Advancing treatment for metastatic bone cancer: consensus recommendations from the Second Cambridge Conference

Targeting cancer-induced skeletal damage: a holistic approach to understanding pathophysiology, mechanisms, and management solutions

Cancer's insidious reach extends far beyond its initial site, particularly manifesting in the skeleton, where it precipitates a spectrum of pathological conditions ranging from bone metastases and cachexia to primary bone cancers. This review highlights the critical impact of cancer on skeletal health, including the development of bone metastases, cachexia, and primary bone cancers, underscoring the importance of understanding the complex interaction between cancer and the bones. It emphasizes the global burden of cancer and its skeletal complications, which severely affect quality of life. The article reviews the prevalence of bone metastases in various cancers, such as breast, prostate, lung, renal cancers, and multiple myeloma, and stresses the need for targeted treatments. It also discusses the mechanisms behind tumor spread to bones and the systemic effects of cancer, including reduced bone mineral density and increased fracture risk, even without direct bone invasion. The challenges posed by primary bone cancers, which are rarer but highly aggressive, are also examined, highlighting the role of genetics and molecular research in treatment development. The review calls for a multidisciplinary approach to manage the severe symptoms of cancer-induced bone damage and explores the potential of personalized medicine to improve treatment outcomes. It concludes by advocating for continued research and collaboration to develop more precise and personalized therapies for cancer-related bone issues, aiming to improve the lives of those affected.

Dual-Targeting Biomimetic Semiconducting Polymer Nanocomposites for Amplified Theranostics of Bone Metastasis

Bone metastasis is a type of metastatic tumors that involves the spreads of malignant tumor cells into skeleton, and its diagnosis and treatment remain a big challenge due to the unique tumor microenvironment. We herein develop osteoclast and tumor cell dual-targeting biomimetic semiconducting polymer nanocomposites (SPFeNOC ) for amplified theranostics of bone metastasis. SPFeNOC contain semiconducting polymer and iron oxide (Fe3 O4 ) nanoparticles inside core and surface camouflaged hybrid membrane of cancer cells and osteoclasts. The hybrid membrane camouflage enables their targeting to both metastatic tumor cells and osteoclasts in bone metastasis through homologous targeting mechanism, thus achieving an enhanced nanoparticle accumulation in tumors. The semiconducting polymer mediates near-infrared (NIR) fluorescence imaging and sonodynamic therapy (SDT), and Fe3 O4 nanoparticles are used for magnetic resonance (MR) imaging and chemodynamic therapy (CDT). Because both cancer cells and osteoclasts are killed synchronously via the combinational action of SDT and CDT, the vicious cycle in bone metastasis is broken to realize high antitumor efficacy. Therefore, 4T1 breast cancer-based bone metastasis can be effectively detected and cured by using SPFeNOC as dual-targeting theranostic nanoagents. This study provides an unusual biomimetic nanoplatform that simultaneously targets osteoclasts and cancer cells for amplified theranostics of bone metastasis.

Breast cancers as ecosystems: a metabolic perspective

Breast cancer (BC) is the most frequently diagnosed cancer and one of the major causes of cancer death. Despite enormous progress in its management, both from the therapeutic and early diagnosis viewpoints, still around 700,000 patients succumb to the disease each year, worldwide. Late recurrency is the major problem in BC, with many patients developing distant metastases several years after the successful eradication of the primary tumor. This is linked to the phenomenon of metastatic dormancy, a still mysterious trait of the natural history of BC, and of several other types of cancer, by which metastatic cells remain dormant for long periods of time before becoming reactivated to initiate the clinical metastatic disease. In recent years, it has become clear that cancers are best understood if studied as ecosystems in which the impact of non-cancer-cell-autonomous events-dependent on complex interaction between the cancer and its environment, both local and systemic-plays a paramount role, probably as significant as the cell-autonomous alterations occurring in the cancer cell. In adopting this perspective, a metabolic vision of the cancer ecosystem is bound to improve our understanding of the natural history of cancer, across space and time. In BC, many metabolic pathways are coopted into the cancer ecosystem, to serve the anabolic and energy demands of the cancer. Their study is shedding new light on the most critical aspect of BC management, of metastatic dissemination, and that of the related phenomenon of dormancy and fostering the application of the knowledge to the development of metabolic therapies.

