Membrane and membrane-associated proteins involved in the aggressive phenotype displayed by highly invasive cancer cells

Invasion, the penetration of tumour cells into adjacent tissues, is a fundamental characteristic of malignant carcinomas and a first step in the metastatic process. The molecular mechanisms involved in tumour cell invasion are complex, but over the last couple of decades the knowledge base has grown quite considerably and many proteins with important roles in invasion have been identified and characterised. Benign tumours typically are encapsulated, which inhibits their ability to behave in a malignant manner, meaning these tumours do not grow in a location-limited less aggressive manner, do not invade surrounding tissues and do not metastasise. The ability of malignant tumours to invade and metastasise is the major cause of death for cancer patients. A greater insight into the molecular basis of cancer invasion and metastasis will lead to the development of novel therapies and specific panels of biomarkers for use in the treatment and diagnosis/monitoring in many types of metastatic cancer.     

A cross-cancer metastasis signature in the microRNA–mRNA axis of paired tissue samples

In the progression of cancer, cells acquire genetic mutations that cause uncontrolled growth. Over time, the primary tumour may undergo additional mutations that allow for the cancerous cells to spread throughout the body as metastases. Since metastatic development typically results in markedly worse patient outcomes, research into the identity and function of metastasis-associated biomarkers could eventually translate into clinical diagnostics or novel therapeutics. Although the general processes underpinning metastatic progression are understood, no clear cross-cancer biomarker profile has emerged. However, the literature suggests that some microRNAs (miRNAs) may play an important role in the metastatic progression of several cancer types. Using a subset of The Cancer Genome Atlas (TCGA) data, we performed an integrated analysis of mRNA and miRNA expression with paired metastatic and primary tumour samples to interrogate how the miRNA–mRNA regulatory axis influences metastatic progression. From this, we successfully built mRNA- and miRNA-specific classifiers that can discriminate pairs of metastatic and primary samples across 11 cancer types. In addition, we identified a number of miRNAs whose metastasis-associated dysregulation could predict mRNA metastasis-associated dysregulation. Among the most predictive miRNAs, we found several previously implicated in cancer progression, including miR-301b, miR-1296, and miR-423. Taken together, our results suggest that metastatic samples have a common cross-cancer signature when compared with their primary tumour pair, and that these miRNA biomarkers can be used to predict metastatic status as well as mRNA expression.

     

Pathobiology of cancer metastasis: a short account

ABSTRACT: Cancer-initiating cells display aberrant functional and phenotypic characteristics of normal stem cells from which they evolved by accumulation of multiple cytogenetic and/or epigenetic alterations. Signal transduction pathways which are essential for normal stem cell function are abnormally expressed by cancer cells, with a cancer cell phenotype playing an essential role in cancerization and metastasis.Local tumour progression, metastasis and metastatic tumour growth are mediated by direct cell-to-cell and paracrine reciprocal interactions between cancer cells and various stromal cells including fibroblasts, macrophages, bone marrow derived stem cells and progenitor cells. These interactions mediate breakdown of basement membrane barriers and angiogenesis both locally at the invasive front of the primary tumour and at the distant metastatic site; attract primary tumour cells to the candidate metastatic site; and promote proliferation, survival and growth of primary tumour cells and of metastatic cells at their distant site.It is the purpose of this article to highlight the analogies between some of the genetic programs of normal stem cells, and of cancer cells participating in the process of metastasis.     

