High-resolution Intravital Imaging Research Articles

Abstract 12676: Psychological Stress Stimulates Vascular Inflammatory Responses and Destabilizes Atherosclerotic Plaques as Assessed by High-Speed, High-Resolution Intravital Imaging

Backgrounds: Psychological stress increases leukocyte accumulation within atherosclerotic lesions and exacerbates plaque vulnerability. However, the stress-induced real-time behavior of immune cells in the atheroma has been poorly defined in vivo . Here, we aim to investigate whether stress stimulates the inflammatory leukocyte dynamics in the atherosclerotic plaques and destabilizes the lesions using customized in vivo cell tracking strategies. Methods and Results: We developed a system and motion reconstruction algorithm that can probe and compensate for respiratory and pulsatile movements. Individual leukocytes near the atherosclerotic plaques were imaged in real-time by adapting a custom-built high-speed intravital microscopy system with multiple fluorescence channels. Stress was achieved by immobilization procedures and/or stereotaxic application of stress stimulus onto the brain amygdala. The high spatial and temporal resolution of our real-time cell tracking system allowed clear identification of rhodamine 6G-positive leukocytes in vivo . In the common femoral artery bifurcation of apolipoprotein E knockout mice, white blood cells firmly adhered to the inner layer of the vessel walls while some slowly flowed along the endothelium (Figure). We further demonstrate that the stress increased the rolling and adhesion of inflammatory leukocyte subsets near the atherosclerotic lesions, and enhanced the plaque macrophage activity as assessed by in vivo imaging. Confocal laser scanning microscopy and immunostaining analyses corroborated the in vivo findings that the stress induced the destabilization of the atherosclerotic plaques. Conclusion: Our data show that stress stimulated the dynamics of inflammatory leukocyte subsets in atherosclerotic environments and increased the plaque vulnerability as assessed by the customized high-resolution motion-compensated in vivo imaging strategy.

Interleukin 4 Controls the Pro-Tumoral Role of Macrophages in Mammary Cancer Pulmonary Metastasis in Mice.

Simple SummaryMetastasis is the main cause of death from breast cancer. In mouse models of breast cancer lung metastasis, macrophages enhance metastasis by promoting tumor cell seeding and persistent growth. Here, we show that interleukin-4 (IL4) is required for this process as IL4 receptor (IL4rα)-null mice develop fewer and smaller lung metastases. This deficiency is partially rescued by adoptive transfer of wild-type monocytes. IL4 signaling in macrophages upregulates the expression of the chemokine receptor CXCR2, necessary for IL4-mediated tumor cell extravasation in vitro. In addition, expression of several other genes already causally associated with lung metastasis including Ccl2, Csf1, Ccr1, Hgf and Flt1 are upregulated in macrophages. High-resolution intravital imaging at the time of metastatic seeding showed reduced physical interaction between tumor cells and IL4rα-deficient macrophages, showing the dependence on IL4. We conclude that IL4 signaling in monocytes and macrophages is important during seeding and growth of breast metastasis in the lung.Metastasis is the systemic manifestation of cancer and the main cause of death from breast cancer. In mouse models of lung metastases, recruitment of classical monocytes from blood to the lung and their differentiation to metastasis-associated macrophages (MAMs) facilitate cancer cell extravasation, survival and growth. Ablation of MAMs or their monocytic progenitors inhibits metastasis. We hypothesized that factors controlling macrophage polarization modulate tumor cell extravasation in the lung. We evaluated whether signaling by Th1 or Th2 cytokines in macrophages affected transendothelial migration of tumor cells in vitro. Interferon gamma and LPS inhibited macrophage-dependent tumor cell extravasation while the Th2 cytokine interleukin-4 (IL4) enhanced this process. We demonstrated that IL4 receptor (IL4rα)-null mice developed fewer and smaller lung metastasis in E0771-LG mammary cancer models of this disease. Adoptive transfer of wild-type monocytes to IL4rα-deficient mice partially rescued this phenotype. IL4 signaling in macrophages controlled the expression of the chemokine receptor CXCR2, necessary for IL4-mediated tumor cell extravasation in vitro. Furthermore, IL4 signaling in macrophages regulated the transcript abundance of several other genes already causally associated with mammary cancer lung metastasis including Ccl2, Csf1, Ccr1, Hgf and Flt1. The central role of IL4 signaling in MAMs was confirmed by high-resolution intravital imaging of the lung in mice at the time of metastatic seeding, which showed reduced physical interaction between tumor cells and IL4rα-deficient macrophages. This interaction with wild-type MAMs enhanced tumor cell survival and seeding, which was lost in the IL4rα mice. These data indicate that IL4 signaling in monocytes and macrophages is key during seeding and growth of breast metastasis in the lung, as it regulates pro-tumoral paracrine signaling between cancer cells and macrophages.

