Tumor metastasis: moving new biological insights into the clinic

Rab11-FIP2 promotes colorectal cancer migration and invasion by regulating PI3K/AKT/MMP7 signaling pathway

Rab11-family interacting proteins (Rab11-FIPs) belong to an evolutionarily conserved protein family and act as effector molecules for the Rab11 family of small GTPases. Recent evidence suggests that Rab11-FIPs have important roles in tumor progression and metastasis. However, the contribution of Rab11-FIPs to colorectal carcinoma (CRC) remains elusive. Our study focuses on elucidating the role of Rab11-FIP2 in the migration and invasion of colorectal cancer cells. We firstly found upregulation of Rab11-FIP2 in CRC tissues compared with peritumor tissues by oncomine data-mining analysis, western blot analysis and immunohistochemistry (IHC) analysis, respectively. Then, we demonstrated that knockdown of Rab11-FIP2 via siRNAs transfection resulted in a decrease in migration and invasion of CRC cells, while overexpression of Rab11-FIP2 via lentiviral infection increased migration and invasion of CRC cells. In addition, we verified that Rab11-FIP2 promoted migration and invasion of CRC cells through upregulating MMP7 expression. Finally, using several kinase inhibitors, our results showed that Rab11-FIP2 regulated MMP7 expression through activating PI3K/Akt signaling. Our data suggested a potential role of Rab11-FIP2 in tumor progression and provided novel insights into the mechanism of how Rab11-FIP2 positively regulated cell migration and invasion in CRC cells.

Therapy with Multipotent Mesenchymal Stromal Cells Protects Lungs from Radiation-Induced Injury and Reduces the Risk of Lung Metastasis

AIMS

Previous thorax irradiation promotes metastatic spread of tumor cells to the lung. We hypothesized that vascular damage facilitates lung metastasis after thorax irradiation and that therapeutically applied multipotent mesenchymal stromal cells (MSCs) with reported repair activity may prevent these adverse effects of ionizing radiation by protecting lung endothelia from radiation-induced damage.

RESULTS

Previous whole-thorax irradiation (WTI) with 15 Gy significantly enhanced seeding and metastatic growth of tumor cells in the lung. WTI was further associated with endothelial cell damage, senescence of lung epithelial cells, and upregulation of invasion- and inflammation-promoting soluble factors, for example, endothelial matrix metalloproteinase 2 (Mmp2), its activator Mmp14, the cofactor tissue inhibitor of metalloproteinases 2 (Timp2), chemokine (C-C motif) ligand 2 (Ccl2), and urokinase-type plasminogen activator (Plau/uPA), and recruitment of CD11b+CD11c- myelomonocytic cells. Inhibition of Mmp2 counteracted radiation-induced vascular dysfunction without preventing increased metastasis. In contrast, therapy with bone marrow or aorta-derived MSCs within 2 weeks postirradiation antagonized radiation-induced damage to resident cells as well as the resulting secretome changes and abrogated the metastasis-promoting effects of WTI.

INNOVATION

Therapy with MSCs protects lungs from radiation-induced injury and reduces the risk of lung metastasis. MSC-mediated inhibition of Mmp2 mediates their protective effects at the vasculature. Furthermore, local and systemic effects such as inhibition of radiation-induced senescence of bronchial epithelial cells and associated secretion of immunomodulatory factors may participate in the inhibitory effect of MSCs on lung metastasis.

CONCLUSION

MSC therapy is a promising strategy to prevent radiation-induced lung injury and the resulting increased risk of metastasis.

The Extraordinary Progress in Very Early Cancer Diagnosis and Personalized Therapy: The Role of Oncomarkers and Nanotechnology

The impact of nanotechnology on oncology is revolutionizing cancer diagnosis and therapy and largely improving prognosis. This is mainly due to clinical translation of the most recent findings in cancer research, that is, the application of bio- and nanotechnologies. Cancer genomics and early diagnostics are increasingly playing a key role in developing more precise targeted therapies for most human tumors. In the last decade, accumulation of basic knowledge has resulted in a tremendous breakthrough in this field. Nanooncology, through the discovery of new genetic and epigenetic biomarkers, has facilitated the development of more sensitive biosensors for early cancer detection and cutting-edge multifunctionalized nanoparticles for tumor imaging and targeting. In the near future, nanooncology is expected to enable a very early tumor diagnosis, combined with personalized therapeutic approaches.

Activation of Hematopoietic Stem/Progenitor Cells Promotes Immunosuppression Within the Pre-metastatic Niche

Metastatic tumors have been shown to establish microenvironments in distant tissues that are permissive to disseminated tumor cells. Hematopoietic cells contribute to this microenvironment, yet the precise initiating events responsible for establishing the pre-metastatic niche remain unclear. Here, we tracked the developmental fate of hematopoietic stem and progenitor cells (HSPC) in tumor-bearing mice. We show that a distant primary tumor drives the expansion of HSPCs within the bone marrow and their mobilization to the bloodstream. Treatment of purified HSPCs cultured ex vivo with tumor-conditioned media induced their proliferation as well as their differentiation into immunosuppressive myeloid cells. We furthered tracked purified HSPCs in vivo and found they differentiated into myeloid-derived suppressor cells in early metastatic sites of tumor-bearing mice. The number of CD11b(+)Ly6g(+) cells in metastatic sites was significantly increased by HSPC mobilization and decreased if tumor-mediated mobilization was inhibited. Moreover, pharmacologic mobilization of HSPCs increased metastasis, whereas depletion of Gr1(+) cells abrogated the metastasis-promoting effects of HSPC mobilization. Finally, we detected elevated levels of HSPCs in the circulation of newly diagnosed cancer patients, which correlated with increased risk for metastatic progression. Taken together, our results highlight bone marrow activation as one of the earliest steps of the metastatic process and identify circulating HSPCs as potential clinical indicators of metastatic niche formation.

