Integrins can directly mediate metastatic tumor cell adhesion within the liver sinusoids

Dormancy in Metastatic Colorectal Cancer: Tissue Engineering Opportunities for In Vitro Modeling

Colorectal cancer (CRC) recurs at a striking rate, specifically in patients with liver metastasis. Dormant CRC cells disseminated following initial primary tumor resection or treatment often resurface years later to form aggressive, therapy-resistant tumors that result in high patient mortality. Routine imaging-based screenings often fail to detect dormant cancer cell clusters, and there are no overt symptomatic presentations, making dormant CRC a major clinical challenge to diagnose and treat. Tissue engineering approaches are ideally suited to model dormant cancer cells and enable the discovery of therapeutic vulnerabilities or unique mechanistic dependencies of dormant CRC. Emerging evidence suggests that tissue-engineered approaches have been successfully used to model dormant breast and lung cancer. With CRC responsible for the second most cancer-related deaths worldwide and CRC patients commonly experiencing recurrence, it is essential to expand dormancy models to understand this phenomenon in the context of CRC. Most published in vitro models of CRC dormancy simplify the complex tumor microenvironment with two-dimensional culture systems to elucidate dormancy-driving mechanisms. Building on this foundation, future research should apply tissue engineering methods to this growing field to generate competent three-dimensional models and increase mechanistic knowledge. This review summarizes the current state of in vitro CRC dormancy models, highlighting the techniques utilized to give rise to dormant CRC cells: nutrient depletion, anticancer drugs, physical extracellular matrix interactions, and genetic manipulation. The metrics used to validate dormancy within each model are also consolidated to demonstrate the lack of established standards and the ambiguity around comparing studies that have been validated differently. The methods of these studies are organized in this review to increase comprehensibility and identify needs and opportunities for future bioengineered in vitro models to address dormancy-driven mortality in patients with CRC liver metastasis. Impact Statement Dormant cancer drives high patient mortality, especially in metastatic colorectal cancer, owing to the clinical inability to identify dormant cells prior to their overt recurrence. Lacking clinical insights, in vitro modeling for mechanistic and therapeutic discovery is hindered. Here, we review models and methods of inducing colorectal cancer dormancy with the goal of consolidating findings for reference. We also highlight the need for advanced, tissue-engineered models to better mimic the organ-specific 3D microenvironment of metastatic colorectal cancer. New models would enable breakthroughs in understanding mechanisms driving dormancy progression and reversal, thereby providing context for therapeutic advances to improve patient survival.

Roles of Integrins in Gastrointestinal Cancer Metastasis

Integrins are a large family of heterodimeric transmembrane receptors which mediate cell adhesion and transmit signals to the cell interior. The mechanistic roles of integrins have long been an enigma in cancer, given its complexity in regulating different cellular behaviors. Recently, however, increasing research is providing new insights into its function and the underlying mechanisms, which collectively include the influences of altered integrin expression on the aberrant signaling pathways and cancer progression. Many studies have also demonstrated the potentiality of integrins as therapeutic targets in cancer treatment. In this review, we have summarized these recent reports and put a particular emphasis on the dysregulated expression of integrins and how they regulate related signaling pathways to facilitate the metastatic progression of gastrointestinal cancer, including gastric cancer (GC) and colorectal cancer (CRC), which will address the crucial roles of integrins in gastrointestinal cancer.

Chemotherapy-Induced Changes in the Lung Microenvironment: The Role of MMP-2 in Facilitating Intravascular Arrest of Breast Cancer Cells

Previously, we showed that mice treated with cyclophosphamide (CTX) 4 days before intravenous injection of breast cancer cells had more cancer cells in the lung at 3 h after cancer injection than control counterparts without CTX. At 4 days after its injection, CTX is already excreted from the mice, allowing this pre-treatment design to reveal how CTX may modify the lung environment to indirectly affect cancer cells. In this study, we tested the hypothesis that the increase in cancer cell abundance at 3 h by CTX is due to an increase in the adhesiveness of vascular wall for cancer cells. Our data from protein array analysis and inhibition approach combined with in vitro and in vivo assays support the following two-prong mechanism. (1) CTX increases vascular permeability, resulting in the exposure of the basement membrane (BM). (2) CTX increases the level of matrix metalloproteinase-2 (MMP-2) in mouse serum, which remodels the BM and is functionally important for CTX to increase cancer abundance at this early stage. The combined effect of these two processes is the increased accessibility of critical protein domains in the BM, resulting in higher vascular adhesiveness for cancer cells to adhere. The critical protein domains in the vascular microenvironment are RGD and YISGR domains, whose known binding partners on cancer cells are integrin dimers and laminin receptor, respectively.

Platelet-Cancer Interplay: Molecular Mechanisms and New Therapeutic Avenues

Although platelets are critically involved in thrombosis and hemostasis, experimental and clinical evidence indicate that platelets promote tumor progression and metastasis through a wide range of physical and functional interactions between platelets and cancer cells. Thrombotic and thromboembolic events are frequent complications in patients with solid tumors. Hence, cancer modulates platelet function by directly inducing platelet-tumor aggregates and triggering platelet granule release and altering platelet turnover. Also, platelets enhance tumor cell dissemination by activating endothelial cell function and recruiting immune cells to primary and metastatic tumor sites. In this review, we summarize current knowledge on the complex interactions between platelets and tumor cells and the host microenvironment. We also critically discuss the potential of anti-platelet agents for cancer prevention and treatment.

The liver metastatic niche: modelling the extracellular matrix in metastasis

Dissemination of malignant cells from primary tumours to metastatic sites is a key step in cancer progression. Disseminated tumour cells preferentially settle in specific target organs, and the success of such metastases depends on dynamic interactions between cancer cells and the microenvironments they encounter at secondary sites. Two emerging concepts concerning the biology of metastasis are that organ-specific microenvironments influence the fate of disseminated cancer cells, and that cancer cell-extracellular matrix interactions have important roles at all stages of the metastatic cascade. The extracellular matrix is the complex and dynamic non-cellular component of tissues that provides a physical scaffold and conveys essential adhesive and paracrine signals for a tissue's function. Here, we focus on how extracellular matrix dynamics contribute to liver metastases - a common and deadly event. We discuss how matrix components of the healthy and premetastatic liver support early seeding of disseminated cancer cells, and how the matrix derived from both cancer and liver contributes to the changes in niche composition as metastasis progresses. We also highlight the technical developments that are providing new insights into the stochastic, dynamic and multifaceted roles of the liver extracellular matrix in permitting and sustaining metastasis. An understanding of the contribution of the extracellular matrix to different stages of metastasis may well pave the way to targeted and effective therapies against metastatic disease.

The fibrotic and immune microenvironments as targetable drivers of metastasis

Although substantial progress has been made over the past 40 years in treating patients with cancer, effective therapies for those who are diagnosed with advanced metastatic disease are still few and far between. Cancer cells do not exist in isolation: rather, they exist within a complex microenvironment composed of stromal cells and extracellular matrix. Within this tumour microenvironment exists an interplay between the two main stromal cell subtypes, cancer-associated fibroblasts (CAFs) and immune cells, that are important in controlling metastasis. A complex network of paracrine signalling pathways between CAFs, immune cells and tumour cells are involved at multiple stages of the metastatic process, from invasion and intravasation at the primary tumour site to extravasation and colonisation in the metastatic site. Heterogeneity and plasticity within stromal cell populations also contribute to the complexity. Although many of these processes are likely to be common to a number of metastatic sites, we will describe in detail the interplay within the liver, a preferred site of metastasis for many tumours. A greater understanding of these networks provides opportunities for the design of new therapeutic approaches for targeting the metastatic disease.

