Modeling metastasis in the mouse

MIND model for triple-negative breast cancer in syngeneic mice for quick and sequential progression analysis of lung metastasis

Mouse models of breast cancer with specific molecular subtypes (e.g., ER or HER2 positive) in an immunocompetent or an immunocompromised environment significantly contribute to our understanding of cancer biology, despite some limitations, and they give insight into targeted therapies. However, an ideal triple-negative breast cancer (TNBC) mouse model is lacking. What has been missing in the TNBC mouse model is a sequential progression of the disease in an essential native microenvironment. This notion inspired us to develop a TNBC-model in syngeneic mice using a mammary intraductal (MIND) method. To achieve this goal, Mvt-1and 4T1 TNBC mouse cell lines were injected into the mammary ducts via nipples of FVB/N mice and BALB/c wild-type immunocompetent mice, respectively. We established that the TNBC-MIND model in syngeneic mice could epitomize all breast cancer progression stages and metastasis into the lungs via lymphatic or hematogenous dissemination within four weeks. Collectively, the syngeneic mouse-TNBC-MIND model may serve as a unique platform for further investigation of the underlying mechanisms of TNBC growth and therapies.

Small cell and non small cell lung cancer form metastasis on cellular 4D lung model

BACKGROUND

Metastasis is the main cause of death for lung cancer patients. The ex vivo 4D acellular lung model has been shown to mimic this metastatic process. However, the main concern is the model's lack of cellular components of the tumor's microenvironment. In this study, we aim to determine if the intact lung microenvironment will still allow lung cancer metastasis to form.

METHODS

We harvested a heart-lung block from a rat and placed it in a bioreactor after cannulating the pulmonary artery, trachea and tying the right main bronchus for 10-15 days without any tumor cells as a control group or with NSCLC (A549, H1299 or H460), SCLC (H69, H446 or SHP77) or breast cancer cell lines (MCF7 or MDAMB231) through the trachea. We performed lobectomy, H&E staining and IHC for human mitochondria to determine the primary tumor's growth and formation of metastatic lesions. In addition, we isolated circulating tumor cells (CTC) from the model seeded with GFP tagged cells.

RESULTS

In the control group, no gross tumor nodules were found, H&E staining showed hyperplastic cells and IHC showed no staining for human mitochondria. All of the models seeded with cancer cell lines formed gross primary tumor nodules that had microscopic characteristics of human cancer cells on H&E staining with IHC showing staining for human mitochondria. CTC were isolated for those cells labeled with GFP and they were viable in culture. Finally, all cell lines formed metastatic lesions with cells stained for human mitochondria.

CONCLUSION

The cellular ex vivo 4D model shows that human cancer cells can form a primary tumor, CTC and metastatic lesions in an intact cellular environment. This study suggests that the natural matrix scaffold is the only necessary component to drive metastatic progression and that cellular components play a role in modulating tumor progression.

Biomimetic on-a-chip platforms for studying cancer metastasis

Cancer metastasis is a multi-step, secondary tumor formation that is responsible for the vast majority of deaths in cancer patients. Animal models have served as one of the major tools for studying metastatic diseases. However, these metastasis models inherently lack the ability to decouple many of the key parameters that might contribute to cancer progression, and therefore ultimately limit detailed, mechanistic investigation of metastasis. Recently, organ-on-a-chip model systems have been developed for various tissue types with the potential to recapitulate major components of metastasis. Here, we discuss recent advances in in vitro biomimetic on-a-chip models for cancer metastasis.

Deregulation of SLIT2-mediated Cdc42 activity is associated with esophageal cancer metastasis and poor prognosis

INTRODUCTION

SLIT2, a secreted protein, has been found to inactivate Cdc42 GTPase to modulate neural cell migration. However, alteration of SLIT2-mediated Cdc42 in terms of migration regulation remains undefined in esophageal squamous cell carcinoma (ESCC).

METHODS

We report here in ESCC cell, animal, and clinical models that SLIT2 acts as a migration suppressor and serves as a prognostic biomarker.

