Direct crosstalk between cancer and osteoblast lineage cells fuels metastatic growth in bone via auto-amplification of IL-6 and RANKL signaling pathways

Intersecting Paths: Unraveling the Complex Journey of Cancer to Bone Metastasis

The phenomenon of bone metastases presents a significant challenge within the context of advanced cancer treatments, particularly pertaining to breast, prostate, and lung cancers. These metastatic occurrences stem from the dissemination of cancerous cells into the bone, thereby interrupting the equilibrium between osteoblasts and osteoclasts. Such disruption results in skeletal complications, adversely affecting patient morbidity and quality of life. This review discusses the intricate interplay between cancer cells and the bone microenvironment, positing the bone not merely as a passive recipient of metastatic cells but as an active contributor to cancer progression through its distinctive biochemical and cellular makeup. A thorough examination of bone structure and the dynamics of bone remodeling is undertaken, elucidating how metastatic cancer cells exploit these processes. This review explores the genetic and molecular pathways that underpin the onset and development of bone metastases. Particular emphasis is placed on the roles of cytokines and growth factors in facilitating osteoclastogenesis and influencing osteoblast activity. Additionally, this paper offers a meticulous critique of current diagnostic methodologies, ranging from conventional radiography to advanced molecular imaging techniques, and discusses the implications of a nuanced understanding of bone metastasis biology for therapeutic intervention. This includes the development of targeted therapies and strategies for managing bone pain and other skeletal-related events. Moreover, this review underscores the imperative of ongoing research efforts aimed at identifying novel therapeutic targets and refining management approaches for bone metastases. It advocates for a multidisciplinary strategy that integrates advancements in medical oncology and radiology with insights derived from molecular biology and genetics, to enhance prognostic outcomes and the quality of life for patients afflicted by this debilitating condition. In summary, bone metastases constitute a complex issue that demands a comprehensive and informed approach to treatment. This article contributes to the ongoing discourse by consolidating existing knowledge and identifying avenues for future investigation, with the overarching objective of ameliorating patient care in the domain of oncology.

Circulating biomarkers for diagnosis and therapeutic monitoring in bone metastasis

Bone is a frequent site of metastasis for multiple types of solid tumors in organs such as prostate, breast, lung, etc., accounting for significant morbidities and mortalities of afflicted patients. One of the major problems of bone metastasis is lack of biomarkers for early diagnosis and for monitoring therapeutic responses. Medical imaging modalities such as computerized tomography, magnetic resonance imaging, and radioactive isotope-based bone scans are currently standard clinical practices, yet these imaging techniques are limited to detect early lesions or to accurately monitor the metastatic disease progression during standard and/or experimental therapies. Accordingly, development of novel blood biomarkers rationalizes extensive basic research and clinical development. This review article covers the up-to-date information on protein- and cell-based biomarkers of bone metastasis that are currently used in the clinical practices and also are under development.

Systemic effects of abnormal bone resorption on muscle, metabolism, and cognition

Skeletal tissue is dynamic, undergoing constant remodeling to maintain musculoskeletal integrity and balance in the human body. Recent evidence shows that apart from maintaining homeostasis in the local microenvironment, the skeleton systemically affects other tissues. Several cancer-associated and noncancer-associated bone disorders can disrupt the physiological homeostasis locally in the bone microenvironment and indirectly contribute to dysregulation of systemic body function. The systemic effects of bone on the regulation of distant organ function have not been widely explored. Recent evidence suggests that bone can interact with skeletal muscle, pancreas, and brain by releasing factors from mineralized bone matrix. Currently available bone-targeting therapies such as bisphosphonates and denosumab inhibit bone resorption, decrease morbidity associated with bone destruction, and improve survival. Bisphosphonates have been a standard treatment for bone metastases, osteoporosis, and cancer treatment-induced bone diseases. The extraskeletal effects of bisphosphonates on inhibition of tumor growth are known. However, our knowledge of the effects of bisphosphonates on muscle weakness, hyperglycemia, and cognitive defects is currently evolving. To be able to identify the molecular link between bone and distant organs during abnormal bone resorption and then treat these abnormalities and prevent their systemic effects could improve survival benefits. The current review highlights the link between bone resorption and its systemic effects on muscle, pancreas, and brain.

