Integrin alpha(v)beta3 expression confers on tumor cells a greater propensity to metastasize to bone

Role of SPRY4 in health and disease

SPRY4 is a protein encoding gene that belongs to the Spry family. It inhibits the mitogen-activated protein kinase (MAPK) signaling pathway and plays a role in various biological functions under normal and pathological conditions. The SPRY4 protein has a specific structure and interacts with other molecules to regulate cellular behavior. It serves as a negative feedback inhibitor of the receptor protein tyrosine kinases (RTK) signaling pathway and interferes with cell proliferation and migration. SPRY4 also influences inflammation, oxidative stress, and cell apoptosis. In different types of tumors, SPRY4 can act as a tumor suppressor or an oncogene. Its dysregulation is associated with the development and progression of various cancers, including colorectal cancer, glioblastoma, hepatocellular carcinoma, perihilar cholangiocarcinoma, gastric cancer, breast cancer, and lung cancer. SPRY4 is also involved in organ development and is associated with ischemic diseases. Further research is ongoing to understand the expression and function of SPRY4 in specific tumor microenvironments and its potential as a therapeutic target.

Synthesis and Biological Evaluation of Cyclobutane-Based β3 Integrin Antagonists: A Novel Approach to Targeting Integrins for Cancer Therapy

The Arg-Gly-Asp (RGD)-binding family of integrin receptors, and notably the β3 subfamily, are key to multiple physiological processes involved in tissue development, cancer proliferation, and metastatic dissemination. While there is compelling preclinical evidence that both αvβ3 and αIIbβ3 are important anticancer targets, most integrin antagonists developed to target the β3 integrins are highly selective for αvβ3 or αIIbβ3. We report the design, synthesis, and biological evaluation of a new structural class of ligand-mimetic β3 integrin antagonist. These new antagonists combine a high activity against αvβ3 with a moderate affinity for αIIbβ3, providing the first evidence for a new approach to integrin targeting in cancer.

Unusual Suspects: Bone and Cartilage ECM Proteins as Carcinoma Facilitators

The extracellular matrix (ECM) is the complex three-dimensional network of fibrous proteins and proteoglycans that constitutes an essential part of every tissue to provide support for normal tissue homeostasis. Tissue specificity of the ECM in its topology and structure supports unique biochemical and mechanical properties of each organ. Cancers, like normal tissues, require the ECM to maintain multiple processes governing tumor development, progression and spread. A large body of experimental and clinical evidence has now accumulated to demonstrate essential roles of numerous ECM components in all cancer types. Latest findings also suggest that multiple tumor types express, and use to their advantage, atypical ECM components that are not found in the cancer tissue of origin. However, the understanding of cancer-specific expression patterns of these ECM proteins and their exact roles in selected tumor types is still sketchy. In this review, we summarize the latest data on the aberrant expression of bone and cartilage ECM proteins in epithelial cancers and their specific functions in the pathogenesis of carcinomas and discuss future directions in exploring the utility of this selective group of ECM components as future drug targets.

SPARC Induces E-Cadherin Repression and Enhances Cell Migration through Integrin αvβ3 and the Transcription Factor ZEB1 in Prostate Cancer Cells

Secreted protein acidic and rich in cysteine (SPARC), or osteonectin, is a matricellular protein that modulates interactions between cells and their microenvironment. SPARC is expressed during extracellular matrix remodeling and is abundant in bone marrow and high-grade prostate cancer (PCa). In PCa, SPARC induces changes associated with epithelial–mesenchymal transition (EMT), enhancing migration and invasion and increasing the expression of EMT transcriptional factor Zinc finger E-box-binding homeobox 1 (ZEB1), but not Zinc finger protein SNAI1 (Snail) or Zinc finger protein SNAI2 (Slug). It is unknown whether the SPARC-induced downregulation of E-cadherin in PCa cells depends on ZEB1. Several integrins are mediators of SPARC effects in cancer cells. Because integrin signaling can induce EMT programs, we hypothesize that SPARC induces E-cadherin repression through the activation of integrins and ZEB1. Through stable knockdown and the overexpression of SPARC in PCa cells, we demonstrate that SPARC downregulates E-cadherin and increases vimentin, ZEB1, and integrin β3 expression. Knocking down SPARC in PCa cells decreases the tyrosine-925 phosphorylation of FAK and impairs focal adhesion formation. Blocking integrin αvβ3 and silencing ZEB1 revert both the SPARC-induced downregulation of E-cadherin and cell migration enhancement. We conclude that SPARC induces E-cadherin repression and enhances PCa cell migration through the integrin αvβ3/ZEB1 signaling pathway.

Advancing Treatment of Bone Metastases through Novel Translational Approaches Targeting the Bone Microenvironment

Bone metastases represent a lethal condition that frequently occurs in solid tumors such as prostate, breast, lung, and renal cell carcinomas, and increase the risk of skeletal-related events (SREs) including pain, pathologic fractures, and spinal cord compression. This unique metastatic niche consists of a multicellular complex that cancer cells co-opt to engender bone remodeling, immune suppression, and stromal-mediated therapeutic resistance. This review comprehensively discusses clinical challenges of bone metastases, novel preclinical models of the bone and bone marrow microenviroment, and crucial signaling pathways active in bone homeostasis and metastatic niche. These studies establish the context to summarize the current state of investigational agents targeting BM, and approaches to improve BM-targeting therapies. Finally, we discuss opportunities to advance research in bone and bone marrow microenvironments by increasing complexity of humanized preclinical models and fostering interdisciplinary collaborations to translational research in this challenging metastatic niche.

The TSH/Thyroid Hormones Axis and Breast Cancer

Breast cancer, the most prevalent female carcinoma, is characterized by the expression of steroid nuclear receptors in a subset of cases. The most important nuclear receptor with prognostic and therapeutic implications is the Estrogen Receptor (ER), which is expressed in about three out of four breast cancers. The Progesterone Receptor (PR) and the Androgen Receptor (AR) are also commonly expressed. Moreover, non-steroid nuclear receptors, including the vitamin D receptor (VDR) and the thyroid receptors (TRs), are also present in breast cancers and have pathophysiologic implications. Circulating thyroid hormones may influence breast cancer risk and breast cancer cell survival, through ligating their canonical receptors TRα and TRβ but also through additional membrane receptors that are expressed in breast cancer. The expression of TR subtypes and their respective isotypes have diverse effects in breast cancers through co-operation with ER and influence on other cancer-associated pathways. Other components of the TSH/thyroid hormone axis, such as TSH and selenoiodinase enzymes, have putative effects in breast cancer pathophysiology. This paper reviews the pathophysiologic and prognostic implications of the thyroid axis in breast cancer and provides a brief therapeutic perspective.

Integrins as attractive targets for cancer therapeutics

Integrins are transmembrane receptors that have been implicated in the biology of various human physiological and pathological processes. These molecules facilitate cell–extracellular matrix and cell–cell interactions, and they have been implicated in fibrosis, inflammation, thrombosis, and tumor metastasis. The role of integrins in tumor progression makes them promising targets for cancer treatment, and certain integrin antagonists, such as antibodies and synthetic peptides, have been effectively utilized in the clinic for cancer therapy. Here, we discuss the evidence and knowledge on the contribution of integrins to cancer biology. Furthermore, we summarize the clinical attempts targeting this family in anti-cancer therapy development.

