Controlling matrix stiffness and topography for the study of tumor cell migration

Cellular studies have long been performed on the bench top, within Petri dishes and flasks that expose cells to surroundings that differ greatly from their native environment. The complexity of a human tissue is such that to truly replicate a cell’s physiologic microenvironment in vitro is currently impossible. It is nevertheless important to determine how various factors of the microenvironment interact to drive cell behavior, particularly with regard to disease states, such as cancer. Here we focus on two key elements of the cellular microenvironment, matrix stiffness and architecture, in the context of tumor cell behavior. We discuss recent work focusing on the effects of these individual properties on cancer cell migration and describe one technique developed by our lab that could be applied to dissect the effects of specific structural and mechanical cues, and which may lead to useful insights into the potentially synergistic effects of these properties on tumor cell behavior.     

Acidic tumor microenvironment in human melanoma

One characteristic of solid tumors such as malignant melanoma is the acidification of the tumor microenvironment. The deregulation of cancer cell metabolism is considered a main cause of extracellular acidosis. Here, cancer cells utilize aerobic glycolysis instead of oxidative phosphorylation even under normoxic conditions, as originally described by Otto Warburg. These metabolic alterations cause enhanced acid production, especially of lactate and carbon dioxide (CO₂). The extensive production of acidic metabolites and the enhanced acid export to the extracellular space cause a consistent acidification of the tumor microenvironment, thus promoting the formation of an acid‐resistant tumor cell population with increased invasive and metastatic potential. As melanoma is one of the deadliest and most metastatic forms of cancer, understanding the effects of this extracellular acidosis on human melanoma cells with distinct metastatic properties is important. The aim of this review was to summarize recent studies of the acidification of the tumor microenvironment, focusing on the specific effects of the acidic milieu on melanoma cells and to give a short overview of therapeutic approaches.     

The role of the microenvironment in tumor growth and invasion

Mathematical modeling and computational analysis are essential for understanding the dynamics of the complex gene networks that control normal development and homeostasis, and can help to understand how circumvention of that control leads to abnormal outcomes such as cancer. Our objectives here are to discuss the different mechanisms by which the local biochemical and mechanical microenvironment, which is comprised of various signaling molecules, cell types and the extracellular matrix (ECM), affects the progression of potentially-cancerous cells, and to present new results on two aspects of these effects. We first deal with the major processes involved in the progression from a normal cell to a cancerous cell at a level accessible to a general scientific readership, and we then outline a number of mathematical and computational issues that arise in cancer modeling. In Section 2 we present results from a model that deals with the effects of the mechanical properties of the environment on tumor growth, and in Section 3 we report results from a model of the signaling pathways and the tumor microenvironment (TME), and how their interactions affect the development of breast cancer. The results emphasize anew the complexities of the interactions within the TME and their effect on tumor growth, and show that tumor progression is not solely determined by the presence of a clone of mutated immortal cells, but rather that it can be ‘community-controlled’.     

Exosomes Derived from Mesenchymal Stem Cells Suppress Angiogenesis by Down-Regulating VEGF Expression in Breast Cancer Cells

Exosomes are small membrane vesicles released by a variety of cell types. Exosomes contain genetic materials, such as mRNAs and microRNAs (miRNAs), implying that they may play a pivotal role in cell-to-cell communication. Mesenchymal stem cells (MSCs), which potentially differentiate into multiple cell types, can migrate to the tumor sites and have been reported to exert complex effects on tumor progression. To elucidate the role of MSCs within the tumor microenvironment, previous studies have suggested various mechanisms such as immune modulation and secreted factors of MSCs. However, the paracrine effects of MSC-derived exosomes on the tumor microenvironment remain to be explored. The hypothesis of this study was that MSC-derived exosomes might reprogram tumor behavior by transferring their molecular contents. To test this hypothesis, exosomes from MSCs were isolated and characterized. MSC-derived exosomes exhibited different protein and RNA profiles compared with their donor cells and these vesicles could be internalized by breast cancer cells. The results demonstrated that MSC-derived exosomes significantly down-regulated the expression of vascular endothelial growth factor (VEGF) in tumor cells, which lead to inhibition of angiogenesis in vitro and in vivo. Additionally, miR-16, a miRNA known to target VEGF, was enriched in MSC-derived exosomes and it was partially responsible for the anti-angiogenic effect of MSC-derived exosomes. The collective results suggest that MSC-derived exosomes may serve as a significant mediator of cell-to-cell communication within the tumor microenvironment and suppress angiogenesis by transferring anti-angiogenic molecules.     

