Step In Extravasation Research Articles

Abstract A018: Exercise stimulates anti-tumoral immunity in metastatic PDAC

Abstract The majority of pancreatic ductal adenocarcinoma (PDAC) patients are metastatic at presentation with limited treatment options and a poor overall 5-year survival of 3%. The liver is the predominant site of distant metastasis in PDAC. Our group has previously shown that aerobic exercise can inhibit tumorigenesis in a primary PDAC mouse model by promoting anti-tumor immunity, however, the effects of exercise in the metastatic setting have not been explored. As such, we developed a model of PDAC liver metastasis by isolating primary pancreatic and liver metastatic cell lines from 18–20-week-old LSL-KRasG12D/+; LSL-Trp53R172H/+; p48Cre; Rosa26LSL-tdTomato/+ (KPCTpancreas or KPCTliver, respectively) mice. KPCTpancreas cells were surgically implanted into the pancreata of syngeneic wild-type mice. One week after pancreatic implantation, KPCTliver cells were implanted into the liver either by direct injection into the parenchyma or via the portal vein. The portal vein method enables us to account for the extravasation step of the metastatic cascade, while the direct parenchymal injection offers a less invasive surgery. Both models preserve the spleen, which is the largest secondary lymphoid organ and essential to the immune response. Treadmill running was initiated in the aerobic exercise cohort 5 days per week for 2 weeks or mice were allowed to rest. Endpoint analysis revealed that aerobic exercise treatment decreased tumor burden in both primary tumors and liver metastasis as measured by tumor weights and tdTomato fluorescence imaging when compared to the rested controls. Immune profiling of the liver metastases revealed elevated IL-15Rɑ+ CD8+ T cells as well as CD19+ B cells in the exercise cohort. While identification of IL-15Rɑ+ CD8+ T cells is consistent with the immune changes we have previously reported in the primary pancreatic tumor of exercised mice, the latter changes reveal organ specific immune cell recruitment not observed in the primary pancreatic tumor of exercised mice. The combined immune profiling and phenotypic changes suggest that aerobic exercise reduces PDAC metastatic growth by modulating systemic and intra-tumoral immunity. The induction of an anti-tumorigenic immune response by aerobic exercise could open avenues for potential pharmacological intervention in downstream pathways to aid in the treatment of metastatic PDAC. Citation Format: Mansour E. Riachi, Carolina G. Alcantara Hirsch, Erica Ma, Beny Shapiro, Ammar Javed, Christopher L. Wolfgang, Dafna Bar-Sagi. Exercise stimulates anti-tumoral immunity in metastatic PDAC [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr A018.

Abstract 3618: The role of endothelial ACKR1 in triple-negative breast cancer metastasis

Abstract Metastasis is the most common cause of breast cancer mortality. Of the breast cancer subtypes, triple-negative breast cancer (TNBC) is the deadliest due to its increased likelihood to metastasize. Tumor cell extravasation is a critical step of metastasis and allows circulating tumor cells to exit the vasculature and seed distant tissues. Clear understanding of the major regulators of tumor cell extravasation will provide insights into the progression of TNBC metastasis. One potential regulator of TNBC cell extravasation is ACKR1. In many contexts, ACKR1 expression is required in endothelial cells (EC) for leukocyte extravasation. Endothelial ACKR1 binds CXCL2, a promigratory chemokine, and localizes it to EC junctions to guide neutrophils through leukocyte extravasation. CXCL2 expression in TNBC cells is also necessary for tumor cell extravasation from lung microvasculature and for tumor metastasis. Our preliminary data show that ACKR1 is required in at least one stromal cell type for TNBC metastasis from the primary tumor to the lung. These data suggest that endothelial ACKR1-CXCL2 interactions may mediate tumor cell extravasation in TNBC metastasis. Therefore, we hypothesize that endothelial ACKR1 promotes metastasis via retention of CXCL2 at EC junctions, increasing tumor cell chemotaxis and extravasation. To address this hypothesis, we will examine the in vivo significance of endothelial ACKR1 expression using our validated ACKR1 endothelial cell-specific knockout mouse model. We will test the requirement for endothelial ACKR1 for metastasis of orthotopically implanted TNBC tumors to distant sites in the lung and for extravasation of circulating tumor cells into lung tissue. We will determine which steps of extravasation require ACKR1 by evaluating ACKR1-low and ACKR1-overexpressing ECs using an Ibidi flow co-culture system that recapitulates the shear stress conditions of pulmonary microvasculature. We will examine whether these steps are dependent on CXCL2 by introducing CXCL2-neutralizing antibodies to the Ibidi flow system and observing their effects on each extravasation step. Our proposed studies will establish the role of endothelial ACKR1 in TNBC metastatic progression and determine the specific steps of tumor cell extravasation in which endothelial ACKR1 and CXCL2 function. Understanding these processes may guide development of ACKR1 as a prognostic marker for metastasis and can provide mechanistic insight into candidate chemokine and chemokine receptor inhibitors under evaluation for treatment of breast cancer. Citation Format: Samuel Tanner Roach, Chinwe Ewenighi-Amankwah, J Dufraine, L.A. Naiche, Jan K. Kitajewski. The role of endothelial ACKR1 in triple-negative breast cancer metastasis. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3618.

