study is to determine the effect of anti-osteoporosis therapy on mortality in OVF patients with and without cancer.

Method

Data from older people over the age of 65 who were hospitalised for OVFs between 1 January 2003 and 31 December 2018 were analysed retrospectively. A total of 6139 persons getting osteoporosis treatment and 28,950 who did not receive treatment were analysed, together with 2 sets of patients, comprising cancer patients (794) and cancer-free patients (5342), using anti-osteoporosis medication or not, in 1:1 propensity score-matched analyses. The hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated.

Results

In all, 35,089 patients with OVFs were included in the population; 29,931 people (85.3%) were women, and the mean (standard deviation) age was 78.13 (9.27) years. Overall survival was considerably higher in those undergoing osteoporosis therapy. This was true both for those without cancer (adjusted HR 0.55; 95% CI 0.51-0.59; P<.0001) as well as those with cancer (adjusted HR 0.72; 95% CI 0.62-0.84; P<.0001). Even among cancer patients, those who received anti-osteoporotic drugs had a lower mortality rate than those who did not.

Conclusion

Our findings suggest that anti-osteoporosis therapy should be initiated regardless of the presence of cancer in the elderly, as it increases survival following OVFs.

Beyond boundaries: unraveling innovative approaches to combat bone-metastatic cancers

Evidence demonstrated that bones, liver, and lungs are the most common metastasis sites in some human malignancies, especially in prostate and breast cancers. Bone is the third most frequent target for spreading tumor cells among these organs and tissues. Patients with bone-metastatic cancers face a grim prognosis characterized by short median survival time. Current treatments have proven insufficient, as they can only inhibit metastasis or tumor progression within the bone tissues rather than providing a curative solution. Gaining a more profound comprehension of the interplay between tumor cells and the bone microenvironment (BME) is of utmost importance in tackling this issue. This knowledge will pave the way for developing innovative diagnostic and therapeutic approaches. This review summarizes the mechanisms underlying bone metastasis and discusses the clinical aspects of this pathologic condition. Additionally, it highlights emerging therapeutic interventions aimed at enhancing the quality of life for patients affected by bone-metastatic cancers. By synthesizing current research, this review seeks to shed light on the complexities of bone metastasis and offer insights for future advancements in patient care.

Bone-Targeted Therapy Regimen and Skeletal-Related Events in Patients Surviving Longer Than 2 Years With Metastatic Breast Cancer and Bone Metastasis

BACKGROUND

Bone-targeted therapy (BTT) including zoledronic acid (ZA) and denosumab decreases the risk of skeletal-related events (SREs) in patients with metastatic breast cancer (MBC) and bone metastasis. The impacts from prolonged BTT on SREs and BTT-associated harms are unknown and are becoming important to understand as these patients survive for longer periods.

METHODS AND MATERIALS

We conducted a retrospective study of 224 patients with MBC and bone metastasis who survived for more than 2 years after diagnosis and received treatment at our institution between 2016 and 2021. We defined 3 BTT patterns: (1) ZA only, (2) denosumab only, (3) both ZA and denosumab. The association between these BTT patterns and SREs and harms was assessed using Fisher exact test and logistic regression.

RESULTS

Rates of SREs overall were 21.2% of patients given ZA only, 8.8% of those given denosumab only, and 20% of those given both, without statistically significant differences (p = .32). However, those treated with denosumab only had significantly fewer compression fractures (0.7%) (p = .02). BTT-associated harm was observed in 5.8% of the ZA-only group, 11.7% of the denosumab-only group, and 14.3% of the group given both, without statistically significant differences (p = .37).

CONCLUSION

Oncologists may have increased flexibility regarding the frequency of administration of BTT along with their choice of agent. Our study showed no significant difference in the prevention of overall SRE or development of BTT-associated harms between the BTT regimens evaluated.

Severe Refractory Hypocalcemia Caused by Denosumab

Denosumab is a fully human monoclonal antibody that binds to the receptor activator of nuclear factor kappa-Β ligand, an essential cytokine factor in bone resorption, which reduces bone resorption and has been shown to decrease the incidence of skeletal-related events in patients with malignancy and bone metastasis. Severe hypocalcemia is a rare and life-threatening adverse effect of denosumab therapy. Here, we discuss the case of a patient with stage 4 estrogen receptor-positive, progesterone receptor-negative, human epidermal growth factor receptor 2-negative breast cancer who was on treatment with denosumab for bony metastases and presented with severe refractory hypocalcemia.

Disorders of Divalent Ions (Magnesium, Calcium, and Phosphorous) in Patients With Cancer

Disorders of the divalent ions (magnesium, calcium, and phosphorous) are frequently encountered in patients with cancer. Of these, hypomagnesemia, hypocalcemia, hypercalcemia, and hypophosphatemia are seen most commonly. These electrolyte disturbances may be related to the underlying malignancy or due to side effects of anticancer therapy. When caused by a paraneoplastic process, these abnormalities may portend a poor prognosis. Importantly, the development of severe electrolyte derangements may be associated with symptoms that negatively impact quality of life, preclude the administration of critical chemotherapeutic agents, or lead to life-threatening complications that require hospitalization and emergent treatment. In accordance, prompt recognition and treatment of these disorders is key to improving outcomes in patients living with cancer. This review will discuss selected derangements of the divalent ions seen in this population, with a focus on paraneoplastic and therapy-associated etiologies.