Optimization of the MB49 mouse bladder cancer model for adenoviral gene therapy

Bladder cancer is regarded as a promising candidate for innovative therapies in the field of immune and gene therapy. In this paper, we present the subcutaneous, metastatic and a novel orthotopic model of murine MB49 bladder cancer in C57BL/6 mice. We further show the potential of using adenoviral vectors together with different transduction enhancers to augment in vivo gene delivery. Finally, we present candidate genes for tumour detection, therapy or targeting.The MB49 tumour grew rapidly in mice. The subcutaneous model allowed for tumour detection within a week and the possibility to monitor growth rate on a day-by-day basis. Injection of MB49 cells intravenously into the tail vein gave rise to lung metastases within 16 days, while instillation of tumour cells into pretreated bladders led to a survival time of 20-40 days. Adenoviral vectors can be used as a vehicle for gene transfer to the bladder. By far, the most potent transduction enhancer was Clorpactin, also known as oxychlorosene. Last, we show that MB49 cells express tumour-associated antigens like bladder cancer-4, prostate stem cell antigen and six-transmembrane epithelial antigen of the prostate.Given the possibility for efficient genetic modification of the bladder and the presence of known tumour antigens, the MB49 models can be used in innovative ways to explore immunogene therapy.     

Contact stimulation of prostate cancer cell migration: the role of gap junctional coupling and migration stimulated by heterotypic cell-to-cell contacts in determination of the metastatic phenotype of Dunning rat prostate cancer cells

BACKGROUND INFORMATION: Motile activity of tumour cells is regarded as a critical factor determining their metastatic potential. We have shown previously that contrary to the majority of normal cells, homotypic contacts between some tumour cells, among them low metastatic (AT-2) and highly metastatic (MAT-LyLu) rat prostate cancer cells, increase the speed of their movements. The aim of the present study was to determine the effect of heterotypic cell-to-cell contacts on the migration of rat prostate cancer cells differing in metastatic potential, and to correlate it with the intensity of homo- and heterologous gap junctional coupling. RESULTS: MAT-LyLu and AT-2 cells moving on the surface of fibroblasts displayed significantly greater cell displacement than those moving on plastic substrata. This effect correlated with the polarization (contact guidance) and increased speed of cell movements. However, in contrast with the migration on plastic substrata, where MAT-LyLu cells displayed considerably higher motility than AT-2 cells, no differences between both cell lines were observed on the surface of fibroblasts. On the other hand, in contrast with AT-2, Mat-LyLu cells displayed extensive homologous coupling mediated by connexin43 and were able to couple with normal fibroblasts. CONCLUSION: Heterotypic contacts between migrating prostatic cancer cells and normal fibroblasts can strongly stimulate their migration during invasion; however, this effect does not correlate with the gap junctional coupling between cancer cells and normal fibroblasts.     

Cancer stem cells: implications for the progression and treatment of metastatic disease

Metastasis is the major cause of death for cancer patients with solid tumours, due mainly to the ineffectiveness of current therapies once metastases begin to form. Further insight into the biology of metastasis is therefore essential in order to gain a greater understanding of this process and ultimately to develop better cancer therapies. Metastasis is an inefficient process, such that very few cells that leave a tumour successfully form macrometastases in distant sites. This suggests that only a small subset of cells can successfully navigate the metastatic cascade and eventually re-initiate tumour growth to form life-threatening metastases. Recently, there has been growing support for the cancer stem cell (CSC) hypothesis which stipulates that primary tumours are initiated and maintained by a small subpopulation of cancer cells that possess "stem-like" characteristics. Classical properties of normal stem cells are strikingly reminiscent of the observed experimental and clinical behaviour of metastatic cancer cells, including an unlimited capacity for self renewal; the requirement for a specific 'niche' or microenvironment to grow; use of the stromal cell-derived factor 1 (SDF-1)/chemokine receptor 4 (CXCR4) axis for migration; enhanced resistance to apoptosis and an increased capacity for drug resistance. Therefore, in addition to playing a role in primary tumour formation, we believe that CSCs are also key players in the metastatic process. We will review the current evidence supporting this idea and discuss the potential implications of the CSC hypothesis with regards to experimental investigation and treatment of metastatic disease.     