The role of vitamin D and vitamin D deficiency in orthopaedics and traumatology-a narrative overview of the literature

Vitamin D is considered to play an important role in musculoskeletal health. It’s classical function is the regulation of calcium and phosphate homeostasis, thus ensuring a balanced bone metabolism that is characterised by an equal amount of bone resorption and bone formation. In the past decades, a plethora of pre-clinical and clinical studies reporting on potential health-beneficial properties of vitamin D have emerged. Moreover, there is an abundance of reports highlighting vitamin D deficiency and insufficiency in patients with almost innumerable diseases. Further, it is estimated that more than one billion people globally are affected by insufficient vitamin D levels. As such, research on vitamin D has been particularly popular over the past years. In orthopaedics and traumatology, most studies describe favourable effects of vitamin D in general. However, the relative importance of vitamin D is oftentimes debated. In this narrative review of the literature, we consider first, the properties of vitamin D and how vitamin D, vitamin D deficiency and the vitamin D receptor (VDR) impact on musculoskeletal health. Secondly, we provide an overview of studies reporting the prevalence of vitamin D deficiency in traumatology and diverse orthopaedic diseases including bone oncology. Lastly, we emphasise recent findings and touch on future perspectives in vitamin D research.

The Role of Inflammation in Breast and Prostate Cancer Metastasis to Bone

Tumor metastasis to bone is a common event in multiple forms of malignancy. Inflammation holds essential functions in homeostasis as a defense mechanism against infections and is a strategy to repair injured tissue and to adapt to stress conditions. However, exaggerated and/or persistent (chronic) inflammation may eventually become maladaptive and evoke diseases such as autoimmunity, diabetes, inflammatory tissue damage, fibrosis, and cancer. In fact, inflammation is now considered a hallmark of malignancy with prognostic relevance. Emerging studies have revealed a central involvement of inflammation in several steps of the metastatic cascade of bone-homing tumor cells through supporting their survival, migration, invasion, and growth. The mechanisms by which inflammation favors these steps involve activation of epithelial-to-mesenchymal transition (EMT), chemokine-mediated homing of tumor cells, local activation of osteoclastogenesis, and a positive feedback amplification of the protumorigenic inflammation loop between tumor and resident cells. In this review, we summarize established and evolving concepts of inflammation-driven tumorigenesis, with a special focus on bone metastasis.

EphA2 Is a Clinically Relevant Target for Breast Cancer Bone Metastatic Disease

EphA2 receptor tyrosine kinase (RTK) is highly expressed in breast tumor cells across multiple molecular subtypes and correlates with poor patient prognosis. In this study, the potential role of EphA2 in this clinically relevant phenomenon is investigated as metastasis of breast cancer to bone is a major cause of morbidity and mortality in patients. It was found that the EphA2 function in breast cancer cells promotes osteoclast activation and the development of osteolytic bone disease. Blocking EphA2 function molecularly and pharmacologically in breast tumors reduced the number and size of bone lesions and the degree of osteolytic disease in intratibial and intracardiac mouse models, which correlated with a significant decrease in the number of osteoclasts at the tumor-bone interface. EphA2 loss of function in tumor cells impaired osteoclast progenitor differentiation in coculture, which is mediated, at least in part, by reduced expression of IL-6. EPHA2 transcript levels are enriched in human breast cancer bone metastatic lesions relative to visceral metastatic sites; EphA2 protein expression was detected in breast tumor cells in bone metastases in patient samples, supporting the clinical relevance of the study's findings. These data provide a strong rationale for the development and application of molecularly targeted therapies against EphA2 for the treatment of breast cancer bone metastatic disease. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Interleukins as Mediators of the Tumor Cell-Bone Cell Crosstalk during the Initiation of Breast Cancer Bone Metastasis

Patients with advanced breast cancer are at high risk of developing bone metastasis. Despite treatment advances for primary breast cancer, metastatic bone disease remains incurable with a low relative survival. Hence, new therapeutic approaches are required to improve survival and treatment outcome for these patients. Bone is among the most frequent sites of metastasis in breast cancer. Once in the bone, disseminated tumor cells can acquire a dormant state and remain quiescent until they resume growth, resulting in overt metastasis. At this stage the disease is characterized by excessive, osteoclast-mediated osteolysis. Cells of the bone microenvironment including osteoclasts, osteoblasts and endothelial cells contribute to the initiation and progression of breast cancer bone metastasis. Direct cell-to-cell contact as well as soluble factors regulate the crosstalk between disseminated breast cancer cells and bone cells. In this complex signaling network interleukins (ILs) have been identified as key regulators since both, cancer cells and bone cells secrete ILs and express corresponding receptors. ILs regulate differentiation and function of bone cells, with several ILs being reported to act pro-osteoclastogenic. Consistently, the expression level of ILs (e.g., in serum) has been associated with poor prognosis in breast cancer. In this review we discuss the role of the most extensively investigated ILs during the establishment of breast cancer bone metastasis and highlight their potential as therapeutic targets in preventing metastatic outgrowth in bone.

