Osteoprotegerin in prostate cancer bone metastasis

Molecular landscape of prostate cancer bone metastasis

Prostate cancer (PC) has a high propensity to develop bone metastases, causing severe pain and pathological fractures that profoundly impact a patients' normal functions. Current clinical intervention is mainly palliative focused on pain management, and tumor progression is refractory to standard therapeutic regimens. This limited treatment efficacy is at least partially due to a lack of comprehensive understanding of the molecular landscape of the disease pathology, along with the intensive overlapping of physiological and pathological molecular signaling. The niche is overwhelmed with diverse cell types with inter- and intra-heterogeneity, along with growth factor-enriched cells that are supportive of invading cell proliferation, providing an additional layer of complexity. This review seeks to provide molecular insights into mechanisms underlying PC bone metastasis development and progression.

Downregulation of osteoprotegerin in colorectal cancer cells promotes liver metastasis via activating tumor-associated macrophage

Osteoprotegerin (OPG) is a secreted cytokine that functions as a decoy receptor for receptor activator of nuclear factor kappa-B (RANK) ligand (RANKL). Anti-RANKL treatment for bone metastasis has been widely accepted for solid tumors. However, the mechanism of OPG-RANKL-RANK signaling in systemic colorectal cancer (CRC) metastasis remains unclear. In this study, we investigated the relevance and function of OPG expression in CRC liver metastasis. First, we performed in silico analysis using The Cancer Genome Atlas public database and found that lower OPG expression in CRC was associated with poor overall survival. Immunohistochemistry analyses using resected specimen from patients with CRC in our institute confirmed the result. Patient-matched primary CRC and liver metastases showed a significant downregulation of OPG expression in metastatic lesions. In CRC cell lines, OPG expression did not suppress cell proliferation and migration. However, OPG expression inhibited macrophage migration by suppressing the RANKL-RANK pathway. Moreover, in vivo mouse liver metastasis models showed that OPG expression in CRC cells suppressed liver metastases. In addition, treatment with an anti-RANKL neutralizing antibody also suppressed liver metastases. These results showed that downregulation of OPG expression in CRC cells promotes liver metastasis by activating tumor-associated macrophage, which can become a candidate for targeted therapy with anti-RANKL neutralizing antibody for CRC liver metastasis.

Prostate cancer bone metastases biology and clinical management (Review)

Prostate cancer (PCa) is one of the most prominent causes of cancer-related mortality in the male population. A highly impactful prognostic factor for patients diagnosed with PCa is the presence or absence of bone metastases. The formation of secondary tumours at the bone is the most commonly observed site for the establishment of PCa metastases and is associated with reduced survival of patients in addition to a cohort of life-debilitating symptoms, including mobility issues and chronic pain. Despite the prevalence of this disease presentation and the high medical relevance of bone metastases, the mechanisms underlying the formation of metastases to the bone and the understanding of what drives the osteotropism exhibited by prostate tumours remain to be fully elucidated. This lack of in-depth understanding manifests in limited effective treatment options for patients with advanced metastatic PCa and culminates in the low rate of survival observed for this sub-set of patients. The present review aims to summarise the most recent promising advances in the understanding of how and why prostate tumours metastasise to the bone, with the ultimate aim of highlighting novel treatment and prognostic targets, which may provide the opportunity to improve the diagnosis and treatment of patients with PCa with bone metastases.

p57Kip2 is an essential regulator of vitamin D receptor-dependent mechanisms

A cyclin-dependent kinase (CDK) inhibitor, p57Kip2, is an important molecule involved in bone development; p57Kip2-deficient (p57-/-) mice display neonatal lethality resulting from abnormal bone formation and cleft palate. The modulator 1α,25-dihydroxyvitamin D3 (l,25-(OH)2VD3) has shown the potential to suppress the proliferation and induce the differentiation of normal and tumor cells. The current study assessed the role of p57Kip2 in the 1,25-(OH)2VD3-regulated differentiation of osteoblasts because p57Kip2 is associated with the vitamin D receptor (VDR). Additionally, 1,25-(OH)2VD3 treatment increased p57KIP2 expression and induced the colocalization of p57KIP2 with VDR in the osteoblast nucleus. Primary p57-/- osteoblasts exhibited higher proliferation rates with Cdk activation than p57+/+ cells. A lower level of nodule mineralization was observed in p57-/- osteoblasts than in p57+/+ cells. In p57+/+ osteoblasts, 1,25-(OH)2VD3 upregulated the p57Kip2 and opn mRNA expression levels, while the opn expression levels were significantly decreased in p57-/- cells. The osteoclastogenesis assay performed using bone marrow cocultured with 1,25-(OH)2VD3-treated osteoblasts revealed a decreased efficiency of 1,25-(OH)2VD3-stimulated osteoclastogenesis in p57-/- cells. Based on these results, p57Kip2 might function as a mediator of 1,25-(OH)2VD3 signaling, thereby enabling sufficient VDR activation for osteoblast maturation.

The roles of osteoprotegerin in cancer, far beyond a bone player

Osteoprotegerin (OPG), also known as tumor necrosis factor receptor superfamily member 11B (TNFRSF11B), is a member of the tumor necrosis factor (TNF) receptor superfamily. Characterized by its ability to bind to receptor activator of nuclear factor kappa B ligand (RANKL), OPG is critically involved in bone remodeling. Emerging evidence implies that OPG is far beyond a bone-specific modulator, and is involved in multiple physiological and pathological processes, such as immunoregulation, vascular function, and fibrosis. Notably, numerous preclinical and clinical studies have been conducted to assess the participation of OPG in tumorigenesis and cancer development. Mechanistic studies have demonstrated that OPG is involved in multiple hallmarks of cancer, including tumor survival, epithelial to mesenchymal transition (EMT), neo-angiogenesis, invasion, and metastasis. In this review, we systematically summarize the basis and advances of OPG from its molecular structure to translational applications. In addition to its role in bone homeostasis, the physiological and pathological impacts of OPG on human health and its function in cancer progression are reviewed, providing a comprehensive understanding of OPG. We aim to draw more attention to OPG in the field of cancer, and to propose it as a promising diagnostic or prognostic biomarker as well as potential therapeutic target for cancer.

Mechanisms, Diagnosis and Treatment of Bone Metastases

Bone and bone marrow are among the most frequent metastatic sites of cancer. The occurrence of bone metastasis is frequently associated with a dismal disease outcome. The prevention and therapy of bone metastases is a priority in the treatment of cancer patients. However, current therapeutic options for patients with bone metastatic disease are limited in efficacy and associated with increased morbidity. Therefore, most current therapies are mainly palliative in nature. A better understanding of the underlying molecular pathways of the bone metastatic process is warranted to develop novel, well-tolerated and more successful treatments for a significant improvement of patients' quality of life and disease outcome. In this review, we provide comparative mechanistic insights into the bone metastatic process of various solid tumors, including pediatric cancers. We also highlight current and innovative approaches to biologically targeted therapy and immunotherapy. In particular, we discuss the role of the bone marrow microenvironment in the attraction, homing, dormancy and outgrowth of metastatic tumor cells and the ensuing therapeutic implications. Multiple signaling pathways have been described to contribute to metastatic spread to the bone of specific cancer entities, with most knowledge derived from the study of breast and prostate cancer. However, it is likely that similar mechanisms are involved in different types of cancer, including multiple myeloma, primary bone sarcomas and neuroblastoma. The metastatic rate-limiting interaction of tumor cells with the various cellular and noncellular components of the bone-marrow niche provides attractive therapeutic targets, which are already partially exploited by novel promising immunotherapies.