E-Selectin Targeted Gold Nanoshells to Inhibit Breast Cancer Cell Binding to Lung Endothelial Cells.

Extravasation of circulating tumor cells (CTCs) from the vasculature is a key step in cancer metastasis. CTCs bind to cell adhesion molecules (CAMs) expressed by endothelial cells (ECs) for flow arrest prior to extravasation. While a number of EC-expressed CAMs have been implicated in facilitating CTC binding, this work investigated the efficacy of inhibiting cancer cell binding to human lung microvascular ECs via antibody blocking of E-selectin using antibody-functionalized gold nanoshells (NS). The antibody-functionalized gold NS were synthesized using both directional and non-directional antibody conjugation techniques with variations in synthesis parameters (linker length, amount of passivating agents, and ratio of antibodies to NS) to gain a better understanding of these properties on the resultant hydrodynamic diameter, zeta potential, and antibody loading density. We quantified the ability of E-selectin antibody-functionalized NS to bind human lung microvascular endothelial cells (HMVEC-Ls) under non-inflamed and inflamed (TNF-α) conditions to inhibit binding of triple-negative MDA-MB-231s. E-selectin-targeted NS prepared using non-directional conjugation had higher antibody loading than those prepared via directional conjugation, resulting in the conjugates having similar overall binding to HMVEC-Ls at a given antibody concentration. E-selectin-targeted NS reduced MDA-MB-231 binding to HMVEC-Ls by up to 41% as determined using an in vitro binding assay. These results provide useful insights into the characteristics of antibody-functionalized NS prepared under different conditions while also demonstrating proof of concept that these conjugates hold potential to inhibit CTC binding to ECs, a critical step in extravasation during metastasis.

Fusobacterium nucleatum promotes colorectal cancer cells adhesion to endothelial cells and facilitates extravasation and metastasis by inducing ALPK1/NF-κB/ICAM1 axis

ABSTRACT Metastasis is the leading cause of death for colorectal cancer (CRC) patients, and the spreading tumor cells adhesion to endothelial cells is a critical step for extravasation and further distant metastasis. Previous studies have documented the important roles of gut microbiota-host interactions in the CRC malignancy, and Fusobacterium nucleatum (F. nucleatum) was reported to increase proliferation and invasive activities of CRC cells. However, the potential functions and underlying mechanisms of F. nucleatum in the interactions between CRC cells and endothelial cells and subsequent extravasation remain unclear. Here, we uncovered that F. nucleatum enhanced the adhesion of CRC cells to endothelial cells, promoted extravasation and metastasis by inducing ICAM1 expression. Mechanistically, we identified that F. nucleatum induced a new pattern recognition receptor ALPK1 to activate NF-κB pathway, resulting in the upregulation of ICAM1. Interestingly, the abundance of F. nucleatum in tumor tissues of CRC patients was positively associated with the expression levels of ALPK1 and ICAM1. Moreover, high expression of ALPK1 or ICAM1 was significantly associated with a shorter overall survival time of CRC patients. This study provides a new insight into the role of gut microbiota in engaging into the distant metastasis of CRC cells.