Analysis of the Gene Expression Profile of Stromal Pro-Tumor Factors in Cancer-Associated Fibroblasts from Luminal Breast Carcinomas

Luminal tumors are the most frequent type of breast carcinomas showing less tumor aggressiveness, although heterogeneity exists in their clinical outcomes. Cancer-associated fibroblasts (CAFs) are a key component of the tumor stroma which contribute to tumor progression. We investigated by real-time PCR the gene expression of 19 factors implicated in tumor progression. Those factors included the calcium-binding protein S100A4, several growth factors (FGF2, FGF7, HGF, PDGFA, PDGFB, TGFβ, VEGFA, and IGF2), and we also studied inflammatory cytokines (IL6 and IL8), chemokines (CCL2, CXCL12), important proteases (uPA, MMP2, MMP9 and MMP11), the nuclear factor NFκB, and the metalloprotease inhibitor TIMP1, from luminal A and luminal B breast carcinoma CAFs. We performed a similar analysis after co-culturing CAFs with MCF-7 and MDA-MB-231 breast cancer cell lines. MMP-9 and CCL2 gene expressions were higher in CAFs from luminal B tumors. We also found different patterns in the induction of pro-tumoral factors from different CAFs populations co-cultured with different cancer cell lines. Globally, CAFs from luminal B tumors showed a higher expression of pro-tumor factors compared to CAFs from luminal A tumors when co-cultured with breast cancer cell lines. Moreover, we found that CAFs from metastatic tumors had higher IGF-2 gene expression, and we detected the same after co-culture with cell lines. Our results show the variability in the capacities of CAFs from luminal breast carcinomas, which may contribute to a better biological and clinical characterization of these cancer subtypes.

To D or not to D: vitamin D in hematopoietic cell transplantation

Vitamin D plays an essential role in bone health, immune tolerance, and immune modulation. Autologous and allogeneic hematopoietic cell transplantation (HCT) recipients are at increased risk of vitamin D deficiency, which may increase risks of bone loss and fracture, graft-versus-host disease (GVHD), and relapse, and can delay hematologic and immune recovery following HCT. Growing evidence indicates that vitamin D may have a role as an immunomodulator, and supplementation during HCT may decrease the risk of GVHD, infection, relapse, and mortality. In this paper, we review the role of vitamin D and its association with HCT outcomes and discuss prevention and treatment of vitamin D deficiency after HCT in adult recipients. We review the role of monitoring of vitamin D levels pre- and post-HCT and its supplementation in appropriate patients. We also review the use of bone densitometry prior to HCT and in long-term follow-up and the treatment of osteoporosis in this high-risk population.

RANK/RANKL Acts as a Protective Factor by Targeting Cholangiocytes in Primary Biliary Cholangitis

BACKGROUND

Primary biliary cholangitis (PBC) is an autoimmune liver disease characterized by the highly selective autoimmune injury of small intrahepatic bile ducts. Studies reported that the cholangiocytes from PBC patients expressed significantly higher levels of both receptor activator of nuclear factor-kappa B (RANK) and its ligand RANKL. However, the accurate role of RANK/RANKL axis in PBC remains unclear.

METHODS

Forty patients with PBC were enrolled according to the inclusion criteria. The biochemical parameters (alkaline phosphatase, ALP; gamma-glutamyltransferase, GGT; alanine aminotransferase, ALT; aspartate transaminase, AST; total bilirubin, TB) were collected at baseline and followed-up after 6 months of treatment with ursodeoxycholic acid (UDCA, 15 mg/kg d). Stages of PBC were diagnosed based on liver biopsy histopathology according to Nakanuma's criteria. RANK expression in hepatic tissues was detected by immunohistochemistry. The cellular immunofluorescence method was used to locate the distribution of RANK in the human intrahepatic biliary epithelial cells (HIBECs) cultured in vitro. HIBECs were treated with RANKL at a concentration of 100 ng/ml or transfected with RANK-overexpressing lentivirus (LV-RANK). CCK-8 assay and cell cycle assay were used to detect the cell proliferation. Real-time PCR was used to detect the expression of IL-6, E-cadherin, VCAM, ICAM-1, TNF-α, and CD80.

