Randomized, double-blind study of denosumab versus zoledronic acid in the treatment of bone metastases in patients with advanced cancer (excluding breast and prostate cancer) or multiple myeloma

Novel therapies in benign and malignant bone diseases

With an ageing population and improving cancer therapies, the two most common benign and malignant bone diseases, osteoporosis and bone metastases, will continue to affect an increasing number of patients. Our expanding knowledge of the molecular processes underlying these conditions has resulted in novel bone targets that are currently being explored in clinical trials. Clearly, the approval of denosumab, a monoclonal antibody directed against RANKL, has just marked the beginning of a new era for bone therapy with several additional new therapies lining up for clinical approval in the coming years. Potential agents targeting the osteoclast include cathepsin K, currently in phase 3 trials, and src inhibitors. Amongst anabolic agents, inhibitors of the Wnt-inhibitor sclerostin and dickkopf-1 are promising in clinical trials. Here, we will provide a comprehensive overview of the most promising agents currently explored for the treatment of bone diseases.

New and emerging agents for the treatment of castration-resistant prostate cancer

Most men with recurrent prostate cancer (CaP) initially respond to androgen deprivation therapy but eventually develop metastatic castration-resistant prostate cancer (CRPC). Over the last decade, new therapeutic targets have been identified in CRPC and several new drugs have reached advanced stages of clinical development. In 2010, the Food and Drug Administration (FDA) approved sipuleucel-T and cabazitaxel, and in 2011, abiraterone for patients with metastatic CRPC based on phase 3 trials showing improved survival. Although not yet available for clinical use, a press release in June 2011 announced that radium 223 also demonstrated a survival advantage in men with metastatic CRPC. Emerging therapies in advanced stages of clinical development in CRPC include the hormonal therapies MDV3100 and TAK 700, and the immunotherapy ipilimumab. Results are also pending on phase 3 studies comparing docetaxel plus prednisone with docetaxel given with the novel agents aflibercept, dasatinib, lenalidomide, and custirsen. In addition to these new and emerging therapeutic agents, denosumab was approved for the prevention of skeletal complications in patients with bone metastases due to solid tumor malignancies, providing an alternative to zoledronic acid. While the addition of these new treatment options is a great advance for men with metastatic CRPC, there are many new questions arising regarding sequencing of these treatments with each other, with previously existing therapies, and with the emerging agents now in clinical trials. Furthermore, there are concerns that on-going phase 3 trials may be contaminated if patients go off study treatment to start 1 of the newly approved agents or take the agent subsequently. These realities make clinical trial design more challenging than ever.

Role of denosumab in prostate cancer

Prostate cancer is known to have a tissue tropism for bone. This tissue tropism coupled with the experience with androgen deprivation therapy (ADT) over the past decade has led to heightened awareness of bone complications. Osteopenia and subsequent skeletal-related events (SREs) are one of the more concerning repercussions of ADT along with cardiovascular sequelae. To combat this decrease in bone mineral density, several agents have been developed for bone protection. The largest experience is with bisphosphonates (BPs), but recently (2011) head to head trials have established the role of monoclonal antibodies, particularly in patients with prostate cancer bone metastasis. For patients initiating ADT, monthly denosumab increased bone mineral density, the time for occurrence of any bone metastasis and time for symptomatic bone metastasis. Denosumab is a fully human monoclonal antibody of the IgG(2) subtype that selectively binds and neutralizes receptor activator NF kappa B ligand (RANKL), inhibiting osteoclastogenesis and bone turnover. In vitro binding assays have shown high-affinity binding of denosumab and osteoprotegerin to both soluble and membrane-bound forms of human RANKL. As clinicians may be less familiar with this newer agent, we compiled this review to summarize denosumab's current clinical indications for bone stabilization and mechanism of reduction in tumor burden.

Antiresorptive therapies in oncology and their effects on cancer progression

Bone health is an emerging concern in the early breast cancer setting. Current adjuvant therapies, especially hormonal therapies in premenopausal patients (e.g. goserelin) and aromatase inhibitors in postmenopausal patients, have been associated with substantial decreases in bone mineral density that may place patients at risk for fractures. Bisphosphonates--and the recently approved anti-RANKL antibody, denosumab--have both demonstrated activity for the treatment of postmenopausal osteoporosis and cancer treatment-induced bone loss (CTIBL) in breast cancer patients, although neither has received widespread approval specifically for CTIBL. However, some bisphosphonates, especially the nitrogen-containing bisphosphonate zoledronic acid, have also demonstrated clinically meaningful anticancer effects in patients receiving adjuvant hormonal therapy for breast cancer and in other oncology settings. The effects of denosumab on cancer disease outcomes in the adjuvant setting remain to be established. This discrepancy has created a dilemma in terms of how to evaluate the complete benefit:risk profile of bone-health management options in the adjuvant breast cancer setting. This review summarises the current data on the course of cancer in clinical trials of the antiresorptive agents and provides important insight into the relative anticancer potential of the various therapies.

Severe hypocalcemia following a single injection of denosumab in a patient with renal impairment

Monitoring renal function and adjusting dosing for patients with impaired renal function are not required with denosumab (60 mg every 6 months). However, these patients have an increased risk for developing hypocalcemia. This case report describes a patient with renal impairment who developed severe hypocalcemia after receiving denosumab.

