Illuminating the metastatic process

The evolution of tumor metastasis during clonal expansion with alterations in metastasis driver genes

Metastasis is a leading cause of cancer-related deaths. Carcinoma generally initiates at a specific organ as a primary tumor, but eventually metastasizes and forms tumor sites in other organs. In this report, we developed a mathematical model of cancer progression with alterations in metastasis-related genes. In cases in which tumor cells acquire metastatic ability through two steps of genetic alterations, we derive formulas for the probability, the expected number, and the distribution of the number of metastases. Moreover, we investigate practical pancreatic cancer disease progression in cases in which both one and two steps of genetic alterations are responsible for metastatic formation. Importantly, we derive a mathematical formula for the survival outcome validated using clinical data as well as direct simulations. Our model provides theoretical insights into how invisible metastases distribute upon diagnosis with respect to growth rates, (epi)genetic alteration rates, metastatic rate, and detection size. Prediction of survival outcome using the formula is of clinical importance in terms of determining therapeutic strategies.

Preclinical imaging and translational animal models of cancer for accelerated clinical implementation of nanotechnologies and macromolecular agents

The majority of animal models of cancer have performed poorly in terms of predicting clinical performance of new therapeutics, which are most often first evaluated in patients with advanced, metastatic disease. The development and use of metastatic models of cancer may enhance clinical translatability of preclinical studies focused on the development of nanotechnology-based drug delivery systems and macromolecular therapeutics, potentially accelerating their clinical implementation. It is recognized that the development and use of such models are not without challenge. Preclinical imaging tools offer a solution by allowing temporal and spatial characterization of metastatic lesions. This paper provides a review of imaging methods applicable for evaluation of novel therapeutics in clinically relevant models of advanced cancer. An overview of currently utilized models of oncology in small animals is followed by image-based development and characterization of visceral metastatic cancer models. Examples of imaging tools employed for metastatic lesion detection, evaluation of anti-tumor and anti-metastatic potential and biodistribution of novel therapies, as well as the co-development and/or use of imageable surrogates of response, are also discussed. While the focus is on development of macromolecular and nanotechnology-based therapeutics, examples with small molecules are included in some cases to illustrate concepts and approaches that can be applied in the assessment of nanotechnologies or macromolecules.

Slope-Dependent Cell Motility Enhancements at the Walls of PEG-Hydrogel Microgroove Structures

In recent years, research utilizing micro- and nanoscale geometries and structures on biomaterials to manipulate cellular behaviors, such as differentiation, proliferation, survival, and motility, have gained much popularity; however, how the surface microtopography of 3D objects, such as implantable devices, can affect these various cell behaviors still remains largely unknown. In this study, we discuss how the walls of microgroove topography can influence the morphology and the motility of unrestrained cells, in a different fashion from 2D line micropatterns. Here adhesive substrates made of tetra(polyethylene glycol) (tetra-PEG) hydrogels with microgroove structures or 2D line micropatterns were fabricated, and cell motility on these substrates was evaluated. Interestingly, despite being unconstrained, the cells exhibited drastically different migration behaviors at the edges of the 2D micropatterns and the walls of microgroove structures. In addition to acquiring a unilamellar morphology, the cells increased their motility by roughly 3-fold on the microgroove structures, compared with the 2D counterpart or the nonpatterned surface. Immunostaining revealed that this behavior was dependent on the alignment and the aggregation of the actin filaments, and by varying the slope of the microgroove walls, it was found that relatively upright walls are necessary for this cell morphology alterations. Further progress in this research will not only deepen our understanding of topography-assisted biological phenomena like cancer metastasis but also enable precise, topography-guided manipulation of cell motility for applications such as cancer diagnosis and cell sorting.

Emetine inhibits migration and invasion of human non-small-cell lung cancer cells via regulation of ERK and p38 signaling pathways

Emetine is a natural compound originated from ipecac roots. It was commonly used as anti-protozoal and vomiting agent. The apoptosis-inducing effect of emetine makes it considered as a potential anti-cancer agent for various human cancers. Here in this study, we report that emetine inhibits migration and invasion of human non-small-cell lung cancer (NSCLC) cells. Modulation of three major mitogen-activated protein kinases (MAPKs), ERK, p38 and JNK, is well known to be involved in regulation of matrix metalloproteinases (MMPs), which are essential in tissue remodeling and extracellular matrix (ECM) degradation, for cancer cells to spread out from the origin of tumorigenesis. Emetine regulates two major MAPKs, p38 and ERK. Differential inhibition/stimulation of ERK and p38 induced differential suppressions of β-catenin and c-myc transcription factors. This leads to the selective down-regulation of MMP-2 and MMP-9, two major gelatinases which can degrade ECM components, and RECK, a negative regulator of MMP-9.

Progression of Osteosarcoma from a Non-Metastatic to a Metastatic Phenotype Is Causally Associated with Activation of an Autocrine and Paracrine uPA Axis

Pulmonary metastasis is the major untreatable complication of osteosarcoma (OS) resulting in 10-20% long-term survival. The factors and pathways regulating these processes remain unclear, yet their identification is crucial in order to find new therapeutic targets. In this study we used a multi-omics approach to identify molecules in metastatic and non-metastatic OS cells that may contribute to OS metastasis, followed by validation in vitro and in vivo. We found elevated levels of the urokinase plasminogen activator (uPA) and of the uPA receptor (uPAR) exclusively in metastatic OS cells. uPA was secreted in soluble form and as part of the protein cargo of OS-secreted extracellular vesicles, including exosomes. In addition, in the tumour microenvironment, uPA was expressed and secreted by bone marrow cells (BMC), and OS- and BMC-derived uPA significantly and specifically stimulated migration of metastatic OS cells via uPA-dependent signaling pathways. Silencing of uPAR in metastatic OS cells abrogated the migratory response to uPA in vitro and decreased metastasis in vivo. Finally, a novel small-molecule inhibitor of uPA significantly (P = 0.0004) inhibited metastasis in an orthotopic mouse model of OS. Thus, we show for the first time that malignant conversion of OS cells to a metastatic phenotype is defined by activation of the uPA/uPAR axis in both an autocrine and paracrine fashion. Furthermore, metastasis is driven by changes in OS cells as well as in the microenvironment. Finally, our data show that pharmacological inhibition of the uPA/uPAR axis with a novel small-molecule inhibitor can prevent the emergence of metastatic foci.

Survival After Resection of Gastrointestinal Stromal Tumor and Sarcoma Liver Metastases in 146 Patients

BACKGROUND

We investigated outcomes by primary tumor type in patients who underwent resection of liver metastases from gastrointestinal stromal tumors (GIST), leiomyosarcomas, and other sarcomas.

