Bisphosphonates--mechanisms of action in multiple myeloma

Bisphosphonates are a class of anti-resorptive drugs, which are effective in the treatment of osteoclast-mediated bone disease, including the osteolytic bone disease, which is a major clinical feature of patients with multiple myeloma. Recently, increases in survival following treatment with pamidronate have been observed in some patients with multiple myeloma, raising the possibility that bisphosphonates may also have an anti-tumour effect. We have demonstrated that bisphosphonates can have an anti-tumour effect in human myeloma cell in vitro, and that these anti-tumour effects induced by potent nitrogen-containing bisphosphonates are a result of inhibition of enzymes of the mevalonate pathway. However, we and others have been unable to demonstrate an anti-tumour effect of the potent bisphosphonate ibandronate in vivo, using murine models of multiple myeloma. It is therefore likely that only by studying patients receiving bisphosphonates will we be able to determine whether these compounds have a clinically important anti-tumour effect.     

Myeloma bone disease: pathophysiology and management.

Bone disease is a major feature of multiple myeloma. Myeloma-induced bone destruction is the result of an increased activity of osteoclasts, which is not accompanied by a comparable increase of osteoblast function. Recent studies have revealed that new molecules such as the receptor activator of nuclear factor-kappa B (RANK), its ligand (RANKL), osteoprotegerin (OPG), and macrophage inflammatory protein-1alpha are implicated in osteoclast activation and differentiation, while proteins such as dickkopf-1 inhibit osteoblastic bone formation. These new molecules seem to interfere not only with the biology of myeloma bone destruction but also with tumour growth and survival, creating novel targets for the development of new antimyeloma treatment. Currently, bisphosphonates play a major role in the management of myeloma bone disease. Clodronate, pamidronate and zoledronic acid are the most effective bisphosphonates in symptomatic myeloma patients. Biochemical markers of bone remodeling have been used in an attempt to identify patients more likely to benefit from early treatment with bisphosphonates. Furthermore, using microarray techniques, myeloma patients may be subdivided into molecular subgroups with certain clinical characteristics, such as propensity for lytic lesions that may need early prophylactic treatment. Recent phase I studies with recombinant OPG and monoclonal antibodies to RANKL appear promising.     

Bone complications in multiple myeloma

Multiple myeloma is the malignant proliferation of plasma cells involving more than 10% of the bone marrow. The bone complications associated with multiple myeloma include bone pain, pathologic fractures, hypercalcemia of malignancy and cord compressions. The principal pathophysiology of bone disease in multiple myeloma is a shift in the balance of bone remodeling toward bone resorption. In recent years, bisphosphonates have become an important treatment for the bone complications of multiple myeloma. Potent inhibitors of osteoclast activity, bisphosphonates interfere with biochemical pathways and induce osteoclast apoptosis. Bisphosphonates also antagonize osteoclastogenesis and promote differentiation of osteoblasts, as well as inhibiting other aspects of osteoclast homeostasis and metabolism. Several studies have evaluated treatment with bisphosphonates in patients with multiple myeloma, and have demonstrated the efficacy of clodronate (Bonefos; Anthra Pharmaceuticals; Princeton, NJ; www.bonefos.com), pamidronate (Aredia; Novartis Pharmaceuticals Corp; East Hanover, NJ; www.pamidronate.com) and zoledronic acid (Zometa; Novartis Pharmaceuticals Corp; East Hanover, NJ; www.us.zometa.com) in reduction of pain, reduction of SREs and survival. Moreover, recent data suggest direct and indirect antimyeloma activity of pamidronate and zoledronic acid.     

Metastatic bone disease: clinical features, pathophysiology and treatment strategies.

Metastatic bone disease develops as a result of the many interactions between tumour cells and bone cells. This leads to disruption of normal bone metabolism, with the increased osteoclast activity seen in most, if not all, tumour types providing a rational target for treatment. The clinical course of metastatic bone disease in multiple myeloma, breast and prostate cancers is relatively long, with patients experiencing sequential skeletal complications over a period of several years. These include bone pain, fractures, hypercalcaemia and spinal cord compression, all of which may profoundly impair a patient's quality of life.External beam radiotherapy and systemic endocrine and cytotoxic treatments are the mainstay of treatment in advanced cancers. However, it is now clear that the bisphosphonates provide an additional treatment strategy, which reduces both the symptoms and complications of bone involvement. Ongoing research is aimed at trying to define the optimum route, dose, schedule and type of bisphosphonate in metastatic bone disease and in the prevention and treatment of osteoporosis in cancer patients. In vitro suggestions of direct anticancer activity and some promising clinical data in early breast cancer have resulted in considerable interest in the possible adjuvant use of bisphosphonates to inhibit the development of bone metastases.     