Small extracellular vesicles deliver osteolytic effectors and mediate cancer-induced osteolysis in bone metastatic niche

Extracellular vesicles (EVs) play critical roles in regulating bone metastatic microenvironment through mediating intercellular crosstalks. However, little is known about the contribution of EVs derived from cancer cells to the vicious cycle of bone metastasis. Here, we report a direct regulatory mode between tumour cells and osteoclasts in metastatic niche of prostate cancer via vesicular miRNAs transfer. Combined analysis of miRNAs profiles both in tumour‐derived small EVs (sEVs) and osteoclasts identified miR‐152‐3p as a potential osteolytic molecule. sEVs were enriched in miR‐152‐3p, which targets osteoclastogenic regulator MAFB. Blocking miR‐152‐3p in sEVs upregulated the expression of MAFB and impaired osteoclastogenesis in vitro. In vivo experiments of xenograft mouse model found that blocking of miR‐152‐3p in sEVs significantly slowed down the loss of trabecular architecture, while systemic inhibition of miR‐152‐3p using antagomir‐152‐3p reduced the osteolytic lesions of cortical bone while preserving basic trabecular architecture. Our findings suggest that miR‐152‐3p carried by prostate cancer‐derived sEVs deliver osteolytic signals from tumour cells to osteoclasts, facilitating osteolytic progression in bone metastasis.

Bone metastasis: mechanisms, therapies, and biomarkers

Skeletal metastases are frequent complications of many cancers, causing bone complications (fractures, bone pain, disability) that negatively affect the patient's quality of life. Here, we first discuss the burden of skeletal complications in cancer bone metastasis. We then describe the pathophysiology of bone metastasis. Bone metastasis is a multistage process: long before the development of clinically detectable metastases, circulating tumor cells settle and enter a dormant state in normal vascular and endosteal niches present in the bone marrow, which provide immediate attachment and shelter, and only become active years later as they proliferate and alter the functions of bone-resorbing (osteoclasts) and bone-forming (osteoblasts) cells, promoting skeletal destruction. The molecular mechanisms involved in mediating each of these steps are described, and we also explain how tumor cells interact with a myriad of interconnected cell populations in the bone marrow, including a rich vascular network, immune cells, adipocytes, and nerves. We discuss metabolic programs that tumor cells could engage with to specifically grow in bone. We also describe the progress and future directions of existing bone-targeted agents and report emerging therapies that have arisen from recent advances in our understanding of the pathophysiology of bone metastases. Finally, we discuss the value of bone turnover biomarkers in detection and monitoring of progression and therapeutic effects in patients with bone metastasis.

Molecular mechanisms and clinical management of cancer bone metastasis

As one of the most common metastatic sites of malignancies, bone has a unique microenvironment that allows metastatic tumor cells to grow and flourish. The fenestrated capillaries in the bone, bone matrix, and bone cells, including osteoblasts and osteoclasts, together maintain the homeostasis of the bone microenvironment. In contrast, tumor-derived factors act on bone components, leading to subsequent bone resorption or excessive bone formation. The various pathways involved also provide multiple targets for therapeutic strategies against bone metastases. In this review, we summarize the current understanding of the mechanism of bone metastases. Based on the general process of bone metastases, we specifically highlight the complex crosstalk between tumor cells and the bone microenvironment and the current management of cancer bone metastases.

Targeting cathepsin K diminishes prostate cancer establishment and growth in murine bone

BACKGROUND

The processes of prostate cancer (PCa) invasion and metastasis are facilitated by proteolytic cascade involving multiple proteases, such as matrix metalloproteinases, serine proteases and cysteine proteases including cathepsin K (CatK). CatK is predominantly secreted by osteoclasts and specifically degrades collagen I leading to bone destruction. PCa and breast cancer preferentially metastasize to the bone. Importantly, CatK expression level is greater in PCa bone metastatic sites compared to primary tumor and normal prostate tissues. However, the underlying mechanism of CatK during PCa metastases into the bone remains to be elucidated. We investigated the functional role of CatK during the PCa establishment and growth process in the murine bone.

METHODS

CatK mRNA expression was validated by RT-PCR, protein expression by immunoblotting in PCa LNCaP, C4-2B, and PC3 cells as well as in PCa tissues. Its protein production was measured using ELISA assay. The effect of both knockdowns via siRNA and CatK inhibitor was compared in regard to PCa cell invasion. We further studied the dose-dependent CatK inhibitor effect on conditioned media-induced bone resorption. In setting up an animal model, C4-2B cells were injected into the tibiae of SCID mice. The animals treated with either vehicle or CatK inhibitor for 8 weeks at the time of tumor cell injection (tumor establishment model; protocol I) or 4 weeks after tumor cell injection (tumor progression model; protocol II) were applied to histological and histomorphometric analyses.

RESULTS

We confirmed CatK expression in PCa LNCaP, C4-2B, and PC3 cells as well as in PCa tissues. Furthermore, we observed the inhibitory effects of a selective CatK inhibitor on PCa cell invasion. The CatK inhibitor dose-dependently inhibited PCa-conditioned media-induced bone resorption. Upon injection of C4-2B cells into the tibiae of SCID mice, the selective CatK inhibitor significantly prevented the tumor establishment in protocol I, and reduced the tumor growth in bone in protocol II. It also decreased serum PSA levels in both animal models. The inhibitory effects of the CatK inhibitor were enhanced in combination with zoledronic acid (ZA).

CONCLUSION

The selective CatK inhibitor may prevent the establishment and progression of PCa in bone, thus making it a novel therapeutic approach for advanced PCa.

Prostate Cancer and Bone Metastases: The Underlying Mechanisms

Patients with advanced prostate cancer often develop bone metastases, leading to bone pain, skeletal fracture, and increased mortality. Bone provides a hospitable microenvironment to tumor cells. The disease manifestation is driven by the interaction between invading tumor cells, bone-forming osteoblasts, and bone-resorbing osteoclasts. The increased level of osteoclast-activating factor (parathyroid hormone-related peptide, PTHrP) is believed to induce bone resorption by upregulating receptor activator of nuclear factor-kappa B ligand (RANKL) and the release of various growth factors into the bone microenvironment to enhance cancer cell growth. However, the underlying molecular mechanisms remain poorly understood. This review outlines the possible molecular mechanisms involved in governing bone metastases driven by prostate cancer, which further provide the basis in searching for new molecular targets for the development of potential therapy.