The driving role of the Cdk5/Tln1/FAKS732 axis in cancer cell extravasation dissected by human vascularized microfluidic models

BackgroundUnderstanding the molecular mechanisms of metastatic dissemination, the leading cause of death in cancer patients, is required to develop novel, effective therapies. Extravasation, an essential rate-limiting process in the metastatic cascade, includes three tightly coordinated steps: cancer cell adhesion to the endothelium, trans-endothelial migration, and early invasion into the secondary site. Focal adhesion proteins, including Tln1 and FAK, regulate the cytoskeleton dynamics: dysregulation of these proteins is often associated with metastatic progression and poor prognosis. MethodsHere, we studied the previously unexplored role of these targets in each extravasation step using engineered 3D in vitro models, which recapitulate the physiological vascular niche experienced by cancer cells during hematogenous metastasis. ResultsHuman breast cancer and fibrosarcoma cell lines respond to Cdk5/Tln1/FAK axis perturbation, impairing their metastatic potential. Vascular breaching requires actin polymerization-dependent invadopodia formation. Invadopodia generation requires the structural function of FAK and Tln1 rather than their activation through phosphorylation. Our data support that the inhibition of FAKS732 phosphorylation delocalizes ERK from the nucleus, decreasing ERK phosphorylated form. These findings indicate the critical role of these proteins in driving trans-endothelial migration. In fact, both knock-down experiments and chemical inhibition of FAK dramatically reduces lung colonization in vivo and TEM in microfluidic setting. Altogether, these data indicate that engineered 3D in vitro models coupled to in vivo models, genetic, biochemical, and imaging tools represent a powerful weapon to increase our understanding of metastatic progression. ConclusionsThese findings point to the need for further analyses of previously overlooked phosphorylation sites of FAK, such as the serine 732, and foster the development of new effective antimetastatic treatments targeting late events of the metastatic cascade.

The Establishment and Utilization of Patient Derived Xenograft Models of Central Nervous System Metastasis.

The development of novel therapies for central nervous system (CNS) metastasis has been hindered by the lack of preclinical models that accurately represent the disease. Patient derived xenograft (PDX) models of CNS metastasis have been shown to better represent the phenotypic and molecular characteristics of the human disease, as well as better reflect the heterogeneity and clonal dynamics of human patient tumors compared to historic cell line models. There are multiple sites that can be used to implant patient-derived tissue when setting up preclinical trials, each with their own advantages and disadvantages, and each suited for studying different aspects of the metastatic cascade. Here, the protocol describes how to establish PDX models and present three different approaches for utilizing CNS metastasis PDX models in pre-clinical studies, discussing each of their applications and limitations. These include flank implantation, orthotopic injection in the brain, and intracardiac injection. Subcutaneous flank implantation is the easiest to monitor and, therefore, most convenient for pre-clinical studies. In addition, metastases to brain and other tissues from flank implantation were observed, indicating that the tumor has undergone multiple steps of metastasis, including intravasation, extravasation, and colonization. Orthotopic injection in the brain is the best option for recapitulating the brain tumor microenvironment and is useful for determining the efficacy of biologics to cross the blood-brain barrier (BBB) but bypasses most steps of the metastatic cascade. Intracardiac injection facilitates metastasis to the brain and is also useful for studying organ tropism. While this method forgoes earlier steps of the metastatic cascade, these cells will still have to survive circulation, extravasate, and colonize. The utility of a PDX model, is therefore, impacted by the route of tumor inoculation and the choice of which one to utilize should be dictated by the scientific question and overall goals of the experiment.

Abstract PO038: Circulating cancer associated fibroblasts (cCAFs) enhance CTC extravasation and establishment of metastases