Optimising treatment of bone metastases by Aredia™ and Zometa™

Metastatic bone disease develops as a result of the many interactions between tumour cells and bone cells. This leads to disruption of normal bone metabolism, with the increased osteoclast activity seen in most, if not all, tumor types providing a rational target for treatment. The clinical course of metastatic bone disease in multiple myeloma, breast and prostate cancers is relatively long, with patients experiencing sequential skeletal complications over a period of several years. These include bone pain, fractures, hypercalcaemia, and spinal cord compression, all of which may profoundly impair a patient's quality of life. External beam radiotherapy and systemic endocrine and cytotoxic treatments are the mainstay of treatment in advanced cancers. However, it is now clear that the bisphosphonates provide an additional treatment strategy, which reduces both the symptoms and complications of bone involvement. Pamidronate (Aredia(TM)) is the most widely evaluated bisphosphonate and is recommended for most patients with multiple myeloma or breast cancer with bone metastases. Current research aims include the evaluation of new potent bisphosphonates such as zoledronic acid (Zometa(TM)). It is hoped that this compound is not only more convenient and easier to administer but also more effective in inhibiting skeletal morbidity. Zometa may also have some direct anticancer activity. Preclinical studies with Zometa have demonstrated its potential in malignant bone disease. Clinical studies in treatment of hypercalcemia of malignancy have been completed, as have Phase I and II trials in patients with cancer and pre-existing bone metastases. Three randomized, double-blind, controlled Phase III trials are now ongoing to establish the efficacy and safety of Zometa in treatment of bone metastases in patients with osteolytic and osteoblastic lesions. Additionally, new specific molecules such as osteoprotogerin have been developed that are based on our improved understanding of the cellular signalling mechanisms involved in cancer induced bone disease. These potent molecules are now entering clinical trials. Ongoing research is aimed at trying to define the optimum route, dose, schedule and type of bisphosphonate in metastatic bone disease and their use in the prevention and treatment of osteoporosis in cancer patients. In vitro suggestions of direct anti-cancer activity and some promising clinical data in early breast cancer have resulted in considerable interest in the possible adjuvant use of bisphosphonates to inhibit the development of bone metastases.     

Management of Metastatic Bone Disease and Hypercalcemia of Malignancy

Thirty years of research have established bisphosphonates as the most effective agents for the inhibition of osteoclast-mediated bone resorption, and they play an important role in the management of malignant bone disease. Bisphosphonates have been systematically improved through chemical engineering, and the newest nitrogen-containing compounds, including zoledronic acid and ibandronate, are 1000-fold more potent than first-generation compounds. Consequently, they can be administered at low molar doses via short intravenous infusions without compromising renal safety. Bisphosphonates have a variety of metabolic effects on osteoclasts. Nitrogen-containing bisphosphonates inhibit protein prenylation via the mevalonate pathway, thereby inhibiting osteoclast activation and inducing apoptosis. Preclinical studies suggest that bisphosphonates also have direct and indirect antitumor activity. In animal models, bisphosphonates reduced skeletal tumor burden and bone metastases. Currently, intravenous bisphosphonates are the standard therapy for hypercalcemia of malignancy, and they have become an integral part of the treatment of bone metastases in conjunction with standard antineoplastic agents. Intravenous bisphosphonates quickly normalize serum calcium, reduce skeletal complications, and palliate bone pain in patients with bone metastases. Intravenous pamidronate (90mg via 2-hour infusion every 3–4 weeks) has, until recently, been the international standard for the treatment of osteolytic bone lesions from breast cancer or multiple myeloma. However, 4mg zoledronic acid (via 15-minute infusion) is quickly becoming the new standard based on evidence that it is as safe and effective as 90mg pamidronate in patients with breast cancer and multiple myeloma and significantly more effective for hypercalcemia of malignancy. Consequently, the American Society of Clinical Oncology guidelines for breast cancer and multiple myeloma recommend pamidronate or zoledronic acid for patients with radiographic evidence of osteolytic bone destruction. Moreover, 4mg zoledronic acid is the only bisphosphonate that has demonstrated significant clinical benefit in patients with other solid tumors, including lung cancer, and prostate cancer patients with primarily osteoblastic bone metastases. Bisphosphonates also may have activity in the adjuvant setting to prevent or delay the development of bone metastases. Studies with oral clodronate in early breast cancer have provided clinical evidence that bone metastases can be inhibited, and the studies are ongoing with more potent bisphosphonates. Bisphosphonates have also been shown to prevent cancer treatment-induced bone loss. These and other studies continue to redefine the role of bisphosphonates in the treatment of malignant bone disease and the management of bone health in cancer patients.     