Visualization of regenerating and repairing hearts.

With heart failure continuing to become more prevalent, investigating the mechanisms of heart injury and repair holds much incentive. In contrast with adult mammals, other organisms such as teleost fish, urodele amphibians, and even neonatal mammals are capable of robust cardiac regeneration to replenish lost or damaged myocardial tissue. Long-term high-resolution intravital imaging of the behaviors and interactions of different cardiac cell types in their native environment could yield unprecedented insights into heart regeneration and repair. However, this task remains challenging for the heart due to its rhythmic contraction and anatomical location. Here, we summarize recent advances in live imaging of heart regeneration and repair, discuss the advantages and limitations of current systems, and suggest future directions for novel imaging technology development.

Primary tumor associated macrophages activate programs of invasion and dormancy in disseminating tumor cells

Metastases are initiated by disseminated tumor cells (DTCs) that colonize distant organs. Growing evidence suggests that the microenvironment of the primary tumor primes DTCs for dormant or proliferative fates. However, the manner in which this occurs remains poorly understood. Here, using the Window for High-Resolution Intravital Imaging of the Lung (WHRIL), we study the live lung longitudinally and follow the fate of individual DTCs that spontaneously disseminate from orthotopic breast tumors. We find that spontaneously DTCs have increased levels of retention, increased speed of extravasation, and greater survival after extravasation, compared to experimentally metastasized tumor cells. Detailed analysis reveals that a subset of macrophages within the primary tumor induces a pro-dissemination and pro-dormancy DTC phenotype. Our work provides insight into how specific primary tumor microenvironments prime a subpopulation of cells for expression of proteins associated with dissemination and dormancy.

An adapted dorsal skinfold model used for 4D intravital followed by whole-mount imaging to reveal endothelial cell\u2013pericyte association

Endothelial cells and pericytes are highly dynamic vascular cells and several subtypes, based on their spatiotemporal dynamics or molecular expression, are believed to exist. The interaction between endothelial cells and pericytes is of importance in many aspects ranging from basic development to diseases like cancer. Identification of spatiotemporal dynamics is particularly interesting and methods to studies these are in demand. Here we describe the technical details of a method combining the benefits of high resolution intravital imaging and whole-mount histology. With intravital imaging using an adapted light weight dorsal skinfold chamber we identified blood flow patterns and spatiotemporal subtypes of endothelial cells and pericytes in a 4D (XYZ, spatial+T, time dimension) manner as representative examples for this model. Thereafter the tissue was extracted and stained as a whole-mount, by which the position and volumetric space of endothelial cells as well as pericytes were maintained, to identify molecular subtypes. Integration of the two imaging methods enabled 4D dissection of endothelial cell–pericyte association at the molecular level.

Healing takes nerve.

Epidermal stem cells display remarkable capacities to restore the barrier upon skin injury. In this issue of Cell Stem Cell, Huang etal. (2021) use innovative high-resolution intravital imaging to identify a vital function of sensory nerves in regulating a subset of epidermal stem cells for wound repair.

