Vascular beds maintain pancreatic tumour explants for ex vivo drug screening

Our understanding of cancer progression or response to therapies would benefit from benchtop, tissue-level assays that preserve the biology and anatomy of human tumours ex vivo. We present a methodology for maintaining patient tumour samples ex vivo for the purpose of drug testing in a clinical setting. The harvested tumour biopsy, excised from mice or patients, is integrated into a support tissue that includes stroma and vasculature. This support tissue preserves tumour histoarchitecture and relevant expression profiles, and tumour tissues cultured using this system display different sensitivities to chemotherapeutics compared with tumour explants with no supporting tissue. The methodology is more rapid than patient-derived xenograft models, easy to implement, and amenable to high-throughput assays, making it an attractive tool for in vitro drug screening or for the guidance of patient-specific chemotherapies.

Abstract 5796: Heparan sulfate proteoglycans mediate tumor cell invasion and metastasis

The surface proteoglycan/glycoprotein layer (glycocalyx) on tumor cells has been associated with cellular functions that can potentially enable invasion and metastasis. In addition, aggressive tumor cells with high metastatic potential have enhanced invasion rates in response to interstitial flow stimuli in vitro. Our previous studies suggest that heparan sulfate (HS) in the glycocalyx plays an important role in this flow mediated mechanostransduction and upregulation of invasive and metastatic potential. In this study, highly metastatic renal cell carcinoma cells were genetically modified to suppress HS production by knocking down its synthetic enzyme NDST1. Using modified Boyden chamber and microfluidic assays, we show that flow-enhanced invasion is suppressed in HS deficient cells. To assess the ability of these cells to metastasize in vivo, parental or knockdown cells expressing fluorescence reporters were injected into kidney capsules in SCID mice. Histological analysis confirmed that there was a large reduction (95%) in metastasis to distant organs by tumors formed from the NDST1 knockdown cells compared to control cells with intact HS. The ability of these cells to invade surrounding tissue was also impaired. The substantial inhibition of metastasis and invasion upon reduction of HS suggests an active role for the tumor cell glycocalyx in tumor progression.

Citation Format: Henry Qazi, Zhong-Dong Shi, Jonathan W. Song, Limary M. Cancel, Lance L. Munn, John M. Tarbell. Heparan sulfate proteoglycans mediate tumor cell invasion and metastasis [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 5796. doi:10.1158/1538-7445.AM2017-5796

Cancer and inflammation

The relationship between inflammation and cancer has been recognized since the 17^th century,¹ and we now know much about the cells, cytokines and physiological processes that are central to both inflammation and cancer.^2-9 Chronic inflammation can induce certain cancers,^10-17 and solid tumors, in turn, can initiate and perpetuate local inflammatory processes that foster tumor growth and dissemination.⁵ ,^18-20 Consequently, inflammatory pathways have been targeted in attempts to control cancer.^21-23 Inflammation is a central aspect of the innate immune system's response to tissue damage or infection, and also facilitates the recruitment of circulating cells and antibodies of the adaptive immune response to the tissue. Components of the innate immune response carry out a robust, but sometimes overly-conservative response, sacrificing specificity for the sake of preservation. Thus, when innate immunity goes awry, it can have profound implications. How the innate and adaptive immune systems cooperate to neutralize pathogens and repair damaged tissues is still an area of intense investigation. Further, how these systems can respond to cancer, which arises from normal 'self' cells that undergo an oncogenic transformation, has profound implications for cancer therapy. Recently, immunotherapies that activate adaptive immunity have shown unprecedented promise in the clinic, producing durable responses and dramatic increases in survival rate in patients with advanced stage melanoma.^24-26 Consequently, the relationship between cancer and inflammation has now returned to the forefront of clinical oncology. WIREs Syst Biol Med 2017, 9:e1370. doi: 10.1002/wsbm.1370 For further resources related to this article, please visit the WIREs website.

Synchronization and Random Triggering of Lymphatic Vessel Contractions

The lymphatic system is responsible for transporting interstitial fluid back to the bloodstream, but unlike the cardiovascular system, lacks a centralized pump-the heart–to drive flow. Instead, each collecting lymphatic vessel can individually contract and dilate producing unidirectional flow enforced by intraluminal check valves. Due to the large number and spatial distribution of such pumps, high-level coordination would be unwieldy. This leads to the question of how each segment of lymphatic vessel responds to local signals that can contribute to the coordination of pumping on a network basis. Beginning with elementary fluid mechanics and known cellular behaviors, we show that two complementary oscillators emerge from i) mechanical stretch with calcium ion transport and ii) fluid shear stress induced nitric oxide production (NO). Using numerical simulation and linear stability analysis we show that the newly identified shear-NO oscillator shares similarities with the well-known Van der Pol oscillator, but has unique characteristics. Depending on the operating conditions, the shear-NO process may i) be inherently stable, ii) oscillate spontaneously in response to random disturbances or iii) synchronize with weak periodic stimuli. When the complementary shear-driven and stretch-driven oscillators interact, either may dominate, producing a rich family of behaviors similar to those observed in vivo.