Breast Cancer-Epidemiology, Risk Factors, Classification, Prognostic Markers, and Current Treatment Strategies-An Updated Review

Simple Summary

Breast cancer is the most common cancer among women. It is estimated that 2.3 million new cases of BC are diagnosed globally each year. Based on mRNA gene expression levels, BC can be divided into molecular subtypes that provide insights into new treatment strategies and patient stratifications that impact the management of BC patients. This review addresses the overview on the BC epidemiology, risk factors, classification with an emphasis on molecular types, prognostic biomarkers, as well as possible treatment modalities.

Abstract

Breast cancer (BC) is the most frequently diagnosed cancer in women worldwide with more than 2 million new cases in 2020. Its incidence and death rates have increased over the last three decades due to the change in risk factor profiles, better cancer registration, and cancer detection. The number of risk factors of BC is significant and includes both the modifiable factors and non-modifiable factors. Currently, about 80% of patients with BC are individuals aged >50. Survival depends on both stage and molecular subtype. Invasive BCs comprise wide spectrum tumors that show a variation concerning their clinical presentation, behavior, and morphology. Based on mRNA gene expression levels, BC can be divided into molecular subtypes (Luminal A, Luminal B, HER2-enriched, and basal-like). The molecular subtypes provide insights into new treatment strategies and patient stratifications that impact the management of BC patients. The eighth edition of TNM classification outlines a new staging system for BC that, in addition to anatomical features, acknowledges biological factors. Treatment of breast cancer is complex and involves a combination of different modalities including surgery, radiotherapy, chemotherapy, hormonal therapy, or biological therapies delivered in diverse sequences.

Bone-modifying Agents (BMAs) in Breast Cancer

Bone-modifying agents (BMAs) are mainstays in breast cancer and prevent and treat osteoporosis in early-stage disease and reduce skeletal metastases complications in advanced disease. There is some evidence to support that BMA also prevents skeletal metastases and improves overall survival. Bone loss occurs with chemotherapy-induced ovarian failure, gonadotrophin-releasing hormone (GnRH) agonists, and aromatase inhibitors. In some women, the bone loss will be of sufficient magnitude to increase the risks of osteoporosis or fractures. Recommended steps in osteoporosis prevention or treatment include risk factor assessment, taking adequate amounts of calcium and vitamin D3, and periodic evaluations with dual-energy x-ray absorptiometry scanning. If clinically indicated by the T-scores and fracture-risk prediction algorithms treat with oral, IV bisphosphonates or subcutaneous denosumab (DEN). Zoledronic acid (ZA) or DEN reduces skeletal metastases complications, including pathological fracture, spinal cord compression, or the necessity for radiation or surgery to bone. Also, both of these drugs have the side-effect of osteonecrosis at a similar incidence. Monthly administration of ZA or DEN is standard, but several recent randomized trials show noninferiority between ZA monthly and every 3-month ZA. Every 3-month ZA is a new standard of care. Similar trials of the schedule of DEN are ongoing. ZA anticancer effect is only in postmenopausal women or premenopausal women rendered postmenopausal by GnRH agonists or bilateral oopherectomy. High-risk women, either postmenopausal or premenopausal, receiving GnRH/oopherctomy should consider adjuvant ZA. There are insufficient data to support DEN in this setting. Herein, this narrative review covers the mechanism of action of BMA, randomized clinical trials, and adverse events, both common and rare.

Monoclonal Antibodies: A Prospective and Retrospective View

BACKGROUND

Monoclonal Antibodies (mAbs) represent one of the most important classes of biotherapeutic agents. They are used to cure many diseases, including cancer, autoimmune diseases, cardiovascular diseases, angiogenesis-related diseases and, more recently also haemophilia. They can be highly varied in terms of format, source, and specificity to improve efficacy and to obtain more targeted applications. This can be achieved by leaving substantially unchanged the basic structural components for paratope clustering.

OBJECTIVES

The objective was to trace the most relevant findings that have deserved prestigious awards over the years, to report the most important clinical applications and to emphasize their latest emerging therapeutic trends.

RESULTS

We report the most relevant milestones and new technologies adopted for antibody development. Recent efforts in generating new engineered antibody-based formats are briefly reviewed. The most important antibody-based molecules that are (or are going to be) used for pharmacological practice have been collected in useful tables.

CONCLUSION

The topics here discussed prove the undisputed role of mAbs as innovative biopharmaceuticals molecules and as vital components of targeted pharmacological therapies.