The extracellular matrix: a dynamic niche in cancer progression

The local microenvironment, or niche, of a cancer cell plays important roles in cancer development. A major component of the niche is the extracellular matrix (ECM), a complex network of macromolecules with distinctive physical, biochemical, and biomechanical properties. Although tightly controlled during embryonic development and organ homeostasis, the ECM is commonly deregulated and becomes disorganized in diseases such as cancer. Abnormal ECM affects cancer progression by directly promoting cellular transformation and metastasis. Importantly, however, ECM anomalies also deregulate behavior of stromal cells, facilitate tumor-associated angiogenesis and inflammation, and thus lead to generation of a tumorigenic microenvironment. Understanding how ECM composition and topography are maintained and how their deregulation influences cancer progression may help develop new therapeutic interventions by targeting the tumor niche.     

Heterotypic signaling between epithelial tumor cells and fibroblasts in carcinoma formation

Tumors arise from cells that have sustained genetic mutations resulting in deregulation of several of their normal growth-controlling mechanisms. Much of the research concerning the origins of cancer has focused on the genetic mutations within tumor cells, treating tumorigenesis as a cell-autonomous process governed by the genes carried by the tumor cells themselves. However, it is increasingly apparent that the stromal microenvironment in which the tumor cells develop profoundly influences many steps of tumor progression. In various experimental tumor models, the microenvironment affects the efficiency of tumor formation, the rate of tumor growth, the extent of invasiveness, and the ability of tumor cells to metastasize. In carcinomas, the influences of the microenvironment are mediated, in large part, by paracrine signaling between epithelial tumor cells and neighboring stromal fibroblasts. In this review, we summarize recent advances in understanding the paracrine signaling interactions between epithelial cancer cells and associated fibroblasts and examine the effects of these bidirectional interactions on various aspects of carcinoma formation. We note, however, that paracrine signaling between other cell types within the carcinomas, such as endothelial cells and inflammatory cells, may play equally important roles in tumor formation and we will refer to these heterotypic interactions where relevant.     

Regulation of tumor invasion by interstitial fluid flow

The importance of the tumor microenvironment in cancer progression is undisputed, yet the significance of biophysical forces in the microenvironment remains poorly understood. Interstitial fluid flow is a nearly ubiquitous and physiologically relevant biophysical force that is elevated in tumors because of tumor-associated angiogenesis and lymphangiogenesis, as well as changes in the tumor stroma. Not only does it apply physical forces to cells directly, but interstitial flow also creates gradients of soluble signals in the tumor microenvironment, thus influencing cell behavior and modulating cell-cell interactions. In this paper, we highlight our current understanding of interstitial fluid flow in the context of the tumor, focusing on the physical changes that lead to elevated interstitial flow, how cells sense flow and how they respond to changes in interstitial flow. In particular, we emphasize that interstitial flow can directly promote tumor cell invasion through a mechanism known as autologous chemotaxis, and indirectly support tumor invasion via both biophysical and biochemical cues generated by stromal cells. Thus, interstitial fluid flow demonstrates how important biophysical factors are in cancer, both by modulating cell behavior and coupling biophysical and biochemical signals.     

Nonlinear simulation of the effect of microenvironment on tumor growth

In this paper, we present and investigate a model for solid tumor growth that incorporates features of the tumor microenvironment. Using analysis and nonlinear numerical simulations, we explore the effects of the interaction between the genetic characteristics of the tumor and the tumor microenvironment on the resulting tumor progression and morphology. We find that the range of morphological responses can be placed in three categories that depend primarily upon the tumor microenvironment: tissue invasion via fragmentation due to a hypoxic microenvironment; fingering, invasive growth into nutrient rich, biomechanically unresponsive tissue; and compact growth into nutrient rich, biomechanically responsive tissue. We found that the qualitative behavior of the tumor morphologies was similar across a broad range of parameters that govern the tumor genetic characteristics. Our findings demonstrate the importance of the impact of microenvironment on tumor growth and morphology and have important implications for cancer therapy. In particular, if a treatment impairs nutrient transport in the external tissue (e.g., by anti-angiogenic therapy) increased tumor fragmentation may result, and therapy-induced changes to the biomechanical properties of the tumor or the microenvironment (e.g., anti-invasion therapy) may push the tumor in or out of the invasive fingering regime.     