METHOD

Our institutional liver database was used to identify patients who underwent resection from 1998 through 2013. Histopathological, clinical, and survival data were analyzed.

RESULTS

One hundred forty-six patients underwent resection of liver metastases from GIST (n = 49), leiomyosarcomas (n = 47), or other sarcomas (n = 50). The 5-year overall survival (OS) rates in patients with GIST, leiomyosarcomas, and other sarcomas were 55.3, 48.4, and 44.9%, respectively, and the 10-year OS rates were 52.5, 9.2, and 23.0%, respectively. The 5-year recurrence-free survival (RFS) rate was better for GIST (35.7%; p = 0.003) than for leiomyosarcomas (3.4%) and other sarcomas (21.4%). Lung recurrence was more common for leiomyosarcomas (36% of patients; p < 0.0001) than for other sarcomas (12%) and GIST (2%). For GIST, the findings support a benefit of imatinib regarding the 5-year RFS rate compared to resection alone (47.1 vs. 9.5%; p = 0.013). For leiomyosarcoma, primary tumor location did not affect the 5-year RFS rate (intraabdominal 14.5%; other location 0%; p = 0.182).

CONCLUSION

Liver metastases from GIST, leiomyosarcomas, and other sarcomas should be assessed separately as their survival and recurrence patterns are different. This is especially important for GIST, for which imatinib is now available.

Invadopodia and basement membrane invasion in vivo

Over 20 years ago, protrusive, F-actin-based membrane structures, termed invadopodia, were identified in highly metastatic cancer cell lines. Invadopodia penetrate artificial or explanted extracellular matrices in 2D culture conditions and have been hypothesized to facilitate the migration of cancer cells through basement membrane, a thin, dense, barrier-like matrix surrounding most tissues. Despite intensive study, the identification of invadopodia in vivo has remained elusive and until now their possible roles during invasion or even existence have remained unclear. Studies in remarkably different cellular contexts-mouse tumor models, zebrafish intestinal epithelia, and C. elegans organogenesis-have recently identified invadopodia structures associated with basement membrane invasion. These studies are providing the first in vivo insight into the regulation, function, and role of these fascinating subcellular devices with critical importance to both development and human disease.

A bibenzyl from Dendrobium ellipsophyllum inhibits migration in lung cancer cells

Metastatic cancer cells have been shown to have aggressive behaviors accounting for the high incidence of chemotherapeutic failure and mortality. Because migration and invasion are crucial behaviors for cancer cell dissemination, promising compounds exhibiting potential antimigration effects are of interest for metastasis-based therapeutic approaches. This study aimed to evaluate the activity of a bibenzyl, 4,5,4'-trihydroxy-3,3'-dimethoxybibenzyl (TDB), isolated from Dendrobium ellipsophyllum Tang and Wang, in the suppression of migration in human lung cancer cells. TDB at nontoxic concentrations (1 and 5 µM) significantly inhibited the motility of lung cancer cells in scratch-wound assay. Chemotaxis-induced migration and invasion assays also revealed that the cell motility dramatically diminished in the cells treated with 1-5 µM TDB. Western blot analysis provided the underlying molecular mechanism, showing that TDB reduced such cell migration and invasion by decreasing migration-regulating proteins, including integrins αv, α4, β1, β3 and β5, as well as downstream signaling proteins, such as activated focal adhesion kinase (pFAK), activated Ras-related C3 botulinum toxin substrate 1 (Rac1-GTP) and cell division control protein 42 (Cdc42). As the presence of cellular protrusion, called filopodia, has been indicated as a hallmark of migrating cells, we showed that the reduction of the mentioned proteins correlated well with the disappearance of filopodia. In summary, this study demonstrates the promising activity of TDB and its mechanism in the inhibition of lung cancer cell migration, which might be useful for encouraging the development of this compound for antimetastatic approaches.

Periostin Is a Key Niche Component for Wound Metastasis of Melanoma

Tissue injury promotes metastasis of several human cancers, although factors associated with wound healing that attract circulating tumor cells have remained unknown. Here, we examined the primary and metastatic lesions that appeared 1 month after trauma in a patient with acral lentiginous melanoma. The levels of mRNA for periostin (POSTN), type 1 collagen, and fibronectin were significantly increased in the metastatic lesion relative to the primary lesion. The increase of these extracellular matrix proteins at the wound site was reproduced in a mouse model of wound healing, with the upregulation of Postn mRNA persisting the longest. POSTN was expressed in the region surrounding melanoma cell nests in metastatic lesions of both wounded mice and the patient. POSTN attenuated the cell adhesion and promoted the migration of melanoma cells without affecting their proliferation in vitro. In the mouse model, the wound site as well as subcutaneously injected osteoblasts that secrete large amounts of POSTN invited the metastasis of remotely-transplanted melanoma cells on the sites. Osteoblasts with suppression of POSTN by shRNA showed a greatly reduced ability to promote such metastasis. Our results suggest that POSTN is a key factor in promoting melanoma cell metastasis to wound sites by providing a premetastatic niche.

Tumor invasion optimization by mesenchymal-amoeboid heterogeneity

Metastasizing tumor cells migrate through the surrounding tissue and extracellular matrix toward the blood vessels, in order to colonize distant organs. They typically move in a dense environment, filled with other cells. In this work we study cooperative effects between neighboring cells of different types, migrating in a maze-like environment with directional cue. Using a computerized model, we measure the percentage of cells that arrive to the defined target, for different mesenchymal/amoeboid ratios. Wall degradation of mesenchymal cells, as well as motility of both types of cells, are coupled to metabolic energy-like resource level. We find that indirect cooperation emerges in mid-level energy, as mesenchymal cells create paths that are used by amoeboids. Therefore, we expect to see a small population of mesenchymals kept in a mostly-amoeboid population. We also study different forms of direct interaction between the cells, and show that energy-dependent interaction strength is optimal for the migration of both mesenchymals and amoeboids. The obtained characteristics of cellular cluster size are in agreement with experimental results. We therefore predict that hybrid states, e.g. epithelial-mesenchymal, should be utilized as a stress-response mechanism.