Melatonin interrupts osteoclast functioning and suppresses tumor-secreted RANKL expression: implications for bone metastases

Cancer-related bone erosion occurs frequently in bone metastasis and is associated with severe complications such as chronic bone pain, fractures, and lower survival rates. In recognition of the fact that the darkness hormone melatonin is capable of regulating bone homeostasis, we explored its therapeutic potential in bone metastasis. We found that melatonin directly reduces osteoclast differentiation, bone resorption activity and promotes apoptosis of mature osteoclasts. We also observed that melatonin inhibits RANKL production in lung and prostate cancer cells by downregulating the p38 MAPK pathway, which in turn prevents cancer-associated osteoclast differentiation. In lung and prostate bone metastasis models, twice-weekly melatonin treatment markedly reduced tumor volumes and numbers of osteolytic lesions. Melatonin also substantially lowered the numbers of TRAP-positive osteoclasts in tibia bone marrow and RANKL expression in tumor tissue. These findings show promise for melatonin in the treatment of bone metastases.

Targeting cancer metastasis with antibody therapeutics

Cancer metastasis, the spread of disease from a primary to a distal site through the circulatory or lymphatic systems, accounts for over 90% of all cancer related deaths. Despite significant progress in the field of cancer therapy in recent years, mortality rates remain dramatically higher for patients with metastatic disease versus those with local or regional disease. Although there is clearly an urgent need to develop drugs that inhibit cancer spread, the overwhelming majority of anticancer therapies that have been developed to date are designed to inhibit tumor growth but fail to address the key stages of the metastatic process: invasion, intravasation, circulation, extravasation, and colonization. There is growing interest in engineering targeted therapeutics, such as antibody drugs, that inhibit various steps in the metastatic cascade. We present an overview of antibody therapeutic approaches, both in the pipeline and in the clinic, that disrupt the essential mechanisms that underlie cancer metastasis. These therapies include classes of antibodies that indirectly target metastasis, including anti-integrin, anticadherin, and immune checkpoint blocking antibodies, as well as monoclonal and bispecific antibodies that are specifically designed to interrupt disease dissemination. Although few antimetastatic antibodies have achieved clinical success to date, there are many promising candidates in various stages of development, and novel targets and approaches are constantly emerging. Collectively, these efforts will enrich our understanding of the molecular drivers of metastasis, and the new strategies that arise promise to have a profound impact on the future of cancer therapeutic development. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Bone metastases: a comprehensive review of the literature

The last report of the World Health Organization (WHO) stated that approximately four million people experience bone pain due to malignant diseases. Among them, metastatic bone pain is one of the most important sources of complaint. The estimated median survival in the presence of bone metastases ranks from 10 to 12 weeks. Bone represents a potential target of distant metastases for the majority of malignant tumours. However, the exact incidence of bone metastases is unknown. Bone metastases have an important socio-economic impact, and due to the enhancement of the overall survivorship, their incidence is increasing. Malignant neoplasms such as lung, thyroid, renal cancer, multiple myeloma, and melanoma often metastasize to the bone. Bone metastases commonly localize to the spinal column, pelvis, shoulder, and distal femur. The proper treatment for painful skeletal metastases is still unknown. Hence, the purpose of this review of the literature was to update current evidence concerning the aetiogenesis, biological behaviour, and treatment algorithms for painful skeletal metastases.

Tumor stem cells fuse with monocytes to form highly invasive tumor-hybrid cells

The 'cancer cell fusion' theory is controversial due to the lack of methods available to identify hybrid cells and to follow the phenomenon in patients. However, it seems to be one of the best explanations for both the origin and metastasis of primary tumors. Herein, we co-cultured lung cancer stem cells with human monocytes and analyzed the dynamics and properties of tumor-hybrid cells (THC), as well as the molecular mechanisms beneath this fusion process by several techniques: electron-microscopy, karyotyping, CRISPR-Cas9, RNA-seq, immunostaining, signaling blockage, among others. Moreover, mice models were assessed for in vivo characterization of hybrids colonization and invasiveness. Then, the presence of THCs in bloodstream and samples from primary and metastatic lesions were detected by FACS and immunofluorescence protocols, and their correlations with TNM stages established. Our data indicate that the generation of THCs depends on the expression of CD36 on tumor stem cells and the oxidative state and polarization of monocytes, the latter being strongly influenced by microenvironmental fluctuations. Highly oxidized M2-like monocytes show the strongest affinity to fuse with tumor stem cells. THCs are able to proliferate, colonize and invade organs. THC-specific cell surface signature CD36⁺CD14⁺PANK⁺ allows identifying them in matched primary tumor tissues and metastases as well as in bloodstream from patients with lung cancer, thus functioning as a biomarker. THCs levels in circulation correlate with TNM classification. Our results suggest that THCs are involved in both origin and spread of metastatic cells. Furthermore, they might set the bases for future therapies to avoid or eradicate lung cancer metastasis.

Multidisciplinary approaches to odontogenic lesions

PURPOSE OF REVIEW

To give an overview of technical considerations and relevant literature in the management odontogenic pathology with involvement of the maxillary sinus.