Abstract 2837: NR2F1 is a barrier to early dissemination of pre-malignant mammary cells

Abstract Cancer cells disseminate during very early and sometimes asymptomatic stages of tumor progression. Granted that biological barriers to tumorigenesis exist, there must also be limiting steps to early dissemination, all of which remain largely unknown. We report that the orphan nuclear receptor NR2F1/COUP-TF1 serves as a barrier to early dissemination. High-resolution intravital imaging revealed that loss of function of NR2F1 in HER2+ early cancer cells increased in vivo dissemination without accelerating mammary tumor formation. NR2F1 expression was positively regulated by the tumor suppressive MMK3/6-p38-MAPK pathway and downregulated by HER2 and Wnt4 oncogenic signaling. NR2F1 downregulation by HER2 in early cancer cells led to decreased E-cadherin expression and β-catenin membrane localization, disorganized laminin 5 deposition, and increased expression of CK14, TWIST1, ZEB1 and PRRX1. Our findings reveal the existence of an inhibitory mechanism of dissemination regulated by NR2F1 downstream of HER2 signaling. Citation Format: Maria Soledad Sosa, Carolina Rodriguez-Tirado, Nupura Kale, Maria Carlini, Nitisha Shrivastava, Bassem Khalil, Javier Bravo-Cordero, Melissa Alexander, Jiayi Ji. NR2F1 is a barrier to early dissemination of pre-malignant mammary cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2837.

Imaging and optogenetic modulation of vascular mural cells in the live brain.

Mural cells (smooth muscle cells and pericytes) are integral components of brain blood vessels that play important roles in vascular formation, blood-brain barrier maintenance, and regulation of regional cerebral blood flow (rCBF). These cells are implicated in conditions ranging from developmental vascular disorders to age-related neurodegenerative diseases. Here we present complementary tools for cell labeling with transgenic mice and organic dyes that allow high-resolution intravital imaging of the different mural cell subtypes. We also provide detailed methodologies for imaging of spontaneous and neural activity-evoked calcium transients in mural cells. In addition, we describe strategies for single- and two-photon optogenetics that allow manipulation of the activity of individual and small clusters of mural cells. Together with measurements of diameter and flow in individual brain microvessels, calcium imaging and optogenetics allow the investigation of pericyte and smooth muscle cell physiology and their role in regulating rCBF. We also demonstrate the utility of these tools to investigate mural cells in the context of Alzheimer's disease and cerebral ischemia mouse models. Thus, these methods can be used to reveal the functional and structural heterogeneity of mural cells in vivo, and allow detailed cellular studies of the normal function and pathophysiology of mural cells in a variety of disease models. The implementation of this protocol can take from several hours to days depending on the intended applications.

The role of the tumor microenvironment in tumor cell intravasation and dissemination

Metastasis, a process that requires tumor cell dissemination followed by tumor growth, is the primary cause of death in cancer patients. An essential step of tumor cell dissemination is intravasation, a process by which tumor cells cross the blood vessel endothelium and disseminate to distant sites. Studying this process is of utmost importance given that intravasation in the primary tumor, as well as the secondary and tertiary metastases, is the key step in the systemic spread of tumor cells, and that this process continues even after removal of the primary tumor. High-resolution intravital imaging of the tumor microenvironment of breast carcinoma has revealed that tumor cell intravasation exclusively occurs at doorways, termed “Tumor MicroEnvironment of Metastasis” (TMEM), composed of three different cell types: a Tie2high/VEGFhigh perivascular macrophage, a Mena overexpressing tumor cell, and an endothelial cell, all in direct contact. In this review article, we discuss the interactions between these cell types, the subsequent signaling events which lead to tumor cell intravasation, and the role of invadopodia in supporting tumor cell invasion and dissemination. We end our review by discussing how the knowledge acquired from the use of intravital imaging is now leading to new clinical trials targeting tumor cell dissemination and preventing metastatic progression.

Abstract PR12: Dynamic single-cell imaging of human cancer growth and therapy responses following engraftment into immunodeficient zebrafish