MicroRNAs Possibly Involved in the Development of Bone Metastasis in Clear-Cell Renal Cell Carcinoma

Simple Summary

Bone metastases cause substantial morbidity and implicate worse clinical outcomes for clear-cell renal cell carcinoma patients. MicroRNAs are small RNA molecules that modulate gene translation and are involved in the development of cancer and metastasis. We identified six microRNAs that are potentially specifically involved in metastasis to bone, of which two seem protective and four implicate a higher risk. This aids further understanding of the process of metastasizing to bone. Furthermore, these microRNA hold potential for biomarkers or therapeutic targets.

Abstract

Bone metastasis in clear-cell renal cell carcinoma (ccRCC) leads to substantial morbidity through skeletal related adverse events and implicates worse clinical outcomes. MicroRNAs (miRNA) are small non-protein coding RNA molecules with important regulatory functions in cancer development and metastasis. In this retrospective analysis we present dysregulated miRNA in ccRCC, which are associated with bone metastasis. In particular, miR-23a-3p, miR-27a-3p, miR-20a-5p, and miR-335-3p specifically correlated with the earlier appearance of bone metastasis, compared to metastasis in other organs. In contrast, miR-30b-3p and miR-139-3p were correlated with less occurrence of bone metastasis. These miRNAs are potential biomarkers and attractive targets for miRNA inhibitors or mimics, which could lead to novel therapeutic possibilities for bone targeted treatment in metastatic ccRCC.

Differential expression of αVβ3 and αVβ6 integrins in prostate cancer progression

Neuroendocrine prostate cancer (NEPrCa) arises de novo or after accumulation of genomic alterations in pre-existing adenocarcinoma tumors in response to androgen deprivation therapies. We have provided evidence that small extracellular vesicles released by PrCa cells and containing the αVβ3 integrin promote neuroendocrine differentiation of PrCa in vivo and in vitro. Here, we examined αVβ3 integrin expression in three murine models carrying a deletion of PTEN (SKO), PTEN and RB1 (DKO), or PTEN, RB1 and TRP53 (TKO) genes in the prostatic epithelium; of these three models, the DKO and TKO tumors develop NEPrCa with a gene signature comparable to those of human NEPrCa. Immunostaining analysis of SKO, DKO and TKO tumors shows that αVβ3 integrin expression is increased in DKO and TKO primary tumors and metastatic lesions, but absent in SKO primary tumors. On the other hand, SKO tumors show higher levels of a different αV integrin, αVβ6, as compared to DKO and TKO tumors. These results are confirmed by RNA-sequencing analysis. Moreover, TRAMP mice, which carry NEPrCa and adenocarcinoma of the prostate, also have increased levels of αVβ3 in their NEPrCa primary tumors. In contrast, the αVβ6 integrin is only detectable in the adenocarcinoma areas. Finally, analysis of 42 LuCaP patient-derived xenografts and primary adenocarcinoma samples shows a positive correlation between αVβ3, but not αVβ6, and the neuronal marker synaptophysin; it also demonstrates that αVβ3 is absent in prostatic adenocarcinomas. In summary, we demonstrate that αVβ3 integrin is upregulated in NEPrCa primary and metastatic lesions; in contrast, the αVβ6 integrin is confined to adenocarcinoma of the prostate. Our findings suggest that the αVβ3 integrin, but not αVβ6, may promote a shift in lineage plasticity towards a NE phenotype and might serve as an informative biomarker for the early detection of NE differentiation in prostate cancer.

Integrin alpha5 in human breast cancer is a mediator of bone metastasis and a therapeutic target for the treatment of osteolytic lesions

Bone metastasis remains a major cause of mortality and morbidity in breast cancer. Therefore, there is an urgent need to better select high-risk patients in order to adapt patient's treatment and prevent bone recurrence. Here, we found that integrin alpha5 (ITGA5) was highly expressed in bone metastases, compared to lung, liver, or brain metastases. High ITGA5 expression in primary tumors correlated with the presence of disseminated tumor cells in bone marrow aspirates from early stage breast cancer patients (n = 268; p = 0.039). ITGA5 was also predictive of poor bone metastasis-free survival in two separate clinical data sets (n = 855, HR = 1.36, p = 0.018 and n = 427, HR = 1.62, p = 0.024). This prognostic value remained significant in multivariate analysis (p = 0.028). Experimentally, ITGA5 silencing impaired tumor cell adhesion to fibronectin, migration, and survival. ITGA5 silencing also reduced tumor cell colonization of the bone marrow and formation of osteolytic lesions in vivo. Conversely, ITGA5 overexpression promoted bone metastasis. Pharmacological inhibition of ITGA5 with humanized monoclonal antibody M200 (volociximab) recapitulated inhibitory effects of ITGA5 silencing on tumor cell functions in vitro and tumor cell colonization of the bone marrow in vivo. M200 also markedly reduced tumor outgrowth in experimental models of bone metastasis or tumorigenesis, and blunted cancer-associated bone destruction. ITGA5 was not only expressed by tumor cells but also osteoclasts. In this respect, M200 decreased human osteoclast-mediated bone resorption in vitro. Overall, this study identifies ITGA5 as a mediator of breast-to-bone metastasis and raises the possibility that volociximab/M200 could be repurposed for the treatment of ITGA5-positive breast cancer patients with bone metastases.

Bone metastasis: mechanisms, therapies, and biomarkers

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

Thermally Triggered, Cell-Specific Enzymatic Glyco-Editing: In Situ Regulation of Lectin Recognition and Immune Response on Target Cells

In situ glyco-editing on the cell surface can endow cellular glycoforms with new structures and properties; however, the lack of cell specificity and dependence on cells' endogenous functions plague the revelation of cellular glycan recognition properties and hamper the application of glyco-editing in complicated authentic biosystems. Herein, we develop a thermally triggered, cell-specific glyco-editing method for regulation of lectin recognition on target live cells in both single- and cocultured settings. The method relies on the aptamer-mediated anchoring of microgel-encapsulated neuraminidase on target cells and subsequent thermally triggered enzyme release for localized sialic acid (Sia) trimming. This temperature-based enzyme accessibility modulation strategy exempts genetic or metabolic engineering operations and, thus for the first time, enables tumor-specific desialylation on complicated tissue slices. The proposed method also provides an unprecedented opportunity to potentiate the innate immune response of natural killer cells toward target tumor cells through thermally triggered cell-specific desialylation, which paves the way for in vivo glycoimmune-checkpoint-targeted cancer therapeutic intervention.

Novel nomogram to predict risk of bone metastasis in newly diagnosed thyroid carcinoma: a population-based study

Background

The aim of this study was to develop and validate a visual nomogram for predicting the risk of bone metastasis (BM) in newly diagnosed thyroid carcinoma (TC) patients.