Tumor Cell Dormancy and Reactivation in Bone: Skeletal Biology and Therapeutic Opportunities

In the advanced stages of many cancers, tumor cells disseminate from the primary site and colonize distant locations such as the skeleton. These disseminated tumor cells colonizing bone can evade treatments and survive for prolonged periods in a dormant state before becoming reactivated to form overt metastases. The precise interactions between tumor cells and the bone microenvironment that promote survival, dormancy, and reactivation are currently unknown; as a result, bone metastases remain incurable. In this review we discuss the unique cellular and microenvironmental features of endosteal bone that tumor cells engage with to persist and survive, and ultimately reactivate and proliferate. Specifically, we provide a detailed summary of current perspectives on the processes of tumor cell colonization of the skeleton, and the endosteal bone cells as critical controllers of the dormant cancer cell phenotype, as well as relevant microenvironmental effects such as hypoxia. Evidence for the role of the osteoclast in controlling dormant cancer cell reactivation in bone is highlighted, preceding a discussion of therapeutics targeting the bone microenvironment, including anti‐RANK ligand and bisphosphonate therapies and their potential utility in preventing tumor cell reactivation in addition to protecting bone from tumor‐induced destruction. © 2018 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Osteoprotegerin rich tumor microenvironment: implications in breast cancer

Osteoprotegerin (OPG) is a soluble decoy receptor for tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL). It belongs to the tumor necrosis factor receptor superfamily (TNFRSF). OPG was initially discovered to contribute to homeostasis of bone turnover due to its capability of binding to receptor activator of nuclear factor-kappaB (NF-kB). However, apart from bone turnover, OPG plays important and diverse role(s) in many biological functions. Besides having anti-osteoclastic activity, OPG is thought to exert a protective anti-apoptotic action in OPG-expressing tumors by overcoming the physiologic mechanism of tumor surveillance exerted by TRAIL. Along with inhibiting TRAIL induced apoptosis, it can induce proliferation by binding to various cell surface receptors and thus turning on the canonical cell survival and proliferative pathways. OPG also induces angiogenesis, one of the hallmarks of cancer, thus facilitating tumor growth. Recently, the understanding of OPG and its different roles has been augmented substantially. This review is aimed at providing a very informative overview as to how OPG affects cancer progression especially breast cancer.

Overexpression of p54nrb/NONO induces differential EPHA6 splicing and contributes to castration-resistant prostate cancer growth

The non-POU domain-containing octamer binding protein p54^nrb/NONO is a multifunctional nuclear protein involved in RNA splicing, processing, and transcriptional regulation of nuclear hormone receptors. Through chromosome copy number analysis via whole-exome sequencing, we revealed amplification of the chromosome Xq11.22-q21.33 locus containing the androgen receptor (AR) and NONO genes in androgen-independent, castration-resistant prostate cancer (CRPC)-like LNCaP-SF cells. Moreover, NONO was frequently amplified and overexpressed in patients with CRPC. RNA sequencing data revealed that a truncated ephrin type-A receptor 6 (EPHA6) splice variant (EPHA6-001) was overexpressed in LNCaP-SF cells, and knockdown of NONO or EPHA6-001 prevented EPHA6-001 expression and reduced proliferation and invasion by LNCaP-SF cells grown under androgen deprivation conditions. Growth inhibition and differential splicing of EPHA6 mRNA by p54^nrb/NONO were confirmed in gene silencing experiments in 22Rv1 PCa cells. Importantly, NONO knockdown in LNCaP-SF cells led to reduced tumor growth in castrated mice. These findings indicate that p54^nrb/NONO is amplified and overexpressed in CRPC cells and clinical samples, and facilitates CRPC growth by mediating aberrant EPHA6 splicing. We therefore propose that p54^nrb/NONO constitutes a novel and attractive therapeutic target for CRPC.

Molecular Pathogenesis and Diagnostic Imaging of Metastatic Jaw Tumors

Metastasis is the spread of malignant cells from a primary tumor to distant sites through lymphatics or blood vessels. Malignant lesions metastasizing to the oral and perioral region are a rarity indeed. Malignant lesions could metastasize to both soft tissue of oral cavity and the hard tissues of the jaws and recent meta-analysis showed that metastasis is more common in the jaws than oral soft tissues because of rich vascular supply. The incidence is very low when compared to the incidence of primary oral cancers; nevertheless, one has to include in the diagnostic workup, metastatic malignant lesions, when an irregular ill-defined radiolucency or radiodensity with ragged edges in noted. It could be a challenging task for a diagnostician, in cases with the presence and location of the primary tumor is unknown. Advanced oral imaging technologies and biochemical markers play a vital role in diagnosing such lesions.

Overcoming immunosuppression in bone metastases

Bone metastases are present in up to 70% of advanced prostate and breast cancers and occur at significant rates in a variety of other cancers. Bone metastases can be associated with significant morbidity. The establishment of bone metastasis activates several immunosuppressive mechanisms. Hence, understanding the tumor-bone microenvironment is crucial to inform the development of novel therapies. This review describes the current standard of care for patients with bone metastatic disease and novel treatment options targeting the microenvironment. Treatments reviewed include immunotherapies, cryoablation, and targeted therapies. Combinatorial treatment strategies including targeted therapies and immunotherapies show promise in pre-clinical and clinical studies to overcome the suppressive environment and improve treatment of bone metastases.

Sortase A-aided Escherichia coli expression system for functional osteoprotegerin cysteine-rich domain

As a natural inhibitor of the receptor activator of nuclear factor-кB ligand (RANKL), osteprotegerin (OPG) is considered a promising treatment for metabolic bone diseases. Typical approaches for preparing recombinant OPG or its derivatives employ eukaryotic expression systems. Due to the advantages of a prokaryotic expression system, which include its convenience, low cost, and abundant production, in this study, we establish a strategy for preparing functional OPG using the Escherichia coli expression system. After initial failures in preparation of OPG and its truncation, OPG cysteine-rich domain (OPG-CRD/OPGT) by using pET and pGEX vectors, we constructed a sortase A (SrtA)-aided E. coli expression system, in which the expressed protein was a self-cleaving SrtA fusion protein. Using this system, we successfully prepared the recombinant OPGT protein. The BIAcore analyses indicated that the prepared OPGT had high affinities in binding with RANKL and TRAIL. Cell experiments confirmed the inhibitory effects of the prepared OPGT on RANKL-induced osteoclast differentiation and TRAIL-induced tumor cell apoptosis. The sortase A-aided E. coli expression system for OPGT established in this study may contribute to further studies and commercial applications of OPG.

Osteoprotegerin regulates cancer cell migration through SDF-1/CXCR4 axis and promotes tumour development by increasing neovascularization

We previously reported that OPG is involved in ischemic tissue neovascularization through the secretion of SDF-1 by pretreated-OPG endothelial colony-forming cells (ECFCs). As the vascularization is one of the key factor influencing the tumour growth and cancer cell dissemination, we investigated whether OPG was able to modulate the invasion of human MNNG-HOS osteosarcoma and DU145 prostate cancer cell lines in vitro and in vivo. Cell motility was analysed in vitro by using Boyden chambers. Human GFP-labelled MMNG-HOS cells were inoculated in immunodeficient mice and the tumour nodules formed were then injected with OPG and/or FGF-2, AMD3100 or 0.9% NaCl (control group). Tumour growth was manually followed and angiogenesis was assessed by immunohistochemistry. In vitro, SDF-1 released by OPG-pretreated ECFCs markedly attracted both MNNG-HOS and DU145 cells and induced spontaneous migration of cancer cells. In vivo, tumour volumes were significantly increased in OPG-treated group compared to the control group and OPG potentiated the effect of FGF-2. Concomitantly, OPG alone or combined with FGF-2 increased the number of new vasculature compared to the control group. Interestingly AMD3100, an inhibitor of SDF-1, prevented the in vivo effects of OPG induced by SDF-1 This study provides experimental evidence that OPG promotes tumour development trough SDF-1/CXCR4 axis.