The bone microenvironment invigorates metastatic seeds for further dissemination

Metastasis has been considered as the terminal step of tumor progression. However, recent genomic studies suggest that many metastases are initiated by further spread of other metastases. Nevertheless, the corresponding pre-clinical models are lacking, and underlying mechanisms are elusive. Using several approaches, including parabiosis and an evolving barcode system, we demonstrated that the bone microenvironment facilitates breast and prostate cancer cells to further metastasize and establish multi-organ secondary metastases. We uncovered that this metastasis-promoting effect is driven by epigenetic reprogramming that confers stem cell-like properties on cancer cells disseminated from bone lesions. Furthermore, we discovered that enhanced EZH2 activity mediates the increased stemness and metastasis capacity. The same findings also apply to single cell-derived populations, indicating mechanisms distinct from clonal selection. Taken together, our work revealed an unappreciated role of the bone microenvironment in metastasis evolution and elucidated an epigenomic reprogramming process driving terminal-stage, multi-organ metastases.

Incidence, risk factors and prognostic characteristics of bone metastases and skeletal-related events (SREs) in breast cancer patients: A systematic review of the real world data

Purpose

The aim was to systematically extrapolate the occurrence, risk factors, prognostic characteristics, management and outcome of bone metastases (BM) and skeletal related events (SREs) of breast cancer survivors in the real world clinical setting.

Methods

A systematic literature search of PubMed, Web of Science, EMBASE OvidSP and EBSCO Academic Search Complete was conducted. Published prospective and retrospective papers investigating BM and SREs in breast cancer patients in non-trial settings were identified and systematically reviewed.

Results

Twenty-four studies met the inclusion criteria. Incidences of BM based on new diagnosis, length of BM-free interval (BMFI) and number and sites of BM were detected by 17 of 24 studies. Seven studies included in the review were subjected to analyses of risk factors for BM. Developments of SREs regarding the occurrence ratio of total and specific SREs, SERs-free interval (SREFI) and the first-line therapy for SREs were observed in 16 of 24 studies. Out of 5 studies, we extracted uni- and multivariate analysis of risk factor for SREs and out of 16 studies - predictors for survival in breast cancer patients with BM.

Conclusions

BM and SREs are common problems in non-trial breast cancer populations. Patient demographics, clinical stage, tumor pathological type, molecular receptors status are significantly risk factors for incidence of BM, SREs and the survival. The unique characteristics of BM and SREs in breast cancer patients should be taken into account in future randomized controlled trials, as to optimize individual treatment options and assure a maximally long good quality of life.

Molecular radiotheragnostics in prostate cancer

Two different molecular radio-theragnostic principles are applied in prostate cancer, providing a personalised management for those patients. Firstly, radiopharmaceuticals with the same or similar mechanism of action but different energy (gamma-γ, eg 99mTc-diphosphonates or positron-β+, eg 18F-NaF emitting isotopes) can be used to identify patients with osteoblastic metastases for a treatment with bone seeking beta (β-) or alpha (α-) emitting radionuclides to deliver targeted molecular radiotherapy. A number of such β- emitting molecules have been used for bone palliation. More recently, an alpha emitting 223Ra-dicholoride demonstrated not only symptomatic relief but also significantly improved overall survival in castration-resistant prostate cancer with predominant bone metastases. The second principle involves utilisation of the same prostatic specific membrane antigen (PSMA) or similar compound (eg PSMA-11, PSMA-617), but different label with either β+ (68Ga) or γ (99mTc) emitting radioisotope for imaging and subsequently β- (177Lu) or α (225Ac) emitting radionuclide for treatment.

Suppression of NADPH Oxidase Activity May Slow the Expansion of Osteolytic Bone Metastases

Lysophosphatidic acid (LPA), generated in the microenvironment of cancer cells, can drive the proliferation, invasion, and migration of cancer cells by activating G protein-coupled LPA receptors. Moreover, in cancer cells that have metastasized to bone, LPA signaling can promote osteolysis by inducing cancer cell production of cytokines, such as IL-6 and IL-8, which can stimulate osteoblasts to secrete RANKL, a key promoter of osteoclastogenesis. Indeed, in cancers prone to metastasize to bone, LPA appears to be a major driver of the expansion of osteolytic bone metastases. Activation of NADPH oxidase has been shown to play a mediating role in the signaling pathways by which LPA, as well as RANKL, promote osteolysis. In addition, there is reason to suspect that Nox4 activation is a mediator of the feed-forward mechanism whereby release of TGF-beta from bone matrix by osteolysis promotes expression of PTHrP in cancer cells, and thereby induces further osteolysis. Hence, measures which can down-regulate NADPH oxidase activity may have potential for slowing the expansion of osteolytic bone metastases in cancer patients. Phycocyanin and high-dose statins may have utility in this regard, and could be contemplated as complements to bisphosphonates or denosumab for the prevention and control of osteolytic lesions. Ingestion of omega-3-rich flaxseed or fish oil may also have potential for controlling osteolysis in cancer patients.