RESULTS

RANK expression in liver biopsies from early PBC patients (stage I + stage II) was significantly lower than that from advanced PBC patients (stage III + stage IV) (1.7 ± 0.63 vs. 2.3 ± 0.45 scores, P < 0.05). High-RANK patients seemed to have better response to UDCA than low-RANK patients (88.9% vs. 40.9%, P < 0.05). The baseline biochemical parameters between the two groups were comparable. The decline percentages of ALP and GGT after UDCA treatment were more obvious in high-RANK patients than those in low-RANK patients (53.90% ± 9.82% vs. 23.93% ± 6.24%, P < 0.05; 74.11% ± 7.18% vs. 48.00% ± 8.17%, P < 0.05, respectively). HIBECs proliferation was significantly inhibited after treatment of RANKL or transfection with LV-RANK. Increased expression of IL-6 and E-cadherin was observed in HIBECs treated with RANKL or LV-RANK.

CONCLUSION

The overall hepatic RANK expression was associated with disease severity and biochemical response in PBC patients. Activation of RANK/RANKL signaling pathway inhibited cholangiocytes proliferation in vitro. Our study suggested that RANK/RANKL pathway might be a potential target of immunotherapy of PBC based on its involvement in the occurrence and development of the disease.

GP130 Cytokines in Breast Cancer and Bone

Breast cancer cells have a high predilection for skeletal homing, where they may either induce osteolytic bone destruction or enter a latency period in which they remain quiescent. Breast cancer cells produce and encounter autocrine and paracrine cytokine signals in the bone microenvironment, which can influence their behavior in multiple ways. For example, these signals can promote the survival and dormancy of bone-disseminated cancer cells or stimulate proliferation. The interleukin-6 (IL-6) cytokine family, defined by its use of the glycoprotein 130 (gp130) co-receptor, includes interleukin-11 (IL-11), leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), and cardiotrophin-1 (CT-1), among others. These cytokines are known to have overlapping pleiotropic functions in different cell types and are important for cross-talk between bone-resident cells. IL-6 cytokines have also been implicated in the progression and metastasis of breast, prostate, lung, and cervical cancer, highlighting the importance of these cytokines in the tumor–bone microenvironment. This review will describe the role of these cytokines in skeletal remodeling and cancer progression both within and outside of the bone microenvironment.

What Is the Role of Interleukins in Breast Cancer Bone Metastases? A Systematic Review of Preclinical and Clinical Evidence

Breast cancer cells produce stimulators of bone resorption known as interleukins (ILs). However, data on the functional roles of ILs in the homing of metastatic breast cancer to bone are still fragmented. A systematic search was carried out in three databases (PubMed, Scopus, Web of Science Core Collection) to identify preclinical reports, and in three clinical registers (ClinicalTrials.gov, World Health Organization (WHO) International Clinical Trials Registry Platform, European Union (EU) Clinical Trials Register) to identify clinical trials, from 2008 to 2019. Sixty-seven preclinical studies and 11 clinical trials were recognized as eligible. Although preclinical studies identified specific key ILs which promote breast cancer bone metastases, which have pro-metastatic effects (e.g., IL-6, IL-8, IL-1β, IL-11), and whose inhibition also shows potential preclinical therapeutic effects, the clinical trials focused principally on ILs (IL-2 and IL-12), which have an anti-metastatic effect and a potential to generate a localized and systemic antitumor response. However, these clinical trials are yet to post any results or conclusions. This inconsistency indicates that further studies are necessary to further develop the understanding of cellular and molecular relations, as well as signaling pathways, both up- and downstream of ILs, which could represent a novel strategy to treat tumors that are resistant to standard care therapies for patients affected by breast cancer bone disease.

Tumor Hypoxia As an Enhancer of Inflammation-Mediated Metastasis: Emerging Therapeutic Strategies

Metastasis is the leading cause of cancer-related deaths. Recent research has implicated tumor inflammation as a promoter of metastasis. Myeloid, lymphoid, and mesenchymal cells in the tumor microenvironment promote inflammatory signaling amongst each other and together with cancer cells to modulate sustained inflammation, which may enhance cancer invasiveness. Tumor hypoxia, a state of reduced available oxygen present in the majority of solid tumors, acts as a prognostic factor for a worse outcome and is known to have a role in tumor inflammation through the regulation of inflammatory mediator signals in both cancer and neighboring cells in the microenvironment. Multiple methods to target tumor hypoxia have been developed and tested in clinical trials, and still more are emerging as the impacts of hypoxia become better understood. These strategies include mechanistic inhibition of the hypoxia inducible factor signaling pathway and hypoxia activated pro-drugs, leading to both anti-tumor and anti-inflammatory effects. This prompts a need for further research on the prevention of hypoxia-mediated inflammation in cancer. Hypoxia-targeting strategies seem to have the most potential for therapeutic benefit when combined with traditional chemotherapy agents. This paper will serve to summarize the role of the inflammatory response in metastasis, to discuss how hypoxia can enable or enhance inflammatory signaling, and to review established and emerging strategies to target the hypoxia-inflammation-metastasis axis.