The contribution of platelets to intravascular arrest, extravasation, and outgrowth of disseminated tumor cells

Platelets are primarily known for their contribution to hemostasis and subsequent wound healing. In addition to these functions, platelets play a role in the process of metastasis. Since the first study that suggested a metastasis-promoting function for platelets was published in 1968, various mechanisms have been proposed to explain how platelets contribute to the metastatic process. These include roles in the intravascular arrest of tumor cells, in tumor cell transendothelial migration, in the degradation of basement membrane barriers, in migration and invasion at the metastatic site, and in the proliferation of disseminated tumor cells. Nevertheless, conflicting observations about the role of platelets in these processes have also been reported. Here, we review the in vivo evidence that supports a role for platelets in metastasis formation, propose several scenarios for the contribution of platelets to tumor cell arrest and transendothelial migration, and discuss the evidence that platelets contribute to metastatic invasion and outgrowth.

Hemodynamic Forces Tune the Arrest, Adhesion, and Extravasation of Circulating Tumor Cells

Metastatic seeding is driven by cell-intrinsic and environmental cues, yet the contribution of biomechanics is poorly known. We aim to elucidate the impact of blood flow on the arrest and the extravasation of circulating tumor cells (CTCs) in vivo. Using the zebrafish embryo, we show that arrest of CTCs occurs in vessels with favorable flow profiles where flow forces control the adhesion efficacy of CTCs to the endothelium. We biophysically identified the threshold values of flow and adhesion forces allowing successful arrest of CTCs. In addition, flow forces fine-tune tumor cell extravasation by impairing the remodeling properties of the endothelium. Importantly, we also observe endothelial remodeling at arrest sites of CTCs in mouse brain capillaries. Finally, we observed that human supratentorial brain metastases preferably develop in areas with low perfusion. These results demonstrate that hemodynamic profiles at metastatic sites regulate key steps of extravasation preceding metastatic outgrowth.

RGD cadherins and α2β1 integrin in cancer metastasis: A dangerous liaison

We propose a new cadherin family classification comprising epithelial cadherins (cadherin 17 [CDH17], cadherin 16, VE-cadherin, cadherin 6 and cadherin 20) containing RGD motifs within their sequences. Expression of some RGD cadherins is associated with aggressive forms of cancer during the late stages of metastasis, and CDH17 and VE-cadherin have emerged as critical actors in cancer metastasis. After binding to α2β1 integrin, these cadherins promote integrin β1 activation, and thereby cell adhesion, invasion and proliferation, in liver and lung metastasis. Activation of α2β1 integrin provokes an affinity increase for type IV collagen, a major component of the basement membrane and a critical partner for cell anchoring in liver and other metastatic organs. Activation of α2β1 integrin by RGD motifs breaks an old paradigm of integrin classification and supports an important role of this integrin in cancer metastasis. Recently, synthetic peptides containing the RGD motif of CDH17 elicited highly specific and selective antibodies that block the ability of CDH17 RGD to activate α2β1 integrin. These monoclonal antibodies inhibit metastatic colonization in orthotopic mouse models of liver and lung metastasis for colorectal cancer and melanoma, respectively. Hopefully, blocking the cadherin RGD ligand capacity will give us control over the integrin activity in solid tumors metastasis, paving the way for development of new agents of cancer treatment.

Simulation of blood and oxygen distributions in a hepatic lobule with sinusoids obstructed by cancer cells

The liver is one of the common metastatic sites for many cancers. The obstruction of sinusoids by circulating tumor cells changes liver microenvironments and is thus considered a source of hepatic metastases. To date, few studies provide detailed information, either experimentally or theoretically, concerning the changes in blood and oxygen distributions induced by the obstruction of sinusoids. In this study, we utilized a 3D porous medium-vascular tree geometric structure to mimic the hepatic lobule and studied theoretical blood flow and oxygen transport in the lobule. The simulation was validated with data from the literature. Then, the distributions of blood and oxygen in the presence of the obstruction by cancer cells were simulated. The area and degree of the liver damage induced by the obstruction were analyzed by comparing the difference of liver microenvironments between physiological (non-blocked sinusoid) and pathological (fully or partially blocked sinusoid) conditions and the minimum cancer cell sizes causing liver damage for various obstruction positions were obtained. The work presented in this study can be used to predict the degree of liver damage induced by the local ischemia caused by the obstruction of sinusoids and to characterize the relationship between hepatic metastases and liver microenvironments.

Biomechanics of the Circulating Tumor Cell Microenvironment

Circulating tumor cells (CTCs) exist in a microenvironment quite different from the solid tumor tissue microenvironment. They are detached from matrix and exposed to the immune system and hemodynamic forces leading to the conclusion that life as a CTC is "nasty, brutish, and short." While there is much evidence to support this assertion, the mechanisms underlying this are much less clear. In this chapter we will specifically focus on biomechanical influences on CTCs in the circulation and examine in detail the question of whether CTCs are mechanically fragile, a commonly held idea that is lacking in direct evidence. We will review multiple lines of evidence indicating, perhaps counterintuitively, that viable cancer cells are mechanically robust in the face of exposures to physiologic shear stresses that would be encountered by CTCs during their passage through the circulation. Finally, we present emerging evidence that malignant epithelial cells, as opposed to their benign counterparts, possess specific mechanisms that enable them to endure these mechanical stresses.

Monoclonal Antibodies Directed against Cadherin RGD Exhibit Therapeutic Activity against Melanoma and Colorectal Cancer Metastasis

Purpose: New targets are required for the control of advanced metastatic disease. We investigated the use of cadherin RGD motifs, which activate the α2β1integrin pathway, as targets for the development of therapeutic monoclonal antibodies (mAb).Experimental Design: Cadherin 17 (CDH17) fragments and peptides were prepared and used for immunization and antibody development. Antibodies were tested for inhibition of β1 integrin and cell adhesion, proliferation, and invasion assays using cell lines from different cancer types (colorectal, pancreatic, melanoma, and breast cancer). Effects of the mAbs on cell signaling were determined by Western blot analysis. Nude mice were used for survival analysis after treatment with RGD-specific mAbs and metastasis development.Results: Antibodies against full-length CDH17 failed to block the binding to α2β1 integrin. However, CDH17 RGD peptides generated highly selective RGD mAbs that blocked CDH17 and vascular-endothelial (VE)-cadherin-mediated β1 integrin activation in melanoma and breast, pancreatic, and colorectal cancer cells. Antibodies provoked a significant reduction in cell adhesion and proliferation of metastatic cancer cells. Treatment with mAbs impaired the integrin signaling pathway activation of FAK in colorectal cancer, of JNK and ERK kinases in colorectal and pancreatic cancers, and of JNK, ERK, Src, and AKT in melanoma and breast cancer. In vivo, RGD-specific mAbs increased mouse survival after inoculation of melanoma and colorectal cancer cell lines to cause lung and liver metastasis, respectively.Conclusions: Blocking the interaction between RGD cadherins and α2β1 integrin with highly selective mAbs constitutes a promising therapy against advanced metastatic disease in colon cancer, melanoma, and, potentially, other cancers. Clin Cancer Res; 24(2); 433-44. ©2017 AACRSee related commentary by Marshall, p. 253.