Oblongifolin C inhibits metastasis by up-regulating keratin 18 and tubulins

Tumor metastasis is the main cause of cancer-related patient death. In this study, we performed a wound healing migration screen to search for a metastatic inhibitor within our library of natural compounds. We found that oblongifolin C (OC), a natural compound extracted from Garcinia yunnanensis Hu, is an effective inhibitor of metastasis in human esophageal squamous carcinoma Eca109 cells. The transwell migration and matrigel invasion assay results also showed that OC inhibits the migration of Eca109 cells and HepG2 cells. OC can increase the expression of tubulin, indicating that OC inhibits metastasis via tubulin aggregation. In addition, the Western blotting, real-time PCR, and immunostaining results indicated that OC increases the expression of keratin18. Furthermore, the knockdown of keratin 18 by small interfering RNAs inhibited the expression of tubulin and increased the metastasis of cancer cells, suggesting that keratin 18 is the upstream signal of tubulin and plays a vital role in metastasis. A subsequent study in a tail vein injection metastasis model showed that OC can significantly inhibit pulmonary metastasis, as revealed by immunohistochemistry staining. Taken together, our results suggest that OC inhibits metastasis through the induction of the expression of keratin 18 and may be useful in cancer therapy.

Can oncology recapitulate paleontology? Lessons from species extinctions

Although we can treat cancers with cytotoxic chemotherapies, target them with molecules that inhibit oncogenic drivers, and induce substantial cell death with radiation, local and metastatic tumours recur, resulting in extensive morbidity and mortality. Indeed, driving a tumour to extinction is difficult. Geographically dispersed species of organisms are perhaps equally resistant to extinction, but >99.9% of species that have ever existed on this planet have become extinct. By contrast, we are nowhere near that level of success in cancer therapy. The phenomena are broadly analogous--in both cases, a genetically diverse population mutates and evolves through natural selection. The goal of cancer therapy is to cause cancer cell population extinction, or at least to limit any further increase in population size, to prevent the tumour burden from overwhelming the patient. However, despite available treatments, complete responses are rare, and partial responses are limited in duration. Many patients eventually relapse with tumours that evolve from cells that survive therapy. Similarly, species are remarkably resilient to environmental change. Paleontology can show us the conditions that lead to extinction and the characteristics of species that make them resistant to extinction. These lessons could be translated to improve cancer therapy and prognosis.

Bone specific immunity and its impact on metastasis

Bone is one of the most common sites of metastasis in solid malignancy. Contributing to this osteotropism are the dynamic interactions between tumor cells and the numerous cell types resident in the normal bone, particularly osteoclasts and osteoblasts, which create a tumor supporting microenvironment. However, disseminated cells are detected in the bone marrow long before evidence of metastatic outgrowth, and it is likely that prolonged survival is also reliant on immunoescape. Compared with other peripheral organs such as the lung and spleen, the bone marrow constitutes a unique immune cell compartment that likely provides an immune privileged niche for disseminated tumor cells. This includes the large proportions of immunosuppressive cells, including myeloid derived suppressor cells and regulatory T cells, that blunt the activity of cytotoxic lymphocytes involved in tumor immunosurveillance. This review highlights key aspects of the osteoimmune landscape and emerging mechanisms by which tumor cells create or co-opt an immunosuppressed niche to support their outgrowth in bone. Future studies in this field are likely to shed light on the differences in immunoregulation between the bone and other sites including the primary tumor, and the potential for immunotherapeutics in treating disseminated disease in the bone. However, more immunocompetent models, that recapitulate tumor heterogeneity and bone metastasis need to be developed to accelerate this field.

Longitudinal Tracing of Spontaneous Regression and Anti-angiogenic Response of Individual Microadenomas during Colon Tumorigenesis

Angiogenesis is essential for the progression of cancer, but its involvement in the initial phase of colon tumorigenesis is not well understood. Using intravital endomicroscopy, we visualized the natural history of early pre-tumorous lesions and adenomas in the colon of conditional Apc-knockout and Apc/Kras double mutant mouse models. Early lesions emerged about 4 weeks after the onset of somatic mutations, accompanying vascular dilation when the size of lesions reached about 200 μm, but most lesions regressed spontaneously and cleared within 10 weeks after their emergence. Anti-angiogenic treatments with vascular endothelial growth factor receptor (VEGFR) antagonists reduced the size of the early lesions and the number of polyps. We found surprisingly that anti-angiogenic treatments delayed the natural clearance of transient lesions by up to several weeks in both genetic models. The results represent the previously unexpected role of early angiogenesis on the spontaneous regression of early-stage colon tumors.

Social defeat stress promotes tumor growth and angiogenesis by upregulating vascular endothelial growth factor/extracellular signal-regulated kinase/matrix metalloproteinase signaling in a mouse model of lung carcinoma

Numerous epidemiological and experimental animal studies have indicated that chronic psychological stress may promote tumor development. However, the underlying molecular mechanisms by which chronic stress promotes tumorigenesis remain to be fully elucidated and animal models have not yet been well established. In the present study, an established mouse model of repeated social defeat stress (RSDS), was generated and used to investigate the effect of stress on tumor growth and metastasis. C57BL/6 mice were exposed to RSDS for 10 days, followed by subcutaneousl inoculation with Lewis lung carcinoma cells for seven days. The tumor weight and volume as well as the number of the lung metastatic nodules were then determined. Vascular endothelial growth factor (VEGF) serum levels were measured using ELISAs. In addition, expression levels of VEGF receptor (VEGFR) and L1 cell adhesion molecule (L1CAM) messenger (m)RNA were confirmed using reverse transcription quantitative polymerase chain reaction. Furthermore, protein expression levels of phosphorlyated extracellular signal-regulated kinase (pERK), matrix metalloproteinase (MMP)-2 and MMP-9 were examined using western blot analysis. The results showed that RSDS significantly increased the weight and the volume of the primary tumor as well as the number of the lung metastatic nodules. Serum VEGF levels were significantly higher in the tumor-stress group compared with those of the unstressed tumor mice. In addition, tumors in stressed animals demonstrated markedly enhanced expression of VEGFR-2 and L1CAM mRNA as well as pERK, MMP-2 and MMP-9 protein expression. In conclusion, these results suggested that RSDS contributed to lung cancer progression, angiogenesis and metastasis, which was partially associated with increased VEGF secretion and therefore the activation of the ERK signaling pathway, resulting in the induction of MMP-2 and MMP-9 protein expression.