Prevention and Treatment of Myeloma Bone Disease

Osteolytic bone disease is the most common complication of multiple myeloma, resulting in skeletal-related events (SREs) that cause significant morbidity. Bone destruction in myeloma is due to an increased activity of osteoclasts coupled with suppressed bone formation by osteoblasts. Currently, bisphosphonates are the mainstay of the treatment of myeloma bone disease. Zoledronic acid and pamidronate have shown similar efficacy in reducing SREs in a randomized study in the conventional chemotherapy era. However, in a recent study (the Myeloma-IX trial of the UK Medical Research Council, MRC), zoledronic acid was found to be superior to clodronate in reducing SREs, but also it produced a survival advantage of approximately 10?months in patients with bone disease at baseline. During recent years, novel agents targeting bone have been used in myeloma. This review focuses on the established therapy of myeloma bone disease and also on recent advances in treatment that take advantage of the better understanding of the pathophysiology of bone disease.     

Antitumor effects of bisphosphonates: promising preclinical evidence

The majority of patients with advanced cancer will ultimately develop bone metastases. The bone microenvironment provides fertile soil for a cycle of tumor growth and bone destruction that increases the risk of debilitating and potentially life-limiting skeletal-related events. Therefore, developing appropriate strategies to prevent bone metastases is critical. Bisphosphonates used to treat and prevent skeletal-related events resulting from multiple myeloma and bone metastases secondary to solid tumors, may also have direct and indirect antitumor effects. Emerging evidence from in vitro and in vivo preclinical studies in several tumor types suggests that bisphosphonates can reduce tumor burden in bone and soft tissue, inhibit angiogenesis, prevent tumor cell invasion and adhesion in bone, and induce tumor cell apoptosis. The powerful antiresorptive properties of bisphosphonates appear to directly prevent tumor cell growth and angiogenesis; in addition, combining bisphosphonates with cytotoxic chemotherapy may provide further antitumor synergies. Sequential application of cytotoxic chemotherapy (e.g., doxorubicin, paclitaxel, and gemcitabine) followed by bisphosphonates has been shown to induce significantly more tumor cell apoptosis than either agent alone in vitro and effectively inhibits tumor growth in vivo. Furthermore, in vivo data suggest that optimizing the dosing schedule may significantly increase survival. Overall, preclinical data suggesting that bisphosphonates have antitumor potential are promising and have provided the impetus for several ongoing clinical studies.     

Pathophysiology of bone metastases from prostate cancer and the role of bisphosphonates in treatment

Metastasis to bone is a common feature in advanced prostate cancer patients. Current treatments, while effective in suppressing tumour growth and relieving tumour associated bone pain, do not provide long term remission or 'cure' for the disease. A greater understanding of prostate cancer metastasis is required if new treatment strategies are to be developed. Growth of tumour foci in skeletal sites is a major cause of morbidity in advanced prostate cancer and has required the development of specialised approaches to treatment, including the use of bisphosphonates. These drugs inhibit tumour induced osteoclastic bone resorption, thereby preventing skeletal related events and treatment induced bone loss. Zoledronic acid is currently the only bisphosphonate with proven benefit in prostate cancer. Bisphosphonates may also modify the bone microenvironment so that it becomes less favourable for the growth and survival of metastases. The most recent developments in our understanding of the advantages for growth and survival gained by metastatic prostate cancer cells in the skeleton are reviewed, along with the clinical evidence supporting the use of bisphosphonates in advanced prostate cancer.     