Methods

The demographics and clinicopathologic variables of TC patients from 2010 to 2015 in the Surveillance, Epidemiology and End Results (SEER) database were retrospectively reviewed. Chi-squared (χ2) test and logistic regression analysis were performed to identify independent risk factors. Based on that, a predictive nomogram was developed and validated for predicting the risk of BM in TC patients. The C-index was used to compute the predictive performance of the nomogram. Calibration curves and decision curve analysis (DCA) were furthermore used to evaluate the clinical value of the nomogram.

Results

According to the inclusion and exclusion criteria, the data of 14,772 patients were used to analyze in our study. After statistical analysis, TC patients with older age, higher T stage, higher N stage, poorly differentiated, follicular thyroid carcinoma (FTC) and black people had a higher risk of BM. We further developed a nomogram with a C-index of 0.925 (95%CI,0.895–0.948) in the training set and 0.842 (95%CI,0.777–0.907) in the validation set. The calibration curves and decision curve analysis (DCA) also demonstrated the reliability and accuracy of the clinical prediction model.

Conclusions

The present study developed a visual nomogram to accurately identify TC patients with high risk of BM, which might help to further provide more individualized clinical decision guidelines.

Inhibition of αvβ3 integrin impairs adhesion and uptake of tumor-derived small extracellular vesicles

BACKGROUND

Extracellular vesicles (EVs) are lipid-bound particles that are naturally released from cells and mediate cell-cell communication. Integrin adhesion receptors are enriched in small EVs (SEVs) and SEV-carried integrins have been shown to promote cancer cell migration and to mediate organ-specific metastasis; however, how integrins mediate these effects is not entirely clear and could represent a combination of EV binding to extracellular matrix and cells.

METHODS

To probe integrin role in EVs binding and uptake, we employed a disintegrin inhibitor (DisBa-01) of integrin binding with specificity for αvβ3 integrin. EVs were purified from MDA-MB-231 cells conditioned media by serial centrifugation method. Isolated EVs were characterized by different techniques and further employed in adhesion, uptake and co-culture experiments.

RESULTS

We find that SEVs secreted from MDA-MB-231 breast cancer cells carry αvβ3 integrin and bind directly to fibronectin-coated plates, which is inhibited by DisBa-01. SEV coating on tissue culture plates also induces adhesion of MDA-MB-231 cells, which is inhibited by DisBa-01 treatment. Analysis of EV uptake and interchange between cells reveals that the amount of CD63-positive EVs delivered from malignant MDA-MB-231 breast cells to non-malignant MCF10A breast epithelial cells is reduced by DisBa-01 treatment. Inhibition of αvβ3 integrin decreases CD63 expression in cancer cells suggesting an effect on SEV content.

CONCLUSION

In summary, our findings demonstrate for the first time a key role of αvβ3 integrin in cell-cell communication through SEVs. Video Abstract.

Bone metastases in thyroid cancer

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Osseous metastases (OMs) occur in only 4% of all thyroid cancer patients but are associated with greatly increased morbidity and mortality.

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OMs are about twice as frequent in follicular, hurthle cell, and medullary thyroid cancers as compared to papillary thyroid cancers.

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OMs are often lytic, triggered via activation of osteoclasts by tumor cells in a “vicious cycle”.

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OMs are often initially asymptomatic, but associated with eventual skeletal related events in >75%.

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Early identification of OMs, preemptive treatment with antiresorptive agents, and aggressive treatment of focal lesions before crisis are key.

Whereas preemptive screening for the presence of lymph node and lung metastases is standard-of-care in thyroid cancer patients, bone metastases are less well studied and are often neglected in thyroid cancer patient surveillance. Bone metastases in thyroid cancer are, however, independently associated with poor/worse prognosis with a median overall survival from detection of only 4 years despite an otherwise excellent prognosis for the vast majority of thyroid cancer patients. In this review we summarize the state of current knowledge as pertinent to bony metastatic disease in thyroid cancer, including clinical implications, impacts on patient function and quality of life, pathogenesis, and therapeutic opportunities, proposing approaches to patient care accordingly. In particular, bone metastasis pathogenesis appears to reflect cooperatively between cancer and the bone microenvironment creating a “vicious cycle” of bone destruction rather than due exclusively to tumor invasion into bone. Additionally, bone metastases are more frequent in follicular and medullary thyroid cancers, requiring closer bone surveillance in patients with these histologies. Emerging data also suggest that treatments such as multikinase inhibitors (MKIs) can be less effective in controlling bone, as opposed to other (e.g. lung), metastases in thyroid cancers, making special attention to bone critical even in the setting of active MKI therapy. Although locoregional therapies including surgery, radiotherapy and ablation play important roles in palliation, antiresorptive agents including bisphosphonates and denosumab appear individually to delay and/or lessen skeletal morbidity and complications, with dosing frequency of every 3 months appearing optimal; their early application should therefore be strongly considered.

RANKL/RANK System-Based Mechanism for Breast Cancer Bone Metastasis and Related Therapeutic Strategies

Breast cancer remains one of the most life-threatening tumors affecting women. Most patients with advanced breast cancer eventually develop metastatic diseases, which cause significant morbidity and mortality. Approximately two-thirds of patients with advanced breast cancer exhibit osteolytic-type bone metastasis, which seriously reduce the quality of life. Therefore, development of novel therapeutic strategies for treating breast cancer patients with bone metastasis is urgently required. The "seed and soil" theory, which describes the interaction between the circulating breast cancer cells (seeds) and bone microenvironment (soil), is widely accepted as the mechanism underlying metastasis. Disruption of any step in this cycle might have promising anti-metastasis implications. The interaction of receptor activator of nuclear factor-κB ligand (RANKL) and its receptor RANK is fundamental in this vicious cycle and has been shown to be a novel effective therapeutic target. A series of therapeutic strategies have been developed to intervene in this cross-talk. Therefore, in this review, we have systematically introduced the functions of the RANKL/RANK signaling system in breast cancer and discussed related therapeutic strategies.

Osteocytes and Bone Metastasis

Bone is the most frequent site of breast cancer and prostate cancer metastasis, and one of the most common sites of metastasis for many solid tumors. Once cancer cells colonize in the bone, it imposes a major clinical challenge for the treatment of the disease, and fatality rates increase drastically. Bone, the largest organ in the body, provides a fertile microenvironment enriched with nutrients, growth factors and hormones, a generous reward for cancer cells. Dependent on cancer type, cancer cells can cause osteoblastic (bone forming) or osteolytic lesions to promote the net resorption and/or release of growth factors from the bone extracellular matrix. These processes activate a "vicious cycle", leading to disruption of bone integrity and promoting cancer cell growth and migration. Cancer cells influence the bone microenvironment favoring their colonization and growth. In order to metastasize to the bone, cancer cells must first migrate from the site of origin, and once established within the bone, they must overcome the dormant inducing effects of resident cells. If successful, cancer cells can then colonize and continually disrupt bone homeostasis that is primarily maintained by osteocytes, the most abundant bone cell type. For example, it has been shown that exercise induces osteocytes to release anabolic factors that inhibit osteoclast resorptive activity, promote dormancy and the release of anti-cancer factors that inhibit breast cancer cell metastasis. In this review, we will summarize recent research findings and provide mechanistic insights related to the role of osteocytes in osteolytic metastasis.