Spatial heterogeneity in drug concentrations can facilitate the emergence of resistance to cancer therapy

Acquired resistance is one of the major barriers to successful cancer therapy. The development of resistance is commonly attributed to genetic heterogeneity. However, heterogeneity of drug penetration of the tumor microenvironment both on the microscopic level within solid tumors as well as on the macroscopic level across metastases may also contribute to acquired drug resistance. Here we use mathematical models to investigate the effect of drug heterogeneity on the probability of escape from treatment and the time to resistance. Specifically we address scenarios with sufficiently potent therapies that suppress growth of all preexisting genetic variants in the compartment with the highest possible drug concentration. To study the joint effect of drug heterogeneity, growth rate, and evolution of resistance, we analyze a multi-type stochastic branching process describing growth of cancer cells in multiple compartments with different drug concentrations and limited migration between compartments. We show that resistance is likely to arise first in the sanctuary compartment with poor drug penetrations and from there populate non-sanctuary compartments with high drug concentrations. Moreover, we show that only below a threshold rate of cell migration does spatial heterogeneity accelerate resistance evolution, otherwise deterring drug resistance with excessively high migration rates. Our results provide new insights into understanding why cancers tend to quickly become resistant, and that cell migration and the presence of sanctuary sites with little drug exposure are essential to this end.

Failure of cancer therapy is commonly attributed to the outgrowth of pre-existing resistant mutants already present prior to treatment, yet there is increasing evidence that the tumor microenvironment influences cell sensitivity to drugs and thus mediates the evolution of resistance during treatment. Here, we take into consideration important aspects of the tumor microenvironment, including spatial drug gradients and differential rates of cell proliferation. We show that the dependence of fitness on space together with cell migration facilitates the emergence of acquired resistance. Our analysis indicates that resistant cells that are selected for in compartments with high concentrations are likely to disseminate from sanctuary sites where they first acquire resistance preceding migration. The results suggest that it would be helpful to improve clinical outcomes by combining targeted therapy with anti-metastatic treatment aimed at constraining cell motility as well as by enhancing drug transportation and distribution throughout all metastatic compartments.

Increased expression of formin-like 3 contributes to metastasis and poor prognosis in colorectal carcinoma

Formin-like 3 (FMNL3), a member of diaphanous-related formins subfamily, plays an important role in cytoskeleton reorganization, cell adhesion and cancer cell invasion in vitro. This study aimed to explore the expression of FMNL3 in colorectal carcinoma (CRC) cell-lines and tissues, and further evaluate its prognostic value and correlation with the clinicopathological parameters, and also investigate the effects of FMNL3 gene silencing on the growth and metastasis of CRC in vivo. Immunohistochemical analysis showed that FMNL3 protein was distributed in a punctuate aggregation pattern and located mainly in the cytoplasm of glandular cavity side, close to the nucleus of CRC cells. The positive rate of FMNL3 expression was 87.5% (84/96) in CRC, which was significantly higher than that in adjacent normal mucosa (30%, 9/30). Moreover, FMNL3 protein expressed far more in primary CRC with metastasis and corresponding lymph nodes metastatic CRC than in primary CRC without metastasis. Increased expression of FMNL3 was closely correlated with tumor size, differentiation, serosal invasion, and both lymph node metastasis and distant metastasis. However, it was not correlated with patients' age and gender. According to Kaplan-Meier survival analyses, patients with FMNL3 high expression level had lower overall survival rate than that with FMNL3 low expression level. Univariate and multivariate analyses revealed that high FMNL3 expression was a significant and independent prognostic predictor of patients with CRC. In addition, FMNL3 mRNA and protein levels were substantially up-regulated in CRC-metastasis-derived cell lines, as compared to those in primary-CRC-derived ones. FMNL3 gene silencing suppressed the growth and metastasis of CRC in vivo. In conclusion, FMNL3 plays an important role in the progression and metastasis of CRC and may be a novel potential prognostic predictor and therapeutic target for patients with CRC.

Methods for rectifying cell motions in vitro: breaking symmetry using microfabrication and microfluidics

Cell motility is an important phenomenon in cell biology, developmental biology, and cancer. Here we report methods that we designed to identify and characterize external factors which direct cell motions by breaking locally the symmetry. We used microfabrication and microfluidics techniques to impose and combine mechanical and chemical cues to moving fibroblasts. Gradients can thereby be engineered at the cellular scale and this approach has allowed to disentangle roles of the nucleus and protrusion activity in setting cell directions.

Crosstalk between cancer cells and blood endothelial and lymphatic endothelial cells in tumour and organ microenvironment

Tumour and organ microenvironments are crucial for cancer progression and metastasis. Crosstalk between multiple non-malignant cell types in the microenvironments and cancer cells promotes tumour growth and metastasis. Blood and lymphatic endothelial cells (BEC and LEC) are two of the components in the microenvironments. Tumour blood vessels (BV), comprising BEC, serve as conduits for blood supply into the tumour, and are important for tumour growth as well as haematogenous tumour dissemination. Lymphatic vessels (LV), comprising LEC, which are relatively leaky compared with BV, are essential for lymphogenous tumour dissemination. In addition to describing the conventional roles of the BV and LV, we also discuss newly emerging roles of these endothelial cells: their crosstalk with cancer cells via molecules secreted by the BEC and LEC (also called angiocrine and lymphangiocrine factors). This review suggests that BEC and LEC in various microenvironments can be orchestrators of tumour progression and proposes new mechanism-based strategies to discover new therapies to supplement conventional anti-angiogenic and anti-lymphangiogenic therapies.

Krüppel-like factors in cancer progression: three fingers on the steering wheel

Krüppel-like factors (KLFs) comprise a highly conserved family of zinc finger transcription factors, that are involved in a plethora of cellular processes, ranging from proliferation and apoptosis to differentiation, migration and pluripotency. During the last few years, evidence on their role and deregulation in different human cancers has been emerging. This review will discuss current knowledge on Krüppel-like transcription in the epithelial-mesenchymal transition (EMT), invasion and metastasis, with a focus on epithelial cancer biology and the extensive interface with pluripotency. Furthermore, as KLFs are able to mediate different outcomes, important influences of the cellular and microenvironmental context will be highlighted. Finally, we attempt to integrate diverse findings on KLF functions in EMT and stem cell biology to ft in the current model of cellular plasticity as a tool for successful metastatic dissemination.

Microenvironment of tumor-draining lymph nodes: opportunities for liposome-based targeted therapy

The World Health Organization (WHO) recently reported that the total number of global cancer cases in 2013 reached 14 million, a 10% rise since 2008, while the total number of cancer deaths reached 8.2 million, a 5.2% increase since 2008. Metastasis is the major cause of death from cancer, accounting for 90% of all cancer related deaths. Tumor-draining lymph nodes (TDLN), the sentinel nodes, are the first organs of metastasis in several types of cancers. The extent of metastasis in the TDLN is often used in disease staging and prognosis evaluation in cancer patients. Here, we describe the microenvironment of the TDLN and review the recent literature on liposome-based therapies directed to immune cells within the TDLN with the intent to target cancer cells.