Amigo2-upregulation in Tumour Cells Facilitates Their Attachment to Liver Endothelial Cells Resulting in Liver Metastases

Since liver metastasis is the main cause of death in cancer patients, we attempted to identify the driver gene involved. QRsP-11 fibrosarcoma cells were injected into the spleens of syngeneic mice to isolate tumour sub-populations that colonize the liver. Cells from liver metastatic nodules were established and subsequently injected intrasplenically for selection. After 12 cycles, the cell subline LV12 was obtained. Intravenous injection of LV12 cells produced more liver metastases than QRsP-11 cells, whereas the incidence of lung metastases was similar to that of QRsP-11 cells. LV12 cells adhered to liver-derived but not to lung-derived endothelial cells. DNA chip analysis showed that amphoterin-induced gene and open reading frame 2 (Amigo2) was overexpressed in LV12 cells. siRNA-mediated knockdown of Amigo2 expression in LV12 cells attenuated liver endothelial cell adhesion. Ex vivo imaging showed that suppression of Amigo2 in luciferase-expressing LV12 cells reduced attachment/metastasis to liver to the same level as that observed with QRsP-11 cells. Forced expression of Amigo2 in QRsP-11 cells increased liver endothelial cell adhesion and liver metastasis. Additionally, Amigo2 expression in human cancers was higher in liver metastatic lesions than in primary lesions. Thus, Amigo2 regulated tumour cell adhesion to liver endothelial cells and formation of liver metastases.

Metastasis of circulating tumor cells: favorable soil or suitable biomechanics, or both?

Metastasis is the end product of a multistep process where cancer cells disseminate and home themselves in distant organs. Tumor cell extravasation is a rare, inefficient and transient event in nature and makes its studies very difficult. Noteworthy, little is known about how cancer cells arrest, adhere and pass through the endothelium of capillaries. Moreover, the key events driving metastatic growth in specific organs are not well understood. Thus, although metastasis is the leading cause of cancer-related death, how cancer cells acquire their abilities to colonize distant organs and why they do so in specific locations remain central questions in the understanding of this deadly disease. In this review, we would like to confront 2 concepts explaining the efficiency and location of metastatic secondary tumors. While the "seed and soil" hypothesis states that metastasis occurs at sites where the local microenvironment is favorable, the "mechanical" concept argues that metastatic seeding occurs at sites of optimal flow patterns. In addition, recent evidence suggests that the primary event driving tumor cell arrest before extravasation is mostly controlled by blood circulation patterns as well as mechanical cues during the process of extravasation. In conclusion, the organ tropism displayed by cancer cells during metastatic colonization is a multi-step process, which is regulated by the delivery and survival of circulating tumor cells (CTCs) through blood circulation, the ability of these CTCs to adhere and cross the physical barrier imposed by the endothelium and finally by the suitability of the soil to favor growth of secondary tumors.

Virgin olive oil phenolics extract inhibit invasion of HT115 human colon cancer cells in vitro and in vivo

The decreased cancer risk associated with consumption of olive oil may be due to the presence of phenolics which can modulate pathways including apoptosis and invasion that are relevant to carcinogenesis. We have previously shown that a virgin olive oil phenolics extract (OVP) inhibited invasion of HT115 colon cancer cells in vitro. In the current study we assessed the in vitro effects of OVP (25 μg mL(-1)) on HT115 cell migration, spreading and integrin expression. Furthermore, the anti-metastatic activity of OVP - at a dose equivalent to 25 mg per kg per day for 2, 8 or 10 weeks - was assessed in a Severe Combined ImmunoDeficiency (SCID) Balb-c mouse model. After 24 h OVP did not inhibit cell migration but significantly reduced cell spreading on fibronectin (65% of control; p < 0.05) and expression of a range of α and β integrins was modulated. In vivo, OVP by gavage significantly (p < 0.05) decreased not only tumour volume but also the number of metastases in SCID Balb-c mice. Collectively, the data suggest that - possibly through modulation of integrin expression - OVP decreases invasion in vitro and also inhibits metastasis in vivo.

Natural history of hepatic metastases from colorectal cancer - pathobiological pathways with clinical significance

Colorectal cancer hepatic metastases represent the final stage of a multi-step biological process. This process starts with a series of mutations in colonic epithelial cells, continues with their detachment from the large intestine, dissemination through the blood and/or lymphatic circulation, attachment to the hepatic sinusoids and interactions with the sinusoidal cells, such as sinusoidal endothelial cells, Kupffer cells, stellate cells and pit cells. The metastatic sequence terminates with colorectal cancer cell invasion, adaptation and colonisation of the hepatic parenchyma. All these events, termed the colorectal cancer invasion-metastasis cascade, include multiple molecular pathways, intercellular interactions and expression of a plethora of chemokines and growth factors, and adhesion molecules, such as the selectins, the integrins or the cadherins, as well as enzymes including matrix metalloproteinases. This review aims to present recent advances that provide insights into these cell-biological events and emphasizes those that may be amenable to therapeutic targeting.

Investigation of the essential role of platelet-tumor cell interactions in metastasis progression using an agent-based model

BACKGROUND

Metastatic tumors are a major source of morbidity and mortality for most cancers. Interaction of circulating tumor cells with endothelium, platelets and neutrophils play an important role in the early stages of metastasis formation. These complex dynamics have proven difficult to study in experimental models. Prior computational models of metastases have focused on tumor cell growth in a host environment, or prediction of metastasis formation from clinical data. We used agent-based modeling (ABM) to dynamically represent hypotheses of essential steps involved in circulating tumor cell adhesion and interaction with other circulating cells, examine their functional constraints, and predict effects of inhibiting specific mechanisms.

METHODS

We developed an ABM of Early Metastasis (ABMEM), a descriptive semi-mechanistic model that replicates experimentally observed behaviors of populations of circulating tumor cells, neutrophils, platelets and endothelial cells while incorporating representations of known surface receptor, autocrine and paracrine interactions. Essential downstream cellular processes were incorporated to simulate activation in response to stimuli, and calibrated with experimental data. The ABMEM was used to identify potential points of interdiction through examination of dynamic outcomes such as rate of tumor cell binding after inhibition of specific platelet or tumor receptors.

RESULTS

The ABMEM reproduced experimental data concerning neutrophil rolling over endothelial cells, inflammation-induced binding between neutrophils and platelets, and tumor cell interactions with these cells. Simulated platelet inhibition with anti-platelet drugs produced unstable aggregates with frequent detachment and re-binding. The ABMEM replicates findings from experimental models of circulating tumor cell adhesion, and suggests platelets play a critical role in this pre-requisite for metastasis formation. Similar effects were observed with inhibition of tumor integrin αV/β3. These findings suggest that anti-platelet or anti-integrin therapies may decrease metastasis by preventing stable circulating tumor cell adhesion.

CONCLUSION

Circulating tumor cell adhesion is a complex, dynamic process involving multiple cell-cell interactions. The ABMEM successfully captures the essential interactions necessary for this process, and allows for in-silico iterative characterization and invalidation of proposed hypotheses regarding this process in conjunction with in-vitro and in-vivo models. Our results suggest that anti-platelet therapies and anti-integrin therapies may play a promising role in inhibiting metastasis formation.

The effect of starvation on blood stream cancer cell metastasis to the liver in rat after laparotomy

BACKGROUND

Preoperative malnutrition worsens the prognosis of cancer patients. However, it is not certain how preoperative malnutrition affects postoperative hematogenous metastasis. We examined the influence of preoperative starvation on liver metastasis in rats using intra-vascular injection of AH109A hepatoma cells.