Targeting tumor metastases: Drug delivery mechanisms and technologies

Primary sites of tumor are the focal triggers of cancers, yet it is the subsequent metastasis events that cause the majority of the morbidity and mortality. Metastatic tumor cells exhibit a phenotype that differs from that of the parent cells, as they represent a resistant, invasive subpopulation of the original tumor, may have acquired additional genetic or epigenetic alterations under exposure to prior chemotherapeutic or radiotherapeutic treatments, and reside in a microenvironment differing from that of its origin. This combination of resistant phenotype and distal location make tracking and treating metastases particularly challenging. In this review, we highlight some of the unique biological traits of metastasis, which in turn, inspire emerging strategies for targeted imaging of metastasized tumors and metastasis-directed delivery of therapeutics.

The isolation and characterization of CTC subsets related to breast cancer dormancy

Uncovering CTCs phenotypes offer the promise to dissect their heterogeneity related to metastatic competence. CTC survival rates are highly variable and this can lead to many questions as yet unexplored properties of CTCs responsible for invasion and metastasis vs dormancy. We isolated CTC subsets from peripheral blood of patients diagnosed with or without breast cancer brain metastasis. CTC subsets were selected for EpCAM negativity but positivity for CD44(+)/CD24(-) stem cell signature; along with combinatorial expression of uPAR and int β1, two markers directly implicated in breast cancer dormancy mechanisms. CTC subsets were cultured in vitro generating 3D CTC tumorspheres which were interrogated for biomarker profiling and biological characteristics. We identified proliferative and invasive properties of 3D CTC tumorspheres distinctive upon uPAR/int β1 combinatorial expression. The molecular characterization of uPAR/int β1 CTC subsets may enhance abilities to prospectively identify patients who may be at high risk of developing BCBM.

Novel (188)Re multi-functional bone-seeking compounds: Synthesis, biological and radiotoxic effects in metastatic breast cancer cells

INTRODUCTION

Radiolabeled bisphosphonates (BPs) have been used for bone imaging and delivery of β(-) emitting radionuclides for bone pain palliation. As a β(-) emitter, (188)Re has been considered particularly promising for bone metastases therapy. Aimed at finding innovative bone-seeking agents for systemic radiotherapy of bone metastases, we describe herein novel organometallic compounds of the type fac-[(188)Re(CO)3(k(3)-L)], (L=BP-containing chelator), their in vitro and in vivo stability, and their cellular damage in MDAMB231 cells, a metastatic breast cancer cell line.

METHODS

After synthesis and characterization of the novel organometallic compounds of the type fac-[(188)Re(CO)3(k(3)-L)] their radiochemical purity and in vitro stability was assessed by HPLC. In vivo stability and pharmacokinetic profile were evaluated in mice and the radiocytotoxic activity and DNA damage were assessed by MTT assay and by the cytokinesis-block micronucleus (CBMN) assay, respectively.

RESULTS

Among all complexes, (188)Re3 was obtained with high radiochemical purity (>95%) and high specific activity and presented high in vitro and in vivo stability. Biodistribution studies of (188)Re3 in Balb/c mice showed fast blood clearance, high bone uptake (16.1 ± 3.3% IA/g organ, 1h p.i.) and high bone-to-blood and bone-to-muscle radioactivity ratios, indicating that it is able to deliver radiation to bone in a very selective way. The radiocytotoxic effect elicited by (188)Re3 in the MDAMB231 cells was dependent on its concentration, and was higher than that induced by identical concentrations of [(188)ReO4](-). Additionally, (188)Re3 elicited morphological changes in the cells and induced DNA damage by the increased number of MN observed.

CONCLUSION

Altogether, our results demonstrate that (188)Re3 could be considered an attractive candidate for further preclinical evaluation for systemic radionuclide therapy of bone metastases considering its ability to deliver radiation to bone in a very selective way and to induce radiation damage.

Iroquois homeobox 2 suppresses cellular motility and chemokine expression in breast cancer cells

Background

Disseminated tumor cells (DTCs) can be detected using ultrasensitive immunocytochemical assays and their presence in the bone marrow can predict the subsequent occurrence of overt metastasis formation and metastatic relapse. Using expression profiling on early stage primary breast tumors, low IRX2 expression was previously shown to be associated with the presence of DTCs in the bone marrow, suggesting a possible role of IRX2 in the early steps of metastasis formation. The purpose of this study is to gain insights into the significance of IRX2 protein function in the progression of breast cancer.

Methods

To assess the physiological relevance of IRX2 in breast cancer, we evaluated IRX2 expression in a large breast cancer cohort (n = 1992). Additionally, constitutive IRX2 over expression was established in BT-549 and Hs578T breast cancer cell lines. Subsequently we analyzed whether IRX2 overexpression effects chemokine secretion and cellular motility of these cells.

Results

Low IRX2 mRNA expression was found to correlate with high tumor grade, positive lymph node status, negative hormone receptor status, and basal type of primary breast tumors. Also in cell lines low IRX2 expression was associated with mainly basal breast cancer cell lines. The functional studies show that overexpression of the IRX2 transcription factor in basal cell lines suppressed secretion of the pro-metastatic chemokines and inhibited cellular motility but did not influence cell proliferation.

Conclusion

Our results imply that the IRX2 transcription factor might represent a novel metastasis associated protein that acts as a negative regulator of cellular motility and as a repressor of chemokine expression. Loss of IRX2 expression could therefore contribute to early hematogenous dissemination of breast cancer by sustaining chemokine secretion and enabling mobilization of tumor cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1907-4) contains supplementary material, which is available to authorized users.

