Evelyne Beerling

In Vivo Imaging Reveals Extracellular Vesicle-Mediated Phenocopying of Metastatic Behavior

Summary Most cancer cells release heterogeneous populations of extracellular vesicles (EVs) containing proteins, lipids, and nucleic acids. In vitro experiments showed that EV uptake can lead to transfer of functional mRNA and altered cellular behavior. However, similar in vivo experiments remain challenging because cells that take up EVs cannot be discriminated from non-EV-receiving cells. Here, we used the Cre-LoxP system to directly identify tumor cells that take up EVs in vivo. We show that EVs released by malignant tumor cells are taken up by less malignant tumor cells located within the same and within distant tumors and that these EVs carry mRNAs involved in migration and metastasis. By intravital imaging, we show that the less malignant tumor cells that take up EVs display enhanced migratory behavior and metastatic capacity. We postulate that tumor cells locally and systemically share molecules carried by EVs in vivo and that this affects cellular behavior.

Intravital microscopy: new insights into metastasis of tumors

Metastasis, the process by which cells spread from the primary tumor to a distant site to form secondary tumors, is still not fully understood. Although histological techniques have provided important information, they give only a static image and thus compromise interpretation of this dynamic process. New advances in intravital microscopy (IVM), such as two-photon microscopy, imaging chambers, and multicolor and fluorescent resonance energy transfer imaging, have recently been used to visualize the behavior of single metastasizing cells at subcellular resolution over several days, yielding new and unexpected insights into this process. For example, IVM studies showed that tumor cells can switch between multiple invasion strategies in response to various densities of extracellular matrix. Moreover, other IVM studies showed that tumor cell migration and blood entry take place not only at the invasive front, but also within the tumor mass at tumor-associated vessels that lack an intact basement membrane. In this Commentary, we will give an overview of the recent advances in high-resolution IVM techniques and discuss some of the latest insights in the metastasis field obtained with IVM.

Plasticity between Epithelial and Mesenchymal States Unlinks EMT from Metastasis-Enhancing Stem Cell Capacity

Summary Forced overexpression and/or downregulation of proteins regulating epithelial-to-mesenchymal transition (EMT) has been reported to alter metastasis by changing migration and stem cell capacity of tumor cells. However, these manipulations artificially keep cells in fixed states, while in vivo cells may adapt transient and reversible states. Here, we have tested the existence and role of epithelial-mesenchymal plasticity in metastasis of mammary tumors without artificially modifying EMT regulators. In these tumors, we found by intravital microscopy that the motile tumor cells have undergone EMT, while their epithelial counterparts were not migratory. Moreover, we found that epithelial-mesenchymal plasticity renders any EMT-induced stemness differences, as reported previously, irrelevant for metastatic outgrowth, because mesenchymal cells that arrive at secondary sites convert to the epithelial state within one or two divisions, thereby obtaining the same stem cell potential as their arrived epithelial counterparts. We conclude that epithelial-mesenchymal plasticity supports migration but additionally eliminates stemness-enhanced metastatic outgrowth differences.

Brief Report: Intravital Imaging of Cancer Stem Cell Plasticity in Mammary Tumors

It is widely debated whether all tumor cells in mammary tumors have the same potential to propagate and maintain tumor growth or whether there is a hierarchical organization. Evidence for the latter theory is mainly based on the ability or failure of transplanted tumor cells to produce detectable tumors in mice with compromised immune systems; however, this assay has lately been disputed to accurately reflect cell behavior in unperturbed tumors. Lineage tracing experiments have recently shown the existence of a small population of cells, referred to as cancer stem cells (CSCs), that maintains and provides growth of squamous skin tumors and intestinal adenomas. However, the lineage tracing techniques used in these studies provide static images and lack the ability to study whether stem cell properties can be obtained or lost, a process referred to as stem cell plasticity. Here, by intravital lineage tracing, we report for the first time the existence of CSCs in unperturbed mammary tumors and demonstrate CSC plasticity. Our data indicate that existing CSCs disappear and new CSCs form during mammary tumor growth, illustrating the dynamic nature of these cells. STEM CELLS2013;31:602–606

