Comparison of Fc-osteoprotegerin and zoledronic acid activities suggests that zoledronic acid inhibits prostate cancer in bone by indirect mechanisms

[Human osteoprotegerin inhibits osteoclasts and promotes hydroxyapatite to repair the mandibular defects in ovariectomized rats]

OBJECTIVE

This study aims to investigate the effect of human osteoprotegerin (hOPG) gene-modified rat bone marrow mesenchymal stem cells (rBMSCs) combined with hydroxyapatite (HA) scaffolds on the repair of mandibular defects in ovariectomized rats.

METHODS

rBMSCs were transfected with adenovirus carrying pDC316-hOPG-EGFP. The expression of hOPG and the inhibition of osteoclast function were detected by Western blot and bone-grinding experiment respectively. The model of mandibular bone defect in rats with osteoporosis was established; HA, untransfected rBMSCs-conjugated HA, and transfected rBMSCs-conjugated HA scaffolds were implanted into the mandibular bone defects. After six weeks, tartrateresistant acid phosphatase staining and hematoxylin-eosin staining were used to observe the number of osteoclasts and repair of bone defect.

RESULTS

Adenovirus carrying hOPG gene in vitro were successfully transfected into rBMSCs. The hOPG with anti-osteoclast activity was expressed by hOPG-rBMSCs, and rBMSCs expressing hOPG combined with HA scaffolds promoted mandibular defect repair.

CONCLUSIONS

rBMSCs transfected with hOPG gene inhibited the function of osteoclasts both in vitro and in vivo, and transfected rBMSCs combined with HA scaffolds promoted the repair of mandibular defects in rats with osteoporosis.

The association between RANKL and Osteoprotegerin gene polymorphisms with breast cancer

Breast cancer is the most common cause of cancer death among women (522,000 deaths in 2012). Imbalance between RANKL and OPG is observed in many cancers, including breast cancer. Consequently, SNPs in the genes of RANKL and OPG may be involved in breast cancer development. This study included 276 subjects. Group I (n = 100) healthy females as a control group, group II (n = 96) breast cancer patients without bone metastases, and group III (n = 80) breast cancer patients with bone metastases. RANKL rs9533156, OPG rs2073618, and OPG rs2073617 SNPs and their serum protein levels were studied for a possible association with breast cancer development. The allele frequency [(OR: 4.832 CI 2.18-10.71, P = 0.001) and genotype distribution (P = 0.001)] of OPG SNP rs2073618 showed a highly significant difference between breast cancer patients and healthy controls. The allele C is more common in breast cancer patients. The allele frequency [(OR: 0.451 CI 0.232-0.879, P = 0.018) and genotype distribution (P = 0.003)] of RANKL SNP rs9533156 differed significantly between breast cancer patients and healthy controls. The allele T is more common in breast cancer patients. The allele frequency [(OR: 0.36 CI 0.184-0.705, P = 0.002) and genotype distribution (P = 0.011)] of OPG SNP rs2073617 differed significantly between breast cancer patients and healthy controls. The allele T is more common in breast cancer patients. The C allele of OPG SNP rs2073618 may be associated with breast cancer development. No association was found between any of the SNPs and the serum protein levels of RANKL and OPG.

RANK rs1805034 T>C polymorphism is associated with susceptibility of esophageal cancer in a Chinese population

Esophageal cancer remains the sixth leading cause of cancer associated death and eighth most common cancer worldwide. Genetic factors, such as single nucleotide polymorphisms (SNPs), may contribute to the carcinogenesis of esophageal cancer. Here, we conducted a hospital based case-control study to evaluate the genetic susceptibility of functional SNPs on the development of esophageal cancer. A total of 629 esophageal squamous cell carcinoma (ESCC) cases and 686 controls were enrolled for this study. The OPG rs3102735 T>C, rs2073618 G>C, RANK rs1805034 T>C, RANKL rs9533156 T>C and rs2277438 A>G were determined by ligation detection reaction method. Our findings suggested that RANK rs1805034 T>C is associated with the susceptibility of ESCC, which is more evident in male and elder (≥63) patients. Our study provides the first evidence that functional polymorphisms RANK rs1805034 T>C may be an indicator for individual susceptibility to ESCC. However, further larger studies among different ethnic populations are warranted to verify our conclusion.