Tumor-Educated Platelets as Liquid Biopsy in Cancer Patients

Real-time monitoring of changes in cells or cell products released from malignant lesions into the blood has opened new diagnostic avenues ("liquid biopsy"). In this issue of Cancer Cell, Best and colleagues describe that tumor-associated blood platelets provide specific information on the location and molecular composition of the primary tumor.

The promise of liquid biopsy in cancer: a clinical perspective

The clinical utility of liquid biopsy in cancer treatment will increase as circulating tumor cells (CTCs) analysis move from the enumeration to the real-time measurement of tumor characteristics. Intratumor heterogeneity is becoming increasingly recognized as a major drawback to the shift to personalized medicine. Spatial and temporal heterogeneity might be reflected by the serial assessment of CTCs. Indeed, the developing technologies for CTCs analysis now allow digital genomic and next-generation sequencing approaches, able to differentiate molecular subtypes of the disease and to monitor genetic variation over time. The liquid biopsy of cancer might offer a real-time assessment of tumor biology, providing the opportunity to serially evaluate patients most likely to benefit from targeted drugs based on a dynamic characterization of the disease at the molecular level. Although hurdles remain before liquid biopsy is seen in routine clinical practice, the information derived from CTCs may facilitate the real-time identification of actionable mutations in cancer leading the way toward personalized medicine.

Mathematical Modelling of Molecular Pathways Enabling Tumour Cell Invasion and Migration

Understanding the etiology of metastasis is very important in clinical perspective, since it is estimated that metastasis accounts for 90% of cancer patient mortality. Metastasis results from a sequence of multiple steps including invasion and migration. The early stages of metastasis are tightly controlled in normal cells and can be drastically affected by malignant mutations; therefore, they might constitute the principal determinants of the overall metastatic rate even if the later stages take long to occur. To elucidate the role of individual mutations or their combinations affecting the metastatic development, a logical model has been constructed that recapitulates published experimental results of known gene perturbations on local invasion and migration processes, and predict the effect of not yet experimentally assessed mutations. The model has been validated using experimental data on transcriptome dynamics following TGF-β-dependent induction of Epithelial to Mesenchymal Transition in lung cancer cell lines. A method to associate gene expression profiles with different stable state solutions of the logical model has been developed for that purpose. In addition, we have systematically predicted alleviating (masking) and synergistic pairwise genetic interactions between the genes composing the model with respect to the probability of acquiring the metastatic phenotype. We focused on several unexpected synergistic genetic interactions leading to theoretically very high metastasis probability. Among them, the synergistic combination of Notch overexpression and p53 deletion shows one of the strongest effects, which is in agreement with a recent published experiment in a mouse model of gut cancer. The mathematical model can recapitulate experimental mutations in both cell line and mouse models. Furthermore, the model predicts new gene perturbations that affect the early steps of metastasis underlying potential intervention points for innovative therapeutic strategies in oncology.

MiR-33a suppresses breast cancer cell proliferation and metastasis by targeting ADAM9 and ROS1

MicroRNAs (miRNAs) are small noncoding RNAs that have a pivotal role in the post-transcriptional regulation of gene expression by sequence-specifically targeting multiple mRNAs. Although miR-33a was recently reported to play an important role in lipid homeostasis, atherosclerosis, and hepatic fibrosis, the functions of miR-33a in tumor progression and metastasis are largely unknown. Here, we found that downregulated miR-33a in breast cancer tissues correlates with lymph node metastasis. MiR-33a expression is significantly lower in the highly metastatic breast cancer cell lines than the noncancerous breast epithelial cells and non-metastatic breast cancer cells. Moreover, the overexpression of miR-33a in metastatic breast cancer cells remarkably decreases cell proliferation and invasion in vitro and significantly inhibits tumor growth and lung metastasis in vivo, whereas its knockdown in non-metastatic breast cancer cells significantly enhances cell proliferation and invasion in vitro and promotes tumor growth and lung metastasis in vivo. Combining bioinformatics prediction and biochemical analyses, we showed that ADAM9 and ROS1 are direct downstream targets of miR-33a. These findings identified miR-33a as a negative regulator of breast cancer cell proliferation and metastasis.

A Versatile Microarray Platform for Capturing Rare Cells

Analyses of rare events occurring at extremely low frequencies in body fluids are still challenging. We established a versatile microarray-based platform able to capture single target cells from large background populations. As use case we chose the challenging application of detecting circulating tumor cells (CTCs) – about one cell in a billion normal blood cells. After incubation with an antibody cocktail, targeted cells are extracted on a microarray in a microfluidic chip. The accessibility of our platform allows for subsequent recovery of targets for further analysis. The microarray facilitates exclusion of false positive capture events by co-localization allowing for detection without fluorescent labelling. Analyzing blood samples from cancer patients with our platform reached and partly outreached gold standard performance, demonstrating feasibility for clinical application. Clinical researchers free choice of antibody cocktail without need for altered chip manufacturing or incubation protocol, allows virtual arbitrary targeting of capture species and therefore wide spread applications in biomedical sciences.

Naringin inhibits the invasion and migration of human glioblastoma cell via downregulation of MMP-2 and MMP-9 expression and inactivation of p38 signaling pathway

Gliomas are the most common and malignant primary brain tumors. They are associated with a poor prognosis despite the availability of multiple therapeutic options. Naringin, a common dietary flavonoid abundantly present in fruits and vegetables, is believed to possess strong anti-proliferative and anti-cancer properties. However, there are no reports describing its effects on the invasion and migration of glioblastoma cell lines. Our results showed that the treatment of U251 glioma cell lines with different concentrations of naringin inhibited the invasion and migration of these cells. In addition, we revealed a decrease in the levels of matrix metalloproteinases (MMP-2) and (MMP-9) expression as well as proteinase activity in U251 glioma cells. In contrast, the expression of tissue inhibitor of metalloproteinases (TIMP-1) and (TIMP-2) was increased. Furthermore, naringin treatment decreased significantly the phosphorylated level of p38. Combined treatment with a p38 inhibitor (SB203580) resulted in the synergistic reduction of MMP-2 and MMP-9 expressions correlated with an increase of TIMP-1 and TIMP-2 expressions and the anti-invasive properties. However, p38 chemical activator (anisomycin) could block these effects produced by naringin, suggesting a direct downregulation of the p38 signaling pathway. These data suggest that naringin may have therapeutic potential for controlling invasiveness of malignant gliomas by inhibiting of p38 signal transduction pathways.