Galectin-3 in bone tumor microenvironment: a beacon for individual skeletal metastasis management

The skeleton is frequently a secondary growth site of disseminated cancers, often leading to painful and devastating clinical outcomes. Metastatic cancer distorts bone marrow homeostasis through tumor-derived factors, which shapes different bone tumor microenvironments depending on the tumor cells' origin. Here, we propose a novel insight on tumor-secreted Galectin-3 (Gal-3) that controls the induction of an inflammatory cascade, differentiation of osteoblasts, osteoclasts, and bone marrow cells, resulting in bone destruction and therapeutic failure. In the approaching era of personalized medicine, the current treatment modalities targeting bone metastatic environments are provided to the patient with limited consideration of the cancer cells' origin. Our new outlook suggests delivering individual tumor microenvironment treatments based on the expression level/activity/functionality of tumor-derived factors, rather than utilizing a commonly shared therapeutic umbrella. The notion of "Gal-3-associated bone remodeling" could be the first step toward a specific personalized therapy for each cancer type generating a different bone niche in patients afflicted with non-curable bone metastasis.

Repression of MicroRNA-372 by Arsenic Sulphide Inhibits Prostate Cancer Cell Proliferation and Migration through Regulation of large tumour suppressor kinase 2

As the main component of realgar, arsenic sulphide (As₄ S₄ ) contains antitumour activity by repressing cancer cell proliferation and migration in many tumours. However, the detailed mechanism of these processes is not clear yet. MicroRNAs (miRNAs) can function as tumour suppressor or oncogene based on their target mRNAs in different tumour tissues. Here, we found that As₄ S₄ could repress the overexpression of microRNA-372 (miR-372) in two prostate cancer cell lines and its overexpression promoted cell proliferation and migration. Large tumour suppressor kinase 2 (LATS2) was confirmed as a direct target of miR-372 using luciferase assays in these two prostate cancer cell lines. Down-regulation of LATS2 could promote prostate cancer cell proliferation and migration just as overexpression of miR-372 did and overexpression of LATS2 could reverse this effect of miR-372. The antitumour activity of As₄ S₄ and the oncogenic function of miR-372 were further confirmed using a mouse xenograft model. Altogether, our data showed evidence that repressing the overexpression of miR-372 by As₄ S₄ could inhibit prostate cancer cell proliferation and migration by targeting LATS2. Therefore, miR-372 may be a possible biomarker for the prediction of prostate cancer and As₄ S₄ may have potential therapeutic function for prostate cancer.

microRNA-372 Suppresses Migration and Invasion by Targeting p65 in Human Prostate Cancer Cells

Prostate cancer (PCa) is one of the most prevalent malignant tumors. microRNAs (miRNAs) play an important role in cancer initiation, progression, and metastasis, and their roles in PCa are becoming more apparent. In this study, we found that microRNA-372 (miR-372) is downregulated in human PCa and inhibits the proliferation activity, migration, and invasion of DU145 cells. Subsequently, p65 is confirmed as a target of miR-372, and knockdown of p65 expression similarly resulted in decreased proliferation activity, migration, and invasion. CDK8, MMP-9, and prostate-specific antigen were involved in both these processes. Taken together, our results show evidence that miR-372 may function as a tumor suppressor gene by regulating p65 in PCa and may provide a strategy for blocking PCa metastasis.

Osteoprotegerin: A novel biomarker for inflammatory bowel disease and gastrointestinal carcinoma

Osteoprotegerin (OPG) is a member of the tumor necrosis factor receptor superfamily of proteins. Although initial data illustrated the key role that OPG plays in bone turnover, numerous recent reports indicate that OPG is also an important factor in inflammatory pathways and tumor cell survival. OPG contributes directly to inflammatory processes and has been evaluated as a novel non-invasive biomarker of gut inflammation. Furthermore, OPG affects cell turn-over, differentiation, death, and survival via extracellular pathways, correlating with worse prognosis in inflammatory bowel diseases and several gastrointestinal carcinomas. It is now clear that OPG has multiple functions and characteristics. This review gives an overview of OPG, highlights its roles in different extracellular pathways, and outlines how OPG could be used as a novel non-invasive biological marker in inflammatory bowel diseases and gastrointestinal carcinomas.

Bone metastasis: the importance of the neighbourhood

During the past decade preclinical studies have defined many of the mechanisms used by tumours to hijack the skeleton and promote bone metastasis. This has led to the development and widespread clinical use of bone-targeted drugs to prevent skeletal-related events. This understanding has also identified a critical dependency between colonizing tumour cells and the cells of bone. This is particularly important when tumour cells first arrive in bone, adapt to their new microenvironment and enter a long-lived dormant state. In this Review, we discuss the role of different bone cell types in supporting disseminated tumour cell dormancy and reactivation, and highlight the new opportunities this provides for targeting the bone microenvironment to control dormancy and bone metastasis.

11C-choline PET/CT identifies osteoblastic and osteolytic lesions in patients with metastatic prostate cancer

AIM

The aim of this study was to compare C-choline PET/CT, prostate-specific antigen (PSA), PSA kinetics, and C-choline uptake in recurrent metastatic prostate cancer patients with osteoblastic and osteolytic bone metastases.

PATIENTS AND METHODS

We retrospectively analyzed 140 patients with the following criteria: (a) positive bone lesions identified with C-choline PET/CT and validated as true positive by histology (14.2%), correlative imaging (33.4%), or clinical follow-up (52.4%); (b) after radical prostatectomy (67.9%) or primary radiotherapy (22.1%); (c) proven biochemical relapse with rising PSA levels; (d) no chemotherapy, zoledronic acid, or palliative bone external beam radiation therapy previously administrated during biochemical relapse; and (f) asymptomatic for bone pain. Lesions were categorized as osteoblastic, osteolytic, or bone marrow lesions. Patients were divided into osteoblastic and osteolytic patient groups.

RESULTS

C-Choline PET/CT detected oligometastatic bone disease (1-3 lesions) in 98 (70%) of the 140 patients and multiple bone lesions in 42 (30%) of the 140 patients. By per-lesion analysis of 304 lesions, there were 184 osteoblastic, 99 osteolytic, and 21 bone marrow lesions.By per-patient analysis, 97 (69.3%) of the 140 patients were in the osteoblastic group, whereas 43 (30.7%) of the 140 patients were in the osteolytic group. Statistically significant differences in SUVmax (P < 0.001), fast PSA doubling time (P = 0.01), and PSA velocity (P = 0.01) were observed between osteoblastic (lower values) and osteolytic (higher values) groups. By multivariate analysis, fast PSA doubling time was a significant predictor for osteolytic lesions.

CONCLUSIONS

We demonstrated differences in PSA kinetics and SUVmax between osteolytic and osteoblastic lesions. C-Choline PET/CT may identify patients that could benefit from early targeted therapies, depending on the type of bone lesions expressed.