For decades, cardiovascular physiology has been an area of intense research, and we have a fundamental understanding of the mechanisms the heart uses to drive blood flow through the distributed network of vessels in the body. The lymphatic system is now receiving similar attention as more is learned about its functional role in disease processes. The importance of the lymphatic system in collecting excess fluid from tissues and returning it to the blood is well known, but how the lymph flow is regulated without a central pump is poorly understood. Each segment of collecting lymphatic vessel can independently contract yielding a network of distributed pump/conduits. This paper shows how the lymphatic muscle cells that squeeze fluid along the lymphatic vessels can be effectively regulated using only chemical and mechanical signals that they receive from their immediate microenvironment. Using stability theory and the tools of nonlinear dynamics we identify two complementary oscillators that respond to stretch of the vessel wall and shear of fluid flowing over the vessel wall. Numerical simulations of the combined oscillators show that they have characteristics well suited to the regulation of distributed systems in general and may have application in other biological and physical contexts.

Flow-induced HDAC1 phosphorylation and nuclear export in angiogenic sprouting

Angiogenesis requires the coordinated growth and migration of endothelial cells (ECs), with each EC residing in the vessel wall integrating local signals to determine whether to remain quiescent or undergo morphogenesis. These signals include vascular endothelial growth factor (VEGF) and flow-induced mechanical stimuli such as interstitial flow, which are both elevated in the tumor microenvironment. However, it is not clear how VEGF signaling and mechanobiological activation due to interstitial flow cooperate during angiogenesis. Here, we show that endothelial morphogenesis is histone deacetylase-1- (HDAC1) dependent and that interstitial flow increases the phosphorylation of HDAC1, its activity, and its export from the nucleus. Furthermore, we show that HDAC1 inhibition decreases endothelial morphogenesis and matrix metalloproteinase-14 (MMP14) expression. Our results suggest that HDAC1 modulates angiogenesis in response to flow, providing a new target for modulating vascularization in the clinic.

Heparan sulfate proteoglycans mediate renal carcinoma metastasis

The surface proteoglycan/glycoprotein layer (glycocalyx) on tumor cells has been associated with cellular functions that can potentially enable invasion and metastasis. In addition, aggressive tumor cells with high metastatic potential have enhanced invasion rates in response to interstitial flow stimuli in vitro. Our previous studies suggest that heparan sulfate (HS) in the glycocalyx plays an important role in this flow mediated mechanostransduction and upregulation of invasive and metastatic potential. In this study, highly metastatic renal cell carcinoma cells were genetically modified to suppress HS production by knocking down its synthetic enzyme NDST1. Using modified Boyden chamber and microfluidic assays, we show that flow-enhanced invasion is suppressed in HS deficient cells. To assess the ability of these cells to metastasize in vivo, parental or knockdown cells expressing fluorescence reporters were injected into kidney capsules in SCID mice. Histological analysis confirmed that there was a large reduction (95%) in metastasis to distant organs by tumors formed from the NDST1 knockdown cells compared to control cells with intact HS. The ability of these cells to invade surrounding tissue was also impaired. The substantial inhibition of metastasis and invasion upon reduction of HS suggests an active role for the tumor cell glycocalyx in tumor progression.

Abstract LB-347: Ang-2/VEGF bispecific antibody reprograms macrophages and resident microglia to anti-tumor phenotype and prolongs glioblastoma survival

OBJECTIVE: We aimed to enhance the efficacy of anti-VEGF therapy in glioblastoma (GBM) through additional inhibition of Angiopoietin-2 (Ang-2), a potential mediator of resistance to antiangiogenic therapy using VEGF inhibition.

INTRODUCTION: Glioblastoma (GBM) is a uniformly lethal primary brain tumor affecting more than 12.000 patients every year in the US alone. The standard therapy regimen for this highly angiogenic tumor entity comprises maximal safe resection and chemoradiation with temozolomide. The addition of antiangiogenic (anti-VEGF) therapy to the standard of care regimen improved progression-free survival, but failed to improve overall survival of GBM patients. Preclinical and clinical data suggest that resistance to anti-VEGF therapy in GBM is mediated by Ang-2, making this pathway a potential target.

EXPERIMENTAL DESIGN: We tested the effect of dual Ang-2/VEGF blockade with A2V on mouse survival using a syngeneic (Gl261) model and a human xenograft (MGG8) model, compared to anti-VEGF antibody therapy (B20). In addition, we used blood-based Gaussian Luciferase (GLUC) assays, immunohistochemistry and flow cytometry to measure changes in tumor growth, microvessel density (MVD), and immune microenvironment, respectively.

RESULTS: Gl261 tumors have a highly abnormal tumor vasculature. In this model, treatment with A2V reduced MVD compared to B20. The decrease in MVD was due to a reduction in pericyte-low tumor vessels, while pericyte-high vessels were unaffected. These vascular changes were accompanied by reduced tumor burden and enhanced survival.

Interestingly, in the MGG8 tumors, which have a vasculature similar to the normal brain, we detected no change in MVD after A2V treatment. Nevertheless, we found a reduced tumor burden and prolonged animal survival in the MGG8 model.

Since vascular normalization may impact immune cell infiltration and function in tumors, we next evaluated these cell populations. We found that A2V therapy reduced pro-tumor M2 polarization of macrophages and microglia and reprogrammed these cells toward the M1 phenotype in both the Gl261 and MGG8 models. Collectively, our data indicate that therapy-induced anti-tumor immunity is mediated by M1-type macrophages but not by T-cell infiltration or function.