Antiangiogenic effects of zoledronate on cancer neovasculature

Angiogenesis, one of the hallmarks of cancer, supplies nutrients to cancerous tissues to facilitate rapid growth. Targeting cancer-associated angiogenesis is an important goal in cancer therapy and there are currently many drugs that affect tumor-associated vasculature. In this article, we will focus on the antiangiogenic effects of zoledronate (ZA), a bisphosphonate drug routinely used in the treatment of cancer-associated bone disease. This article covers the known effects of ZA throughout the clinical process. It also covers the animal models of cancer that have been treated with ZA and evaluated for angiogenes is, concluding with the current clinical data pertaining to angiogenic factors after ZA treatment.

Denosumab for the prevention of skeletal-related events in patients with bone metastasis from solid tumor

Most patients with advanced malignancy develop bone metastases during the course of their disease. For the remainder of the patient's life, these bone metastases lead to skeletal-related events such as pathologic fractures and spinal cord compression, as well as bone pain or lesions requiring palliative radiation therapy or surgery to prevent or treat fractures. Skeletal-related events result in increased morbidity, mortality and health care costs. For the past decade, intravenous bisphosphonates (zoledronic acid, pamidronate) have been recognized as the primary pharmacologic options in the prevention or treatment of skeletal-related events in patients with bone metastasis. Recently, the United States Food and Drug Administration approved denosumab, a fully human monoclonal antibody, for the prevention of skeletal-related events in patients with bone metastases from solid tumors. Three prominent clinical trials were conducted to establish the efficacy of denosumab. In two of three trials, denosumab was found to delay the time to first skeletal-related event significantly more than zoledronic acid in patients with breast or castration-resistant prostate cancer with bone metastasis. The third trial found denosumab to be noninferior to zoledronic acid in patients with metastases from solid tumors, excluding breast and prostate solid tumors. Overall survival and progression-free survival were similar between zoledronic acid and denosumab. Thus, evidence is insufficient to prove a greater efficacy of one agent over the other. According to the American Society of Clinical Oncology and the National Comprehensive Cancer Network, patients with bone metastasis should have zoledronic acid, pamidronate, or denosumab (with calcium and vitamin D supplementation) added to their chemotherapy regimen if they have an expected survival of 3 months or longer and have adequate renal function.

Denosumab and the current status of bone-modifying drugs in breast cancer

BACKGROUND

Bone-modifying therapy is a primary research interest in breast cancer. Several features contribute to the importance of the bone environment in the management of breast cancer. Firstly, bone metastases represent the most common site of breast cancer metastases and secondly, the emergence of cancer treatment-induced bone loss (CTIBL) among breast cancer survivors and patients is of increasing concern. Furthermore, concordant with the "seed and soil" theory, agents that alter the bone microenvironment may even prevent tumor cell seeding in bone and limit cancer growth.

MATERIAL AND METHODS

Medical databases and conference proceedings were searched to identify articles, abstracts and clinical trials that have or are investigating denosumab and bisphosphonates in cancer therapy. Our search included a predefined focus on bone-modifying therapies in early and advanced breast cancer.

RESULTS AND DISCUSSION

Bisphosphonates (BPs) have an established role both in the prevention and treatment of CTIBL and have been studied in the adjuvant setting for early breast cancer (EBC). Denosumab is a monoclonal antibody directed against RANK ligand and thereby inhibits osteoclastogenesis and bone resportion. It is the newest agent approved for the treatment of postmenopausal osteoporosis and the prevention of skeletal-related events (SRE) in cancer patients with solid tumors and bone metastases. Denosumab has a favorable toxicity profile in comparison to BPs and has the potential to improve cancer outcomes.

CONCLUSION

This review examines the existing role of denosumab in the treatment of bone complications of breast cancer and its potential role as adjuvant therapy.

New understanding and treatments for osteoporosis

To summarize promising areas of investigation in osteoporosis and to stimulate further research in this area, as discussed in a recent international conference. Over the recent years, there has been an improvement in the knowledge of molecular pathways involved in bone formation and resorption with the development of new drugs to treat osteoporosis. Intact parathyroid hormone, teriparatide, and anti-sclerostin monoclonal antibody are anabolic drugs, whereas denosumab and odanacatib are anti-resorptive drugs with more reversible effects as compared to bisphosphonates. Anabolic and anti-resorptive agents have different effects on bone, and research in this area includes the efficacy of combination and sequential therapies with them. New insights in the molecular pathways of bone remodeling have clarified the mechanisms responsible for skeletal fragility in several forms of secondary osteoporosis, such as that occurring in type 2 diabetes, following drug exposure and systemic inflammatory diseases. Future research is needed to address the efficacy of anti-osteoporotic drugs in these more recently recognized conditions of skeletal fragility. Osteoporosis continues to be an important field of biomedical research.

Should the denosumab metastasis prevention trial change practice for men with nonmetastatic prostate cancer?

Presentation of the case. A 68-year-old man presents for management of prostate-specific antigen (PSA)-recurrent prostate cancer. His PSA level had become undetectable after prostatectomy for a high-risk localized tumor but began to rise 8 months later. This later led to the initiation of androgen deprivation therapy (ADT), which he has received for the last 3.5 years. After initially falling in response to ADT, his PSA level again trended steadily upward and is now 13.2. Restaging with an abdominal and pelvic computed tomography scan and a bone scan reveals no evidence of metastases. Is this man likely to benefit from denosumab? Bone is the most common site of metastasis for advanced prostate cancer. Bone metastases can cause considerable morbidity in the form of pain, pathologic fractures, and even spinal cord compression. Two bone-targeted therapies (zoledronic acid and denosumab) have been shown to reduce the risk for skeletal events (SREs) among men with bone metastases and a rising PSA level despite a testosterone level <50 ng/dL (castration-resistant prostate cancer [CRPC]). Until recently, no therapy had been shown to reduce the risk for developing bone metastases for the first time. Denosumab 147 was a randomized, placebo-controlled, phase III trial that enrolled 1,432 men with CRPC, no bone metastases, and at least one feature consistent with a high risk for the development of bone metastases (PSA ≥8 ng/mL or PSA doubling time ≤10 months). Participants were treated every 4 weeks with s.c. denosumab (120 mg) or placebo. The trial was positive because denosumab led to a 4.2-month significantly longer bone-metastasis-free survival time relative to placebo (median, 29.5 months versus 25.2 months; hazard ratio [HR], 0.85; 95% confidence interval [CI], 0.73-0.98; p = .028) [1]. The time to first bone metastasis and risk for symptomatic bone metastasis were also significantly better with denosumab treatment. Dror Michaelson and Philip Saylor discuss the potential implications of this trial.

