The hypoxic cancer secretome induces pre-metastatic bone lesions through lysyl oxidase

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.

Distinct roles for the hypoxia-inducible transcription factors HIF-1α and HIF-2α in human osteoclast formation and function

Bone homeostasis is maintained by a balance between osteoblast-mediated bone formation and osteoclast-driven bone resorption. Hypoxia modulates this relationship partially via direct and indirect effects of the hypoxia-inducible factor-1 alpha (HIF-1α) transcription factor on osteoclast formation and bone resorption. Little data is available on the role(s) of the HIF-2α isoform of HIF in osteoclast biology. Here we describe induction of HIF-1α and HIF-2α during the differentiation of human CD14+ monocytes into osteoclasts. Knockdown of HIF-1α did not affect osteoclast differentiation but prevented the increase in bone resorption that occurs under hypoxic conditions. HIF-2α knockdown did not affect bone resorption but moderately inhibited osteoclast formation. Growth of osteoclasts in 3D gels reversed the effect of HIF-2α knockdown; HIF-2α siRNA increasing osteoclast formation in 3D. Glycolysis is the main HIF-regulated pathway that drives bone resorption. HIF knockdown only affected glucose uptake and bone resorption in hypoxic conditions. Inhibition of glycolysis with 2-deoxy-d-glucose (2-DG) reduced osteoclast formation and activity under both basal and hypoxic conditions, emphasising the importance of glycolytic metabolism in osteoclast biology. In summary, HIF-1α and HIF-2α play different but overlapping roles in osteoclast biology, highlighting the importance of the HIF pathway as a potential therapeutic target in osteolytic disease.

A glitch in the matrix: Age-dependent changes in the extracellular matrix facilitate common sites of metastasis

People over 55 years old represent the majority of cancer patients and suffer from increased metastatic burden compared to the younger patient population. As the aging population increases globally, it is prudent to understand how the intrinsic aging process contributes to cancer progression. As we age, we incur aberrant changes in the extracellular matrix (ECM) of our organs, which contribute to numerous pathologies, including cancer. Notably, the lung, liver, and bone represent the most common sites of distal metastasis for all cancer types. In this review, we describe how age-dependent changes in the ECM of these organs influence cancer progression. Further, we outline how these alterations prime the premetastatic niche and why these may help explain the disparity in outcome for older cancer patients.

Biophysical and epigenetic regulation of cancer stemness, invasiveness and immune action

PURPOSE OF REVIEW

The tumor microenvironment (TME) is an amalgam of multiple dysregulated biophysical cues that can alter cellular behavior through mechanotransductive signaling and epigenetic modifications. Through this review, we seek to characterize the extent of biophysical and epigenetic regulation of cancer stemness and tumor-associated immune cells in order to identify ideal targets for cancer therapy.

RECENT FINDINGS

Recent studies have identified cancer stemness and immune action as significant contributors to neoplastic disease, due to their susceptibility to microenvironmental influences. Matrix stiffening, altered vasculature, and resultant hypoxia within the TME can influence cancer stem cell (CSC) and immune cell behavior, as well as alter the epigenetic landscapes involved in cancer development.

SUMMARY

This review highlights the importance of aberrant biophysical cues in driving cancer progression through altered behavior of CSCs and immune cells, which in turn sustains further biophysical dysregulation. We examine current and potential therapeutic approaches that break this self-sustaining cycle of disease progression by targeting the presented biophysical and epigenetic signatures of cancer. We also summarize strategies including the normalization of the TME, targeted drug delivery, and inhibition of cancer-enabling epigenetic players.

Stepwise cell fate decision pathways during osteoclastogenesis at single-cell resolution

Osteoclasts are the exclusive bone-resorbing cells, playing a central role in bone metabolism, as well as the bone damage that occurs under pathological conditions^1,2. In postnatal life, haematopoietic stem-cell-derived precursors give rise to osteoclasts in response to stimulation with macrophage colony-stimulating factor and receptor activator of nuclear factor-κB ligand, both of which are produced by osteoclastogenesis-supporting cells such as osteoblasts and osteocytes^1-3. However, the precise mechanisms underlying cell fate specification during osteoclast differentiation remain unclear. Here, we report the transcriptional profiling of 7,228 murine cells undergoing in vitro osteoclastogenesis, describing the stepwise events that take place during the osteoclast fate decision process. Based on our single-cell transcriptomic dataset, we find that osteoclast precursor cells transiently express CD11c, and deletion of receptor activator of nuclear factor-κB specifically in CD11c-expressing cells inhibited osteoclast formation in vivo and in vitro. Furthermore, we identify Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (Cited2) as the molecular switch triggering terminal differentiation of osteoclasts, and deletion of Cited2 in osteoclast precursors in vivo resulted in a failure to commit to osteoclast fate. Together, the results of this study provide a detailed molecular road map of the osteoclast differentiation process, refining and expanding our understanding of the molecular mechanisms underlying osteoclastogenesis.

Premetastasis

Sterile inflammation within primary tumor tissues can spread to distant organs that are devoid of tumor cells. This happens in a manner dependent on tumor-led secretome, before the actual metastasis occurs. The premetastatic microenvironment is established in this way and is at least partly regulated by hijacking the host innate immune system. The biological manifestation of premetastasis include increased vascular permeability, cell mobilization via the blood stream, degradation of the extracellular matrix, immunosuppression, and host antineoplastic activities.

Tumor cell endogenous HIF-1α activity induces aberrant angiogenesis and interacts with TRAF6 pathway required for colorectal cancer development

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Findings provide evidence that hypoxia response deficient tumors show more functionally perfused vasculature and that TRAF6, an upstream effector of NF-κB, is directly interacting with HIF-1α thereby contributing to enhanced angiogenesis.

Hypoxia and inflammation are key factors for colorectal cancer tumorigenesis. The colonic epithelium belongs to the tissues with the lowest partial pressure of oxygen in the body, and chronic inflammation is associated with an increased chance to develop colon cancer. How the colonic epithelium responds to hypoxia and inflammation during tumorigenesis remains to be elucidated. Here we show, that murine colon adenocarcinoma cells with attenuated response to hypoxia, due to a knock-down (KD) of HIF-1α, produce smaller and less hypoxic tumors in an orthotopic mouse model when compared to tumors induced with control cells. HIF-1α-KD tumors showed more functional perfused vasculature associated with increased levels of vessel-stabilizing factors and reduced levels of proangiogenic factors, including extracellular matrix protein Cyr61/CCN1. Intratumoral injection of Cyr61 in HIF-1α-KD tumors revealed an in increased vessel permeability and tumor hypoxia. Further bioinformatics analysis identified a possible interaction between HIF-1α and TRAF6, an upstream effector of the NF-κB pathway that was confirmed by coimmunoprecipitation in MC-38 and CT26 colon adenocarcinoma cells and in situ by proximity ligation assay. Down-regulation of TRAF6 resulted in virtual abrogation of orthotopic tumor growth. Subcutaneous TRAF6-KD tumors were smaller and contained reduced vessel size and differently polarized macrophages. These data demonstrate that the tumor cell response to increased hypoxia in the colon leads to promotion of nonfunctional angiogenesis, regulated by both hypoxia and TRAF6 pathways.

