Contributions of the host microenvironment to cancer-induced bone disease

Total flavonoids of Litchi chinensis Sonn. seed inhibit prostate cancer growth in bone by regulating the bone microenvironment via inactivation of the HGFR/NF-κB signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Litchi chinensis Sonn. (Litchi) seed, a traditional Chinese medicine, is habitually used in the clinical treatment of prostate cancer (PCa)-induced bone pain. In our previous study, flavonoids have been identified as the active ingredient of litchi seed against PCa. However, its anti-tumor activities in bone and associated molecular mechanisms are still unclear.

AIM OF THE STUDY

To investigate the effects and underlying mechanisms of total flavonoids of litchi seed (TFLS) on the growth of PCa in bone.

MATERIALS AND METHODS

The effect of TFLS on the growth of PCa in bone was observed using a mouse model constructed with tibial injection of luciferase-expressing RM1-luc cells. Conditioned medium (CM) from bone marrow stromal cells OP9 and CM treated with TFLS (T-CM) was used to investigate the effect on the proliferation, colony formation, and apoptosis of PCa cells (LNCaP, PC3, RM1). An antibody microarray was performed to detect cytokine expression in the supernatant fraction of OP9 cell cultures treated with TFLS or left untreated. Western blot assay was employed to determine the expression and activity of HGFR and its key downstream proteins, Akt, mTOR, NF-κB, and Erk, in PCa cells. The potential target was further verified using immunofluorescence and immunohistochemistry assays.

RESULTS

Treatment with TFLS (80 mg/kg, 24 days) significantly suppressed the growth of RM1 cells in bone. CM from bone marrow stromal cells OP9 stimulated the proliferation and colony formation of the PCa cells as well as inhibited the apoptosis of PC3 cells, while T-CM reversed the effects mediated by OP9 cells in vitro. In an antibody array assay, TFLS regulated the majority of cytokines in OP9 cell culture supernatant, among which HGF, HGFR, IGF-1R, and PDGF-AA showed the greatest fold changes. Mechanistically, CM upregulated HGFR and promoted phosphorylation of NF-κB while T-CM induced reduction of HGFR and dephosphorylation of NF-κB in PC3 cells. Moreover, T-CM inhibited NF-κB entry into PC3 cell nuclei. Data from in vivo experiments further confirmed the inhibitory effects of TFLS on NF-κB.

CONCLUSION

TFLS suppresses the growth of PCa in bone through regulating bone microenvironment and the underlying mechanism potentially involves attenuation of the HGFR/NF-κB signaling axis.

SCUBE2 mediates bone metastasis of luminal breast cancer by modulating immune-suppressive osteoblastic niches

Estrogen receptor (ER)-positive luminal breast cancer is a subtype with generally lower risk of metastasis to most distant organs. However, bone recurrence occurs preferentially in luminal breast cancer. The mechanisms of this subtype-specific organotropism remain elusive. Here we show that an ER-regulated secretory protein SCUBE2 contributes to bone tropism of luminal breast cancer. Single-cell RNA sequencing analysis reveals osteoblastic enrichment by SCUBE2 in early bone-metastatic niches. SCUBE2 facilitates release of tumor membrane-anchored SHH to activate Hedgehog signaling in mesenchymal stem cells, thus promoting osteoblast differentiation. Osteoblasts deposit collagens to suppress NK cells via the inhibitory LAIR1 signaling and promote tumor colonization. SCUBE2 expression and secretion are associated with osteoblast differentiation and bone metastasis in human tumors. Targeting Hedgehog signaling with Sonidegib and targeting SCUBE2 with a neutralizing antibody both effectively suppress bone metastasis in multiple metastasis models. Overall, our findings provide a mechanistic explanation for bone preference in luminal breast cancer metastasis and new approaches for metastasis treatment.

Extracellular citrate and metabolic adaptations of cancer cells

It is well established that cancer cells acquire energy via the Warburg effect and oxidative phosphorylation. Citrate is considered to play a crucial role in cancer metabolism by virtue of its production in the reverse Krebs cycle from glutamine. Here, we review the evidence that extracellular citrate is one of the key metabolites of the metabolic pathways present in cancer cells. We review the different mechanisms by which pathways involved in keeping redox balance respond to the need of intracellular citrate synthesis under different extracellular metabolic conditions. In this context, we further discuss the hypothesis that extracellular citrate plays a role in switching between oxidative phosphorylation and the Warburg effect while citrate uptake enhances metastatic activities and therapy resistance. We also present the possibility that organs rich in citrate such as the liver, brain and bones might form a perfect niche for the secondary tumour growth and improve survival of colonising cancer cells. Consistently, metabolic support provided by cancer-associated and senescent cells is also discussed. Finally, we highlight evidence on the role of citrate on immune cells and its potential to modulate the biological functions of pro- and anti-tumour immune cells in the tumour microenvironment. Collectively, we review intriguing evidence supporting the potential role of extracellular citrate in the regulation of the overall cancer metabolism and metastatic activity.

Crucial contribution of GPR56/ADGRG1, expressed by breast cancer cells, to bone metastasis formation

From a mouse triple-negative breast cancer cell line, 4T1, we previously established 4T1.3 clone with a high capacity to metastasize to bone after its orthotopic injection into mammary fat pad of immunocompetent mice. Subsequent analysis demonstrated that the interaction between cancer cells and fibroblasts in a bone cavity was crucial for bone metastasis focus formation arising from orthotopic injection of 4T1.3 cells. Here, we demonstrated that a member of the adhesion G-protein-coupled receptor (ADGR) family, G-protein-coupled receptor 56 (GPR56)/adhesion G-protein-coupled receptor G1 (ADGRG1), was expressed selectively in 4T1.3 grown in a bone cavity but not under in vitro conditions. Moreover, fibroblasts present in bone metastasis sites expressed type III collagen, a ligand for GPR56/ADGRG1. Consistently, GPR56/ADGRG1 proteins were detected in tumor cells in bone metastasis foci of human breast cancer patients. Deletion of GPR56/ADGRG1 from 4T1.3 cells reduced markedly intraosseous tumor formation upon their intraosseous injection. Conversely, intraosseous injection of GPR56/ADGRG1-transduced 4T1, TS/A (mouse breast cancer cell line), or MDA-MB-231 (human breast cancer cell line) exhibited enhanced intraosseous tumor formation. Furthermore, we proved that the cleavage at the extracellular region was indispensable for GPR56/ADGRG1-induced increase in breast cancer cell growth upon its intraosseous injection. Finally, inducible suppression of Gpr56/Adgrg1 gene expression in 4T1.3 cells attenuated bone metastasis formation with few effects on primary tumor formation in the spontaneous breast cancer bone metastasis model. Altogether, GPR56/ADGRG1 can be a novel target molecule to develop a strategy to prevent and/or treat breast cancer metastasis to bone.