Variants of Osteoprotegerin Lacking TRAIL Binding for Therapeutic Bone Remodeling in Osteolytic Malignancies

Osteolytic bone damage is a major cause of morbidity in several metastatic pathologies. Current therapies using bisphosphonates provide modest improvement, but cytotoxic side effects still occur prompting the need to develop more effective therapies to target aggressive osteoclastogenesis. Increased levels of receptor activator of NF-κB ligand (TNFSF11/RANKL), leading to RANKL-RANK signaling, remain the key axis for osteoclast activation and bone resorption. Osteoprotegerin (TNFRSF11B/OPG), a decoy receptor for RANKL, is significantly decreased in patients who present with bone lesions. Despite its potential in inhibiting osteoclast activation, OPG also binds to TNF-related apoptosis-inducing ligand (TNFSF10/TRAIL), making tumor cells resistant to apoptosis. Toward uncoupling the events of TRAIL binding of OPG and to improve its utility for bone remodeling without inducing tumor resistance to apoptosis, OPG mutants were developed by structural homology modeling based on interactive domain identification and by superimposing models of OPG, TRAIL, and its receptor DR5 (TNFRSF10B) to identify regions of OPG for rational design. The OPG mutants were purified and extensively characterized for their ability to decrease osteoclast damage without affecting tumor apoptosis pathway both in vitro and in vivo, confirming their potential in bone remodeling following cancer-induced osteolytic damage.

IMPLICATIONS

OPG variants were developed that lack TRAIL binding, yet retain RANKL binding and suggest new possibilities for therapeutic targeting in osteolytic malignancies.

Pharmacologic inhibition of bone resorption prevents cancer-induced osteolysis but enhances soft tissue metastasis in a mouse model of osteolytic breast cancer

Osteoprotegerin (OPG) is a secreted member of the TNF receptor superfamily, which binds to the receptor activator of nuclear factor κB ligand (RANKL) and inhibits osteoclast activity and bone resorption. Systemic administration of recombinant OPG was previously shown to inhibit tumor growth in bone and to prevent cancer-induced osteolysis. In this study, we examined the effect of OPG, when produced locally by breast cancer cells located within bone, using a mouse model of osteolytic breast cancer. MDA-MB-231-TXSA breast cancer cells, tagged with a luciferase reporter gene construct and engineered to overexpress full-length human OPG, were transplanted directly into the tibial marrow cavity of nude mice. Overexpression of OPG by breast cancer cells protected the bone from breast cancer-induced osteolysis and diminished intra-osseous tumor growth but had no effect on extra-skeletal tumor growth. This effect was associated with a significant reduction in the number of osteoclasts that lined the bone surface, resulting in a net increase in bone volume. Despite limiting breast cancer-mediated bone loss, OPG overexpression resulted in a significant increase in the incidence of pulmonary metastasis. Our results demonstrate that inhibition of osteoclastic bone resorption by OPG when secreted locally by tumors in bone may affect the behaviour of cancer cells within the bone microenvironment and their likelihood of spreading and establishing metastasis elsewhere in the body.

Key roles of the OPG–RANK–RANKL system in bone oncology

Osteoprotegerin (OPG)-receptor activator of nuclear factor-kappaB (RANK) and RANK ligand (RANKL) have been identified as members of a ligand-receptor system that directly regulates osteoclast differentiation and osteolysis. RANKL may be a powerful inducer of bone resorption through its interaction with RANK, and OPG is a soluble decoy receptor that acts as a strong inhibitor of osteoclastic differentiation. Any dysregulation of their respective expression leads to pathological conditions. Furthermore, recent data demonstrate that the OPG-RANK-RANKL system modulates cancer cell migration, thus controlling the development of bone metastases. This review describes the most recent knowledge on the OPG-RANK-RANKL system, its involvement in bone oncology and the new therapeutic approaches based on this molecular triad.

Molecular signaling pathways mediating osteoclastogenesis induced by prostate cancer cells

Background

Advanced prostate cancer commonly metastasizes to bone leading to osteoblastic and osteolytic lesions. Although an osteolytic component governed by activation of bone resorbing osteoclasts is prominent in prostate cancer metastasis, the molecular mechanisms of prostate cancer-induced osteoclastogenesis are not well-understood.

Methods

We studied the effect of soluble mediators released from human prostate carcinoma cells on osteoclast formation from mouse bone marrow and RAW 264.7 monocytes.

Results

Soluble factors released from human prostate carcinoma cells significantly increased viability of naïve bone marrow monocytes, as well as osteoclastogenesis from precursors primed with receptor activator of nuclear factor κ-B ligand (RANKL). The prostate cancer-induced osteoclastogenesis was not mediated by RANKL as it was not inhibited by osteoprotegerin (OPG). However inhibition of TGFβ receptor I (TβRI), or macrophage-colony stimulating factor (MCSF) resulted in attenuation of prostate cancer-induced osteoclastogenesis. We characterized the signaling pathways induced in osteoclast precursors by soluble mediators released from human prostate carcinoma cells. Prostate cancer factors increased basal calcium levels and calcium fluctuations, induced nuclear localization of nuclear factor of activated t-cells (NFAT)c1, and activated prolonged phosphorylation of ERK1/2 in RANKL-primed osteoclast precursors. Inhibition of calcium signaling, NFATc1 activation, and ERK1/2 phosphorylation significantly reduced the ability of prostate cancer mediators to stimulate osteoclastogenesis.

Conclusions

This study reveals the molecular mechanisms underlying the direct osteoclastogenic effect of prostate cancer derived factors, which may be beneficial in developing novel osteoclast-targeting therapeutic approaches.

Osteoprotegerin (OPG) activates integrin, focal adhesion kinase (FAK), and Akt signaling in ovarian cancer cells to attenuate TRAIL-induced apoptosis

BACKGROUND

Resistance to apoptosis is a major problem in ovarian cancer (OC) and correlates with poor prognosis. Osteoprotegerin (OPG) is a soluble secreted factor that acts as a decoy receptor for receptor activator of NF-κB ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). OPG has been reported to attenuate TRAIL-induced apoptosis in a variety of cancer cells, including OC cells. OPG-mediated protection against TRAIL has been attributed to its decoy receptor function. However, OPG activates integrin/focal adhesion kinase (FAK) signaling in endothelial cells. In OC cells, activation of integrin/FAK signaling inhibits TRAIL-induced apoptosis. Based on these observations, we hypothesized that OPG could attenuate TRAIL-induced apoptosis in OC cells through integrin/FAK signaling.

METHODS

In vitro experiments including immunoblots, colony formation assays, and apoptosis measurements were used to assess the effect of OPG on TRAIL-induced apoptosis.

RESULTS

Exogenous OPG protected from TRAIL-induced apoptosis in a TRAIL binding-independent manner and OPG protection was αvβ3 and αvβ5 integrin/FAK signaling-dependent. Moreover, OPG-mediated activation of integrin/FAK signaling resulted in the activation of Akt. Inhibition of both integrin/FAK and Akt signaling significantly inhibited OPG-mediated attenuation of TRAIL-induced apoptosis. Although OPG also stimulated ERK1/2 phosphorylation, inhibition of ERK1/2 signaling did not significantly altered OPG protection.

CONCLUSIONS

Our studies provide evidence, for the first time, that OPG can attenuate TRAIL-induced apoptosis in a TRAIL binding-independent manner through the activation of integrin/FAK/Akt signaling in OC cells.

Identification of five serum protein markers for detection of ovarian cancer by antibody arrays

BACKGROUND

Protein and antibody arrays have emerged as a promising technology to study protein expression and protein function in a high-throughput manner. These arrays also represent a new opportunity to profile protein expression levels in cancer patients' samples and to identify useful biosignatures for clinical diagnosis, disease classification, prediction, drug development and patient care. We applied antibody arrays to discover a panel of proteins which may serve as biomarkers to distinguish between patients with ovarian cancer and normal controls.