CONCLUSION: Dual Ang-2/VEGF therapy with A2V reprogrammed macrophages and microglia from pro-tumor M2 toward the anti-tumor M1 phenotype in two GBM models, in addition to normalizing vasculature in tumors with abnormal vessels. These data indicate that dual anti-angiogenic therapy has the potential to overcome resistance to anti-VEGF therapy and confer clinical benefits in GBM patients through vascular and immuno-modulatory effects.

Citation Format: Jonas Kloepper, Lars Riedemann, Zohreh Amoozgar, Giorgio Seano, Katharina H. Susek, Veronica Yu, Nisha Dalvie, Robin L. Amelung, Meenal Datta, Jonathan W. Song, Vasileios Askoxylakis, Jennie W. Taylor, Christine Lu-Emerson, Ana Batista, Nathaniel D. Kirkpatrick, Keehoon Jung, Matija Snuderl, Alona Muzikansky, Kay G. Stubenrauch, Oliver Krieter, Hiroaki Wakimoto, Lei Xu, Lance L. Munn, Dan G. Duda, Dai Fukumura, Tracy T. Batchelor, Rakesh K. Jain. Ang-2/VEGF bispecific antibody reprograms macrophages and resident microglia to anti-tumor phenotype and prolongs glioblastoma survival. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-347.

Implantable tissue isolation chambers for analyzing tumor dynamics in vivo

Recruitment of new blood vessels from the surrounding tissue is central to tumor progression and involves a fundamental transition of the normal, organized vasculature into a dense disarray of vessels that infiltrates the tumor. At present, studying the co-development of the tumor and recruited normal tissue is experimentally challenging because many of the important events occur rapidly and over short length scales in a dense three-dimensional space. To overcome these experimental limitations, we partially confined tumors within biocompatible and optically clear tissue isolation chambers (TICs) and implanted them in mice to create a system that is more amenable to microscopic analysis. Our goal was to integrate the tumor into a recruited host tissue - complete with vasculature - and demonstrate that the system recapitulates relevant features of the tumor microenvironment. We show that the TICs allow clear visualization of the cellular events associated with tumor growth and progression at the host-tumor interface including cell infiltration, matrix remodeling and angiogenesis. The tissue within the chamber is viable for more than a month, and the process is robust in both the skin and brain. Treatment with losartan, an angiotensin II receptor antagonist, decreased the collagen density and fiber length in the TIC, consistent with the known activity of this drug. We further show that collagen fibers display characteristic tumor signatures and play a central role in angiogenesis, guiding the migration of tethered endothelial sprouts. The methodology combines accessible methods of microfabrication with animal models and will enable more informative studies of the cellular mechanisms of tumor progression.

Ang-2/VEGF bispecific antibody reprograms macrophages and resident microglia to anti-tumor phenotype and prolongs glioblastoma survival

Inhibition of the vascular endothelial growth factor (VEGF) pathway has failed to improve overall survival of patients with glioblastoma (GBM). We previously showed that angiopoietin-2 (Ang-2) overexpression compromised the benefit from anti-VEGF therapy in a preclinical GBM model. Here we investigated whether dual Ang-2/VEGF inhibition could overcome resistance to anti-VEGF treatment. We treated mice bearing orthotopic syngeneic (Gl261) GBMs or human (MGG8) GBM xenografts with antibodies inhibiting VEGF (B20), or Ang-2/VEGF (CrossMab, A2V). We examined the effects of treatment on the tumor vasculature, immune cell populations, tumor growth, and survival in both the Gl261 and MGG8 tumor models. We found that in the Gl261 model, which displays a highly abnormal tumor vasculature, A2V decreased vessel density, delayed tumor growth, and prolonged survival compared with B20. In the MGG8 model, which displays a low degree of vessel abnormality, A2V induced no significant changes in the tumor vasculature but still prolonged survival. In both the Gl261 and MGG8 models A2V reprogrammed protumor M2 macrophages toward the antitumor M1 phenotype. Our findings indicate that A2V may prolong survival in mice with GBM by reprogramming the tumor immune microenvironment and delaying tumor growth.

The Lymphatic System in Disease Processes and Cancer Progression

Advances in our understanding of the structure and function of the lymphatic system have made it possible to identify its role in a variety of disease processes. Because it is involved not only in fluid homeostasis but also in immune cell trafficking, the lymphatic system can mediate and ultimately alter immune responses. Our rapidly increasing knowledge of the molecular control of the lymphatic system will inevitably lead to new and effective therapies for patients with lymphatic dysfunction. In this review, we discuss the molecular and physiological control of lymphatic vessel function and explore how the lymphatic system contributes to many disease processes, including cancer and lymphedema.