Inflammatory conversion of quiescent osteoblasts by metastatic breast cancer cells through pERK1/2 aggravates cancer-induced bone destruction

Disruption of bone homeostasis caused by metastatic osteolytic breast cancer cells increases inflammatory osteolysis and decreases bone formation, thereby predisposing patients to pathological fracture and cancer growth. Alteration of osteoblast function induces skeletal diseases due to the disruption of bone homeostasis. We observed increased activation of pERK1/2 in osteolytic breast cancer cells and osteoblasts in human pathological specimens with aggressive osteolytic breast cancer metastases. We confirmed that osteolytic breast cancers with high expression of pERK1/2 disrupt bone homeostasis via osteoblastic ERK1/2 activation at the bone-breast cancer interface. The process of inflammatory osteolysis modulates ERK1/2 activation in osteoblasts and breast cancer cells through dominant-negative MEK1 expression and constitutively active MEK1 expression to promote cancer growth within bone. Trametinib, an FDA-approved MEK inhibitor, not only reduced breast cancer-induced bone destruction but also dramatically reduced cancer growth in bone by inhibiting the inflammatory skeletal microenvironment. Taken together, these findings suggest that ERK1/2 activation in both breast cancer cells and osteoblasts is required for osteolytic breast cancer-induced inflammatory osteolysis and that ERK1/2 pathway inhibitors may represent a promising adjuvant therapy for patients with aggressive osteolytic breast cancers by altering the shared cancer and bone microenvironment.

Constitutive Hedgehog/GLI2 signaling drives extracutaneous basaloid squamous cell carcinoma development and bone remodeling

Uncontrolled activation of the Hedgehog (Hh) signaling pathway, operating through GLI transcription factors, plays a central role in the pathogenesis of cutaneous basal cell carcinoma and contributes to the development of several malignancies arising in extracutaneous sites. We now report that K5-tTA;tetO-Gli2 bitransgenic mice develop distinctive epithelial tumors within their jaws. These tumors consist of large masses of highly proliferative, monomorphous, basaloid cells with scattered foci of keratinization and central necrosis, mimicking human basaloid squamous cell carcinoma (BSCC), an aggressive upper aerodigestive tract tumor. Like human BSCC, these tumors express epidermal basal keratins, and differentiation-specific keratins within squamous foci. Mouse BSCCs express high levels of Gli2 and Hh target genes, including Gli1 and Ptch1, which we show are also upregulated in a subset of human BSCCs. Mouse BSCCs appear to arise from distinct epithelial sites, including the gingival junctional epithelium and epithelial rests of Malassez, a proposed stem cell compartment. Although Gli2 transgene expression is restricted to epithelial cells, we also detect striking alterations in bone adjacent to BSCCs, with activated osteoblasts, osteoclasts, and osteal macrophages, indicative of active bone remodeling. Gli2 transgene inactivation resulted in rapid BSCC regression and reversal of the bone remodeling phenotype. This first-reported mouse model of BSCC supports the concept that uncontrolled Hh signaling plays a central role in the pathogenesis of a subset of human BSCCs, points to Hh/GLI2 signaling as a potential therapeutic target, and provides a powerful new tool for probing the mechanistic underpinnings of tumor-associated bone remodeling.

Bone marrow-derived mesenchymal stem cells inhibit CD8+ T cell immune responses via PD-1/PD-L1 pathway in multiple myeloma

High expression of the inhibitory receptor programmed cell death ligand 1 (PD-L1) on tumor cells and tumor stromal cells have been found to play a key role in tumor immune evasion in several human malignancies. However, the expression of PD-L1 on bone marrow mesenchymal stem cells (BMSCs) and whether the programmed cell death 1 (PD-1)/PD-L1 signal pathway is involved in the BMSCs versus T cell immune response in multiple myeloma (MM) remains poorly defined. In this study, we explored the expression of PD-L1 on BMSCs from newly diagnosed MM (NDMM) patients and the role of PD-1/PD-L1 pathway in BMSC-mediated regulation of CD8⁺ T cells. The data showed that the expression of PD-L1 on BMSCs in NDMM patients was significantly increased compared to that in normal controls (NC) (18·81 ± 1·61 versus 2·78± 0·70%; P < 0·001). Furthermore, the PD-1 expression on CD8⁺ T cells with NDMM patients was significantly higher than that in normal controls (43·22 ± 2·98 versus 20·71 ± 1·08%; P < 0·001). However, there was no significant difference in PD-1 expression of CD4⁺ T cells and natural killer (NK) cells between the NDMM and NC groups. Additionally, the co-culture assays revealed that BMSCs significantly suppressed CD8⁺ T cell function. However, the PD-L1 inhibitor effectively reversed BMSC-mediated suppression in CD8⁺ T cells. We also found that the combination of PD-L1 inhibitor and pomalidomide can further enhance the killing effect of CD8⁺ T cells on MM cells. In summary, our findings demonstrated that BMSCs in patients with MM may induce apoptosis of CD8⁺ T cells through the PD-1/PD-L1 axis and inhibit the release of perforin and granzyme B from CD8⁺ T cells to promote the immune escape of MM.

In vitro bone metastasis dwelling in a 3D bioengineered niche

Bone is the most frequent metastasis site for breast cancer. As well as dramatically increasing disease burden, bone metastases are also an indicator of poor prognosis. One of the main challenges in investigating bone metastasis in breast cancer is engineering in vitro models that replicate the features of in vivo bone environments. Such in vitro models ideally enable the biology of the metastatic cells to mimic their in vivo behavior as closely as possible. Here, taking benefit of cutting-edge technologies both in microfabrication and cancer cell biology, we have developed an in vitro breast cancer bone-metastasis model. To do so we first 3D printed a bone scaffold that reproduces the trabecular architecture and that can be conditioned with osteoblast-like cells, a collagen matrix, and mineralized calcium. We thus demonstrated that this device offers an adequate soil to seed primary breast cancer bone metastatic cells. In particular, patient-derived xenografts being considered as a better approach than cell lines to achieve clinically relevant results, we demonstrate the ability of this biomimetic bone niche model to host patient-derived xenografted metastatic breast cancer cells. These patient-derived xenograft cells show a long-term survival in the bone model and maintain their cycling propensity, and exhibit the same modulated drug response as in vivo. This experimental system enables access to the idiosyncratic features of the bone microenvironment and cancer bone metastasis, which has implications for drug testing.

Obesity and Cancer Metastasis: Molecular and Translational Perspectives

Obesity is a modern health problem that has reached pandemic proportions. It is an established risk factor for carcinogenesis, however, evidence for the contribution of adipose tissue to the metastatic behavior of tumors is also mounting. Over 90% of cancer mortality is attributed to metastasis and metastatic tumor cells must communicate with their microenvironment for survival. Many of the characteristics observed in obese adipose tissue strongly mirror the tumor microenvironment. Thus in the case of prostate, pancreatic and breast cancer and esophageal adenocarcinoma, which are all located in close anatomical proximity to an adipose tissue depot, the adjacent fat provides an ideal microenvironment to enhance tumor growth, progression and metastasis. Adipocytes provide adipokines, fatty acids and other soluble factors to tumor cells whilst immune cells infiltrate the tumor microenvironment. In addition, there are emerging studies on the role of the extracellular vesicles secreted from adipose tissue, and the extracellular matrix itself, as drivers of obesity-induced metastasis. In the present review, we discuss the major mechanisms responsible for the obesity-metastatic link. Furthermore, understanding these complex mechanisms will provide novel therapies to halt the tumor-adipose tissue crosstalk with the ultimate aim of inhibiting tumor progression and metastatic growth.