Abstract Background: Cancer associated fibroblasts (CAFs) are the most abundant non-cancerous cell component of the breast cancer (BC) TME and have been shown to participate in most all steps of metastasis. We have previously shown that CTCs cluster with circulating CAFs (cCAFs) in BC patients at all disease stages, and this observation is recapitulated in the mouse PYMT BC model. Our central hypothesis is that cCAF/CTC co-clusters comprise the functional metastatic unit, and here we sought to determine the role of cCAFs in co-clusters on CTC extravasation and metastatic seeding. Methods: Xenografts: In vitro co-clusters were produced by culturing human CAF23 cells and MDA231(Ffluc) cells in ULA plates for 18 hrs. Clusters were injected via tail vein into NSG mice and metastatic growth was monitored by BLI. Endothelial binding assays: In vitro clusters, single CAFs or single BC cells were labeled with Cell Tracker dyes, pipetted onto confluent HUVEC monolayers, and allowed to bind for 30 minutes before gentle washing. Bound cells were counted on a fluorescent microscope. Ex vivo extravasation assays: Cell Tracker labeled co-clusters were injected via tail vein into FVB mice. One hour before sacrifice, FITC-lectin was injected via tail vein to label lung endothelia. Lungs were then extracted and imaged by confocal microscopy. Results/Discussion: Xenograft experiments demonstrate that within the first week, CAF23/MDA231 co-clusters produce durable, proliferative lung metastases faster than MDA231 monoclusters. This early difference in metastatic growth suggests that CAFs help BC cells establish metastases faster, possibly by aiding extravasation into the lung parenchyma. Using our ex vivo model of lung extravasation, we saw that significantly more CAF23/MDA231 co-clusters than MDA231 monoclusters were in the process of and/or had extravasated into the lung parenchyma at 8 and 24 hrs post-injection. In vitro binding experiments revealed that HUVEC endothelial cells bind more CAF23/BC co-clusters than BC monoclusters. Similarly, HUVEC cells bound significantly more single CAF23 or CAF19 cells than BC cells. CAF binding increased when endothelial e-selectin expression was induced with IL1-b; binding to e-selectin being the first step in cancer cell rolling and extravasation. Immunofluorescence and flow cytometry showed that CAFs express the CA19-9 antigen, sialyl-Lewis A (sLeA), which acts as an e-selectin ligand. Tannic acid, an inhibitor of the chemokine SDF1/CXCL12, decreased binding, as did 5mM EDTA. CD44 siRNA had no effect on binding whereas depletion of hyaluronin, a ligand of CD44, had a significant effect on CAFs but not on BC cells. Together, these experiments point to CAFs in co-clusters as critical enhancers of endothelial binding and extravasation, which may ultimately result in faster establishment of metastases and enhanced survival of CTCs. Future investigations will focus on therapeutic targeting of the mechanisms we have identified to block cCAF/CTC extravasation and metastasis. Citation Format: Angela Spartz, Benjamin Troness, Utsav Sharma, Geneva Taylor, Dorraya El Ashry. Circulating cancer associated fibroblasts (cCAFs) enhance CTC extravasation and establishment of metastases [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PO038.

Abstract PO015: JAGGED-1 as a novel metastatic extravasation promoter of triple negative breast cancer cells

Abstract Though survival is improving for breast cancer patients, clinical outcomes remain poor for patients with aggressive molecular subtypes. Triple negative breast cancer (TNBC) is considered the most aggressive breast cancer subtype, and despite having a 90% five-year relative survival rate for localized disease, that number drops to as low as 11% for patients with distant TNBC metastasis. The poor clinical outcomes for TNBC patients are largely due to lack of clinically actionable molecular targets and pathways compared to other breast cancer subtypes. Given the lack of effective treatment strategies for advanced TNBC, there is an urgent and unmet need to understand the means through which tumor cells disseminate and metastasize to distant tissues in hopes of identifying new targets for therapeutic intervention. For tumor cells to metastasize, they acquire complex series of pathophysiological phenotypes, starting with invasion into surrounding tissue and intravasation into systemic lymphatic or blood vascular systems. Only a small fraction of tumor cells can survive in circulation, with a smaller fraction able to extravasate from vessels and establish distant metastases. While some cancer cells partially coopt the mechanisms that leukocytes use to extravasate, circulating TNBC cells also use distinct mechanisms to breach an endothelial barrier. However, the mechanism(s) of TNBC extravasation remains largely unknown, underlying the need to study further. High expression of Notch ligand JAGGED-1 (JAG1) is associated with increased metastasis and mortality in patients with breast cancer. While JAG1 enhances tumor angiogenesis and tumor growth, the means through which JAG1 promotes tumor cell dissemination is not clear. Our preliminary data supports a role for JAG1 as a key regulator of tumor cell interactions with the endothelium, controlling tumor cell adhesion, transendothelial migration (TEM), and transcription of critical paracrine-acting extravasation proteins, such as SPARC and ICAM1. Using both JAG-specific ligand traps as well as CRISPR/Cas9 mediated deletion of JAG1, we show that JAG1 promotes TEM in static transwell models, promotes primary tumor growth, and directs a tumor cell transcriptional program that upregulates cell surface interaction pathways distinct from global Notch inhibition. It is our central hypothesis that JAG1 promotes TNBC migration across the vascular endothelium, thereby allowing disseminated cancer cells to exit from circulation and enhancing TNBC metastasis. To define the JAG1-mediated elements of extravasation, we will examine five CRISPR/Cas9 JAG1 knockout lines in a cutting-edge flow system that recapitulates the vascular shear stress microenvironments where extravasation is thought to occur in vivo. We will evaluate multiple steps of extravasation including tumor cell binding, rolling, and TEM under various flow parameters. Moreover, we will study in vivo lung extravasation using a murine tail vein injection model and interrogate transcriptional candidates downstream of JAG1 as identified by our RNAseq data. Citation Format: Benjamin Gordon, Reyhaan A. Chaudhri, Tim Sargis, L.A. Naiche, Jan K. Kitajewski. JAGGED-1 as a novel metastatic extravasation promoter of triple negative breast cancer cells [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PO015.