The antineoplastic role of bisphosphonates: from basic research to clinical evidence.

Bisphosphonates are now well established as successful agents for the prevention and treatment of postmenopausal osteoporosis, corticosteroid-induced bone loss and Paget's disease. Bisphosphonates have also recently become important in the management of cancer-induced bone disease, and they now have a widely recognized role for patients with multiple myeloma and bone metastases secondary to breast cancer and prostate cancer. Recent studies suggest that, besides the strong antiosteoclastic activity, the efficacy of such compounds in the oncological setting could also be due also to direct antitumor effect, exerted at different levels. Here, after a brief analysis of the chemical structure, we will review the antineoplastic and biological properties of bisphosphonates. We will start from well estabilished mechanisms of action and go on to discuss the latest evidence and hypotheses. In particular, we will review the antiresorptive properties in malignant osteolysis and the recent evidence of a direct antitumor effect. Furthermore, this review will analyze the influence of bisphosphonates on cancer growth factor release, their effect on cancer cell adhesion, invasion and viability, the proapoptotic potential on cancer cells, the antiangiogenic effect, and, finally, the immunomodulating properties of bisphosphonates on the gammadelta T cell population.     

Direct and indirect anticancer activity of bisphosphonates: a brief review of published literature

The bone marrow microenvironment provides a site for cancer cells to evade systemic anticancer therapy. Dormant tumor micrometastases are believed to be the source of disease persistence and relapse; however, the exact characteristics of cancer stem cells vs. cancer cells with limited metastatic potential have yet to be elucidated. Bisphosphonates inhibit osteoclast-mediated bone resorption, are approved for treating malignant bone disease from advanced cancers, and have shown efficacy for preventing cancer treatment-induced bone loss. Altering the bone marrow microenvironment to make it less conducive to cancer cell survival is now emerging as an important means to prevent cancer recurrence. This review aims to distill the diverse literature and provide a brief overview of the numerous preclinical and early clinical studies of bisphosphonates demonstrating a variety of direct and indirect anticancer activities that affect both the tumor cell (the "seed") and surrounding microenvironment (the "soil"). Recently, zoledronic acid was found to improve disease-free survival and overall survival in some adjuvant breast cancer settings and prolonged survival in patients with multiple myeloma and other advanced cancers. In the prostate cancer setting, antiresorptive therapy was reported to delay the development of overt bone metastases. Ongoing studies will provide further insight regarding the anticancer potential of bisphosphonates and other antiresorptive agents.     

The potential application of zoledronic acid as anticancer therapy in patients with non-small-cell lung cancer

Non-small-cell lung cancer (NSCLC) is frequently characterized by metastases to bone. Bisphosphonates have demonstrated efficacy in reducing the risk of skeletal-related events in cancer patients with bone metastases, including those with NSCLC. Zoledronic acid (ZA) is one of the most potent bisphosphonates and is approved for the first-line treatment of patients with multiple myeloma and bone metastases from solid tumors. Recent preclinical and clinical data suggest that ZA may also have direct and indirect anticancer effects. Several preclinical studies have provided insight into the potential mechanisms responsible for the anticancer activity of ZA, including inhibiting farnesyl pyrophosphate or geranylgeranyl pyrophosphate and activation of immune-mediated anticancer response by γδ T cells. In patients with NSCLC, ZA has been shown to reduce vascular endothelial growth factor levels with a direct correlation to clinical response. Clinical studies in this setting have shown that ZA may also provide a survival benefit and prolong time to progression. Ongoing studies are evaluating the efficacy of ZA for anticancer activity and prevention of bone metastases. Bisphosphonates, particularly ZA, are generally well tolerated and may likely offer an adjunct therapeutic option for patients with NSCLC.     