Metabolic adaptation of acute lymphoblastic leukemia to the central nervous system microenvironment is dependent on Stearoyl CoA desaturase

Metabolic reprogramming is a key hallmark of cancer, but less is known about metabolic plasticity of the same tumor at different sites. Here, we investigated the metabolic adaptation of leukemia in two different microenvironments, the bone marrow and the central nervous system (CNS). We identified a metabolic signature of fatty-acid synthesis in CNS leukemia, highlighting Stearoyl-CoA desaturase (SCD1) as a key player. In vivo SCD1 overexpression increases CNS disease, whilst genetic or pharmacological inhibition of SCD1 decreases CNS load. Overall, we demonstrated that leukemic cells dynamically rewire metabolic pathways to suit local conditions and that targeting these adaptations can be exploited therapeutically.

Autonomic nervous system control of multiple myeloma

The autonomic nervous system (ANS), which consists of antagonistic sympathetic (adrenergic) and parasympathetic (cholinergic) arms, has emerged as an important regulator of neoplastic development, yet little is known about its role in multiple myeloma (MM). Clinical findings that anti-adrenergic β-blocker intake reduces risk of disease-specific death and overall mortality in patients with MM have indicated that adrenergic input may worsen myeloma outcome. However, preclinical studies using β-adrenergic receptor agonists or antagonists produced controversial results as to whether sympathetic pathways promote or inhibit myeloma. Retrospective outcome data demonstrating that high message levels of cholinergic receptor genes predict inferior survival in the Multiple Myeloma Research Foundation CoMMpass trial suggest that parasympathetic input may drive myeloma progression in a subset of patients. Here we review the ill-defined role of the ANS in MM, put myeloma in the context of other cancers, and discuss knowledge gaps that may afford exciting research opportunities going forward.

Multiple Myeloma as a Bone Disease? The Tissue Disruption-Induced Cell Stochasticity (TiDiS) Theory

The standard model of multiple myeloma (MM) relies on genetic instability in the normal counterparts of MM cells. MM-induced lytic bone lesions are considered as end organ damages. However, bone is a tissue of significance in MM and bone changes could be at the origin/facilitate the emergence of MM. We propose the tissue disruption-induced cell stochasticity (TiDiS) theory for MM oncogenesis that integrates disruption of the microenvironment, differentiation, and genetic alterations. It starts with the observation that the bone marrow endosteal niche controls differentiation. As decrease in cellular stochasticity occurs thanks to cellular interactions in differentiating cells, the initiating role of bone disruption would be in the increase of cellular stochasticity. Thus, in the context of polyclonal activation of B cells, memory B cells and plasmablasts would compete for localizing in endosteal niches with the risk that some cells cannot fully differentiate if they cannot reside in the niche because of a disrupted microenvironment. Therefore, they would remain in an unstable state with residual proliferation, with the risk that subclones may transform into malignant cells. Finally, diagnostic and therapeutic perspectives are provided.

Role of Altered Metabolic Microenvironment in Osteolytic Metastasis

Metastatic bone disease is generally incurable and leads to pathological fractures, pain, hypercalcemia, spinal cord compression and decreased mobility. The skeleton is the major site of bone metastases from solid cancers, including breast and prostate carcinoma. Bone metastasis is facilitated by activation of bone-resorbing osteoclasts, terminally differentiated multinucleated cells formed by fusion from monocytic precursors. Cancer cells are known to produce specific factors that stimulate osteoclast differentiation and function. Of interest, cancer cells are also known to alter their own bioenergetics increasing the use of glycolysis for their survival and function. Such change in energy utilization by cancer cells would result in altered levels of cell-permeable metabolites, including glucose, lactate, and pyruvate. Osteoclast resorption is energy-expensive, and we have previously demonstrated that during differentiation osteoclasts actively adapt to their bioenergetics microenvironment. We hypothesize that altered bioenergetics state of cancer cells will also modify the bioenergetics substrate availability for the tissue-resident bone cells, potentially creating a favorable milieu for pathological osteolysis. The goals of this review are to analyze how metastasizing cancer cells change the availability of energy substrates in bone microenvironment; and to assess how the altered bioenergetics may affect osteoclast differentiation and activity.

Therapeutic targets in myeloma bone disease

Multiple myeloma (MM) is the second most common haematological malignancy and is characterized by a clonal proliferation of neoplastic plasma cells within the bone marrow. MM is the most frequent cancer involving the skeleton, causing osteolytic lesions, bone pain and pathological fractures that dramatically decrease MM patients' quality of life and survival. MM bone disease (MBD) results from uncoupling of bone remodelling in which excessive bone resorption is not compensated by new bone formation, due to a persistent suppression of osteoblast activity. Current management of MBD includes antiresorptive agents, bisphosphonates and denosumab, that are only partially effective due to their inability to repair the existing lesions. Thus, research into agents that prevent bone destruction and more importantly repair existing lesions by inducing new bone formation is essential. This review discusses the mechanisms regulating the uncoupled bone remodelling in MM and summarizes current advances in the treatment of MBD. LINKED ARTICLES: This article is part of a themed issue on The molecular pharmacology of bone and cancer-related bone diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.9/issuetoc.

Methods to Determine the Effects of MIF on In Vitro Osteoclastogenesis Using Murine Bone Marrow-Derived Cells and Human Peripheral Blood Mononuclear Cells

Osteoclasts are the only cells that are capable of resorbing bones, and they are involved in multiple diseases and disorders. This chapter will describe several in vitro osteoclastogenesis methods, which allows further investigation of molecular mechanisms of osteoclastogenesis in normal physiological and disease conditions. This chapter includes a protocol for isolating osteoclast progenitors from mouse bone marrow and human peripheral blood, as well as obtaining murine osteoblasts for the coculture system. Furthermore, culture and identification of multinucleated osteoclasts in vitro is also described in this chapter.

miR-181b/Oncostatin m axis inhibits prostate cancer bone metastasis via modulating osteoclast differentiation

The activation of osteoblasts is significantly correlated to prostate tumor bone metastasis and bone loss. Oncostatin M (OSM) could promote breast cancer metastasis to bone. However, its role and mechanism in prostate cancer bone metastasis remain unclear. MicroRNAs (miRNAs) could play important roles in cancers via post-transcriptionally regulating target genes via binding to specific sequences in the 3' UTR of downstream target genes. In the present study, we performed microarray profiling analyses to identify differentially-expressed miRNAs in preosteoclast before and after osteoclast differentiation that could target OSM. miR-181b-5p was downregulated during Raw264.7 cells differentiation into osteoclast. By direct targeting OSM 3' UTR, miR-181b-5p inhibited OSM messenger RNA expression and protein levels, subsequently decreasing IL-6 and AREG and increasing OPG, while OSM overexpression exerted an opposing effect. More importantly, co-culture with miR-181b-5p-overexpressing differentiated Raw264.7 cells suppressed proliferation, migration, and invasion of mouse prostate cancer RM-1 cells, while co-culture with OSM-overexpressing Raw264.7 cells led to opposing cellular effects. More importantly, the effects of miR-181b-5p on osteoclastogenic factors and RM-1 cells could be significantly reversed by OSM overexpression. In summary, miR-181b-5p/OSM axis could be a viable therapeutic target for patients with surgically removed primary tumors to reduce bone metastasis and prevent bone loss.