Denosumab in patients with cancer-a surgical strike against the osteoclast

Elucidation of the molecular pathways underlying bone turnover has revealed potential therapeutic targets, including receptor activator of nuclear factor-κB ligand (RANKL), which is a mediator of osteoclast formation, function and survival. Denosumab is a fully human monoclonal antibody that binds to and inhibits RANKL. This agent has been developed for use in patients with early-stage and advanced-stage cancer, as well as for the treatment of osteoporosis, and can prevent bone loss and reduce fragility fractures in both types of disease. In the bone metastasis setting, several large phase III studies have shown that denosumab is more effective than bisphosphonates, namely zoledronic acid, in reducing skeletal morbidity arising from a wide range of tumors. In addition, a remarkable activity of denosumab has been demonstrated in giant-cell tumors of the bone. Subsequent studies of denosumab have demonstrated that it can delay bone metastasis in patients with castration-resistant prostate cancer; adjuvant studies in patients with breast cancer are in progress. This Review critically explores the emerging role of denosumab in maintaining bone health in the oncology setting, and discusses the factors that are likely to influence the choice between bisphosphonates and denosumab in clinical practice.

Cost-effectiveness of denosumab vs zoledronic acid for prevention of skeletal-related events in patients with solid tumors and bone metastases in the United States

OBJECTIVE

With increasing healthcare resource constraints, it has become important to understand the incremental cost-effectiveness of new medicines. Subcutaneous denosumab is superior to intravenous zoledronic acid (ZA) for the prevention of skeletal-related events (SREs) in patients with advanced solid tumors and bone metastases. This study sought to determine the lifetime cost-effectiveness of denosumab vs ZA in this setting, from a US managed-care perspective.

METHODS

A lifetime Markov model was developed, with relative rate reductions in SREs for denosumab vs ZA derived from three pivotal Phase 3 trials involving patients with castration-resistant prostate cancer (CRPC), breast cancer, and non-small-cell lung cancer (NSCLC), and bone metastases. The real-world SRE rates in ZA-treated patients were derived from a large commercial database. SRE and treatment administration quality-adjusted life year (QALY) decrements were estimated with time-trade-off studies. SRE costs were estimated from a nationally representative commercial claims database. Drug, drug administration, and renal monitoring costs were included. Costs and QALYs were discounted at 3% annually. One-way and probabilistic sensitivity analyses were conducted.

RESULTS

Across tumor types, denosumab was associated with a reduced number of SREs, increased QALYs, and increased lifetime total costs vs ZA. The costs per QALY gained for denosumab vs ZA in CRPC, breast cancer, and NSCLC were $49,405, $78,915, and $67,931, respectively, commonly considered good value in the US. Costs per SRE avoided were $8567, $13,557, and $10,513, respectively. Results were sensitive to drug costs and SRE rates.

LIMITATIONS

Differences in pain severity and analgesic use favoring denosumab over ZA were not captured. Mortality was extrapolated from fitted generalized gamma function beyond the trial duration.

CONCLUSION

Denosumab is a cost-effective treatment option for the prevention of SREs in patients with advanced solid tumors and bone metastases compared to ZA. The overall value of denosumab is based on superior efficacy, favorable safety, and more efficient administration.

Targeting bone in myeloma

Myeloma bone disease (BD) not only impairs quality of life, but is also associated with impaired survival. Studies of the biology underlying BD support the notion that the increased osteoclastogenesis and suppressed osteoblastogenesis is both a consequence and a necessity for tumour growth and clonal expansion. Survival and expansion of the myeloma clone are dependent on its interactions with bone elements; thus, targeting these interactions should have anti-myeloma activities. Indeed, both experimental and clinical findings indicate that bone-targeted therapies, not only improve BD, but also create an inhospitable environment for myeloma cell growth and survival, favouring improved clinical outcome. This chapter summarizes recent progress in our understandings of the biology of myeloma BD, highlighting the role of osteoclasts and osteoblasts in this process and how they can be targeted therapeutically. Unravelling the mechanisms underlying myeloma-bone interactions will facilitate the development of novel therapeutic agents to treat BD, which as a consequence are likely to improve the clinical outcome of myeloma patients.

Infections in postmenopausal women with osteoporosis treated with denosumab or placebo: coincidence or causal association?

Serious adverse events of infections that occurred in subjects receiving denosumab or placebo in the Fracture Reduction Evaluation of Denosumab in Osteoporosis every 6 Months (FREEDOM) study were examined in detail. Serious adverse events of infections in denosumab subjects had heterogeneous etiology, with no clear clinical pattern to suggest a relationship to time or duration of exposure to denosumab.

INTRODUCTION

Denosumab reduces the risk for new vertebral, hip, and nonvertebral fractures compared with placebo. In the pivotal phase 3 fracture trial (FREEDOM), the overall safety profile and incidence of adverse events including adverse events of infections were similar between groups. Serious adverse events of erysipelas and cellulitis were more frequent in denosumab-treated subjects. In this report, we further evaluate the details of infectious events in FREEDOM to better understand if RANKL inhibition with denosumab influences infection risk.