Cell polarity in morphogenesis and metastasis

Most human cancers arise either from epithelial cells or their progenitors. Epithelial cells possess a distinctive apical–basal polarity and loss of polarity is frequently assumed to be a common feature of cancer progression. In particular, cancer cell dissemination to ectopic sites, and metastatic growth at those sites, is often considered to require a mesenchymal transition in which the transformed epithelial cells lose their apical–basal polarity. However, many cancers retain epithelial characteristics, and until recently there has been little conclusive evidence for an involvement of the cell polarity machinery in tumour growth and metastasis. In this article, we discuss evidence that polarity proteins can be potent invasion suppressors but that loss of epithelial character is not essential either for tumour growth and invasion, or metastatic colonization.     

Modelling Circulating Tumour Cells for Personalised Survival Prediction in Metastatic Breast Cancer

Ductal carcinoma is one of the most common cancers among women, and the main cause of death is the formation of metastases. The development of metastases is caused by cancer cells that migrate from the primary tumour site (the mammary duct) through the blood vessels and extravasating they initiate metastasis. Here, we propose a multi-compartment model which mimics the dynamics of tumoural cells in the mammary duct, in the circulatory system and in the bone. Through a branching process model, we describe the relation between the survival times and the four markers mainly involved in metastatic breast cancer (EPCAM, CD47, CD44 and MET). In particular, the model takes into account the gene expression profile of circulating tumour cells to predict personalised survival probability. We also include the administration of drugs as bisphosphonates, which reduce the formation of circulating tumour cells and their survival in the blood vessels, in order to analyse the dynamic changes induced by the therapy.We analyse the effects of circulating tumour cells on the progression of the disease providing a quantitative measure of the cell driver mutations needed for invading the bone tissue. Our model allows to design intervention scenarios that alter the patient-specific survival probability by modifying the populations of circulating tumour cells and it could be extended to other cancer metastasis dynamics.     

Circulating tumour cells and cancer stem cells: A role for proteomics in defining the interrelationships between function,phenotype and differentiation with potential clinical applications

Research on the discovery and implementation of valid cancer biomarkers is one of the most challenging fields in oncology and oncoproteomics in particular. Moreover, it is generally accepted that an evaluation of cancer biomarkers from the blood could significantly enable biomarker assessments by providing a relatively non-invasive source of representative tumour material. In this regard, circulating tumour cells (CTCs) isolated from the blood of metastatic cancer patients have significant promise. It has been demonstrated that localised and metastatic cancers may give rise to CTCs, which are detectable in the bloodstream. Despite technical difficulties, recent studies have highlighted the prognostic significance of the presence and number of CTCs in the blood. Future studies are necessary not only to detect CTCs but also to characterise them. Furthermore, another pathogenically significant type of cancer cells, known as cancer stem cells (CSCs) or more recently termed circulating tumour stem cells (CTSCs), appears to have a significant role as a subpopulation of CTCs.     

Mechanisms of cancer cell invasion

The movement of cancer cells into tissue surrounding the tumour and the vasculature is the first step in the spread of metastatic cancers. Recent advances in imaging, the use of 3D model systems and the application of microarray technologies have yielded new insights into these processes. This work has challenged our views about what causes cancer cells to become motile in the first place, and has demonstrated that cancer cells can move in many different ways.     

Sialylation regulates galectin-3/ligand interplay during mammary tumour progression--a case of targeted uncloaking