Bone markers for monitoring efficacy in patients with bone metastases receiving zoledronic acid: a review of published data

Bone metastases occur frequently in patients with advanced solid tumors and can create serious clinical problems that are commonly referred to as skeletal-related events. Although bisphosphonates, especially zoledronic acid, have emerged as an integral determinant of managing metastatic bone disease, their application remains a challenge because of the lack of standardized measures and their side effects. Since factors derived from bone metabolism are potentially useful to measure the efficacy of zoledronic acid, several clinical trials have investigated these bone markers with respect to their monitoring values. The results suggest that a greater decline in bone marker levels is associated with a more reduced incidence of skeletal-related events and a better improvement of symptoms. This review summarizes the available evidence on the clinical use of bone markers in monitoring zoledronic acid in various cancers with bone metastases including breast, prostate and lung cancer.

Expression of osteoprotegerin from a replicating adenovirus inhibits the progression of prostate cancer bone metastases in a murine model

Metastatic involvement of the skeleton is a frequent consequence of advanced prostate cancer. These skeletal metastases cause a number of debilitating complications and are refractory to current treatments. New therapeutic options are being explored, including conditionally replicating adenoviruses (CRAds). CRAds are engineered to selectively replicate in and destroy tumor cells and can be 'armed' with exogenous transgenes for enhanced potency. We hypothesized that a CRAd armed with osteoprotegerin (OPG), an inhibitor of osteoclastogenesis, would inhibit the progression of prostate cancer bone metastases by directly lysing tumor cells and by reducing osteoclast activity. Although prostate cancer bone metastases are predominantly osteoblastic in nature, increased osteoclast activity is critical for the growth of these lesions. Ad5-Δ24-sOPG-Fc-RGD is a CRAd that carries a fusion of the ligand-binding domains of OPG and the Fc region of human IgG1 in place of the viral E3B genes. To circumvent low tumor cell expression of the native adenoviral receptor, an arginine-glycine-aspartic acid (RGD) peptide insertion within the viral fiber knob allows infection of cells expressing α(v) integrins. A 24-base pair deletion (Δ24) within viral E1A limits replication to cells with aberrant retinoblastoma cell cycle regulator/tumor suppressor expression. We have confirmed that Ad5-Δ24-sOPG-Fc-RGD replicates within and destroys prostate cancer cells and, in both murine and human coculture models, that infection of prostate cancer cells inhibits osteoclastogenesis in vitro. In a murine model, progression of advanced prostate cancer bone metastases was inhibited by treatment with Ad5-Δ24-sOPG-Fc-RGD but not by an unarmed control CRAd.

The role of the bone microenvironment in skeletal metastasis

The bone microenvironment provides a fertile soil for cancer cells. It is therefore not surprising that the skeleton is a frequent site of cancer metastasis. It is believed that reciprocal interactions between tumour and bone cells, known as the “vicious cycle of bone metastasis” support the establishment and orchestrate the expansion of malignant cancers in bone. While the full range of molecular mechanisms of cancer metastasis to bone remain to be elucidated, recent research has deepened our understanding of the cell-mediated processes that may be involved in cancer cell survival and growth in bone. This review aims to address the importance of the bone microenvironment in skeletal cancer metastasis and discusses potential therapeutic implications of novel insights.

Bench to bedside: elucidation of the OPG-RANK-RANKL pathway and the development of denosumab

Bone is a complex tissue that provides mechanical support for muscles and joints, protection for vital organs, a mineral reservoir that is essential for calcium homeostasis, and the environment and niches required for haematopoiesis. The regulation of bone mass in mammals is governed by a complex interplay between bone-forming cells termed osteoblasts and bone-resorbing cells termed osteoclasts, and is guided physiologically by a diverse set of hormones, cytokines and growth factors. The balance between these processes changes over time, causing an elevated risk of fractures with age. Osteoclasts may also be activated in the cancer setting, leading to bone pain, fracture, spinal cord compression and other significant morbidities. This Review chronicles the events that led to an increased understanding of bone resorption, the elucidation of the signalling pathway mediated by osteoprotegerin, receptor activator of NF-κB (RANK) and RANK ligand (RANKL) and its role in osteoclast biology, as well as the evolution of recombinant RANKL antagonists, which culminated in the development of the therapeutic RANKL-targeted antibody denosumab.