METHODS

FREEDOM was an international multicenter, randomized, double-blind, placebo-controlled study in postmenopausal women with osteoporosis randomly assigned to receive placebo (n = 3,906) or denosumab 60 mg every 6 months (n = 3,902). The incidence of adverse events and serious adverse events categorized within the Medical Dictionary for Regulatory Activities system organ class, "Infections and Infestations," was compared between the placebo and denosumab groups by body systems and preferred terms. The temporal relationship between occurrence of serious adverse events of infections of interest and administration of denosumab was explored.

RESULTS

Serious adverse events of infections involving the gastrointestinal system, renal and urinary system, ear, and endocarditis were numerically higher in the denosumab group compared with placebo, but the number of events was small. No relationship was observed between serious adverse events of infections and timing of administration or duration of exposure to denosumab.

CONCLUSIONS

Serious adverse events of infections that occurred with denosumab treatment had heterogeneous etiology, with no clear clinical pattern to suggest a relationship to time or duration of exposure to denosumab.

Osteolytic and osteoblastic bone metastases: two extremes of the same spectrum?

Normal bone development and maintenance are sustained through a balanced communication between osteoclasts and osteoblasts. Invasion of the bone compartment by cancer cells causes an imbalance in their activities and results in predominantly bone lysing or bone forming phenotypes depending on the origin of the cancer. Tumor-induced bone lesions usually exhibit disturbances of both cell types. Thus, osteoclast activity is activated in a predominantly osteoblastic lesion and vice versa. These cancer-induced bone responses favor the survival and growth of cancer cells in their new environment. Therapies that can restore the balance may limit the growth of cancer cells in the bone. The recent development of agents that target the osteolytic components of bone metastasis, including bisphosphonates and denosumab, showed promising results in osteolytic bone diseases such as multiple myeloma but were less effective in improving the osteoblastic bone disease found in prostate cancer. Thus, while osteolytic components are present in both osteoblastic and osteolytic bone lesions, inhibition of the osteolytic component is not sufficient to alter the vicious cycle leading to tumors with an osteoblastic phenotype. These observations suggest that osteolytic and osteoblastic bone metastases are not the same and tumor-induced osteoblastic and osteolytic activity play different roles in supporting their growth and survival.

Denosumab for the management of bone disease in patients with solid tumors

Many patients with advanced cancer develop bone metastases, which reduces their quality of life. Bone metastases are associated with an increased risk of skeletal-related events, which can lead to increased morbidity and mortality. In patients with bone metastases, tumor cells disrupt the normal process of bone remodeling, leading to increased bone destruction. Denosumab is a fully human monoclonal antibody against receptor activator of NF-κB ligand (RANKL), a key regulatory factor in bone remodeling. By binding to RANKL, denosumab disrupts the cycle of bone destruction. In clinical studies in patients with prostate or breast cancer and bone metastases, denosumab was superior to the current standard of care, zoledronic acid, for delaying skeletal-related events, while in patients with other solid tumors or multiple myeloma, denosumab was noninferior to zoledronic acid. This article examines the pharmacokinetics, efficacy, and safety and tolerability of denosumab for the management of bone events in patients with cancer.

Bone cancer in 2011: Prevention and treatment of bone metastases

Bone-targeting treatments have transformed the quality of life of patients with metastatic bone disease. 2011 saw the emergence of denosumab—a RANK ligand-specific antibody—as a more-effective alternative treatment to bisphosphonates and of data on the use of bone-targeting treatments to prevent metastasis from breast and prostate cancers.

OPG/RANKL/RANK pathway as a therapeutic target in cancer

Bone metastases play an important role in the morbidity and mortality of patients with malignant disease. Despite therapeutic advances in the treatment of solid organ malignancy such as lung cancer, less development on metastasis interventions has been forthcoming. More recent research has focused on molecular pathway manipulation in the prevention and treatment of metastatic bone disease and associated complications such as bone pain and hypercalcemia. The osteoprotegerin/receptor activator of nuclear factor-кβ ligand/receptor activator of nuclear factor-кβ pathway, which is physiologically involved in bone turnover, has been of considerable interest, and recent promising data have been revealed. In this study, we describe this molecular pathway in terms of its natural physiological function, manipulation for therapeutic benefit, and recent clinical trial results.

Denosumab for the treatment of osteoporosis and cancer-related conditions

Osteoporotic fractures and adverse skeletal effects of malignancies are associated with high bone turnover. Denosumab is a potent inhibitor of bone resorption with a novel mechanism of action. It is administered as an infrequent subcutaneous injection with no restrictions relating to renal function. This review summarizes data on the efficacy and safety of denosumab that led to its approval for the treatment of postmenopausal osteoporosis, cancer treatment-induced bone loss, and skeletal complications of malignancies.

Update on the pharmacological prevention of skeletal-related events in cancer patients

Metastases to the bone are a frequent complication of advanced cancer. Bone metastases have been linked to skeletal-related events, which is the composite endpoint used in clinical trials evaluating therapy to minimize these complications. This article discusses bisphosphonates, which are the historical standard for the prevention of skeletal-related events in patients with metastases from solid tumors and multiple myeloma, and denosumab, which is the first Food and Drug Administration-approved receptor activator of nuclear factor kappa-β ligand (RANKL) inhibitor.

