Endothelial Regulation of Drug Transport in a 3D Vascularized Tumor Model

Drug discovery and efficacy in cancer treatments are limited by the inability of pre-clinical models to predict successful outcomes in humans. Limitations remain partly due to their lack of a physiologic tumor microenvironment (TME), which plays a considerable role in drug delivery and tumor response to therapy. Chemotherapeutics and immunotherapies rely on transport through the vasculature, via the smallest capillaries and stroma to the tumor, where passive and active transport processes are at play. Here, a 3D vascularized tumor on-chip is used to examine drug delivery in a relevant TME within a large bed of perfusable vasculature. This system demonstrates highly localized pathophysiological effects of two tumor spheroids (Skov3 and A549) which cause significant changes in vessel density and barrier function. Paclitaxel (Taxol) uptake is examined through diffusivity measurements, functional efflux assays and accumulation of the fluorescent-conjugated drug within the TME. Due to vascular and stromal contributions, differences in the response of vascularized tumors to Taxol (shrinkage and CD44 expression) are apparent compared with simpler models. This model specifically allows for examination of spatially resolved tumor-associated endothelial dysfunction, likely improving the representation of in vivo drug distribution, and has potential for development into a more predictable model of drug delivery.

Cysteine cathepsins are altered by flow within an engineered in vitro microvascular niche

Throughout the process of vascular growth and remodeling, the extracellular matrix (ECM) concurrently undergoes significant changes due to proteolytic activity—regulated by both endothelial and surrounding stromal cells. The role of matrix metalloproteinases has been well-studied in the context of vascular remodeling, but other proteases, such as cysteine cathepsins, could also facilitate ECM remodeling. To investigate cathepsin-mediated proteolysis in vascular ECM remodeling, and to understand the role of shear flow in this process, in vitro microvessels were cultured in previously designed microfluidic chips and assessed by immunostaining, zymography, and western blotting. Primary human vessels (HUVECs and fibroblasts) were conditioned by continuous fluid flow and/or small molecule inhibitors to probe cathepsin expression and activity. Luminal flow (in contrast to static culture) decreases the activity of cathepsins in microvessel systems, despite a total protein increase, due to a concurrent increase in the endogenous inhibitor cystatin C. Observations also demonstrate that cathepsins mostly co-localize with fibroblasts, and that fibrin (the hydrogel substrate) may stabilize cathepsin activity in the system. Inhibitor studies suggest that control over cathepsin-mediated ECM remodeling could contribute to improved maintenance of in vitro microvascular networks; however, further investigation is required. Understanding the role of cathepsin activity in in vitro microvessels and other engineered tissues will be important for future regenerative medicine applications.

The effects of luminal and trans-endothelial fluid flows on the extravasation and tissue invasion of tumor cells in a 3D in vitro microvascular platform

Throughout the process of metastatic dissemination, tumor cells are continuously subjected to mechanical forces resulting from complex fluid flows due to changes in pressures in their local microenvironments. While these forces have been associated with invasive phenotypes in 3D matrices, their role in key steps of the metastatic cascade, namely extravasation and subsequent interstitial migration, remains poorly understood. In this study, an in vitro model of the human microvasculature was employed to subject tumor cells to physiological luminal, trans-endothelial, and interstitial flows to evaluate their effects on those key steps of metastasis. Luminal flow promoted the extravasation potential of tumor cells, possibly as a result of their increased intravascular migration speed. Trans-endothelial flow increased the speed with which tumor cells transmigrated across the endothelium as well as their migration speed in the matrix following extravasation. In addition, tumor cells possessed a greater propensity to migrate in close proximity to the endothelium when subjected to physiological flows, which may promote the successful formation of metastatic foci. These results show important roles of fluid flow during extravasation and invasion, which could determine the local metastatic potential of tumor cells.

Tumor-Derived cGAMP Regulates Activation of the Vasculature

Intratumoral recruitment of immune cells following innate immune activation is critical for anti-tumor immunity and involves cytosolic dsDNA sensing by the cGAS/STING pathway. We have previously shown that KRAS-LKB1 (KL) mutant lung cancer, which is resistant to PD-1 blockade, exhibits silencing of STING, impaired tumor cell production of immune chemoattractants, and T cell exclusion. Since the vasculature is also a critical gatekeeper of immune cell infiltration into tumors, we developed a novel microfluidic model to study KL tumor-vascular interactions. Notably, dsDNA priming of LKB1-reconstituted tumor cells activates the microvasculature, even when tumor cell STING is deleted. cGAS-driven extracellular export of 2'3' cGAMP by cancer cells activates STING signaling in endothelial cells and cooperates with type 1 interferon to increase vascular permeability and expression of E selectin, VCAM-1, and ICAM-1 and T cell adhesion to the endothelium. Thus, tumor cell cGAS-STING signaling not only produces T cell chemoattractants, but also primes tumor vasculature for immune cell escape.