RECENT FINDINGS

Infections, cysts, benign neoplasms (odontogenic and nonodontogenic), and inflammatory conditions impact the maxillary sinus in various ways, could result in significant expansion within the maxillary sinus and significant infections.

SUMMARY

This manuscript provides an overview of common pathologic entities of the oral cavity proper that impacts the maxillary sinus health, with discussion of the role of the otorhinolaryngologist and the dental specialist.

The Roles of ROS Generation in RANKL-Induced Osteoclastogenesis: Suppressive Effects of Febuxostat

Receptor activator of NF-κB ligand (RANKL), a critical mediator of osteoclastogenesis, is upregulated in multiple myeloma (MM). The xanthine oxidase inhibitor febuxostat, clinically used for prevention of tumor lysis syndrome, has been demonstrated to effectively inhibit not only the generation of uric acid but also the formation of reactive oxygen species (ROS). ROS has been demonstrated to mediate RANKL-mediated osteoclastogenesis. In the present study, we therefore explored the role of cancer-treatment-induced ROS in RANKL-mediated osteoclastogenesis and the suppressive effects of febuxostat on ROS generation and osteoclastogenesis. RANKL dose-dependently induced ROS production in RAW264.7 preosteoclastic cells; however, febuxostat inhibited the RANKL-induced ROS production and osteoclast (OC) formation. Interestingly, doxorubicin (Dox) further enhanced RANKL-induced osteoclastogenesis through upregulation of ROS production, which was mostly abolished by addition of febuxostat. Febuxostat also inhibited osteoclastogenesis enhanced in cocultures of bone marrow cells with MM cells. Importantly, febuxostat rather suppressed MM cell viability and did not compromise Dox's anti-MM activity. In addition, febuxostat was able to alleviate pathological osteoclastic activity and bone loss in ovariectomized mice. Collectively, these results suggest that excessive ROS production by aberrant RANKL overexpression and/or anticancer treatment disadvantageously impacts bone, and that febuxostat can prevent the ROS-mediated osteoclastic bone damage.

Endocrine Therapy-related Endocrinopathies-Biology, Prevalence and Implications for the Management of Breast Cancer

Nearly 270,000 new breast cancer cases are predicted to be diagnosed in the USA in 2019 with more than 70% being estrogen receptor positive and treated using endocrine therapy. The suppression of estrogen biosynthesis or action via the use of ovarian suppression, aromatase inhibitors and selective estrogen receptor modulators/degraders, respectively, is effective in approximately 70% of women. The systemic inhibition of estrogen during breast cancer treatment is also associated with side effects due to the important endocrine functions of this steroid hormone, including its role in the maintenance of energy homeostasis and bone health. The current work will present perspectives of the impact of endocrine therapy from the point of view of breast medical oncology, endocrinology, and basic science.

Rare Distant Metastatic Disease of Ovarian and Peritoneal Carcinomatosis: A Review of the Literature

Background: Although metastases of ovarian and peritoneal carcinomatosis are most commonly found within the peritoneal cavity, there is a number of other rare distant sites that have been reported. Our goal is to provide an evidence-based summary of the available literature considering the rare distant metastatic sites of ovarian and peritoneal carcinomatosis. Methods: A comprehensive search of the literature was conducted, with Medline/PubMed being searched for cases of rare metastatic disease originated from primary ovarian and peritoneal cancer with related articles up to 2019 including terms such as "ovarian cancer", "metastases", "peritoneal" and others. Results: The most common mechanism of ovarian cancer metastases consists of primarily dissemination within the peritoneal cavity, while, rare and distant sites can either occur at the beginning or during the course of the disease and they are usually associated with hematogenous route and lymphatic invasion, having poor prognosis, with the least common sites being skin, bone, CNS, eye, placenta, central airways, rare lymph nodes, intra-abdominal organs, heart and breast. Conclusions: The occurrence of metastatic sites described in this review represents the most common rare distant metastatic sites, and even though their patterns of metastases are still not fully clarified due to the rarity of the reports, they offer valuable information considering the pathophysiology of the disease.

Denosumab versus bisphosphonates for the treatment of bone metastases from solid tumors: a systematic review

BACKGROUND

Bone metastases are highly prevalent in breast, prostate, lung and colon cancers. Their symptoms negatively affect quality of life and functionality and optimal management can mitigate these problems. There are two different targeted agents to treat them: bisphosphonates (pamidronate and zoledronic acid) and the monoclonal antibody denosumab. Estimates of cost-effectiveness are still mixed.

OBJECTIVE

To conduct a systematic review of economic studies that compares these two options.

METHOD

Literature search comprised eight databases and keywords for bone metastases, bisphosphonates, denosumab, and economic studies were used. Data were extracted regarding their methodologic characteristics and cost-effectiveness analyses. All studies were evaluated regarding to its methodological quality.