Multiple myeloma increases nerve growth factor and other pain-related markers through interactions with the bone microenvironment

Interactions between multiple myeloma (MM) and bone marrow (BM) are well documented to support tumour growth, yet the cellular mechanisms underlying pain in MM are poorly understood. We have used in vivo murine models of MM to show significant induction of nerve growth factor (NGF) by the tumour-bearing bone microenvironment, alongside other known pain-related characteristics such as spinal glial cell activation and reduced locomotion. NGF was not expressed by MM cells, yet bone stromal cells such as osteoblasts expressed and upregulated NGF when cultured with MM cells, or MM-related factors such as TNF-α. Adiponectin is a known MM-suppressive BM-derived factor, and we show that TNF-α-mediated NGF induction is suppressed by adiponectin-directed therapeutics such as AdipoRON and L-4F, as well as NF-κB signalling inhibitor BMS-345541. Our study reveals a further mechanism by which cellular interactions within the tumour-bone microenvironment contribute to disease, by promoting pain-related properties, and suggests a novel direction for analgesic development.

Subtypes of minimal residual disease, association with Gleason score, risk and time to biochemical failure in pT2 prostate cancer treated with radical prostatectomy

INTRODUCTION

The Gleason score is a strong prognostic factor for treatment failure in pathologically organ-confined prostate cancer (pT2) treated by radical prostatectomy (RP). However, within each Gleason score, there is clinical heterogeneity with respect to treatment outcome, even in patients with the same pathological stage and prostate-specific antigen (PSA) at diagnosis. This may be due to minimal residual disease (MRD) remaining after surgery. We hypothesise that the sub-type of MRD determines the risk of and timing of treatment failure, is a biological classification, and may explain in part clinical heterogeneity. We present a study of pT2 patients treated with RP, the subtypes of MRD for each Gleason score and clinical outcomes.

PATIENTS AND METHODS

Patients with Gleason ≤6 (G6) or Gleason 7 (G7) pT2 cancer participated in the study. One month after surgery, blood was taken for circulating prostate cell (CPCs); mononuclear cells were obtained by differential gel centrifugation and identified using immunocytochemistry with anti-PSA. The detection of one CPC/sample was defined as a positive test. Touch-preparations from bone-marrow biopsies were used to detect micro-metastasis using immunocytochemistry with anti-PSA. Biochemical failure was defined as a PSA >0.2 ng/mL. Patients were classified as: Group A MRD negative (CPC and micro-metastasis negative), Group B (only micro-metastasis positive) and Group C (CPC positive). Biochemical failure-free survival (BFFS) using Kaplan-Meier and time to failure using Restricted Mean Survival Time (RMST) after 10 years of follow-up were calculated for each group based on the Gleason score.

RESULTS

Of a cohort of 253 men, four were excluded for having Gleason 8 or 9 prostate cancer, leaving a study group of 249 men of whom 52 had G7 prostate cancer. G7 patients had a higher frequency of MRD (69% versus 36%) and worse prognosis. G6 and G7 patients negative for MRD had similar BBFS rates, 98% at 10 years, time to failure 9.9 years. Group C, G6 patients had a higher BFFS and longer time to failure compared to G7 patients (19% versus 5% and 7 versus 3 years). Group B showed similar results up to 5 years, thereafter G6 had a lower BFFS 63% versus 90%.

CONCLUSIONS

G7 and G6 pT2 patients have different patterns of MRD and relapse. Risk stratification using MRD sub-types may help to define the need for adjuvant therapy. This needs confirmation with large randomised long-term trials.

Animal Models of Multiple Myeloma

Multiple myeloma (MM) is a plasma cell neoplasm which is defined by strong interactions with the bone marrow microenvironment, a compartment with high cellular heterogeneity and unique structural and extracellular components. This necessitates the use of in vivo models for research to fully recapitulate MM growth conditions. The selection of appropriate model system is crucial, as each has advantages and shortcomings. Here, we describe the murine models available for studying MM, and focus on the methods for inoculating mice with MM cells via intravenous, intratibial or subcutaneous delivery, as well as monitoring of disease and organ processing for further analysis. The interaction and destruction of bone is a hallmark symptom of MM, and therefore many other complementary techniques used in calcified tissue research can be used, such as microCT, histomorphometry, and biomechanical testing.

Osteoblastic Factors in Prostate Cancer Bone Metastasis

PURPOSE OF REVIEW

Prostate cancer bone metastasis is the lethal progression of the disease. The disease frequently presents with osteoblastic lesions in bone. The tumor-induced bone can cause complications that significantly hamper the quality of life of patients. A better understanding of how prostate cancer induces aberrant bone formation and how the aberrant bone affects the progression and treatment of the disease may improve the therapies for this disease.

RECENT FINDINGS

Prostate cancer-induced bone was shown to enhance tumor growth and confer therapeutic resistance in bone metastasis. Clinically, Radium-223, an alpha emitter that selectively targets bone, was shown to improve overall survival in patients, supporting a role of tumor-induced bone in prostate cancer progression in bone. Recently, it was discovered that PCa-induced aberrant bone formation is due, in part, from tumor-associated endothelial cells that were converted into osteoblasts through endothelial-to-osteoblast (EC-to-OSB) conversion by tumor-secreted BMP4. The unique bone-forming phenotype of prostate cancer bone metastasis plays a role in prostate cancer progression in bone and therapy resistance. Therapies that incorporate targeting the tumor-induced osteoblasts or EC-to-OSB conversion mechanism may reduce tumor-induced bone formation and improve therapy outcomes.

Roles of Myeloid-Derived Suppressor Cells in Cancer Metastasis: Immunosuppression and Beyond

Metastasis is the direst face of cancer, and it is not a feature solely dependent on cancer cells; however, a complex interaction between cancer cells and host causes this process. Investigating the mechanisms of metastasis can lead to its control. Myeloid-derived suppressor cells (MDSCs) are key components of tumor microenvironment that favor cancer progression. These cells result from altered myelopoiesis in response to the presence of tumor. The most recognized function of MDSCs is suppressing anti-tumor immune responses. Strikingly, these cells are among important players in cancer dissemination and metastasis. They can exert their effect on metastatic process by affecting anti-cancer immunity, epithelial-mesenchymal transition, cancer stem cell formation, angiogenesis, establishing premetastatic niche, and supporting cancer cell survival and growth in metastatic sites. In this article, we review and discuss the mechanisms by which MDSCs contribute to cancer metastasis.

Osteoblast suppression in multiple myeloma bone disease

Multiple myeloma (MM) is the most frequent cancer to involve the skeleton with patients developing osteolytic bone lesions due to hyperactivation of osteoclasts and suppression of BMSCs differentiation into functional osteoblasts. Although new therapies for MM have greatly improved survival, MM remains incurable for most patients. Despite the major advances in current anti-MM and anti-resorptive treatments that can significantly improve osteolytic bone lysis, many bone lesions can persist even after therapeutic remission of active disease. Bone marrow mesenchymal stem cells (BMSCs) from MM patients are phenotypically distinct from their healthy counterparts and the mechanisms associated with the long-term osteogenic suppression are largely unknown. In this review we will highlight recent results of transcriptomic profiling studies that provide new insights into the establishment and maintenance of the persistent pathological alterations in MM-BMSCs that occur in MM. We will we discuss the role of genomic instabilities and senescence in propagating the chronically suppressed state and pro-inflammatory phenotype associated with MM-BMSCs. Lastly we describe the role of epigenetic-based mechanisms in regulating osteogenic gene expression to establish and maintain the pro-longed suppression of MM-BMSC differentiation into functional OBs.