Niche inheritance: a cooperative pathway to enhance cancer cell fitness through ecosystem engineering

Cancer cells can be described as an invasive species that is able to establish itself in a new environment. The concept of niche construction can be utilized to describe the process by which cancer cells terraform their environment, thereby engineering an ecosystem that promotes the genetic fitness of the species. Ecological dispersion theory can then be utilized to describe and model the steps and barriers involved in a successful diaspora as the cancer cells leave the original host organ and migrate to new host organs to successfully establish a new metastatic community. These ecological concepts can be further utilized to define new diagnostic and therapeutic areas for lethal cancers. 115: 1478–1485, 2014. © 2014 Wiley Periodicals, Inc.

Towards elucidating the connection between epithelial-mesenchymal transitions and stemness

Epithelial cells undergoing epithelial-to-mesenchymal transitions have often been shown to behave as cancer stem cells, but the precise molecular connection remains elusive. At the genetic level, stemness is governed by LIN28/let-7 double inhibition switch, whereas EMT/MET is controlled by miR-200/ZEB double inhibition circuit and LIN28 is inhibited by miR-200, coupling the two modules. Here, using a specially devised theoretical framework to investigate the dynamics of the LIN28/let-7 system, we show that it can operate as a three-way switch (between low, high and intermediate LIN28 levels termed the D, U and hybrid D/U states) similar to the three-way operation of the miR-200/ZEB circuit that allows for the existence of a hybrid epithelial/mesenchymal (E/M) phenotype. We find significant correspondence between the existence of the three states of the two circuits: E-D, M-U and E/M-D/U. Incorporating the activation of OCT4 by LIN28, we find that the hybrid E/M phenotype has high likelihood (when compared with either the E or M states) to gain stemness. Combining the LIN28/let-7 regulation by NF-κB and c-MYC, we find that NF-κB, but not c-MYC, elevates the likelihood of E/M phenotype to gain stemness. Our results are consistent with emerging concept that partial EMT can lead to stemness.

Bone antiresorptive agents in the treatment of bone metastases associated with solid tumours or multiple myeloma

Skeletal lesions contribute substantially to morbidity and mortality in patients with cancer. The disease manifestation course during metastatic bone disease is driven by tumour cells in the bone marrow, which alter the functions of bone-resorbing (osteoclasts) and bone-forming (osteoblasts) cells, promoting skeletal destruction. Successful therapeutic strategies for the treatment of metastatic bone disease include bisphosphonates and denosumab that inhibit osteoclast-mediated bone resorption. Inhibitors of cathepsin K, Src and activin A are under clinical investigation as potential anti-osteolytics. In this review, we describe current knowledge and future directions of antiresorptive therapies that may reduce or prevent destructive bone lesions from solid tumours and multiple myeloma.

Surviving at a Distance: Organ-Specific Metastasis

The clinical manifestation of metastasis in a vital organ is the final stage of cancer progression and the main culprit of cancer-related mortality. Once established, metastasis is devastating, but only a small proportion of the cancer cells that leave a tumor succeed at infiltrating, surviving, and ultimately overtaking a distant organ. The bottlenecks that challenge cancer cells in newly invaded microenvironments are organ-specific and consequently demand distinct mechanisms for metastatic colonization. We review the metastatic traits that allow cancer cells to colonize distinct organ sites.

[Metastasis of pancreatic tumors]

With a 5-year survival rate that has remained stagnant at 6 % for decades, pancreatic ductal adenocarcinoma (PDAC) is still one of the most fatal malignancies. Despite intensive research, currently available therapy options are less than adequate. As more than half of the patients already show distant metastases at the time of diagnosis, metastatic disease should be a primary focus in the development of new therapeutic strategies. New findings from basic research provide various interesting approaches: molecular profiling of the primary tumor seems to be a possible method to gain knowledge about the prognosis, metastatic potential and therapy response of each individual case of PDAC. Certain subpopulations of cancer stem cells also seem to be of importance in metastasis of PDAC and could become potential therapeutic targets in the future. Interactions between tumor cells and their microenvironment are another crucial factor in the metastasis of pancreatic cancer and present various new starting points for potential therapies. As the number of cell types and signaling pathways that are found to play a role in PDAC metastasis continue to grow, the next big challenge will be to translate these findings into viable clinical applications.

Ras Signaling Is a Key Determinant for Metastatic Dissemination and Poor Survival of Luminal Breast Cancer Patients

Breast cancer is associated with alterations in a number of growth factor and hormone-regulated signaling pathways. Mouse models of metastatic breast cancer typically feature mutated oncoproteins that activate PI3K, Stat3, and Ras signaling, but the individual and combined roles of these pathways in breast cancer progression are poorly understood. In this study, we examined the relationship between oncogenic pathway activation and breast cancer subtype by analyzing mouse mammary tumor formation in which each pathway was activated singly or pairwise. All three oncogenes showed cooperation during primary tumor formation, but efficient dissemination was only dependent on Ras. In addition, transcriptional profiling demonstrated that Ras induced adenocarcinomas with molecular characteristics related to human basal-like and HER2(+) tumors. In contrast, Ras combined with PIK3CA(H1047R), an oncogenic mutant linked to ERα(+)/luminal breast cancer in humans, induced metastatic luminal B-like tumors. Consistent with these data, elevated Ras signaling was associated with basal-like and HER2(+) subtype tumors in humans and showed a statistically significant negative association with estrogen receptor (ER) signaling across all breast cancer. Despite this, there are luminal tumors with elevated Ras signaling. Importantly, when considered as a continuous variable, Ras pathway activation was strongly linked to reduced survival of patients with ERα(+) disease independent of PI3K or Stat3 activation. Therefore, our studies suggest that Ras activation is a key determinant for dissemination and poor prognosis of ERα(+)/luminal breast cancer in humans, and hormone therapy supplemented with Ras-targeting agents may be beneficial for treating this aggressive subtype.