METHODOLOGY/PRINCIPAL FINDINGS

Using a case-control study design of 34 ovarian cancer patients and 53 age-matched healthy controls, we profiled the expression levels of 174 proteins using antibody array technology and determined the CA125 level using ELISA. The expression levels of those proteins were analyzed using 3 discriminant methods, including artificial neural network, classification tree and split-point score analysis. A panel of 5 serum protein markers (MSP-alpha, TIMP-4, PDGF-R alpha, and OPG and CA125) was identified, which could effectively detect ovarian cancer with high specificity (95%) and high sensitivity (100%), with AUC =0.98, while CA125 alone had an AUC of 0.87.

CONCLUSIONS/SIGNIFICANCE

Our pilot study has shown the promising set of 5 serum markers for ovarian cancer detection.

Induction of retinol-binding protein 4 and placenta-specific 8 expression in human prostate cancer cells remaining in bone following osteolytic tumor growth inhibition by osteoprotegerin

New drugs that inhibit the osteoprotegerin (OPG)/receptor activator of NF-κB ligand (RANKL)/RANK pathway have demonstrated efficacy for the treatment of bone metastasis. Toxicities induced by these drugs, however, including osteonecrosis of the jaw and hypocalcemia, may adversely affect therapy. The aim of this study was to identify additional therapeutic targets that can be combined with OPG/RANKL/RANK pathway inhibition in the treatment of prostate cancer bone metastasis. We established a stable transfectant that produces high levels of OPG mRNA and protein from PC-3 human prostate cancer cells (PC3-OPG). The culture medium of PC3-OPG cells significantly inhibited the differentiation of mouse monocytes into mature osteoclasts. Furthermore, when PC3-OPG cells were injected into the bones of nude mice, bone destruction and tumor-induced osteoclast formation were reduced. Injection into bone of the mixtures containing equal amounts of green fluorescent protein (GFP)-expressing PC-3 cells (PC3-GFP) and PC3-OPG cells also reduced bone destruction, compared to the control mixture. PC3-GFP cells were subsequently isolated from bone tumors and used for microarray analysis to assess changes in gene expression following osteolytic tumor growth inhibition by OPG. We selected the top 10 upregulated genes based on results from microarrays and confirmed mRNA expression of each gene by RT-PCR. The expression patterns of retinol-binding protein 4 (RBP4) and placenta-specific 8 (PLAC8) were consistent with microarray results. Expression of these genes was also increased in the bone tumors of PC3-GFP/PC3-OPG-injected mice. Knockdown of both RBP4 and PLAC8 by siRNA inhibited the growth of PC-3 cells in vitro. Thus, RBP4 and PLAC8 may become new therapeutic targets for prostate cancer bone metastasis, in combination with OPG/RANKL/RANK pathway inhibition.

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.

Osteoprotegerin (OPG) protects ovarian cancer cells from TRAIL-induced apoptosis but does not contribute to malignant ascites-mediated attenuation of TRAIL-induced apoptosis

BACKGROUND

Resistance to apoptosis is a major problem in ovarian cancer and correlates with poor prognosis. Osteoprotegerin (OPG) is a secreted factor in malignant ascites and acts as a decoy receptor for receptor activator of NF-κB ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). TRAIL promotes apoptosis in ovarian cancer cells. Ovarian cancer ascites attenuate TRAIL-induced apoptosis raising the possibility that OPG contained in ascites may abrogate the anti-tumor activity of TRAIL.

METHODS

Determination of OPG levels in ascites was measured by ELISA. Effect of OPG on TRAIL-induced cell death was determined by XTT and colony forming assays in ovarian cancer cell lines and primary tumor cells. Apoptosis was assessed by ELISA.

RESULTS

We found that recombinant OPG and malignant ascites attenuates TRAIL-induced cell death and apoptosis in a dose-dependent manner in ovarian cancer cell lines and primary ovarian tumor cells. OPG is present at high levels in the ascites of patients with ovarian cancer. We found a positive correlation between the levels of OPG in ascites and the ability of the ascites to attenuate TRAIL-induced cell death. The anti-apoptotic effect of ascites was not reversed by co-incubation with an OPG blocking antibody.

CONCLUSIONS

OPG and malignant ascites protect ovarian cancer cells from TRAIL-induced apoptosis. Although malignant ascites contain high levels of OPG, OPG is not a critical component that contributes to ascites-mediated attenuation of TRAIL-induced apoptosis.

Osteoprotegerin in bone metastases: mathematical solution to the puzzle

Bone is a common site for cancer metastasis. To create space for their growth, cancer cells stimulate bone resorbing osteoclasts. Cytokine RANKL is a key osteoclast activator, while osteoprotegerin (OPG) is a RANKL decoy receptor and an inhibitor of osteoclastogenesis. Consistently, systemic application of OPG decreases metastatic tumor burden in bone. However, OPG produced locally by cancer cells was shown to enhance osteolysis and tumor growth. We propose that OPG produced by cancer cells causes a local reduction in RANKL levels, inducing a steeper RANKL gradient away from the tumor and towards the bone tissue, resulting in faster resorption and tumor expansion. We tested this hypothesis using a mathematical model of nonlinear partial differential equations describing the spatial dynamics of OPG, RANKL, PTHrP, osteoclasts, tumor and bone mass. We demonstrate that at lower expression rates, tumor-derived OPG enhances the chemotactic RANKL gradient and osteolysis, whereas at higher expression rates OPG broadly inhibits RANKL and decreases osteolysis and tumor burden. Moreover, tumor expression of a soluble mediator inducing RANKL in the host tissue, such as PTHrP, is important for correct orientation of the RANKL gradient. A meta-analysis of OPG, RANKL and PTHrP expression in normal prostate, carcinoma and metastatic tissues demonstrated an increase in expression of OPG, but not RANKL, in metastatic prostate cancer, and positive correlation between OPG and PTHrP in metastatic prostate cancer. The proposed mechanism highlights the importance of the spatial distribution of receptors, decoys and ligands, and can be applied to other systems involving regulation of spatially anisotropic processes.

Breast and prostate cancers commonly metastasize to bone. To create more space for their expansion, metastatic tumors activate osteoclasts, the only cells capable of bone destruction. The main osteoclast stimulator is the cytokine RANKL, while osteoprotegerin (OPG) acts as a RANKL inhibitor. Systemic application of OPG leads to a decrease in tumor-associated bone destruction, but surprisingly, OPG produced locally by metastasizing cancer cells can enhance bone destruction and tumor growth. Here, we provide a novel explanation for these apparently contradictory experimental results: the osteolysis-promoting effect of OPG is due to a local reduction in RANKL levels, resulting in a spatial RANKL gradient oriented from tumor towards bone tissue. At low rates of OPG expression by cancer cells, such gradients result in the correct orientation of osteoclast movement and intensified bone resorption. We positively test our hypothesis by means of a partial differential equations model, and further substantiate our results with a meta-analysis of gene expression. Even though developed for the specific problem of bone metastases, our model naturally applies to other systems operating within a geometrically anisotropic environment.