Angiogenesis in multiple myeloma

Multiple myeloma (MM) was the first haematological malignancy in which a prognostic relevance of bone marrow microvessel density (MVD) was shown. Myeloma-induced angiogenesis involves either the direct production of angiogenic molecules by myeloma cells or their induction in bone marrow stromal cells or endothelial cells (EC). Recent data demonstrate an increased angiogenic potential and a paracrine stimulatory effect of bone marrow EC on plasma cells (PC) in MM. Soluble angiogenic factors are elevated in bone marrow (BM) and in peripheral blood samples from myeloma patients. Furthermore, correlation with disease stage and prognosis was shown for serum levels of the angiogenic factors basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF). In this review we summarize recent data which give strong evidence for an increased angiogenic activity in bone marrow microenvironment and support the hypothesis that angiogenesis is not only an epiphenomenon of tumour growth but may also promote PC growth in MM.     

Effects of bone-targeted agents on cancer progression and mortality

Bone-targeted treatments with bisphosphonates and denosumab, which reduce bone resorption, are known to reduce the risk of skeletal complications and prevent treatment-induced bone loss in patients with malignant bone disease. Additionally, these drugs may modify the course of bone destruction via inhibitory effects on the "vicious cycle" of growth factor and cytokine signaling between tumor and bone cells within the bone marrow microenvironment. Effects of the drugs on the stem cell niche, direct effects on the cancer cells, and immune modulation may also contribute. In early-stage (stages I, II, and III) breast cancer, treatment with the bisphosphonate zoledronic acid has shown improvements in disease-free and overall survival. Improved survival was particularly notable in women with established menopause at diagnosis and in premenopausal women with endocrine-responsive disease who received treatment with goserelin, which suppresses ovarian function by inhibiting the production of ovarian hormones. Additionally, in castrate-resistant prostate cancer, treatment with denosumab delays the development of bone metastases. These results strongly support the adjuvant use of bone-targeted treatments but suggest that reproductive hormones are an important treatment modifier to take into account. In advanced-stage (stage IV, ie, metastatic) cancers, survival benefits have been observed in patients with multiple myeloma and in patients with other solid tumors with rapid rates of bone destruction who received treatment with zoledronic acid. Here, we have critically reviewed the increasing evidence to support a disease-modifying effect of bone-targeted treatment and discussed the impact on clinical management.     

Bisphosphonates in oncology: physiopathologic bases and clinical activity

Osteoclastic activation is the ultimate way of bone resorption in neoplasia, induced by the combined effects of tumor-secreted humoral factors (especially parathyroid hormone-related peptides) and osteoclastic-osteoblastic interaction. Bisphosphonates inhibit the osteoclast activity and reduce bone resorption and are a valuable supportive measure for bone disease of neoplasms. Experimental models also suggest an activity of bisphosphonates against cancer cells. Controlled studies, especially in advanced breast cancer and multiple myeloma, indicate different effectiveness against the distinct skeletal-related events. Intravenous clodronate and, especially, pamidronate and zoledronate are the first-choice drugs for hypercalcemia, and they play a significant role in reducing metastatic bone pain. Their prolonged use delays, without hampering, the progression of bone disease, including the appearance of osteolysis and the occurrence of pathologic fractures. This effect is probably more valuable when bisphosphonates are administered early in the course of the disease. The evidence that adjuvant bisphosphonates improve survival needs to be confirmed in ongoing studies. Although poorly absorbed by the gastrointestinal tract, oral bisphosphonates are effective in preventing and treating cancer-induced osteoporosis in long-living patients with operable breast cancer. At present, there is little hope that newer bisphosphonates are more effective than those currently used.     

Aetiology of bone disease and the role of bisphosphonates in multiple myeloma

Osteolytic bone disease is a major cause of morbidity in patients with multiple myeloma. Our understanding of the pathophysiology of multiple myeloma has increased substantially during the past decade. However the underlying mechanisms of bone destruction and the treatments available have, until recently, received relatively little specific attention. In this review, we provide an overview of the RANK/RANKL/osteoprotegerin system; we describe its interaction with other cellular mechanisms, through which malignant plasma cells drive osteolysis, and explain how bisphosphonates can be used to block this action. We also review the supporting evidence for bisphosphonates as the treatment of choice for patients with bone complications related to multiple myeloma, and discuss possible developments for targeted therapy in the future.     