Dissecting Tumor-Stromal Interactions in Breast Cancer Bone Metastasis

Bone metastasis is a frequent occurrence in breast cancer, affecting more than 70% of late stage cancer patients with severe complications such as fracture, bone pain, and hypercalcemia. The pathogenesis of osteolytic bone metastasis depends on cross-communications between tumor cells and various stromal cells residing in the bone microenvironment. Several growth factor signaling pathways, secreted micro RNAs (miRNAs) and exosomes are functional mediators of tumor-stromal interactions in bone metastasis. We developed a functional genomic approach to systemically identified molecular pathways utilized by breast cancer cells to engage the bone stroma in order to generate osteolytic bone metastasis. We showed that elevated expression of vascular cell adhesion molecule 1 (VCAM1) in disseminated breast tumor cells mediates the recruitment of pre-osteoclasts and promotes their differentiation to mature osteoclasts during the bone metastasis formation. Transforming growth factor β (TGF-β) is released from bone matrix upon bone destruction, and signals to breast cancer to further enhance their malignancy in developing bone metastasis. We furthered identified Jagged1 as a TGF-β target genes in tumor cells that engaged bone stromal cells through the activation of Notch signaling to provide a positive feedback to promote tumor growth and to activate osteoclast differentiation. Substantially change in miRNA expression was observed in osteoclasts during their differentiation and maturation, which can be exploited as circulating biomarkers of emerging bone metastasis and therapeutic targets for the treatment of bone metastasis. Further research in this direction may lead to improved diagnosis and treatment strategies for bone metastasis.

The osteogenic niche promotes early-stage bone colonization of disseminated breast cancer cells

Breast cancer bone micrometastases can remain asymptomatic for years before progressing into overt lesions. The biology of this process, including the microenvironment niche and supporting pathways, is unclear. We find that bone micrometastases predominantly reside in a niche that exhibits features of osteogenesis. Niche interactions are mediated by heterotypic adherens junctions (hAJs) involving cancer-derived E-cadherin and osteogenic N-cadherin, the disruption of which abolishes niche-conferred advantages. We elucidate that hAJ activates the mTOR pathway in cancer cells, which drives the progression from single cells to micrometastases. Human data set analyses support the roles of AJ and the mTOR pathway in bone colonization. Our study illuminates the initiation of bone colonization, and provides potential therapeutic targets to block progression toward osteolytic metastases.

Recent advances in cancer pain management

Pain is the most feared symptom of cancer. New oncological cancer treatments are improving survival, but advanced cancer presents challenges that have not been seen before, often with pain that is very difficult to manage because of a recurrent tumour that is invading the central nervous system. In some of the older interventional techniques of destroying nerve pathways, expertise has diminished or has been deemed unnecessary with the development of specialist palliative care. Not all pain is managed adequately with the analgesic ladder. Knowledge of pain mechanisms, careful assessment and selection of the right technique at the right time will enhance cancer pain management. New techniques include intrathecal drug therapy, vertebroplasty, cordotomy, ultra-sound guided nerve blocks, neuromodulation and advances in drug therapies.

Health state utilities associated with adult attention-deficit/hyperactivity disorder

OBJECTIVES

With growing awareness of the importance of adult attention-deficit/hyperactivity disorder (ADHD) treatment, cost-effectiveness analyses, including utilities, are needed to compare the value of treatment options. Although utilities have been reported for childhood ADHD, little is known about utilities representing adult ADHD. Therefore, the purpose of this study was to estimate utilities associated with adult ADHD.

METHODS

Health-state descriptions of adult ADHD were drafted based on literature review, interviews with four clinicians, and clinical trial data. Health states were revised based on a pilot study with 26 participants. Final health states were rated in time trade-off interviews with general population respondents in London and Edinburgh, UK.

RESULTS

A total of 158 participants completed interviews (mean age =47.0 years; 49.4% female; Edinburgh =80 participants). Mean (standard deviation [SD]) utilities were 0.82 (0.17), 0.68 (0.28), and 0.67 (0.28) for health states describing treatment responders (health state A), nonresponders (health state B), and untreated patients (health state C), respectively. Most participants rated health state A as preferable to B (n=92; 58.2%) and C (n=97; 61.4%). The majority rated B and C as equal (n=125; 79.1%). Paired Student's t-tests found that A had a significantly greater mean utility than B (t=10.0; P<0.0001) and C (t=10.2; P<0.0001).

CONCLUSION

The current study provides utilities that may be used in cost-utility models of treatment for adult ADHD. Results reflected clear differences between health states representing treatment responders and nonresponders/untreated patients. Current utilities were comparable to those previously reported for childhood ADHD.