Liquid biopsy in cancer patients: advances in capturing viable CTCs for functional studies using the EPISPOT assay

Circulating tumor cells (CTCs) in the blood of cancer patients have received increasing attention as new diagnostic tool enabling 'liquid biopsies'. In contrast to the wealth of descriptive studies demonstrating the clinical relevance of CTCs as biomarkers, the extremely low concentration of CTCs in the peripheral blood of most cancer patients challenges further functional studies. This article discusses the current possibilities to enrich and, in particular, detect viable CTCs with emphasis on the EPithelial ImmunoSPOT technology. This functional assay detects viable CTCs at the single-cell level and has been used on hundreds of patients with different tumor types including epithelial tumors (breast, prostate and colon cancer) and melanomas. Moreover, the article summarizes recent advances in the in vitro and in vivo expansion of CTCs from cancer patients. These functional analyses will contribute to identifying the biological properties of metastatic cells and reveal new therapeutic targets against disseminating cancer cells.

Epithelial to Mesenchymal Transition in a Clinical Perspective

Tumor growth and metastatic dissemination rely on cellular plasticity. Among the different phenotypes acquired by cancer cells, epithelial to mesenchymal transition (EMT) has been extensively illustrated. Indeed, this transition allows an epithelial polarized cell to acquire a more mesenchymal phenotype with increased mobility and invasiveness. The role of EMT is quite clear during developmental stage. In the neoplastic context in many tumors EMT has been associated with a more aggressive tumor phenotype including local invasion and distant metastasis. EMT allows the cell to invade surrounding tissues and survive in the general circulation and through a stem cell phenotype grown in the host organ. The molecular pathways underlying EMT have also been clearly defined and their description is beyond the scope of this review. Here we will summarize and analyze the attempts made to block EMT in the therapeutic context. Indeed, till today, most of the studies are made in animal models. Few clinical trials are ongoing with no obvious benefits of EMT inhibitors yet. We point out the limitations of EMT targeting such tumor heterogeneity or the dynamics of EMT during disease progression.

Clinical and molecular complexity of breast cancer metastases

Clinical oncology is advancing toward a more personalized treatment orientation, making the need to understand the biology of metastasis increasingly acute. Dissecting the complex molecular, genetic and clinical phenotypes underlying the processes involved in the development of metastatic disease, which remains the principal cause of cancer-related deaths, could lead to the identification of more effective prognostication and targeted approaches to prevent and treat metastases. The past decade has witnessed significant progress in the field of cancer metastasis research. Clinical and technological milestones have been reached which have tremendously enriched our understanding of the complex pathways undertaken by primary tumors to progress into lethal metastases and how some of these processes might be amenable to therapy. The aim of this review article is to highlight the recent advances toward unraveling the clinical and molecular complexity of breast cancer metastases. We focus on genes mediating breast cancer metastases and organ-specific tropism, and discuss gene signatures for prediction of metastatic disease. The challenges of translating this information into clinically applicable tools for improving the prognostication of the metastatic potential of a primary breast tumor, as well as for therapeutic interventions against latent and active metastatic disease are addressed.

The role of endocytic Rab GTPases in regulation of growth factor signaling and the migration and invasion of tumor cells

Metastasis is characterized pathologically by uncontrolled cell invasion, proliferation, migration and angiogenesis. It is a multistep process that encompasses the modulation of membrane permeability and invasion, cell spreading, cell migration and proliferation of the extracellular matrix, increase in cell adhesion molecules and interaction, decrease in cell attachment and induced survival signals and propagation of nutrient supplies (blood vessels). In cancer, a solid tumor cannot expand and spread without a series of synchronized events. Changes in cell adhesion receptor molecules (e.g., integrins, cadherin-catenins) and protease expressions have been linked to tumor invasion and metastasis. It has also been determined that ligand-growth factor receptor interactions have been associated with cancer development and metastasis via the endocytic pathway. Specifically, growth factors, which include IGF-1 and IGF-2 therapy, have been associated with most if not all of the features of metastasis. In this review, we will revisit some of the key findings on perhaps one of the most important hallmarks of cancer metastasis: cell migration and cell invasion and the role of the endocytic pathway in mediating this phenomenon.

An orthotopic xenograft model with survival hindlimb amputation allows investigation of the effect of tumor microenvironment on sarcoma metastasis

Overall survival rates for pediatric high-grade sarcoma have improved greatly in the past few decades, but prevention and treatment of distant metastasis remain the most compelling problems facing these patients. Traditional preclinical mouse models have not proven adequate to study the biology and treatment of spontaneous distant sarcoma metastasis. To address this deficit, we developed an orthotopic implantation/amputation model in which patient-derived sarcoma xenografts are surgically implanted into mouse hindlimbs, allowed to grow, then subsequently amputated and the animals observed for development of metastases. NOD/SCID/IL-2Rγ-null mice were implanted with either histologically intact high grade sarcoma patient-derived xenografts or cell lines in the pretibial space and affected limbs were amputated after tumor growth. In contrast to subcutaneous flank tumors, we were able to consistently detect spontaneous distant spread of the tumors using our model. Metastases were seen in 27-90 % of animals, depending on the xenograft, and were repeatable and predictable. We also demonstrate the utility of this model for studying the biology of metastasis and present preliminary new insights suggesting the role of arginine metabolism and macrophage phenotype polarization in creating a tumor microenvironment that facilitates metastasis. Subcutaneous tumors express more arginase than inducible nitric oxide synthase and demonstrate significant macrophage infiltration, whereas orthotopic tumors express similar amounts of inducible nitric oxide synthase and arginase and have only a scant macrophage infiltrate. Thus, we present a model of spontaneous distant sarcoma metastasis that mimics the clinical situation and is amenable to studying the biology of the entire metastatic cascade.