METHODS

Male donryu rats were divided into Fasting and Control groups. Rats received laparotomy and (125)I-iodo-deoxyuridine labeled AH109A hepatoma cells were inoculated via superior mesenteric vein. Radioactivity in the organs, macroscopic liver metastasis, white blood cell count, leukocyte count, NK cell activity, endogenous serum corticosterone and ACTH concentration and mRNA expression of cytokine in the liver and brain were evaluated at certain time points.

RESULTS

48hours preoperative starvation reduced body weight and induced a state of malnutrition. Accumulation of radioactivity in the liver was more than 4 times higher, and the number of liver metastases was 3.5 times higher in the Fasting than in the Control group. Preoperative starvation caused an almost 2 fold increase in plasma endogenous corticosterone levels and a 66% reduction in white blood cell and lymphocyte counts. Postoperative hypothalamus pituitary adrenal axis response was preserved. In addition, inflammatory cytokine expression in the liver was suppressed in the starved animals, suggesting that preoperative starvation led to a state of cellular immunosuppression, which would be an important factor for liver metastasis.

CONCLUSION

Preoperative malnutrition by 48 hours starvation reduced inflammatory cytokine response and cellular immunity, resulting in an increase in hematogenous liver metastasis.

CD49f-positive cell population efficiently enriches colon cancer-initiating cells

Cancer stem cells (CSCs) also known as cancer-initiating cells (CICs) show high tumorigenic activity and high chemo- and radiation resistance. It is, therefore, important to identify CSCs reliably to develop novel curative cancer treatments. In this study, we re-evaluated CSC markers of colorectal cancer for their cellular differentiation and tumorigenic activity, with the aim to identify reliable CSC markers. The rates of change in CD44, CD133, CD166, CD24, CD49f and CXCR4 expression during sodium butyrate (NaBT)-induced cell differentiation were assessed in HT29 and Caco2 colon cancer cell lines. Expression levels of target markers were assessed in clinical CRC samples. Tumorigenic activity was assessed on isolated cell fractions identified by multicolor flow cytometric analysis. In the cell differentiation assay, the average percent change was higher in CD44 (-98.2%) and CD49f (-74.4%) compared to CD133 (-17.9%) and CD166 (-49.4%). Expression of CD24 and CXCR4 appeared random in HT29 and Caco2. Expression of CD44, CD49f, CD133 and CD166 was confirmed in all four clinical CRC samples. Limiting dilution assay of CD44- and CD133-expressing cells revealed that only the CD133⁺CD44⁺ population possessed tumorigenic activity. Tumorigenesis was not affected by CD166 expression. Highly tumorigenic cells could be enriched in samples with higher CD49f expression; CD49f⁺ cells showed high tumorigenesis, whereas CD133⁺ and CD44⁺ cells that were negative for CD49f exhibited no tumorigenic activity. Multicolor analysis revealed that CD49f⁺ cells localized in CD44⁺ and CD133⁺ cell fractions. These findings demonstrated that CD49f is an important marker for identifying colorectal CSCs and suggest that the CD49f⁺ cell fraction may be the best candidate for colorectal CSCs.

A complex of α6 integrin and E-cadherin drives liver metastasis of colorectal cancer cells through hepatic angiopoietin-like 6

Homing of colorectal cancer (CRC) cells to the liver is a non-random process driven by a crosstalk between tumour cells and components of the host tissue. Here we report the isolation of a liver metastasis-specific peptide ligand (CGIYRLRSC) that binds a complex of E-cadherin and α(6) integrin on the surface of CRC cells. We identify angiopoietin-like 6 protein as a peptide-mimicked natural ligand enriched in hepatic blood vessels of CRC patients. We demonstrate that an interaction between hepatic angiopoietin-like 6 and tumoural α(6) integrin/E-cadherin drives liver homing and colonization by CRC cells, and that CGIYRLRSC inhibits liver metastasis through interference with this ligand/receptor system. Our results indicate a mechanism for metastasis whereby a soluble factor accumulated in normal vessels functions as a specific ligand for circulating cancer cells. Consistently, we show that high amounts of coexpressed α(6) integrin and E-cadherin in primary tumours represent a poor prognostic factor for patients with advanced CRC.

CXCR4/CXCL12 participate in extravasation of metastasizing breast cancer cells within the liver in a rat model

INTRODUCTION

Organ-specific composition of extracellular matrix proteins (ECM) is a determinant of metastatic host organ involvement. The chemokine CXCL12 and its receptor CXCR4 play important roles in the colonization of human breast cancer cells to their metastatic target organs. In this study, we investigated the effects of chemokine stimulation on adhesion and migration of different human breast cancer cell lines in vivo and in vitro with particular focus on the liver as a major metastatic site in breast cancer.

METHODS

Time lapse microscopy, in vitro adhesion and migration assays were performed under CXCL12 stimulation. Activation of small GTPases showed chemokine receptor signalling dependence from ECM components. The initial events of hepatic colonisation of MDA-MB-231 and MDA-MB-468 cells were investigated by intravital microscopy of the liver in a rat model and under shRNA inhibition of CXCR4.

RESULTS

In vitro, stimulation with CXCL12 induced increased chemotactic cell motility (p<0.05). This effect was dependent on adhesive substrates (type I collagen, fibronectin and laminin) and induced different responses in small GTPases, such as RhoA and Rac-1 activation, and changes in cell morphology. In addition, binding to various ECM components caused redistribution of chemokine receptors at tumour cell surfaces. In vivo, blocking CXCR4 decreased extravasation of highly metastatic MDA-MB-231 cells (p<0.05), but initial cell adhesion within the liver sinusoids was not affected. In contrast, the less metastatic MDA-MB-468 cells showed reduced cell adhesion but similar migration within the hepatic microcirculation.

CONCLUSION

Chemokine-induced extravasation of breast cancer cells along specific ECM components appears to be an important regulator but not a rate-limiting factor of their metastatic organ colonization.

Mechanisms regulating colorectal cancer cell metastasis into liver (Review)

The metastatic spread of tumor cells is one of the most common causes of mortality in cancer patients. The elucidation of the molecular mechanisms that underlie the formation of metastatic colonies has been one of the major objectives of cancer research. Organ-specific colonization of cancer cells is a significant and noteworthy feature of metastasis. Colorectal cancer (CRC) is one of the most common causes of cancer-related mortality. The liver is commonly the sole site of metastasis for CRC and represents a major cause of mortality in CRC patients. However, what regulates CRC cell metastasis into liver and the reasons for the liver-specific metastasis of CRC have yet to be adequately elucidated. Recent progress provides indications and a conceptual framework with which to investigate this issue. This review evaluated experimental and clinical evidence to support a mechanistic role for circulation patterns and microvessels in liver, metastasis-related genes, chemokines and their receptors, and cellular adhesion molecules in the process of CRC liver metastasis.