Bone metastases

Bone is the most frequent site for metastasis for many cancers, notably for tumours originating in the breast and the prostate. Tumour cells can escape from the primary tumour site and colonize the bone microenvironment. Within the bone, these disseminated tumour cells, as well as those arising in the context of multiple myeloma, may assume a state of dormancy, remaining quiescent for years before resuming proliferation and causing overt metastasis, which causes bone destruction via activation of osteoclast-mediated osteolysis. This structural damage can lead to considerable morbidity, including pain, fractures and impaired quality of life. Although treatment of bone metastases and myeloma bone disease is rarely curative, disease control is often possible for many years through the use of systemic anticancer treatments on a background of multidisciplinary supportive care. This care should include bone-targeted agents to inhibit tumour-associated osteolysis and prevent skeletal morbidity as well as use of appropriate local treatments such as radiation therapy, orthopaedic surgery and specialist palliative care to minimize the impact of metastatic bone disease on physical functioning. In this Primer, we provide an overview of the clinical features, the pathophysiology and the specific treatment approaches to prevent and treat bone metastases from solid tumours as well as myeloma bone disease.

The prognostic value of the lysyl oxidase family in ovarian cancer

BACKGROUND

Our study intended to evaluate the prognostic value of lysyl oxidase (LOX) and its four relevant members, the lysyl oxidase-like genes (LOXL1-4), in ovarian cancer (OC) patients.

MATERIAL AND METHODS

The Kaplan-Meier plotter (KM plotter) database was used to investigate the prognostic power of the LOX family for OC patients. Overall survival (OS) and progression-free survival (PFS) were the clinical endpoints. The prognostic roles of the LOX family in OC patients were also analyzed according to various clinicopathological characteristics, including histological subtypes, clinical stages, pathological grades, and chemotherapeutic treatments.

RESULTS

Overexpression of LOX, LOXL1, LOXL2, and LOXL3 mRNA indicated poor OS and PFS in OC patients, particularly in serous and grade II + III OC patients. Overexpression of LOXL4 mRNA resulted in worse PFS in OC patients. Overexpression of LOX and LOXL1 mRNA showed worse OS and PFS in stage III + IV OC patients, and overexpression of LOXL3 mRNA indicated worse OS and PFS in stage I + II OC patients. Overexpression of LOX, LOXL3, and LOXL4 mRNA indicated worse OS and PFS among OC patients who received platinum, taxol, and taxol + platinum chemotherapy. Overexpression of LOXL1 and LOXL2 mRNA was related to lower OS and PFS in OC patients who received platinum chemotherapy.

CONCLUSION

LOX, LOXL1, LOXL2, and LOXL3 may become potential predictive markers for negative outcomes in OC patients. Moreover, the LOX family can serve as new molecular predictors for the efficiency of platinum-based chemotherapy in OC patients.

Emergence of Cancer-Associated Fibroblasts as an Indispensable Cellular Player in Bone Metastasis Process

Bone metastasis is frequently complicated in patients with advanced solid cancers such as breast, prostate and lung cancers, and impairs patients' quality of life and prognosis. At the first step of bone metastasis, cancer cells adhere to the endothelium in bone marrow and survive in a dormant state by utilizing hematopoietic niches present therein. Once a dormant stage is disturbed, cancer cells grow through the interaction with various bone marrow resident cells, particularly osteoclasts and osteoblasts. Consequently, osteoclast activation is a hallmark of bone metastasis. As a consequence, the drugs targeting osteoclast activation are frequently used to treat bone metastasis but are not effective to inhibit cancer cell growth in bone marrow. Thus, additional types of resident cells are presumed to contribute to cancer cell growth in bone metastasis sites. Cancer-associated fibroblasts (CAFs) are fibroblasts that accumulate in cancer tissues and can have diverse roles in cancer progression and metastasis. Given the presence of CAFs in bone metastasis sites, CAFs are emerging as an important cellular player in bone metastasis. Hence, in this review, we will discuss the potential roles of CAFs in tumor progression, particularly bone metastasis.

Concepts of extracellular matrix remodelling in tumour progression and metastasis

Tissues are dynamically shaped by bidirectional communication between resident cells and the extracellular matrix (ECM) through cell-matrix interactions and ECM remodelling. Tumours leverage ECM remodelling to create a microenvironment that promotes tumourigenesis and metastasis. In this review, we focus on how tumour and tumour-associated stromal cells deposit, biochemically and biophysically modify, and degrade tumour-associated ECM. These tumour-driven changes support tumour growth, increase migration of tumour cells, and remodel the ECM in distant organs to allow for metastatic progression. A better understanding of the underlying mechanisms of tumourigenic ECM remodelling is crucial for developing therapeutic treatments for patients.

Tumors are more than cancer cells — the extracellular matrix is a protein structure that organizes all tissues and is altered in cancer. Here, the authors review recent progress in understanding how the cancer cells and tumor-associated stroma cells remodel the extracellular matrix to drive tumor growth and metastasis.

Bone Marrow Adipocytes, Adipocytokines, and Breast Cancer Cells: Novel Implications in Bone Metastasis of Breast Cancer

Accumulating discoveries highlight the importance of interaction between marrow stromal cells and cancer cells for bone metastasis. Bone is the most common metastatic site of breast cancer and bone marrow adipocytes (BMAs) are the most abundant component of the bone marrow microenvironment. BMAs are unique in their origin and location, and recently they are found to serve as an endocrine organ that secretes adipokines, cytokines, chemokines, and growth factors. It is reasonable to speculate that BMAs contribute to the modification of bone metastatic microenvironment and affecting metastatic breast cancer cells in the bone marrow. Indeed, BMAs may participate in bone metastasis of breast cancer through regulation of recruitment, invasion, survival, colonization, proliferation, angiogenesis, and immune modulation by their production of various adipocytokines. In this review, we provide an overview of research progress, focusing on adipocytokines secreted by BMAs and their potential roles for bone metastasis of breast cancer, and investigating the mechanisms mediating the interaction between BMAs and metastatic breast cancer cells. Based on current findings, BMAs may function as a pivotal modulator of bone metastasis of breast cancer, therefore targeting BMAs combined with conventional treatment programs might present a promising therapeutic option.

Hypoxia in bone metastasis and osteolysis

Hypoxia is a common feature in tumors, driving pathways that promote epithelial-to-mesenchymal transition, invasion, and metastasis. Clinically, high levels of hypoxia-inducible factor (HIF) expression and stabilization at the primary site in many cancer types is associated with poor patient outcomes. Experimental evidence suggests that HIF signaling in the primary tumor promotes their dissemination to the bone, as well as the release of factors such as LOX that act distantly on the bone to stimulate osteolysis and form a pre-metastatic niche. Additionally, the bone itself is a generally hypoxic organ, fueling the activation of HIF signaling in bone resident cells, promoting tumor cell homing to the bone as well as osteoclastogenesis. The hypoxic microenvironment of the bone also stimulates the vicious cycle of tumor-induced bone destruction, further fueling tumor cell growth and osteolysis. Furthermore, hypoxia appears to regulate key tumor dormancy factors. Thus, hypoxia acts both on the tumor cells as well as the metastatic site to promote tumor cell metastasis.

Bone Tropism in Cancer Metastases

Bone is a frequent site of metastases in many cancers. Both bone properties and the tumor-intrinsic traits are associated with the metastatic propensity to bone (i.e., the bone tropism). Whereas an increasing body of mechanistic studies expanded our understanding on bone tropism, they also revealed complexity across the bone lesions originated from different cancer types. In this review, we will discuss the physical, chemical, and biological properties of bone microenvironment, identify potential players in every stage of bone metastases, and introduce some of the known mechanisms regulating the bone colonization. Our objectives are to integrate the knowledge established in different biological contexts and highlight the determinants of bone tropism.