Bone metastasis and the metastatic niche

The bone marrow has been long known to host a unique environment amenable to colonization by metastasizing tumor cells. Yet, the underlying molecular interactions within this specialized microenvironment which give rise to the high incidence of bone metastasis in breast and prostate cancer patients have long remained uncharacterized. With the recent description of the bone metastatic "niche," considerable focus has been placed on understanding how the bone stroma contributes to each step of metastasis. Discoveries within this field have demonstrated that when cancer cells home to the niche in which hematopoietic and mesenchymal stem/progenitor cells normally reside, a bidirectional crosstalk emerges between the tumor cells and the bone metastatic stroma. This communication modulates every step of cancer cell metastasis to the bone, including the initial homing and seeding, formation of micrometastases, outgrowth of macrometastases, and the maintenance of long-term dormancy of disseminated tumor cells in the bone. In clinical practice, targeting the bone metastatic niche is evolving into a promising avenue for the prevention of bone metastatic relapse, therapeutic resistance, and other aspects of cancer progression. Here, we review the current knowledge concerning the role of the bone metastatic niche in bone metastasis.

Tumor microenvironment: Sanctuary of the devil

Tumor cells constantly interact with the surrounding microenvironment. Increasing evidence indicates that targeting the tumor microenvironment could complement traditional treatment and improve therapeutic outcomes for these malignancies. In this paper, we review new insights into the tumor microenvironment, and summarize selected examples of the cross-talk between tumor cells and their microenvironment, which have enhanced our understanding of pathophysiology of the microenvironment. We believe that this rapidly moving field promises many more to come, and they will guide the rational design of combinational therapies for success in cancer eradication.

A novel vascular pattern promotes metastasis of hepatocellular carcinoma in an epithelial-mesenchymal transition-independent manner

Early metastasis is responsible for frequent relapse and high mortality of hepatocellular carcinoma (HCC), but its underlying mechanisms remain unclear. Epithelial-mesenchymal transition (EMT) has been considered a key event in metastasis. Based on histological examination of serial HCC sections and three-dimensional reconstruction, we found a novel and prevalent vascular pattern, vessels that encapsulated tumor clusters (VETC) and formed cobweb-like networks. The presence of VETC (VETC(+) ) predicted higher metastasis and recurrence rates of HCC. Using clinical samples and mouse xenograft models, we further showed that VETC was composed of functional vessels with blood perfusion and induced by tumor cells at the early stage of HCC. Subsequent investigations revealed that HCC cell-derived angiopoietin-2 was a prerequisite for VETC formation and that the VETC pattern was a critical factor promoting HCC metastasis as knockdown of angiopoietin-2 abolished this vascular pattern and consequently attenuated in vivo tumor metastasis. Interestingly, abrogation of EMT by knockdown of Snail or Slug significantly diminished in vivo metastasis of VETC(-) xenografts but did not affect that of VETC(+) ones, although silencing of Snail or Slug substantially reduced the in vitro migration of both VETC(+) and VETC(-) HCC cells. In contrast to human VETC(-) cases, EMT signatures were rarely observed in VETC(+) cases with metastatic potential. Further analysis revealed that VETC provided an efficient metastasis mode by facilitating the release of whole tumor clusters into the bloodstream.

CONCLUSION

Our findings identify a novel metastasis mechanism that relies on vascular pattern but is independent of EMT, which may provide new targets for antimetastasis therapy and offer a basis for selecting patients who may benefit from certain molecularly targeted drugs.

Biology, detection, and clinical implications of circulating tumor cells

Cancer metastasis is the main cause of cancer-related death, and dissemination of tumor cells through the blood circulation is an important intermediate step that also exemplifies the switch from localized to systemic disease. Early detection and characterization of circulating tumor cells (CTCs) is therefore important as a general strategy to monitor and prevent the development of overt metastatic disease. Furthermore, sequential analysis of CTCs can provide clinically relevant information on the effectiveness and progression of systemic therapies (e.g., chemo-, hormonal, or targeted therapies with antibodies or small inhibitors). Although many advances have been made regarding the detection and molecular characterization of CTCs, several challenges still exist that limit the current use of this important diagnostic approach. In this review, we discuss the biology of tumor cell dissemination, technical advances, as well as the challenges and potential clinical implications of CTC detection and characterization.

IRGM1 enhances B16 melanoma cell metastasis through PI3K-Rac1 mediated epithelial mesenchymal transition

Melanoma is one of the most aggressive skin cancers and is well known for its high metastatic rate. Studies have shown that epithelial mesenchymal transition (EMT) is essential for melanoma cell metastasis. However, the molecular mechanisms underlying EMT are still not fully understood. We have shown that IRGM1, a member of immunity-related GTPase family that regulates immune cell motility, is highly expressed by melanoma cells. The current study aimed to explore whether and how IRGM1 may regulate melanoma cell metastasis. To test this, we modified IRGM1 expression in B16 melanoma cells. We found that over-expression of IRGM1 substantially enhanced pulmonary metastasis in vivo. In keeping with that, knocking-in IRGM1 strongly enhanced while knocking-down IRGM1 impaired B16 cell migration and invasion ability in vitro. Interestingly, we observed that IRGM1 enhanced F-actin polymerization and triggers epithelial mesenchymal transition (EMT) through a mechanism involved in PIK3CA mediated Rac1 activation. Together, these data reveals a novel molecular mechanism that involved in melanoma metastasis.