Type IV collagen-initiated signals provide survival and growth cues required for liver metastasis

The liver is a major site of metastasis for human malignancies, yet the factors that regulate tumor cell survival and growth in this organ remain elusive. Previously, we reported that M-27(IGF-IR) murine lung carcinoma cells with ectopic insulin-like growth factor-1 (IGF-I) receptor overexpression acquired a site-specific, liver-metastasizing potential. Gene expression profiling and subsequent RNA and protein analyses revealed that this was associated with major changes to the expression of extracellular matrix (ECM) protein-encoding genes including type III, IV and XVIII collagen genes, and these changes were also observed in the respective tumors in vivo. Because type IV collagen was the most prominently altered ECM protein in this model, we further analyzed its functional relevance to liver metastasis. M-27 cells stably overexpressing type IV collagen α1 and α2 chains were generated and their growth and metastatic properties investigated. We found that these cells acquired a site-selective growth advantage in the liver and this was associated with cell rescue from anoikis in a collagen IV/α2 integrin/FAK-dependent manner and increased responsiveness to IGF-I. Conversely, collagen IV or focal adhesion kinase (FAK) silencing by small-interfering RNA in highly metastatic tumor cells enhanced anoikis and decreased liver metastases formation. Moreover, analysis of human surgical specimens revealed uniformly high collagen IV expression in 65/65 hepatic metastases analyzed, regardless of tissue of origin, whereas it was variable and generally low in 50/50 primary colorectal carcinoma specimens examined. The results suggest that collagen IV-conveyed signals are essential cues for liver metastasis in diverse tumor types and identify mediators of collagen IV signaling as potential therapeutic targets in the management of hepatic metastases.

Epithelial and mesenchymal phenotypic switchings modulate cell motility in metastasis

The most ominous stage of cancer progression is metastasis, or the dissemination of carcinoma cells from the primary site into distant organs. Metastases are often resistant to current extirpative therapies and even the newest biological agents cure only a small subset of patients. Therefore a greater understanding of tumor biology that integrates properties intrinsic to carcinomas with tissue environmental modulators of behavior is needed. In no aspect of tumor progression is this more evident than the acquisition of cell motility that is critical for both escape from the primary tumor and colonization. In this overview, we discuss how this behavior is modified by carcinoma cell phenotypic plasticity that is evidenced by reversible switching between epithelial and mesenchymal phenotypes. The presence or absence of intercellular adhesions mediate these switches and dictate the receptivity towards signals from the extracellular milieu. These signals, which include soluble growth factors, cytokines, and extracellular matrix embedded with matrikines and matricryptines will be discussed in depth. Finally, we will describe a new mode of discerning the balance between epithelioid and mesenchymal movement.

Claudin-2 is selectively enriched in and promotes the formation of breast cancer liver metastases through engagement of integrin complexes

The liver represents the third most frequent site of metastasis in patients with breast cancer. We performed in vivo selection using 4T1 breast cancer cells to identify genes associated with the liver metastatic phenotype. Coincident with the loss of numerous tight-junctional proteins, we observe claudin-2 overexpression, specifically in liver-aggressive breast cancer cells. We further demonstrate that claudin-2 is both necessary and sufficient for the ability of 4T1 breast cancer cells to colonize and grow in the liver. The liver-aggressive breast cancer cells display a claudin-2-mediated increase in their ability to adhere to extracellular matrix (ECM) components, such as fibronectin and type IV collagen. Claudin-2 facilitates these cell/matrix interactions by increasing the cell surface expression of α(2)β(1)- and α(5)β(1)-integrin complexes in breast cancer cells. Indeed, claudin-2-mediated adhesion to fibronectin and type IV collagen can be blocked with neutralizing antibodies that target α(5)β(1) and α(2)β(1) complexes, respectively. Immunohistochemical analyses reveal that claudin-2, although weakly expressed in primary human breast cancers, is readily detected in all liver metastasis samples examined to date. Together, these results uncover novel roles for claudin-2 in promoting breast cancer adhesion to the ECM and define its importance during breast cancer metastasis to the liver.

Significance of integrin αvβ5 and erbB3 in enhanced cell migration and liver metastasis of colon carcinomas stimulated by hepatocyte-derived heregulin

To study the mechanisms of the highly liver-metastatic character of colon carcinoma cells, we studied the expression pattern of surface integrins on LS-LM6 (a highly liver-metastatic human colon cancer cell line) and the effects of hepatocyte-derived soluble factors on cell migration. LS-LM6 showed significantly higher expression of integrin αvβ5, a ligand for vitronectin (VN), as compared with its parental cell line (LS174T). A conditioned medium of cultured mouse hepatocytes enhanced VN-mediated cell migration of LS-LM6, which was blocked by neutralizing antibody against integrin αvβ5, while the medium did not affect cell adhesion to VN-coated plastic surfaces. The conditioned medium induced phosphorylation of erbB3 and its heterodimeric partner, erbB2. Heregulin (HRG), a ligand for erbB3, exerted similar effects on VN-mediated cell migration and phosphorylation of erbB3 and erbB2. The conditioned medium contained HRG, and depletion of HRG from the medium by pre-absorption with HRG antibody abolished its effects on cell migration. Heregulin (HRG) was expressed in some hepatocytes in the liver with carcinoma cell metastasis. Furthermore, knockdown of integrin αv and erbB3 by small-interfering RNAs significantly inhibited cell migration induced by HRG as well as liver metastasis in vivo. Finally, we found that HRG-induced cell migration was associated with marked phosphorylation of Akt and that cell migration was suppressed by treatment with specific inhibitors of phosphatidylinositol 3-kinase. Our study suggests that hepatocyte-derived HRG might participate in a highly liver-metastatic phenotype of LS-LM6 through enhancement of integrin αvβ5-mediated cell migration and erbB3/erbB2 signaling.

Effects of down-regulation of integrin-beta1 expression on migration and hepatic metastasis of human colon carcinoma

Organ-specific tumor cell adhesion to extracellular matrix (ECM) components and cell migration into host organs often involve integrin-mediated cellular processes. Direct integrin-mediated cell adhesion to ECM components in the space of Disse appears to be required for the successful liver metastatic formation of colon cancer. In the present study, human colon cancer HT-29 cells were transfected by liposome with integrin-beta1 antisense oligodeoxynucleotide (ASODN). The integrin-beta1 gene expression in HT-29 cells was significantly down-regulated. The migration of HT-29 cells was assayed using transwell cell culture chambers in vitro. The number of migrating HT-29 cells in experimental group was far less than that in control group (P<0.05). The models of hepatic metastasis in nude mice were established by the intrasplenic injection of transfected HT-29 cells. Thirty days later, the nude mice were killed and the average number of hepatic metastases (4.00+/-0.93 per mouse), average volume (10.10+/-6.50 mm3 per mouse), average weight (0.0440+/-0.0008 g per mouse) in experimental group were remarkably reduced as compared with those in control group (P<0.05). Integrin-beta1 expression in the hepatic metastasis was studied by immunohistochemistry (SP). Positive cell percentage of hepatic metastases in experimental group was markedly decreased as compared with that in control group (P<0.05). It was concluded that integrin-beta1 may take part in hepatic metastasis, and down-regulation of integrin-beta1 expression may play a key role in decreasing migration and hepatic metastasis of human colon carcinoma cells (HT-29).

In vivo tumor cell adhesion in the pulmonary microvasculature is exclusively mediated by tumor cell--endothelial cell interaction

BACKGROUND

Metastasis formation is the leading cause of death among colon cancer patients. We established a new in-situ model of in vivo microscopy of the lung to analyse initiating events of metastatic tumor cell adhesion within this typical metastatic target of colon cancer.

METHODS

Anaesthetized CD rats were mechanically ventilated and 106 human HT-29LMM and T84 colon cancer cells were injected intracardially as single cell suspensions. Quantitative in vivo microscopy of the lung was performed in 10 minute intervals for a total of 40 minutes beginning with the time of injection.