Galectin-3 is involved both in facilitating detachment of cells from primary tumour sites and favouring cancer cell adhesion and survival to anoikis in the blood stream. The mechanisms behind these apparently contradictory roles of the lectin have not yet been resolved. In order to investigate possible interplays between galectin-3 and its ligands underlying their role in the metastatic process, we examined mucin-1 (MUC1) and epidermal growth factor receptor (EGFR), well-known galectin-3 ligands, as well as galectin-3-binding site expression in a series of spontaneous canine malignant mammary tumours (CMMT) and a metastatic CMMT cell line. Despite the fact that CMMT cells expressed MUC1 and EGFR homogeneously over their plasma membrane, intravascular tumour cells, positive for galectin-3, expressed MUC1 and EGFR in a more focal membrane localization. Moreover, MUC1 overexpression in primary CMMT was present in parallel with down-regulation of galectin-3. Furthermore, in the CMT-U27 cell line, galectin-3 knock-down led to increased MUC1 expression, while MUC1 knock-down led to down-regulation of the lectin. Finally, removal of sialic acid from both CMMT and CMT-U27 xenograft samples exposed galectin-3-ligands throughout the tumour tissue, whereas these ligands were only present in galectin-3-positive invading cells in untreated samples. Interestingly indeed, we show that in vessel-invading cells, there is interaction between galectin-3 and the T antigen in vivo. We therefore hypothesized that loss of galectin-3 and sialylation-related masking of its ligands, in conjunction with their overexpression in specific tumour cell subpopulations, are crucial in regulating adhesive/de-adhesive events in the progression and invasive capacity of metastatic cells.     

Targeting Notch signalling by the conserved miR-8/200 microRNA family in development and cancer cells

Notch signalling is crucial for the correct development and growth of numerous organs and tissues, and when subverted it can cause cancer. Loss of miR-8/200 microRNAs (miRNAs) is commonly observed in advanced tumours and correlates with their invasion and acquisition of stem-like properties. Here, we show that this miRNA family controls Notch signalling activation in Drosophila and human cells. In an overexpression screen, we identified the Drosophila miR-8 as a potent inhibitor of Notch-induced overgrowth and tumour metastasis. Gain and loss of mir-8 provoked developmental defects reminiscent of impaired Notch signalling and we demonstrated that miR-8 directly inhibits Notch ligand Serrate. Likewise, miR-200c and miR-141 directly inhibited JAGGED1, impeding proliferation of human metastatic prostate cancer cells. It has been suggested that JAGGED1 may also be important for metastases. Although in metastatic cancer cells, JAGGED1 modestly regulated ZEB1, the miR-200c's target in invasion, studies in Drosophila revealed that only concurrent overexpression of Notch and Zfh1/ZEB1 induced tumour metastases. Together, these data define a new way to attenuate or boost Notch signalling that may have clinical interest.     

Circulating tumour cells lacking cytokeratin in breast cancer: the importance of being mesenchymal

Circulating tumour cells (CTCs) are independent predictor of prognosis in metastatic breast cancer. Nevertheless, in one third of patients, circulating tumour cells are undetected by conventional methods. Aim of the study was to assess the prognostic value of circulating tumour cells expressing mesenchymal markers in metastatic breast cancer patients. We isolated CTC from blood of 55 metastatic breast cancer patients. CTC were characterized for cytokeratins and markers of epithelial mesenchymal transition. The gain of mesenchymal markers in CTC was correlated to prognosis of patients in a follow-up of 24 months. The presence of mesenchymal markers on CTC more accurately predicted worse prognosis than the expression of cytokeratins alone. Because of the frequent loss of epithelial antigens by CTC, assays targeting epithelial antigens may miss the most invasive cell population. Thus, there is an urgent need to improve detection methods to identify CTC which undergone epithelial mesenchymal transition program.     

Sequential biphasic changes in claudin1 and claudin4 expression are correlated to colorectal cancer progression and liver metastasis