Metastasis Organotropism: Redefining the Congenial Soil

Metastasis is the most devastating stage of cancer progression and causes the majority of cancer-related deaths. Clinical observations suggest that most cancers metastasize to specific organs, a process known as "organotropism." Elucidating the underlying mechanisms may help identify targets and treatment strategies to benefit patients. This review summarizes recent findings on tumor-intrinsic properties and their interaction with unique features of host organs, which together determine organ-specific metastatic behaviors. Emerging insights related to the roles of metabolic changes, the immune landscapes of target organs, and variation in epithelial-mesenchymal transitions open avenues for future studies of metastasis organotropism.

Bisphosphonates and Cancer: A Relationship Beyond the Antiresorptive Effects

Bisphosphonates (BPs) are stable analogues of the Inorganic Pyrophosphate (PPi), an endogenous regulator of bone mineralization, which can resist the hydrolysis in the gastrointestinal tract. Their conformation allows targeting the bone as a result of their three-dimensional structure, which makes them primary agents against osteoclast-mediated bone loss. They are used in many bone pathological conditions, like bone metastasis, because of its ability to modulate bone metabolism into a less favorable place to cancer cell growth, through the inhibition of osteoclastogenesis and bone resorption. This review is focused on the mechanisms of action through which BPs affect the cellular activity and survival, mainly on their antitumoral effects. In conclusion, BPs are considered the primary therapy for skeletal disorders due to its high affinity for bone, but now they are also considered as potential antitumor agents due to its ability to induce tumor cell apoptosis, inhibition of cell adhesion, invasion and proliferation, modulation of the immune system to target and eliminate cancer cells as well as affect the angiogenic mechanisms. Like any other drug, they also have some adverse effects, but the most common, the acute phase reaction, can be minimized with the intake of calcium and vitamin D.

The Emerging Role of Osteocytes in Cancer in Bone

Advances in the last decade have established the osteocyte, the most abundant cell in bone, as a dynamic and multifunctional cell capable of controlling bone homeostasis by regulating the function of both osteoblasts and osteoclasts. In addition, accumulating evidence demonstrates that osteocyte function is altered in several skeletal disorders, and targeting osteocytes and their derived factors improves skeletal health. Despite the remarkable progress in our understanding of osteocyte biology, there has been a paucity of information regarding the role of osteocytes in the progression of cancer in bone. Exciting, recent discoveries suggest that tumor cells communicate with osteocytes to generate a microenvironment that supports the growth and survival of cancer cells and stimulates bone destruction. This review features these novel findings and discussions regarding the impact of chemotherapy on osteocyte function and the potential of targeting osteocytes for the treatment of cancer in bone. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Bone Metastasis: Find Your Niche and Fit in

Metastasis to bones is determined by both intrinsic traits of metastatic tumor cells and properties appertaining to the bone microenvironment. Bone marrow niches are critical for all major steps of metastasis, including the seeding of disseminated tumor cells (DTCs) to bone, the survival of DTCs and microscopic metastases under dormancy, and the eventual outgrowth of overt metastases. In this review, we discuss the role of bone marrow niches in bone colonization. The emphasis is on complicated and dynamic nature of cancer cells-niche interaction, which may underpin the long-standing mystery of metastasis dormancy, and represent a therapeutic target for elimination of minimal residue diseases and prevention of life-taking, overt metastases.

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.

Animal Models of Breast Cancer Bone Metastasis

This chapter is designed to provide a comprehensive overview outlining the different in vivo models available for research into breast cancer bone metastasis. The main focus is to guide the researcher through the methodological processes required to establish and utilize these models within their own laboratory. These detailed methods are designed to enable the acquisition of accurate and meaningful results that can be used for publication and future translation into clinical benefit for women with breast cancer-induced bone metastasis.

Autotaxin-β interaction with the cell surface via syndecan-4 impacts on cancer cell proliferation and metastasis

Autotaxin (ATX) promotes cancer cell metastasis through the production of lysophosphatidic acid (LPA). ATX binds to αvβ3 integrins controlling metastasis of breast cancer cells. We screened a series of cancer cell lines derived from diverse human and mouse solid tumors for the capacity of binding to ATX and found only a modest correlation with their level of αvβ3 integrin expression. These results strongly suggested the existence of another cell surface ATX-interacting factor. Indeed, ATXα has been shown to bind heparan-sulfate chains because of its unique polybasic insertion sequence, although the biological significance is unknown. We demonstrated here, that among all cell surface heparan-sulfate proteoglycans, syndecan-4 (SDC4) was essential for cancer cell interaction with ATXβ but was restrained by heparan-sulfate chains. In addition, exogenous ATXβ-induced MG63 osteosarcoma cell proliferation required physical interaction of ATXβ with the cell surface via an SDC4-dependent mechanism. In a preclininal mouse model, targeting SDC4 on 4T1 mouse breast cancer cells inhibited early bone metastasis formation. Furthermore, SDC4-prometastatic activity was totally abolished in absence of ATX expression. In conclusion our results determined that ATX and SDC4 are engaged in a reciprocal collaboration for cancer cell metastasis providing the rational for the development of novel anti-metastasis therapies.

miRNA-30 Family Members Inhibit Breast Cancer Invasion, Osteomimicry, and Bone Destruction by Directly Targeting Multiple Bone Metastasis-Associated Genes

miRNAs are master regulators of gene expression that play key roles in cancer metastasis. During bone metastasis, metastatic tumor cells must rewire their biology and express genes that are normally expressed by bone cells (a process called osteomimicry), which endow tumor cells with full competence for outgrowth in the bone marrow. Here, we establish miR-30 family members miR-30a, miR-30b, miR-30c, miR-30d, and miR-30e as suppressors of breast cancer bone metastasis that regulate multiple pathways, including osteomimicry. Low expression of miR-30 in primary tumors from patients with breast cancer were associated with poor relapse-free survival. In addition, estrogen receptor (ER)-negative/progesterone receptor (PR)-negative breast cancer cells expressed lower miR-30 levels than their ER/PR-positive counterparts. Overexpression of miR-30 in ER/PR-negative breast cancer cells resulted in the reduction of bone metastasis burden in vivoIn vitro, miR-30 did not affect tumor cell proliferation, but did inhibit tumor cell invasion. Furthermore, overexpression of miR-30 restored bone homeostasis by reversing the effects of tumor cell-conditioned medium on osteoclastogenesis and osteoblastogenesis. A number of genes associated with osteoclastogenesis stimulation (IL8, IL11), osteoblastogenesis inhibition (DKK-1), tumor cell osteomimicry (RUNX2, CDH11), and invasiveness (CTGF, ITGA5, ITGB3) were identified as targets for repression by miR-30. Among these genes, silencing CDH11 or ITGA5 in ER-/PR-negative breast cancer cells recapitulated inhibitory effects of miR-30 on skeletal tumor burden in vivo Overall, our findings provide evidence that miR-30 family members employ multiple mechanisms to impede breast cancer bone metastasis and may represent attractive targets for therapeutic intervention.Significance: These findings suggest miR-30 family members may serve as an effective means to therapeutically attenuate metastasis in triple-negative breast cancer. Cancer Res; 78(18); 5259-73. ©2018 AACR.