The Use of Microfluidic Platforms to Probe the Mechanism of Cancer Cell Extravasation

Powerful experimental tools have contributed a wealth of novel insight into cancer etiology from the organ to the subcellular levels. However, these advances in understanding have outpaced improvements in clinical outcomes. One possible reason for this shortcoming is the reliance on animal models that do not fully replicate human physiology. An alternative in vitro approach that has recently emerged features engineered microfluidic platforms to investigate cancer progression. These devices allow precise control over cellular components, extracellular constituents, and physical forces, while facilitating detailed microscopic analysis of the metastatic process. This review focuses on the recent use of microfluidic platforms to investigate the mechanism of cancer cell extravasation.

Migration of vascular endothelial cells in monolayers under hypoxic exposure

The hypoxic microenvironment existing in vivo is known to significantly affect cell morphology and dynamics, and cell group behaviour. Collective migration of vascular endothelial cells is essential for vasculogenesis and angiogenesis, and for maintenance of monolayer integrity. Although hypoxic stress increases vascular endothelial permeability, the changes in collective migration and intracellular junction morphology of vascular endothelial cells remain poorly understood. This study reveals the migration of confluent vascular endothelial cells and changes in their adherens junction, as reflected by changes in the vascular endothelial (VE)-cadherin distribution, under hypoxic exposure. Vascular endothelial monolayers of human umbilical vein endothelial cells (HUVECs) were formed in microfluidic devices with controllability of oxygen tension. The oxygen tension was set to either normoxia (21% O2) or hypoxia (<3% O2) by supplying gas mixtures into separate gas channels. The migration velocity of HUVECs was measured using particle image velocimetry with a time series of phase-contrast microscopic images of the vascular endothelial monolayers. Hypoxia inducible factor-1α (HIF-1α) and VE-cadherin in HUVECs were observed after exposure to normoxic or hypoxic conditions using immunofluorescence staining and quantitative confocal image analysis. Changes in the migration speed of HUVECs were observed in as little as one hour after exposure to hypoxic condition, showing that the migration speed was increased 1.4-fold under hypoxia compared to that under normoxia. Nuclear translocation of HIF-1α peaked after the hypoxic gas mixture was supplied for 2 h. VE-cadherin expression was also found to be reduced. When ethanol was added to the cell culture medium, cell migration increased. By contrast, by strengthening VE-cadherin junctions with forskolin, cell migration decreased gradually in spite the effect of ethanol to stimulate migration. These results indicate that the increase of cell migration by hypoxic exposure was attributable to loosening of intercellular junction resulting from the decrease of VE-cadherin expression.

Microfluidic platform for three-dimensional cell culture under spatiotemporal heterogeneity of oxygen tension

Cells in a tumor microenvironment are exposed to spatial and temporal variations in oxygen tension due to hyperproliferation and immature vascularization. Such spatiotemporal oxygen heterogeneity affects the behavior of cancer cells, leading to cancer growth and metastasis, and thus, it is essential to clarify the cellular responses of cancer cells to oxygen tension. Herein, we describe a new double-layer microfluidic device allowing the control of oxygen tension and the behavior of cancer cells under spatiotemporal oxygen heterogeneity. Two parallel gas channels were located above the media and gel channels to enhance gas exchange, and a gas-impermeable polycarbonate film was embedded in the device to prevent the diffusion of atmospheric oxygen. Variations in oxygen tension in the device with the experimental parameters and design variables were investigated computationally and validated by using oxygen-sensitive nanoparticles. The present device can generate a uniform hypoxic condition at oxygen levels down to 0.3% O2, as well as a linear oxygen gradient from 3% O2 to 17% O2 across the gel channel within 15 min. Moreover, human breast cancer cells suspended in type I collagen gel were introduced in the gel channel to observe their response under controlled oxygen tension. Hypoxic exposure activated the proliferation and motility of the cells, which showed a local maximum increase at 5% O2. Under the oxygen gradient condition, the increase in the cell number was relatively high in the central mild hypoxia region. These findings demonstrate the utility of the present device to study cellular responses in an oxygen-controlled microenvironment.