Embryonic stem-cell-preconditioned microenvironment induces loss of cancer cell properties in human melanoma cells

The cancer microenvironment affects cancer cell proliferation and growth. Embryonic stem (ES)-preconditioned 3-dimensional (3-D) culture of cancer cells induces cancer cell reprogramming and results in a change in cancer cell properties such as differentiation and migration in skin melanoma. However, the mechanism has not yet been clarified. Using the ES-preconditioned 3-D microenvironment model, we provide evidence showing that the ES microenvironment inhibits proliferation and anchorage-independent growth of SK-MEL-28 melanoma cells. We also found that the ES microenvironment suppresses telomerase activity and thereby induces senescence in SK-MEL-28 cells. Furthermore, we observed that gremlin, an antagonist of BMP4, is secreted from ES cells and plays an important role in cellular senescence. Knocking down gremlin in the ES microenvironment increases proliferation and anchorage-independent growth of SK-MEL-28 melanoma cells. Taken together, these results demonstrated that gremlin is a crucial factor responsible for abrogating melanoma properties in the ES-preconditioned 3-D microenvironment.     

Effect of mesenchymal stem cells-derived exosomes on tumor microenvironment: Tumor progression versus tumor suppression

Mesenchymal stem cells (MSCs) are multipotent cells with the potential to differentiate into different cell types. Owing to their immunosuppressive and anti-inflammatory properties, they are widely used in regenerative medicine, but they have a dual effect on cancer progression and exert both growth-stimulatory or -inhibitory effects on different cancer types. It has been proposed that these controversial effects of MSC in tumor microenvironment (TME) are mediated by their polarization to proinflammatory or anti-inflammatory phenotype. In addition, they can polarize the immune system cells that in turn influence tumor progression. One of the mechanisms involved in the TME communications is extracellular vesicles (EVs). MSCs, as one of cell populations in TME, produce a large amount of EVs that can influence tumor development. Similar to MSC, MSC-EVs can exert both anti- or protumorigenic effects. In the current study, we will investigate the current knowledge related to MSC role in cancer progression with a focus on the MSC-EV content in limiting tumor growth, angiogenesis, and metastasis. We suppose MSC-EVs can be used as safe vehicles for delivering antitumor agents to TME.     

Plumbagin inhibits breast tumor bone metastasis and osteolysis by modulating the tumor-bone microenvironment

Bone metastasis is a common and serious consequence of breast cancer. Bidirectional interaction between tumor cells and the bone marrow microenvironment drives a so-called 'vicious cycle' that promotes tumor cell malignancy and stimulates osteolysis. Targeting these interactions and pathways in the tumor-bone microenvironment has been an encouraging strategy for bone metastasis therapy. In the present study, we examined the effects of plumbagin on breast cancer bone metastasis. Our data indicated that plumbagin inhibited cancer cell migration and invasion, suppressed the expression of osteoclast-activating factors, altered the cancer cell induced RANKL/OPG ratio in osteoblasts, and blocked both cancer cell- and RANKL-stimulated osteoclastogenesis. In mouse model of bone metastasis, we further demonstrated that plumbagin significantly repressed breast cancer cell metastasis and osteolysis, inhibited cancer cell induced-osteoclastogenesis and the secretion of osteoclast-activating factors in vivo. At the molecular level, we found that plumbagin abrogated RANKL-induced NF-κB and MAPK pathways by blocking RANK association with TRAF6 in osteoclastogenesis, and by inhibiting the expression of osteoclast-activating factors through the suppression of NF-κB activity in breast cancer cells. Taken together, our data demonstrate that plumbagin inhibits breast tumor bone metastasis and osteolysis by modulating the tumor-bone microenvironment and that plumbagin may serve as a novel agent in the treatment of tumor bone metastasis.     

基质力学对肿瘤发生发展及肿瘤细胞生物学行为影响的研究进展

实体瘤的发生发展常伴随着细胞外基质的异常沉积、交联和基质刚度增加.基质刚度增加和肿瘤细胞软化引起肿瘤微环境的力学异质性.基质力学通过影响肿瘤细胞的增殖、迁移、转移、上皮间质转换、肿瘤干细胞特性和耐药性等调控肿瘤的发生、恶性转变和转移.研究基质力学对肿瘤发生发展的影响不仅可深化对肿瘤发展的认识,也可为研究新的诊治方法提供理论基础.本文论述了细胞外基质力学特性对肿瘤发生发展及肿瘤细胞生物学行为影响的研究进展,并展望了其发展前景.     