Abstract Cancer xenograft engraftment studies using immune-deficient mice are indispensable for preclinical drug discovery and are required for IND filings that lead to clinical trials. While immune-deficient mice robustly engraft a wide variety of human cancers, high-resolution intravital imaging of transplanted cells is tedious and its high husbandry costs often limit the scale of experiments. In contrast, zebrafish are an ideal cell transplantation model. They are highly fecund; optically clear, permitting dynamic single-cell imaging of fluorescent cancer cells; and are an excellent platform for high-throughput, large-scale studies. We have recently generated two optically clear prkdc-/-, il2rga-/- and rag2-/-, il2rga-/- immune-compromised zebrafish models that lack T-, B-, and NK-cells. These immune-deficient animals can be grown at 37°C and robustly engraft a variety of human cancers including patient-derived xenografts for >30 days. Importantly, tumors grown in immune-deficient zebrafish and mice are indistinguishable in terms of morphology, proliferation rates, apoptosis, and response to therapy. Engraftment of human cells into the superficial periocular muscle also allowed high-resolution, single-cell imaging using conventional confocal microscopy. Using this approach, we performed photoconversion cell lineage tracing of human rhabdomyosarcoma (RMS), a pediatric cancer of the muscle, and identified mutually exclusive migratory and proliferative cell states. We also demonstrated the preclinical efficacy of combination therapy involving olaparib (PARP-inhibitor) and temozolomide (DNA-damaging agent), including the dynamic visualization of therapeutic responses at single-cell resolution through use of the four-color FUCCI cell cycle fluorescent reporter and serial confocal imaging over days. Importantly, this same drug combination also exhibited remarkable efficacy in studies performed in NSG mice and is now moving forward for clinical evaluation in RMS patients. Finally, recent work has focused on assessing the efficacy of immunotherapies in curbing tumor growth, including assessing CAR-T cell and bispecific T-cell engager antibodies (BITES) in vivo. In both of these platforms, dynamic live cell imaging and automated 3D modeling allowed quantification of migratory potential of T cells into the tumor, dynamic remodeling of T-cell morphology changes following interaction with tumor cells, and real-time visualization of T cell-mediated cancer cell killing using fluorescent caspase reporters. In total, our studies have credentialed the immune-deficient zebrafish as a new platform for preclinical drug studies and provides novel technologies that utilize real-time, single-cell imaging for early endpoint analysis. These models are likely to be particularly useful for discovery of immunomodulatory antibodies and immunomedicines in the future. Citation Format: Chuan Yan, Qiqi Yang, Daniel Do, Dalton Brunson, John Iafrate, John Rawls, David M. Langenau. Dynamic single-cell imaging of human cancer growth and therapy responses following engraftment into immunodeficient zebrafish [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr PR12.

In Vivo Assessment of Size-Selective Glomerular Sieving in Transplanted Human Induced Pluripotent Stem Cell-Derived Kidney Organoids.

The utility of kidney organoids in regenerative medicine will rely on the functionality of the glomerular and tubular structures in these tissues. Recent studies have demonstrated the vascularization and subsequent maturation of human pluripotent stem cell-derived kidney organoids after renal subcapsular transplantation. This raises the question of whether the glomeruli also become functional upon transplantation. We transplanted kidney organoids under the renal capsule of the left kidney in immunodeficient mice followed by the implantation of a titanium imaging window on top of the kidney organoid. To assess glomerular function in the transplanted human pluripotent stem cell-derived kidney tissue 1, 2, and 3 weeks after transplantation, we applied high-resolution intravital multiphoton imaging through the imaging window during intravenous infusion of fluorescently labeled low and high molecular mass dextran molecules or albumin. After vascularization, glomerular structures in the organoid displayed dextran and albumin size selectivity across their glomerular filtration barrier. We also observed evidence of proximal tubular dextran reuptake. Our results demonstrate that human pluripotent stem cell-derived glomeruli can develop an appropriate barrier function and discriminate between molecules of varying size. These characteristics together with tubular presence of low molecular mass dextran provide clear evidence of functional filtration. This approach to visualizing glomerular filtration function will be instrumental for translation of organoid technology for clinical applications as well as for disease modeling.

Frontline Science: Dynamic cellular and subcellular features of migrating leukocytes revealed by in vivo lattice lightsheet microscopy.