Integrin αvβ3-associated DAAM1 is essential for collagen-induced invadopodia extension and cell haptotaxis in breast cancer cells

The formin protein dishevelled-associated activator of morphogenesis 1 (DAAM1) polymerizes straight actin filaments and mediates migration of cancer cells. However, how DAAM1 governs cell haptotaxis in response to collagen remains unexplored in breast cancer cells. We hypothesized that DAAM1 mediates invadopodia extension and cell haptotaxis in response to type IV collagen in association with integrin receptors. Using Boyden chamber membranes coated with type IV collagen, we show here that type IV collagen activates both DAAM1 and Ras homolog family member A (RHOA) and promotes haptotaxis of MDA-MB-231 and MDA-MB-453 breast cancer cells, a process abolished by treatment with the integrin αvβ3 inhibitor cyclo(-RGDfK). shRNA-mediated knockdown of DAAM1 or a dominant-negative DAAM1 mutation (N-DAAM1) significantly decreased collagen-induced RHOA activity and the assembly of stress fibers, invadopodia extension, and cell haptotaxis. Immunoprecipitation and pulldown assays revealed that integrin αvβ3 is associated with, but only indirectly binds to, the C-terminal DAD domain of DAAM1 in mammalian cells. Blockade of RHOA activation with a specific inhibitor (CCG-1423) or via a dominant-negative RHOA mutation (RHOA-N19) suppressed collagen-induced invadopodia extension and haptotaxis of the MDA-MB-231 and MDA-MB-453 cells. Immunoblotting and immunofluorescence assays indicated high DAAM1 and RHOA expression in invadopodia, which was abolished by cyclo(-RGDfK) treatment or DAAM1 knockdown. These findings have uncovered an integrin αvβ3/DAAM1/RHOA signaling pathway for type IV collagen-induced invadopodia extension and haptotaxis in breast cancer cells. Targeting this pathway may be a means for reducing invasiveness and metastasis of breast cancer.

Integrin αvβ3 Signaling in Tumor-Induced Bone Disease

Tumor-induced bone disease is common among patients with advanced solid cancers, especially those with breast, prostate, and lung malignancies. The tendency of these cancers to metastasize to bone and induce bone destruction is, in part, due to alterations in integrin expression and signaling. Substantial evidence from preclinical studies shows that increased expression of integrin αvβ3 in tumor cells promotes the metastatic and bone-invasive phenotype. Integrin αvβ3 mediates cell adhesion to several extracellular matrix proteins in the bone microenvironment which is necessary for tumor cell colonization as well as the transmission of mechanical signals for tumor progression. This review will discuss the αvβ3 integrin receptor in the context of tumor-induced bone disease. Specifically, the focus will be the role of αvβ3 in modulating cancer metastasis to bone and tumor cell response to the bone microenvironment, including downstream signaling pathways that contribute to tumor-induced osteolysis. A better understanding of integrin dysregulation in cancer is critical to developing new therapeutics for the prevention and treatment of bone metastases.

Breast cancer metastasis: Putative therapeutic role of vascular cell adhesion molecule-1

BACKGROUND

Breast cancer is a notable cause of cancer-related death in women worldwide. Metastasis to distant organs is responsible for ~90% of this death. Breast cells convert to malignant cancer cells after acquiring the capacity of invasion/intravasation into surrounding tissues and, finally, extravasation/metastasis to distant organs (i.e., lymph nodes, lungs, bone, brain). Metastasis to distant organs depends on interactions between disseminated tumor cells (DTCs) and the endothelium of blood vessels present in the tumor microenvironment. Among several known endothelial adhesion molecules, vascular cell adhesion molecule-1 (VCAM-1) has been found to be involved in this process. It has been shown that VCAM-1 is aberrantly expressed in breast cancer cells and that it can bind to its natural ligand α4β1integrin, also denoted as very late antigen 4 (VLA-4). This binding appears to be responsible for the metastasis of breast cancer cells to lung, bone and brain. The α4β1 integrin - VCAM-1 interaction thus represents a potential therapeutic target for metastatic breast cancer cells. The development of inhibitors of this interaction may be instrumental for the clinical management of breast cancer patients.

CONCLUSIONS

This study focuses on recent progress on the role of VCAM-1, an important glycoprotein belonging to the immunoglobulin (Ig) superfamily of cell surface adhesion molecules in breast cancer angiogenesis, survival and metastasis. Targeting VCAM-1, expressed on the surface of breast cancer cells, and/or its specific ligand VLA-4/α4β1 integrin, expressed on cells at the site of metastasis, may be a useful strategy to reduce breast cancer cell invasion and metastasis. Various approaches to therapeutically target VCAM-1 and VLA-4 are also discussed.

TGFβ1 induces endometrial cancer cell adhesion and migration by up-regulating integrin αvβ3 via SMAD-independent MEK-ERK1/2 signaling

Endometrial cancer is the most common, and second most lethal, gynecological malignancy, and its rates of incidence and death are growing. This is likely attributable to increased numbers of high-risk type II endometrial cancers which account for ~30% of cases but ~75% of deaths due to their aggressive and metastatic behaviour. Histopathological and in vitro functional studies suggest that aberrant TGFβ1 signaling may contribute to endometrial cancer development and the acquisition of invasive/metastatic characteristics. However, little is known about the cellular and molecular mechanisms of TGFβ1 in high-risk endometrial cancers. In the present study, we examined the roles and mechanisms of TGFβ1 on cell adhesion and motility in type II endometrial cancer cell lines, KLE and HEC-1B. We show that treatment with TGFβ1 increases cell adhesion to vitronectin and transwell cell migration. We also demonstrate that TGFβ1 treatment increases integrin β3 and αv mRNA and protein levels via SMAD-independent MEK-ERK1/2 signaling. Importantly, siRNA depletion or antibody-mediated blocking of integrin αvβ3 reversed the effects of TGFβ1 on cell adhesion and migration. Our results suggest that TGFβ1-MEK-ERK1/2-integrin αvβ3 signaling could contribute to the invasive behaviour of high-risk endometrial cancer by promoting cell adhesion and migration.

Activin B induces human endometrial cancer cell adhesion, migration and invasion by up-regulating integrin β3 via SMAD2/3 signaling

Endometrial cancer is the fourth most common female cancer and the most common gynecological malignancy. Although it comprises only ~10% of all endometrial cancers, the serous histological subtype accounts for ~40% of deaths due to its aggressive behavior and propensity to metastasize. Histopathological studies suggest that elevated expression of activin/inhibin βB subunit is associated with reduced survival in non-endometrioid endometrial cancers (type II, mostly serous). However, little is known about the specific roles and mechanisms of activin (βB dimer) in serous endometrial cancer growth and progression. In the present study, we examined the biological functions of activin B in type II endometrial cancer cell lines, HEC-1B and KLE. Our results demonstrate that treatment with activin B increases cell migration, invasion and adhesion to vitronectin, but does not affect cell viability. Moreover, we show that activin B treatment increases integrin β3 mRNA and protein levels via SMAD2/3-SMAD4 signaling. Importantly, siRNA knockdown studies revealed that integrin β3 is required for basal and activin B-induced cell migration, invasion and adhesion. Our results suggest that activin B-SMAD2/3-integrin β3 signaling could contribute to poor patient survival by promoting the invasion and/or metastasis of type II endometrial cancers.