Mechanobiology of lymphatic contractions

The lymphatic system is responsible for controlling tissue fluid pressure by facilitating flow of lymph (i.e. the plasma and cells that enter the lymphatic system). Because lymph contains cells of the immune system, its transport is not only important for fluid homeostasis, but also immune function. Lymph drainage can occur via passive flow or active pumping, and much research has identified the key biochemical and mechanical factors that affect output. Although many studies and reviews have addressed how tissue properties and fluid mechanics (i.e. pressure gradients) affect lymph transport [1-3] there is less known about lymphatic mechanobiology. As opposed to passive mechanical properties, mechanobiology describes the active coupling of mechanical signals and biochemical pathways. Lymphatic vasomotion is the result of a fascinating system affected by mechanical forces exerted by the flowing lymph, including pressure-induced vessel stretch and flow-induced shear stresses. These forces can trigger or modulate biochemical pathways important for controlling the lymphatic contractions. Here, I review the current understanding of lymphatic vessel function, focusing on vessel mechanobiology, and summarize the prospects for a comprehensive understanding that integrates the mechanical and biomechanical control mechanisms in the lymphatic system.

Microfluidic model of angiogenic sprouting

Microfluidic systems have emerged as an important technology for modeling cellular microenvironments in vitro. These systems enable unprecedented levels of control of chemical gradients, fluid flow, and localized 3-D extracellular matrices (ECM), all of which can be integrated to provide a physiologically relevant context for studying complex cellular processes such as angiogenesis. Here, we describe the design and use of microfluidic systems for reproducing the dynamic events of vascular morphogenesis.

Video-rate resonant scanning multiphoton microscopy: An emerging technique for intravital imaging of the tumor microenvironment

The abnormal tumor microenvironment fuels tumor progression, metastasis, immune suppression, and treatment resistance. Over last several decades, developments in and applications of intravital microscopy have provided unprecedented insights into the dynamics of the tumor microenvironment. In particular, intravital multiphoton microscopy has revealed the abnormal structure and function of tumor-associated blood and lymphatic vessels, the role of aberrant tumor matrix in drug delivery, invasion and metastasis of tumor cells, the dynamics of immune cell trafficking to and within tumors, and gene expression in tumors. However, traditional multiphoton microscopy suffers from inherently slow imaging rates-only a few frames per second, thus unable to capture more rapid events such as blood flow, lymphatic flow, and cell movement within vessels. Here, we report the development and implementation of a video-rate multiphoton microscope (VR-MPLSM) based on resonant galvanometer mirror scanning that is capable of recording at 30 frames per second and acquiring intravital multispectral images. We show that the design of the system can be readily implemented and is adaptable to various experimental models. As examples, we demonstrate the utility of the system to directly measure flow within tumors, capture metastatic cancer cells moving within the brain vasculature and cells in lymphatic vessels, and image acute responses to changes in a vascular network. VR-MPLSM thus has the potential to further advance intravital imaging and provide new insight into the biology of the tumor microenvironment.

Imaging the lymphatic system

Visualization of the lymphatic system is clinically necessary during diagnosis or treatment of many conditions and diseases; it is used for identifying and monitoring lymphedema, for detecting metastatic lesions during cancer staging and for locating lymphatic structures so they can be spared during surgical procedures. Imaging lymphatic anatomy and function also plays an important role in experimental studies of lymphatic development and function, where spatial resolution and accessibility are better. Here, we review technologies for visualizing and imaging the lymphatic system for clinical applications. We then describe the use of lymphatic imaging in experimental systems as well as some of the emerging technologies for improving these methodologies.

Dynamics of tissue topology during cancer invasion and metastasis

During tumor progression, cancer cells mix with other cell populations including epithelial and endothelial cells. Although potentially important clinically as well as for our understanding of basic tumor biology, the process of mixing is largely a mystery. Furthermore, there is no rigorous, analytical measure available for quantifying the mixing of compartments within a tumor. I present here a mathematical model of tissue repair and tumor growth based on collective cell migration that simulates a wide range of observed tumor behaviors with correct tissue compartmentalization and connectivity. The resulting dynamics are analyzed in light of the Euler characteristic number (χ), which describes key topological features such as fragmentation, looping and cavities. The analysis predicts a number of regimes in which the cancer cells can encapsulate normal tissue, form a co-interdigitating mass, or become fragmented and encapsulated by endothelial or epithelial structures. Key processes that affect the topological changes are the production of provisional matrix in the tumor, and the migration of endothelial or epithelial cells on this matrix. Furthermore, the simulations predict that topological changes during tumor invasion into blood vessels may contribute to metastasis. The topological analysis outlined here could be useful for tumor diagnosis or monitoring response to therapy and would only require high resolution, 3D image data to resolve and track the various cell compartments.

Cancer cell glycocalyx mediates mechanotransduction and flow-regulated invasion

Mammalian cells are covered by a surface proteoglycan (glycocalyx) layer, and it is known that blood vessel-lining endothelial cells use the glycocalyx to sense and transduce the shearing forces of blood flow into intracellular signals. Tumor cells in vivo are exposed to forces from interstitial fluid flow that may affect metastatic potential but are not reproduced by most in vitro cell motility assays. We hypothesized that glycocalyx-mediated mechanotransduction of interstitial flow shear stress is an un-recognized factor that can significantly enhance metastatic cell motility and play a role in augmentation of invasion. Involvement of MMP levels, cell adhesion molecules (CD44, α3 integrin), and glycocalyx components (heparan sulfate and hyaluronan) was investigated in a cell/collagen gel suspension model designed to mimic the interstitial flow microenvironment. Physiological levels of flow upregulated MMP levels and enhanced the motility of metastatic cells. Blocking the flow-enhanced expression of MMP activity or adhesion molecules (CD44 and integrins) resulted in blocking the flow-enhanced migratory activity. The presence of a glycocalyx-like layer was verified around tumor cells, and the degradation of this layer by hyaluronidase and heparinase blocked the flow-regulated invasion. This study shows for the first time that interstitial flow enhancement of metastatic cell motility can be mediated by the cell surface glycocalyx - a potential target for therapeutics.