Terminal progression of colorectal cancer (CRC) culminates in liver metastasis. To identify genes that are involved in the metastatic phenotype, cDNA microarrays were used to analyse mRNA expression profiles of colorectal carcinoma (CC)531 rat colon adenocarcinoma cells for changes related to their homing into the liver. Briefly, CC531 cells were intraportally implanted into the liver of Wag-Rij rats and re-isolated after 3, 6, 9, 14 and 21 days. Compared to control CC531 cells, claudin1 and claudin4 were among the ≥8-fold initially down-regulated genes. The co-culture of tumour cells with isolated rat hepatocytes and Kupffer cells did not induce down-regulation of either claudin1 or 4. When the environment effective on circulating tumour cells was simulated by cell culture conditions favouring their adhesion, only claudin4 showed augmented expression. Knockdown of claudin1 and claudin4 mediated by small interfering RNA caused significantly increased migration and decreased clonogenic growth of tumour cells (P < 0.05), but had no effect on their proliferation. These experimental results were paralleled by increased claudin1 and claudin4 expression in human CRC samples in Union for International Cancer Control (UICC) stages I-III, as evaluated by real-time PCR. Increased claudin4 levels were correlated with significantly reduced overall survival (log-rank test, P= 0.018). Further, significantly (P < 0.05) reduced expression of claudin1 and claudin4 was observed in stage IV and liver metastasis by immunohistochemistry. In conclusion, sequential biphasic changes in claudin1 and claudin4 expression occur during the homing of rat CC531 CRC cells to the liver. This modulation is reflected by significant changes in claudin expression in human primary and metastatic CRC.     

CXCR4–SDF-1 Signalling, Locomotion, Chemotaxis and Adhesion

Chemokines, small pro-inflammatory chemoattractant cytokines, that bind to specific G-protein-coupled seven-span transmembrane receptors present on plasma membranes of target cells are the major regulators of cell trafficking. In addition some chemokines have been reported to modulate cell survival and growth. Moreover, compelling evidence is accumulating that cancer cells may employ several mechanisms involving chemokine-chemokine receptor axes during their metastasis that also regulate the trafficking of normal cells. Of all the chemokines, stromal-derived factor-1 (SDF-1), an alpha-chemokine that binds to G-protein-coupled CXCR4, plays an important and unique role in the regulation of stem/progenitor cell trafficking. First, SDF-1 regulates the trafficking of CXCR4+ haemato/lymphopoietic cells, their homing/retention in major haemato/lymphopoietic organs and accumulation of CXCR4+ immune cells in tissues affected by inflammation. Second, CXCR4 plays an essential role in the trafficking of other tissue/organ specific stem/progenitor cells expressing CXCR4 on their surface, e.g., during embryo/organogenesis and tissue/organ regeneration. Third, since CXCR4 is expressed on several tumour cells, these CXCR4 positive tumour cells may metastasize to the organs that secrete/express SDF-1 (e.g., bones, lymph nodes, lung and liver). SDF-1 exerts pleiotropic effects regulating processes essential to tumour metastasis such as locomotion of malignant cells, their chemoattraction and adhesion, as well as plays an important role in tumour vascularization. This implies that new therapeutic strategies aimed at blocking the SDF-1-CXCR4 axis could have important applications in the clinic by modulating the trafficking of haemato/lymphopoietic cells and inhibiting the metastatic behaviour of tumour cells as well. In this review, we focus on a role of the SDF-1-CXCR4 axis in regulating the metastatic behaviour of tumour cells and discuss the molecular mechanisms that are essential to this process.     

Subcutaneous preconditioning increases invasion and metastatic dissemination in mouse colorectal cancer models