Anti-nicastrin monoclonal antibodies elicit pleiotropic anti-tumour pharmacological effects in invasive breast cancer cells

The goal of targeted cancer therapies is to specifically block oncogenic signalling, thus maximising efficacy, while reducing side-effects to patients. The gamma-secretase (GS) complex is an attractive therapeutic target in haematological malignancies and solid tumours with major pharmaceutical activity to identify optimal inhibitors. Within GS, nicastrin (NCSTN) offers an opportunity for therapeutic intervention using blocking monoclonal antibodies (mAbs). Here we explore the role of anti-nicastrin monoclonal antibodies, which we have developed as specific, multi-faceted inhibitors of proliferation and invasive traits of triple-negative breast cancer cells. We use 3D in vitro proliferation and invasion assays as well as an orthotopic and tail vail injection triple-negative breast cancer in vivo xenograft model systems. RNAScope assessed nicastrin in patient samples. Anti-NCSTN mAb clone-2H6 demonstrated a superior anti-tumour efficacy than clone-10C11 and the RO4929097 small molecule GS inhibitor, acting by inhibiting GS enzymatic activity and Notch signalling in vitro and in vivo. Confirming clinical relevance of nicastrin as a target, we report evidence of increased NCSTN mRNA levels by RNA in situ hybridization (RNAScope) in a large cohort of oestrogen receptor negative breast cancers, conferring independent prognostic significance for disease-free survival, in multivariate analysis. We demonstrate here that targeting NCSTN using specific mAbs may represent a novel mode of treatment for invasive triple-negative breast cancer, for which there are few targeted therapeutic options. Furthermore, we propose that measuring NCSTN in patient samples using RNAScope technology may serve as companion diagnostic for anti-NCSTN therapy in the clinic.

Clinico-pathological correlation of E-cadherin expression at the invasive tumor front of Indian oral squamous cell carcinomas: An immunohistochemical study

Background:

Recent studies have indicated that although malignant cells at the invasive tumor front, bare morphological resemblance to the cells at central portion of the tumor, their molecular character differs significantly. E-cadherin is a cell-cell adhesion molecule that connects epithelial cells. This study attempts to correlate the E-cadherin expression at the invasive tumor front with tumor differentiation along with its clinico-pathological parameters.

Materials and Methods:

Immunohistochemical staining with E-cadherin was carried out on archival cases of primary oral squamous cell carcinomas (n = 30). The E-cadherin expression at the invasive tumor front was analyzed and was linked to clinico-pathological parameters including patient prognosis.

Results:

The downregulation of E-cadherin expression at the invasive tumor edge when compared with patient's prognosis yielded a significant correlation (P = 0.041) but its correlation with the degree of differentiation determined was not significant (P = 0.27). Also, its association with tumor size and lymph node status was negative.

Conclusions:

Loss of E-cadherin expression at the invasive tumor front is an important event in the progression of oral squamous cell carcinomas. Tumors with a loss of expression of E-cadherin are those which had a poor prognosis

Intravital multiphoton imaging reveals multicellular streaming as a crucial component of in vivo cell migration in human breast tumors

Metastasis is the main cause of death in breast cancer patients. Cell migration is an essential component of almost every step of the metastatic cascade, especially the early step of invasion inside the primary tumor. In this report, we have used intravital multiphoton microscopy to visualize the different migration patterns of human breast tumor cells in live primary tumors. We used xenograft tumors of MDA-MB-231 cells as well as a low passage xenograft tumor from orthotopically injected patient-derived breast tumor cells. Direct visualization of human tumor cells in vivo shows two patterns of high-speed migration inside primary tumors: (1) single cells and (2) multicellular streams (i.e., cells following each other in a single file but without cohesive cell junctions). Critically, we found that only streaming and not random migration of single cells was significantly correlated with proximity to vessels, with intravasation and with numbers of elevated circulating tumor cells in the bloodstream. Finally, although the two human tumors were derived from diverse genetic backgrounds, we found that their migratory tumor cells exhibited coordinated gene expression changes that led to the same end-phenotype of enhanced migration involving activating actin polymerization and myosin contraction. Our data are the first direct visualization and assessment of in vivo migration within a live patient-derived breast xenograft tumor.

High-throughput 3D cell invasion chip enables accurate cancer metastatic assays

Chemotaxis is the phenomenon by which the migration and invasion of cells is directed in response to an extracellular chemical gradient. Chemotaxis of tumor cells and tumor-associated inflammatory and stromal cells is mediated by chemokines, chemokine receptors, growth factors, and growth factor receptors. Current techniques used to study chemotactic driven cell invasion and metastasis utilize two-dimensional migration assays involving imaging and analyzing tumor cells on glass slides or plastic surfaces, which requires large numbers of cells and often lacks real-time monitoring of vertical cell movement and systematically controlled chemotactic gradients, leading to contradictory results compared to those from clinical investigations and animal models. We addressed such challenges by developing a high-throughput microdevice with 4000 ultraminiaturized wells to monitor real-time, three-dimensional cell invasion over a wide range of cell densities and also screen drugs that inhibit cell invasion and potentially prevent metastatic malignancy. Additionally, this microdevice generates opposing gradients for two types of cells on the same chip, which builds a controlled system with sequentially changing components to study environmental effects from basal and immune cells.

Targeting JAK1/STAT3 signaling suppresses tumor progression and metastasis in a peritoneal model of human ovarian cancer

JAK/STAT3 is one of the major signaling pathways that is aberrantly activated in ovarian cancer and associated with tumor progression and poor prognosis in patients with ovarian cancer. In this study, we evaluated the therapeutic potential of targeting JAK/STAT3 signaling in ovarian cancer using a peritoneal dissemination mouse model. We developed this mouse model by injecting a metastatic human ovarian cancer cell line, SKOV3-M-Luc, into the peritoneal cavity of immunodeficient mice. This model displayed a phenotype similar to late-stage ovarian cancer, including extensive peritoneal metastasis and ascites production. The constitutive activation of STAT3 in human ovarian cancer cells appeared to be mediated by an autocrine cytokine loop involving the IL6 family of cytokines and JAK1 kinase. shRNA-mediated knockdown of JAK1 or STAT3 in ovarian cancer cells led to reduced tumor growth, decreased peritoneal dissemination, and diminished ascites production, suggesting a critical role of STAT3 in ovarian cancer progression. Similar results were obtained when a small-molecule inhibitor (JAKi) of the JAK1 kinase was used to treat ovarian cancer in this model. In addition, we found that the expression level of IL6 was correlated with activation of STAT3 in ovarian cancer cells both in vitro and in vivo, suggesting a potential application of IL6 as a biomarker. Altogether, our results demonstrate that targeting JAK1/STAT3, using shRNA knockdown or a small-molecule inhibitor, effectively suppressed ovarian tumor progression and, therefore, could be a potential novel therapeutic approach for treating advanced ovarian cancer.