2D and 3D In Vitro Co-Culture for Cancer and Bone Cell Interaction Studies

Co-culture assays are used to study the mutual interaction between cells in vitro. This chapter describes 2D and 3D co-culture systems used to study cell-cell signaling crosstalk between cancer cells and bone marrow adipocytes, osteoblasts, osteoclasts, and osteocytes. The chapter provides a step-by-step guide to the most commonly used cell culture techniques, functional assays, and gene expression.

Upregulation of interleukin-8 and activin A induces osteoclastogenesis in ameloblastoma

Ameloblastoma is a common odontogenic benign tumor located in the jaws and is characterized by severe local bone destruction. The current study aimed to investigate the effect of interactions between tumor cells and bone marrow stromal cells (BMSCs) on osteoclast formation in ameloblastoma. The impact of ameloblastoma/BMSC interactions on cytokine production, gene expression and osteoclastogenesis was examined using an immortalized ameloblastoma cell line that the authors' previously established. The results demonstrated that interactions between ameloblastoma cells and BMSCs increased interleukin (IL)‑8 and activin A secretion by BMSCs. IL‑8 expression in BMSCs was modulated by tumor‑derived tumor necrosis factor‑α and IL‑8 contributed to osteoclast formation not only directly but also by stimulating receptor activator of NF‑κB ligand (RANKL) expression in BMSCs. Activin A secretion in BMSCs was stimulated by ameloblastoma cells via cell‑to‑cell‑mediated activation of c‑Jun N‑terminal kinase activation, acting as a cofactor of RANKL to induce osteoclast formation and function. The present study highlights the critical role of communication between BMSCs and ameloblastoma cells in bone resorption in ameloblastoma.

Bone as a Preferential Site for Metastasis

Bone marrow provides a unique microenvironment favoring the colonization and outgrowth of metastatic tumor cells. Despite the high incidence of bone metastasis in breast and prostate cancer patients, many of the molecular mechanisms controlling metastatic progression remain unclear. Several gene signatures associated with bone metastasis have been reported, but no metastasis-specific gene alterations have been identified. Therefore, there has been considerable interest in understanding how the bone microenvironment impacts the behavior of disseminated tumor cells (DTCs) prior to and following colonization of the bone. Substantial evidence indicates that disruption of normal bone homeostasis by tumor-derived factors establishes a premetastatic niche within the bone that favors DTC colonization. Following dissemination, bone resident cells and the surrounding stroma provide critical signals that support tumor cell colonization, survival, and eventual outgrowth. Clinical data suggest that patients can harbor DTCs for years to decades prior to developing overt bone metastases, suggesting a period of tumor dormancy occurs in the bone marrow. Several dormancy-promoting factors have been recently identified; however, critical questions surrounding the molecular triggers and timing of tumor cell emergence from dormancy remain. Here, we review how metastatic tumor cells co-opt the bone marrow microenvironment for metastatic progression and discuss emerging insights into how to more effectively target DTCs and prevent metastasis. © 2018 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

The vitamin D receptor is involved in the regulation of human breast cancer cell growth via a ligand-independent function in cytoplasm

Vitamin D has pleiotropic effects on multiple tissues, including malignant tumors. Vitamin D inhibits breast cancer growth through activation of the vitamin D receptor (VDR) and via classical nuclear signaling pathways. Here, we demonstrate that the VDR can also function in the absence of its ligand to control behaviour of human breast cancer cells both outside and within the bone microenvironment. Stable shRNA expression was used to knock down VDR expression in MCF-7 cells, generating two VDR knockdown clonal lines. In ligand-free culture, knockdown of VDR in MCF-7 cells significantly reduced proliferation and increased apoptosis, suggesting that the VDR plays a ligand-independent role in cancer cell growth. Implantation of these VDR knockdown cells into the mammary fat pad of nude mice resulted in reduced tumor growth in vivo compared with controls. In the intra-tibial xenograft model, VDR knockdown greatly reduced the ability of the cells to form tumors in the bone microenvironment. The in vitro growth of VDR knockdown cells was rescued by the expression of a mutant form of VDR which is unable to translocate to the nucleus and hence accumulates in the cytoplasm. Thus, our data indicate that in the absence of ligand, the VDR promotes breast cancer growth both in vitro and in vivo and that cytoplasmic accumulation of VDR is sufficient to produce this effect in vitro. This new mechanism of VDR action in breast cancer cells contrasts the known anti-proliferative nuclear actions of the VDR-vitamin D ligand complex.