Platelet decoys inhibit thrombosis and prevent metastatic tumor formation in preclinical models

Platelets are crucial for normal hemostasis; however, their hyperactivation also contributes to many potentially lethal pathologies including myocardial infarction, stroke, and cancer. We hypothesized that modified platelets lacking their aggregation and activation capacity could act as reversible inhibitors of platelet activation cascades. Here, we describe the development of detergent-extracted human modified platelets (platelet decoys) that retained platelet binding functions but were incapable of functional activation and aggregation. Platelet decoys inhibited aggregation and adhesion of platelets on thrombogenic surfaces in vitro, which could be immediately reversed by the addition of normal platelets; in vivo in a rabbit model, pretreatment with platelet decoys inhibited arterial injury-induced thromboembolism. Decoys also interfered with platelet-mediated human breast cancer cell aggregation, and their presence decreased cancer cell arrest and extravasation in a microfluidic human microvasculature on a chip. In a mouse model of metastasis, simultaneous injection of the platelet decoys with tumor cells inhibited metastatic tumor growth. Thus, our results suggest that platelet decoys might represent an effective strategy for obtaining antithrombotic and antimetastatic effects.

On-chip 3D neuromuscular model for drug screening and precision medicine in neuromuscular disease

This protocol describes the design, fabrication and use of a 3D physiological and pathophysiological motor unit model consisting of motor neurons coupled to skeletal muscles interacting via the neuromuscular junction (NMJ) within a microfluidic device. This model facilitates imaging and quantitative functional assessment. The 'NMJ chip' enables real-time, live imaging of axonal outgrowth, NMJ formation and muscle maturation, as well as synchronization of motor neuron activity and muscle contraction under optogenetic control for the study of normal physiological events. The proposed protocol takes ~2-3 months to be implemented. Pathological behaviors associated with various neuromuscular diseases, such as regression of motor neuron axons, motor neuron death, and muscle degradation and atrophy can also be recapitulated in this system. Disease models can be created by the use of patient-derived induced pluripotent stem cells to generate both the motor neurons and skeletal muscle cells used. This is demonstrated by the use of cells from a patient with sporadic amyotrophic lateral sclerosis but can be applied more generally to models of neuromuscular disease, such as spinal muscular atrophy, NMJ disorder and muscular dystrophy. Models such as this hold considerable potential for applications in precision medicine, drug screening and disease risk assessment.

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

The 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 EMT-induced 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.

Pericytes Contribute to Dysfunction in a Human 3D Model of Placental Microvasculature through VEGF-Ang-Tie2 Signaling

Placental vasculopathies are associated with a number of pregnancy-related diseases, including pre-eclampsia (PE)-a leading cause of maternal-fetal morbidity and mortality worldwide. Placental presentations of PE are associated with endothelial dysfunction, reduced vessel perfusion, white blood cell infiltration, and altered production of angiogenic factors within the placenta (a candidate mechanism). Despite maintaining vascular quiescence in other tissues, how pericytes contribute to vascular growth and signaling in the placenta remains unknown. Here, pericytes are hypothesized to play a detrimental role in the pathogenesis of placental vascular growth. A perfusable triculture model is developed, consisting of human endothelial cells, fibroblasts, and pericytes, capable of recapitulating growth and remodeling in a system that mimics inflamed placental microvessels. Placental pericytes are shown to contribute to growth restriction of microvessels over time, an effect that is strongly regulated by vascular endothelial growth factor and Angiopoietin/Tie2 signaling. Furthermore, this model is capable of recapitulating essential processes including tumor necrosis factor alpha (TNFα)-mediated vascular leakage and leukocyte infiltration, both important aspects associated with placental PE. This placental vascular model highlights that an imbalance in endothelial-pericyte crosstalk can play a critical role in the development of vascular pathology and associated diseases.