Bisphosphonates regulate cell proliferation, apoptosis and pro-osteoclastic expression in MG-63 human osteosarcoma cells

Bisphosphonates are well established in the management of cancer-induced skeletal complications. Recent studies suggest that nitrogen-containing bisphosphonates (N-BPs) promote the apoptosis of cancer cells as well as osteoclasts in bone metastatic sites. To investigate whether N-BPs exhibit a direct antitumor effect on osteoclasts, the current study investigated the effects of zoledronic acid (ZOL) on MG-63 cells in vitro. MG-63 cells were treated with ZOL. The inhibitory effect of ZOL on the growth of MG-63 cells was measured by MTT assay. ZOL-induced apoptosis of the MG-63 cells was examined by Hoechst 33258 staining, electron microscopy, Annexin V-FITC and propidium iodide staining. Reverse-transcription polymerase chain reaction (RT-PCR) and western blotting analysis were employed to assess the expression of osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL). The MTT assay showed that ZOL induced a distinct dose- and time-dependent reduction of cell viability with an IC(50) value of 52.37±1.0 μM for 72 h. Flow cytometric analysis further revealed that the cell apoptosis was induced by arrest of the cell cycle in the G(1) phase. RT-PCR and western blot analysis demonstrated that ZOL upregulated OPG expression. These results suggest that ZOL has direct effects on osteosarcoma cell growth and apoptosis. Increased OPG expression is an indirect effect, possibly via changes in the local microenvironment.

Zoledronic acid preserves bone structure and increases survival but does not limit tumour incidence in a prostate cancer bone metastasis model

BACKGROUND

The bisphosphonate, zoledronic acid (ZOL), can inhibit osteoclasts leading to decreased osteoclastogenesis and osteoclast activity in bone. Here, we used a mixed osteolytic/osteoblastic murine model of bone-metastatic prostate cancer, RM1(BM), to determine how inhibiting osteolysis with ZOL affects the ability of these cells to establish metastases in bone, the integrity of the tumour-bearing bones and the survival of the tumour-bearing mice.

METHODS

The model involves intracardiac injection for arterial dissemination of the RM1(BM) cells in C57BL/6 mice. ZOL treatment was given via subcutaneous injections on days 0, 4, 8 and 12, at 20 and 100 µg/kg doses. Bone integrity was assessed by micro-computed tomography and histology with comparison to untreated mice. The osteoclast and osteoblast activity was determined by measuring serum tartrate-resistant acid phosphatase 5b (TRAP 5b) and osteocalcin, respectively. Mice were euthanased according to predetermined criteria and survival was assessed using Kaplan Meier plots.

FINDINGS

Micro-CT and histological analysis showed that treatment of mice with ZOL from the day of intracardiac injection of RM1(BM) cells inhibited tumour-induced bone lysis, maintained bone volume and reduced the calcification of tumour-induced endochondral osteoid material. ZOL treatment also led to a decreased serum osteocalcin and TRAP 5b levels. Additionally, treated mice showed increased survival compared to vehicle treated controls. However, ZOL treatment did not inhibit the cells ability to metastasise to bone as the number of bone-metastases was similar in both treated and untreated mice.

CONCLUSIONS

ZOL treatment provided significant benefits for maintaining the integrity of tumour-bearing bones and increased the survival of tumour bearing mice, though it did not prevent establishment of bone-metastases in this model. From the mechanistic view, these observations confirm that tumour-induced bone lysis is not a requirement for establishment of these bone tumours.

Clinical development of anti-RANKL therapies for treatment and prevention of bone metastasis

The clinical sequelae from bone metastases, termed skeletal-related events, are among the most frequent and debilitating complications in patients with advanced cancer. Bone metastases are characterized by pathologically increased osteoclast activity, and accumulating evidence indicates that tumor cells interact within the bone to stimulate the RANK-RANK ligand (RANKL) pathway. RANKL is an essential mediator of osteoclast formation, function, and survival. Because of the central role of RANKL in cancer-induced bone destruction, the inhibition of RANKL has the potential to result in the reduction of pathologic bone resorption. Denosumab is a fully human monoclonal antibody specific for RANKL that inhibits the formation, activation, and survival of osteoclasts. This in turn decreases bone resorption and reduces cancer-induced bone destruction. As a result of its unique and specific mechanism of action, denosumab is being investigated for use in patients with advanced malignancies involving bone to prevent the occurrence of skeletal-related events.