Measuring interstitial diffusion, convection, and binding parameters in mouse tumors

Noninvasive techniques have been developed for the assessment of various parameters in normal and diseased tissues of mice. This protocol describes the measurement of extravascular parameters, including interstitial diffusion, convection, and binding parameters, in mouse tumors. A fluorescently labeled molecule of interest is infused into the tumor interstitium, followed by imaging using single-photon microscopy or multiphoton laser-scanning microscopy (MPLSM). Fluorescence recovery after photobleaching (FRAP) with spatial Fourier analysis is performed. To measure interstitial diffusion coefficients, multiphoton FRAP is performed.

Measuring interstitial pH and pO2 in mouse tumors

This protocol outlines methods to measure two extravascular parameters, interstitial pH and partial pressure of oxygen (pO2), in mouse tumors. The method for measuring interstitial pH uses fluorescence ratio imaging microscopy (FRIM) of the pH-sensitive fluorescent dye 2',7'-bis-(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF). The method for measuring interstitial pO2 is based on the oxygen-dependent quenching of the phosphorescence of albumin-bound palladium meso-tetra(4-carboxyphenyl)porphyrin, and can be used to measure microvascular as well as interstitial pO2. In addition, the two methods can be used sequentially to measure both pH and pO2 in the same tissues.

Measuring leukocyte-endothelial interactions in mice

Intravital imaging techniques are powerful tools in the study of tumor pathophysiology. These techniques can be used to measure vascular parameters (e.g., angiogenesis, hemodynamics, and leukocyte-endothelial interactions) in tumors and normal vascular networks in mice. This protocol describes the use of single-photon microscopy and multiphoton laser-scanning microscopy to follow the migration of Rhodamine-6G, a fluorescently labeled tracer, following injection into the tail vein of a mouse. The Rhodamine-6G enters the circulatory system and labels leukocytes. It is possible to monitor changes in the interactions between leukocytes and the endothelium by determining the numbers of rolling and adhering leukocytes as well as the total flux of these cells.

Measuring vascular permeability in mice

Noninvasive techniques have been developed for the assessment of vascular parameters, including vascular permeability, in normal and diseased tissues of mice. In this protocol, mice are injected with an appropriate fluorescent tracer. The effective average vascular permeability (P) of a region of vessels is measured by single-photon microscopy. Additionally, the vascular permeability of individual vessel segments within ~600 µm of a tumor/window interface is measured by multiphoton laser-scanning microscopy (MPLSM).

Abstract LB-348: Evolution of physical forces in the tumor microenvironment and implications for therapeutic resistance

In solid tumors a fraction of vessels are compressed or totally collapsed (1). As a consequence, the vascular network in tumors is poorly perfused and insufficient for delivery of oxygen and drugs from the blood. This creates a hypoxic microenvironment and reduces delivery of therapeutics, resulting in resistance to radio-, chemo- and immunotherapy. We hypothesized that physical forces in tumors compress tumor vessels. These forces stem from fluid and solid components of tumors. Interstitial fluid pressure (IFP), the isotropic stress exerted by fluid, increases in tumors because of leaky blood vessels and dysfunctional lymphatic vessels. In previous research, we showed that IFP is uniformly elevated in tumors and drops precipitously in the tumor margin. Moreover, elevated IFP cannot compress leaky vessels and thus, vessel compression must result from forces exerted by the solid components of a tumor (2). Despite important in vitro work on solid stress in avascular tumor spheroids, little work has been performed in vivo for the evolution of solid forces in a growing tumor.

To this end, we combined in vivo experiments in mice bearing tumors with a novel mathematical model to analyze the evolution of fluid and solid forces in tumors (3). First, we performed experiments and found that the evolution of solid stress is related to tumor volume. Then, we incorporated this information into our mathematical model and showed that solid stress levels are higher in the tumor interior and lower in the periphery. Elevated compressive stress in the interior of the tumor was found to be sufficient to cause the collapse of blood vessels and result in a lower growth rate of cancer cells compared to the tumor periphery, independently from that caused by the lack of nutrients due to vessel collapse. Furthermore, solid stress levels in the periphery of the tumor can cause blood vessels in the surrounding normal tissue to deform to elliptical shapes but not collapse. We present histological sections of human carcinomas, liposarcomas and pancreatic neuroendocrine tumors that demonstrate such vessel deformations. Contrary to solid stress that is accumulated during progression, model predictions confirmed that IFP levels depend only on the microvascular pressure and the permeability of the tumor vessels.

1. Padera TP, et al. Nature 2004;427(6976):695. 2. Boucher Y, Jain RK. Cancer Res 1992;52(18):5110-4. 3. Stylianopoulos T, Martin JD, Chauhan VP, et al. PNAS 2012;109 (38):15101-8.