Restriction of intramolecular motions: the general mechanism behind aggregation-induced emission

Aggregation-induced emission (AIE) has been harnessed in many systems through the principle of restriction of intramolecular rotations (RIR) based on mechanistic understanding from archetypal AIE molecules such as tetraphenylethene (TPE). However, as the family of AIE-active molecules grows, the RIR model cannot fully explain some AIE phenomena. Here, we report a broadening of the AIE mechanism through analysis of 10,10',11,11'-tetrahydro-5,5'-bidibenzo[a,d][7]annulenylidene (THBDBA), and 5,5'-bidibenzo[a,d][7]annulenylidene (BDBA). Analyses of the computational QM/MM model reveal that the novel mechanism behind the AIE of THBDBA and BDBA is the restriction of intramolecular vibration (RIV). A more generalized mechanistic understanding of AIE results by combining RIR and RIV into the principle of restriction of intramolecular motions (RIM).

Trichostatin A induces mesenchymal-like morphological change and gene expression but inhibits migration and colony formation in human cancer cells

Histone deacetylases (HDACs) are enzymes that catalyze the removal of acetyl from lysine residues in histones and other proteins, which results in gene transcriptional repression and subsequent changes in signaling events. HDACs inhibitors (HDACIs) have been used to reverse the aberrant epigenetic changes associated with cancer. However, the effects of HDACIs on epithelial-mesenchymal transition (EMT) in human cancer cells remain unclear. EMT is a fundamental process governing morphogenesis in multicellular organisms and promotes cancer invasion and metastasis. In this study, human cancer cells were treated with the HDACI trichostatin A (TSA). TSA was found to induce mesenchymal‑like morphological changes in BGC-823 human gastric cancer and MCF-7 breast cancer cells, and increase the expression levels of the mesenchymal markers Vimentin and Twist. However, the expression levels of the epithelial cell marker E-cadherin were also increased in response to TSA treatment, while cell migration was reduced by TSA. Furthermore, TSA decreased cancer cell colony formation in BGC-823 and MCF-7 cells, and led to the deregulation of β-catenin, a critical signaling molecule involved in EMT. In conclusion, the results suggested that TSA exhibits dual functions in EMT induction and inhibition in human cancer cells, but the detailed mechanisms require further investigation.

Advances and challenges in label-free nonlinear optical imaging using two-photon excitation fluorescence and second harmonic generation for cancer research

Nonlinear optical imaging (NLOI) has emerged to be a promising tool for bio-medical imaging in recent times. Among the various applications of NLOI, its utility is the most significant in the field of pre-clinical and clinical cancer research. This review begins by briefly covering the core principles involved in NLOI, such as two-photon excitation fluorescence (TPEF) and second harmonic generation (SHG). Subsequently, there is a short description on the various cellular components that contribute to endogenous optical fluorescence. Later on the review deals with its main theme--the challenges faced during label-free NLO imaging in translational cancer research. While this review addresses the accomplishment of various label-free NLOI based studies in cancer diagnostics, it also touches upon the limitations of the mentioned studies. In addition, areas in cancer research that need to be further investigated by label-free NLOI are discussed in a latter segment. The review eventually concludes on the note that label-free NLOI has and will continue to contribute richly in translational cancer research, to eventually provide a very reliable, yet minimally invasive cancer diagnostic tool for the patient.

A microfluidic platform for quantitative analysis of cancer angiogenesis and intravasation

Understanding the mechanism behind cancer metastasis is a major challenge in cancer biology. Several in vitro models have been developed to mimic a cancer microenvironment by engineering cancer-endothelial cell (EC) and cancer-stromal cell interactions. It has been challenging to realistically mimic angiogenesis, intravasation, and extravasation using macro-scale approaches but recent progress in microfluidics technology has begun to yield promising results. We present a metastasis chip that produce microvessels, where EC and stromal cells can be patterned in close proximity to tumor cells. The vessels are formed following a natural morphogenic process and have smooth boundaries with proper cell-cell junctions. The engineered microvessels are perfusable and have well-defined openings toward inlet and outlet channels. The ability to introduce cancer cells into different locations bordering to the microvessel wall allowed generation and maintenance of appropriate spatial gradients of growth factors and attractants. Cancer angiogenesis and its inhibition by anti-vascular endothelial growth factor (bevacizumab) treatment were successfully reproduced in the metastasis chip. Cancer intravasation and its modulation by treatment of tumor necrosis factor-α were also modeled. Compared to other models, the unique design of the metastasis chip that engineers a clear EC-cancer interface allows precise imaging and quantification of angiogenic response as well as tumor cell trans-endothelial migration. The metastasis chip presented here has potential applications in the investigation of fundamental cancer biology as well as in drug screening.

Illuminating breast cancer invasion: diverse roles for cell-cell interactions

Metastasis begins when tumors invade into surrounding tissues. In breast cancer, the study of cell interactions has provided fundamental insights into this complex process. Powerful intravital and 3D organoid culture systems have emerged that enable biologists to model the complexity of cell interactions during cancer invasion in real-time. Recent studies utilizing these techniques reveal distinct mechanisms through which multiple cancer cell and stromal cell subpopulations interact, including paracrine signaling, direct cell-cell adhesion, and remodeling of the extracellular matrix. Three cell interaction mechanisms have emerged to explain how breast tumors become invasive: epithelial-mesenchymal transition, collective invasion, and the macrophage-tumor cell feedback loop. Future work is needed to distinguish whether these mechanisms are mutually exclusive or whether they cooperate to drive metastasis.

Metastasis review: from bench to bedside

Cancer is the final result of uninhibited cell growth that involves an enormous group of associated diseases. One major aspect of cancer is when cells attack adjacent components of the body and spread to other organs, named metastasis, which is the major cause of cancer-related mortality. In developing this process, metastatic cells must successfully negotiate a series of complex steps, including dissociation, invasion, intravasation, extravasation, and dormancy regulated by various signaling pathways. In this review, we will focus on the recent studies and collect a comprehensive encyclopedia in molecular basis of metastasis, and then we will discuss some new potential therapeutics which target the metastasis pathways. Understanding the new aspects on molecular mechanisms and signaling pathways controlling tumor cell metastasis is critical for the development of therapeutic strategies for cancer patients that would be valuable for researchers in both fields of molecular and clinical oncology.