Neutrophil and macrophage (Mϕ) migration underpin the inflammatory response. However, the fast velocity, multidirectional instantaneous movement, and plastic, ever-changing shape of phagocytes confound high-resolution intravital imaging. Lattice lightsheet microscopy (LLSM) captures highly dynamic cell morphology at exceptional spatiotemporal resolution. We demonstrate the first extensive application of LLSM to leukocytes in vivo, utilizing optically transparent zebrafish, leukocyte-specific reporter lines that highlighted subcellular structure, and a wounding assay for leukocyte migration. LLSM revealed details of migrating leukocyte morphology, and permitted intricate, volumetric interrogation of highly dynamic activities within their native physiological setting. Very thin, recurrent uropod extensions must now be considered a characteristic feature of migrating neutrophils. LLSM resolved trailing uropod extensions, demonstrating their surprising length, and permitting quantitative assessment of cytoskeletal contributions to their evanescent form. Imaging leukocytes in blood vessel microenvironments at LLSM's spatiotemporal resolution displayed blood-flow-induced neutrophil dynamics and demonstrated unexpected leukocyte-endothelial interactions such as leukocyte-induced endothelial deformation against the intravascular pressure. LLSM of phagocytosis and cell death provided subcellular insights and uncovered novel behaviors. Collectively, we provide high-resolution LLSM examples of leukocyte structures (filopodia lamellipodia, uropod extensions, vesicles), and activities (interstitial and intravascular migration, leukocyte rolling, phagocytosis, cell death, and cytoplasmic ballooning). Application of LLSM to intravital leukocyte imaging sets the stage for transformative studies into the cellular and subcellular complexities of phagocyte biology.

In Vivo Imaging of Venous Thrombus and Pulmonary Embolism Using Novel Murine Venous Thromboembolism Model

This work established a new murine venous thromboembolism (VTE) model. This model has multiple novel features representing clinical VTE that include the following: 1) deep venous thrombosis (DVT) was formed and extended in the long axis of femoral/saphenous vein; 2) thrombus was formed in a venous valve pocket; 3) deligation of suture-induced spontaneous pulmonary emboli of fibrin-rich DVT; and 4) cardiac motion-free femoral/saphenous vein allowed high-resolution intravital microscopic imaging of fibrin-rich DVT. This new model requires only commercially available epifluorescence microscopy. Therefore, this model has significant potential for better understanding of VTE pathophysiology.

High Resolution Intravital Imaging of the Renal Immune Response to Injury and Infection in Mice.

We developed an experimental set up that enables longitudinal studies of immune cell behavior in situ in the challenged as well as unchallenged kidney of anesthetized mice over several hours. Using highly controlled vacuum to stabilize the kidney, the superficial renal cortex could continuously be visualized with minimal disruption of the local microenvironment. No visible changes in blood flow or neutrophils and macrophages numbers were observed after several hours of visualizing the unchallenged kidney, indicating a stable tissue preparation without apparent tissue damage. Applying this set up to monocyte/macrophage (CX3CR1GFP/+) reporter mice, we observed the extensive network of stellate-shaped CX3CR1 positive cells (previously identified as renal mononuclear phagocytes). The extended dendrites of the CX3CR1 positive cells were found to bridge multiple capillaries and tubules and were constantly moving. Light induced sterile tissue injury resulted in rapid neutrophil accumulation to the site of injury. Similarly, microinfusion of uropathogenic Escherichia coli into a single nephron induced a rapid and massive recruitment of neutrophils to the site of infection, in addition to active bacterial clearance by neutrophils. In contrast, the kidney resident mononuclear phagocytes were observed to not increase in numbers or migrate toward the site of injury or infection. In conclusion, this model allows for longitudinal imaging of responses to localized kidney challenges in the mouse.

Abstract BS1-1: High resolution intravital imaging of the mechanism of how breast cancer initiates and sustains systemic dissemination