RESULTS

The immunohistochemistry data indicated that 31.8% (49 of 154) of tumors from ESCC patients showed low expression of SLIT2 protein which correlated with poor overall survival and disease-free survival. DNA methylation analysis suggested that promoter hypermethylation is responsible for low expression of SLIT2 in ESCC. Knockdown of SLIT2 increased ESCC cell migration, while SLIT2 stable overexpression reduced cell migration. ESCC cells treated with conditioned media from cells overexpressing SLIT2 also suppressed cell migration. Importantly, silencing of SLIT2 decreased the complex formation, and thus induced Cdc42 activity and promoted membrane localization of focal adhesion kinase and Paxillin. Anti-metastatic effect of SLIT2 was confirmed in an experimental metastasis model of SLIT2 knockdown ESCC cells.

CONCLUSION

Our results provide novel evidence that low expression of SLIT2 correlates with poor prognosis and promotes metastasis in ESCC, which may be regulated by the Cdc42-mediated pathways.

Ex vivo four-dimensional lung cancer model mimics metastasis

BACKGROUND

We have developed a four-dimensional (4D) lung cancer model that forms perfusable tumor nodules. We determined if the model could be modified to mimic metastasis.

METHODS

We modified the 4D lung cancer model by seeding H1299, A549, or H460 cells through the trachea only to the left lobes of the acellular lung matrix. The model was modified so that the tumor cells can reach the right lobes of the acellular lung matrix only through the pulmonary artery as circulating tumor cells (CTC). We determined the gene expressions of the primary tumor, CTCs, and metastatic lesions using the Human OneArray chip.

RESULTS

All cell lines formed a primary tumor in the left lobe of the ex vivo 4D lung cancer model. The CTCs were identified in the media and increased over time. All cell lines formed metastatic lesions with H460 forming significantly more metastatic lesions than H1299 and A549 cells. The CTC gene signature predicted poor survival in lung cancer patients. Unique genes were significantly expressed in CTC compared with the primary tumor and metastatic lesion.

CONCLUSIONS

The 4D lung cancer model can isolate tumor cells in 3 phases of tumor progression. This 4D lung cancer model may mimic the biology of lung cancer metastasis and may be used to determine its mechanism and potential therapy in the future.

Transplantable mouse tumor models of breast cancer metastasis

Metastatic spread of cancer cells is the main cause of death of breast cancer patients. A better understanding of the molecular mechanism of cancer metastasis is essential for the development of novel and effective therapies. The biological complexity of the metastasis process requires the combination of multiple experimental systems to model distinct steps of cancer metastasis. Several animal models have been generated to mimic the process of breast cancer metastasis, with unique advantages and drawbacks of each model. In this chapter, we describe transplantable xenograft and allograft methods to introduce human or mouse breast tumor cells into mice in order to generate spontaneous and experimental metastasis.

Murine precision-cut liver slices (PCLS): a new tool for studying tumor microenvironments and cell signaling ex vivo

Background

One of the most insidious characteristics of cancer is its spread to and ability to compromise distant organs via the complex process of metastasis. Communication between cancer cells and organ-resident cells via cytokines/chemokines and direct cell-cell contacts are key steps for survival, proliferation and invasion of metastasized cancer cells in organs. Precision-cut liver slices (PCLS) are considered to closely reflect the in vivo situation and are potentially useful for studying the interaction of cancer cells with liver-resident cells as well as being a potentially useful tool for screening anti-cancer reagents. Application of the PCLS technique in the field of cancer research however, has not yet been well developed.

Results

We established the mouse PCLS system using perfluorodecalin (PFD) as an artificial oxygen carrier. Using this system we show that the adherence of green fluorescent protein (GFP) labeled MDA-MB-231 (highly invasive) cells to liver tissue in the PCLS was 5-fold greater than that of SK-BR-3 (less invasive) cells. In addition, we generated PCLS from THOC5, a member of transcription/export complex (TREX), knockout (KO) mice. The PCLS still expressed Gapdh or Albumin mRNAs at normal levels, while several chemokine/growth factor or metalloprotease genes, such as Cxcl12, Pdgfa, Tgfb, Wnt11, and Mmp1a genes were downregulated more than 2-fold. Interestingly, adhesion of cancer cells to THOC5 KO liver slices was far less (greater than 80% reduction) than to wild-type liver slices.