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

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

Dysregulation of developmental pathways in bone metastasis

It is well-known that pathways normally functioning during embryonic development are dysregulated in cancer. Experimental and clinical studies have established strong connections between aberrant developmental pathways and transformation, as well as other early stage events of cancer progression. There is now emerging evidence that also indicates the contribution of developmental pathways to the pathogenesis of distant metastasis, including bone metastasis. In particular, the Wnt, BMP, and Hedgehog signaling pathways have all been implicated in the development of bone metastasis. These developmental pathways participate in the regulation of cell-autonomous functions in tumor cells as well as tumor-stromal interactions in the bone microenvironment, eventually promoting the formation of osteolytic or osteoblastic bone metastasis.

Effect of artemisinin derivatives on apoptosis and cell cycle in prostate cancer cells

Artemisinin is a plant-derived anti-malarial drug that has relatively low toxicity in humans and is activated by heme and/or intracellular iron leading to intracellular free radical formation. Interestingly, artemisinin has displayed anti-cancer activity, with artemisinin dimers being more potent than monomeric artemisinin. Intracellular iron uptake is regulated by the transferrin receptor (TfR), and the activity of artemisinin depends on the availability of iron. We examined the level of TfR in prostate cancer (PCa) tumor cells, synthesized two new artemisinin dimers, and evaluated the effect of dihydroartemisinin and artemisinin dimers, ON-2Py and 2Py, on proliferation and apoptosis in PCa cells. TfR was expressed in the majority of PCa bone and soft tissue metastases, all 24 LuCaP PCa xenografts, and PCa cell lines. After treatment with dihydroartemisinin, ON-2Py, or 2Py all PCa cell lines displayed dose-dependent decrease in cell number. 2Py was most effective in decreasing cell number. An increase in apoptotic events and growth arrest was observed in the C4-2 and LNCaP cell lines. Growth arrest was observed in PC-3 cells, but no significant change was observed in DU 145 cells. Treatment with 2Py resulted in a loss of the anti-apoptotic protein survivin in all four cell lines. 2Py treatment also decreased androgen receptor and prostate-specific antigen expression in C4-2 and LNCaP cells, with a concomitant loss of cell cycle regulatory proteins cyclin D1 and c-Myc. This study shows the potential use of artemisinin derivatives as therapeutic candidates for PCa and warrants the initiation of preclinical studies.

Clinical significance of tumor necrosis factor receptor superfamily member 11b polymorphism in prostate cancer

BACKGROUND

Bone metastases are the most critical complication of prostate cancer (PCa), resulting in severe morbidity and mortality. Tumor necrosis factor receptor superfamily member 11b (TNFRSF11B) is a critical regulator between PCa cells and the bone environment. Recently, TNFRSF11B rs10505346 has been implicated in PCa risk in the Cancer Genetic Markers of Susceptibility genomewide association study. However, the association between this variant and biochemical failure in PCa patients receiving radical prostatectomy (RP) has not been determined.

METHODS

Associations of TNFRSF11B rs10505346 with age at diagnosis, preoperative prostate-specific antigen (PSA) level, Gleason score, pathologic stage, surgical margin, and PSA recurrence were evaluated in a cohort of 314 localized PCa patients receiving RP. The prognostic significance on PSA recurrence was assessed by Kaplan-Meier analysis and Cox regression model.

RESULTS

The mean level of preoperative PSA and the relative risks of PSA recurrence after RP were lower in individuals with T allele than in those with the G allele at TNFRSF11B rs10505346 (P = 0.019 and 0.014, respectively). The T allele of rs10505346 remained a protective factor against PSA recurrence (P = 0.022) in multivariate Cox regression model after considering all clinicopathological risk factors except PSA level.

CONCLUSIONS

Our data suggest that TNFRSF11B rs10505346 is associated with PSA level and might be a prognostic factor for the recurrence of PSA in PCa patients receiving RP.

The expression of osteoclastogenesis-associated factors and osteoblast response to osteolytic prostate cancer cells

BACKGROUND

Prostate cancer (PCa) has a propensity to metastasize to bone. Tumor cells replace bone marrow and can elicit an osteoblastic, osteolytic, or mixed bone response. Our objective was to elucidate the mechanisms and key factors involved in promoting osteoclastogenesis in PCa bone metastasis.

METHODS

We cultured osteoblast-like MC3T3-E1 cells with conditioned medium (CM) from PC-3 and C4-2B cells. MC3T3-E1 mineralization decreased in the presence of PC-3 CM, whereas C4-2B CM had no effect on mineralization. Using oligo arrays and validating by real-time PCR, we observed a decrease in the expression of mineralization-associated genes in MC3T3-E1 cells grown in the presence of PC-3 CM. In addition, PC-3 CM induced the expression of osteoclastogenesis-associated genes IGFBP-5, IL-6, MCP-1, and RANKL while decreasing OPG expression in MC3T3-E1 cells. Furthermore, CM from MC3T3-E1 cells cultured in the presence of PC-3 CM, in association with soluble RANKL, increased osteoclastogenesis in RAW 264.7 cells. Investigation of PCa metastases and xenografts by immunohistochemistry revealed that the osteoclastic factor IL-6 was expressed in the majority of PCa bone metastases and to a lesser extent in PCa soft tissue metastases. In vitro it was determined that soluble IL-6R (sIL-6R) was necessary for IL-6 to inhibit mineralization in MC3T3-E1 cells.

RESULTS

PC-3 cells inhibit osteoblast activity and induce osteoblasts to produce osteoclastic factors that promote osteoclastogenesis, and one of these factors, IL-6, is highly expressed in PCa bone metastases.

CONCLUSIONS

IL-6 may have an important role in promoting osteoclastogenesis in PCa bone metastasis through its' interaction with sIL-6R.

DNA methylation and histone modification regulate silencing of OPG during tumor progression

The identification of molecules that are down-regulated in malignant phenotype is important for understanding tumor biology and their role in tumor suppression. We compared the expression profile of four normal nasal mucosal (NNM) epithelia and a series of nasopharyngeal cancinoma (NPC) cell lines using cDNA microarray and confirmed the actual expression of the selected genes, and found osteoprotegerin (OPG) to be ubiquitously deficient in NPC cells. We also found OPG to be down-regulated in various cancer cell lines, including oral, cervical, ovarian, lung, breast, pancreas, colon, renal, prostate cancer, and hepatoma. Administration of recombinant OPG (rOPG) brought about a reduction in cancer cell growth through apoptotic mechanism. We generated eleven monoclonal antibodies (MAbs) against OPG to study OPG's expression and biological functions in cancer cells. OPG was detected in the tumor stromal regions, but not in the cancer cell per se in surgical specimens of liver cancer. Quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR) revealed that OPG was down-regulated in NPC tissues compared with normal nasal polyp (NNP) tissues. In addition, we showed OPG silencing to be associated with promoter methylation as well as histone modifications. In OPG-silenced cancer cell lines, the OPG gene promoter CpG dinucleotides were highly methylated. Compared to normal cells, silenced OPG gene in cancer cells were found to have reduced histone 3 lysine 4 tri-methylation (H3K4me3) and increased histone 3 lysine 27 tri-methylation (H3K27me3). Taken together, these results suggest that OPG silencing in carcinoma cancer cells occurs through epigenetic repression.