TRIM27/MRTF-B-dependent integrin β1 expression defines leading cells in cancer cell collectives

For collective invasion, cancer cells form cohesive groups comprised of leading cells (LCs) at the forefront and following cells (FCs) at the rear. However, the molecular mechanisms that define LCs and FCs remain elusive. Here, we demonstrated that LCs, but not FCs, upregulated the expression of integrin β1 after the loss of intercellular adhesion. The LC-specific expression of integrin β1 was posttranscriptionally regulated by the TRIM27/MRTF-B complex in response to the loss of intercellular adhesion, thereby regulating the stability and translation of integrin β1 mRNA via microRNA-124 in LCs. Accordingly, depletion of TRIM27 and MRTF-B abrogated the upregulation of integrin β1 in LCs and blocked the invasion of cancer cell groups in vitro and in vivo. Therefore, our findings revealed that the specific function of LCs was defined by intrinsic mechanisms related to the presence of the cell's free surface, providing insights into the regulation of intratumor heterogeneity.

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.

Mesenchymal to amoeboid transition is associated with stem-like features of melanoma cells

Background

Cellular plasticity confers cancer cells the ability to adapt to microenvironmental changes, a fundamental requirement for tumour progression and metastasis. The epithelial to mesenchymal transition (EMT) is a transcriptional programme associated with increased cell motility and stemness. Besides EMT, the mesenchymal to amoeboid transition (MAT) has been described during tumour progression but to date, little is known about its transcriptional control and involvement in stemness. The aim of this manuscript is to investigate (i) the transcriptional profile associated with the MAT programme and (ii) to study whether MAT acquisition in melanoma cancer cells correlates with clonogenic potential to promote tumour growth.

Results

By using a multidisciplinary approach, we identified four different treatments able to induce MAT in melanoma cells: EphA2 overexpression, Rac1 functional inhibition using its RacN17 dominant negative mutant, stimulation with Ilomastat or treatment with the RhoA activator Calpeptin. First, gene expression profiling identified the transcriptional pathways associated with MAT, independently of the stimulus that induces the MAT programme. Notably, gene sets associated with the repression of mesenchymal traits, decrease in the secretion of extracellular matrix components as well as increase of cellular stemness positively correlate with MAT. Second, the link between MAT and stemness has been investigated in vitro by analysing stemness markers and clonogenic potential of melanoma cells undergoing MAT. Finally, the link between MAT inducing treatments and tumour initiating capability has been validated in vivo.

Conclusion

Taken together, our results demonstrate that MAT programme in melanoma is characterised by increased stemness and clonogenic features of cancer cells, thus sustaining tumour progression. Furthermore, these data suggest that stemness is not an exclusive feature of cells undergoing EMT, but more generally is associated with an increase in cellular plasticity of cancer cells.

Downregulation of BRAF activated non-coding RNA is associated with poor prognosis for non-small cell lung cancer and promotes metastasis by affecting epithelial-mesenchymal transition

Background

Recent evidence indicates that long noncoding RNAs (lncRNAs) play a critical role in the regulation of cellular processes, such as differentiation, proliferation and metastasis. These lncRNAs are found to be dysregulated in a variety of cancers. BRAF activated non-coding RNA (BANCR) is a 693-bp transcript on chromosome 9 with a potential functional role in melanoma cell migration. The clinical significance of BANCR, and its’ molecular mechanisms controlling cancer cell migration and metastasis are unclear.

Methods

Expression of BANCR was analyzed in 113 non-small cell lung cancer (NSCLC) tissues and seven NSCLC cell lines using quantitative polymerase chain reaction (qPCR) assays. Gain and loss of function approaches were used to investigate the biological role of BANCR in NSCLC cells. The effects of BANCR on cell viability were evaluated by MTT and colony formation assays. Apoptosis was evaluated by Hoechst staining and flow cytometry. Nude mice were used to examine the effects of BANCR on tumor cell metastasis in vivo. Protein levels of BANCR targets were determined by western blotting and fluorescent immunohistochemistry.

Results

BANCR expression was significantly decreased in 113 NSCLC tumor tissues compared with normal tissues. Additionally, reduced BANCR expression was associated with larger tumor size, advanced pathological stage, metastasis distance, and shorter overall survival of NSCLC patients. Reduced BANCR expression was found to be an independent prognostic factor for NSCLC. Histone deacetylation was involved in the downregulation of BANCR in NSCLC cells. Ectopic expression of BANCR impaired cell viability and invasion, leading to the inhibition of metastasis in vitro and in vivo. However, knockdown of BANCR expression promoted cell migration and invasion in vitro. Overexpression of BANCR was found to play a key role in epithelial-mesenchymal transition (EMT) through the regulation of E-cadherin, N-cadherin and Vimentin expression.

Conclusion

We determined that BANCR actively functions as a regulator of EMT during NSCLC metastasis, suggesting that BANCR could be a biomarker for poor prognosis of NSCLC.

Mechanical decision trees for investigating and modulating single-cell cancer invasion dynamics

Physical cues exist across all biological scales, from the geometries of molecules to the shapes of complex organisms. While their roles have been identified across a range of scales, i.e. the arrangements of biomolecules and the form and function of tissues, less is known in some intermediate lengths. Particularly, at the cell scale, there is emerging evidence demonstrating the impact of mechanical signals, such as substrate stiffness and confinement, on many critical biological processes and malignancies, especially cancer dissemination. In the context of cell invasion, it is currently unclear how cells select from accessible mechanical paths that result in migratory patterns observed in physiological environments. Here, we devise microchannel decision trees to explore how fundamental and ubiquitous mechanical factors, specifically dimensionality and directionality, affect migratory cell decision making. We then implement strategies based purely on mechanical asymmetries to induce repetitive, non-disseminating motions, in a phenomenon we call iteratio ad nauseam.

β-catenin inhibitor ICAT modulates the invasive motility of melanoma cells

Inhibitor of β-catenin and TCF (ICAT) inhibits β-catenin transcriptional activity by competing with T-cell factor/lymphoid enhancer factor. We documented high ICAT levels in human melanoma cells, in which β-catenin signaling is frequently deregulated, finding a correlation with the capacity to form metastases in nude mice. Ectopic expression of ICAT in melanoma cells did not affect their proliferation but increased cell motility and Matrigel invasion of metastatic cells in a manner relying upon stable ICAT-β-catenin interaction. This effect was associated with conversion of an elongated/mesenchymal phenotype to a round/amoeboid phenotype in the absence of similar effects on elongated morphology of nonmetastatic melanoma cells. Transition from mesenchymal to amoeboid movement was associated with decreased levels of NEDD9 and activated Rac1, a positive regulator of mesenchymal movement. Ectopic ICAT promoted colonization of melanoma cells in the lungs of nude mice, suggesting an increase in metastatic potential. Together, our results showed that by downregulating Rac signaling in metastatic melanoma cells, ICAT increased their invasive motility by promoting a morphologic variation that facilitates a favorable adaptation to their microenvironment.