RESULTS

After vehicle treatment of HT-29LMM controls 15.2 +/- 5.3; 14.2 +/- 7.5; 11.4 +/- 5.5; and 15.4 +/- 6.5 cells/20 microscopic fields were found adherent within the pulmonary microvasculature in each 10 minute interval. Similar numbers were found after injection of the lung metastasis derived T84 cell line and after treatment of HT-29LMM with unspecific mouse control-IgG. Subsequently, HT-29LMM cells were treated with function blocking antibodies against beta1-, beta4-, and alphav-integrins wich also did not impair tumor cell adhesion in the lung. In contrast, after hydrolization of sialylated glycoproteins on the cells' surface by neuraminidase, we observed impairment of tumor cell adhesion by more than 50% (p < 0.05). The same degree of impairment was achieved by inhibition of P- and L-selectins via animal treatment with fucoidan (p < 0.05) and also by inhibition of the Thomson-Friedenreich (TF)-antigen (p < 0.05).

CONCLUSIONS

These results demonstrate that the initial colon cancer cell adhesion in the capillaries of the lung is predominantly mediated by tumor cell - endothelial cell interactions, possibly supported by platelets. In contrast to reports of earlier studies that metastatic tumor cell adhesion occurs through integrin mediated binding of extracellular matrix proteins in liver, in the lung, the continuously lined endothelium appears to be specifically targeted by circulating tumor cells.

Laminin-binding integrins and their tetraspanin partners as potential antimetastatic targets

Within the integrin family of cell adhesion receptors, integrins alpha3beta1, alpha6beta1, alpha6beta4 and alpha7beta1 make up a laminin-binding subfamily. The literature is divided on the role of these laminin-binding integrins in metastasis, with different studies indicating either pro- or antimetastatic functions. The opposing roles of the laminin-binding integrins in different settings might derive in part from their unusually robust associations with tetraspanin proteins. Tetraspanins organise integrins into multiprotein complexes within discrete plasma membrane domains termed tetraspanin-enriched microdomains (TEMs). TEM association is crucial to the strikingly rapid cell migration mediated by some of the laminin-binding integrins. However, emerging data suggest that laminin-binding integrins also promote the stability of E-cadherin-based cell-cell junctions, and that tetraspanins are essential for this function as well. Thus, TEM association endows the laminin-binding integrins with both pro-invasive functions (rapid migration) and anti-invasive functions (stable cell junctions), and the composition of TEMs in different cell types might help determine the balance between these opposing activities. Unravelling the tetraspanin control mechanisms that regulate laminin-binding integrins will help to define the settings where inhibiting the function of these integrins would be helpful rather than harmful, and may create opportunities to modulate integrin activity in more sophisticated ways than simple functional blockade.

Role of Kupffer cells in the outgrowth of colorectal cancer liver metastases

Colorectal cancer is one of the commonest malignancies in the "developed" world. The liver constitutes the main host organ for its distant metastases which, when present, augur a bad prognosis for the disease. Kupffer cells (KCs) are macrophages that constantly reside within the liver and form an effective first line defence against multiple harmful agents which reach the hepatic sinusoids via the portal circulation. KCs remove chemical compounds and dead or damaged cells, eliminate bacteria and protect against invading tumour cells. They may play a crucial tumouricidal role, exerting cytotoxic and cytostatic functions through the release of multiple cytokines and chemokines. Subsequently, colorectal metastasising cells are destroyed either by KC-performed phagocytosis or via the stimulation of other immune cells which migrate into the sinusoids and act accordingly. On the contrary, KC products, including cytokines, growth factors and matrix-degrading enzymes may promote liver metastasis, supporting tumour cell extravasation, motility and invasion. Current research aims to exploit the antineoplastic properties of KCs in new therapeutic approaches of colorectal cancer liver metastasis. Numerous agents, such as the granulocyte macrophage-colony stimulating factor, interferon gamma, muramyl peptide analogues and various antibody based treatments, have been tested in experimental models with promising results. Future trials may investigate their use in everyday clinical practice and compare their therapeutic value with current treatment of the disease.

Cell adhesion molecules: role and clinical significance in cancer

There is a growing body of evidence suggesting that alterations in the adhesion properties of neoplastic cells endow them with an invasive and migratory phenotype. Indeed, changes in the expression or function of cell adhesion molecules have been implicated in all steps of tumor progression, including detachment of tumor cells from the primary site, intravasation into the blood stream, extravasation into distant target organs, and formation of the secondary lesions. This review presents recent data regarding the role of cell adhesion molecules in tumor development and progress with concern to their clinical exploitation as potential biomarkers in neoplastic diseases.

CXCR4 regulates the early extravasation of metastatic tumor cells in vivo

Recent studies have demonstrated that the chemokine receptor CXCR4 plays a crucial role in organ-specific metastasis formation. Although a variety of studies showed the expression of chemokine receptors, in particular, CXCR4, by gastrointestinal tumors, the precise mechanisms of chemokine receptor-mediated homing of cancer cells to specific sites of metastasis remained elusive. Here, we used liver metastatic human HEP-G2 hepatoma and HT-29LMM colon cancer cells expressing functional CXCR4 to dissect the metastatic cascade by intravital fluorescence microscopy. Immunohistochemistry revealed that the CXCR4 ligand CXCL12 is expressed by endothelial cells and likely Kupffer cells lining the liver sinusoids. Tumor cell adhesion and extravasation in vivo was quantitatively analyzed using intravital fluorescence microscopy. Treatment of cells with an anti-CXCR4 antibody did not affect cell adhesion but significantly impaired tumor cell extravasation (HEP-G2; isotype control: 22.3% +/- 4.3% vs anti-CXCR4: 6.0% +/- 5.0%, P < .001). In addition, pretreatment of tumor cells with the ligand CXCL12 enhanced the activation of the small GTPases Rho, Rac, and cdc42 as well as tumor cell extravasation without affecting tumor cell adhesion within liver sinusoids. Taken together, the findings of the present study provide first in vivo insights into the early events of chemokine ligand/receptor-mediated liver metastasis formation of tumor cells and define tumor cell extravasation rather than tumor cell arrest as the rate-limiting event.

Constitutively active MEK1 is sufficient to induce epithelial-to-mesenchymal transition in intestinal epithelial cells and to promote tumor invasion and metastasis

Constitutive activation of the MAP kinase kinase MEK1 induces oncogenic transformation in intestinal epithelial cells. Loss of cell-cell adhesion followed by the dissociation of epithelial structures is a prerequisite for increased cell motility and tumor invasion. This phenotypic switch is designated epithelial-to-mesenchymal transition (EMT). EMT also plays an important role in determining the dissemination of tumors. However, the role of MEK1 in intestinal EMT, tumor invasion and metastasis has not been elucidated. To determine the functions of activated MEK1 in intestinal tumorigenesis, we established intestinal epithelial cell lines that overexpress wild-type MEK1 (wtMEK) or activated MEK1 (caMEK). Our results indicate that expression of caMEK is sufficient to induce EMT as confirmed with the induction of N-cadherin, vimentin, Snail1 and Snail2, whereas a reduction in E-cadherin, occludin, ZO-1 and cortical F-actin was noted. The Snail1 and Snail2 promoter analyses revealed that Egr-1 and Fra-1, an AP-1 protein, are responsible for MEK1-induced Snail1 and Snail2 expression, respectively. Cells expressing activated MEK1 clearly acquired an invasive capacity when compared to wtMEK-expressing cells. Zymography studies confirmed elevated levels of MMP2 and MMP9 activities in media of caMEK-expressing cells. Importantly, cells expressing activated MEK1 induced tumors with short latency in correlation with their ability to induce experimental metastasis in vivo and to express factors known to promote colorectal cancer cell metastasis. In conclusion, our results demonstrate, for the first time, that constitutive activation of MEK1 in intestinal epithelial cells is sufficient to induce an EMT associated with tumor invasion and metastasis.