Lysyl oxidases: Emerging biomarkers and therapeutic targets for various diseases

Therapeutic targeting of extracellular proteins has attracted huge attention in treating human diseases. The lysyl oxidases (LOXs) are a family of secreted copper-dependent enzymes which initiate the covalent crosslinking of collagen and elastin fibers in the extracellular microenvironment, thereby facilitating extracellular matrix (ECM) remodeling and ECM homeostasis. Apart from ECM-dependent roles, LOXs are also involved in other biological processes such as epithelial-to-mesenchymal transition (EMT) and transcriptional regulation, especially following hypoxic stress. Dysregulation of LOXs is found to underlie the onset and progression of multiple pathologies, such as carcinogenesis and cancer metastasis, fibrotic diseases, neurodegeneration and cardiovascular diseases. In this review, we make a comprehensive summarization of clinical and experimental evidences that support roles of for LOXs in disease pathology and points out LOXs as promising therapeutic targets for improving prognosis. Additionally, we also propose that LOXs reshape cell-ECM interaction or cell-cell interaction due to ECM-dependent and ECM-independent roles for LOXs. Therapeutic intervention of LOXs may have advantages in the maintenance of communication between ECM and cell or intercellular signaling, finally recovering organ function.

Engineered Niches to Analyze Mechanisms of Metastasis and Guide Precision Medicine

Cancer metastasis poses a challenging problem both clinically and scientifically, as the stochastic nature of metastatic lesion formation introduces complexity for both early detection and the study of metastasis in preclinical models. Engineered metastatic niches represent an emerging approach to address this stochasticity by creating bioengineered sites where cancer can preferentially metastasize. As the engineered niche captures the earliest metastatic cells at a nonvital location, both noninvasive and biopsy-based monitoring of these sites can be performed routinely to detect metastasis early and monitor alterations in the forming metastatic niche. The engineered metastatic niche also provides a new platform technology that serves as a tunable site to molecularly dissect metastatic disease mechanisms. Ultimately, linking the engineered niches with advances in sensor development and synthetic biology can provide enabling tools for preclinical cancer models and fosters the potential to impact the future of clinical cancer care.

The Role of the ECM in Lung Cancer Dormancy and Outgrowth

The dissemination of tumor cells to local and distant sites presents a significant challenge in the clinical management of many solid tumors. These cells may remain dormant for months or years before overt metastases are re-awakened. The components of the extracellular matrix, their posttranslational modifications and their associated factors provide mechanical, physical and chemical cues to these disseminated tumor cells. These cues regulate the proliferative and survival capacity of these cells and lay the foundation for their engraftment and colonization. Crosstalk between tumor cells, stromal and immune cells within primary and secondary sites is fundamental to extracellular matrix remodeling that feeds back to regulate tumor cell dormancy and outgrowth. This review will examine the role of the extracellular matrix and its associated factors in establishing a fertile soil from which individual tumor cells and micrometastases establish primary and secondary tumors. We will focus on the role of the lung extracellular matrix in providing the architectural support for local metastases in lung cancer, and distant metastases in many solid tumors. This review will define how the matrix and matrix associated components are collectively regulated by lung epithelial cells, fibroblasts and resident immune cells to orchestrate tumor dormancy and outgrowth in the lung. Recent advances in targeting these lung-resident tumor cell subpopulations to prevent metastatic disease will be discussed. The development of novel matrix-targeted strategies have the potential to significantly reduce the burden of metastatic disease in lung and other solid tumors and significantly improve patient outcome in these diseases.

MacroH2A1 Immunoexpression in Breast Cancer

MacroH2A1 has two splice isoforms, macroH2A1.1 and macroH2A1.2, that have been studied in several form of cancer. In the literature there are not many scientific papers dealing with the role of macroH2A1 in breast cancer. Breast cancer is the most frequent form of malignancy in females. It tend to metastasize to the bone in ~70% of patients. Despite treatment, new bone metastases will still occur in 30–50% of cases with advanced disease. Overall 5-year survival after the diagnosis of bone metastasis is ~20%. Osteoclasts and osteoblasts of the bone microenvironment are engaged by soluble factors released by neoplastic cells, resulting in bone matrix breakdown. This malfunction enhances the proliferation of the cancer cells, creating a vicious cycle. We investigated immunohistochemical expression of macroH2A1 in primitive breast cancer, focusing on the comparison of metastatic and non-metastatic cases. Furthermore, the immunohistochemical expression of macroH2A1 has been evaluated both in all cases of nodal metastases and in distant metastases. Our data demonstrated that macroH2A1 expression was higher expressed in metastatic breast cancer (77%) vs. non-metastatic breast cancer (32%). Also in analyzed metastases cases, a high macroH2A1 expression was detected: 85 and 80% in nodal and distant metastases cases, respectively. These results supported the fact that macroH2A1 is more highly expressed in breast cancer with worst prognosis.

Exosomes-Mediated Transfer of Itga2 Promotes Migration and Invasion of Prostate Cancer Cells by Inducing Epithelial-Mesenchymal Transition

Although integrin alpha 2 subunit (ITGA2) mediates cancer progression and metastasis, its transfer by exosomes has not been investigated in prostate cancer (PCa). We aimed to determine the role of exosomal ITGA2 derived from castration-resistant PCa (CRPC) cells in promoting aggressive phenotypes in androgen receptor (AR)-positive cells. Exosomes were co-incubated with recipient cells and tested for different cellular assays. ITGA2 was enriched in exosomes derived from CRPC cells. Co-culture of AR-positive cells with CRPC-derived exosomes increased their proliferation, migration, and invasion by promoting epithelial-mesenchymal transition, which was reversed via ITGA2 knockdown or inhibition of exosomal uptake by methyl-β-cyclodextrin (MβCD). Ectopic expression of ITGA2 reproduced the effect of exosomal ITGA2 in PCa cells. ITGA2 transferred by exosomes exerted its effect within a shorter time compared to that triggered by its endogenous expression. The difference of ITGA2 protein expression in localized tumors and those with lymph node metastatic tissues was indistinguishable. Nevertheless, its abundance was higher in circulating exosomes collected from PCa patients when compared with normal subjects. Our findings indicate the possible role of the exosomal-ITGA2 transfer in altering the phenotype of AR-positive cells towards more aggressive phenotype. Thus, interfering with exosomal cargo transfer may inhibit the development of aggressive phenotype in PCa cells.

Bone metastasis is associated with acquisition of mesenchymal phenotype and immune suppression in a model of spontaneous breast cancer metastasis

The most common site of breast cancer metastasis is the bone, occurring in approximately 70% of patients with advanced disease. Bone metastasis is associated with severe morbidities and high mortality. Therefore, deeper understanding of the mechanisms that enable bone-metastatic relapse are urgently needed. We report the establishment and characterization of a bone-seeking variant of breast cancer cells that spontaneously forms aggressive bone metastases following surgical resection of primary tumor. We characterized the modifications in the immune milieu during early and late stages of metastatic relapse and found that the formation of bone metastases is associated with systemic changes, as well as modifications of the bone microenvironment towards an immune suppressive milieu. Furthermore, we characterized the intrinsic changes in breast cancer cells that facilitate bone-tropism and found that they acquire mesenchymal and osteomimetic features. This model provides a clinically relevant platform to study the functional interactions between breast cancer cells and the bone microenvironment, in an effort to identify novel targets for intervention.