Conclusion

Mouse PCLS cultures in the presence of PFD may serve as a useful tool for screening local adherence and invasiveness of individual cancer cells, since single cells can be observed. This method may also prove useful for identification of genes in liver-resident cells that support cancer invasion by using PCLS from transgenic liver.

GAGE12 mediates human gastric carcinoma growth and metastasis

The spontaneous metastasis from human gastric carcinoma (GC) remains poorly reproduced in animal models. Here, we established an experimental mouse model in which GC progressively developed in the orthotopic stomach wall and metastasized to multiple organs; the tumors colonized in the ovary exhibited typical characteristics of Krukenberg tumor. The expression of mesenchymal markers was low in primary tumors and high in those in intravasating and extravasating veins. However, the expression of epithelial markers did not differ, indicating that the acquisition of mesenchymal markers without a concordant loss of typical epithelial markers was associated with metastasis. We identified 35 differentially expressed genes (DEGs) in GC cells metastasized to ovary, among which overexpression of GAGE12 family genes, the top-ranked DEGs, were validated. In addition, knockdown of the GAGE12 gene family affected transcription of many of the aforementioned 35 DEGs and inhibited trans-well migration, tumor sphere formation in vitro and tumor growth in vivo. In accordance, GAGE12 overexpression augmented migration, tumor sphere formation and sustained in vivo tumor growth. Taken together, the GAGE12 gene family promotes GC growth and metastasis by modulating the expression of GC metastasis-related genes.

Functional genomic analysis of cancer metastasis: biologic insights and clinical implications

Metastasis, the spread of cancer from primary tumors to distant vital organs, has devastating consequences. Lack of effective tools to study this complex problem has hindered the development of accurate prognostic methods and effective treatments for metastatic cancer. In the postgenomic era, the application of genomic profiling methods to the analysis of clinical metastasis samples and animal metastasis models has revolutionized the field of metastasis research. This article reviews recent breakthroughs in the functional genomic analysis of metastasis. In addition, its impacts on our understanding of the molecular basis of metastasis and on clinical practice are discussed.

Orthotopic mouse models for the preclinical and translational study of targeted therapies against metastatic human thyroid carcinoma with BRAF(V600E) or wild-type BRAF

Molecular signature of advanced and metastatic thyroid carcinoma involves deregulation of multiple fundamental pathways activated in the tumor microenvironment. They include BRAF(V600E) and AKT that affect tumor initiation, progression and metastasis. Human thyroid cancer orthotopic mouse models are based on human cell lines that generally harbor genetic alterations found in human thyroid cancers. They can reproduce in vivo and in situ (into the thyroid) many features of aggressive and refractory human advanced thyroid carcinomas, including local invasion and metastasis. Humanized orthotopic mouse models seem to be ideal and commonly used for preclinical and translational studies of compounds and therapies not only because they may mimic key aspects of human diseases (e.g. metastasis), but also for their reproducibility. In addition, they might provide the possibility to evaluate systemic effects of treatments. So far, human thyroid cancer in vivo models were mainly used to test single compounds, non selective and selective. Despite the greater antitumor activity and lower toxicity obtained with different selective drugs in respect to non-selective ones, most of them are only able to delay disease progression, which ultimately could restart with similar aggressive behavior. Aggressive thyroid tumors (for example, anaplastic or poorly differentiated thyroid carcinoma) carry several complex genetic alterations that are likely cooperating to promote disease progression and might confer resistance to single-compound approaches. Orthotopic models of human thyroid cancer also hold the potential to be good models for testing novel combinatorial therapies. In this article, we will summarize results on preclinical testing of selective and nonselective single compounds in orthotopic mouse models based on validated human thyroid cancer cell lines harboring the BRAF(V600E) mutation or with wild-type BRAF. Furthermore, we will discuss the potential use of this model also for combinatorial approaches, which are expected to take place in the upcoming human thyroid cancer basic and clinical research.