Invading cancer cells are predominantly in G0/G1 resulting in chemoresistance demonstrated by real-time FUCCI imaging

Invasive cancer cells are a critical target in order to prevent metastasis. In the present report, we demonstrate real-time visualization of cell cycle kinetics of invading cancer cells in 3-dimensional (3D) Gelfoam® histoculture, which is in vivo-like. A fluorescence ubiquitination cell cycle indicator (FUCCI) whereby G0/G1 cells express a red fluorescent protein and S/G2/M cells express a green fluorescent protein was used to determine the cell cycle position of invading and non-invading cells. With FUCCI 3D confocal imaging, we observed that cancer cells in G0/G1 phase in Gelfoam® histoculture migrated more rapidly and further than cancer cells in S/G2/M phases. Cancer cells ceased migrating when they entered S/G2/M phases and restarted migrating after cell division when the cells re-entered G0/G1. Migrating cancer cells also were resistant to cytotoxic chemotherapy, since they were preponderantly in G0/G1, where cytotoxic chemotherapy is not effective. The results of the present report suggest that novel therapy targeting G0/G1 cancer cells should be developed to prevent metastasis.

Microvesicles as mediators of intercellular communication in cancer

The discovery that cancer cells generate large membrane-enclosed packets of epigenetic information, known as microvesicles (MVs), that can be transferred to other cells and influence their behavior (Antonyak et al., Small GTPases 3:219-224, 2012; Cocucci et al., Trends Cell Biol 19:43-51, 2009; Rak, Semin Thromb Hemost 36:888-906, 2010; Skog et al., Nat Cell Biol 10:1470-1476, 2008) has added a unique perspective to the classical paracrine signaling paradigm. This is largely because, in addition to growth factors and cytokines, MVs contain a variety of components that are not usually thought to be released into the extracellular environment by viable cells including plasma membrane-associated proteins, cytosolic- and nuclear-localized proteins, as well as nucleic acids, particularly RNA transcripts and micro-RNAs (Skog et al., Nat Cell Biol 10:1470-1476, 2008; Al-Nedawi et al., Nat Cell Biol 10:619-624, 2008; Antonyak et al., Proc Natl Acad Sci U S A 108:4852-4857, 2011; Balaj et al., Nat Commun 2:180, 2011; Choi et al., J Proteome Res 6:4646-4655, 2007; Del Conde et al., Blood 106:1604-1611, 2005; Gallo et al., PLoS One 7:e30679, 2012; Graner et al., FASEB J 23:1541-1557, 2009; Grange et al., Cancer Res 71:5346-5356, 2011; Hosseini-Beheshti et al., Mol Cell Proteomics 11:863-885, 2012; Martins et al., Curr Opin Oncol 25:66-75, 2013; Noerholm et al., BMC Cancer 12:22, 2012; Zhuang et al., EMBO J 31:3513-3523, 2012). When transferred between cancer cells, MVs have been shown to stimulate signaling events that promote cell growth and survival (Al-Nedawi et al., Nat Cell Biol 10:619-624, 2008). Cancer cell-derived MVs can also be taken up by normal cell types that surround the tumor, an outcome that helps shape the tumor microenvironment, trigger tumor vascularization, and even confer upon normal recipient cells the transformed characteristics of a cancer cell (Antonyak et al., Proc Natl Acad Sci U S A 108:4852-4857, 2011; Martins et al., Curr Opin Oncol 25:66-75, 2013; Al-Nedawi et al., Proc Natl Acad Sci U S A 106:3794-3799, 2009; Ge et al., Cancer Microenviron 5:323-332, 2012). Thus, the production of MVs by cancer cells plays crucial roles in driving the expansion of the primary tumor. However, it is now becoming increasingly clear that MVs are also stable in the circulation of cancer patients, where they can mediate long-range effects and contribute to the formation of the pre-metastatic niche, an essential step in metastasis (Skog et al., Nat Cell Biol 10:1470-1476, 2008; Noerholm et al., BMC Cancer 12:22, 2012; Peinado et al., Nat Med 18:883-891, 2012; Piccin et al., Blood Rev 21:157-171, 2007; van der Vos et al., Cell Mol Neurobiol 31:949-959, 2011). These findings, when taken together with the fact that MVs are being aggressively pursued as diagnostic markers, as well as being considered as potential targets for intervention against cancer (Antonyak et al., Small GTPases 3:219-224, 2012; Hosseini-Beheshti et al., Mol Cell Proteomics 11:863-885, 2012; Martins et al., Curr Opin Oncol 25:66-75, 2013; Ge et al., Cancer Microenviron 5:323-332, 2012; Peinado et al., Nat Med 18:883-891, 2012; Piccin et al., Blood Rev 21:157-171, 2007; Al-Nedawi et al., Cell Cycle 8:2014-2018, 2009; Cocucci and Meldolesi, Curr Biol 21:R940-R941, 2011; D'Souza-Schorey and Clancy, Genes Dev 26:1287-1299, 2012; Shao et al., Nat Med 18:1835-1840, 2012), point to critically important roles for MVs in human cancer progression that can potentially be exploited to develop new targeted approaches for treating this disease.

Liprin-α1, ERC1 and LL5 identify a polarized, dynamic compartment implicated in cell migration

Cell migration during development and metastatic invasion requires the coordination of actin and adhesion dynamics to promote the protrusive activity at the cell front. The knowledge of the molecular mechanisms required to achieve such coordination is fragmentary. Here we identify a new functional complex that drives cell motility. The adaptor proteins ERC1a and LL5 are required with liprin-α1 for effective migration and tumor cell invasion, and do so by stabilizing the protrusive activity at the cell front. Depletion of either protein negatively affects invasion, migration on extracellular matrix, lamellipodial persistence, as well as the internalization of active integrin β1 receptors needed for adhesion turnover at the cell front. Liprin-α1, ERC1a and LL5 also define new highly polarized and dynamic cytoplasmic structures uniquely localized near the protruding cell edge. Our results indicate that the functional complex and the associated structures described here represent an important mechanism to drive tumor cell migration.