Mouse colorectal cancer (CRC) models generated by orthotopic microinjection of human CRC cell lines reproduce the pattern of lymphatic, haematological and transcoelomic spread but generate low metastatic efficiency. Our aim was to develop a new strategy that could increase the metastatic efficiency of these models. We used subcutaneous implantation of the human CRC cell lines HCT116 or SW48 prior to their orthotopic microinjection in the cecum of nude mice (SC+ORT). This subcutaneous preconditioning significantly enhanced metastatic dissemination. In the HCT116 model it increased the number and size of metastatic foci in lymph nodes, lung, liver and peritoneum, whereas, in the SW48 model, it induced a shift from non-metastatic to metastatic. In both models the number of apoptotic bodies in the primary tumour in the SC+ORT group was significantly reduced compared with that in the direct orthotopic injection (ORT) group. Moreover, in HCT116 tumours the number of keratin-positive tumour buddings and single epithelial cells increased at the invasion front in SC+ORT mice. In the SW48 tumour model, we observed a trend towards a higher number of tumour buds and single cells in the SC+ORT group but this did not reach statistical significance. At a molecular level, the enhanced metastatic efficiency observed in the HCT116 SC+ORT model was associated with an increase in AKT activation, VEGF-A overexpression and downregulation of β1 integrin in primary tumour tissue, whereas, in SW48 SC+ORT mice, the level of expression of these proteins remained unchanged. In summary, subcutaneous preconditioning increased the metastatic dissemination of both orthotopic CRC models by increasing tumour cell survival and invasion at the tumour invasion front. This approach could be useful to simultaneously study the mechanisms of metastases and to evaluate anti-metastatic drugs against CRC.KEY WORDS: Collective invasion, Colorectal cancer model, Metastasis, Orthotopic injection, Single tumour cell, Subcutaneous preconditioning     

Vitamin E analogues as a novel group of mitocans: anti-cancer agents that act by targeting mitochondria

Mitochondria have recently emerged as new and promising targets for cancer prevention and therapy. One of the reasons for this is that mitochondria are instrumental to many types of cell death and often lie downstream from the initial actions of anti-cancer drugs. Unlike the tumour suppressor gene encoding p53 that is notoriously prone to inactivating mutations but whose function is essential for induction of apoptosis by DNA-targeting agents (such as doxorubicin or 5-fluorouracil), mitochondria present targets that are not so compromised by genetic mutation and whose targeting overcomes problems with mutations of upstream targets such as p53. We have recently proposed a novel class of anti-cancer agents, mitocans that exert their anti-cancer activity by destabilising mitochondria, promoting the selective induction of apoptotic death in tumour cells. In this communication, we review recent findings on mitocans and propose a common basis for their mode of action in inducing apoptosis of cancer cells. We use as an example the analogues of vitamin E that are proving to be cancer cell-specific and may soon be developed into efficient anti-cancer drugs.     

The methylation landscape of tumour metastasis

The metastatic cascade which leads to the death of cancer patients results from a multi‐step process of tumour progression caused by genetic and epigenetic alterations in key regulatory molecules. It is, therefore, crucial to improve our understanding of the regulation of genes controlling the metastatic process to identify predictive biomarkers and to develop more effective therapies to treat advanced disease. The study of epigenetic mechanisms of gene regulation offers a novel approach for innovative diagnosis and treatment of cancer patients. Recent discoveries provide compelling evidence that the methylation landscape (changes in both DNA methylation and histone post‐translational modifications) is profoundly altered in cancer cells and contributes to the altered expression of genes regulating tumour phenotypes. However, the impact of methylation events specifically on the advanced metastatic process is poorly understood compared with the initial oncogenic events. Moreover, the characterisation of a large number of histone‐modifying enzymes has revealed their active roles in cancer progression, via the regulation of specific target genes controlling different metastatic phenotypes. Here, we discuss two main methylating events (DNA methylation and histone‐tail methylation) involved in oncogenesis and metastasis formation. The potential reversibility of these molecular events makes them promising biomarkers of metastatic potential and potential therapeutic targets.     

Invasion and metastasis.

Malignant tumours cause sickness and death largely because they invade and metastasize. Such spread is made possible by many cellular properties, including the ability of neoplastic cells to move and to release degradative enzymes. These properties enable tumour cells to break free of the primary tumour, penetrate blood or lymphatic vessels and, after being transported to distant sites, pass out of the vessels to establish new tumours. Not all cells in a tumour, however, are able to metastasize, so the process tends to select for greater malignancy in the secondary tumour. The heterogeneity of tumours probably accounts for the difficulty of providing effective treatment, in that the various subpopulations of cells arising from each tumour vary in their responses to chemotherapeutic agents. We do not yet understand the process sufficiently to treat cancer patients by interfering selectively with the metastatic mechanisms.