Circulating tumor cells in early breast cancer: A connection with vascular invasion

Although circulating tumor cells (CTCs) have been studied in early breast cancer (EBC), their value in this setting is still not fully understood. We isolated and studied CTCs in the peripheral blood (PB) of 48 EBC patients pre-surgery and one and 6 months post-surgery using an approach involving EpCAM-independent enrichment and a dielectrophoresis-based device. Method feasibility and the correlation between CTCs and primary tumor features were evaluated. CTCs were found in 27.1% of pre-surgery patients, 20.9% of patients one-month post-surgery, and about 33% of patients 6-months post-surgery. CTCs were recovered singly for further molecular characterization. Pre-surgery CTC-positive patients more frequently had negative prognostic features, i.e. high proliferation, large tumor dimension, lymph node positivity and negative receptor status than the other subgroup. In particular, vascular invasion showed a statistically significant correlation with CTC-positivity. Our procedure proved feasible and capable of recovering CTCs from EBC patients. Furthermore, our results suggest that CTCs may be linked to vascular invasion and to other known negative prognostic factors.

The roles of microRNAs in the regulation of tumor metastasis

MicroRNAs (miRNAs) are small noncoding regulatory RNAs that regulate gene expression post-transcriptionally by either inhibiting protein translation or degrading target mRNAs. The differential expression profiles of miRNAs in different types of cancers and in the multi-step process of tumor progression indicate that miRNAs are involved in tumor onset, growth and progression. Metastasis is the most common cause of cancer-related mortality. Current evidence demonstrates that aberrant miRNA expression promotes or inhibits tumor metastasis by modulating the expression of numerous target genes. Therefore, the identification of metastasis-related miRNAs and a better understanding of the complex functions of miRNAs in tumor metastasis will provide potential diagnostic and prognostic biomarkers, as well as therapeutic targets for clinical application. Here, we review the functions of miRNAs in the control of multiple steps of tumor metastasis.

Drastic morphological and molecular differences between lymph node micrometastatic tumors and macrometastatic tumors of lung adenocarcinoma

PURPOSE

The expansion of micrometastatic tumors to macrometastatic ones is thought to be tightly regulated by several microenvironmental factors. The aim of this study was to elucidate the morphological and phenotypical differences between micrometastatic and macrometastatic tumors.

METHOD

We first examined the morphological characteristics of 66 lymph node (LN) micrometastatic tumors (less than 2 mm in size) and 51 macrometastatic tumors (more than 10 mm in size) in 42 lung adenocarcinoma cases. Then, we evaluated the expression level of E-cadherin, S100A4, ALDH1, and Geminin in cancer cells and the number of smooth muscle actin (SMA), CD34, and CD204 (+) stromal cells in the primary tumors, matched micrometastatic tumors, and macrometastatic tumors (n = 34, each).

RESULTS

Tumor budding reflects the process of EMT, and stromal reactions were observed more frequently in macrometastatic tumors (P < 0.001). E-cadherin staining score for the micrometastatic tumors was significantly higher than that for the primary tumors (P < 0.001). In contrast, the E-cadherin staining score for the macrometastatic tumors was significantly lower than that for the micrometastatic tumors (P = 0.017). As for the stromal cells, the numbers of SMA (+) fibroblasts, CD34 (+) microvessels, and CD204 (+) macrophages were significantly higher for the macrometastatic tumors and primary tumors than for the micrometastatic tumors (P < 0.001, all).

CONCLUSION

The present study clearly showed that dynamic microenvironmental changes (e.g., EMT-related changes in cancer cells and structural changes in stromal cells) occur during the growth of micrometastases into macrometastases.

Targeted inhibition of fascin function blocks tumour invasion and metastatic colonization

One of the key steps during tumour metastasis is tumour cell migration and invasion, which require actin cytoskeletal reorganization. Among the critical actin cytoskeletal protrusion structures are the filopodia, which act like cell sensory organs to communicate with the extracellular microenvironment and participate in fundamental cell functions such as cell adhesion, spreading and migration in the three-dimensional environment. Fascin is the main actin-bundling protein in filopodia. Using high-throughput screening, here we identify and characterize small molecules that inhibit the actin-bundling activity of fascin. Focusing on one such inhibitor, we demonstrate that it specifically blocks filopodial formation, tumour cell migration and invasion in vitro, and metastasis in vivo. Hence, target-specific anti-fascin agents have a therapeutic potential for cancer treatment.

The biology of circulating tumor cells

Metastasis is a biologically complex process consisting of numerous stochastic events which may tremendously differ across various cancer types. Circulating tumor cells (CTCs) are cells that are shed from primary tumors and metastatic deposits into the blood stream. CTCs bear a tremendous potential to improve our understanding of steps involved in the metastatic cascade, starting from intravasation of tumor cells into the circulation until the formation of clinically detectable metastasis. These efforts were propelled by novel high-resolution approaches to dissect the genomes and transcriptomes of CTCs. Furthermore, capturing of viable CTCs has paved the way for innovative culturing technologies to study fundamental characteristics of CTCs such as invasiveness, their kinetics and responses to selection barriers, such as given therapies. Hence the study of CTCs is not only instrumental as a basic research tool, but also allows the serial monitoring of tumor genotypes and may therefore provide predictive and prognostic biomarkers for clinicians. Here, we review how CTCs have contributed to significant insights into the metastatic process and how they may be utilized in clinical practice.