Improving knowledge on the activation of bone marrow fibroblasts in MGUS and MM disease through the automatic extraction of genes via a nonnegative matrix factorization approach on gene expression profiles

Background

Multiple myeloma (MM) is a cancer of terminally differentiated plasma that is part of a spectrum of blood diseases. The role of the micro-environment is crucial for MM clonal evolution.

Methods

This paper describes the analysis carried out on a limited number of genes automatically extracted by a nonnegative matrix factorization (NMF) based approach from gene expression profiles of bone marrow fibroblasts of patients with monoclonal gammopathy of undetermined significance (MGUS) and MM.

Results

Automatic exploration through NMF, combined with a motivated post-processing procedure and a pathways analysis of extracted genes, allowed to infer that a functional switch is required to lead fibroblasts to acquire pro-tumorigenic activity in the progression of the disease from MGUS to MM.

Conclusion

The extracted biologically relevant genes may be representative of the considered clinical conditions and may contribute to a deeper understanding of tumor behavior.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1589-1) contains supplementary material, which is available to authorized users.

Multidisciplinary Approach for Bone Metastasis: A Review

Progress in cancer treatment has improved the survival of patients with advanced-stage cancers. Consequently, the clinical courses of patients are prolonged and often accompanied by morbidity due to bone metastases. Skeletal-related events (SREs), such as pathological fractures and spinal paralysis, cause impairment in activities of daily life and quality of life (QOL). To avoid serious SREs causing impairment in QOL and survival, early diagnosis and a prophylactic approach are required. It is necessary to initiate a bone management program concurrently with the initiation of cancer treatment to prevent complications of bone metastasis. In addition, the requirement of a multidisciplinary approach through a cancer board focusing on the management of bone metastases and involving a team of specialists in oncology, palliative care, radiotherapy, orthopedics, nuclear medicine, radiology, and physiatrists has been emphasized. In the cancer board, a strong focus is placed on the prevention of complications due to bone metastases and on reductions in the high morbidity, hospitalization rate, and overall costs associated with advanced-stage cancers. Recent reports suggest the usefulness of such approaches. The multidisciplinary approach through a cancer board would improve QOL and prognosis of patients, leading to new or continued systemic therapy for primary cancers.

Dysregulation of macrophage polarization is associated with the metastatic process in osteosarcoma

Osteosarcoma (OS) is the most common bone sarcoma in adolescents, and has poor prognosis. A vicious cycle is established between OS cells and their microenvironment in order to facilitate the tumor growth and cell spreading. The present work aims to better characterize the tumor microenvironment in OS in order to identify new therapeutic targets relating to metastatic process. Tissue microarrays of pre-chemotherapy OS biopsies were used for characterizing the tumor niche by immunohistochemistry. Parameters studies included: immune cells (M1, M2-subtypes of tumor-associated macrophages (TAM); T, B lymphocytes; mast cells), vascularization (endothelial, perivascular cells), OPG, RANKL, and mitotic index. Two groups of patients were defined, 22 localized OS (OS Meta-) and 28 metastatic OS (OS Meta+). The OS Meta- group was characterized by a higher infiltration of INOS+ M1-polarizedmacrophages and upregulated OPG immunostaining. OS Meta+ tumors showed a significant increase in CD146+ cells. INOS+ M1-macrophages were correlated with OPG staining, and negatively with the presence of metastases. CD163+ M2-macrophages were positively correlated with CD146+ cells. In multivariate analysis, INOS and OPG were predictive factors for metastasis. An older age, non-metastatic tumor, good response to chemotherapy, and higher macrophage infiltration were significantly associated with better overall survival. TAMs are associated with better overall survival and a dysregulation of M1/M2 polarized-macrophages in favor of M1 subtype was observed in non-metastatic OS.

The bone-marrow niche in MDS and MGUS: implications for AML and MM

Several haematological malignancies, including multiple myeloma (MM) and acute myeloid leukaemia (AML), have well-defined precursor states that precede the development of overt cancer. MM is almost always preceded by monoclonal gammopathy of undetermined significance (MGUS), and at least a quarter of all patients with myelodysplastic syndromes (MDS) have disease that evolves into AML. In turn, MDS are frequently anteceded by clonal haematopoiesis of indeterminate potential (CHIP). The acquisition of additional genetic and epigenetic alterations over time clearly influences the increasingly unstable and aggressive behaviour of neoplastic haematopoietic clones; however, perturbations in the bone-marrow microenvironment are increasingly recognized to have key roles in initiating and supporting oncogenesis. In this Review, we focus on the concept that the haematopoietic neoplasia-microenvironment relationship is an intimate rapport between two partners, provide an overview of the evidence supporting a role for the bone-marrow niche in promoting neoplasia, and discuss the potential for niche-specific therapeutic targets.

Sclerostin: an Emerging Target for the Treatment of Cancer-Induced Bone Disease

PURPOSE OF REVIEW

This review provides a summary of the current knowledge on Sost/sclerostin in cancers targeting the bone, discusses novel observations regarding its potential as a therapeutic approach to treat cancer-induced bone loss, and proposes future research needed to fully understand the potential of therapeutic approaches that modulate sclerostin function.

RECENT FINDINGS

Accumulating evidence shows that sclerostin expression is dysregulated in a number of cancers that target the bone. Further, new findings demonstrate that pharmacological inhibition of sclerostin in preclinical models of multiple myeloma results in a robust prevention of bone loss and preservation of bone strength, without apparent effects on tumor growth. These data raise the possibility of targeting sclerostin for the treatment of cancer patients with bone metastasis. Sclerostin is emerging as a valuable target to prevent the bone destruction that accompanies the growth of cancer cells in the bone. Further studies will focus on combining anti-sclerostin therapy with tumor-targeted agents to achieve both beneficial skeletal outcomes and inhibition of tumor progression.

The emerging role of bone marrow adipose tissue in bone health and dysfunction

Replacement of red hematopoietic bone marrow with yellow adipocyte-rich marrow is a conserved physiological process among mammals. The extent of this conversion is influenced by a wide array of pathological and non-pathological conditions. Of particular interest is the observation that some marrow adipocyte-inducing factors seem to oppose each other, for instance obesity and caloric restriction. Intriguingly, several important molecular characteristics of bone marrow adipose tissue (BMAT) are distinct from the classical depots of white and brown fat tissue. This depot of fat has recently emerged as an active part of the bone marrow niche that exerts paracrine and endocrine functions thereby controlling osteogenesis and hematopoiesis. While some functions of BMAT may be beneficial for metabolic adaptation and bone homeostasis, respectively, most findings assign bone fat a detrimental role during regenerative processes, such as hematopoiesis and osteogenesis. Thus, an improved understanding of the biological mechanisms leading to formation of BMAT, its molecular characteristics, and its physiological role in the bone marrow niche is warranted. Here we review the current understanding of BMAT biology and its potential implications for health and the development of pathological conditions.