RESULTS

A total of 263 unique studies were retrieved and six met inclusion criteria. All studies were based on clinical trials and other existing literature data, and they had high methodological quality. Most found unfavorable cost-effectiveness for denosumab compared with zoledronic acid, with adjusted ICERS that ranged from $4638-87,354 per SRE avoided and from US$57,274-4.81 M. per QALY gained, which varied widely according to type of tumor, time horizon, among others. Results were sensitive to drug costs, time to first skeletal-related event (SRE), time horizon, and utility.

CONCLUSIONS

Denosumab had unfavorable cost-effectiveness compared with zoledronic acid in most of the included studies. New economic studies based on real-world data and longer time horizons comparing these therapeutic options are needed.

Anti-receptor activator of nuclear factor κB ligand antibody treatment increases osteoclastogenesis-promoting IL-8 in patients with rheumatoid arthritis

The receptor activator of nuclear factor κB ligand (RANKL) is an important factor for osteoclastogenesis and contributes to the pathology of rheumatoid arthritis (RA); thus, the anti-RANKL antibody (Ab) has been expected to protect joint destruction in RA patients. IL-8 also has osteoclastogenic activity; however, the role of IL-8 in the bone pathology of RA as well as the relation between IL-8 and RANKL remain unclear. In the present study, clinical observation revealed serum IL-8 levels of 611 pg ml-1 in RA patients with anti-RANKL Ab and 266 pg ml-1 in the same patients without anti-RANKL Ab. In vitro assay showed that anti-RANKL Ab induced production of IL-8 from pre-osteoclast-like cells (OCLs), and IL-8 promoted the formation of OCLs from peripheral monocytes even without RANKL activity. We further showed that treatment with FK506 (tacrolimus) possibly inhibits the increase in IL-8 levels in RA patients with anti-RANKL Ab, and in vitro assay confirmed that FK506 suppressed IL-8 production in pre-OCLs. These results suggest that inhibition of RANKL induces the change in osteoclastogenesis-promoting factor from RANKL to IL-8, and FK506 may be a valuable combination drug to support the use of anti-RANKL Ab in treatment of RA.

Monoclonal antibodies for the treatment of non-hematological tumors: a safety review

Introduction: The introduction of monoclonal antibodies (moAbs) into clinical practice revolutionized the treatment strategies in several solid tumors. These agents differ from cytotoxic chemotherapy for their mechanism of action and toxicity. By targeting specific antigens present on healthy cells and modulating immune system activity, these biological drugs are able to generate a wide spectrum of peculiar adverse events that can negatively impact on patients' quality of life. Areas covered: In this review, the main side effects associated with the use of moAbs have been described to show their incidence and current management strategies, which may drive clinicians in their daily practice. Expert opinion: The majority of these drugs represents an example of successful innovation, since they are able to induce a significant improvement of patients' survival and quality of life without any increase in related side effects as compared to standard cancer treatments. For this reason, they have become new milestones in personalized therapy for different non-hematological malignancies. With the increasing use of moAbs in treatment regimens, it is strongly recommended that clinicians are knowledgeable about the side effects associated with these agents, their management and monitoring, to optimize the clinical treatment of cancer patients.

The possible different roles of denosumab in prevention and cure breast cancer bone metastases: A 'hypothesis-generator' study from clinical practice

The most frequent site of recurrence in breast cancer (BC) is the bone, particularly in patients with ‘luminal-like’ disease. Denosumab has been shown to prevent aromatase inhibitors (AIs) induced bone resorption in postmenopausal early BC patients and reduce skeletal-related events (SREs) in bone metastatic breast cancer (BMBC). A ‘real life’ analysis of 90 BMBC patients treated with denosumab was performed. Eighty-six patients (95.6%) had ‘luminal-like’ disease, 72 (80%) had bone metastases at the time of first recurrence of disease. Among 50 patients with metachronous ‘luminal-like’ disease, 40 (80%) had first recurrence to the bone. Among these patients median time to skeletal recurrence (TSkR) was shorter for patients who were previously exposed to AIs compared to those who were not (53.0 vs. 102.0 months, respectively; P=0.0300) and longer for patients previously treated with tamoxifen compared to those who were not (102.0 vs. 59.0 months, respectively; P=0.0466). Both of them were not confirmed at multivariate analysis. In the overall population, 17 first SREs were observed (16 radiation therapy) and median time to first SRE was not reached. A statistically significant difference in the incidence of SREs was detected only between patients with exclusively osteolytic bone metastases vs. those without (P=0.013). The presence of exclusively-osteolytic bone metastases was the only factor significantly associated with a shorter time to first SRE (P=0.011). The only G3 toxicity reported was hypocalcemia in one patient. No osteonecrosis of the jaw events (ONJ) occurred. This study demonstrated that a pro-active attitude enables the treatment of the majority of patients with denosumab without significant class-related toxicities. The majority of SREs were from radiation therapy, so pain still remains the clinical hallmark of bone metastases, particularly for osteolytic ones. The suggestion that estrogen deprivation with AIs can favor a ‘bone-related’ risk conditions for developing bone metastases must be considered with caution and surely needs further validations.