Abstract Multiphoton microscopy of live animals (IVI) has revolutionized our understanding of cancer metastasis. IVI demonstrates that TMEM, the intravasation doorway, composed of a three cell complex: Mena-Hi tumor cell, endothelial cell and Tie2-Hi/VEGF-Hi macrophage, is the only site in breast tumors where tumor cell intravasation occurs1. During tumor progression, macrophage progenitor cells undergo unidirectional transition from migratory to TMEM-associated macrophages2. During and after this macrophage programming, tumor cells migrate with macrophages and chemotax with high persistence to blood vessels under the control of HGF gradients3 arriving at TMEM1. The TMEM structure itself, as well as the signaling pathways unique to tumor cells interacting with TMEM, have been validated as prognostic markers for predicting metastasis in breast cancer patients4-6. These were the first markers of metastasis in clinical use derived from multiphoton intravital imaging. TMEM are found in both primary and metastatic tumor sites of breast cancer7 and in primary and metastatic sites of pancreatic ductal and neuro-endocrine tumors. Clinical trials of TMEM inhibitors, targeting TMEM in both primary and secondary sites8,9, are now underway in breast cancer patients (clinical trials study number NCT02824575). As tumor cells interact with TMEM, MenaINV. expression in the tumor cells occurs in response to macrophage-induced NOTCH signaling10, which drives invadopod assembly/ function, and metastatic seeding11,12. MenaINV expression is necessary for invadopod-mediated transendothelial migration during intravasation at TMEM13 and assures the efficient dissemination of seeding competent and non-dividing tumor cells which, after a delay, contribute to metastatic recurrence at multiple systemic sites. These findings support TMEM as a critical therapeutic target for inhibiting breast cancer metastasis. 1.Harney, A.S. et al. (2015) PMC4560669 2.Arwert, E.N. et al. (2018) PMC5946803 3.Leung, E. et al. (2017) PMC5426963 4.Karagiannis, G.S. et al (2016) PMC4893654 5.Rohan, T.E. et al. (2014) PMC4133559 6.Sparano, J.A. et al. (2017)PMC5678158 7.Entenberg, D. et al. (2018)PMC5755704 8.Harney, A.S. et al. (2017)PMC5669998 9.Karagiannis, G.S. et al. (2017) PMC5592784 10.Pignatelli, J. et al. (2016) PMC5129016 11.Eddy, R.J. et al (2017) PMC5524604 12.Linde, N. et al. (2018) PMC5750231 13.Pignatelli, J. et al.(2014) PMC4266931 Citation Format: Condeelis J. High resolution intravital imaging of the mechanism of how breast cancer initiates and sustains systemic dissemination [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr BS1-1.

Study of Osteocyte Behavior by High-Resolution Intravital Imaging Following Photo-Induced Ischemia

Ischemic injuries and local hypoxia can result in osteocytes dysfunction and play a key role in the pathogenesis of avascular osteonecrosis. Conventional imaging techniques including magnetic resonance imaging (MRI) and computed tomography (CT) can reveal structural and functional changes within bony anatomy; however, characterization of osteocyte behavioral dynamics in the setting of osteonecrosis at the single cell resolution is limited. Here, we demonstrate an optical approach to study real-time osteocyte functions in vivo. Using nicotinamide adenine dinucleotide (NADH) as a biomarker for metabolic dynamics in osteocytes, we showed that NADH level within osteocytes transiently increase significantly after local ischemia through non-invasive photo-induced thrombosis of afferent arterioles followed by a steady decline. Our study presents a non-invasive optical approach to study osteocyte behavior through the modulation of local environmental conditions. Thus it provides a powerful toolkit to study cellular processes involved in bone pathologies in vivo.

Abstract 494: Intravital discovery of miRNA drivers of human cancer cell directional invasion

Abstract Metastatic cancer cells use directional ECM cues such as blood vessels or collagen fibers when invading through live tissue. Oncogenic miRNAs have been implicated as key regulators of cancer progression, yet the systemic discovery of miRNAs that drive directional cancer cell invasion has not been achieved. Here we describe the first in vivo quantitative whole human miRNAome screen for miRNA drivers of directional cancer cell invasion that is based on high-resolution intravital imaging. We identified several novel miRNAs that promote cancer cell invasion during the key rate-limiting step of cancer metastasis: the initiation of overt metastatic lesions. In vivo 4D cancer cell tracking revealed that these prometastatic miRNAs are required for successful invasion into collagen-rich tissue and for attachment to the outer surface of the vascular wall. Deregulation of these miRNAs led to formation of loose contacts with the vasculature and chaotic, nondirectional cancer cell invasion patterns in living tissue. Intravital SHG microscopy showed that inhibition of the expression of these miRNAs blocked the ability of cancer cells to rearrange the disorganized collagen network into collagen fiber bundles and stably protrude along these bundles. Further imaging analysis revealed that this miRNA expression specifically blocks vesicular transport of key cell invasion machinery proteins such as MT1-MMP to the cancer cell invadopodia. Human cancer gene expression database analysis showed that our top miRNA candidates are specifically deregulated in invasive pancreatic cancer. Indeed, intravital imaging analysis showed that blocking of metastatic miRNA function inhibited MT1-MMP secretion and ECM degradation by human pancreatic cancer cells. In summary, we identified a novel panel of human miRNAs that are functionally involved in the regulation of directional invasion and metastasis. This work establishes these miRNAs as promising therapeutic targets to block the metastatic spread of lethal cancers. Citation Format: Konstantin V. Stoletov, Lian Willetts, Juan Jovel, Emma Woolner, John D. Lewis. Intravital discovery of miRNA drivers of human cancer cell directional invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 494.