Clinical relevance of androgen receptor alterations in prostate cancer

Prostate cancer (PC) remains a leading cause of cancer-related deaths among men worldwide, despite continuously improved treatment strategies. Patients with metastatic disease are treated by androgen deprivation therapy (ADT) that with time results in the development of castration-resistant prostate cancer (CRPC) usually established as metastases within bone tissue. The androgen receptor (AR) transcription factor is the main driver of CRPC development and of acquired resistance to drugs given for treatment of CRPC, while a minority of patients have CRPC that is non-AR driven. Molecular mechanisms behind epithelial AR reactivation in CRPC include AR gene amplification and overexpression, AR mutations, expression of constitutively active AR variants, intra-tumoural and adrenal androgen synthesis and promiscuous AR activation by other factors. This review will summarize AR alterations of clinical relevance for patients with CRPC, with focus on constitutively active AR variants, their possible association with AR amplification and structural rearrangements as well as their ability to predict patient resistance to AR targeting drugs. The review will also discuss AR signalling in the tumour microenvironment and its possible relevance for metastatic growth and therapy.

Soluble bone-derived osteopontin promotes migration and stem-like behavior of breast cancer cells

Breast cancer is a leading cause of cancer death in women, with the majority of these deaths caused by metastasis to distant organs. The most common site of breast cancer metastasis is the bone, which has been shown to provide a rich microenvironment that supports the migration and growth of breast cancer cells. Additionally, growing evidence suggests that breast cancer cells that do successfully metastasize have a stem-like phenotype including high activity of aldehyde dehydrogenase (ALDH) and/or a CD44⁺CD24^- phenotype. In the current study, we tested the hypothesis that these ALDH^hiCD44⁺CD24^- breast cancer cells interact with factors in the bone secondary organ microenvironment to facilitate metastasis. Specifically, we focused on bone-derived osteopontin and its ability to promote the migration and stem-like phenotype of breast cancer cells. Our results indicate that bone-derived osteopontin promotes the migration, tumorsphere-forming ability and colony-forming ability of whole population and ALDH^hiCD44⁺CD24^- breast cancer cells in bone marrow-conditioned media (an ex vivo representation of the bone microenvironment) (p≤0.05). We also demonstrate that CD44 and RGD-dependent cell surface integrins facilitate this functional response to bone-derived osteopontin (p≤0.05), potentially through activation of WNK-1 and PRAS40-related pathways. Our findings suggest that soluble bone-derived osteopontin enhances the ability of breast cancer cells to migrate to the bone and maintain a stem-like phenotype within the bone microenvironment, and this may contribute to the establishment and growth of bone metastases.

Bone marrow adipose tissue as an endocrine organ: close to the bone?

White adipose tissue (WAT) is a major endocrine organ, secreting a diverse range of hormones, lipid species, cytokines and other factors to exert diverse local and systemic effects. These secreted products, known as 'adipokines', contribute extensively to WAT's impact on physiology and disease. Adipocytes also exist in the bone marrow (BM), but unlike WAT, study of this bone marrow adipose tissue (MAT) has been relatively limited. We recently discovered that MAT contributes to circulating adiponectin, an adipokine that mediates cardiometabolic benefits. Moreover, we found that MAT expansion exerts systemic effects. Together, these observations identify MAT as an endocrine organ. Additional studies are revealing further secretory functions of MAT, including production of other adipokines, cytokines and lipids that exert local effects within bone. These observations suggest that, like WAT, MAT has secretory functions with diverse potential effects, both locally and systemically. A major limitation is that these findings are often based on in vitro approaches that may not faithfully recapitulate the characteristics and functions of BM adipocytes in vivo. This underscores the need to develop improved methods for in vivo analysis of MAT function, including more robust transgenic models for MAT targeting, and continued development of techniques for non-invasive analysis of MAT quantity and quality in humans. Although many aspects of MAT formation and function remain poorly understood, MAT is now attracting increasing research focus; hence, there is much promise for further advances in our understanding of MAT as an endocrine organ, and how MAT impacts human health and disease.

A loss of host-derived MMP-7 promotes myeloma growth and osteolytic bone disease in vivo

Matrix metalloproteinases (MMPs) play a critical role in cancer pathogenesis, including tumor growth and osteolysis within the bone marrow microenvironment. However, the anti-tumor effects of MMPs are poorly understood, yet have significant implications for the therapeutic potential of targeting MMPs. Host derived MMP-7 has previously been shown to support the growth of bone metastatic breast and prostate cancer. In contrast and underscoring the complexity of MMP biology, here we identified a tumor-suppressive role for host MMP-7 in the progression of multiple myeloma in vivo. An increase in tumor burden and osteolytic bone disease was observed in myeloma-bearing MMP-7 deficient mice, as compared to wild-type controls. We observed that systemic MMP-7 activity was reduced in tumor-bearing mice and, in patients with multiple myeloma this reduced activity was concomitant with increased levels of the endogenous MMP inhibitor, tissue inhibitor of metalloproteinases-1 (TIMP-1). Our studies have identified an unexpected tumour-suppressive role for host-derived MMP-7 in myeloma bone disease in vivo, and highlight the importance of elucidating the effect of individual MMPs in a disease-specific context.

CYR61/CCN1 stimulates proliferation and differentiation of osteoblasts in vitro and contributes to bone remodeling in vivo in myeloma bone disease

Cysteine-rich 61 (CYR61/CCN1), a secreted protein in bone marrow (BM) microenvironment, has diverse effects on many cellular activities such as growth and differentiation. However, the effect of CCN1 on osteoblasts (OBs) in myeloma bone disease remains unclear. In our study, the level of CCN1 in multiple myeloma (MM) patients was detected by ELISA and RT-PCR. The proliferation and differentiation of OBs from MM patients were observed after stimulated by CCN1 in vitro. The myeloma cells transduced with CYR61 gene (RPMI‑8226/CYR61) were injected in a mouse model to evaluate the efficacy of CCN1 in vivo and compare with zoledronic acid. The results showed that CYR61/CCN1 levels in BM supernatant and OBs both elevated significantly in all newly diagnosed MM patients, especially in patients without bone disease (P=0.001 and P<0.001). After 30 ng/l CCN1 stimulation for 24 h, the quantity and mineralization of OBs increased significantly in vitro (P=0.046 and 0.048). The transcription factors of Wnt pathway, runt-related transcription factor 2 (Runx2) and β-catenin were upregulated in OBs after CCN1 stimulation (P=0.012 and 0.011). After injection of RPMI‑8226 cells, bone lesions were observed obviously by microCT and histochemistry at 7 weeks. Radiographic analysis of the bones showed decreased resorption in CCN1 overexpression group and zoledronic acid group, while severe resorption in negative control. Furthermore, trabecular bone volume in CCN1 overexpression group (1.7539±0.16949) was significantly higher than zoledronic acid group (1.2839±0.077) (P=0.012). In conclusion, CCN1 can stimulate the proliferation and differentiation of OBs in vitro and contribute to bone remodeling in vivo in MBD.

Marsdenia tenacissima extract suppresses A549 cell migration through regulation of CCR5-CCL5 axis, Rho C, and phosphorylated FAK

Marsdenia tenacissima, a traditional Chinese medicine, is long been used to treat various diseases including asthma, cancer, trachitis, tonsillitis, pharyngitis, cystitis, and pneumonia. Although Marsdenia tenacissima has been demonstrated to have strong anti-tumor effects against primary tumors, its effect on cancer metastasis remains to be defined, and the molecular mechanism underlying the anti-metastatic effect is unknown. In the present study, we investigated the effects of XAP (an extract of Marsdenia tenacissima) on A549 lung cancer cell migration and explored the role of CCR5-CCL5 axis in the anti-metastatic effects of XAP. Our resutls showed that XAP inhibited A549 lung cancer cell migration and invasion in a dose-dependent manner. The protein levels of CCR5, but not CCR9 and CXCR4, were decreased by XAP. The secretion of CCL5, the ligand of CCR5, was reduced by XAP. XAP down-regulated Rho C expression and FAK phosphorylation. In conclusion, XAP inhibited A549 cell migration and invasion through down-regulation of CCR5-CCL5 axis, Rho C, and FAK.