Rebuilding cancer metastasis in the mouse

Most cancer deaths are due to the systemic dissemination of cancer cells and the formation of secondary tumors (metastasis) in distant organs. Recent years have brought impressive progress in metastasis research, yet we still lack sufficient insights into how cancer cells migrate out of primary tumors and invade into neighboring tissue, intravasate into the blood or the lymphatic circulation, survive in the blood stream, and target specific organs to initiate metastatic outgrowth. While a large number of cellular and animal models of cancer have been crucial in delineating the molecular mechanisms underlying tumor initiation and progression, experimental models that faithfully recapitulate the multiple stages of metastatic disease are still scarce. The advent of sophisticated genetic engineering in mice, in particular the ability to manipulate gene expression in specific tissue and at desired time points at will, have allowed to rebuild the metastatic process in mice. Here, we describe a selection of cellular experimental systems, tumor transplantation mouse models and genetically engineered mouse models that are used for monitoring specific processes involved in metastasis, such as cell migration and invasion, and for investigating the full metastatic process. Such models not only aid in deciphering the pathomechanisms of metastasis, but are also instrumental for the preclinical testing of anti-metastatic therapies and further refinement and generation of improved models.

Dysregulation of ezrin phosphorylation prevents metastasis and alters cellular metabolism in osteosarcoma

Ezrin links the plasma membrane to the actin cytoskeleton where it plays a pivotal role in the metastatic progression of several human cancers; however, the precise mechanistic basis for its role remains unknown. Here, we define transitions between active (phosphorylated open) and inactive (dephosphorylated closed) forms of Ezrin that occur during metastatic progression in osteosarcoma. In our evaluation of these conformations we expressed C-terminal mutant forms of Ezrin that are open (phosphomimetic T567D) or closed (phosphodeficient T567A) and compared their biologic characteristics to full-length wild-type Ezrin in osteosarcoma cells. Unexpectedly, cells expressing open, active Ezrin could form neither primary orthotopic tumors nor lung metastases. In contrast, cells expressing closed, inactive Ezrin were also deficient in metastasis but were unaffected in their capacity for primary tumor growth. By imaging single metastatic cells in the lung, we found that cells expressing either open or closed Ezrin displayed increased levels of apoptosis early after their arrival in the lung. Gene expression analysis suggested dysregulation of genes that are functionally linked to carbohydrate and amino acid metabolism. In particular, cells expressing closed, inactive Ezrin exhibited reduced lactate production and basal or ATP-dependent oxygen consumption. Collectively, our results suggest that dynamic regulation of Ezrin phosphorylation at amino acid T567 that controls structural transitions of this protein plays a pivotal role in tumor progression and metastasis, possibly in part by altering cellular metabolism.

Matrix metalloproteinase 11/stromelysin-3 exerts both activator and repressor functions during the hematogenous metastatic process in mice

MMP11 expression is a poor prognosis factor in human carcinomas. Although it has been shown to favor primary tumor development, its role in metastatic processes remains unclear. We studied the hematogenous metastatic activity of C26 mouse colon cancer cells injected into the tail vain of wild-type or MMP11-deficient mice during 2 months. Using X-ray computed tomography to image metastasis development in recipient living mice, lung metastases were found to occur earlier and to grow faster in wild-type mice. Histological analyses of the lung, liver, kidney, adrenal gland, mammary gland, ovary and salivary gland, performed at the end of experiment, also showed lower numbers of metastases in wild-type mice, regardless of organ. Lung metastases showed similar Factor VIII-positive vascular networks regardless of the mouse MMP11 status. However, those found in MMP11-deficient mice also exhibited vessel-like structures that did not express Factor VIII, Lyve-1 and vimentin, and were not stained with PAS. Consequently, they did not correspond to vascular or lymphatic vessels or to vascular mimicry channels. Collectively, these results revealed significant spatio-temporal variability that is dependent on host MMP11 status. Furthermore, they point-out the paradoxical role of MMP11 in favoring the onset and growth of lung metastases but limiting lung foci number, and inhibiting the cancer cell dissemination to other organs. These data highlight the complexity of the metastatic process in which the same factor can play activator or repressor functions depending on the metastatic step.