Brain Metastases and Microenvironment.

The formidable advances in cancer treatment have led to remarkable improvements in patient's survival, so that the major concern shifted from primary tumors to metastatic disease. Brain metastases represent a life-threatening condition with a poor prognosis due to the lack of reliable biomarkers that preclude their timely identification and to the scarce therapeutic possibilities considering that the blood-brain barrier limits the access of most of the drugs to the brain and surgical resection is discouraged in cases of multiple metastases. Moreover, brain metastases have been scarcely investigated, which precludes a comprehensive understanding of the determinants and players, as well as of the complex cross-talk and signaling pathways involved. This chapter summarizes the impressive numbers about cancer and brain metastases and the estimates of progression in the years to come. It also gathers together the relevant concepts about the metastatic cascade, focusing in the extravasation step across the microvascular endothelium that leads to the formation of brain metastases. Moreover, it comprehensively explores the brain tumor microenvironment, detailing on the pre-metastatic niches and their relevance for tumor cell development in the target organ. Additionally, the cellular and acellular components, as well as their interplay, activation status, and acquired phenotypes, are addressed. Collectively, by bringing together historical concepts and state-of-the-art knowledge, this chapter shall contribute to a better understanding of the brain metastasization process, essential for the development of novel approaches to improve patients' life quality and expectancy.

Prevention of Melanoma Extravasation as a New Treatment Option Exemplified by p38/MK2 Inhibition.

Melanoma releases numerous tumor cells into the circulation; however, only a very small fraction of these cells is able to establish distant metastasis. Intravascular survival of circulating tumor cells is limited through hemodynamic forces and by the lack of matrix interactions. The extravasation step is, thus, of unique importance to establish metastasis. Similar to leukocyte extravasation, this process is under the control of adhesion molecule pairs expressed on melanoma and endothelial cells, and as for leukocytes, ligands need to be adequately presented on cell surfaces. Based on melanoma plasticity, there is considerable heterogeneity even within one tumor and one patient resulting in a mixture of invasive or proliferative cells. The molecular control for this switch is still ill-defined. Recently, the balance between two kinase pathways, p38 and JNK, has been shown to determine growth characteristics of melanoma. While an active JNK pathway induces a proliferative phenotype with reduced invasive features, an active p38/MK2 pathway results in an invasive phenotype and supports the extravasation step via the expression of molecules capable of binding to endothelial integrins. Therapeutic targeting of MK2 to prevent extravasation might reduce metastatic spread.

Cancer and Metastasis: Importance of Cell Adhesion Molecules and Cell Junctions

Metastasis is a complex process which is driven by several biochemical and molecular factors. Metastasis is a condition which severely limits cancer therapies and is responsible for 90% of cancer deaths. Therefore, it is of crucial importance to gain a greater understanding of the underlying mechanisms of metastasis in terms of developing treatment methods for metastasis prevention. Included in metastasis are multiple steps such as local invasion (epithelial-mesenchymal transition), intravasation, survival in the circulatory system, extravasation (transendothelial migration/ diapedesis), formation of micrometastasis and metastatic colony. Tumor cells escape from circulating immune cells and apoptosis using platelets as a ‘‘shield’’ and a ‘‘link’’ for binding to endothelium via altering expression patterns of adhesion molecules. Extravasation in tumor cells is one of the key steps of metastasis and despite small differences in molecules, the whole process is basically the same in leukocytes; rolling, adhesion, and transmigration. Cell adhesion molecules such as integrins, and cell junctions such as Jam proteins, are key players in the extravasation step. Therefore, cell adhesion molecules and cell junctions can be used as potential targets for cancer therapy. In this review, the general processes of metastasis and the roles of cell adhesion molecules/cell junctions on metastasis were summarized.