Citation Format: Triantafyllos Stylianopoulos, John D. Martin, Saloni Jain, Matija Snuderl, Vikash P. Chauhan, Lance L. Munn, Yves Boucher, Rakesh K. Jain. Evolution of physical forces in the tumor microenvironment and implications for therapeutic resistance. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-348. doi:10.1158/1538-7445.AM2013-LB-348

Measuring angiogenesis and hemodynamics in mice

This protocol outlines methods to measure vascular parameters, including angiogenesis (e.g., vascular density, length, diameter) and hemodynamics (e.g., erythrocyte velocity), in tumors and normal vascular networks in mice. Fluorescein-isothiocyanate (FITC)-dextran is injected into the tail vein of mice to visualize microvessels within 150 μm (using single-photon microscopy) or ~600 μm (using multiphoton laser-scanning microscopy [MPLSM]) of a tumor/window interface. Randomly selected areas (three to six locations/tumor or animal) are investigated using long-working-distance objectives with appropriate magnification. During each observation period, FITC-fluorescence images are recorded for 60 sec, and the videotapes are analyzed off-line for single-photon microscopy; or a three-dimensional (3D) image stack of the vessel network is generated, and vessel properties are measured for MPLSM. If desired, red blood cell (RBC) flux can be measured on a vessel-by-vessel basis using fluorescent tracer RBCs.

Lung window preparation in mice

A thoracic window model has been developed in mice that allows temporal observation of the microcirculation of tumors implanted on the pleural surface without surgical manipulation at the time of observation. Preparation of this lung window model is described here. It allows the study of pleural metastases of various origins as well as primary lung cancer in an orthotopic setting.

RhoA mediates flow-induced endothelial sprouting in a 3-D tissue analogue of angiogenesis

Endothelial cells (ECs) integrate signals from the local microenvironment to guide their behaviour. RhoA is involved in vascular endothelial growth factor (VEGF)-driven angiogenesis, but its role in mechanotransduction during sprouting has not been established. Using dominant negative cell transfections in a microfluidic device that recapitulates angiogenic sprouting, we show that endothelial cells respond to interstitial flow in a RhoA-dependent manner while invading a 3-D extracellular matrix. Furthermore, RhoA regulates flow-induced, but not VEGF gradient-induced, tip cell filopodial extensions. Thus, RhoA pathways mediate mechanically-activated but not VEGF-induced endothelial morphogenesis.

Lymphatic vessels in health and disease

The lymphatic vasculature plays vital roles in tissue fluid balance, immune defense, metabolism, and cancer metastasis. In adults, lymphatic vessel formation and remodeling occur primarily during inflammation, development of the corpus luteum, wound healing, and tumor growth. Unlike the blood circulation, where unidirectional flow is sustained by the pumping actions of the heart, pumping actions intrinsic to the lymphatic vessels themselves are important drivers of lymphatic flow. This review summarizes critical components that control lymphatic physiology.

Pancreatic tumor preparation in mice

Pancreatic cancer has a poor prognosis, and treatment strategies conducted from preclinical research have not succeeded in extending a patient's survival appreciably. This protocol describes how to prepare an abdominal window in mice. This allows both direct intravital microscopy and chronic observation during pancreas tumor growth and the response to treatment.

Lymphangiography of the mouse tail

The lymphatic system is an important route for metastasis of cancer cells. Lymphatic microvessels have been studied by adapting lymphangiography to the mouse tail. In this technique, a high-molecular-weight fluorescently labeled tracer is injected into the interstitial compartment of the tail tissue. The tracer migrates to the local lymphatic vessels and fills the network, allowing visualization. By implanting a tumor in the tail, the structure and function of the lymphatics at the tumor periphery can be monitored. This protocol describes a method for injecting tumor cells into a mouse tail and for microlymphangiography.

Lymphangiography of the mouse ear

The lymphatic system is an important route for metastasis of cancer cells. Lymphatic microvessels have been studied by adapting lymphangiography to the mouse ear. In this technique, a high-molecular-weight fluorescently labeled tracer is injected into the interstitial compartment of the ear chamber. The tracer migrates to the local lymphatic vessels and fills the network, allowing visualization. Lymphangiography with Evan's blue dye or fluorescein isothiocyanate (FITC)-dextran reveals a dense auricular network of lymphatic capillaries, draining to a larger vessel at the ear base and subsequently to the exposed superficial cervical lymph node.

Mammary fat pad tumor preparation in mice

The host microenvironment influences tumor biology, affecting parameters such as gene expression, angiogenesis, growth, invasion, metastasis, and responses to therapy. Consequently, the use of tumor models growing in appropriate orthotopic locations is necessary to obtain a rigorous understanding of tumor pathophysiology and to correctly study antitumor treatments. The mouse mammary fat pad serves as an orthotopic site for breast cancer and can be used to study various aspects of this disease, including the effect of host-tumor interactions on tumor biology and therapeutic response. This protocol describes mammary fat pad tumor preparation in mice.

Mammary fat pad chamber preparation in mice

This protocol describes a procedure to implant mammary fat pad chambers in mice. These chambers can then be used for studying breast cancer. In comparison to the classical mammary fat pad flap model, the chamber described here has the advantage of allowing multiple observation time points in the same animal with simple anesthesia.