A mouse model of pulmonary metastasis from spontaneous osteosarcoma monitored in vivo by Luciferase imaging

Background

Osteosarcoma (OSA) is lethal when metastatic after chemotherapy and/or surgical treatment. Thus animal models are necessary to study the OSA metastatic spread and to validate novel therapies able to control the systemic disease. We report the development of a syngeneic (Balb/c) murine OSA model, using a cell line derived from a spontaneous murine tumor.

Methodology

The tumorigenic and metastatic ability of OSA cell lines were assayed after orthotopic injection in mice distal femur. Expression profiling was carried out to characterize the parental and metastatic cell lines. Cells from metastases were propagated and engineered to express Luciferase, in order to follow metastases in vivo.

Principal Findings

Luciferase bioluminescence allowed to monitor the primary tumor growth and revealed the appearance of spontaneous pulmonary metastases. In vivo assays showed that metastasis is a stable property of metastatic OSA cell lines after both propagation in culture and luciferase trasduction. When compared to parental cell line, both unmodified and genetically marked metastatic cells, showed comparable and stable differential expression of the enpp4, pfn2 and prkcd genes, already associated to the metastatic phenotype in human cancer.

Conclusions

This OSA animal model faithfully recapitulates some of the most important features of the human malignancy, such as lung metastatization. Moreover, the non-invasive imaging allows monitoring the tumor progression in living mice. A great asset of this model is the metastatic phenotype, which is a stable property, not modifiable after genetic manipulation.

Exploring the molecular basis of tumor metastasis by microarray analysis

Over the past decade, microarray technology has become a powerful tool to provide a genome-wide view of genetic or epigenetic changes associated with tumor metastasis. To extract biologically meaningful information from the vast amounts of microarray data, it is crucial to choose suitable biological systems and have vigilant experimental design. In this review, I will discuss several experimental systems that are used to identify genes involved in tumor metastasis by microarray analysis. Also highlighted are the pros and cons for each system. In particular, I will describe our experience of using microarray technology to identify the transcription factor Twist as an essential player in tumor metastasis.

Mouse models in oncogenesis and cancer therapy

Animal models have been critical in the study of the molecular mechanisms of cancer and in the development of new antitumor agents; nevertheless, there is still much room for improvement. The relevance of each particular model depends on how close it replicates the histology, physiological effects, biochemical pathways and metastatic pattern observed in the same human tumor type. Metastases are especially important because they are the main determinants of the clinical course of the disease and patient survival, and are the target of systemic therapy. The generation of clinically relevant models using the mouse requires their humanization, since differences exist in transformation and oncogenesis between human and mouse. Although genetically modified (GM) mice have been instrumental in understanding the molecular mechanisms involved in tumor initiation, they have been less successful in replicating advanced cancer. Moreover, a particular genetic alteration frequently leads to different tumor types in human and mouse and to lower metastastatic rates in GM mice than in humans. These findings question the capacity of current GM mouse carcinoma models to predict clinical response to therapy. On the other hand, orthotopic (ORT) xenografts of human tumors, or tumor cell lines, in nude mice reproduce the histology and metastatic pattern of most human tumors at advanced stage. Using ex vivo genetic manipulation of human tumor cells, ORT models can be used to molecularly dissect the metastatic process and to evaluate in vivo tumor response to therapy, using non-invasive procedures. Nevertheless, this approach is not useful in the study of the initial stages of tumorigenesis or the contribution of the immune system in this process. Despite ORT models are more promising than the most commonly used subcutaneous xenografts in preclinical drug development, their capacity to predict clinical response to antitumor agents remains to be studied. Humanizing mouse models of cancer will most likely require the combined use of currently available methodologies.