Established Models and New Paradigms for Hypoxia-Driven Cancer-Associated Bone Disease

The five-year survival rate for primary bone cancers is ~ 70% while almost all cases of secondary metastatic bone cancer are terminal. Hypoxia, the deficiency of oxygen which occurs as the rate of tumour growth exceeds the supply of vascularisation, is a key promoter of tumour progression. Hypoxia-driven effects in the primary tumour are wide ranging including changes in gene expression, dysregulation of signalling pathways, resistance to chemotherapy, neovascularisation, increased tumour cell proliferation and migration. Paget's seed and soil theory states that for a metastasising tumour cell 'the seed' it requires the correct microenvironment 'soil' to colonise. Why and how metastasising tumour cells colonise the bone is a complex and intriguing problem. However, once present tumour cells are able to disrupt bone homeostasis through increasing osteoclast activity and downregulating osteoblast function. Osteoclast resorption releases growth factors from the bone matrix that subsequently contribute to the proliferation of invasive tumour cells creating the vicious cycle of bone loss and metastatic cancer progression. Recently, we have shown that hypoxia increases expression and release of lysyl oxidase (LOX) from primary mammary tumours, which in turn disrupts bone homeostasis to favour osteolytic degradation to create pre-metastatic niches in the bone microenvironment. We also demonstrated how treatment with bisphosphonates could block this cancer-induced bone remodelling and reduce secondary bone metastases. This review describes the roles of hypoxia in primary tumour progression to metastasis, with a focus on key signalling pathways and treatment options to reduce patient morbidity and increase survival.

Bone morphogenetic proteins, breast cancer, and bone metastases: striking the right balance

Bone morphogenetic proteins (BMPs) belong to the TGF-β super family, and are essential for the regulation of foetal development, tissue differentiation and homeostasis and a multitude of cellular functions. Naturally, this has led to the exploration of aberrance in this highly regulated system as a key factor in tumourigenesis. Originally identified for their role in osteogenesis and bone turnover, attention has been turned to the potential role of BMPs in tumour metastases to, and progression within, the bone niche. This is particularly pertinent to breast cancer, which commonly metastasises to bone, and in which studies have revealed aberrations of both BMP expression and signalling, which correlate clinically with breast cancer progression. Ultimately a BMP profile could provide new prognostic disease markers. As the evidence suggests a role for BMPs in regulating breast tumour cellular function, in particular interactions with tumour stroma and the bone metastatic microenvironment, there may be novel therapeutic potential in targeting BMP signalling in breast cancer. This review provides an update on the current knowledge of BMP abnormalities and their implication in the development and progression of breast cancer, particularly in the disease-specific bone metastasis.

MDA-MB-231 breast cancer cells fuel osteoclast metabolism and activity: A new rationale for the pathogenesis of osteolytic bone metastases

Recent progress in dissecting the molecular paracrine circuits of cancer and stromal cells in bone metastases (BM) are offering new options to improve current merely palliative approach. The study of tumor-stroma metabolic interplay may further ameliorate this scenario. In this context, we demonstrated that highly glycolytic MDA-MB-231 cancer cells, that form osteolytic BM in vivo, release a large amount of lactate at a significantly higher level than MCF7 cells. Thus, we speculated that lactate released from carcinoma cells is uptaken and metabolically used by osteoclasts, the key players of osteolysis associated with BM. First, we demonstrated that the release of lactate at the bone site is mediated by monocarboxylate transporter 4 (MCT4), as revealed by immunostaining and MCT4 localization at the plasma membrane of tumor cells in mouse model of BM and in human tissue sections of BM. Then, we showed that in vitro lactate is uptaken by osteoclasts to be used as a fuel for the oxidative metabolism of osteoclasts, ultimately enhancing Type I collagen resorption. The passive transport of lactate into osteoclasts was mediated by MCT1: MCT1 expression is significantly upregulated during osteoclast differentiation and Type I collagen resorption is significantly impaired when osteoclasts are treated with 7-(N-benzyl-N-methylamino)-2-oxo-2H-chromene-3-carboxylic acid, an MCT-1 inhibitor. Together, these data demonstrate that lactate released by glycolytic breast carcinoma cells in the bone microenvironment promotes the formation of osteolytic lesions, and provide the rationale for further studies on the use of MCT1 targeting as a novel therapeutic approach in advanced cancer patients with BM.

Bone Metastases: An Overview

Bone is a frequent site of metastases and typically indicates a short-term prognosis in cancer patients. Once cancer has spread to the bones it can rarely be cured, but often it can still be treated to slow its growth. The majority of skeletal metastases are due to breast and prostate cancer. Bone metastasis is actually much more common than primary bone cancers, especially in adults. The diagnosis is based on signs, symptoms and imaging. New classes of drugs and new interventions are given a better quality of life to these patients and improved the expectancy of life. It is necessary a multidisciplinary approach to treat patients with bone metastasis. In this paper we review the types, clinical approach and treatment of bone metastases.