Intravital FRET imaging of tumor cell viability and mitosis during chemotherapy

Taxanes, such as docetaxel, are microtubule-targeting chemotherapeutics that have been successfully used in the treatment of cancer. Based on data obtained from cell cultures, it is believed that taxanes induce tumor cell death by specifically perturbing mitotic progression. Here, we report on data that suggest that this generally accepted view may be too simplified. We describe a high-resolution intravital imaging method to simultaneously visualize mitotic progression and the onset of apoptosis. To directly compare in vitro and in vivo data, we have visualized the effect of docetaxel on mitotic progression in mouse and human colorectal tumor cell lines both in vitro and in isogenic tumors in mice. We show that docetaxel-induced apoptosis in vitro occurs via mitotic cell death, whereas the vast majority of tumor cells in their natural environment die independent of mitotic defects. This demonstrates that docetaxel exerts its anti-tumor effects in vivo through means other than mitotic perturbation. The differences between in vitro and in vivo mechanisms of action of chemotherapeutics may explain the limited response to many of the anti-mitotic agents that are currently validated in clinical trials. Our data illustrate the requirement and power of our intravital imaging technique to study and validate the mode of action of chemotherapeutic agents in vivo, which will be essential to understand and improve their clinical efficacy.

Real-time intravital imaging of cancer models

High-resolution intravital imaging (IVM) has proven to be a powerful technique to visualise dynamic processes that are important for tumour progression, such as the interplay between tumour cells and cellular components of the tumour microenvironment. The development of IVM tools, including imaging windows and photo-marking of individual cells, has led to the visualisation of dynamic processes and tracking of individual cells over a time span of days. In order to visualise these dynamic processes, several strategies have been described to develop fluorescent IVM tumour models. Genetic tools to engineer fluorescent tumour cell lines have advanced the applications of cell line-based tumour models to study, for example, changes in behaviour or transcriptional and differentiation state of individual cells in a tumour. In order to study tumour progression, fluorescent genetic mouse models have been engineered that better recapitulate human tumours. These technically challenging tumour models are key in visualising dynamic processes during cancer progression and in the translational aspects of IVM experiments.

LIM Kinase Inhibitor Pyr1 Reduces the Growth and Metastatic Load of Breast Cancers

LIM kinases (LIMK) are emerging targets for cancer therapy, and they function as network hubs to coordinate actin and microtubule dynamics. When LIMKs are inhibited, actin microfilaments are disorganized and microtubules are stabilized. Owing to their stabilizing effect on microtubules, LIMK inhibitors may provide a therapeutic strategy to treat taxane-resistant cancers. In this study, we investigated the effect of LIMK inhibition on breast tumor development and on paclitaxel-resistant tumors, using a novel selective LIMK inhibitor termed Pyr1. Treatment of breast cancer cells, including paclitaxel-resistant cells, blocked their invasion and proliferation in vitro and their growth in vivo in tumor xenograft assays. The tumor-invasive properties of Pyr1 were investigated in vivo by intravital microscopy of tumor xenografts. A striking change of cell morphology was observed with a rounded phenotype arising in a subpopulation of cells, while other cells remained elongated. Notably, although Pyr1 decreased the motility of elongated cells, it increased the motility of rounded cells in the tumor. Pyr1 administration prevented the growth of metastasis but not their spread. Overall, our results provided a preclinical proof of concept concerning how a small-molecule inhibitor of LIMK may offer a strategy to treat taxane-resistant breast tumors and metastases. Cancer Res; 76(12); 3541-52. ©2016 AACR.

A surgical orthotopic organoid transplantation approach in mice to visualize and study colorectal cancer progression

Most currently available colorectal cancer (CRC) mouse models are not suitable for studying progression toward the metastatic stage. Recently, establishment of tumor organoid lines, either from murine CRC models or patients, and the possibility of engineering them with genome-editing technologies, have provided a large collection of tumor material faithfully recapitulating phenotypic and genetic heterogeneity of native tumors. To study tumor progression in the natural in vivo environment, we developed an orthotopic approach based on transplantation of CRC organoids into the cecal epithelium. The 20-min procedure is described in detail here and enables growth of transplanted organoids into a single tumor mass within the intestinal tract. Due to long latency, tumor cells are capable of spreading through the blood circulation and forming metastases at distant sites. This method is designed to generate tumors suitable for studying CRC progression, thereby providing the opportunity to visualize tumor cell dynamics in vivo in real time by intravital microscopy.

Intravital characterization of tumor cell migration in pancreatic cancer

ABSTRACT Curing pancreatic cancer is difficult as metastases often determine the poor clinical outcome. To gain more insight into the metastatic behavior of pancreatic cancer cells, we characterized migratory cells in primary pancreatic tumors using intravital microscopy. We visualized the migratory behavior of primary tumor cells of a genetically engineered pancreatic cancer mouse model and found that pancreatic tumor cells migrate with a mesenchymal morphology as single individual cells or collectively as a stream of non-cohesive single motile cells. These findings may improve our ability to conceive treatments that block metastatic behavior.