Reversal of chemotherapy-induced leukopenia using granulocyte macrophage colony-stimulating factor promotes bone metastasis that can be blocked with osteoclast inhibitors

Hematopoietic growth factors are used to reverse chemotherapy-induced leukopenia. However, some factors such as granulocyte macrophage colony-stimulating factor (GM-CSF) induce osteoclast-mediated bone resorption that can promote cancer growth in the bone. Accordingly, we evaluated the ability of GM-CSF to promote bone metastases of breast cancer or prostate cancer in a mouse model of chemotherapy-induced leukopenia. In this model, GM-CSF reversed cyclophosphamide-induced leukopenia but also promoted breast cancer and prostate cancer growth in the bone but not in soft tissue sites. Bone growth was associated with the induction of osteoclastogenesis, yet in the absence of tumor GM-CSF, it did not affect osteoclastogenesis. Two osteoclast inhibitors, the bisphosphonate zoledronic acid and the RANKL inhibitor osteoprotegerin, each blocked GM-CSF-induced tumor growth in the bone but did not reverse the ability of GM-CSF to reverse chemotherapy-induced leukopenia. Our findings indicate that it is possible to dissociate the bone-resorptive effects of GM-CSF, to reduce metastatic risk, from the benefits of this growth factor in reversing leukopenia caused by treatment with chemotherapy.

RANK ligand inhibition plus docetaxel improves survival and reduces tumor burden in a murine model of prostate cancer bone metastasis

Tumor cells induce excessive osteoclastogenesis, mediating pathologic bone resorption and subsequent release of growth factors and calcium from bone matrix, resulting in a "vicious cycle" of bone breakdown and tumor proliferation. RANK ligand (RANKL) is an essential mediator of osteoclast formation, function, and survival. In metastatic prostate cancer models, RANKL inhibition directly prevents osteolysis via blockade of osteoclastogenesis and indirectly reduces progression of skeletal tumor burden by reducing local growth factor and calcium concentrations. Docetaxel, a well-established chemotherapy for metastatic hormone-refractory prostate cancer, arrests the cell cycle and induces apoptosis of tumor cells. Suppression of osteoclastogenesis through RANKL inhibition may enhance the effects of docetaxel on skeletal tumors. We evaluated the combination of the RANKL inhibitor osteoprotegerin-Fc (OPG-Fc) with docetaxel in a murine model of prostate cancer bone metastasis. Tumor progression, tumor area, and tumor proliferation and apoptosis were assessed. OPG-Fc alone reduced bone resorption (P < 0.001 versus PBS), inhibited progression of established osteolytic lesions, and reduced tumor area (P < 0.0001 versus PBS). Docetaxel alone reduced tumor burden (P < 0.0001 versus PBS) and delayed the development of osteolytic lesions. OPG-Fc in combination with docetaxel suppressed skeletal tumor burden (P = 0.0005) and increased median survival time by 16.7% (P = 0.0385) compared with docetaxel alone. RANKL inhibition may enhance docetaxel effects by increasing tumor cell apoptosis as evident by increased active caspase-3. These studies show that inhibition of RANKL provides an additive benefit to docetaxel treatment in a murine model of prostate cancer bone metastasis and supports clinical evaluation of this treatment option in patients.

RAD001 (Everolimus) inhibits growth of prostate cancer in the bone and the inhibitory effects are increased by combination with docetaxel and zoledronic acid

INTRODUCTION

mTOR activity is increased in advanced prostate cancer (CaP) as a result of a high rate of PTEN mutations. RAD001 (Everolimus) is a new orally available mTOR inhibitor. The objective of our study was to evaluate the effects of RAD001 on the growth of CaP in the bone, both alone and in combination with docetaxel and zoledronic acid.

METHODS

C4-2 CaP cells were injected into tibiae of mice and the animals were treated with RAD001, docetaxel, and zoledronic acid alone or in combination. Histomorphometrical analysis, serum PSA measurements, bone mineral density (BMD), and microCT were used to determine the effects of treatment on tumor and bone.