Inhibition of p38alpha mitogen-activated protein kinase prevents the development of osteolytic bone disease, reduces tumor burden, and increases survival in murine models of multiple myeloma

The bone microenvironment plays a critical role in supporting the growth and survival of multiple myeloma as well as in the development of osteolytic bone disease. Signaling through p38alpha mitogen-activated protein kinase (MAPK) mediates synthesis of multiple myeloma cell growth factors, and its inhibition reduces proliferation in vitro. However, it is unclear whether targeting p38alpha MAPK prevents multiple myeloma growth and the development of bone disease in vivo. In this study, we determined whether SCIO-469, a selective p38alpha MAPK inhibitor, inhibits multiple myeloma growth and prevents bone disease in the 5T2MM and 5T33MM models. SCIO-469 decreased constitutive p38alpha MAPK phosphorylation of both 5T2MM and 5T33MM cells in vitro. This was associated with decreased DNA synthesis and an induction of apoptosis when the cells were cultured with bone marrow stromal cells. Treatment of C57Bl/KaLwRij mice bearing 5T33MM cells with SCIO-469 inhibited p38alpha MAPK phosphorylation and was associated with a significant decrease in serum paraprotein, an almost complete reduction in tumor cells in the bone marrow, a decrease in angiogenesis, and a significant increase in disease-free survival. Injection of 5T2MM murine myeloma cells into C57Bl/KaLwRij mice resulted in myeloma bone disease characterized by increased osteoclast occupation of the bone surface, reduced cancellous bone, and the development of osteolytic bone lesions. Treatment of 5T2MM-injected mice with SCIO-469 reduced this development of bone disease. Together, these data show that targeting p38alpha MAPK with SCIO-469 decreases myeloma burden in vivo, in addition to preventing the development of myeloma bone disease.     

Bone marrow stromal cells create a permissive microenvironment for myeloma development: a new stromal role for Wnt inhibitor Dkk1

The rapid progression of multiple myeloma is dependent upon cellular interactions within the bone marrow microenvironment. In vitro studies suggest that bone marrow stromal cells (BMSC) can promote myeloma growth and survival and osteolytic bone disease. However, it is not possible to recreate all cellular aspects of the bone marrow microenvironment in an in vitro system, and the contributions of BMSCs to myeloma pathogenesis in an intact, immune competent, in vivo system are unknown. To investigate this, we used a murine myeloma model that replicates many features of the human disease. Coinoculation of myeloma cells and a BMSC line, isolated from myeloma-permissive mice, into otherwise nonpermissive mice resulted in myeloma development, associated with tumor growth within bone marrow and osteolytic bone disease. In contrast, inoculation of myeloma cells alone did not result in myeloma. BMSCs inoculated alone induced osteoblast suppression, associated with an increase in serum concentrations of the Wnt signaling inhibitor, Dkk1. Dkk1 was highly expressed in BMSCs and in myeloma-permissive bone marrow. Knockdown of Dkk1 expression in BMSCs decreased their ability to promote myeloma and the associated bone disease in mice. Collectively, our results show novel roles of BMSCs and BMSC-derived Dkk1 in the pathogenesis of multiple myeloma in vivo.     

Anti-tumour activity of bisphosphonates in preclinical models of breast cancer

There is increasing evidence of anti-tumour effects of bisphosphonates from pre-clinical studies, supporting a role for these drugs beyond their traditional use in treatment of cancer-induced bone disease. A range of model systems have been used to investigate the effects of different bisphosphonates on tumour growth, both in bone and at peripheral sites. Most of these studies conclude that bisphosphonates cause a reduction in tumour burden, but that early intervention and the use of high and/or repeated dosing is required. Successful eradication of cancer may only be achievable by targeting the tumour cells directly whilst also modifying the tumour microenvironment. In line with this, bisphosphonates are demonstrated to be particularly effective at reducing breast tumour growth when used in combination with agents that directly target cancer cells. Recent studies have shown that the effects of bisphosphonates on breast tumours are not limited to bone, and that prolonged anti-tumour effects may be achieved following their inclusion in combination therapy. This has opened the field to a new strand of bisphosphonate research, focussed on elucidating their effects on cells and components of the local, regional and distal tumour microenvironment. This review highlights the recent developments in relation to proposed anti-tumour effects of bisphosphonates reported from in vitro and in vivo models, and summarises the data from key breast cancer studies. Evidence for effects on different processes and cell types involved in cancer development and progression is discussed, and the main outstanding issues identified.