Understanding the Role of Innate Immune Cells and Identifying Genes in Breast Cancer Microenvironment

The innate immune system is the first line of defense against invading pathogens and has a major role in clearing transformed cells, besides its essential role in activating the adaptive immune system. Macrophages, dendritic cells, NK cells, and granulocytes are part of the innate immune system that accumulate in the tumor microenvironment such as breast cancer. These cells induce inflammation in situ by secreting cytokines and chemokines that promote tumor growth and progression, in addition to orchestrating the activities of other immune cells. In breast cancer microenvironment, innate immune cells are skewed towards immunosuppression that may lead to tumor evasion. However, the mechanisms by which immune cells could interact with breast cancer cells are complex and not fully understood. Therefore, the importance of the mammary tumor microenvironment in the development, growth, and progression of cancer is widely recognized. With the advances of using bioinformatics and analyzing data from gene banks, several genes involved in NK cells of breast cancer individuals have been identified. In this review, we discuss the activities of certain genes involved in the cross-talk among NK cells and breast cancer. Consequently, altering tumor immune microenvironment can make breast tumors more responsive to immunotherapy.

MEK activation modulates glycolysis and supports suppressive myeloid cells in TNBC

Triple-negative breast cancers (TNBCs) are heterogeneous and aggressive, with high mortality rates. TNBCs frequently respond to chemotherapy, yet many patients develop chemoresistance. The molecular basis and roles for tumor cell-stromal crosstalk in establishing chemoresistance are complex and largely unclear. Here we report molecular studies of paired TNBC patient-derived xenografts (PDXs) established before and after the development of chemoresistance. Interestingly, the chemoresistant model acquired a distinct KRASQ61R mutation that activates K-Ras. The chemoresistant KRAS-mutant model showed gene expression and proteomic changes indicative of altered tumor cell metabolism. Specifically, KRAS-mutant PDXs exhibited increased redox ratios and decreased activation of AMPK, a protein involved in responding to metabolic homeostasis. Additionally, the chemoresistant model exhibited increased immunosuppression, including expression of CXCL1 and CXCL2, cytokines responsible for recruiting immunosuppressive leukocytes to tumors. Notably, chemoresistant KRAS-mutant tumors harbored increased numbers of granulocytic myeloid-derived suppressor cells (gMDSCs). Interestingly, previously established Ras/MAPK-associated gene expression signatures correlated with myeloid/neutrophil-recruiting CXCL1/2 expression and negatively with T cell-recruiting chemokines (CXCL9/10/11) across patients with TNBC, even in the absence of KRAS mutations. MEK inhibition induced tumor suppression in mice while reversing metabolic and immunosuppressive phenotypes, including chemokine production and gMDSC tumor recruitment in the chemoresistant KRAS-mutant tumors. These results suggest that Ras/MAPK pathway inhibitors may be effective in some breast cancer patients to reverse Ras/MAPK-driven tumor metabolism and immunosuppression, particularly in the setting of chemoresistance.

Molecular mechanisms and clinical management of cancer bone metastasis

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

Critical steps to tumor metastasis: alterations of tumor microenvironment and extracellular matrix in the formation of pre-metastatic and metastatic niche

For decades, cancer metastasis has been a heated topic for its high mortality. Previous research has shown that pre-metastatic niche and metastatic niche are the 2 crucial steps in cancer metastasis, assisting cancerous cells' infiltration, survival, and colonization at target sites. More recent studies have unraveled details about the specific mechanisms related to the modification of pro-invasion environments. Here, we will review literatures on extracellular matrix (ECM) alterations, general cancer metastasis, organ specificity, pre-metastatic niche, metastatic niche, colony formation and impact on the course of metastasis. Respectively, the metastatic mechanisms like effect of hypoxia or inflammation on pre-metastatic niche construction, as well as the interaction between cancer cells and local milieu will be discussed. Based on the evidences of metastatic niches, we revisit and discussed the "Seed and Soil" hypothesis by Paget. This review will seek to provide insight into the mechanism of metastatic organ specificity which pre-metastatic niche and metastatic niche might suggest from an evolutionary aspect.

Role of Tumor-Associated Myeloid Cells in Breast Cancer

Stromal immune cells constitute the tumor microenvironment. These immune cell subsets include myeloid cells, the so-called tumor-associated myeloid cells (TAMCs), which are of two types: tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs). Breast tumors, particularly those in human epidermal growth factor receptor 2 (HER-2)-positive breast cancer and triple-negative breast cancer, are solid tumors containing immune cell stroma. TAMCs drive breast cancer progression via immune mediated, nonimmune-mediated, and metabolic interactions, thus serving as a potential therapeutic target for breast cancer. TAMC-associated breast cancer treatment approaches potentially involve the inhibition of TAM recruitment, modulation of TAM polarization/differentiation, reduction of TAM products, elimination of MDSCs, and reduction of MDSC products. Furthermore, TAMCs can enhance or restore immune responses during cancer immunotherapy. This review describes the role of TAMs and MDSCs in breast cancer and elucidates the clinical implications of TAMs and MDSCs as potential targets for breast cancer treatment.

Endoplasmic Reticulum Stress in Bone Metastases

Metastases-the spreading of cancer cells from primary tumors to distant organs, including bone-is often incurable and is the major cause of morbidity in cancer patients. Understanding how cancer cells acquire the ability to colonize to bone and become overt metastases is critical to identify new therapeutic targets and develop new therapies against bone metastases. Recent reports indicate that the endoplasmic reticulum (ER) stress and, as its consequence, the unfolded protein response (UPR) is activated during metastatic dissemination. However, their roles in this process remain largely unknown. In this review, we discuss the recent progress on evaluating the tumorigenic, immunoregulatory and metastatic effects of ER stress and the UPR on bone metastases. We explore new opportunities to translate this knowledge into potential therapeutic strategies for patients with bone metastases.

Evolving roles of lysyl oxidase family in tumorigenesis and cancer therapy

The lysyl oxidase (LOX) family is comprised of LOX and four LOX-like proteins (LOXL1, LOXL2, LOXL3, and LOXL4), and mainly functions in the remodeling of extracellular matrix (ECM) and the cross-linking of collagen and elastic fibers. Recently, a growing body of research has demonstrated that LOX family is critically involved in the regulation of cancer cell proliferation, migration, invasion and metastasis. In this review, we discuss the roles of LOX family members in the development and progression of different types of human cancers. Furthermore, we also describe the potential inhibitors of LOX family proteins and highlight that LOX family might be an important therapeutic target for cancer therapy.

Copper homeostasis: Emerging target for cancer treatment

Copper (Cu) is an essential micronutrient involved in a variety of fundamental biological processes. Recently, disorder of Cu homeostasis can be observed in many malignancies. Elevated Cu levels in serum and tissue are correlated with cancer progression. Hence, targeting Cu has emerged as a novel strategy in cancer treatment. This review provides an overview of physiological Cu metabolism and its homeostasis, followed by a discussion of the dysregulation of Cu homeostasis in cancer and the effects of Cu on cancer progression. Finally, recent therapeutic advances using Cu coordination complexes as anticancer agents, as well as the mechanisms of their anti-cancer action are discussed. This review contributes full comprehension to the role of Cu in cancer and demonstrates the broad application prospect of Cu coordination compounds as potential therapeutic agents.