The Role of the Microenvironment in Prostate Cancer-Associated Bone Disease

The bone is a common site for metastasis in patients with advanced prostate carcinoma, and provides a 'fertile' milieu which stimulates tumour growth and associated bone disease. For years, the concept of treatment strategies has remained targeting the tumour itself; however, the occurrence of chemoresistance remains a challenge now more than ever. The attraction of targeting the bone microenvironment in order to disrupt tumour localisation and proliferation stems from the idea that stromal cells are superiorly stable at a genetic level, thus decreasing the risk of resistance manifestation. In this review, we will discuss recent findings with regards to the pathogenesis of prostate cancer-induced bone disease and recent therapeutic strategies in an aim to evaluate the ever increasing role of the microenvironment in disease progression.

Spontaneous metastases in immunocompetent mice harboring a primary tumor driven by oncogene latent membrane protein 1 from Epstein-Barr virus

Background

In vitro and clinical studies suggest that the oncogene LMP1 (latent membrane protein 1) encoded by Epstein–Barr virus (EBV) plays a role in the development of nasopharyngeal carcinoma (NPC) and the formation of metastases in immunocompetent individuals. However, whether LMP1 itself is sufficient to drive these events in immunocompetent hosts remains elusive due to the lack of appropriate experimental models. The aim of this study was to study LMP1-dependent tumorigenesis and metastasis in BALB/c mice inoculated with BALB/c-3T3 cells expressing N-LMP1 (a Taiwanese NPC variant).

Methods

Following cancer cell inoculation, metastasis formation was monitored over time using PCR analysis of LMP1 as tumor marker. We also used a luciferase (Luc)-containing N-LMP1 and bioluminescent imaging (BLI) to monitor metastasis formation in a non-invasive manner.

Results

N-LMP1 appeared early in draining lymph nodes and in various distant organs before the rapid growth of the primary tumor. Lung metastasis was observed by BLI and further confirmed by histological examination. Furthermore, we detected luciferase signals in the lungs, even before the animals were sacrificed.

Conclusions

Our results demonstrate the high metastatic character of N-LMP1 in immunocompetent hosts. Systemic tumor dissemination occurs even before aggressive tumor growth at the primary site, suggesting that early treatment of primary LMP1-associated tumors and distant micro-metastases is critical to achieve positive results.

The MET/Vascular Endothelial Growth Factor Receptor (VEGFR)-targeted Tyrosine Kinase Inhibitor Also Attenuates FMS-dependent Osteoclast Differentiation and Bone Destruction Induced by Prostate Cancer

The tyrosine kinase inhibitor TAS-115 that blocks VEGF receptor and hepatocyte growth factor receptor MET signaling exhibits antitumor properties in xenografts of human gastric carcinoma. In this study, we have evaluated the efficacy of TAS-115 in preventing prostate cancer metastasis to the bone and bone destruction using the PC3 cell line. When PC3 cells were injected into proximal tibiae in nude mouse, severe trabecular and cortical bone destruction and subsequent tumor growths were detected. Oral administration of TAS-115 almost completely inhibited both PC3-induced bone loss and PC3 cell proliferation by suppressing osteoclastic bone resorption. In an ex vivo bone organ culture, PC3 cells induced osteoclastic bone resorption when co-cultured with calvarial bone, but TAS-115 effectively suppressed the PC3-induced bone destruction. We found that macrophage colony-stimulating factor-dependent macrophage differentiation and subsequent receptor activator of NF-κB ligand-induced osteoclast formation were largely suppressed by adding TAS-115. The phosphorylation of the macrophage colony-stimulating factor receptor FMS and osteoclast related kinases such as ERK and Akt were also suppressed by the presence of TAS-115. Gene expression profiling showed that FMS expression was only seen in macrophage and in the osteoclast cell lineage. Our study indicates that tyrosine kinase signaling in host pre-osteoclasts/osteoclasts is critical for bone destruction induced by tumor cells and that targeting of MET/VEGF receptor/FMS activity makes it a promising therapeutic candidate for the treatment of prostate cancer patients with bone metastasis.

Target therapy of multiple myeloma by PTX-NPs and ABCG2 antibody in a mouse xenograft model

Multiple myeloma (MM) remains to be an incurable disease. The purpose of this study was to evaluate the effect of ABCG2 monoclonal antibody (McAb) combined with paclitaxel (PTX) conjugated with Fe₃O₄ nanoparticles (NPs) on MM progressed from cancer stem cells (CSCs)in non-obese-diabetic/severe-combined-immunodeficiency (NOD/SCID) mouse model. Mice were injected with MM CSCs as marked by CD138⁻CD34⁻ phenotypes through tail veins. The developed MM mice were examined by micro-computer tomography scanning, ultrasonography and enzyme-linked immunosorbent analysis. These mice were then intravenously treated with different combinations of NPs, PTX, McAb, PTX-NPs and melphalan/prednisone once a week for four weeks. The injected mice developed characteristic MM-associated syndromes, including lytic bone lesions, renal damages and proteinuria. All the treated mice showed decrease in bone lesions, renal damages and anemia but increase in apoptosis compared with the mice treated with NPs only. In particular, the treatment with ABCG2 McAb plus PTX-NPs induced the strongest therapeutic response and had an efficacy even better than that of melphalan/prednisone, a conventional regimen for MM patients. These data suggest that PTX-NPs with ABCG2 McAb can be developed into potential treatment regimens for patients with relapsed/refractory MM.

Skeletal complications in cancer patients with bone metastases

As a result of significant improvements in current therapies, the life expectancy of cancer patients with bone metastases has dramatically improved. Unfortunately, these patients often experience skeletal complications that significantly impair their quality of life. The major skeletal complications associated with bone metastases include: cancer-induced bone pain, hypercalcemia, pathological bone fractures, metastatic epidural spinal cord compression and cancer cachexia. Once cancer cells invade the bone, they perturb the normal physiology of the marrow microenvironment, resulting in bone destruction, which is believed to be a direct cause of skeletal complications. However, full understanding of the mechanisms responsible for these complications remains unknown. In the present review, we discuss the complications associated with bone metastases along with matched conventional therapeutic strategies. A better understanding of this topic is crucial, as targeting skeletal complications can improve both the morbidity and mortality of patients suffering from bone metastases.