Safety and tolerability of denosumab for the treatment of postmenopausal osteoporosis

Denosumab is a fully human monoclonal antibody to receptor activator of nuclear factor kappa-B ligand (RANKL), a cytokine member of the tumor necrosis factor family that is the principal regulator of osteoclastic bone resorption. Postmenopausal osteoporosis (PMO) is a systemic skeletal disease associated with high levels of RANKL, resulting in a high rate of bone remodeling and an imbalance of bone resorption over bone formation. By inhibiting RANKL in women with PMO, denosumab reduces the rate of bone remodeling, thereby increasing bone mineral density, improving bone strength, and reducing the risk of fractures. In clinical trials of women with osteoporosis and low bone mineral density, denosumab has been well tolerated, with overall rates of adverse events and serious adverse events in women treated with denosumab similar to those receiving placebo. In the largest clinical trial of denosumab for the treatment of women with PMO, there was a significantly greater incidence of cellulitis reported as a serious adverse event, with no difference in the overall incidence of cellulitis, and a significantly lower incidence of the serious adverse event of concussions with denosumab compared with placebo. The evidence supports a favorable balance of benefits versus risks of denosumab for the treatment of PMO. Assessments of the long-term safety of denosumab are ongoing. Denosumab 60 mg subcutaneously every 6 months is an approved treatment for women with PMO who are at high risk for fracture.

Pathophysiology of atypical femoral fractures and osteonecrosis of the jaw

In recent years, atypical femoral fractures and osteonecrosis of the jaw have emerged as potential complications of long-term bisphosphonate therapy; osteonecrosis of the jaw has also been reported in patients receiving high doses of denosumab. The pathophysiology of both conditions is poorly defined, and the underlying mechanisms are likely to differ. The initiation of atypical fractures in the lateral femoral shaft suggests that reduced tensile strength, possibly secondary to alterations in the material properties of bone resulting from low bone turnover, may be an important pathogenetic factor. Osteonecrosis of the jaw is characterised by infection, inflammation, bone resorption and bone necrosis, but the sequence in which these occur has not been established. However, the observation that bone resorption occurs in close proximity to microbial structures suggests that infection may be the most important trigger, often as a result of dental disease. Other possible pathogenetic factors include suppression of bone turnover, altered immune status and adverse effects of bisphosphonates on the oral mucosa.

Denosumab for bone diseases: translating bone biology into targeted therapy

Signalling of receptor activator of nuclear factor-κB (RANK) ligand (RANKL) through RANK is a critical pathway to regulate the differentiation and activity of osteoclasts and, hence, a master regulator of bone resorption. Increased RANKL activity has been demonstrated in diseases characterised by excessive bone loss such as osteoporosis, rheumatoid arthritis and osteolytic bone metastases. The development and approval of denosumab, a fully MAB against RANKL, has heralded a new era in the treatment of bone diseases by providing a potent, targeted and reversible inhibitor of bone resorption. This article summarises the molecular and cellular biology of the RANKL/RANK system and critically reviews preclinical and clinical studies that have established denosumab as a promising novel therapy for metabolic and malignant bone diseases. We will discuss the potential indications for denosumab along with a critical review of safety and analyse its potential within the concert of established therapies.

Emerging drugs in metastatic breast cancer: an update

INTRODUCTION

The incidence of breast cancer at an advanced stage has decreased in the modern world due to screening programs and usage of novel chemotherapy agents at an adjuvant setting. Recurrence is the major problem seen in > 50% of breast cancer patients diagnosed at an early stage. Developing new drugs for metastatic breast cancer is a huge and challenging research area.

AREAS COVERED

Emerging drugs showed positive results in clinical studies and agents in routine clinical usage are updated. Current treatment strategies as a combination of biologic agents and overcoming drug resistance are discussed. Literature search is made from PubMed, ASCO and San Antonio Breast Cancer Symposium Meeting abstracts.

EXPERT OPINION

A number of drugs caused survival benefit for advanced breast cancer. Hundreds of new studies with tens of agents are conducted for treatment of metastatic breast cancer. Tumor resistance and treatment related toxicities are unavoidable which are two main search areas for improving metastatic breast cancer management. Understanding the pathways of genesis and progression yielded many targets for treatment. However, cure in metastatic breast cancer is still a far aim and new agents and treatment strategies are needed.

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

INTRODUCTION

Denosumab, a fully human monoclonal antibody, targets the receptor activator of nuclear factor-kappaB (RANK) ligand, a protein essential for osteoclast differentiation, activity and survival. Loss of osteoclasts from the bone surface reduces bone turnover and bone loss in malignant and benign diseases. In breast cancer, bone metastases are frequently observed; cancer treatment-induced bone loss (CTIBL) may result as a consequence of endocrine treatment or chemotherapy. Furthermore, preclinical studies suggest a direct role of the RANK/RANK-ligand pathway in breast tumorigenesis. This paper reviews preclinical and clinical data on denosumab in breast cancer.

MATERIALS AND METHODS

Studies were identified through the Medline database. Key search terms included: AMG-162, bisphosphonates, denosumab, RANK-ligand and zoledronic acid. Information available in abstract form only was retrieved from major oncology meetings, such as the American Society of Clinical Oncology (ASCO) annual meeting, ASCO breast meeting, European Cancer Organization, European Society of Medical Oncology and the San Antonio Breast Cancer Symposium.

RESULTS

Denosumab was consistently well tolerated throughout clinical trials, although the observed incidence of osteonecrosis of the jaw was comparable to that with bisphosphonates. Efficacy as determined by a reduction of skeletal-related events was at least equal to zoledronic acid, and superior in one phase III study conducted in patients with metastatic breast cancer. Clinical trials investigating the role of denosumab for the prevention of CTIBL and breast cancer recurrences are currently ongoing.