EGCG regulates the cross-talk between JWA and topoisomerase IIα in non-small-cell lung cancer (NSCLC) cells

(-)-epigallocatechin-3-gallate (EGCG) is a well-known cancer chemopreventive agent. The potential mechanisms include regulation of multiple molecules. Carcinogenesis in lung cancer is related to the imbalance of tumor suppressor and oncogene. JWA is a structurally novel microtubule-binding protein and is a potential tumor suppressor. DNA topoisomerase IIα is a nuclear enzyme that governs DNA topology and is usually highly expressed in many types of cancer. It serves as a target of anticancer drugs. In the current study, the regulation of JWA and topoisomerase IIα by EGCG, and thereafter the mutual interaction between them was investigated. The results revealed that EGCG up-regulated JWA while decreased topoisomerase IIα expression in both human non-small cell lung cancer (NSCLC) cells and an NSCLC xenograft mice model. There was a negative correlation between JWA and topoisomerase IIα in NSCLC as well as in human NSCLC tissue specimens. Topoisomerase IIα overexpression reduced JWA at the translational level. Meanwhile, JWA-induced topoisomerase IIα degradation was regulated both in the transcriptional and post-translational level. Interestingly, JWA and topoisomerase IIα regulated each other in the cells arrested in G2/M. Furthermore, JWA and topoisomerase IIα synergistically affected NCI-H460 cells invasion. These results may serve a novel mechanism for cancer prevention.

Primary Tumor and MEF Cell Isolation to Study Lung Metastasis

In breast tumorigenesis, the metastatic stage of the disease poses the greatest threat to the affected individual. Normal breast cells with altered genotypes now possess the ability to invade and survive in other tissues. In this protocol, mouse mammary tumors are removed and primary cells are prepared from tumors. The cells isolated from this procedure are then available for gene profiling experiments. For successful metastasis, these cells must be able to intravasate, survive in circulation, extravasate to distant organs, and survive in that new organ system. The lungs are the typical target of breast cancer metastasis. A set of genes have been discovered that mediates the selectivity of metastasis to the lung. Here we describe a method of studying lung metastasis from a genetically engineered mouse model.. Furthermore, another protocol for analyzing mouse embryonic fibroblasts (MEFs) from the mouse embryo is included. MEF cells from the same animal type provide a clue of non-cancer cell gene expression. Together, these techniques are useful in studying mouse mammary tumorigenesis, its associated signaling mechanisms and pathways of the abnormalities in embryos.

Diverse functions of miR-373 in cancer

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression post-transcriptionally. They are involved in almost all cellular processes, and many have been described as potential oncogenes or tumor suppressors. MicroRNA-373 (miR-373), which was first identified as a human embryonic stem cell (ESC)-specific miRNA, is suggested to be implicated in the regulation of cell proliferation, apoptosis, senescence, migration and invasion, as well as DNA damage repair following hypoxia stress. Deregulation of miR-373 has been demonstrated in a number of cancers, whether it acts as an oncogene or a tumor suppressor, however, seems to be context dependent. In this review, we focus on the diverse functions of miR-373 and its implication in cancers.

The emerging molecular machinery and therapeutic targets of metastasis

Metastasis is a 100-year-old research topic. Technological advances during the past few decades have led to significant progress in our understanding of metastatic disease. However, metastasis remains the leading cause of cancer-related mortalities. The lack of appropriate clinical trials for metastasis preventive drugs and incomplete understanding of the molecular machinery are major obstacles in metastasis prevention and treatment. Numerous processes, factors, and signaling pathways are involved in regulating metastasis. Here we discuss recent progress in metastasis research, including epithelial-mesenchymal plasticity, cancer stem cells, emerging molecular determinants and therapeutic targets, and the link between metastasis and therapy resistance.

Transcriptional regulation of tenascin-W by TGF-beta signaling in the bone metastatic niche of breast cancer cells

Tenascin‐W is a matricellular protein with a dynamically changing expression pattern in development and disease. In adults, tenascin‐W is mostly restricted to stem cell niches, and is also expressed in the stroma of solid cancers. Here, we analyzed its expression in the bone microenvironment of breast cancer metastasis. Osteoblasts were isolated from tumor‐free or tumor‐bearing bones of mice injected with MDA‐MB231‐1833 breast cancer cells. We found a fourfold upregulation of tenascin‐W in the osteoblast population of tumor‐bearing mice compared to healthy mice, indicating that tenascin‐W is supplied by the bone metastatic niche. Transwell and co‐culture studies showed that human bone marrow stromal cells (BMSCs) express tenascin‐W protein after exposure to factors secreted by MDA‐MB231‐1833 breast cancer cells. To study tenascin‐W gene regulation, we identified and analyzed the tenascin‐W promoter as well as three evolutionary conserved regions in the first intron. 5′RACE analysis of mRNA from human breast cancer, glioblastoma and bone tissue showed a single tenascin‐W transcript with a transcription start site at a noncoding first exon followed by exon 2 containing the ATG translation start. Site‐directed mutagenesis of a SMAD4‐binding element in proximity of the TATA box strongly impaired promoter activity. TGFβ1 induced tenascin‐W expression in human BMSCs through activation of the TGFβ1 receptor ALK5, while glucocorticoids were inhibitory. Our experiments show that tenascin‐W acts as a niche component for breast cancer metastasis to bone by supporting cell migration and cell proliferation of the cancer cells.

What's new?

Once breast cancer metastasizes, it is generally incurable. Proteins in the extracellular matrix play a crucial role in launching the tumor cells to a new site. These authors investigated one such protein, tenascin‐W, which can be found surrounding not only tumor cells but also in bone tissue. Among other things, they studied how breast cancer cells affected tenascin‐W expression. The tumor cells induced bone marrow stromal cells to make more tenascin‐W, suggesting that the protein may pave the way for the cancer to spread to the bone.