Abstract P3-01-28: Circulating cancer associated fibroblasts (cCAFs) enhance CTC extravasation and establishment of metastases

Abstract Introduction: Breast cancer metastasis is a multi-step process that involves cellular migration, invasion, travel through the circulation, extravasation and secondary site proliferation. Circulating tumor cell (CTC) travel is thought to be via rolling on vascular endothelium, and CTC clusters have been shown to have a shorter circulation half-life than single CTCs due to increased entrapment within capillaries. We have previously shown that CTCs cluster with circulating cancer associated fibroblasts (cCAFs) in breast cancer patients and this observation is recapitulated in the mouse PYMT breast cancer model. Circulating CAF/CTC clusters are seen in patients of all stages and in all PyMT mice with tumors, before overt metastases. Our central hypothesis is that cCAF/CTC co-clusters comprise the functional metastatic unit and here we sought to determine the role of cCAFs in co-clusters on metastatic seeding. Methods: Xenografts: In vitro co-clusters were produced by culturing 75,000 human CAF23 cells and 75,000 MDA231(Ffluc) cells in ultra-low attachment plates for 18 hrs. Clusters were injected via tail vein into NSG mice and metastatic growth was monitored by bioluminescent imaging. Endothelial binding assays: In vitro clusters were made as for xenografts except that CAFs and BC cells were labeled with Cell Tracker dyes. Clusters were pipetted onto confluent HUVEC monolayers and allowed to bind for 30 minutes before gentle washing. Bound cells were counted on a fluorescent microscope. Ex vivo extravasation assays: Co-clusters were made as above with Cell Tracker labeled MDA231 and CAF23 cells and injected via tail vein into FVB mice. Lung endothelia was labeled by tail vein injection of FITC-lectin an hour before lungs were extracted and imaged by confocal microscopy. Results: Xenograft experiments demonstrate that within the first week, CAF23/MDA231(Ffluc) co-clusters produce durable, proliferative lung metastases faster than MDA231(Ffluc) monoclusters. This early difference in metastatic growth suggests that CAFs help cancer cells establish metastases faster, possibly by enhancing the binding and rolling of CTCs along the vascular endothelium and/or by aiding extravasation into the lung parenchyma. In vitro binding experiments revealed that CAF23/MDA231 co-clusters bind to HUVEC endothelial cells better than MDA231 monoclusters under static conditions. Similar results were observed with the aggressive basal cell line, DT28. To determine the effect of shear stress, we performed endothelial binding assays in an orbital shaker at 100 rpm (used to mimic oscillatory and continuous flow shear stress), and under these conditions, CAFs continue to bind to HUVECs at significantly higher numbers than MDA231 cells. CAF binding increased two-fold when endothelial e-selectin expression was induced with IL1-β. Immunofluorescence and flow cytometry showed that CAFs express the CA19-9 antigen, sialyl-Lewis A (sLeA), which acts as an e-selectin ligand; binding to e-selectin being the first step in cancer cell rolling and extravasation. Using our ex-vivo extravasation imaging protocol, we observed that significantly more CAF23/MDA231 co-clusters than MDA231 monoclusters were in the process of extravasation and/or had extravasated into the lung parenchyma at 8 and 24 hrs post-injection. Conclusions: Together, these experiments point to CAFs in co-clusters as critical enhancers of endothelial binding and extravasation, which may ultimately result in quicker establishment of metastases and enhanced survival of CTCs in clusters. Future studies will focus on identifying the molecular mechanisms in these processes facilitated by cCAFs that could be amenable to therapeutic targeting. Citation Format: Angela Spartz, Benjamin Troness, Utsav Sharma, Dorraya El-Ashry. Circulating cancer associated fibroblasts (cCAFs) enhance CTC extravasation and establishment of metastases [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-01-28.

Using Evans Blue Dye to Determine Blood-Brain Barrier Integrity in Rodents.

The blood-brain barrier (BBB) is an active and selective barrier that shields the brain from endogenous and exogenous insults. Different stimuli may lead to the disruption of this barrier, including inflammation and trauma. Several methods are used to evaluate BBB disruption. The most widely used method is Evans blue (EB) dye extravasation. EB cannot normally pass through the BBB and thus its presence in brain tissue indicates alterations in permeability. This protocol details the steps of EB extravasation in rodents. Important aspects regarding critical steps and advantages are also provided. © 2019 by John Wiley & Sons, Inc.

LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) distinctly regulate neutrophil extravasation through hotspots I and II

Precise spatiotemporal regulation of leukocyte extravasation is key for generating an efficient immune response to injury or infection. The integrins LFA-1(CD11a/CD18) and Mac-1(CD11b/CD18) play overlapping roles in neutrophil migration because they bind the same as well as different ligands in response to extracellular signaling. Using two-photon intravital imaging and transmission electron microscopy, we observed the existence of preferred sites for neutrophil entrance into the endothelial cell monolayer and exit from the basement membrane and pericyte sheath during neutrophil extravasation, namely, hotspots I and II, by elucidating distinctive roles of LFA-1 and Mac-1. To penetrate the vascular endothelium, neutrophils must first penetrate the endothelial cell layer through hotspot I (i.e., the point of entry into the endothelium). Neutrophils frequently remain in the space between the endothelial cell layer and the basement membrane for a prolonged period (>20 min). Subsequently, neutrophils penetrate the basement membrane and pericyte sheath at hotspot II, which is the final stage of exiting the vascular endothelium. To further investigate the roles of LFA-1 and Mac-1, we newly generated LFA-1 FRET (CD11a-YFP/CD18-CFP) mice and Mac-1 FRET (CD11b-YFP/CD18-CFP) mice. Using both FRET mice, we were able to determine that LFA-1 and Mac-1 distinctly regulate the neutrophil extravasation cascade. Our data suggest that the vascular endothelium functions as a double-layered barrier in the steps of neutrophil extravasation. We propose that the harmonized regulation of neutrophil penetration through the endothelium via hotspots I and II may be critical for vascular homeostasis during inflammation.

Epithelial-Mesenchymal Transition Induces Podocalyxin to Promote Extravasation via Ezrin Signaling

SUMMARYThe epithelial-mesenchymal transition (EMT) endows carcinoma cells with traits needed to complete many of the steps leading to metastasis formation, but its contributions specifically to the late step of extravasation remain understudied. We find that breast cancer cells that have undergone an EMT extravasate more efficiently from blood vessels both in vitro and in vivo. Analysis of gene expression changes associated with the EMT program led to the identification of an EMTinduced cell-surface protein, podocalyxin (PODXL), as a key mediator of extravasation in mesenchymal breast and pancreatic carcinoma cells. PODXL promotes extravasation through direct interaction of its intracellular domain with the cytoskeletal linker protein ezrin. Ezrin proceeds to establish dorsal cortical polarity, enabling the transition of cancer cells from a non-polarized, rounded cell morphology to an invasive extravasation-competent shape. Hence, the EMT program can directly enhance the efficiency of extravasation and subsequent metastasis formation through a PODXL-ezrin signaling axis.

Hemodynamic Forces Tune the Arrest, Adhesion, and Extravasation of Circulating Tumor Cells

Metastatic seeding is driven by cell-intrinsic and environmental cues, yet the contribution of biomechanics is poorly known. We aim to elucidate the impact of blood flow on the arrest and the extravasation of circulating tumor cells (CTCs) invivo. Using the zebrafish embryo, we show that arrest of CTCs occurs in vessels with favorable flow profiles where flow forces control the adhesion efficacy of CTCs to the endothelium. We biophysically identified the threshold values of flow and adhesion forces allowing successful arrest ofCTCs. In addition, flow forces fine-tune tumor cellextravasation by impairing the remodeling properties of the endothelium. Importantly, we also observe endothelial remodeling at arrest sites of CTCs in mouse brain capillaries. Finally, we observed that human supratentorial brain metastases preferably develop in areas with low perfusion. These results demonstrate that hemodynamic profiles at metastatic sites regulate key steps of extravasation preceding metastatic outgrowth.

Endothelial Cell Focal Adhesion Regulates Transendothelial Migration and Subendothelial Crawling of T Cells.

Leukocytes circulating in the blood stream leave out of blood vessels and infiltrate into inflamed tissues to perform immune responses. Endothelial cells (ECs) lining interior of the post-capillary venules regulate various steps of leukocyte extravasation. In response to inflammatory signals, ECs upregulate adhesion molecules and produce/present chemokines to support firm adhesion and intraluminal crawling of leukocytes. They also remodel junctions to facilitate leukocyte transendothelial migration (TEM). While roles of apical/lateral components of EC layers in regulating leukocyte extravasation have been extensively investigated, relatively little attention has been paid to the basal part of EC layers comprising subendothelial spaces. In this study, we employed interference reflection microscopy (IRM), a microscopy technique specialized for label-free visualization of cell–substrate contact, to study detailed dynamic interactions between basal part of ECs and T cells underneath EC monolayer. For TEM, T cells on EC monolayer extended protrusions through junctions to explore subendothelial spaces, and EC focal adhesions (EC-FAs) acted as physical barrier for the protrusion. Therefore, preferential TEM occurred through junctions where near-junction focal adhesion (NJ-FA) density of ECs was low. After TEM, T cells performed subendothelial crawling (SEC) with flattened morphology and reduced migration velocity due to tight confinement. T cell SEC mostly occurred through gaps formed in between EC-FAs with minimally breaking EC-FAs. Tumor necrosis factor-α (TNF-α) treatment significantly loosened confinement in subendothelial spaces and reduced NJ-FA density of ECs, thus remodeled basal part of EC layer to facilitate leukocyte extravasation.