Influence of Fibroblasts on Mammary Gland Development, Breast Cancer Microenvironment Remodeling, and Cancer Cell Dissemination

The stromal microenvironment regulates mammary gland development and tumorigenesis. In normal mammary glands, the stromal microenvironment encompasses the ducts and contains fibroblasts, the main regulators of branching morphogenesis. Understanding the way fibroblast signaling pathways regulate mammary gland development may offer insights into the mechanisms of breast cancer (BC) biology. In fact, the unregulated mammary fibroblast signaling pathways, associated with alterations in extracellular matrix (ECM) remodeling and branching morphogenesis, drive breast cancer microenvironment (BCM) remodeling and cancer growth. The BCM comprises a very heterogeneous tissue containing non-cancer stromal cells, namely, breast cancer-associated fibroblasts (BCAFs), which represent most of the tumor mass. Moreover, the different components of the BCM highly interact with cancer cells, thereby generating a tightly intertwined network. In particular, BC cells activate recruited normal fibroblasts in BCAFs, which, in turn, promote BCM remodeling and metastasis. Thus, comparing the roles of normal fibroblasts and BCAFs in the physiological and metastatic processes, could provide a deeper understanding of the signaling pathways regulating BC dissemination. Here, we review the latest literature describing the structure of the mammary gland and the BCM and summarize the influence of epithelial-mesenchymal transition (EpMT) and autophagy in BC dissemination. Finally, we discuss the roles of fibroblasts and BCAFs in mammary gland development and BCM remodeling, respectively.

Osteoclast Signal Transduction During Bone Metastasis Formation

Osteoclasts are myeloid lineage-derived bone-resorbing cells of hematopoietic origin. They differentiate from myeloid precursors through a complex regulation process where the differentiation of preosteoclasts is followed by intercellular fusion to generate large multinucleated cells. Under physiological conditions, osteoclastogenesis is primarily directed by interactions between CSF-1R and macrophage colony-stimulating factor (M-CSF, CSF-1), receptor activator of nuclear factor NF-κB (RANK) and RANK ligand (RANKL), as well as adhesion receptors (e.g., integrins) and their ligands. Osteoclasts play a central role in physiological and pathological bone resorption and are also required for excessive bone loss during osteoporosis, inflammatory bone and joint diseases (such as rheumatoid arthritis) and cancer cell-induced osteolysis. Due to the major role of osteoclasts in these diseases the better understanding of their intracellular signaling pathways can lead to the identification of potential novel therapeutic targets. Non-receptor tyrosine kinases and lipid kinases play major roles in osteoclasts and small-molecule kinase inhibitors are emerging new therapeutics in diseases with pathological bone loss. During the last few years, we and others have shown that certain lipid (such as phosphoinositide 3-kinases PI3Kβ and PI3Kδ) and tyrosine (Src-family and Syk) kinases play a critical role in osteoclast differentiation and function in humans and mice. Some of these signaling pathways shows similarity to immunoreceptor-like receptor signaling and involves important other enzymes (e.g., PLCγ2) and adapter proteins (such as the ITAM-bearing adapters DAP12 and the Fc-receptor γ-chain). Here, we review recently identified osteoclast signaling pathways and their role in osteoclast differentiation and function as well as pathological bone loss associated with osteolytic tumors of the bone. A better understanding of osteoclast signaling may facilitate the design of novel and more efficient therapies for pathological bone resorption and osteolytic skeletal metastasis formation.

Hypoxia-responsive miR-141-3p is involved in the progression of breast cancer via mediating the HMGB1/HIF-1α signaling pathway

Background

Hypoxia‐responsive miRs have been frequently reported in the growth of various malignant tumors. The present study aimed to investigate whether hypoxia‐responsive miR‐141–3p was implicated in the pathogenesis of breast cancer via mediating the high‐mobility group box protein 1 (HMGB1)/hypoxia‐inducible factor (HIF)‐1α signaling pathway.

Materials and methods

miRs expression profiling was filtrated by miR microarray assays. Gene and protein expression levels, respectively, were examined by a quantitative reverse transcriptase‐polymerase chaion reaction and western blotting. Cell migration and invasion were analyzed using a transwell assay. Cell growth was determined using nude‐mouse transplanted tumor experiments.

Results

miR‐141–3p was observed as a hypoxia‐responsive miR in breast cancer. miR‐141–3p was down‐regulated in breast cancer specimens and could serve as an independent prognostic factor for predicting overall survival in breast cancer patients. In addition, the overexpression of miR‐141–3p could inhibit hypoxia‐induced cell migration and impede human breast cancer MDA‐MB‐231 cell growth in vivo. Mechanistically, the hypoxia‐related HMGB1/HIF‐1α signaling pathway might be a possible target of miR‐141–3p with respect to preventing the development of breast cancer.

Conclusions

Our finding provides a new mechanism by which miR‐141–3p could prevent hypoxia‐induced breast tumorigenesis via post‐transcriptional repression of the HMGB1/HIF‐1α signaling pathway.

Berberine Inhibits the Apoptosis-Induced Metastasis by Suppressing the iPLA2/LOX-5/LTB4 Pathway in Hepatocellular Carcinoma

Purpose

Hepatocellular carcinoma (HCC) is one of the most malignant cancers around the world. HCC is less sensitive to conventional cytotoxic agents and easily develops into systemic metastases. However, the molecular mechanisms of the metastasis of HCC are poorly understood and need elucidation.

Materials and Methods

Transwell system of the chemotherapy-challenged and unchallenged HepG2 cells was established. Adhesion assay and scratch-wound assay were utilized to analyze the adhesion and migration of HepG2 cells. iPLA2 and LOX-5 expression were analyzed by Western blot. LTB4 level was analyzed by ELISA.

Results

Chemotherapeutics are traditionally regarded as a way of killing tumor cells; on the other hand, we proved that the chemotherapeutics-induced tumor cell apoptosis can also change the tumor microenvironment by activating the LOX pathway and subsequently release inflammatory factors such as LTB4 which can stimulate the adhesion and migration of the small number of surviving cells. Berberine can reverse the adhesion and migration of HepG2 cells by inhibiting the expression of LOX-5 and reducing the LTB4 production in the tumor microenvironment.

Conclusion

Our study sheds light on a novel anti-metastasis strategy that the combination of Berberine and chemotherapy may prevent the chemotherapy-induced metastasis in HCC.

Switching Homes: How Cancer Moves to Bone

Bone metastases (BM) are a very common complication of the most prevalent human cancers. BM are extremely painful and may be life-threatening when associated with hypercalcaemia. BM can lead to kidney failure and cardiac arrhythmias and arrest, but why and how do cancer cells decide to "switch homes" and move to bone? In this review, we will present what answers science has provided so far, with focus on the molecular mechanisms and cellular aspects of well-established findings, such as the concept of "vicious cycle" and "osteolytic" vs. "osteosclerotic" bone metastases; as well as on novel concepts, such as cellular dormancy and extracellular vesicles. At the molecular level, we will focus on hypoxia-associated factors and angiogenesis, the Wnt pathway, parathyroid hormone-related peptide (PTHrP) and chemokines. At the supramolecular/cellular level, we will discuss tumour dormancy, id est the mechanisms through which a small contingent of tumour cells coming from the primary site may be kept dormant in the endosteal niche for many years. Finally, we will present a potential role for the multimolecular mediators known as extracellular vesicles in determining bone-tropism and establishing a premetastatic niche by influencing the bone microenvironment.