CONCLUSION

In conclusion, denosumab appears to be an effective and safe treatment option in patients with bone metastases from breast cancer with the potential of also preventing CTIBL.

A novel patient-derived intra-femoral xenograft model of bone metastatic prostate cancer that recapitulates mixed osteolytic and osteoblastic lesions

Prostate cancer metastasizes to bone in the majority of patients with advanced disease leading to painfully debilitating fractures, spinal compression and rapid decline. In addition, prostate cancer bone metastases often become resistant to standard therapies including androgen deprivation, radiation and chemotherapy. There are currently few models to elucidate mechanisms of interaction between the bone microenvironment and prostate cancer. It is, thus, essential to develop new patient-derived, orthotopic models. Here we report the development and characterization of PCSD1 (Prostate Cancer San Diego 1), a novel patient-derived intra-femoral xenograft model of prostate bone metastatic cancer that recapitulates mixed osteolytic and osteoblastic lesions.

Methods

A femoral bone metastasis of prostate cancer was removed during hemiarthroplasty and transplanted into Rag2^-/-;γ_c^-/- mice either intra-femorally or sub-cutaneously. Xenograft tumors that developed were analyzed for prostate cancer biomarker expression using RT-PCR and immunohistochemistry. Osteoblastic, osteolytic and mixed lesion formation was measured using micro-computed tomography (microCT).

Results

PCSD1 cells isolated directly from the patient formed tumors in all mice that were transplanted intra-femorally or sub-cutaneously into Rag2^-/-;γ_c^-/- mice. Xenograft tumors expressed human prostate specific antigen (PSA) in RT-PCR and immunohistochemical analyses. PCSD1 tumors also expressed AR, NKX3.1, Keratins 8 and 18, and AMACR. Histologic and microCT analyses revealed that intra-femoral PCSD1 xenograft tumors formed mixed osteolytic and osteoblastic lesions. PCSD1 tumors have been serially passaged in mice as xenografts intra-femorally or sub-cutaneously as well as grown in culture.

Conclusions

PCSD1 xenografts tumors were characterized as advanced, luminal epithelial prostate cancer from a bone metastasis using RT-PCR and immunohistochemical biomarker analyses. PCSD1 intra-femoral xenografts formed mixed osteoblastic/osteolytic lesions that closely resembled the bone lesions in the patient. PCSD1 is a new primary prostate cancer bone metastasis-derived xenograft model to study metastatic disease in the bone and to develop novel therapies for inhibiting prostate cancer growth in the bone-niche.

Molecular pathways: osteoclast-dependent and osteoclast-independent roles of the RANKL/RANK/OPG pathway in tumorigenesis and metastasis

Receptor activator of nuclear factor-kappa B ligand (RANKL) is a TNF ligand superfamily member that is essential for the formation, activation, and function of osteoclasts. RANKL functions via its cognate receptor RANK, and it is inhibited by the soluble decoy receptor osteoprotegerin (OPG). In skeletal metastases, the ratio of RANKL to OPG is upregulated, which leads to increased osteoclast-mediated bone destruction. These changes in the bone microenvironment not only compromise the structural integrity of bone, leading to severe clinical morbidities, but have also been implicated in establishment of de novo bone metastasis and the progression of existing skeletal tumors. Evaluation of RANKL inhibitors, including the fully human anti-RANKL antibody denosumab, in patients with cancer has shown reductions in tumor-induced bone resorption activity and successful management of skeletal complications of bone metastases. RANKL also functions as a major paracrine effector of the mitogenic action of progesterone in mouse mammary epithelium, and it has a role in ovarian hormone-dependent expansion and regenerative potential of mammary stem cells. RANKL inhibition attenuates mammary tumorigenesis and pulmonary metastases in mouse models. These data suggest that the contribution of progesterone to increased mammary cancer incidence is mediated, at least in part, by RANKL-dependent changes in the mammary epithelium; RANKL also directly promotes distant metastases. In summary, the antitumor and antimetastatic effects of RANKL inhibition can occur by at least 2 distinct mechanisms, one in the bone via osteoclast-dependent effects, and the second via direct effects on the tumor cells of various origins and/or mammary epithelium.

Bone-bound bisphosphonate inhibits growth of adjacent non-bone cells

The conventional view of the mode of action of bisphosphonates is that they are taken up by bone surfaces and then ingested by bone-resorbing osteoclasts, the activity of which they inhibit through their actions on the enzyme, farnesyl pyrophosphate (FPP) synthase. This model suggests that these compounds should only have effects on osteoclasts, and does not provide an explanation for their other actions, such as the epithelial abnormalities seen in osteonecrosis of the jaw, and their possible prolongation of disease-free survival in some malignancies. The present studies set out to determine whether cells other than osteoclasts are affected by bone-bound bisphosphonates. Bone slices were incubated overnight in PBS or in solutions of bisphosphonates (100 μM), washed, then transferred to 96-well plates (1 slice/well). Cells from 2 cell lines were seeded onto the bone slices: Caco-2 human colorectal adenocarcinoma epithelial cells and Chinese hamster ovary (CHO) cells. Cell proliferation (cell numbers and thymidine incorporation) was assessed at 4-72 h. Cell adhesion at 4 h was normal on bone slices pre-treated with bisphosphonates, but there were progressive reductions in cell numbers from 48 h and even greater reductions in thymidine incorporation from 24 h (>90% with zoledronate at 72 h). Growth inhibition was related to the clinical potency of the bisphosphonate used. There was no evidence of increased apoptosis in cells grown on bisphosphonate-coated bone, but levels of unprenylated Rap1A were increased, indicating inhibition of FPP synthase. Similar growth inhibition was observed in primary cultures of rat osteoblasts on bone, indicating that this was not specific to transformed cells. It is concluded that bisphosphonates bound to a bone surface can act on adjacent non-bone cells and inhibit their growth. This greatly widens the range of potential target cells for these drugs.