Platelets govern pre-metastatic tumor communication to bone

Although the survival rate for early detected cancers is high, once a cancer metastasizes to bone, it is incurable. Interestingly, patients without visible metastases display abnormal bone formation and resorption, suggesting a link between primary cancers and the bone microenvironment prior to metastasis, and this link likely facilitates preparation of the pre-metastatic niche. We hypothesized that communication with the primary tumor would result in bone remodeling alterations, and that platelets could facilitate this communication. By using three tumor models, we demonstrate that primary tumor growth stimulates bone formation measured by microcomputed tomography. Further, platelet depletion prevented tumor-induced bone formation, highlighting the importance of platelets in the communication between tumors and the bone microenvironment. Finally, we determine that platelets sequester a variety of tumor-derived proteins, TGF-β1 and MMP-1 in particular, which regulate bone formation. Thus, our data reveal that platelets function as mediators of tumor-bone communication prior to metastasis.

Utilities associated with subcutaneous injections and intravenous infusions for treatment of patients with bone metastases

INTRODUCTION

Although cost-utility models are often used to estimate the value of treatments for metastatic cancer, limited information is available on the utility of common treatment modalities. Bisphosphonate treatment for bone metastases is frequently administered via intravenous infusion, while a newer treatment is administered as a subcutaneous injection. This study estimated the impact of these treatment modalities on health state preference.

METHODS

Participants from the UK general population completed time trade-off interviews to assess the utility of health state vignettes. Respondents first rated a health state representing cancer with bone metastases. Subsequent health states added descriptions of treatment modalities (ie, injection or infusion) to this basic health state. The two treatment modalities were presented with and without chemotherapy, and infusion characteristics were varied by duration (30 minutes or 2 hours) and renal monitoring.

RESULTS

A total of 121 participants completed the interviews (52.1% female, 76.9% white). Cancer with bone metastases had a mean utility of 0.40 on a standard utility scale (1 = full health; 0 = dead). The injection, 30-minute infusion, and 2-hour infusion had mean disutilities of -0.004, -0.02, and -0.04, respectively. The mean disutility of the 30-minute infusion was greater with renal monitoring than without. Chemotherapy was associated with substantial disutility (-0.17). When added to health states with chemotherapy, the mean disutilities of injection, 30-minute infusion, and 2-hour infusion were -0.02, -0.03, and -0.04, respectively. The disutility associated with injection was significantly lower than the disutility of the 30-minute and 2-hour infusions (P < 0.05), regardless of chemotherapy status.

CONCLUSION

Respondents perceived an inconvenience with each type of treatment modality, but injections were preferred over infusions. The resulting utilities may be used in cost-utility models examining the value of treatments for the prevention of skeletal-related events in patients with bone metastases.

Omic-profiling in breast cancer metastasis to bone: implications for mechanisms, biomarkers and treatment

Despite well-recognised advances in breast cancer treatment, there remain substantial numbers of patients who develop metastatic disease, of which up to 70% involves spread to bone, resulting in skeletal complications which have a major negative impact on mortality and quality of life. Bisphosphonates and newer bone-targeted agents have reduced the prevalence of skeletal complications, yet there remains significant unmet clinical need, particularly for the development of more specific therapies for the prevention and treatment of metastatic bone disease, for the prediction of risk of its development in individual patients and for the prediction of response to treatments. Modern 'omic' strategies can potentially make a major contribution to meeting this need. Technological advances in the field of nucleic acid sequencing, mass spectrometry and metabolic profiling have driven progress in genomics, transcriptomics (functional genomics), proteomics and metabolomics. This review appraises the recent application of these approaches to studies of breast cancer metastasis (particularly to bone), with a focus on understanding how omic approaches may lead to new therapeutic options and to novel biomarker molecules or molecular signatures with potential value in clinical practise. The increasingly recognised need for rigorous sample quality control and both pre-clinical and clinical validation to meet the ultimate goals of clinical utility and patient benefit is discussed. Future directions of omic driven research in breast cancer metastasis are considered, in particular micro-RNAs and their role in the post-transcriptional regulation of gene function and the possible role of cancer-stem cells and epigenetic modifications in the development of distant metastases.

Eradication of breast cancer with bone metastasis by autologous formalin-fixed tumor vaccine (AFTV) combined with palliative radiation therapy and adjuvant chemotherapy: a case report

Skeletal metastasis of breast carcinoma is refractory to intensive chemo-radiation therapy and therefore is assumed impossible to cure. Here, we report an advanced case of breast cancer with vertebra-Th7 metastasis that showed complete response to combined treatments with formalin-fixed autologous tumor vaccine (AFTV), palliative radiation therapy with 36 Gy, and adjuvant chemotherapy with standardized CEF (cyclophosphamide, epirubicin, and 5FU), zoledronic acid, and aromatase inhibitors following mastectomy for the breast tumor. The patient has been disease-free for more than 4 years after the mammary surgery and remains well with no evidence of metastasis or local recurrence. Thus, a combination of AFTV, palliative radiation therapy, and adjuvant chemotherapy may be an effective treatment for this devastating disease.