Metastatic tumor cell arrest in the liver-lumen occlusion and specific adhesion are not exclusive

INTRODUCTION

In metastasis research, modern microscopic techniques shed a new light on the mechanisms of metastatic tumor cell arrest in the microcirculation of potential metastasis target organs. In this study, we differentiated the contribution of mechanical cell arrest, determined as lumen occlusion of liver sinusoids by tumor cells, and specific cell adhesion mediated by integrins for the arrest of human colon cancer cells in rat livers.

MATERIALS AND METHODS

Using in vivo microscopy, the diameters of liver sinusoids of two different rat strains (CD, 250-300 g and RNU, 80-120 g) were determined. Cells (HT-29LMM) were intracardially injected, and the numbers of arrested cells and the rates of sinusoid occluding cells were determined.

RESULTS

Mean sinusoid diameter in CD rats was 6.98 +/- 1.42 microm compared to 5.14 +/- 1.11 microm in RNU rats (p < 0.001). The numbers of arrested tumor cells and the rates of extravasated tumor cells did not differ between the two rat strains. Nevertheless, 5 and 30 min after cell injection, 35 +/- 15% and 19 +/- 8% of arrested cells, respectively, appeared lumen occluding in RNU rats and 9 +/- 6% and 3 +/- 3%, respectively, in CD rats (p < 0.05). Despite the higher rates of lumen occlusive cells in RNU rats, inhibition of beta-1 or beta-4 integrins significantly impaired cell arrest by 30-60% in both strains.

DISCUSSION

In summary, these results demonstrate that lumen occlusion alone, as determined by in vivo microscopy, is insufficient to establish stable tumor cell arrest of colon carcinoma cells in metastatic target organs and does therefore not rule out the requirement of specific adhesive interactions for tumor cell arrest in the microcirculation.

Functional blocking of specific integrins inhibit colonic cancer migration

For more effective oncological management of disseminated colorectal cancer, therapies must be devised that target the different individual stages of metastasis development. Recent work showed that integrin subunits alpha2, alpha6 and beta4 are involved in the colorectal cancer cell extravasation process. By means of Immunocytochemistry and Western blotting, it was shown that all three integrins are expressed not only in human colorectal cancer cells (HT29) but also in rat colonic cancer cells (DHDK12). Using in vivo models and intravital video microscopy techniques, it was shown that functional blocking of these integrin subunits by specific antibodies produced a significant reduction in cancer cell extravasation and migration. In conclusion, integrin subunits alpha2, alpha6 and beta4 are expressed in unrelated colorectal cancer cell strains and appear to play a key role in cancer cell migration.

Shear stress induces internalization of E-cadherin and invasiveness in metastatic oesophageal cancer cells by a Src-dependent pathway

Metastatic disease is dependent on tumor cell migration through the venous and lymphatic systems and requires dynamic rearrangement of adherens junctions. Endocytosis of cadherins is a key mechanism to dynamically arrange adherens junctions, signaling, and motility in tumor cells; however, the role of shear in regulating this process in metastatic cells is unknown. In this study, the role of shear in regulating cell surface expression of E-cadherin was investigated. We found that exposure to venous shear (shear rate, 200/s) induced internalization of E-cadherin in adherent metastatic oesophageal tumor cells (OC-1 tumor cell line). Internalized E-cadherin was found localized to Rab5-positive endosomes and was not present in lysosomes. As the Src family of tyrosine kinase have been implicated in regulating cadherin expression, we investigated the role of shear in regulating E-cadherin through Src activity. Pretreatment of OC-1 cells with the specific Src kinase inhibitor 4-amino-5- (4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1) prevented shear-induced internalization of E-cadherin. Direct measurement of Src activity (phosphorylation on Y416) showed that Src is activated in sheared OC-1 cells and that the shear-induced increase in phospho-Src is inhibited by the presence of PP1. Moreover, we show that shear stress significantly increased the invasive capacity of OC-1 cells (P < 0.001), a process inhibited by the presence of PP1. These results indicate a novel role for shear in regulating the endocytosis of E-cadherin and invasiveness in metastatic cells.

An in vivo rat model for early development of colorectal cancer metastasis to liver

At diagnosis of colorectal cancer, approximately 25% of the patients have established colorectal liver metastasis. Optimal management of disseminated disease requires therapies targeting multiple stages in hepatic colorectal cancer metastasis development. To facilitate this, biologically accurate in vivo models are required. Early colonic cancer liver metastases development was studied using BDIX and Sprague-Dawley rat strains with human HT29 and rat DHDK12 colonic cancer cell lines. Different cancer cell-host combinations were used. Rat DHDK12 was previously chemically induced in the BDIX rat. Real-time intra-vital microscopy was employed to analyse the early development of liver metastases in four groups (n = 6 per group) (HT29-BDIX, DHDK12-BDIX, HT29-SD and DHDK12-SD). Data were compared using one-way anova with Bonferroni's multiple comparison test. The total number of tumour cells visualized, adherent cells within the hepatic sinusoids, extravasated tumour cells and migration rates were significantly higher in the DHDK12-BDIX combination. Maximum number of visualized cells and maximum migration rate were also significantly higher in this group. No significant differences were observed in these experimental parameters among the other three groups or in the haemodynamic parameters among all groups. In conclusion, cancer cell line-host selection has a significant effect on early colonic cancer liver metastasis development.

Salvicine inactivates beta 1 integrin and inhibits adhesion of MDA-MB-435 cells to fibronectin via reactive oxygen species signaling

Integrin-mediated adhesion to the extracellular matrix plays a fundamental role in tumor metastasis. Salvicine, a novel diterpenoid quinone compound identified as a nonintercalative topoisomerase II poison, possesses a broad range of antitumor and antimetastatic activity. Here, the mechanism underlying the antimetastatic capacity of salvicine was investigated by exploring the effect of salvicine on integrin-mediated cell adhesion. Salvicine inhibited the adhesion of human breast cancer MDA-MB-435 cells to fibronectin and collagen without affecting nonspecific adhesion to poly-l-lysine. The fibronectin-dependent formation of focal adhesions and actin stress fibers was also inhibited by salvicine, leading to a rounded cell morphology. Furthermore, salvicine down-regulated beta(1) integrin ligand affinity, clustering and signaling via dephosphorylation of focal adhesion kinase and paxillin. Conversely, salvicine induced extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) phosphorylation. The effect of salvicine on beta(1) integrin function and cell adhesion was reversed by U0126 and SB203580, inhibitors of MAPK/ERK kinase 1/2 and p38 MAPK, respectively. Salvicine also induced the production of reactive oxygen species (ROS) that was reversed by ROS scavenger N-acetyl-l-cysteine. N-acetyl-l-cysteine additionally reversed the salvicine-induced activation of ERK and p38 MAPK, thereby maintaining functional beta(1) integrin activity and restoring cell adhesion and spreading. Together, this study reveals that salvicine activates ERK and p38 MAPK by triggering the generation of ROS, which in turn inhibits beta(1) integrin ligand affinity. These findings contribute to a better understanding of the antimetastatic activity of salvicine and shed new light on the complex roles of ROS and downstream signaling molecules, particularly p38 MAPK, in the regulation of integrin function and cell adhesion.