Cancer cells stemness: A doorstep to targeted therapy

Recent advances in research on cancer have led to understand the pathogenesis of cancer and development of new anticancer drugs. Despite of these advancements, many tumors have been found to recur, undergo metastasis and develop resistance to therapy. Accumulated evidences suggest that small population of cancer cells known as cancer stem cells (CSC) are responsible for reconstitution and propagation of the disease. CSCs possess the ability to self-renew, differentiate and proliferate like normal stem cells. CSCs also appear to have resistance to anti-cancer therapies and subsequent relapse. The underlying stemness properties of the CSCs are reliant on multiple molecular targets such as signaling pathways, cell surface molecules, tumor microenvironment, apoptotic pathways, microRNA, stem cell differentiation, and drug resistance markers. Thus an effective therapeutic strategy relies on targeting CSCs to overcome the possible tumor relapse and chemoresistance. The targeted inhibition of these stem cell biomarkers is one of the promising approaches to eliminate cancer stemness. This review article summarizes possible targets of cancer cell stemness for the complete treatment of cancer.     

Blocking αvβ3 integrin by a recombinant RGD disintegrin impairs VEGF signaling in endothelial cells

Vascular endothelial growth factor (VEGF) and αvβ3 integrin are key molecules that actively participate in tumor angiogenesis and metastasis. Some integrin-blocking molecules are currently under clinical trials for cancer and metastasis treatment. However, the mechanism of action of such inhibitors is not completely understood. We have previously demonstrated the anti-angiogenic and anti-metastatic properties of DisBa-01, a recombinant His-tag RGD-disintegrin from Bothrops alternatus snake venom in some experimental models. DisBa-01 blocks αvβ3 integrin binding to vitronectin and inhibits integrin-mediated downstream signaling cascades and cell migration. Here we add some new information on the mechanism of action of DisBa-01 in the tumor microenvironment. DisBa-01 supports the adhesion of fibroblasts and MDA-MB-231 breast cancer cells but it inhibits the adhesion of these cells to type I collagen under flow in high shear conditions, as a simulation of the blood stream. DisBa-01 does not affect the release of VEGF by fibroblasts or breast cancer cells but it strongly decreases the expression of VEGF mRNA and of its receptors, vascular endothelial growth factor receptors 1 and 2 (VEGFR1 and VEGFR2) in endothelial cells. DisBa-01 at nanomolar concentrations also modulates metalloprotease 2 (MMP-2) and 9 (MMP-9) activity, the latter being decreased in fibroblasts and increased in MDA-MB-231 cells. In conclusion, these results demonstrate that αvβ3 integrin inhibitors may induce distinct effects in the cells of the tumor microenvironment, resulting in blockade of angiogenesis by impairing of VEGF signaling and in inhibition of tumor cell motility.     

Blocking ovarian cancer progression by targeting tumor microenvironmental leukocytes

Current therapies for metastatic ovarian carcinoma are based on surgical debulking followed by chemotherapy. After more than three decades implementing treatments that selectively target the tumor cell, the 5-year survival rate for metastatic ovarian cancer patients is still lower than 30%. Novel strategies are therefore urgently needed to complement classical treatments for this malignancy. Recently, leukocytes in the ovarian cancer microenvironment such as regulatory T cells and immature pro-angiogenic/tolerogenic myeloid cells have been demonstrated to play a fundamental role in tumor progression. This review focuses on our recent understanding of the potential of eliminating and/or modulating the phenotype of these leukocytes in vivo and in situ as a novel intervention to complement standard ovarian cancer treatments. The significant effects of targeting these crucial microenvironmental players on cancer vascularization, local tumor growth, distal metastatic spreading and spontaneous anti-tumor immune responses are discussed.     

肿瘤酸性微环境的研究进展

研究表明,肿瘤转移是恶性肿瘤的临床治疗失败的根本原因。肿瘤转移不仅取决于肿瘤细胞自身的特性,还涉及其与肿瘤酸性微环境之间的相互作用。肿瘤微环境构成非常复杂,可促进肿瘤的增生、转移、侵袭,以及逃避宿主免疫监视和治疗耐药性。肿瘤细胞的生存依赖于在酸性微环境条件下的适应,肿瘤细胞可以通过一些离子交换体维持酸性微环境,缺氧的肿瘤组织酸化可以释放蛋白酶如纤维蛋白酶及MMPs降解细胞外基质、上调VEGF基因表达促进肿瘤新生血管生成等促进肿瘤侵袭转移。近年来,影响肿瘤微环境的因素已经成为癌症研究领域中的新兴话题。