Corneal pocket assay in rabbits

The anterior chamber of the eye is a natural site for observing tumor growth, and implantation in a corneal pocket can be used for this purpose. This protocol describes the corneal pocket assay in rabbits. Because of the 3D nature of vessel growth, it is difficult to quantify the vascular response except in the early stages when the vessel length/number can be assessed. The assay can be used for mice with modification. Although it is less expensive to use rats/mice compared with rabbits, surgery on smaller eyes is more difficult. Furthermore, because the rat/mouse cornea is thinner than the rabbit's, the three-dimensional (3D) growth of vessels is even more limited.

Rabbit ear chambers

This protocol describes a procedure to surgically implant transparent chambers in the ears of male New Zealand white rabbits. Such chambers allow continuous, noninvasive, long-term monitoring of angiogenesis during wound healing, as well as the study of tumor angiogenesis. A method for tumor implantation is also provided.

Anastomosis of endothelial sprouts forms new vessels in a tissue analogue of angiogenesis

Here we describe a microfluidic device that accurately reproduces the dynamics of vascular anastomosis, the process by which vascular sprouts connect to achieve perfusion during angiogenesis. The micro-device features two parallel endothelial cell-lined vessel analogues separated by a 300 μm wide collagenous matrix into which the vessels can sprout and form perfused bridging connections. By accurately recapitulating anastomosis in vitro, the device will enable a new generation of studies of the mechanisms of angiogenesis and provide a novel and practical platform for drug screening.

Neovascularization after irradiation: what is the source of newly formed vessels in recurring tumors?

Local relapse of tumors after radiation therapy remains a challenge in oncology. To devise rational approaches for preventing this relapse, we have to improve our understanding of how new vessels form in previously irradiated tumors. We propose that tumor regrowth after local irradiation is dependent on blood vessel formation by local endothelial cells without the need for recruitment of endothelial precursor cells from distant nonirradiated tissues or bone marrow. We also suggest that infiltrating myeloid bone marrow-derived cells promote survival of local endothelial cells during the early period after irradiation and angiogenesis during the later stage of tumor regrowth, both via paracrine mechanisms.

Quantitative assessment of whole-body tumor burden in adult patients with neurofibromatosis

PURPOSE

Patients with neurofibromatosis 1 (NF1), NF2, and schwannomatosis are at risk for multiple nerve sheath tumors and premature mortality. Traditional magnetic resonance imaging (MRI) has limited ability to assess disease burden accurately. The aim of this study was to establish an international cohort of patients with quantified whole-body internal tumor burden and to correlate tumor burden with clinical features of disease.

METHODS

We determined the number, volume, and distribution of internal nerve sheath tumors in patients using whole-body MRI (WBMRI) and three-dimensional computerized volumetry. We quantified the distribution of tumor volume across body regions and used unsupervised cluster analysis to group patients based on tumor distribution. We correlated the presence and volume of internal tumors with disease-related and demographic factors.

RESULTS

WBMRI identified 1286 tumors in 145/247 patients (59%). Schwannomatosis patients had the highest prevalence of tumors (P = 0.03), but NF1 patients had the highest median tumor volume (P = 0.02). Tumor volume was unevenly distributed across body regions with overrepresentation of the head/neck and pelvis. Risk factors for internal nerve sheath tumors included decreasing numbers of café-au-lait macules in NF1 patients (P = 0.003) and history of skeletal abnormalities in NF2 patients (P = 0.09). Risk factors for higher tumor volume included female gender (P = 0.05) and increasing subcutaneous neurofibromas (P = 0.03) in NF1 patients, absence of cutaneous schwannomas in NF2 patients (P = 0.06), and increasing age in schwannomatosis patients (p = 0.10).

CONCLUSION

WBMRI provides a comprehensive phenotype of neurofibromatosis patients, identifies distinct anatomic subgroups, and provides the basis for investigating molecular biomarkers that correlate with unique disease manifestations.

Mechanical compression drives cancer cells toward invasive phenotype

Uncontrolled growth in a confined space generates mechanical compressive stress within tumors, but little is known about how such stress affects tumor cell behavior. Here we show that compressive stress stimulates migration of mammary carcinoma cells. The enhanced migration is accomplished by a subset of "leader cells" that extend filopodia at the leading edge of the cell sheet. Formation of these leader cells is dependent on cell microorganization and is enhanced by compressive stress. Accompanied by fibronectin deposition and stronger cell-matrix adhesion, the transition to leader-cell phenotype results in stabilization of persistent actomyosin-independent cell extensions and coordinated migration. Our results suggest that compressive stress accumulated during tumor growth can enable coordinated migration of cancer cells by stimulating formation of leader cells and enhancing cell-substrate adhesion. This novel mechanism represents a potential target for the prevention of cancer cell migration and invasion.