New developments for treatment and prevention of bone metastases

PURPOSE OF REVIEW

To provide a critical review of recent trials of bone resorption inhibitory drugs (bisphosphonates and denosumab) for the treatment and the prevention of bone metastases in solid tumors.

RECENT FINDINGS

The bisphosphonate zoledronic acid is now part of the standard treatment for metastatic bone disease. Comparative trials in this setting between zoledronic acid and denosumab have shown superior (in breast and in prostate cancer) or noninferior (in other solid tumors) skeletal-related event-prevention activity for denosumab. Osteonecrosis of the jaw is the most important side-effect of both compounds. Recent data also indicate the potential of zoledronic acid to reduce the recurrence rate in breast cancer.

SUMMARY

Much progress has been accomplished for the treatment of tumor bone disease with bone resorption inhibitory drugs. Advances are now awaited in the setting of prevention of bone metastases.

Emerging therapies to prevent skeletal morbidity in men with prostate cancer

Skeletal morbidity is a prominent burden to men with advanced prostate cancer throughout the natural history of the disease. Bone metastases can cause pain and greatly elevate the risk for fractures and other structural complications. Distinct from the problem of metastases, treatment-related osteoporosis and associated fragility fractures are potential complications of androgen-deprivation therapy. Bone-targeted therapies for prostate cancer have therefore been the focus of considerable research and drug development efforts. The osteoclast is a validated therapeutic target in the management of prostate cancer. Osteoclast inhibition with zoledronic acid (a bisphosphonate) or with denosumab (a monoclonal antibody to RANK ligand) reduces risk for skeletal events in men with castration-resistant prostate cancer metastatic to bone. Osteoclast inhibition with any of several bisphosphonates improves bone mineral density, a surrogate for osteoporotic fracture risk. Denosumab and toremifene (a selective estrogen receptor modulator) have each been shown to reduce osteoporotic fracture risk among men receiving androgen-deprivation therapy. Beta-emitting radiopharmaceuticals reduce pain due to metastatic disease. Investigations involving alpha-emitting radium-223, endothelin-A receptor antagonists atrasentan and zibotentan, proto-oncogene tyrosine-protein kinase (SRC) inhibitor dasatinib, and tyrosine kinase inhibitor cabozantinib (XL184) are ongoing in clinical trials and are also discussed.

[The role of RANK/RANKL/osteoprotegerin (OPG) triad in cancer-induced bone diseases: physiopathology and clinical implications]

Bone homeostasis is maintained by the remodelling of bone which depends on a balance between osteoclast-mediated bone resorption and osteoblast-mediated bone formation. Malignant bone lesions are very common in patients with cancer; whether they result from a tumor in bone (giant cell tumour of bone, osteosarcoma, multiple myeloma...) or they are bony metastases from advanced cancers of which the most osteotropic are breast and prostate cancer. Malignant cells within the bone disrupt the normal bone remodelling process, leading to increased bone destruction and occurence of pathological fractures. Receptor activator of NF-kB (RANK) and its ligand (RANKL) play a pivotal role in the regulation of bone remodelling; by binding to RANK, RANKL stimulates osteoclastogenesis and bone resorption, whereas its cognate decoy receptor osteoprotegerin (OPG) blocks this process by interacting with RANKL. Tumour cells produce different factors that manipulate the RANK/RANKL/OPG pathway in order to stimulate bone destruction. Furthermore, pending on the tumour type, RANKL plays a role in the migration, invasion and proliferation of malignant cells within the bone, while OPG increases survival of tumour cells. Inhibition of RANK/RANKL system may therefore offer new therapeutic perspectives for the treatment of primitive and secondary bone cancers.

The immune microenvironment of myeloma

The bone marrow (BM) is the site of disease in myeloma and possesses unique immune characteristics involved in the pathobiology of the disease. Interactions of plasma cells with stromal cells, osteoclasts, osteoblasts, myeloid and lymphoid cells make up the unique bone marrow milieu that mediates myeloma disease progression. Independently or through a complex network of interactions these cells impart immune changes leading to immune evasion and disease progression. The critical role of these factors in disease progression has led to the intense development of therapeutic strategies aimed at either disrupting the immune mechanisms mediating disease progression or augmenting those with anti-tumor benefits. This review discusses the major contributors of immunity in the bone marrow microenvironment, their interactions, and mechanisms whereby immune modulation can be translated into therapies with anti-myeloma efficacy.

Monoclonal antibody-based therapy as a new treatment strategy in multiple myeloma

The introduction of autologous stem cell transplantation combined with the introduction of immunomodulatory drugs (IMiDs) and proteasome inhibitors has significantly improved survival of multiple myeloma patients. However, ultimately the majority of patients will develop refractory disease, indicating the need for new treatment modalities. In preclinical and clinical studies, promising results have been obtained with several monoclonal antibodies (mAbs) targeting the myeloma tumor cell or the bone marrow microenvironment. The mechanisms underlying the therapeutic efficacy of these mAbs include direct induction of tumor cell apoptosis via inhibition or activation of target molecules, complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity (ADCC). The capability of IMiDs to enhance ADCC and the modulation of various important signaling cascades in myeloma cells by both bortezomib and IMiDs forms the rationale to combine these novel agents with mAbs as new treatment strategies for myeloma patients. In this review, we will give an overview of various mAbs directly targeting myeloma tumor cells or indirectly via effects on the bone marrow microenvironment. Special focus will be on the combination of these mAbs with IMiDs or bortezomib.