MicroRNA delivery through nanoparticles

MicroRNAs (miRNAs) are attracting a growing interest in the scientific community due to their central role in the etiology of major diseases. On the other hand, nanoparticle carriers offer unprecedented opportunities for cell specific controlled delivery of miRNAs for therapeutic purposes. This review critically discusses the use of nanoparticles for the delivery of miRNA-based therapeutics in the treatment of cancer and neurodegenerative disorders and for tissue regeneration. A fresh perspective is presented on the design and characterization of nanocarriers to accelerate translation from basic research to clinical application of miRNA-nanoparticles. Main challenges in the engineering of miRNA-loaded nanoparticles are discussed, and key application examples are highlighted to underline their therapeutic potential for effective and personalized medicine.

Application of Transmural Flow Across In Vitro Microvasculature Enables Direct Sampling of Interstitial Therapeutic Molecule Distribution

In vitro prediction of physiologically relevant transport of therapeutic molecules across the microcirculation represents an intriguing opportunity to predict efficacy in human populations. On-chip microvascular networks (MVNs) show physiologically relevant values of molecular permeability, yet like most systems, they lack an important contribution to transport: the ever-present fluid convection through the endothelium. Quantification of transport through the MVNs by current methods also requires confocal imaging and advanced analytical techniques, which can be a bottleneck in industry and academic laboratories. Here, it is shown that by recapitulating physiological transmural flow across the MVNs, the concentration of small and large molecule therapeutics can be directly sampled in the interstitial fluid and analyzed using standard analytical techniques. The magnitudes of transport measured in MVNs reveal trends with molecular size and type (protein versus nonprotein) that are expected in vivo, supporting the use of the MVNs platform as an in vitro tool to predict distribution of therapeutics in vivo.

Blood-Brain Barrier Dysfunction in a 3D In Vitro Model of Alzheimer's Disease

Harmful materials in the blood are prevented from entering the healthy brain by a highly selective blood-brain barrier (BBB), and impairment of barrier function has been associated with a variety of neurological diseases. In Alzheimer's disease (AD), BBB breakdown has been shown to occur even before cognitive decline and brain pathology. To investigate the role of the cerebral vasculature in AD, a physiologically relevant 3D human neural cell culture microfluidic model is developed having a brain endothelial cell monolayer with a BBB-like phenotype. This model is shown to recapitulate several key aspects of BBB dysfunction observed in AD patients: increased BBB permeability, decreased expression of claudin-1, claudin-5, and VE-cadherin, increased expression of matrix-metalloproteinase-2 and reactive oxygen species, and deposition of β-amyloid (Aβ) peptides at the vascular endothelium. Thus, it provides a well-controlled platform for investigating BBB function as well as for screening of new drugs that need to pass the BBB to gain access to neural tissues.

Quantitative screening of the effects of hyper-osmotic stress on cancer cells cultured in 2- or 3-dimensional settings

The maintenance of precise cell volume is critical for cell survival. Changes in extracellular osmolarity affect cell volume and may impact various cellular processes such as mitosis, mitochondrial functions, DNA repair as well as cell migration and proliferation. Much of what we know about the mechanisms of cell osmoregulation comes from in vitro two-dimensional (2D) assays that are less physiologically relevant than three-dimensional (3D) in vitro or in vivo settings. Here, we developed a microfluidic model to study the impact of hyper-osmotic stress on the migration, proliferation and ion channel/transporter expression changes of three metastatic cell lines (MDA-MB-231, A549, T24) in 2D versus 3D environments. We observed a global decrease in cell migration and proliferation upon hyper-osmotic stress treatment, with similar responses between 2D and 3D conditions. Specific ion channels/aquaporins are over-expressed in metastatic cells and play a central role during osmo-regulation. Therefore, the effects of hyper-osmotic stress on two transporters, aquaporin 5 (AQP5) and the transient receptor potential cation channel (TRPV4), was investigated. While hyper-osmotic stress had no major impact on the transporters of cells cultured in 2D, cells embedded in collagen gel (3D) decreased their AQP5 expression and exhibited a reduction in intra-cellular translocation of TRPV4. Furthermore, cell dispersion from T24 aggregates embedded in 3D collagen gel decreased with higher levels of hyper-osmotic stress. In conclusion, this study provides evidence on the impact of hyper-osmotic stress on various aspects of metastatic cell progression and highlights the importance of having a 3D cell culture platform in investigating molecular players involved in cancer cell migration.