Reduction of Liver Metastasis Stiffness Improves Response to Bevacizumab in Metastatic Colorectal Cancer

Tumors are influenced by the mechanical properties of their microenvironment. Using patient samples and atomic force microscopy, we found that tissue stiffness is higher in liver metastases than in primary colorectal tumors. Highly activated metastasis-associated fibroblasts increase tissue stiffness, which enhances angiogenesis and anti-angiogenic therapy resistance. Drugs targeting the renin-angiotensin system, normally prescribed to treat hypertension, inhibit fibroblast contraction and extracellular matrix deposition, thereby reducing liver metastases stiffening and increasing the anti-angiogenic effects of bevacizumab. Patients treated with bevacizumab showed prolonged survival when concomitantly treated with renin-angiotensin inhibitors, highlighting the importance of modulating the mechanical microenvironment for therapeutic regimens.

LOX gene polymorphisms are associated with osteoporotic vertebral compression fracture in postmenopausal Chinese women

INTRODUCTION

Collagen cross-linking, which is regulated by lysyl oxidase (LOX), plays critical roles in bone mechanical strength. LOX can influence bone remodeling by modulating osteoblast and osteoclast activity. This study aimed to explore the effect of LOX gene polymorphisms on osteoporotic fractures susceptibility in postmenopausal Chinese women.

METHODS

This was a prospective study of postmenopausal women who visited the outpatient and community clinics of the local Hospital. Five tagging single nucleotide polymorphisms (SNPs) in the LOX gene were determined. Bone mineral density (BMD) was measured at the lumbar spine, femoral neck, and hip using dual-energy X-ray absorptiometry. Fractures were confirmed by X-ray and divided into: vertebral compression fracture (OVCF) and non-OVCF (all other fractures).

RESULTS

This study included 602 patients with non-traumatic fractures and 1343 healthy volunteers. The rs1800449 was significantly associated with vertebral compression fracture (OVCF) after adjusting for age and BMI (P = 0.012). Compared with subjects with the GG genotype, the risk of having OVCF was 1.28 and 1.74, respectively for subjects with the GA and AA genotypes (P = 0.043 and P = 0.018). A recessive genetic model showed that carriers of the AA genotype had higher fracture risk compared to G carriers (GA and GG genotypes) (P = 0.015). The rs2288393 SNP exhibited marginally significant association with OVCF (P = 0.051). Haplotype analyses corroborated our single SNP results: both haplotype CGA and CCG contained rs10519694, rs2288393, and rs1800449, and were significant associated with OVCF (P = 0.048 and P = 0.032, respectively). On the other hand, we found no evidence of an association of LOX gene allelic variants with either BMD or non-OVCF (all P > 0.05).

CONCLUSION

The results suggest that genetic polymorphisms in LOX may contribute to susceptibility to OVCF in Chinese postmenopausal women.

Exosomes in hypoxia-induced remodeling of the tumor microenvironment

Exosomes are structurally and functionally pleiotropic nano-sized (~30-150 nm in diameter) extracellular vesicles (EVs) with endosomal origin. These vesicles are secreted by almost all cells and play a significant role in intercellular communication and bio-waste disposal. To a great extent, exosomes represent biological "snapshot" of parent cells, and their cargos (protein, nucleotides, lipids, and metabolites) are loaded uniquely under different pathophysiological conditions. For example, most cancerous cells secrete a higher amount of exosomes loaded with distinct cargos under stressful low oxygen condition i.e. hypoxia, a key characteristic of solid tumors responsible for disease aggressiveness and poor survival. Exosomes secreted under hypoxia (Exo^Hypoxic) play a vital role in aiding cancer cells crosstalk with its microenvironment constituents to create conditions advantageous for cancer growth and metastatic spread. In this review article, we have highlighted the effects of Exo^Hypoxic on various tumor microenvironment components involved in angiogenesis, survival, proliferation, pre-metastatic niches preparation, immunomodulation, epithelial-to-mesenchymal transition, invasion, metastasis, and drug resistance. We have also described key Exo^Hypoxic cargos (miRNA, proteins, etc) and their targets in the receipt cells, responsible for various biological effects. Finally, we have emphasized the applicability of Exo^Hypoxic as a biomarker of tumor hypoxia and disease prognosis.

Antifibrotic therapy to normalize the tumor microenvironment

Most tumors develop abnormal fibrotic regions consisting of fibroblasts, immune cells, and a dense extracellular matrix (ECM) immersed in a viscous interstitial fluid, and an abundant fibrotic tumor microenvironment (TME) is associated with poor outcome of treatment. It has been hypothesized that the treatment of cancer may be improved by interventions aiming to normalize this TME. The approaches used in attempts to normalize the fibrotic TME can be categorized into three strategies of targeted antifibrotic therapy: targeting of components of the ECM, targeting of the producers of the ECM components-the activated cancer-associated fibroblasts (CAFs), and targeting of the signaling pathways activating CAFs. To target the ECM, enzymes against components of the ECM have been used, including collagenase, relaxin, hyaluronidase, and lyxyl oxidase. Targeting of CAFs have been investigated by using agents aiming to eliminate or reprogram CAFs. CAFs are activated primarily by transforming growth factor-β (TGF-β), hedgehog, or focal adhesion kinase signaling, and several agents have been used to target these signaling pathways, including angiotensin II receptor I blockers (e.g., losartan) to inhibit the TGF-β pathway. Taken together, these studies have revealed that antifibrotic therapy is a two-edged sword: while some studies suggest enhanced response to treatment after antifibrotic therapy, others suggest that antifibrotic therapy may lead to increased tumor growth, metastasis, and impaired outcome of treatment. There are several possible explanations of these conflicting observations. Most importantly, tumors contain different subpopulations of CAFs, and while some subpopulations may promote tumor growth and metastasis, others may inhibit malignant progression. Furthermore, the outcome of antifibrotic therapy may depend on stage of disease, duration of treatment, treatment-induced activation of alternative profibrotic signaling pathways, and treatment-induced recruitment of tumor-supporting immune cells. Nevertheless, losartan-induced suppression of TGF-β signaling appears to be a particularly promising strategy. Losartan is a widely prescribed antihypertensive drug and highly advantageous therapeutic effects have been observed after losartan treatment of pancreatic cancer. However, improved understanding of the mechanisms governing the development of fibrosis in tumors is needed before safe antifibrotic treatments can be established.