RESULTS

All three agents alone decreased tumor volume, and RAD001 and docetaxel also decreased levels of serum PSA by 68% and 65%, respectively (both P < 0.01). Combinations of the agents were more effective in decreasing tumor volume than single agents. Three-drug treatment showed the greatest effect: 64% inhibition versus control (P < 0.01). Treatment with RAD001 interfered with the weight loss associated with growth of this tumor in the bone (non-RAD001 groups: 4.0% decrease in body weight, P = 0.0014; RAD001 groups: increase of 3.6% in body weight, P = 0.0037).

CONCLUSIONS

RAD001 inhibited growth of C4-2 cells in bone, an effect augmented by addition of docetaxel and zoledronic acid. Moreover RAD001 had a significant impact on maintenance of body weight. RAD001 may hold promise for its effects on both metastatic CaP and the important syndrome of tumor cachexia.

RANKL inhibition is an effective adjuvant for docetaxel in a prostate cancer bone metastases model

BACKGROUND

Docetaxel induces an anti-tumor response in men with advanced prostate cancer (PCa); however, the side effects associated with docetaxel treatment can be severe, resulting in discontinuation of therapy. Thus, identification of an effective adjuvant therapy to allow lower doses of docetaxel is needed. Advanced PCa is typically accompanied by skeletal metastasis. Receptor activator of NFkB ligand (RANKL) is a key pro-osteoclastic factor. Targeting RANKL decreases establishment and progression of PCa growth in bone in murine models.

METHODS

The efficacy of inhibiting RANKL, using a recombinant soluble RANK extracellular domain fused with the immunoglobulin Fc domain (RANK-Fc), was tested as an adjuvant therapy with docetaxel for PCa bone metastasis in a murine intra-tibial model.

RESULT

The combination of RANK-Fc and docetaxel reduced tumor burden in bone greater than either treatment alone.

CONCLUSION

The combination of docetaxel with a RANKL-inhibiting agent merits further investigation for treatment of advance PCa.

Receptor activator of nuclear factor kappaB ligand and osteoprotegerin regulation of bone remodeling in health and disease

Osteoclasts and osteoblasts dictate skeletal mass, structure, and strength via their respective roles in resorbing and forming bone. Bone remodeling is a spatially coordinated lifelong process whereby old bone is removed by osteoclasts and replaced by bone-forming osteoblasts. The refilling of resorption cavities is incomplete in many pathological states, which leads to a net loss of bone mass with each remodeling cycle. Postmenopausal osteoporosis and other conditions are associated with an increased rate of bone remodeling, which leads to accelerated bone loss and increased risk of fracture. Bone resorption is dependent on a cytokine known as RANKL (receptor activator of nuclear factor kappaB ligand), a TNF family member that is essential for osteoclast formation, activity, and survival in normal and pathological states of bone remodeling. The catabolic effects of RANKL are prevented by osteoprotegerin (OPG), a TNF receptor family member that binds RANKL and thereby prevents activation of its single cognate receptor called RANK. Osteoclast activity is likely to depend, at least in part, on the relative balance of RANKL and OPG. Studies in numerous animal models of bone disease show that RANKL inhibition leads to marked suppression of bone resorption and increases in cortical and cancellous bone volume, density, and strength. RANKL inhibitors also prevent focal bone loss that occurs in animal models of rheumatoid arthritis and bone metastasis. Clinical trials are exploring the effects of denosumab, a fully human anti-RANKL antibody, on bone loss in patients with osteoporosis, bone metastasis, myeloma, and rheumatoid arthritis.

Bone Directed Therapies for Prostate Cancer

PURPOSE

Bone is the most common site of metastatic disease in prostate cancer and the lead cause of significant morbidity. Preclinical and clinical studies have provided insight into the pathophysiology of bone metastases and the changes that occur in the bone microenvironment that result in a favorable site of growth for prostate cancer. We provide an overview of recent advances in understanding bone biology, and bone targeted therapy research and development.

MATERIALS AND METHODS

We reviewed recent research findings related to the biology of bone metastases, approaches to targeting osteoclast function, approaches to targeting osteoblasts and advances in assessing the treatment response to bone targeted therapies in the context of prostate cancer management.