Balance of interstitial flow magnitude and vascular endothelial growth factor concentration modulates three-dimensional microvascular network formation

Hemodynamic and biochemical factors play important roles in critical steps of angiogenesis. In particular, interstitial flow has attracted attention as an important hemodynamic factor controlling the angiogenic process. Here, we applied a wide range of interstitial flow magnitudes to an in vitro three-dimensional (3D) angiogenesis model in a microfluidic device. This study aimed to investigate the effect of interstitial flow magnitude in combination with the vascular endothelial growth factor (VEGF) concentration on 3D microvascular network formation. Human umbilical vein endothelial cells (HUVECs) were cultured in a series of interstitial flow generated by 2, 8, and 25 mmH₂O. Our findings indicated that interstitial flow significantly enhanced vascular sprout formation, network extension, and the development of branching networks in a magnitude-dependent manner. Furthermore, we demonstrated that the proangiogenic effect of interstitial flow application could not be substituted by the increased VEGF concentration. In addition, we found that HUVECs near vascular sprouts significantly elongated in >8 mmH₂O conditions, while activation of Src was detected even in 2 mmH₂O conditions. Our results suggest that the balance between the interstitial flow magnitude and the VEGF concentration plays an important role in the regulation of 3D microvascular network formation in vitro.

Engineered Models of Metastasis with Application to Study Cancer Biomechanics

Three-dimensional complex biomechanical interactions occur from the initial steps of tumor formation to the later phases of cancer metastasis. Conventional monolayer cultures cannot recapitulate the complex microenvironment and chemical and mechanical cues that tumor cells experience during their metastatic journey, nor the complexity of their interactions with other, noncancerous cells. As alternative approaches, various engineered models have been developed to recapitulate specific features of each step of metastasis with tunable microenvironments to test a variety of mechanistic hypotheses. Here the main recent advances in the technologies that provide deeper insight into the process of cancer dissemination are discussed, with an emphasis on three-dimensional and mechanical factors as well as interactions between multiple cell types.

Abstract 958: Tumor-vascular interactions promote STING-driven inflammation in the tumor microenvironment

The recruitment of T cells following intratumoral administration of Stimulation of Interferon Genes (STING) agonists in the tumor microenvironment (TME) is a critical event in the STING-driven antitumor immune response, a pathway with great relevance in the context of cancer immunotherapy. We have previously demonstrated that LKB1 mutation is associated with suppression of tumor cell STING levels and reduced production of T-cell chemoattractants such as CXCL10 in KRAS-driven non-small cell lung cancer (NSCLC). Consistent with this, immunohistochemical staining of patient samples showed poor infiltration of CD3, CD4, and CD8 T cells into LKB1 negative versus LKB1 intact cancer epithelium, and instead, retention of T-cells in stroma. To examine how LKB1 alters immune cell recruitment in a STING-dependent manner, we used a 3-D microfluidic co-culture system to study interactions between vasculature and tumor spheroids derived from a KRAS/LKB1 mutated (KL) cell line with LKB1 reconstitution +/- STING deletion. To form the vasculature, we co-cultured tumor spheroids with fibroblasts and endothelial cells for 7 days, and identified changes in morphology, cytokine production, and gene expression that occur in co-culture. We first observed that co-culture induced synergistic production of multiple immune cell chemo-attractants such as CXCL10, CCL2, CCL5, and G-CSF. Interestingly, this more physiologic ex vivo tumor model of LKB1 reconstitution revealed particularly strong cooperative production of STING-dependent cytokines such as CXCL10 in the vasculature. Moreover, STING depletion in LKB1 reconstituted tumor cells did not significantly attenuate production of CXCL10 and other cytokines in co-culture, suggesting that tumor/vessel interaction may promote STING activation in the vasculature regardless of cancer cell-intrinsic STING function. Furthermore, although there was no appreciable response after treatment of KL cancer cells with cGAMP based STING agonists, treatment of isolated 3-D vascular networks with cGAMP enhanced vascular permeability and increased production of CXCL10 and CCL5, possibly contributing to defective chemokine gradients that retain T cells near the vasculature. Thus, developing these more complex models that incorporate the vasculature may elucidate important aspects of STING biology and may ultimately aid further development of effective immunotherapies targeting this signaling axis.

Citation Format: Marco Campisi, Shriram K. Sundararaman, Shunsuke Kitajima, Valeria Chiono, Roger D. Kamm, David A. Barbie. Tumor-vascular interactions promote STING-driven inflammation in the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 958.