Chikungunya Virus-Induced Arthritis: Role of Host and Viral Factors in the Pathogenesis

Chikungunya virus (CHIKV), a member of Alphavirus genus, is responsible for chikungunya fever (CHIKF), which is characterized by the presence of fever, rash, myalgia, and arthralgia. Reemergence of CHIKV has become a significant public health concern in Asian and African countries and is newly emerging in the Middle East, Pacific, American, and European countries. Cytokines, innate (monocytes, natural killer cells) and adaptive immune response (role of B cells and T cells i.e. CD4⁺ and CD8⁺), and/or viral factors contribute to CHIKV-induced arthritis. Vector factors such as vector competence (that includes extrinsic and intrinsic factors) and effect of genome mutations on viral replication and fitness in mosquitoes are responsible for the spread of virus, although they are not directly responsible for CHIKV-induced arthritis. CHIKV-induced arthritis mimics arthritis by involving joints and a common pattern of leukocyte infiltrate, cytokine production, and complement activation. Successful establishment of CHIKV infection and induction of arthritis depends on its ability to manipulate host cellular processes or host factors. CHIKV-induced joint damage is due to host inflammatory response mediated by macrophages, T cells, and antibodies, as well as the possible persistence of the virus in hidden sites. This review provides insight into mechanisms of CHIKV-induced arthritis. Understanding the pathogenesis of CHIKV-induced arthritis will help in developing novel strategies to predict and prevent the disease in virus-infected subjects and combat the disease, thereby decreasing the worldwide burden of the disease.

Loss of the vitamin D receptor in human breast and prostate cancers strongly induces cell apoptosis through downregulation of Wnt/β-catenin signaling

Vitamin D co-regulates cell proliferation, differentiation and apoptosis in numerous tissues, including cancers. The known anti-proliferative and pro-apoptotic actions of the active metabolite of vitamin D, 1,25-dihydroxy-vitamin D [1,25(OH)₂D] are mediated through binding to the vitamin D receptor (VDR). Here, we report on the unexpected finding that stable knockdown of VDR expression in the human breast and prostate cancer cell lines, MDA-MB-231 and PC3, strongly induces cell apoptosis and inhibits cell proliferation in vitro. Implantation of these VDR knockdown cells into the mammary fat pad (MDA-MB-231), subcutaneously (PC3) or intra-tibially (both cell lines) in immune-incompetent nude mice resulted in reduced tumor growth associated with increased apoptosis and reduced cell proliferation compared with controls. These growth-retarding effects of VDR knockdown occur in the presence and absence of vitamin D and are independent of whether cells were grown in bone or soft tissues. Transcriptome analysis of VDR knockdown and non-target control cell lines demonstrated that loss of the VDR was associated with significant attenuation in the Wnt/β-catenin signaling pathway. In particular, cytoplasmic and nuclear β-catenin protein levels were reduced with a corresponding downregulation of downstream genes such as Axin2, Cyclin D1, interleukin-6 (IL-6), and IL-8. Stabilization of β-catenin using the GSK-3β inhibitor BIO partly reversed the growth-retarding effects of VDR knockdown. Our results indicate that the unliganded VDR possesses hitherto unknown functions to promote breast and prostate cancer growth, which appear to be operational not only within but also outside the bone environment. These novel functions contrast with the known anti-proliferative nuclear actions of the liganded VDR and may represent targets for new diagnostic and therapeutic approaches in breast and prostate cancer.

Poor prognosis of patients with triple-negative breast cancer can be stratified by RANK and RANKL dual expression

PURPOSE

As clinical studies have correlated RANK expression levels with survival in breast cancer, and that RANK signaling is dependent on its cognate ligand RANKL, we hypothesized that dual protein expression further stratifies the poor outcome in TNBC.