RESULTS

To date targeting some of the key players in the bone microenvironment has not been associated with a significant antitumor effect or with meaningful clinical benefit in phase III randomized trials. A significant limitation in the development of bone targeted therapy has been the inability to objectively assess treatment response. Investigation of improved imaging techniques are ongoing to provide better treatment assessment and, therefore, allow more rapid drug screening and development.

CONCLUSIONS

It is our recommendation that future therapy development should be combination based, focusing on simultaneous targeting of multiple relevant pathways. Most important of all is the direct targeting of prostate cancer cells.

Host-derived RANKL is responsible for osteolysis in a C4-2 human prostate cancer xenograft model of experimental bone metastases

BACKGROUND

C4-2 prostate cancer (CaP) cells grown in mouse tibiae cause a mixed osteoblastic/osteolytic response with increases in osteoclast numbers and bone resorption. Administration of osteoprotegerin (OPG) blocks these increases, indicating the critical role of RANKL in osteolysis in this model. The objective of our study was to investigate whether RANKL expressed by tumor cells (human origin) directly stimulates osteolysis associated with the growth of these cells in bone or whether the increased osteolysis is caused by RANKL expressed by the host environment cells (murine origin). The relative contribution of tumor-vs. host-derived RANKL has been difficult to establish, even with human xenografts, because murine and human RANKL are both capable of stimulating osteolysis in mice, and the RANKL inhibitors used to date (OPG and RANK-Fc) inhibit human and murine RANKL.

METHODS

To address this question we used a neutralizing, antibody (huRANKL MAb), which specifically neutralizes the biological activities of human RANKL and thereby the contribution of C4-2 derived RANKL in this tibial injection model of experimental bone metastases.

RESULTS

Administration of huRANKL MAb did not inhibit the osteolytic response of the bone to these cells, or affect the establishment and growth of the C4-2 tumors in this environment.

CONCLUSION

In conclusion, our results suggest that in this model, murine RANKL and not the tumor-derived human RANKL is the mediator of the osteolytic reaction associated with C4-2 growth in bone. We hypothesize that C4-2 cells express other factor/s inducing host production of RANKL, thereby driving tumor-associated osteolysis.

Effect of zoledronic acid on the doxycycline-induced decrease in tumour burden in a bone metastasis model of human breast cancer

Bone is one of the most frequent sites for metastasis in breast cancer patients often resulting in significant clinical morbidity and mortality. Bisphosphonates are currently the standard of care for breast cancer patients with bone metastasis. We have shown previously that doxycycline, a member of the tetracycline family of antibiotics, reduces total tumour burden in an experimental bone metastasis mouse model of human breast cancer. In this study, we combined doxycycline treatment together with zoledronic acid, the most potent bisphosphonate. Drug administration started 3 days before the injection of the MDA-MB-231 cells. When mice were administered zoledronic acid alone, the total tumour burden decreased by 43% compared to placebo treatment. Administration of a combination of zoledronic acid and doxycycline resulted in a 74% decrease in total tumour burden compared to untreated mice. In doxycycline- and zoledronate-treated mice bone formation was significantly enhanced as determined by increased numbers of osteoblasts, osteoid surface and volume, whereas a decrease in bone resorption was also observed. Doxycycline greatly reduced tumour burden and could also compensate for the increased bone resorption. The addition of zoledronate to the regimen further decreased tumour burden, caused an extensive decrease in bone-associated soft tissue tumour burden (93%), and sustained the bone volume, which could result in a smaller fracture risk. Treatment with zoledronic acid in combination with doxycycline may be very beneficial for breast cancer patients at risk for osteolytic bone metastasis.

Inhibition of bone resorption, rather than direct cytotoxicity, mediates the anti-tumour actions of ibandronate and osteoprotegerin in a murine model of breast cancer bone metastasis