Biomimetic postcapillary expansions for enhancing rare blood cell separation on a microfluidic chip

Blood cells naturally auto-segregate in postcapillary venules, with the erythrocytes (red blood cells, RBCs) aggregating near the axis of flow and the nucleated cells (NCs)--which include leukocytes, progenitor cells and, in cancer patients, circulating tumor cells--marginating toward the vessel wall. We have used this principle to design a microfluidic device that extracts nucleated cells (NCs) from whole blood. Fabricated using polydimethylsiloxane (PDMS) soft lithography, the biomimetic cell extraction device consists of rectangular microchannels that are 20-400 μm wide, 11 μm deep and up to 2 cm long. The key design feature is the use of repeated expansions/contractions of triangular geometry mimicking postcapillary venules, which enhance margination and optimize the extraction. The device operates on unprocessed whole blood and is able to extract 94 ± 4.5% of NCs with 45.75 ± 2.5-fold enrichment in concentration at a rate of 5 nl s(-1). The device eliminates the need to preprocess blood via centrifugation or RBC lysis, and is ready to be implemented as the initial stage of lab-on-a-chip devices that require enriched nucleated cells. The potential downstream applications are numerous, encompassing all preclinical and clinical assays that operate on enriched NC populations and include on-chip flow cytometry (A. Y. Fu et al., Anal. Chem., 2002, 74, 2451-2457; A. Y. Fu et al., Nat. Biotechnol., 1999, 17, 1109-1111), genetic analyses (M. M. Wang et al., Nat. Biotechnol., 2005, 23, 83-87; L. C. Waters et al., Anal. Chem., 1998, 70, 5172-5176) and circulating tumor cell extraction (S. Nagrath et al., Nature, 2007, 450, 1235-1241; S. L. Stott et al., Proc. Natl. Acad. Sci. U. S. A., 2010, 18392-18397; H. K. Lin et al., Clin. Cancer Res., 2010, 16, 5011-5018).

Normalization of the vasculature for treatment of cancer and other diseases

New vessel formation (angiogenesis) is an essential physiological process for embryologic development, normal growth, and tissue repair. Angiogenesis is tightly regulated at the molecular level. Dysregulation of angiogenesis occurs in various pathologies and is one of the hallmarks of cancer. The imbalance of pro- and anti-angiogenic signaling within tumors creates an abnormal vascular network that is characterized by dilated, tortuous, and hyperpermeable vessels. The physiological consequences of these vascular abnormalities include temporal and spatial heterogeneity in tumor blood flow and oxygenation and increased tumor interstitial fluid pressure. These abnormalities and the resultant microenvironment fuel tumor progression, and also lead to a reduction in the efficacy of chemotherapy, radiotherapy, and immunotherapy. With the discovery of vascular endothelial growth factor (VEGF) as a major driver of tumor angiogenesis, efforts have focused on novel therapeutics aimed at inhibiting VEGF activity, with the goal of regressing tumors by starvation. Unfortunately, clinical trials of anti-VEGF monotherapy in patients with solid tumors have been largely negative. Intriguingly, the combination of anti-VEGF therapy with conventional chemotherapy has improved survival in cancer patients compared with chemotherapy alone. These seemingly paradoxical results could be explained by a "normalization" of the tumor vasculature by anti-VEGF therapy. Preclinical studies have shown that anti-VEGF therapy changes tumor vasculature towards a more "mature" or "normal" phenotype. This "vascular normalization" is characterized by attenuation of hyperpermeability, increased vascular pericyte coverage, a more normal basement membrane, and a resultant reduction in tumor hypoxia and interstitial fluid pressure. These in turn can lead to an improvement in the metabolic profile of the tumor microenvironment, the delivery and efficacy of exogenously administered therapeutics, the efficacy of radiotherapy and of effector immune cells, and a reduction in number of metastatic cells shed by tumors into circulation in mice. These findings are consistent with data from clinical trials of anti-VEGF agents in patients with various solid tumors. More recently, genetic and pharmacological approaches have begun to unravel some other key regulators of vascular normalization such as proteins that regulate tissue oxygen sensing (PHD2) and vessel maturation (PDGFRβ, RGS5, Ang1/2, TGF-β). Here, we review the pathophysiology of tumor angiogenesis, the molecular underpinnings and functional consequences of vascular normalization, and the implications for treatment of cancer and nonmalignant diseases.

Cancer cell-associated MT1-MMP promotes blood vessel invasion and distant metastasis in triple-negative mammary tumors

Functional roles for the cancer cell-associated membrane type I matrix metalloproteinase (MT1-MMP) during early steps of the metastatic cascade in primary tumors remain unresolved. In an effort to determine its significance, we determined the in vivo effects of RNAi-mediated downregulation in mammary cancer cells on the migration, blood and lymphatic vessel invasion (LVI), and lymph node and lung metastasis. We also correlated the expression of cancer cell MT1-MMP with blood vessel invasion (BVI) in 102 breast cancer biopsies. MT1-MMP downregulation in cancer cells decreased lung metastasis without affecting primary tumor growth. The inhibition of lung metastasis correlated with reduced cancer cell migration and BVI. Furthermore, cancer cell-expressed MT1-MMP upregulated the expression of MT1-MMP in vascular endothelial cells, but did not affect MT1-MMP expression in lymphatic endothelial cells, LVI, or lymph node metastasis. Of clinical importance, we observed that elevated MT1-MMP expression correlated with BVI in biopsies from triple-negative breast cancers (TNBC), which have a poor prognosis and high incidence of distant metastasis, relative to other breast cancer subtypes. Together, our findings established that MT1-MMP activity in breast tumors is essential for BVI, but not LVI, and that MT1-MMP should be further explored as a predictor and therapeutic target of hematogenous metastasis in TNBC patients.