Key Factors in Breast Cancer Dissemination and Establishment at the Bone: Past, Present and Future Perspectives

Bone metastases associated with breast cancer remain a clinical challenge due to their associated morbidity, limited therapeutic intervention and lack of prognostic markers. With a continually evolving understanding of bone biology and its dynamic microenvironment, many potential new targets have been proposed. In this chapter, we discuss the roles of well-established bone markers and how their targeting, in addition to tumour-targeted therapies, might help in the prevention and treatment of bone metastases. There are a vast number of bone markers, of which one of the best-known families is the bone morphogenetic proteins (BMPs). This chapter focuses on their role in breast cancer-associated bone metastases, associated signalling pathways and the possibilities for potential therapeutic intervention. In addition, this chapter provides an update on the role receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG) play on breast cancer development and their subsequent influence during the homing and establishment of breast cancer-associated bone metastases. Beyond the well-established bone molecules, this chapter also explores the role of other potential factors such as activated leukocyte cell adhesion molecule (ALCAM) and its potential impact on breast cancer cells' affinity for the bone environment, which implies that ALCAM could be a promising therapeutic target.

Design and synthesis of pyrimidinyl acyl thioureas as novel Hsp90 inhibitors in invasive ductal breast cancer and its bone metastasis

Invasive ductal carcinoma is the most common breast malignancies tumors and has tendency to bone metastases. Many oncogenic client proteins involved in formation of metastatic pathways. Stabilization, regulation, and maintenance of these oncogenic client proteins are provided with Heat Shock Protein 90 (Hsp90). Hsp90 perform these processes through its ATP binding and subsequent hydrolysis energy. Therefore, designing Hsp90 inhibitors is a novel cancer treatment method. However, many Hsp90 inhibitors have solubility problems and showed adverse effects in clinical trials. Thus, we designed and synthesized novel pyrimidinyl acyl thiourea derivatives to selectively inhibit Hsp90 alpha in human invasive ductal breast (MCF-7) and human bone osteosarcoma (Saos-2) cell lines. In vitro experiments showed that the compounds inhibited cell proliferation, ATP hydrolysis, and exhibited cytotoxic effect on these cancer cell lines. Further, gene expression was analyzed by microarray studies on MCF-7 cell lines. Several genes that play vital roles in breast cancer pathogenesis displayed altered gene expression in the presence of a selected pyrimidinyl acyl thiourea compound. Molecular docking studies were also performed to determine interaction between Hsp90 ATPase domain and pyrimidinyl acyl thiourea derivatives. The results indicated that the compounds are able to interact with Hsp90 ATP binding pocket and inhibit ATPase function. The designed compounds powerfully inhibit Hsp90 by an average of 1 μM inhibition constant. And further, the compounds perturb Hsp90 N terminal domain proper orientation and ATP may not provide required conformational change for Hsp90 function as evidenced by in silico experiments. Therefore, the designed compounds effectively inhibited both invasive ductal breast carcinoma and bone metastasis. Pyrimidinyl acyl thiourea derivatives may provide a drug template for effective treatment of invasive ductal breast carcinoma and its bone metastasis as well as new therapeutic perspective for drug design.

Use of Animal Models in Understanding Cancer-induced Bone Pain

Many common cancers have a propensity to metastasize to bone. Although malignancies often go undetected in their native tissues, bone metastases produce excruciating pain that severely compromises patient quality of life. Cancer-induced bone pain (CIBP) is poorly managed with existing medications, and its multifaceted etiology remains to be fully elucidated. Novel analgesic targets arise as more is learned about this complex and distinct pain state. Over the past two decades, multiple animal models have been developed to study CIBP’s unique pathology and identify therapeutic targets. Here, we review animal models of CIBP and the mechanistic insights gained as these models evolve. Findings from immunocompromised and immunocompetent host systems are discussed separately to highlight the effect of model choice on outcome. Gaining an understanding of the unique neuromolecular profile of cancer pain through the use of appropriate animal models will aid in the development of more effective therapeutics for CIBP.

MAPK11 in breast cancer cells enhances osteoclastogenesis and bone resorption

Breast cancer cells frequently metastasize to bone and induce osteolytic bone destruction in patients. These metastases cause severe bone pain, high risk of fractures and hypercalcemia, and are essentially incurable and fatal. Recent studies show that breast cancer cells in bone activate osteoclastogenesis and bone resorption. However the underlying mechanism is poorly understood. This study shows that the p38 MAPK (p38) isoform MAPK11 (p38β) is expressed in breast cancer cells. By using specific small hairpin RNAs for MAPK11, we demonstrated that p38β-mediated p38 activity in breast cancer cells is responsible for breast cancer-induced osteolytic bone destruction. The addition of conditioned media from breast cancer cell lines MDA-MB-231 and MDA-MB-468, which have high expression of p38β, induced osteoclast differentiation and bone resorption. In contrast, knockdown of p38β in breast cancer cells reduced osteoclast differentiation in vitro and reduced bone destruction in severe combined immunodeficiency (SCID) mouse models. The knockdown of p38β did not affect tumor growth or survival or the ability of cancer cells to home to bone. Furthermore, our results showed that p38β upregulated the expression and secretion of monocyte chemotactic protein-1 (MCP-1) in breast cancer cells, and upregulated MCP-1 activates osteoclast differentiation and activity. This study elucidates a novel molecular mechanism of breast cancer cell-induced osteolytic bone destruction. This study also indicates that targeting breast cancer cell p38β and its product MCP-1 may be a viable approach to treat or prevent bone destruction in patients with bone-metastatic breast cancer.