Neutrophils expressing lysyl oxidase-like 4 protein are present in colorectal cancer liver metastases resistant to anti-angiogenic therapy

Colorectal cancer liver metastases (CRCLM) that present with a replacement histopathological growth pattern (HGP) are resistant to neoadjuvant anti-angiogenic therapy. Surrogate biomarkers are not available to preoperatively identify patients with these tumors. Here we identify differentially expressed genes between CRCLM with a replacement HGP and those with a desmoplastic HGP using RNA sequencing. We demonstrate that LOXL4 is transcriptionally upregulated in replacement HGP CRCLM compared with desmoplastic HGP CRCLM and the adjacent normal liver. Interestingly, lysyl oxidase-like 4 (LOXL4) protein was expressed by neutrophils present in the tumor microenvironment in replacement HGP CRCLM. We further demonstrate that LOXL4 expression is higher in circulating neutrophils of cancer patients compared with healthy control patients and its expression can be induced by stimulation with lipopolysaccharide and TNF-α. Our study is the first to show the expression of LOXL4 in neutrophils and reveals the potential for LOXL4-expressing neutrophils to support the replacement HGP phenotype and to serve as a surrogate biomarker for this subtype of CRCLM. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Novel insights into breast cancer copy number genetic heterogeneity revealed by single-cell genome sequencing

Copy number alterations (CNAs) play an important role in molding the genomes of breast cancers and have been shown to be clinically useful for prognostic and therapeutic purposes. However, our knowledge of intra-tumoral genetic heterogeneity of this important class of somatic alterations is limited. Here, using single-cell sequencing, we comprehensively map out the facets of copy number alteration heterogeneity in a cohort of breast cancer tumors. Ou/var/www/html/elife/12-05-2020/backup/r analyses reveal: genetic heterogeneity of non-tumor cells (i.e. stroma) within the tumor mass; the extent to which copy number heterogeneity impacts breast cancer genomes and the importance of both the genomic location and dosage of sub-clonal events; the pervasive nature of genetic heterogeneity of chromosomal amplifications; and the association of copy number heterogeneity with clinical and biological parameters such as polyploidy and estrogen receptor negative status. Our data highlight the power of single-cell genomics in dissecting, in its many forms, intra-tumoral genetic heterogeneity of CNAs, the magnitude with which CNA heterogeneity affects the genomes of breast cancers, and the potential importance of CNA heterogeneity in phenomena such as therapeutic resistance and disease relapse.

Molecular Insights Into Lysyl Oxidases in Cartilage Regeneration and Rejuvenation

Articular cartilage remains among the most difficult tissues to regenerate due to its poor self-repair capacity. The lysyl oxidase family (LOX; also termed as protein-lysine 6-oxidase), mainly consists of lysyl oxidase (LO) and lysyl oxidase-like 1-4 (LOXL1-LOXL4), has been traditionally defined as cuproenzymes that are essential for stabilization of extracellular matrix, particularly cross-linking of collagen and elastin. LOX is essential in the musculoskeletal system, particularly cartilage. LOXs-mediated collagen cross-links are essential for the functional integrity of articular cartilage. Appropriate modulation of the expression or activity of certain LOX members selectively may become potential promising strategy for cartilage repair. In the current review, we summarized the advances of LOX in cartilage homeostasis and functioning, as well as copper-mediated activation of LOX through hypoxia-responsive signaling axis during recent decades. Also, the molecular signaling network governing LOX expression has been summarized, indicating that appropriate modulation of hypoxia-responsive-signaling-directed LOX expression through manipulation of bioavailability of copper and oxygen is promising for further clinical implications of cartilage regeneration, which has emerged as a potential therapeutic approach for cartilage rejuvenation in tissue engineering and regenerative medicine. Therefore, targeted regulation of copper-mediated hypoxia-responsive signalling axis for selective modulation of LOX expression may become potential effective therapeutics for enhanced cartilage regeneration and rejuvenation in future clinical implications.

Basic and clinical associations between bone and cancer

Bone is one of the most common distant organs in which tumor cells tend to metastasize depending on complicated immune system and bone microenvironments. Clinical symptoms such as severe pain and bone fractures associated with bone metastases severely affect patients' quality of life. According to the pathological types of bone destruction caused by the biological characteristics of different primary cancer cells, bone metastases are classified as osteolytic, osteoblastic and mixed types. Herein, we discuss the molecular mechanisms of bone metastasis and the therapeutic strategy with focus on bone metabolism.

The Endosteal Niche in Breast Cancer Bone Metastasis

The establishment of bone metastasis remains one of the most frequent complications of patients suffering from advanced breast cancer. Patients with bone metastases experience high morbidity and mortality caused by excessive, tumor-induced and osteoclast-mediated bone resorption. Anti-resorptive treatments, such as bisphosphonates, are available to ease skeletal related events including pain, increased fracture risk, and hypercalcemia. However, the disease remains incurable and 5-year survival rates for these patients are below 25%. Within the bone, disseminated breast cancer cells localize in “metastatic niches,” special microenvironments that are thought to regulate cancer cell colonization and dormancy as well as tumor progression and subsequent development into overt metastases. Precise location and composition of this “metastatic niche” remain poorly defined. However, it is thought to include an “endosteal niche” that is composed of key bone cells that are derived from both, hematopoietic stem cells (osteoclasts), and mesenchymal stromal cells (osteoblasts, fibroblasts, adipocytes). Our knowledge of how osteoclasts drive the late stage of the disease is well-established. In contrast, much less is known about the interaction between osteogenic cells and disseminated tumor cells prior to the initiation of the osteolytic phase. Recent studies suggest that mesenchymal-derived cells, including osteoblasts and fibroblasts, play a key role during the early stages of breast cancer bone metastasis such as tumor cell homing, bone marrow colonization, and tumor cell dormancy. Hence, elucidating the interactions between breast cancer cells and mesenchymal-derived cells that drive metastasis progression could provide novel therapeutic approaches and targets to treat breast cancer bone metastasis. In this review we discuss evidences reporting the interaction between tumor cells and endosteal niche cells during the early stages of breast cancer bone metastasis, with a particular focus on mesenchymal-derived osteoblasts and fibroblasts.

Cross talk between oxidative stress and hypoxia via thioredoxin and HIF-2α drives metastasis of hepatocellular carcinoma

Oxidative stress and hypoxia are two opposite microenvironments involved in HCC metastasis. Thioredoxin (TXN) and hypoxia-inducible factor 2α (HIF-2α) are typical proteins involved in these two different microenvironments, respectively. How these two factors interact to influence the fate on tumor cells remains unknown. Hypoxia facilitated HCC cells withstood oxidative stress and eventually promoted HCC cells metastasis, in which TXN and HIF-2α were mostly involved. Upregulation of TXN/HIF-2α correlated with poor HCC prognosis and promoted HCC metastasis both in vitro and in vivo. Epithelial-mesenchymal transition (EMT) process was involved in TXN/HIF-2α-enhanced invasiveness of HCC cells. Additionally, the stability and activity of HIF-2α were precisely regulated by TXN via SUMOylation and acetylation, which contributed to HCC metastasis. Our data revealed that the redox protein TXN and HIF-2α are both associated with HCC metastasis, and the fine regulation of TXN on HIF-2α contributes essentially during the process of metastasis. Our study provides new insight into the interaction mechanism between hypoxia and oxidative stress and implies potential therapeutic benefits by targeting both TXN and HIF-2α in the treatment of HCC metastasis.

Desmoplasia and Biophysics in Pancreatic Ductal Adenocarcinoma: Can We Learn From Breast Cancer?

Pancreatic ductal adenocarcinoma (PDAC) treatments have historically focused on targeting tumor cells directly. However, in pancreatic masses, the stroma encasing the malignant epithelial cells constitutes up to 80% to 90% of the tumor bulk. This extracellular matrix, which was previously neglected when designing cancer therapies, is now considered fundamental for tumor progression and drug delivery. Desmoplastic tissue is extensively cross-linked, resulting in tremendous tensile strength. This key pathological feature is procarcinogenic, linking PDAC and breast cancer (BC). Physical forces exerted onto cellular surfaces are detected intracellularly and transduced via biochemical messengers in a process called mechanotransduction. Mechanotransduction and tensional homeostasis are linked, with an integral role in influencing tumor growth, metastasis, and interactions with the immune system. It is essential to enhance our knowledge of these integral elements of parenchymal tumors. We aim to review the topic, with a special emphasis on desmoplastic processes and their importance in pancreatic and BC development and treatments, mindful that innovative diagnostic and therapeutic strategies cannot focus on biochemical pathways alone. We then focus on common therapeutic targets identified in both PDAC and BC models and/or patients, aiming to understand these treatments and draw similarities between the two tumors.