Arg1 expression defines immunosuppressive subsets of tumor-associated macrophages.

Tumor-associated macrophages (TAM) have attracted attention as they can modulate key cancer-related activities, yet TAM represent a heterogenous group of cells that remain incompletely characterized. In growing tumors, TAM are often referred to as M2-like macrophages, which are cells that display immunosuppressive and tumorigenic functions and express the enzyme arginase 1 (Arg1).Methods: Here we combined high resolution intravital imaging with single cell RNA seq to uncover the topography and molecular profiles of immunosuppressive macrophages in mice. We further assessed how immunotherapeutic interventions impact these cells directly in vivo.Results: We show that: i) Arg1+ macrophages are more abundant in tumors compared to other organs; ii) there exist two morphologically distinct subsets of Arg1 TAM defined by previously unknown markers (Gbp2b, Bst1, Sgk1, Pmepa1, Ms4a7); iii) anti-Programmed Cell Death-1 (aPD-1) therapy decreases the number of Arg1+ TAM while increasing Arg1- TAM; iv) accordingly, pharmacological inhibition of arginase 1 does not synergize with aPD-1 therapy.Conclusion: Overall, this research shows how powerful complementary single cell analytical approaches can be used to improve our understanding of drug action in vivo.

A permanent window for the murine lung enables high-resolution imaging of cancer metastasis.

Stable, high-resolution intravital imaging of the lung has become possible through the utilization of vacuum-stabilized imaging windows. However, this technique is extremely invasive and limited to only hours in duration. Here we describe a minimally invasive, permanently implantable window for high-resolution intravital imaging of the murine lung that allows the mouse to survive surgery, recover from anesthesia, and breathe independently. Compared to vacuum-stabilized windows, this window produces the same high-quality images without vacuum-induced artifacts; it is also less invasive, which allows imaging of the same lung tissue over a period of weeks. We further adapt the technique of microcartography for reliable relocalization of the same cells longitudinally. Using commonly employed experimental, as well as more clinically relevant, spontaneous metastasis models, we visualize all stages of metastatic seeding, including: tumor cell arrival; extravasation; growth and progression to micrometastases; as well as tumor microenvironment of metastasis function, the hallmark of hematogenous dissemination of tumor cells.

Time-lapsed, large-volume, high-resolution intravital imaging for tissue-wide analysis of single cell dynamics.

Pathologists rely on microscopy to diagnose disease states in tissues and organs. They utilize both high-resolution, high-magnification images to interpret the staining and morphology of individual cells, as well as low-magnification overviews to give context and location to these cells. Intravital imaging is a powerful technique for studying cells and tissues in their native, live environment and can yield sub-cellular resolution images similar to those used by pathologists. However, technical limitations prevent the straightforward acquisition of low-magnification images during intravital imaging, and they are hence not typically captured. The serial acquisition, mosaicking, and stitching together of many high-resolution, high-magnification fields of view is a technique that overcomes these limitations in fixed and ex vivo tissues. The technique however, has not to date been widely applied to intravital imaging as movements caused by the living animal induce image distortions that are difficult to compensate for computationally. To address this, we have developed techniques for the stabilization of numerous tissues, including extremely compliant tissues, that have traditionally been extremely difficult to image. We present a novel combination of these stabilization techniques with mosaicked and stitched intravital imaging, resulting in a process we call Large-Volume High-Resolution Intravital Imaging (LVHR-IVI). The techniques we present are validated and make large volume intravital imaging accessible to any lab with a multiphoton microscope.