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.

Antagonizing Integrin β3 Increases Immunosuppression in Cancer

Integrin β3 is critical for tumor invasion, neoangiogenesis, and inflammation, making it a promising cancer target. However, preclinical and clinical data of integrin β3 antagonists have demonstrated no benefit or worse outcomes. We hypothesized that integrin β3 could affect tumor immunity and evaluated tumors in mice with deletion of integrin β3 in macrophage lineage cells (β3KOM). β3KOM mice had increased melanoma and breast cancer growth with increased tumor-promoting M2 macrophages and decreased CD8(+) T cells. Integrin β3 antagonist, cilengitide, also enhanced tumor growth and increased M2 function. We uncovered a negative feedback loop in M2 myeloid cells, wherein integrin β3 signaling favored STAT1 activation, an M1-polarizing signal, and suppressed M2-polarizing STAT6 activation. Finally, disruption of CD8(+) T cells, macrophages, or macrophage integrin β3 signaling blocked the tumor-promoting effects of integrin β3 antagonism. These results suggest that effects of integrin β3 therapies on immune cells should be considered to improve outcomes. Cancer Res; 76(12); 3484-95. ©2016 AACR.

Murine models of breast cancer bone metastasis

Bone metastases cause significant morbidity and mortality in late-stage breast cancer patients and are currently considered incurable. Investigators rely on translational models to better understand the pathogenesis of skeletal complications of malignancy in order to identify therapeutic targets that may ultimately prevent and treat solid tumor metastasis to bone. Many experimental models of breast cancer bone metastases are in use today, each with its own caveats. In this methods review, we characterize the bone phenotype of commonly utilized human- and murine-derived breast cell lines that elicit osteoblastic and/or osteolytic destruction of bone in mice and report methods for optimizing tumor-take in murine models of bone metastasis. We then provide protocols for four of the most common xenograft and syngeneic inoculation routes for modeling breast cancer metastasis to the skeleton in mice, including the intra-cardiac, intra-arterial, orthotopic and intra-tibial methods of tumor cell injection. Recommendations for in vivo and ex vivo assessment of tumor progression and bone destruction are provided, followed by discussion of the strengths and limitations of the available tools and translational models that aid investigators in the study of breast cancer metastasis to bone.

Suppression of Spry4 enhances cancer stem cell properties of human MDA-MB-231 breast carcinoma cells

BACKGROUND

Cancer stem cells contribute to tumor initiation, heterogeneity, and recurrence, and are critical targets in cancer therapy. Sprouty4 (Spry4) is a potent inhibitor of signal transduction pathways elicited by receptor tyrosine kinases, and has roles in regulating cell proliferation, migration and differentiation. Spry4 has been implicated as a tumor suppressor and in modulating embryonic stem cells.

OBJECTIVES

The purpose of this research was to test the novel idea that Spry4 regulates cancer stem cell properties in breast cancer.

METHODS

Loss-of function of Spry4 in human MDA-MB-231 cell was used to test our hypothesis. Spry4 knockdown or control cell lines were generated using lentiviral delivery of human Spry4 or non-targeting control shRNAs, and then selected with 2 μg/ml puromycin. Cell growth and migratory abilities were determined using growth curve and cell cycle flow cytometry analyses and scratch assays, respectively. Xenograft tumor model was used to determine the tumorigenic activity and metastasis in vivo. Cancer stem cell related markers were evaluated using immunoblotting assays and fluorescence-activated cell sorting. Cancer stem cell phenotype was evaluated using in vitro mammosphere formation and drug sensitivity tests, and in vivo limiting dilution tumor formation assay.

RESULTS

Two out of three tested human Spry4 shRNAs significantly suppressed the expression of endogenous Spry4 in MDA-MB-231 cells. Suppressing Spry4 expression increased MDA-MB-231 cell proliferation and migration. Suppressing Spry4 increased β3-integrin expression, and CD133(+)CD44(+) subpopulation. Suppressing Spry4 increased mammosphere formation, while decreasing the sensitivity of MDA-MB-231 cells to Paclitaxel treatment. Finally, suppressing Spry4 increased the potency of MDA-MB-231 cell tumor initiation, a feature attributed to cancer stem cells.

CONCLUSIONS

Our findings provide novel evidence that endogenous Spry4 may have tumor suppressive activity in breast cancer by suppressing cancer stem cell properties in addition to negative effects on tumor cell proliferation and migration.

Matricellular proteins as regulators of cancer metastasis to bone

Metastasis is the major cause of death in cancer patients, and a frequent site of metastasis for many cancers is the bone marrow. Therefore, understanding the mechanisms underlying the metastatic process is necessary for future prevention and treatment. The tumor microenvironment is now known to play a role in the metastatic cascade, both at the primary tumor and in metastatic sites, and includes both cellular and non-cellular components. The extracellular matrix (ECM) provides structural support and signaling cues to cells. One particular group of molecules associated with the ECM, known as matricellular proteins, modulate multiple aspects of tumor biology, including growth, migration, invasion, angiogenesis and metastasis. These proteins are also important for normal function in the bone by regulating bone formation and bone resorption. Recent studies have described a link between some of these proteins and metastasis of various tumors to the bone. The aim of this review is to summarize what is currently known about matricellular protein influence on bone metastasis. Particular attention to the contribution of both tumor cells and non-malignant cells in the bone has been given.

A novel tumor suppressor function of Kindlin-3 in solid cancer

Kindlin-3 (FERMT-3) is known to be central in hemostasis and thrombosis control and its deficiency disrupts platelet aggregation and causes Leukocyte Adhesion Deficiency disease. Here we report that Kindlin-3 has a tumor suppressive role in solid cancer. Our present genetic and functional data show that Kindlin-3 is downregulated in several solid tumors by a mechanism involving gene hypermethylation and deletions. In vivo experiments demonstrated that Kindlin-3 knockdown in 2 tumor cell models (breast cancer and melanoma) markedly increases metastasis formation, in accord with the in vitro increase of tumor cell malignant properties. The metastatic phenotype was supported by a mechanism involving alteration in β3-integrin activation including decreased phosphorylation, interaction with talin and the internalization of its active form leading to less cell attachment and more migration/invasion. These data uncover a novel and unexpected tumor suppressor role of Kindin-3 which can influence integrins targeted therapies development.

The TGF-β Signaling Regulator PMEPA1 Suppresses Prostate Cancer Metastases to Bone

Transforming growth factor-β (TGF-β) regulates the expression of genes supporting breast cancer cells in bone, but little is known about prostate cancer bone metastases and TGF-β. Our study reveals that the TGFBR1 inhibitor SD208 effectively reduces prostate cancer bone metastases. TGF-β upregulates in prostate cancer cells a set of genes associated with cancer aggressiveness and bone metastases, and the most upregulated gene was PMEPA1. In patients, PMEPA1 expression decreased in metastatic prostate cancer and low Pmepa1 correlated with decreased metastasis-free survival. Only membrane-anchored isoforms of PMEPA1 interacted with R-SMADs and ubiquitin ligases, blocking TGF-β signaling independently of the proteasome. Interrupting this negative feedback loop by PMEPA1 knockdown increased prometastatic gene expression and bone metastases in a mouse prostate cancer model.