METHODS

RANK mRNA and protein expression was evaluated in TNBC using genomic databases, cell lines and in a tissue microarray of curated primary tumor samples derived from 87 patients with TNBC. RANK expression was evaluated either by Mann-Whitney U test on log-normalized gene expression data or by Student's t test on FACS data. Analysis of RANK and RANKL immunostaining was calculated by H-score, and correlations to clinical factors performed using χ ² or Fisher's exact test. Associations with RFS and OS were assessed using univariate and multivariate Cox proportional hazard models. Survival estimates were generated using the Kaplan-Meier method.

RESULTS

In three distinct datasets spanning 684 samples, RANK mRNA expression was higher in primary tumors derived from TNBC patients than from those with other molecular subtypes (P < 0.01). Cell surface-localized RANK protein was consistently higher in TNBC cell lines (P = 0.037). In clinical samples, TNBC patients that expressed both RANK and RANKL proteins had significantly worse RFS (P = 0.0032) and OS (P = 0.004) than patients with RANK-positive, RANKL-negative tumors. RANKL was an independent, poor prognostic factor for RFS (P = 0.04) and OS (P = 0.01) in multivariate analysis in samples that expressed both RANK and RANKL.

CONCLUSIONS

RANK and RANKL co-expression is associated with poor RFS and OS in patients with TNBC.

In Vitro Co-Culture Models of Breast Cancer Metastatic Progression towards Bone

Advanced breast cancer frequently metastasizes to bone through a multistep process involving the detachment of cells from the primary tumor, their intravasation into the bloodstream, adhesion to the endothelium and extravasation into the bone, culminating with the establishment of a vicious cycle causing extensive bone lysis. In recent years, the crosstalk between tumor cells and secondary organs microenvironment is gaining much attention, being indicated as a crucial aspect in all metastatic steps. To investigate the complex interrelation between the tumor and the microenvironment, both in vitro and in vivo models have been exploited. In vitro models have some advantages over in vivo, mainly the possibility to thoroughly dissect in controlled conditions and with only human cells the cellular and molecular mechanisms underlying the metastatic progression. In this article we will review the main results deriving from in vitro co-culture models, describing mechanisms activated in the crosstalk between breast cancer and bone cells which drive the different metastatic steps.

PTHrP attenuates osteoblast cell death and apoptosis induced by a novel class of anti-cancer agents

The effectiveness of chemotherapeutic agents often limits their use due to their negative effects on normal cells. Apoptosis regulatory protein (CARP)-1 functional mimetics (CFMs) belong to a novel class of compounds that possess anti-cancer properties with potential utility in breast and other cancers. In this study, we investigated the growth inhibitory action of CFM-4 and -5 in bone-forming osteoblasts and role of a skeletal regulator, parathyroid hormone (PTH)-related peptide (PTHrP), which is frequently associated with oncologic pathologies. MC3T3E1-clone4 (MC-4) or primary osteoblasts were treated with CFMs. Western blots were performed to determine specific protein expressions. MTT, TUNEL assay, ethidium bromide/acridine orange staining, and ApoAlert caspase profiling were used to investigate cell viability and apoptosis of osteoblasts. Immunofluorescence staining was performed to observe intracellular localization of CARP-1. Our studies revealed that CFM-4 and -5 suppressed growths of mature differentiated, but not proliferating, MC-4 cells and PTHrP attenuated this effect. Mechanistically, induction of CARP-1 protein by CFM-4 and -5 was partially decreased by PTHrP. While CARP-1 increased by CFM-4 or -5 correlated with activated caspase-3, PTHrP remarkably blocked caspase-3 activation. PTHrP also influenced translocation of CFM-induced CARP-1 from the nucleus to the cytoplasm. Our data identify a new function of PTHrP in maintaining osteoblast homeostasis in chemotherapy and define a role of CARP-1 in this process. The crosstalk of PTHrP and CFM-4 and -5 signaling highlights the importance of CFMs as potential anti-cancer therapeutics in breast and other cancers which adversely affect bone.

Olive oil in the prevention and treatment of osteoporosis after artificial menopause

Purpose

The goal of this study was to investigate the anti-osteoporosis effect of extra virgin olive oil (EVOO) in vivo, and explore its antioxidant, anti-inflammatory properties in Sprague Dawley rats and its anticancer properties in patients.