Comparing cost-effectiveness analyses of denosumab versus zoledronic acid for the treatment of bone metastases

BACKGROUND

Bone metastases from various cancers have been traditionally treated with bisphosphonates, such as zoledronic acid (ZA), to prevent future skeletal-related events (SREs). Denosumab (Dmab) has been shown to have more advantages in preventing SREs in clinical trials than ZA, but the cost to administer Dmab is significantly higher.

METHODS

A literature review was conducted to investigate the methodologies used to compare the cost-effectiveness of Dmab and ZA. MEDLINE and EMBASE were searched systematically for all cost-effectiveness analyses published between January week 1, 2006 to August week 1, 2012. Search strategies were designed to retrieve articles analyzing the cost-effectiveness and cost utility of Dmab compared to ZA in patients with bone metastases. From 12 references obtained in the initial database search, eight satisfied the predetermined criteria for full article review. Articles were analyzed for incremental costs per skeletal-related event avoided or incremental cost per quality-adjusted life year gained.

RESULTS

All the studies identified received funding from Novartis Pharmaceuticals (the manufacturer of ZA) or Amgen Incorporated (the manufacturer of Dmab). The studies looked at the economic analysis using different associated costs and over various time periods, ranging from a 1-year to a lifetime time horizon.

CONCLUSION

It is not clear whether the methods used across studies are consistent, which may account for the differences between estimated costs and effects. Future research is suggested to explore the cost-effectiveness between Dmab and ZA using a standardize time frame and endpoint.

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.

Implication of platelet-derived growth factor receptor alpha in prostate cancer skeletal metastasis

Metastasis represents by far the most feared complication of prostate carcinoma and is the main cause of death for patients. The skeleton is frequently targeted by disseminated cancer cells and represents the sole site of spread in more than 80% of prostate cancer cases. Compatibility between select malignant phenotypes and the microenvironment of colonized tissues is broadly recognized as the culprit for the organ-tropism of cancer cells. Here, we review our recent studies showing that the expression of platelet-derived growth factor receptor alpha (PDGFRα ) supports the survival and growth of prostate cancer cells in the skeleton and that the soluble fraction of bone marrow activates PDGFRα in a ligand-independent fashion. Finally, we offer pre-clinical evidence that this receptor is a viable target for therapy.

Mesenchymal stem cells in tumor development: emerging roles and concepts

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that participate in the structural and functional maintenance of connective tissues under normal homeostasis. They also act as trophic mediators during tissue repair, generating bioactive molecules that help in tissue regeneration following injury. MSCs serve comparable roles in cases of malignancy and are becoming increasingly appreciated as critical components of the tumor microenvironment. MSCs home to developing tumors with great affinity, where they exacerbate cancer cell proliferation, motility, invasion and metastasis, foster angiogenesis, promote tumor desmoplasia and suppress anti-tumor immune responses. These multifaceted roles emerge as a product of reciprocal interactions occurring between MSCs and cancer cells and serve to alter the tumor milieu, setting into motion a dynamic co-evolution of both tumor and stromal tissues that favors tumor progression. Here, we summarize our current knowledge about the involvement of MSCs in cancer pathogenesis and review accumulating evidence that have placed them at the center of the pro-malignant tumor stroma.

Differential proteomic analysis of a human breast tumor and its matched bone metastasis identifies cell membrane and extracellular proteins associated with bone metastasis

The classical fate of metastasizing breast cancer cells is to seed and form secondary colonies in bones. The molecules closely associated with these processes are predominantly present at the cell surface and in the extracellular space, establishing the first contacts with the target tissue. In this study, we had the rare opportunity to analyze a bone metastatic lesion and its corresponding breast primary tumor obtained simultaneously from the same patient. Using mass spectrometry, we undertook a proteomic study on cell surface and extracellular protein-enriched material. We provide a repertoire of significantly modulated proteins, some with yet unknown roles in the bone metastatic process as well as proteins notably involved in cancer cell invasiveness and in bone metabolism. The comparison of these clinical data with those previously obtained using a human osteotropic breast cancer cell line highlighted an overlapping group of proteins. Certain differentially expressed proteins are validated in the present study using immunohistochemistry on a retrospective collection of breast tumors and matched bone metastases. Our exclusive set of selected proteins supports the setup of further investigations on both clinical samples and experimental bone metastasis models that will help to reveal the finely coordinated expression of proteins that favor the development of metastases in the bone microenvironment.

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.