The Impact of Immune System in Regulating Bone Metastasis Formation by Osteotropic Tumors

Bone metastases are frequent and debilitating consequence for many tumors, such as breast, lung, prostate, and kidney cancer. Many studies report the importance of the immune system in the pathogenesis of bone metastasis. Indeed, bone and immune system are strictly linked to each other because bone regulates the hematopoietic stem cells from which all cells of the immune system derive, and many immunoregulatory cytokines influence the fate of bone cells. Furthermore, both cytokines and factors produced by immune and bone cells promote the growth of tumor cells in bone, contributing to supporting the vicious cycle of bone metastasis. This review summarizes the current knowledge on the interactions among bone, immune, and tumor cells aiming to provide an overview of the osteoimmunology field in bone metastasis from solid tumors.

Tissue invasion and metastasis: Molecular, biological and clinical perspectives

Cancer is a key health issue across the world, causing substantial patient morbidity and mortality. Patient prognosis is tightly linked with metastatic dissemination of the disease to distant sites, with metastatic diseases accounting for a vast percentage of cancer patient mortality. While advances in this area have been made, the process of cancer metastasis and the factors governing cancer spread and establishment at secondary locations is still poorly understood. The current article summarizes recent progress in this area of research, both in the understanding of the underlying biological processes and in the therapeutic strategies for the management of metastasis. This review lists the disruption of E-cadherin and tight junctions, key signaling pathways, including urokinase type plasminogen activator (uPA), phosphatidylinositol 3-kinase/v-akt murine thymoma viral oncogene (PI3K/AKT), focal adhesion kinase (FAK), β-catenin/zinc finger E-box binding homeobox 1 (ZEB-1) and transforming growth factor beta (TGF-β), together with inactivation of activator protein-1 (AP-1) and suppression of matrix metalloproteinase-9 (MMP-9) activity as key targets and the use of phytochemicals, or natural products, such as those from Agaricus blazei, Albatrellus confluens, Cordyceps militaris, Ganoderma lucidum, Poria cocos and Silybum marianum, together with diet derived fatty acids gamma linolenic acid (GLA) and eicosapentanoic acid (EPA) and inhibitory compounds as useful approaches to target tissue invasion and metastasis as well as other hallmark areas of cancer. Together, these strategies could represent new, inexpensive, low toxicity strategies to aid in the management of cancer metastasis as well as having holistic effects against other cancer hallmarks.

Molecular alterations that drive breast cancer metastasis to bone

Epithelial cancers including breast and prostate commonly progress to form incurable bone metastases. For this to occur, cancer cells must adapt their phenotype and behaviour to enable detachment from the primary tumour, invasion into the vasculature, and homing to and subsequent colonisation of bone. It is widely accepted that the metastatic process is driven by the transformation of cancer cells from a sessile epithelial to a motile mesenchymal phenotype through epithelial-mesenchymal transition (EMT). Dissemination of these motile cells into the circulation provides the conduit for cells to metastasise to distant organs. However, accumulating evidence suggests that EMT is not sufficient for metastasis to occur and that specific tissue-homing factors are required for tumour cells to lodge and grow in bone. Once tumour cells are disseminated in the bone environment, they can revert into an epithelial phenotype through the reverse process of mesenchymal-epithelial transition (MET) and form secondary tumours. In this review, we describe the molecular alterations undertaken by breast cancer cells at each stage of the metastatic cascade and discuss how these changes facilitate bone metastasis.

Genetic depletion and pharmacological targeting of αv integrin in breast cancer cells impairs metastasis in zebrafish and mouse xenograft models

Introduction

Increased expression of αv integrins is frequently associated with tumor cell adhesion, migration, invasion and metastasis, and correlates with poor prognosis in breast cancer. However, the mechanism by which αv integrins can enhance breast cancer progression is still largely unclear. The effects of therapeutic targeting of αv integrins in breast cancer also have yet to be investigated.

Methods

We knocked down αv integrin in MDA-MB-231 and MCF10A-M4 breast cancer cells, or treated these cells with the αv antagonist GLPG0187. The effects of αv integrin depletion on mesenchymal markers, transforming growth factor-β (TGF-β)/Smad signaling and TGF-β-induced target gene expression were analyzed in MDA-MB-231 cells by RNA analysis or Western blotting. The function of αv integrin on breast cancer cell migration was investigated by transwell assay in vitro, and its effect on breast cancer progression was assessed by both zebrafish and mouse xenografts in vivo. In the mouse model, GLPG0187 was administered separately, or in combination with the standard-of-care anti-resorptive agent zoledronate and the chemotherapeutic drug paclitaxel, to study the effects of combinational treatments on breast cancer metastasis.

Results

Genetic interference and pharmacological targeting of αv integrin with GLPG0187 in different breast cancer cell lines inhibited invasion and metastasis in the zebrafish or mouse xenograft model. Depletion of αv integrin in MDA-MB-231 cells inhibited the expression of mesenchymal markers and the TGF-β/Smad response. TGF-β induced αv integrin mRNA expression and αv integrin was required for TGF-β-induced breast cancer cell migration. Moreover, treatment of MDA-MB-231 cells with non-peptide RGD antagonist GLPG0187 decreased TGF-β signaling. In the mouse xenografts GLPG0187 inhibited the progression of bone metastasis. Maximum efficacy of inhibition of bone metastasis was achieved when GLPG0187 was combined with the standard-of-care metastatic breast cancer treatments.

Conclusion

These findings show that αv integrin is required for efficient TGF-β/Smad signaling and TGF-β-induced breast cancer cell migration, and for maintaining a mesenchymal phenotype of the breast cancer cells. Our results also provide evidence that targeting αv integrin could be an effective therapeutic approach for treatment of breast cancer tumors and/or metastases that overexpress αv integrin.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0537-8) contains supplementary material, which is available to authorized users.

Tumour but not stromal expression of β3 integrin is essential, and is required early, for spontaneous dissemination of bone-metastatic breast cancer

Although many preclinical studies have implicated β3 integrin receptors (αvβ3 and αIIbβ3) in cancer progression, β3 inhibitors have shown only modest efficacy in patients with advanced solid tumours. The limited efficacy of β3 inhibitors in patients could arise from our incomplete understanding of the precise function of β3 integrin and, consequently, inappropriate clinical application. Data from animal studies are conflicting and indicate heterogeneity with respect to the relative contributions of β3-expressing tumour and stromal cell populations in different cancers. Here we aimed to clarify the function and relative contributions to metastasis of tumour versus stromal β3 integrin in clinically relevant models of spontaneous breast cancer metastasis, with particular emphasis on bone metastasis. We show that stable down-regulation of tumour β3 integrin dramatically impairs spontaneous (but not experimental) metastasis to bone and lung without affecting primary tumour growth in the mammary gland. Unexpectedly, and in contrast to subcutaneous tumours, orthotopic tumour vascularity, growth and spontaneous metastasis were not altered in mice null for β3 integrin. Tumour β3 integrin promoted migration, protease expression and trans-endothelial migration in vitro and increased vascular dissemination in vivo, but was not necessary for bone colonization in experimental metastasis assays. We conclude that tumour, rather than stromal, β3 expression is essential and is required early for efficient spontaneous breast cancer metastasis to bone and soft tissues. Accordingly, differential gene expression analysis in cohorts of breast cancer patients showed a strong association between high β3 expression, early metastasis and shorter disease-free survival in patients with oestrogen receptor-negative tumours. We propose that β3 inhibitors may be more efficacious if used in a neoadjuvant setting, rather than after metastases are established.