Trials, tribulations, and trends in tumor modeling in mice

Selection of mouse models of cancer is often based simply on availability of a mouse strain and a known compatible tumor. Frequently this results in use of tumor models long on history but short on homology and quality control. Other factors including genetics, sex, immunological status, method and site of tumor implantation, technical competence, biological activity of the tumor, protocol sequence and timing, and selection of endpoints interact to produce outcomes in tumor models. Common reliance on survival and tumor burden data in a single mouse model often skews expectations towards high remission and cure rates; a finding seldom duplicated in clinical trials. Inherent limitations of tumor models coupled with the advent of new therapeutic targets reinforce need for careful attention to design, conduct, and stringent selection of in vivo and ex vivo endpoints. Preclinical efficacy testing for anti-tumor therapies should progress through a series of models of increasing sophistication that includes incorporation of genetically engineered animals, and orthotopic and combination therapy models. Pharmacology and safety testing in tumor-bearing animals may also help to improve predictive value of these models for clinical efficacy. Trends in bioinformatics, genetic refinements, and specialized imaging techniques are helping to maintain mice as the most scientifically and economically powerful model of malignant neoplasms.

In vivo expression and function of the sodium iodide symporter following gene transfer in the MATLyLu rat model of metastatic prostate cancer

BACKGROUND

The sodium iodide symporter (NIS) mediates iodide uptake in thyroid follicular cells and provides a mechanism for effective radioiodide treatment of residual, recurrent, and metastatic thyroid cancers. This study investigated the clinical applications of NIS gene transfer for prostate cancer using the MATLyLu metastatic rat model.

METHODS

MATLyLu cells expressing NIS were injected subcutaneously in Copenhagen rats, which developed metastases in lymph nodes and lungs. NIS protein expression was evaluated by Western blot and immunohistochemistry, and function was measured by tissue gamma counts and whole-body imaging following radionuclide administration.

RESULTS

In vitro radioiodide-concentrating activity was increased up to 72-fold in a mixed population of MATLyLu-hNIS cells. NIS protein expression was confirmed in subcutaneous MATLyLu-hNIS tumors by immunohistochemistry and Western blot. Gamma counts of subcutaneous MATLyLu-hNIS tumors were 23-fold higher than parental MATLyLu tumors and radionuclide uptake in subcutaneous MATLyLu-hNIS tumors and lymph node metastases was visualized by whole-body image analysis.

CONCLUSIONS

NIS expression by a proportion of cells in a population was sufficient to confer radionuclide-concentrating function in subcutaneous and metastatic MATLyLu tumors. Ablation of residual normal and neoplastic prostate tissues by radioiodide after prostate-restricted NIS gene transfer might be a novel adjuvant therapy to prostatectomy for the treatment of advanced prostate cancer.

Ras and TGF[beta] cooperatively regulate epithelial cell plasticity and metastasis: dissection of Ras signaling pathways

Multistep carcinogenesis involves more than six discrete events also important in normal development and cell behavior. Of these, local invasion and metastasis cause most cancer deaths but are the least well understood molecularly. We employed a combined in vitro/in vivo carcinogenesis model, that is, polarized Ha-Ras-transformed mammary epithelial cells (EpRas), to dissect the role of Ras downstream signaling pathways in epithelial cell plasticity, tumorigenesis, and metastasis. Ha-Ras cooperates with transforming growth factor beta (TGFbeta) to cause epithelial mesenchymal transition (EMT) characterized by spindle-like cell morphology, loss of epithelial markers, and induction of mesenchymal markers. EMT requires continuous TGFbeta receptor (TGFbeta-R) and oncogenic Ras signaling and is stabilized by autocrine TGFbeta production. In contrast, fibroblast growth factors, hepatocyte growth factor/scatter factor, or TGFbeta alone induce scattering, a spindle-like cell phenotype fully reversible after factor withdrawal, which does not involve sustained marker changes. Using specific inhibitors and effector-specific Ras mutants, we show that a hyperactive Raf/mitogen-activated protein kinase (MAPK) is required for EMT, whereas activation of phosphatidylinositol 3-kinase (PI3K) causes scattering and protects from TGFbeta-induced apoptosis. Hyperactivation of the PI3K pathway or the Raf/MAPK pathway are sufficient for tumorigenesis, whereas EMT in vivo and metastasis required a hyperactive Raf/MAPK pathway. Thus, EMT seems to be a close in vitro correlate of metastasis, both requiring synergism between TGFbeta-R and Raf/MAPK signaling.