Dasatinib inhibits both osteoclast activation and prostate cancer PC-3-cell-induced osteoclast formation

PURPOSE

Therapies to target prostate cancer bone metastases have only limited effects. New treatments are focused on the interaction between cancer cells, bone marrow cells and the bone matrix. Osteoclasts play an important role in the development of bone tumors caused by prostate cancer. Since Src kinase has been shown to be necessary for osteoclast function, we hypothesized that dasatinib, a Src family kinase inhibitor, would reduce osteoclast activity and prostate cancer (PC-3) cell-induced osteoclast formation.

RESULTS

Dasatinib inhibited RANKL-induced osteoclast differentiation of bone marrow-derived monocytes with an EC(50) of 7.5 nM. PC-3 cells, a human prostate cancer cell line, were able to differentiate RAW 264.7 cells, a murine monocytic cell line, into osteoclasts, and dasatinib inhibited this differentiation. In addition, conditioned medium from PC-3 cell cultures was able to differentiate RAW 264.7 cells into osteoclasts and this too, was inhibited by dasatinib. Even the lowest concentration of dasatinib, 1.25 nmol, inhibited osteoclast differentiation by 29%. Moreover, dasatinib inhibited osteoclast activity by 58% as measured by collagen 1 release.

EXPERIMENTAL DESIGN

We performed in vitro experiments utilizing the Src family kinase inhibitor dasatinib to target osteoclast activation as a means of inhibiting prostate cancer bone metastases.

CONCLUSION

Dasatinib inhibits osteoclast differentiation of mouse primary bone marrow-derived monocytes and PC-3 cell-induced osteoclast differentiation. Dasatinib also inhibits osteoclast degradation activity. Inhibiting osteoclast differentiation and activity may be an effective targeted therapy in patients with prostate cancer bone metastases.

Therapeutic implications of osteoprotegerin

Osteoprotegerin (OPG), a member of the tumor necrosis factor (TNF) receptor superfamily, contributes determinatively to the bone remodeling as well as to the pathogenetic mechanism of bone malignancies and disorders of mineral metabolism. There is additional evidence that OPG can promote cell survival by inhibiting TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. A number of recent in vitro, in vivo and clinical studies have defined the role of the RANK/RANKL/OPG pathway in skeletal and vascular diseases. These works were the milestone of the deep understanding of the mechanism of OPG. This review provides an overview of the potential innovative therapeutic strategies of OPG in metastatic breast and prostate carcinoma, multiple myeloma, postmenopausal osteoporosis, glucocorticoid-induced osteoporosis and rheumatoid arthritis. Special reference is given to the increasing evidence that RANKL and OPG may link the skeletal with the vascular system.

RANK, RANKL and osteoprotegerin in bone biology and disease

Upon the discovery of RANK, RANKL and OPG in the late 1990s, their importance in the maintenance of the skeletal structure and their dramatic role in bone disease were largely unexpected. In recent years the understanding of these proteins, in particular their regulation, has greatly increased. This review aims to bring the interested reader up to date with the latest news and views on the mechanisms controlling bone resorption in normal and pathological conditions.

Glycosaminoglycans as potential regulators of osteoprotegerin therapeutic activity in osteosarcoma

Osteosarcoma is the most frequent primary bone malignant tumor that develops mainly in children and adolescents. Despite recent improvements in chemotherapy and surgery, survival rate is approximately 50% after 5 years. Osteoprotegerin (OPG) is a potent inhibitor of osteoclast differentiation and activation, but its use as therapeutic agent in cancer-associated osteolysis remains controversial due to its ability to bind and inhibit the apoptotic effect of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on tumor cells. The therapeutic effects of full-length OPG (1-401) and OPG 1-194 lacking its heparin-binding domain delivered by nonviral gene therapy were compared in a murine model of osteolytic osteosarcoma. Tumor incidence, progression, and associated bone lesions were significantly diminished in the OPG 1-194 group, but not in the OPG 1-401 group, compared with controls. As receptor activator of nuclear factor-kappaB ligand (RANKL), TRAIL, and glycosaminoglycans (GAG) were shown to be overexpressed in osteosarcoma environment compared with control tissue, OPG 1-401 bioactivity may be modulated by one of these protagonists. Surface plasmon resonance analyses performed with OPG, TRAIL, and GAGs revealed that TRAIL binds both forms of OPG with the same affinity. In addition, as OPG 1-194 and OPG 1-401 similarly inhibit TRAIL-induced apoptosis, it suggests that TRAIL is not involved in the modulation of OPG bioactivity. However, as GAGs inhibit OPG 1-401 but not OPG 1-194 binding to TRAIL or to RANKL, they may represent potent regulators of OPG availability and antitumor activity in bone tumor microenvironment.

Mechanism of bone metastasis: the role of osteoprotegerin and of the host-tissue microenvironment-related survival factors

Osteoprotegerin (OPG), member of tumor necrosis factor (TNF) receptor superfamily, has various biological functions including bone remodeling. OPG binds to receptor activator of nuclear factor-kB ligand (RANKL) and prevents osteoclastic bone resorption. Recently, OPG has gained more clinical interest as its role in cancer-mediated bone destruction and the potential of RANKL inhibition could act as a novel treatment in tumor-induced bone disease. OPG protects prostate cancer cells from apoptotic effects of TRAIL and therefore provides tumor cells producing OPG with survival advantages. Additionally, the increased RANKL/OPG ratio in metastatic breast cancer results in severe osteolysis. Thus, bone formation and resorption are the crux of cancer metastasis, resulting in bone pain and pathological fractures. This review provides an overview of the role of OPG in cancer-induced bone disease.

Osteoclasts are active in bone forming metastases of prostate cancer patients

Background

Bone forming metastases are a common and disabling consequence of prostate cancer (CaP). The potential role of osteoclast activity in CaP bone metastases is not completely explained. In this study, we investigated ex vivo whether the osteolytic activity is present and how it is ruled in CaP patients with bone forming metastases.

Methodology

Forty-six patients affected by newly diagnosed CaP and healthy controls were enrolled. At diagnosis, 37 patients had a primary tumour only, while 9 had primary tumour and concomitant bone forming metastases. In all patients there was no evidence of metastasis to other non-bone sites. For all patients and controls we collected blood and urinary samples. We evaluated patients' bone homeostasis; we made peripheral blood mononuclear cell (PBMC) cultures to detect in vitro osteoclastogenesis; we dosed serum expression of molecules involved in cancer induced osteoclatogenesis, such as RANKL, OPG, TNF-alpha, DKK-1 and IL-7. By Real-Time PCR, we quantified DKK-1 and IL-7 gene expression on micro-dissected tumour and healthy tissue sections.

Principal Findings

CaP bone metastatic patients showed bone metabolism disruption with increased bone resorption and formation compared to non-bone metastatic patients and healthy controls. The CaP PBMC cultures showed an enhanced osteoclastogenesis in bone metastatic patients, due to an increase of RANKL/OPG ratio. We detected increased DKK-1 serum levels and tissue gene expression in patients compared to controls. IL-7 resulted high in patients' sera, but its tissue gene expression was comparable in patients and controls.

Conclusions

We demonstrated ex vivo that osteoclastogenesis is an active mechanism in tumour nesting of bone forming metastatic cancer and that serum DKK-1 levels are increased in CaP patients, suggesting to deeply investigate its role as tumour marker.