An osteoblast-derived proteinase controls tumor cell survival via TGF-beta activation in the bone microenvironment

BACKGROUND

Breast to bone metastases frequently induce a "vicious cycle" in which osteoclast mediated bone resorption and proteolysis results in the release of bone matrix sequestered factors that drive tumor growth. While osteoclasts express numerous proteinases, analysis of human breast to bone metastases unexpectedly revealed that bone forming osteoblasts were consistently positive for the proteinase, MMP-2. Given the role of MMP-2 in extracellular matrix degradation and growth factor/cytokine processing, we tested whether osteoblast derived MMP-2 contributed to the vicious cycle of tumor progression in the bone microenvironment.

METHODOLOGY/PRINCIPAL FINDINGS

To test our hypothesis, we utilized murine models of the osteolytic tumor-bone microenvironment in immunocompetent wild type and MMP-2 null mice. In longitudinal studies, we found that host MMP-2 significantly contributed to tumor progression in bone by protecting against apoptosis and promoting cancer cell survival (caspase-3; immunohistochemistry). Our data also indicate that host MMP-2 contributes to tumor induced osteolysis (μCT, histomorphometry). Further ex vivo/in vitro experiments with wild type and MMP-2 null osteoclast and osteoblast cultures identified that 1) the absence of MMP-2 did not have a deleterious effect on osteoclast function (cd11B isolation, osteoclast differentiation, transwell migration and dentin resorption assay); and 2) that osteoblast derived MMP-2 promoted tumor survival by regulating the bioavailability of TGFβ, a factor critical for cell-cell communication in the bone (ELISA, immunoblot assay, clonal and soft agar assays).

CONCLUSION/SIGNIFICANCE

Collectively, these studies identify a novel "mini-vicious cycle" between the osteoblast and metastatic cancer cells that is key for initial tumor survival in the bone microenvironment. In conclusion, the findings of our study suggest that the targeted inhibition of MMP-2 and/or TGFβ would be beneficial for the treatment of bone metastases.

Intravenous bisphosphonate therapy and atrial fibrillation/flutter risk in cancer patients: a nationwide cohort study

Background:

There is conflicting evidence regarding bisphosphonates and atrial fibrillation (AF) risk in osteoporosis patients. However, bisphosphonates are used in much higher doses in treatment of bone metastasis and hypercalcemia, but little is known about the AF risk in cancer patients.

Methods:

We conducted a nationwide population-based cohort study using Danish databases. All cancer patients exposed to intravenous bisphosphonates during 2000–2008 were matched with two non-exposed cancer patients by cancer type, distant metastasis presence at diagnosis, age, and gender. We used Cox proportional hazard regression to estimate hazards ratios (HRs) of AF/flutter adjusting for important confounding factors.

Results:

Of the 3981 cancer patients exposed to intravenous bisphosponates, 128 (3.2%) developed AF/flutter. This condition occurred in 192 (2.4%) of the 7906 non-exposed cancer patients, corresponding to an adjusted HR of 1.7 (95% CI: 1.2–2.4).

Conclusion:

Intravenous bisphosphonates may increase AF/flutter risk in cancer patients.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

Matrix metalloproteinases as master regulators of the vicious cycle of bone metastasis

Bone remodeling is a delicate balancing act between the bone matrix synthesizing osteoblasts and bone resorbing osteoclasts. Active bone metastases typically subvert this process to generate lesions that are comprised of extensive areas of pathological osteogenesis and osteolysis. The resultant increase in bone matrix remodeling enhances cytokine/growth factor bioavailability thus creating a vicious cycle that stimulates tumor progression. Given the extent of matrix remodeling occurring in the tumor-bone microenvironment, the expression of matrix metalloproteinases (MMPs) would be expected, since collectively they have the ability to degrade all components of the extracellular matrix (ECM). However, in addition to being "matrix bulldozers", MMPs control the bioavailability and bioactivity of factors such as RANKL and TGFβ that have been described as crucial for tumor-bone interaction, thus implicating MMPs as key regulators of the vicious cycle of bone metastases.