FITC-conjugated cyclic RGD peptides as fluorescent probes for staining integrin αvβ3/αvβ5 in tumor tissues

This study sought to evaluate FITC-conjugated cyclic RGD peptides (FITC-RGD₂, FITC-3P-RGD₂, and FITC-Galacto-RGD₂) as fluorescent probes for in vitro assays of integrin α_vβ₃/α_vβ₅ expression in tumor tissues. FITC-RGD₂, FITC-3P-RGD₂, and FITC-Galacto-RGD₂ were prepared, and their integrin α_vβ₃/α_vβ₅ binding affinity was determined using the displacement assay against ¹²⁵I-echistatin bound to U87MG glioma cells. IC₅₀ values of FITC-Galacto-RGD₂, FITC-3P-RGD₂, and FITC-RGD₂ were calculated to be 28 ± 8, 32 ± 7, and 89 ± 17 nM, respectively. The integrin α_vβ₃/α_vβ₅ binding affinity followed a general trend: FITC-Galacto-RGD₂ ∼ FITC-3P-RGD₂ > FITC-RGD₂. The xenografted tumor-bearing models were established by subcutaneous injection of 5 × 10⁶ tumor cells into shoulder flank (U87MG, A549, HT29, and PC-3) or mammary fat pad (MDA-MB-435) of each athymic nude mouse. Three to six weeks after inoculation, the tumor size was 0.1–0.3 g. Tumors were harvested for integrin α_vβ₃/α_vβ₅ staining, as well as hematoxylin and eosin (H&E) staining. Six human carcinoma tissues (colon cancer, pancreatic cancer, lung adenocarcinoma, squamous cell lung cancer, gastric cancer, and esophageal cancer) were obtained from recently diagnosed cancer patients. Human carcinoma slides were deparaffinized in xylene, rehydrated with ethanol, and then used for integrin α_vβ₃/α_vβ₅ staining, as well as H&E staining. It was found that the tumor staining procedures with FITC-conjugated cyclic RGD peptides were much simpler than those with the fluorescence-labeled integrin α_vβ₃ antibodies. Since FITC-RGD₂, FITC-3P-RGD₂, and FITC-Galacto-RGD₂ were able to co-localize with the fluorescence-labeled integrin β₃ antibody, their tumor localization and tumor cell binding are integrin α_vβ₃-specific. Quantification of the fluorescent intensity in five xenografted tumors (U87MG, MDA-MB-435, A549, HT29, and PC-3) and six human carcinoma tissues revealed an excellent linear relationship between the relative integrin α_vβ₃/α_vβ₅ expression levels determined with FITC-Galacto-RGD₂ and those obtained with the fluorescence-labeled anti-human integrin β₃ antibody. There was also an excellent linear relationship between the tumor uptake (%ID/g) of ^99mTc-3P-RGD₂ (an integrin α_vβ₃/α_vβ₅-targeted radiotracer) and the relative integrin α_vβ₃/α_vβ₅ expression levels from the quantification of fluorescent intensity in the tumor tissues stained with FITC-Galacto-RGD₂. These results suggest that FITC-conjugated cyclic RGD peptides might be useful to correlate the in vitro findings with the in vivo imaging data from an integrin α_vβ₃/α_vβ₅-targeted radiotracer. The results from this study clearly showed that the FITC-conjugated cyclic RGD peptides (particularly FITC-3P-RGD₂ and FITC-Galacto-RGD₂) are useful fluorescent probes for assaying relative integrin α_vβ₃/α_vβ₅ expression levels in tumor tissues.

Serum amyloid A promotes osteosarcoma invasion via upregulating αvβ3 integrin

Serum amyloid A (SAA) is regarded as an important acute phase protein involved in tumor progression and metastasis. However, at present there is no evidence of its involvement in osteosarcoma. The present study aimed to investigate the effect of SAA on the invasion of osteosarcoma cells. The effects of SAA on the migration and invasion of osteosarcoma cells were detected using scratch wound healing and transwell assays, respectively. The expression of αvβ3 integrin was detected at the protein and mRNA levels in U2OS cells. Agonists, inhibitors or siRNA of formyl peptide receptor like‑1 (FPRL‑1), mitogen‑activated protein kinases and αvβ3 integrin were used to investigate the mechanism underlying the effects of SAA on the regulation of U2OS cell migration and invasion. The present study revealed that SAA promoted osteosarcoma cell migration and invasion. SAA upregulated the expression of αvβ3 integrin in a concentration‑ and time‑dependent manner. When inhibiting αvβ3 integrin with its antagonist, the migration and invasion abilities of the U2OS cells were markedly inhibited. SAA‑induced αvβ3 integrin production was significantly downregulated by inhibiting FPRL‑1 with siRNA and inhibitors. The present study also found that extracellular signal‑regulated kinase (ERK) 1/2, but not c‑Jun N‑terminal kinase or p38, was important in this process. These findings demonstrated that SAA regulated osteosarcoma cell migration and invasion via the FPRL‑1/ERK/αvβ3 integrin pathway.

Interaction of platelet-derived autotaxin with tumor integrin αVβ3 controls metastasis of breast cancer cells to bone

Autotaxin (ATX), through its lysophospholipase D activity controls physiological levels of lysophosphatidic acid (LPA) in blood. ATX is overexpressed in multiple types of cancers, and together with LPA generated during platelet activation promotes skeletal metastasis of breast cancer. However, the pathophysiological sequelae of regulated interactions between circulating LPA, ATX, and platelets remain undefined in cancer. In this study, we show that ATX is stored in α-granules of resting human platelets and released upon tumor cell-induced platelet aggregation, leading to the production of LPA. Our in vitro and in vivo experiments using human breast cancer cells that do not express ATX (MDA-MB-231 and MDA-B02) demonstrate that nontumoral ATX controls the early stage of bone colonization by tumor cells. Moreover, expression of a dominant negative integrin αvβ3-Δ744 or treatment with the anti-human αvβ3 monoclonal antibody LM609, completely abolished binding of ATX to tumor cells, demonstrating the requirement of a fully active integrin αvβ3 in this process. The present results establish a new mechanism for platelet contribution to LPA-dependent metastasis of breast cancer cells, and demonstrate the therapeutic potential of disrupting the binding of nontumor-derived ATX with the tumor cells for the prevention of metastasis.