Role of cancer microenvironment in metastasis: focus on colon cancer

One person on three will receive a diagnostic of cancer during his life. About one third of them will die of the disease. In most cases, death will result from the formation of distal secondary sites called metastases. Several events that lead to cancer are under genetic control. In particular, cancer initiation is tightly associated with specific mutations that affect proto-oncogenes and tumour suppressor genes. These mutations lead to unrestrained growth of the primary neoplasm and a propensity to detach and to progress through the subsequent steps of metastatic dissemination. This process depends tightly on the surrounding microenvironment. In fact, several studies support the point that tumour development relies on a continuous cross-talk between cancer cells and their cellular and extracellular microenvironments. This signaling cross-talk is mediated by transmembrane receptors expressed on cancer cells and stromal cells. The aim of this manuscript is to review how the cancer microenvironment influences the journey of a metastatic cell taking liver invasion by colorectal cancer cells as a model.

Integrins as antimetastatic targets of RGD-independent snake venom components in liver metastasis [corrected]

Metastasis comprises several subsequent steps including local invasion and intravasation at the primary site, then their adhesion/arrest within the vessels of host organs followed by their extravasation and infiltration into the target organ stroma. In contrast to previous studies which have used aspartate-glycine-arginine (RGD) peptides and antibodies against integrins, we used rare collagen- and laminin-antagonizing integrin inhibitors from snake venoms to analyze the colonization of the liver by tumor cells both by intravital microscopy and in vitro. Adhesion of liver-targeting tumor cells to the sinusoid wall components, laminin-1 and fibronectin, is essential for liver metastasis. This step is inhibited by lebein-1, but not by lebein-2 or rhodocetin. Both lebeins from the Vipera lebetina venom block integrin interactions with laminins in an RGD-independent manner. Rhodocetin is an antagonist of alpha2beta1 integrin, a collagen receptor on many tumor cells. Subsequent to tumor cell arrest, extravasation into the liver stroma and micrometastasis are efficiently delayed by rhodocetin. This underlines the importance of alpha2beta1 integrin interaction with the reticular collagen I-rich fibers in liver stroma. Antagonists of laminin- and collagen-binding integrins could be valuable tools to individually block the direct interactions of tumor cells with distinct matrix components of the Disse space, thereby reducing liver metastasis.

Interactions between colon cancer cells and hepatocytes in rats in relation to metastasis

Adhesion of cancer cells to endothelium is considered an essential step in metastasis. However, we have shown in a previous study that when rat colon cancer cells are administered to the vena portae, they get stuck mechanically in liver sinusoids. Then, endothelial cells retract rapidly and cancer cells bind to hepatocytes. We investigated the molecular nature of these interactions between colon cancer cells and hepatocytes. Cancer cells in coculture with hepatocytes became rapidly activated with distinct morphological changes. Cancer cells formed long cytoplasmic protrusions towards hepatocytes in their close vicinity and these protrusions attached to microvilli of hepatocytes. Then, adhering membrane areas were formed by both cell types. Integrin subunits alphav, alpha6 and beta1 but not alphaL, beta2, beta3 and CD44 and CD44v6 were expressed on the cancer cells. In conclusion, colon cancer cells show an active behaviour to bind to hepatocytes, likely involving the integrin subunits alphav, alpha6 and beta1, indicating that early events in colon cancer metastasis in liver are distinctly different than assumed thus far.

In vivo models for early development of colorectal liver metastasis

In Europe, colorectal cancer is the second most prevalent form of cancer diagnosed. Globally each year, almost one million cases of colorectal cancer are registered and almost half a million deaths are attributed to this disease. This high mortality is associated with the development of liver metastases. For oncological advances to occur, accurate in vivo models are required to study colorectal cancer metastasis development. These models, by increasing our understanding of the early stages of colorectal liver establishment, will facilitate the development of novel therapeutic interventions and allow the clinical effects of these interventions to be studied. By analysis of current in vivo models for early development of colorectal liver metastasis, this review examines available methods of the tumour cell preparation, introduction and monitoring in vivo. An insight into the technical problems which can occur will be discussed. The implications of these different techniques on the resulting metastasis picture will be analysed. Existing in vivo models are assessed regarding the accuracy of the metastatic picture they portray.

The tumor cell-host organ interface in the early onset of metastatic organ colonisation

Metastatic lesions are the leading cause of death among cancer patients. These lesions usually originate from clonal proliferation of single tumor cells dispersed from the primary tumor into the circulation which finally arrest in the capillary bed of distant organs. The microenvironment within the circulation of potential metastatic target organs provides a variety of pro- and anti- metastatic stimuli regulating the onset of organ colonisation by metastatic tumor cells. Mechanical shear stress, anoikis and cell mediated cytotoxicity within the microcirculation probably clear most circulating tumor cells. Adhesion, and eventually extravasation, are essential initial interactions of circulating tumor cells with distant organs and can provide escape from the cytotoxic environment within the circulation. Adhesion to the capillary wall is mostly controlled by the organ-specific availability of adhesion molecules on tumor cells, the endothelium, and the composition of the underlying extracellular matrix. The availability of pro-adhesive and pro-migratory paracrine signals provided by the organ specific microenvironment can further initiate the onset of metastatic organ colonisation. Tumor cell and microenvironment factors regulating survival within the microcirculation, adhesion and extravasation of tumor cells are highlighted in the review.

Adhesion molecules and chemokines: the navigation system for circulating tumor (stem) cells to metastasize in an organ-specific manner

To date, cancer is still the second most prevalent cause of death after cardiovascular diseases in the industrialized word, whereby the primary cause of cancer is not attributed to primary tumor formation, but rather to the growth of metastases at distant organ sites. For several years it was considered that the well-known phenomenon of organ-specific spreading of tumor cells is mostly a mechanical process either directed passively due to size constraints (mechanical trapping theory) or due to a fertile environment provided by the organ in which tumor cells can proliferate (seed and soil hypothesis). Both mechanisms strongly depend on the adhesive properties of tumor cells either to endothelial cells and/or cancer cells, which are facilitated by a variety of cell adhesion molecules including carbohydrates and integrins. Within the past years it became evident that the organ-specific metastatic spreading of tumor cells does not only rely on heterotypic and homotypic adhesive interactions, but also on the interplay of chemokines and their appropriate receptors. Moreover, the identification of cancer stem cells in various tumor tissues has opened new questions. Cancer stem cells possess self-renewal, differentiation, and tumor-initiating capacities. Thus these cells are ideal candidates to be the seed of a secondary tumor. In the present review we will give a brief overview about the complex process of organ-specific metastasis formation depending on the interplay of adhesion molecules, chemokines, and the putative role of cancer stem cells in metastasis formation.

Clinical, biological, and molecular aspects of metastasis in colorectal cancer

Colorectal cancer is one of the most frequent malignant tumors with a still increasing incidence in Western countries. Currently, colorectal cancer is the second most common cancer in Europe both in terms of incidence and mortality. Approximately 90% of all cancer deaths arise from the metastatic dissemination of primary tumors. Thus, metastasis is the most lethal attribute of colorectal cancer. Today, colorectal cancer and metastasis thereof are understood as the results of early changes during tumor progression that determine the metastasis capacity. Much is known about molecules contributing to the metastasis phenotype, the pathways they control, and the genes they regulate. However, patient prognosis is mainly defined by histopathological staging, a static description of the anatomical extent of tumor spread within a surgical specimen. This review demonstrates the need for and possibilities of molecular-based staging as an essential prerequisite for improved diagnosis, prognosis, and therapy. Molecular determinants for progression and metastasis of colorectal cancer are discussed representing both potential markers for metastasis prognosis and targets for intervention strategies aiming at the ultimate goal of metastasis prevention.