Inhibition of bone resorption either by bisphosphonate (BP) treatment or by blocking RANKL signalling with osteoprotegerin (OPG) has been shown to reduce tumour burden in bone and inhibit bone destruction in murine xenograft models of breast cancer. However, whether the anti-tumour effect of OPG or BP in bone is mediated by inhibition of bone resorption or by direct effects on tumour cells is uncertain. The current study is designed to investigate anti-tumour effects of OPG and ibandronate (IBN), dosed alone or in combination, on tumour growth to determine if there is experimental support for combination treatments and to provide evidence for the presence of direct anti-tumour effects. To this aim, 10 microl (5 x 10(6) cells/ml) of the bone-seeking MDA-MB-231 (Tx-SA) cell line was injected intra-tibially into nude mice. After 10 days, when the tumours were evident radiologically, mice were treated with vehicle, OPG (1 mg/kg/day), ibandronate (IBN) (160 microg/kg/day) or IBN and OPG at the same doses (IBN+OPG) for a week, and the effects of each treatment on lytic lesions, tumour cell growth, cell apoptosis and proliferation were measured by radiography, immunohistochemistry and histomorphometry. Compared to vehicle controls, in vivo treatment with OPG, IBN, or IBN+OPG, each prevented the expansion of osteolytic bone lesions (increase in lytic lesion area day 10 to day 17: OPG -3.2%, IBN 6.6%, IBN+OPG 3.6%, Vehicle 232.5%; p<0.01). Treatment with OPG, IBN or IBN+OPG each produced similar reductions in tumour area relative to vehicle-treated mice (OPG 52%, IBN 54%, IBNp and OPG 48%, p<0.01 vs. vehicle) OPG and IBN alone and in combination each produced a similar increase in cancer cell apoptosis (OPG 330%, IBN 342%, IBN and OPG 347%, p<0.01 vs. vehicle) and a decrease in cancer cell proliferation (OPG 59%, IBN 62%, IBN and OPG 58%, p<0.05 vs. vehicle). Our findings indicate that (i) combined treatment with OPG and a bisphosphonate is not significantly more effective than either agent alone; and that (ii) inhibition of bone resorption, rather than direct anti-tumour action, mediates the effects of these agents on tumour growth in this in vivo model.

Targeting factors involved in bone remodeling as treatment strategies in prostate cancer bone metastasis

Prostate cancer is the most commonly diagnosed cancer in men within the western world and the third leading cause of cancer-related deaths. Even if the cancer is considered localized to the prostate, there is a 15% to 20% incidence of subsequent metastatic disease. Prostate cancer has a very high proclivity for metastasizing to bone, with approximately 90% of men with advanced disease having skeletal lesions. The prostate cancer metastases are characteristically osteoblastic, with extensive new bone deposition, unlike other tumors that metastasize to bone and cause an osteolytic response reflective of bone degradation. There are a considerable number of studies relating to inhibition of the osteoblastic response, including interference with endothelin-1, bone morphogenetic proteins, and Wnt signaling pathways. Within the past few years, several studies showed that increased osteolytic activity also occurs in the background of the prostate cancer skeletal metastases. Because growth factors are being released from the bone matrix during degradation, it suggests that inhibition of osteolysis might be effective in slowing tumor growth. Several strategies are being developed and applied to affect directly the osteolytic events, including use of bisphosphonates and targeting the critical biological regulators of osteoclastogenesis, receptor activator of nuclear factor-kappaB and receptor activator of nuclear factor-kappaB ligand. This review focuses on several of the clinical and preclinical strategies to inhibit the growth of prostate cancer cells in bone and to alleviate the multitude of associated skeletal-related events.

Administration of zoledronic acid enhances the effects of docetaxel on growth of prostate cancer in the bone environment

Background

After development of hormone-refractory metastatic disease, prostate cancer is incurable. The recent history of chemotherapy has shown that with difficult disease targets, combinatorial therapy frequently offers the best chance of a cure. In this study we have examined the effects of a combination of zoledronic acid (ZOL), a new-generation bisphosphonate, and docetaxel on LuCaP 23.1, a prostate cancer xenograft that stimulates the osteoblastic reaction when grown in the bone environment.

Methods

Intra-tibial injections of LuCaP 23.1 cells were used to generate tumors in the bone environment, and animals were treated with ZOL, docetaxel, or a combination of these. Effects on bone and tumor were evaluated by measurements of bone mineral density and histomorphometrical analysis.

Results

ZOL decreased proliferation of LuCaP 23.1 in the bone environment, while docetaxel at a dose that effectively inhibited growth of subcutaneous tumors did not show any effects in the bone environment. The combination of the drugs significantly inhibited the growth of LuCaP 23.1 tumors in the bone.

Conclusion

In conclusion, the use of the osteolysis-inhibitory agent ZOL in combination with docetaxel inhibits growth of prostate tumors in bone and represents a potential treatment option.