Abrogation of prostaglandin E-EP4 signaling in osteoblasts prevents the bone destruction induced by human prostate cancer metastases

The metastasis of tumors to bone is known to be promoted by prostaglandin E2 (PGE2) produced by the tumor host stromal tissue. Although bone metastases frequently occur in prostate cancer patients, the significance of PGE2 in stromal responses to the tumor is not known. In this study, we report that PGE2 and its receptor EP4 play a pivotal role in bone destruction and metastasis in an experimental metastasis model of prostate cancer in nude mice. Using human prostate cancer PC-3 cells that are stably transfected with luciferase, we showed that the development of bone metastasis was accompanied by increased osteoclastic bone resorption in the bone metastasis microenvironment, and could be abrogated by an EP4 receptor antagonist. The growth of PC-3 cells in vitro was not influenced by PGE2 or by the EP4 receptor. However, cell-cell interactions between fixed PC-3 cells and host osteoblasts induced PGE2 production and RANKL expression in the osteoblasts. Addition of an EP4 antagonist suppressed both PGE2 and RANKL expression induced by the PC3-osteoblast interaction, which would have consequent effects on osteoclast activation and osteolysis. These results indicate that the blockage of PGE2-EP4 signaling prevents the bone destruction required for prostate cancer metastases, and that this is, in part due to the abrogation of bone cell responses. The study provides further evidence that an EP4 antagonist is a candidate for the treatment of prostate cancer in the blockade of bone metastasis.

RUNX2 promotes breast cancer bone metastasis by increasing integrin α5-mediated colonization

Runt-related transcription factor 2 (RUNX2) is regarded as an important contributor to breast cancer bone metastasis. However, previous studies did not provide direct clinical evidence for a role of RUNX2 in bone-specific metastasis in breast cancer, and the mechanism of RUNX2 in cancer cell recruitment and adhesion to the bone remains unclear. In this study, we showed that RUNX2 expression is positively correlated with the risk of bone-specific metastasis in lymph node-negative breast cancer patients. Then, we identified ITGA5 as a transcriptional target of RUNX2 from multiple candidate genes encoding adhesion molecules or chemokine receptors. We further provided experimental and clinical evidence that RUNX2, in an integrin α5-dependent manner, promotes the attraction and adhesion of breast cancer cells to the bone and confers cancer cell survival and bone colonization advantages. Overall, our findings clarify an adhesion-dependent mechanism of RUNX2 for the osteotropism and bone colonization of breast cancer cells and implicate RUNX2 and integrin α5 as potential molecular markers for the prediction of bone metastasis and therapeutic targets for the treatment of breast cancer bone metastasis.

Adipocytes contribute to the growth and progression of multiple myeloma: Unraveling obesity related differences in adipocyte signaling

The prevalence of obesity over the last several decades in the United States has tripled among children and doubled among adults. Obesity increases the incidence and progression of multiple myeloma (MM), yet the molecular mechanisms by which adipocytes contribute to cancer development and patient prognosis have yet to be fully elucidated. Here, we obtained human adipose-derived stem cells (ASCs) from twenty-nine normal (BMI = 20-25 kg/m(2)), overweight (25-30 kg/m(2)), obese (30-35 kg/m(2)), or super obese (35-40 kg/m(2)) patients undergoing elective liposuction. Upon differentiation, adipocytes were co-cultured with RPMI-8226 and NCI-H929 MM cell lines. Adipocytes from overweight, obese and super obese patients displayed increased PPAR-gamma, cytochrome C, interleukin-6, and leptin protein levels, and decreased fatty acid synthase protein. 8226 MM cells proliferated faster and displayed increased pSTAT-3/STAT-3 signaling when cultured in adipocyte conditioned media. Further, adipocyte conditioned media from obese and super obese patients significantly increased MM cell adhesion, and conditioned media from overweight, obese and super obese patients enhanced tube formation and expression of matrix metalloproteinase-2. In summary, our data suggest that adipocytes in the MM microenvironment contribute to MM growth and progression and should be further evaluated as a possible therapeutic target.

Inhibition of bone loss with surface-modulated, drug-loaded nanoparticles in an intraosseous model of prostate cancer

Advanced-stage prostate cancer usually metastasizes to bone and is untreatable due to poor biodistribution of intravenously administered anticancer drugs to bone. In this study, we modulated the surface charge/composition of biodegradable nanoparticles (NPs) to sustain their blood circulation time and made them small enough to extravasate through the openings of the bone's sinusoidal capillaries and thus localize into marrow. NPs with a neutral surface charge, achieved by modulating the NP surface-associated emulsifier composition, were more effective at localizing to bone marrow than NPs with a cationic or anionic surface charge. These small neutral NPs (~150nm vs. the more usual ~320nm) were also ~7-fold more effective in localizing in bone marrow than large NPs. We hypothesized that NPs that effectively localize to marrow could improve NP-mediated anticancer drug delivery to sites of bone metastasis, thereby inhibiting cancer progression and preventing bone loss. In a PC-3M-luc cell-induced osteolytic intraosseous model of prostate cancer, these small neutral NPs demonstrated greater accumulation in bone within metastatic sites than in normal contralateral bone as well as co-localization with the tumor mass in marrow. Significantly, a single-dose intravenous administration of these small neutral NPs loaded with paclitaxel (PTX-NPs), but not anionic PTX-NPs, slowed the progression of bone metastasis. In addition, neutral PTX-NPs prevented bone loss, whereas animals treated with the rapid-release drug formulation Cremophor EL (PTX-CrEL) or saline (control) showed >50% bone loss. Neutral PTX-NPs did not cause acute toxicity, whereas animals treated with PTX-CrEL experienced weight loss. These results indicate that NPs with appropriate physical and sustained drug-release characteristics could be explored to treat bone metastasis, a significant clinical issue in prostate and other cancers.

The role of bone marrow adipocytes in bone metastasis

Adipocytes are a significant component of the bone marrow microenvironment. Although bone marrow adipocytes were first identified more than 100 years ago, it is only in recent years that an understanding of their complex physiological role is emerging. Bone marrow adipocytes act as local regulators of skeletal biology and homeostasis, with recent studies suggesting that marrow adipose tissue is metabolically active, and can function as an endocrine organ. As such, bone marrow adipocytes have the potential to interact with tumour cells, influencing both tumour growth and bone disease. This review discusses the current evidence for the role of bone marrow adipocytes in tumour growth within the bone marrow microenvironment and the development of the associated bone disease.

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Bone marrow adipocytes are a metabolically active source of lipids and adipokines.

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Marrow adipocytes increase with age, but their role in bone metastasis is ill-defined.

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Marrow adipocytes have tumour-promoting and -suppressive effects in bone metastasis.

The Role of Sonic Hedgehog Signaling in Osteoclastogenesis and Jaw Bone Destruction

Sonic hedgehog (SHH) and its signaling have been identified in several human cancers, and increased levels of its expression appear to correlate with disease progression and metastasis. However, the role of SHH in bone destruction associated with oral squamous cell carcinomas is still unclear. In this study we analyzed SHH expression and the role played by SHH signaling in gingival carcinoma-induced jawbone destruction. From an analysis of surgically resected lower gingival squamous cell carcinoma mandible samples, we found that SHH was highly expressed in tumor cells that had invaded the bone matrix. On the other hand, the hedgehog receptor Patched and the signaling molecule Gli-2 were highly expressed in the osteoclasts and the progenitor cells. SHH stimulated osteoclast formation and pit formation in the presence of the receptor activator for nuclear factor-κB ligand (RANKL) in CD11b⁺ mouse bone marrow cells. SHH upregulated phosphorylation of ERK1/2 and p38 MAPK, NFATc1, tartrate-resistant acid phosphatase (TRAP), and Cathepsin K expression in RAW264.7 cells. Our results suggest that tumor-derived SHH stimulated the osteoclast formation and bone resorption in the tumor jawbone microenvironment.