Materials and methods

A total of 120 healthy female Sprague Dawley rats aged 6 months were divided into four groups: 1) sham-operated control (Sham group, n=30); 2) ovariectomized (OVX group, n=30); 3) ovariectomized rats supplemented with EVOO (OVX + Olive, n=30); 4) ovariectomized rats supplemented with estrogen (OVX + E₂, n=30). EVOO and estrogen were administered by oral gavage at a dose of 1 mL/100 g weight on a daily basis for 12 consecutive weeks. Twelve weeks later blood samples were obtained to detect the levels of calcium, alkaline phosphatase, phosphorus, interleukin-6 (IL-6), malonyldialdehyde (MDA), and nitrate content. Dual energy X-ray absorptiometer measured bone mineral density (BMD) of ovariectomized Sprague Dawley rats that had been fed olive oil for 3 months. Blood samples from patients, who regularly consumed olive oil over a 1 year period were also used to measure carbohydrate antigen 125, carcino-embryonic antigen, α-fetoprotein, and carbohydrate antigen 19-9 levels. BMD of lumbar spine and left femur was also evaluated by dual energy X-ray absorptiometry.

Results

Animal experiments showed that EVOO significantly increased BMD and decreased phosphatase, alkaline phosphatase, IL-6, MDA, and nitrate levels. However, it had no significant effect on the Ca²⁺ level. In clinical follow-up, EVOO also improved patient BMD levels on L3, L4, and left femoral neck, and reduced carbohydrate antigen 125, α-fetoprotein, and carcino-embryonic antigen levels. But it had no significant effect on the carbohydrate antigen 19-9 level.

Conclusion

EVOO illustrated significant anti-osteoporosis, antioxidant, anti-inflammatory, and anticancer properties in vivo. However, further studies are required to determine the active component(s) responsible for these effects.

Tumor-expressed adrenomedullin accelerates breast cancer bone metastasis

Introduction

Adrenomedullin (AM) is secreted by breast cancer cells and increased by hypoxia. It is a multifunctional peptide that stimulates angiogenesis and proliferation. The peptide is also a potent paracrine stimulator of osteoblasts and bone formation, suggesting a role in skeletal metastases—a major site of treatment-refractory tumor growth in patients with advanced disease.

Methods

The role of adrenomedullin in bone metastases was tested by stable overexpression in MDA-MB-231 breast cancer cells, which cause osteolytic bone metastases in a standard animal model. Cells with fivefold increased expression of AM were characterized in vitro, inoculated into immunodeficient mice and compared for their ability to form bone metastases versus control subclones. Bone destruction was monitored by X-ray, and tumor burden and osteoclast numbers were determined by quantitative histomorphometry. The effects of AM overexpression on tumor growth and angiogenesis in the mammary fat pad were determined. The effects of AM peptide on osteoclast-like multinucleated cell formation were tested in vitro. A small-molecule AM antagonist was tested for its effects on AM-stimulated ex vivo bone cell cultures and co-cultures with tumor cells, where responses of tumor and bone were distinguished by species-specific real-time PCR.

Results

Overexpression of AM mRNA did not alter cell proliferation in vitro, expression of tumor-secreted factors or cell cycle progression. AM-overexpressing cells caused osteolytic bone metastases to develop more rapidly, which was accompanied by decreased survival. In the mammary fat pad, tumors grew more rapidly with unchanged blood vessel formation. Tumor growth in the bone was also more rapid, and osteoclasts were increased. AM peptide potently stimulated bone cultures ex vivo; responses that were blocked by small-molecule adrenomedullin antagonists in the absence of cellular toxicity. Antagonist treatment dramatically suppressed tumor growth in bone and decreased markers of osteoclast activity.

Conclusions

The results identify AM as a target for therapeutic intervention against bone metastases. Adrenomedullin potentiates osteolytic responses in bone to metastatic breast cancer cells. Small-molecule antagonists can effectively block bone-mediated responses to tumor-secreted adrenomedullin, and such agents warrant development for testing in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0458-y) contains supplementary material, which is available to authorized users.

Arthritogenic alphaviruses: new insights into arthritis and bone pathology

Arthritogenic alphaviral infection begins as a febrile illness and often progresses to joint pain and rheumatic symptoms that are described as polyarthritis. Alphaviral arthritis and classical arthritides share many similar cellular and immune mediators involved in their pathogenesis. Recent in vitro and in vivo evidence suggests that bone loss resulting from increased expression of bone resorption mediators may accompany alphaviral infection. In addition, several longitudinal studies have reported more severe and delayed recovery of alphaviral disease in patients with pre-existing arthritic conditions. This review aims to provide insights into alphavirus-induced bone loss and focuses on aspects of disease exacerbation in patients with underlying arthritis and on possible therapeutic targets.