Integrins and bone metastasis: integrating tumor cell and stromal cell interactions

Integrins on both tumor cells and the supporting host stromal cells in bone (osteoclasts, new blood vessels, inflammatory cells, platelets and bone marrow stromal cells) play key roles in enhancing bone metastasis. Tumor cells localize to specific tissues through integrin-mediated contacts with extracellular matrix and stromal cells. Integrin expression and signaling are perturbed in cancer cells, allowing them to "escape" from cell-cell and cell-matrix tethers, invade, migrate and colonize within new tissues and matrices. Integrin signaling through αvβ3 and VLA-4 on tumor cells can promote tumor metastasis to and proliferation in the bone microenvironment. Osteoclast (OC) mediated bone resorption is a critical component of bone metastasis and can promote tumor growth in bone and αvβ3 integrins are critical to OC function and development. Tumors in the bone microenvironment can recruit new blood vessel formation, platelets, pro-tumor immune cells and bone marrow stromal cells that promote tumor growth and invasion in bone. Integrins and their ligands play critical roles in platelet aggregation (αvβ3 and αIIbβ3), hematopoietic cell mobilization (VLA-4 and osteopontin), neoangiogenesis (αvβ3, αvβ5, α6β4, and β1 integrin) and stromal function (osteopontin and VLA-4). Integrins are involved in the pathogenesis of bone metastasis at many levels and further study to define integrin dysregulation by cancer will yield new therapeutic targets for the prevention and treatment of bone metastasis.

Targeting the {alpha} receptor for platelet-derived growth factor as a primary or combination therapy in a preclinical model of prostate cancer skeletal metastasis

PURPOSE

Platelet-derived growth factor α (PDGFRα) is highly expressed in primary prostate cancer and associated skeletal metastases. Here, we tested whether targeting this receptor could impair metastatic colonization and progression, as well as prolong survival, either as primary or as combination therapy.

EXPERIMENTAL DESIGN

We used a preclinical animal model of metastasis in which PC3-ML human prostate cancer cells are inoculated directly in the blood circulation. First, the humanized, monoclonal antibody IMC-3G3 was administered to mice bearing established skeletal metastases. Second, we targeted the stromal PDGFRα with IMC-1E10, an antibody specific for the murine receptor. Third, IMC-3G3 and the bisphosphonate zoledronic acid (ZA), administered separately or in combination, were tested on the progression of skeletal lesions and overall survival. In addition, the ability of IMC-3G3 and ZA to impair initial colonization of the bone marrow by prostate cancer cells was investigated.

RESULTS

The blockade of PDGFRα on prostate cancer cells by IMC-3G3 reduces the size of established skeletal metastases, whereas the IMC-1E10 antibody directed against the stromal PDGFRα fails to inhibit metastatic progression. IMC-3G3 and ZA, either separately or in combination, significantly slow tumor growth and seem to prolong survival. Lastly, the blockade of PDGFRα by IMC-3G3 inhibits the initial phase of bone colonization, whereas ZA is ineffective at this stage.

CONCLUSION

This study presents compelling evidence that targeting PDGFRα with IMC-3G3 delays the progression of early metastatic foci and reduces the size of more established lesions. In addition, IMC-3G3, either alone or in combination with ZA, prolongs survival in animal models.

Assessment of Response to Therapy for Bone Metastases: Is it Still a Challenge in Oncology?

Bone is one of the most common sites of metastases from cancer. Most anticancer treatments are highly toxic but only a fraction of all patients respond to them. Guidelines are needed to evaluate the response in the routine practice of oncology as well as in clinical trials in which new treatment options are evaluated. All current imaging procedures have major limitations. This article reviews old and new criteria for response evaluation. The major problem of accurate response evaluation in bone disease is discussed in detail. Some examples from our daily practice illustrate the difficulties. The indications for bone biopsy are also reviewed.

Gender difference in bone metastasis of human small cell lung cancer, SBC-5 cells in natural killer-cell depleted severe combined immunodeficient mice

Lung cancer frequently develops multiple organ metastases, which thus makes this disease a leading cause of malignancy-related death worldwide. A gender difference is reported to affect the incidence and mortality of lung cancer; however, whether and how the gender difference is involved in lung cancer metastasis is unclear. This study evaluated the gender difference in multiple organ metastases in human small cell lung cancer (SBC-5) cells by using natural killer cell-depleted severe combined immunodeficient mice. Among multiple organ metastases, only bone metastasis formation significantly increased in female mice in comparison to males, while no significant difference was observed in the metastases to the liver and lungs. The suppression of androgen by castration or androgen receptor antagonist treatment in male mice also induced a significant increase of bone metastases. The number of osteoclasts in the bone metastatic lesions was greater in female mice and in mice with androgen suppression than in control male. However, there was no significant difference in the serum concentration of parathyroid hormone-related protein (PTHrP) associated with gender or androgen suppression. An in vitro study also indicated that sex steroid treatment had no effect on the proliferation or PTHrP production in SBC-5 cells. These results indicate that the balance of sex steroids therefore plays an important role in the formation of bone metastasis in small cell lung cancer, and suggests diverse mechanisms of interaction between cancer cells and host cells in the bone microenvironment.