Hemodynamic Forces Tune the Arrest, Adhesion, and Extravasation of Circulating Tumor Cells

Metastatic seeding is driven by cell-intrinsic and environmental cues, yet the contribution of biomechanics is poorly known. We aim to elucidate the impact of blood flow on the arrest and the extravasation of circulating tumor cells (CTCs) in vivo. Using the zebrafish embryo, we show that arrest of CTCs occurs mostly in vessels with favorable flow profiles where flow forces control the adhesion efficacy of CTCs to the endothelium. We biophysically identified the threshold values of flow and adhesion forces allowing successful arrest of CTCs. In addition, flow forces fine-tune tumor cell extravasation by impairing the remodeling properties of the endothelium. Importantly, we also observe endothelial remodeling at arrest sites of CTCs in mouse brain capillaries. Finally, we observed that human supratentorial brain metastases preferably develop in areas with low perfusion. Altogether, these results demonstrate that hemodynamic profiles at metastatic sites regulate key steps of extravasation preceding metastatic outgrowth.

Impaired Transmigration of Myeloid-Derived Suppressor Cells across Human Sinusoidal Endothelium Is Associated with Decreased Expression of CD13.

Human monocytic myeloid-derived suppressor cells (MO-MDSCs) within the hepatic compartment suppress inflammation and impair immune surveillance in liver cancer. It is currently not known whether recruitment of MO-MDSCs from blood via hepatic sinusoidal endothelium (HSEC) contributes to their enrichment within the hepatic compartment. We compared the transmigratory potential of MO-MDSCs and monocytes after adhesion to hepatic endothelial monolayers in flow-based assays that mimic in vivo shear stress in the sinusoids. Despite comparable binding to HSEC monolayers, proportionally fewer MO-MDSCs underwent transendothelial migration, indicating that the final steps of extravasation, where actin polymerization plays an important role, are impaired in MO-MDSCs. In this article, we found reduced levels of CD13 on MO-MDSCs, which has recently been reported to control cell motility in monocytes, alongside reduced VLA-4 expression, an integrin predominantly involved in adherence to the apical side of the endothelium. CD13 and VLA-4 blocking and activating Abs were used in flow-based adhesion assays, live-cell imaging of motility, and actin polymerization studies to confirm a role for CD13 in impaired MO-MDSC transmigration. These findings indicate that CD13 significantly contributes to tissue infiltration by MO-MDSCs and monocytes, thereby contributing to the pathogenesis of hepatic inflammation.

Abstract 3055: A permanent lung imaging window reveals, for the first time, the steps of extravasation, seeding and growth of early metastatic dissemination

Abstract Metastatic disease is the major cause of cancer mortality and is responsible for over 1/2 million deaths each year in the U.S. alone. Of the three most common sites of metastasis observed clinically (bone, lung and liver), the most difficult to study using intravital microscopy is the lung; a delicate organ in perpetual motion. We have recently developed and validated an implantable, permanent, lung imaging window which allows high-resolution multiphoton imaging of the intact, breathing (without ventilation), murine lung over days to weeks of repeated imaging. This window does not use vacuum to immobilize the lung tissue thereby avoiding well know artifacts associated with vacuum lung windows. Using our new window, we have been able to visualize, with single cell resolution, the steps of metastasis in a clinically relevant, spontaneously-metastasizing murine breast cancer model. We present the first direct visualization of tumor cell arrival, extravasation, and progression to micro-metastases. Further, we have observed, for the first time, the activity of the tripartite structure called Tumor MicroEnvironment of Metastasis (TMEM) in metastatic lung lesions directly demonstrating the mechanism of dissemination from metastatic lung tumors. Using this approach to imaging live lung tissue serially, within a single animal, we are investigating the mechanisms underlying the fate of tumor cells arriving in the lung with the ultimate goal of directly identifying signals behind seeding and survival of metastatic tumor cells and their responses to interventions in real time. Citation Format: Sonia E. Voiculescu, Yarong Wang, Maja Oktay, John Condeelis, David Entenberg. A permanent lung imaging window reveals, for the first time, the steps of extravasation, seeding and growth of early metastatic dissemination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3055. doi:10.1158/1538-7445.AM2017-3055