Framing cancer progression: influence of the organ- and tumour-specific matrisome

The extracellular matrix (ECM) plays a crucial role in regulating organ homeostasis. It provides mechanical and biochemical cues directing cellular behaviour and, therefore, has control over the progression of diseases such as cancer. Recent efforts have greatly enhanced our knowledge of the protein composition of the ECM and its regulators, the so-called matrisome, in healthy and cancerous tissues; yet, an overview of the common signatures and organ-specific ECM in cancer is missing. Here, we address this by taking a detailed approach to review why cancer grows in certain organs, and focus on the influence of the matrisome at primary and metastatic tumour sites. Our in-depth and comprehensive review of the current literature and general understanding identifies important commonalities and distinctions, providing insight into the biology of metastasis, which could pave the way to improve future diagnostics and therapies.

Fluids and their mechanics in tumour transit: shaping metastasis

Metastasis is a dynamic succession of events involving the dissemination of tumour cells to distant sites within the body, ultimately reducing the survival of patients with cancer. To colonize distant organs and, therefore, systemically disseminate within the organism, cancer cells and associated factors exploit several bodily fluid systems, which provide a natural transportation route. Indeed, the flow mechanics of the blood and lymphatic circulatory systems can be co-opted to improve the efficiency of cancer cell transit from the primary tumour, extravasation and metastatic seeding. Flow rates, vessel size and shear stress can all influence the survival of cancer cells in the circulation and control organotropic seeding patterns. Thus, in addition to using these fluids as a means to travel throughout the body, cancer cells exploit the underlying physical forces within these fluids to successfully seed distant metastases. In this Review, we describe how circulating tumour cells and tumour-associated factors leverage bodily fluids, their underlying forces and imposed stresses during metastasis. As the contribution of bodily fluids and their mechanics raises interesting questions about the biology of the metastatic cascade, an improved understanding of this process might provide a new avenue for targeting cancer cells in transit.

Extracellular Vesicles From Osteotropic Breast Cancer Cells Affect Bone Resident Cells

Extracellular vesicles (EVs) are emerging as mediators of a range of pathological processes, including cancer. However, their role in bone metastases has been poorly explored. We investigated EV-mediated effects of osteotropic breast cancer cells (MDA-MB-231) on bone resident cells and endothelial cells. Pretreatment of osteoblasts with conditioned medium (CM) of MDA-MB-231 (MDA) cells promoted pro-osteoclastogenic and pro-angiogenic effects by osteoblast EVs (OB-EVs), as well as an increase of RANKL-positive OB-EVs. Moreover, when treating osteoblasts with MDA-EVs, we observed a reduction of their number, metabolic activity, and alkaline phosphatase (Alp) activity. MDA-EVs also reduced transcription of Cyclin D1 and of the osteoblast-differentiating genes, while enhancing the expression of the pro-osteoclastogenic factors Rankl, Lcn2, Il1b, and Il6. Interestingly, a cytokine array on CM from osteoblasts treated with MDA-EVs showed an increase of the cytokines CCL3, CXCL2, Reg3G, and VEGF, while OPG and WISP1 were downregulated. MDA-EVs contained mRNAs of genes involved in bone metabolism, as well as cytokines, including PDGF-BB, CCL3, CCL27, VEGF, and Angiopoietin 2. In line with this profile, MDA-EVs increased osteoclastogenesis and in vivo angiogenesis. Finally, intraperitoneal injection of MDA-EVs in mice revealed their ability to reach the bone microenvironment and be integrated by osteoblasts and osteoclasts. In conclusion, we showed a role for osteoblast-derived EVs and tumor cell-derived EVs in the deregulation of bone and endothelial cell physiology, thus fueling the vicious cycle induced by bone tumors. © 2019 American Society for Bone and Mineral Research.

GPER Activation Inhibits Cancer Cell Mechanotransduction and Basement Membrane Invasion via RhoA

The invasive properties of cancer cells are intimately linked to their mechanical phenotype, which can be regulated by intracellular biochemical signalling. Cell contractility, induced by mechanotransduction of a stiff fibrotic matrix, and the epithelial-mesenchymal transition (EMT) promote invasion. Metastasis involves cells pushing through the basement membrane into the stroma-both of which are altered in composition with cancer progression. Agonists of the G protein-coupled oestrogen receptor (GPER), such as tamoxifen, have been largely used in the clinic, and interest in GPER, which is abundantly expressed in tissues, has greatly increased despite a lack of understanding regarding the mechanisms which promote its multiple effects. Here, we show that specific activation of GPER inhibits EMT, mechanotransduction and cell contractility in cancer cells via the GTPase Ras homolog family member A (RhoA). We further show that GPER activation inhibits invasion through an in vitro basement membrane mimic, similar in structure to the pancreatic basement membrane that we reveal as an asymmetric bilayer, which differs in composition between healthy and cancer patients.

Low oxygen enhances trophoblast column growth by potentiating differentiation of the extravillous lineage and promoting LOX activity

Early placental development and the establishment of the invasive trophoblast lineage take place within a low oxygen environment. However, conflicting and inconsistent findings have obscured the role of oxygen in regulating invasive trophoblast differentiation. In this study, the effect of hypoxic, normoxic and atmospheric oxygen on invasive extravillous pathway progression was examined using a human placental explant model. Here, we show that exposure to low oxygen enhances extravillous column outgrowth and promotes the expression of genes that align with extravillous trophoblast (EVT) lineage commitment. By contrast, supra-physiological atmospheric levels of oxygen promote trophoblast proliferation while simultaneously stalling EVT progression. Low oxygen-induced EVT differentiation coincided with elevated transcriptomic levels of lysyl oxidase (LOX) in trophoblast anchoring columns, in which functional experiments established a role for LOX activity in promoting EVT column outgrowth. The findings of this work support a role for low oxygen in potentiating the differentiation of trophoblasts along the extravillous pathway. In addition, these findings generate insight into new molecular processes controlled by oxygen during early placental development.

Establishment and characterization of highly osteolytic luminal breast cancer cell lines by intracaudal arterial injection

Bone is one of the most common metastatic sites of breast cancer, and bone metastasis profoundly affects the quality of life of breast cancer patients. Bone metastasis is commonly observed among all the subtypes of breast cancer; however, its molecular mechanism has been analyzed only in triple-negative subtype of breast cancer (TNBC). To characterize the molecular mechanisms of bone metastasis of luminal breast cancer, we established a bone-metastatic model of the MCF7, luminal breast cancer cell line, with enhanced osteolytic activity by intracaudal arterial injection (CAI). Pathological analysis of the established cell lines revealed that they exhibited fierce osteolytic ability by promoting osteoclast differentiation and activity. The signature genes extracted from highly osteolytic MCF7 cell lines were differed from those of bone-metastatic TNBC cell lines. Our results suggest that unique mechanisms of osteolysis in bone-metastatic lesions of luminal breast cancer. In addition, several up-regulated genes in MCF7-BM (Bone Metastasis) 02 cell lines correlated with poor prognosis with luminal breast cancer patients. Our findings support further study on the bone-metastatic mechanisms of luminal breast cancer.