Osteosarcoma

It has been difficult to identify the molecular features central to the pathogenesis of osteosarcoma owing to a lack of understanding of the cell or origin, the absence of identifiable precursor lesions, and its marked genetic complexity at the time of presentation. Interestingly, several human genetic disorders and familial cancer syndromes, such as Li-Fraumeni syndrome, are linked to an increased risk of osteosarcoma. Association of these same genetic alterations and osteosarcoma risk have been confirmed in murine models. Osteosarcoma is associated with a variety of genetic abnormalities that are among the most commonly observed in human cancer; it remains unclear, however, what events initiate and are necessary to form osteosarcoma. The availability of new resources for studying osteosarcoma and newer research methodologies offer an opportunity and promise to answer these currently unanswered questions. Even in the absence of a more fundamental understanding of osteosarcoma, association studies and preclinical drug testing may yield clinically relevant information.

Emerging therapeutic targets in breast cancer bone metastasis

In the past decade, our understanding of the molecular mechanisms that underlie breast cancer pathology and progression has dramatically improved. Using this knowledge, we have identified additional targets and developed novel therapeutic interventions in breast cancer. Together, these translational research efforts are helping to usher us into an age of personalized cancer therapy. Metastasis to bone is a common and devastating consequence of breast cancer. Bisphosphonates, which represent the current gold standard in bone metastasis therapies, are being improved with newer and more efficacious generations of these compounds being developed. Breast cancer growth in the bone requires activation of various signaling pathways in both cancer cells and stromal cells, including those that are stimulated by TGF-β and RANKL, and mediated through the Src tyrosine kinase. Bone cells and cancer cells alike express promising targets for therapeutic intervention, including Cathepsin K, CXCR4 and GPNMB. In this article we discuss the molecular mechanisms behind these pro-metastatic molecules and review the most recent findings in the clinical development of their associated targeted therapies.

A single pretreatment by zoledronic acid converts metastases from osteolytic to osteoblastic in the rat

Bone metastases are severe complications of cancers associated with increased morbidity, pain, risk fracture, and reduced life span for patients. Bisphosphonates emerged as a relief treatment in bone metastases. A single dose of zoledronic acid (78 microg/kg) was injected into six Copenhagen rats 4 days before receiving an intraosseous inoculation of metastatic anaplastic tumor of lymph node and lung cell (MLL) prostate cancer cells. Rat femurs were analyzed for changes by microCT and histomorphometry; trabecular volume, trabecular characteristics, osteoid parameters, osteoblastic surfaces, and osteoclast number were measured. Values were compared to a group of SHAM animals, a group of SHAM animals having received zoledronic acid and animals inoculated with MLL cells. All rats were euthanized after 1 month. MLL cells induced osteolysis in the metaphysis with extension of the tumor to soft tissues through cortical perforations. Zoledronic acid induced a marked osteosclerosis in the primary spongiosa in both SHAM and rats inoculated with MLL. Osteosclerosis was obtained in the secondary spongiosa of MLL rats. The bisphosphonate preserved cortical integrity in all animals, and no extension to soft tissues was observed in most animals. The number of osteoclasts was elevated, indicating that there was no apoptosis of osteoclasts but they became inactive. Osteosclerosis was associated with increased osteoblastic surfaces. A single zoledronic acid injection turned osteolytic metastases into osteosclerotic and preserved cortical integrity.

Expression of PGK1 by prostate cancer cells induces bone formation

Prostate cancer (PCa) is one of the solid tumors that metastasize to the bone. Once there, the phenotype of the bone lesions is dependent upon the balance between osteoblastogenesis and osteoclastogenesis. We previously reported that overexpression of phosphoglycerate kinase 1 (PGK1) in PCa cell lines enhanced bone formation at the metastatic site in vivo. Here, the role of PGK1 in the bone formation was further explored. We show that PCa-derived PGK1 induces osteoblastic differentiation of bone marrow stromal cells. We also found that PGK1 secreted by PCa inhibits osteoclastogenesis. Finally, the expression levels of the bone-specific markers in PCa cells were higher in cells overexpressing PGK1 than controls. Together, these data suggest that PGK1 secreted by PCa regulates bone formation at the metastatic site by increasing osteoblastic activity, decreasing osteoclastic function, and expressing an osteoblastic phenotype by PCa cells.

The pharmacological management of skeletal-related events from metastatic tumors

Bone is one of the most common sites of metastatic disease from cancer, affecting around 400,000 patients each year. Skeletal-related events (SRE) include hypercalcemia, fractures, spinal cord compression or severe bone pain and may occur as a complication of metastasis. Bisphosphonate therapy is crucial in the prevention and treatment of SREs; zoledronic acid and pamidronate have both been shown to significantly reduce the development of SREs. Other agents such as corticosteroids and analgesics are also used in symptomatic management. The use of these agents in conjunction with radiation and surgery can help to improve patient outcomes.