Antiresorptive drug-related osteonecrosis of the jaw

Nitrogen-containing and non-nitrogen-containing bisphosphonates have been implicated in the development of osteonecrosis of the jaw (ONJ), a condition termed bisphosphonate-related OHJ. Other antiresorptive drugs have been implicated in the development of OHJ, hence the new term antiresorptive drug-related ONJ. The underlying pathogenesis remains unclear, and no definite diagnosis or cure has been established for this debilitating condition. This article reviews some of the most common antiresorptive drugs with their associated risks of ONJ and the current understanding of the pathogenesis ONJ, and summarizes current clinical guidelines.

Preclinical evaluation of sunitinib as a single agent in the prophylactic setting in a mouse model of bone metastases

Background

A substantial number of breast cancer patients are identified as being at high risk of developing metastatic disease. With increasing number of targeted therapeutics entering clinical trials, chronic administration of these agents may be a feasible approach for the prevention of metastases within this subgroup of patients. In this preclinical study we examined whether Sunitinib, a multi-tyrosine kinase inhibitor which has anti-angiogenic and anti-resorptive activity, is effective in the prevention of bone metastases.

Method

Sunitinib was administered daily with the first dose commencing prior to tumor cell inoculation. Intracardiac injection was performed with MDA-MB23 bone-seeking cells, which were stably transfected with DsRed2. In vivo plain radiography and fluorescent imaging (Berthold NightOwl) was used in the analysis of bone metastases. Histomorphometry was used for the quantification of TRAP⁺ cells from bone sections and immunohistochemistry was performed using an antibody reactive to CD34 for quantification of microvessel density.

Results

Preventive dosing administration of Sunitinib does not inhibit colonization of tumor cells to bone or reduce the size of osteolytic lesions. There was a decrease in the number of TRAP⁺ cells with Sunitinib treatment but this did not reach significance. Sunitinib inhibited tumor growth as determined by imaging of fluorescent tumor area. Immunohistochemical analyses of microvessel density revealed a concomitant decrease in the number of tumor blood vessels.

Conclusions

The findings suggest that Sunitinib can be used as a therapeutic agent for the treatment of bone metastases but as a single agent it is not effective in terms of prevention. Therefore a combination approach with other cytostatic drugs should be pursued.

The RANKL/RANK system as a therapeutic target for bone invasion by oral squamous cell carcinoma (Review)

Squamous cell carcinomas (SCCs) of the gingiva frequently invade the mandible or maxilla; this invasion is associated with a worse prognosis. The bone destruction associated with carcinomal invasion is mediated by osteoclasts rather than directly by the carcinoma. Therefore, if the cellular and molecular mechanisms by which oral SCC regulates bone invasion were known, it could inform the development of new therapeutic targets. Recently, dysregulation of the functional equilibrium in the receptor activator of NF-κB ligand (RANKL)/RANK/osteoprotegerin (OPG) triad has been shown to be responsible for osteolysis associated with the development of malignant tumors in bone sites. Furthermore, the administration of OPG or soluble RANK prevents bone metastasis by cancer cells. In this review, we discuss recent findings indicating that bone invasion by oral SCC is mediated via RANKL/RANK and may be successfully prevented by RANKL inhibition.

Efficacy and safety of denosumab for the treatment of bone metastases in patients with advanced cancer

Bone metastases are known to be caused by all types of cancer. Cancer metastasis to bone has been said to considerably compromise patients' quality of life and adversely affect lifetime prognosis. Although progress in cancer treatment has prolonged survival significantly, this may make increased numbers of patients suffer from bone metastases. Until now, as for the treatment of bone metastases, local therapies, including radiation therapy and surgery, were performed mainly as palliative therapies. However, bisphosphonate-based therapies have recently become available and are frequently administered to delay or prevent skeletal-related events, which include pathologic bone fracture, spinal cord compression, radiologic treatment for bone lesions, surgical procedures for bone lesions and hypercalcemia. Moreover, denosumab, the first fully human monoclonal antibody to receptor activator of nuclear factor κ-B ligand, was approved in the USA because of its evidence-supported clinical effects. Denosumab was effective for prolonging the time to skeletal-related events and inhibiting the onset of pain via the suppression of osteoclast activation. Denosumab has been shown to have a greater effect compared with zoledronic acid, most notably in patients with breast or prostate cancer. In this article, the efficacy and safety of denosumab for the treatment of bone metastases in patients with various advanced cancers are discussed.