Targeting bone as a therapy for myeloma

Myeloma bone disease (BD) not only impairs quality of life, but is also associated with impaired survival. Studies of the biology underlying BD support the notion that the increased osteoclastogenesis and suppressed osteoblastogenesis, is both a consequence and a necessity for tumour growth and clonal expansion. Survival and expansion of the myeloma clone is dependent on its interactions with bone elements, thus targeting these interactions should have antimyeloma activities. Indeed both experimental and clinical findings indicate that bone-targeted therapies not only improve BD, but also create an inhospitable environment for myeloma cell growth and survival, favouring improved clinical outcome. This review summarizes recent progress in our understandings of the biology of myeloma BD, highlighting the role of osteoclasts and osteoblasts in this process and how they can be targeted therapeutically. Unravelling the mechanisms underlying myeloma-bone interactions will facilitate the development of novel therapeutic agents to treat BD, which as a consequence are likely to improve the clinical outcome of myeloma patients.

Optimising the use of bone-targeted agents in patients with metastatic cancers: a practical guide for medical oncologists

Bone metastases can be associated with a significant worsening of patient morbidity and mortality. Bisphosphonates have been extensively researched and shown to delay the onset and reduce the incidence of complications from bone metastases. The most commonly used bisphosphonates are intravenous pamidronate, intravenous ibandronate, intravenous zoledronic acid and oral/intravenous clodronate. Several bone-targeted agents with innovative mechanisms of action are currently being developed. These include receptor activator of nuclear factor-kB ligand (RANKL) inhibitors, CCR1 inhibitors, Src inhibitors, DKK1-neutralising antibodies, activin antagonists and endothelin-1 inhibitors. In an era of individualised medicine, oncologists are being faced with an increasing number of questions when dealing with bone-targeted agents. These questions not only include the choice of which drug to use (i.e. bisphosphonates or RANKL inhibitor) but also the best treatment strategy to use. This review will provide medical oncologists with a practical guide to the use of bone-targeted agents.

Bone disease in multiple myeloma and precursor disease: novel diagnostic approaches and implications on clinical management

The manifestations of bone involvement in patients with multiple myeloma (MM) can have devastating clinical effects and increase mortality. Recent studies demonstrate that patients with the precursor conditions smoldering MM (SMM) and monoclonal gammopathy of undetermined significance (MGUS) show evidence of bone disease and increased risk of fractures. The understanding of the pathogenesis of bone disease in MM has expanded in recent years. The traditional skeletal survey will probably be replaced by newer and more sensitive imaging techniques, which may have a prognostic impact and change our definition of MGUS and SMM. Bisphosphonates are recommended to prevent skeletal events in patients with MM, and have also been studied in SMM and MGUS. This article summarizes the current knowledge of bone disease in plasma cell disorders, and discusses the current standard and future role of novel imaging techniques, as well as the evidence and current guidelines for bisphosphonates in MM, SMM and MGUS.

Could targeting bone delay cancer progression? Potential mechanisms of action of bisphosphonates

Although dissemination may occur early in the course of many cancers, the development of overt metastases depends upon a variety of factors inherent to the cancer cells and the tissue(s) they colonize. The time lag between initial dissemination and established metastases could be several years, during which period the bone marrow may provide an unwitting sanctuary for disseminated tumor cells (DTCs). Survival in a dormant state within the bone marrow may help DTCs weather the effects of anticancer therapies and seed posttreatment relapses. The importance of the bone marrow for facilitating DTC survival may vary depending on the type of cancer and mechanisms of tumor cell dissemination. By altering the bone microenvironment, bisphosphonates may reduce DTC viability. Moreover, some bisphosphonates have demonstrated multiple anticancer activities. These multiple mechanisms may help explain the improvement in disease outcomes with the use of zoledronic acid in malignancies like breast cancer and multiple myeloma.

Under usage of zoledronic acid in non-small cell lung cancer patients with metastatic bone disease--a short communication

BACKGROUND AND AIM

The use of zoledronic acid (ZA) is now recommended for patients with NSCLC and metastatic bone disease (MBD). We thus examined the rates of ZA administration in NSCLC looking specifically at the use of this drug with systemic chemotherapy (ZCt) and comparing overall survival between patients who had ZCt from diagnosis to those who had chemotherapy (Ct) alone.

METHOD

In this retrospective audit, we analysed the data of 114 consecutive patients with stage IV NSCLC and MBD at presentation. Forty-three of these patients had received zoledronic acid and chemotherapy (ZCt) and 71 had received chemotherapy alone (Ct).

RESULTS

Forty-three (37.7%, 43/114) of NSCLC patients diagnosed with MBD received ZA with their first chemotherapy (ZCt). Patients on ZCt, after adjustment for the planned prognostic factors (sites of disease, histology and PS), had better overall survival (OS), with a median of 34 weeks, compared to those who received chemotherapy alone, who had a median of 19 weeks (p = 0.03), HR = 0.60 (95%CI: 0.38-0.96). After adjusting for prognostic factors (sex, age. single versus doublet chemotherapy), ZCt patients still maintained a trend to better OS (p = 0.06) HR 0.63 (95%CI: 0.39-1.02) 34 versus 21 weeks.

CONCLUSIONS

The percentage of patients with MBD treated with ZA at first chemotherapy (37.7%) is low. The addition of ZA increased OS in NSCLC patients with MBD in this audit. More formal policies and dedicated trials on the treatment of MBD in NSCLC patients need to be put in place.