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Lance L. Munn, PhD Associate Professor of Radiation Oncology Harvard Medical School
Associate Biologist Edwin L. Steele Laboratory for Tumor Biology
As part of the Edwin L. Steele Laboratory for Tumor Biology, research at the Munn Laboratory focuses on blood vessel structure and function in normal and pathological conditions. Within this broad area, I have projects that address:
Flow of fluid within the lymphatic system is central to many aspects of physiology, including fluid homeostasis and immune function, and poor lymphatic drainage results in significant morbidity in millions of patients each year. We are investigating the mechanisms of lymphatic pumping, considering the nitric oxide and calcium dynamics driven by mechanobiological mechanisms.
During angiogenesis, endothelial cells abandon their normal arrangement in the vessel wall to migrate into the extravascular matrix. This process is controlled by mul-tiple signals and is necessary for tissue regeneration and tumor growth. Using in vitro models and microfluidic devices, we are investigating the biochemical and mechanical determinants of this morphogenic transformation.
To form new, patent blood vessels, angiogenic sprouts must connect. The process by which this happens -anastomosis – is poorly understood, but represents new targets for vascular therapy. Using intravital microscopy and engineered vascular devices, we are following the steps of anastomosis to identify cellular and molecular mechanisms that may eventually be targeted for enhancing wound healing or inhibiting pathological angiogenesis.
In many normal physiological responses, endothelial cells and the blood vessel networks they form undergo dramatic changes in morphology and function. Examples include angiogenesis in wound healing, vessel dilation/hyperpermeability in inflammation, and endometrial angiogenesis in the female reproductive cycle.
Endothelial cells, in cooperation with other stromal cells, have to accomplish these diverse changes by responding to a limited number of growth factors including VEGF, PlGF and bFGF. We are using a systems biology approach to understand how the various growth factors and cells cooperate to produce these seemingly diverse functions. Because tumor angiogenesis relies on many of these same growth factors and cellular mechanisms (but in an abnormal, poorly controlled way), these studies will allow a better understanding of tumor angiogenesis and anti-angiogenic therapy.
During the initial stage of metastasis, cancer cells must breach the vessel wall and enter the circulation. Despite intense research in this area, the cellular mechanisms by which this occurs are poorly understood. Some tumors seem to metastasize as single rogue cells, while others travel in groups or clusters; some seem to actively migrate into the vessel, while others may be passively pushed. Using gene array analysis and carefully designed coculture systems, we are assessing the mechanical and cellular determinants of the initiation of metastasis.
With sufficient understanding of the underlying mechanisms, mathematical models can be assembled to validate existing hypotheses and generate new ones.
Lance Munn, PhDPrincipal InvestigatorContact by email
Despina Bazou, PhDResearch FellowContact by email
Gabriel Gruionu, PhDInstructor in SurgeryContact by email
Christian Kunert, PhDContact by email
Nir Maimon, PhDResearch Fellow in Radiation OncologyContact by email
Jonathan Song, PhDContact by email
We developed 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.
Integr Biol (Camb). 2012;4(8):857-62 - PMID: 22673771 - PMCID: PMC3759296
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 µ wide, 11 µ 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.
Lab Chip. 2011;11(17):2941-7 - PMID: 21773633 - PMCID: PMC3743538
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.
Proc Natl Acad Sci U S A. 2011;109(3):911-6 - PMID: 22203958 - PMCID: PMC3271885
During angiogenesis, endothelial cells (ECs) from intact blood vessels quickly infiltrate avascular regions via vascular sprouting. This process is fundamental to many normal and pathological processes such as wound healing and tumor growth, but its initiation and control are poorly understood.
Vascular endothelial cell growth factor (VEGF) can promote vessel dilation and angiogenic sprouting, but given the complex nature of vascular morphogenesis, additional signals are likely necessary to determine, for example, which vessel segments sprout, which dilate, and which remain quiescent.
Fluid forces exerted by blood and plasma are prime candidates that might co-direct these processes, but it is not known whether VEGF cooperates with mechanical fluid forces to mediate angiogenesis.
Using a microfluidic tissue analog of angiogenic sprouting, we found that fluid shear stress, such as exerted by flowing blood, attenuates EC sprouting in a nitric oxide-dependent manner and that interstitial flow, such as produced by extravasating plasma, directs endothelial morphogenesis and sprout formation.
Furthermore, positive VEGF gradients initiated sprouting but negative gradients inhibited sprouting, promoting instead sheet-like migration analogous to vessel dilation. These results suggest that ECs integrate signals from fluid forces and local VEGF gradients to achieve such varied goals as vessel dilation and sprouting.
Proc Natl Acad Sci U S A. 2011;108(37):15342-7 - PMID: 21876168 - PMCID: PMC3174629
Not all tumor vessels are equal. Tumor-associated vasculature includes immature vessels, regressing vessels, transport vessels undergoing arteriogenesis and peritumor vessels influenced by tumor growth factors.
Current techniques for analyzing tumor blood flow do not discriminate between vessel subtypes and only measure average changes from a population of dissimilar vessels. We developed methodologies for simultaneously quantifying blood flow (velocity, flux, hematocrit and shear rate) in extended networks at single-capillary resolution in vivo.
Our approach relies on deconvolution of signals produced by labeled red blood cells as they move relative to the scanning laser of a confocal or multiphoton microscope and provides fully resolved three-dimensional flow profiles within vessel networks.
Using this methodology, we show that blood velocity profiles are asymmetric near intussusceptive tissue structures in tumors in mice. Furthermore, we show that subpopulations of vessels, classified by functional parameters, exist in and around a tumor and in normal brain tissue.
Nat Methods. 2010;7(8):655-60 - PMID: 20581828 - PMCID: PMC2921873
Song JW, Bazou D, Munn LL Anastomosis of endothelial sprouts forms new vessels in a tissue analogue of angiogenesis. Integr Biol (Camb). 2012;4(8):857-62 - PMID: 22673771 - PMCID: PMC3759296
Kozin SV, Duda DG, Munn LL, Jain RK Neovascularization After Irradiation: What is the Source of Newly Formed Vessels in Recurring Tumors? J Natl Cancer Inst. 2012;104(12):899-905 - PMID: 22572994 - PMCID: PMC3379722
Tse JM, Cheng G, Tyrrell JA, Wilcox-Adelman SA, Boucher Y, Jain RK, Munn LL Mechanical compression drives cancer cells toward invasive phenotype. Proc Natl Acad Sci U S A. 2011;109(3):911-6 - PMID: 22203958 - PMCID: PMC3271885
Song JW, Munn LL Fluid forces control endothelial sprouting. Proc Natl Acad Sci U S A. 2011;108(37):15342-7 - PMID: 21876168 - PMCID: PMC3174629
Cheng G, Liao S, Kit Wong H, Lacorre DA, di Tomaso E, Au P, Fukumura D, Jain RK, Munn LL Engineered blood vessel networks connect to host vasculature via wrapping-and-tapping anastomosis. Blood. 2011;118(17):4740-9 - PMID: 21835951 - PMCID: PMC3208287
Kamoun WS, Chae SS, Lacorre DA, Tyrrell JA, Mitre M, Gillissen MA, Fukumura D, Jain RK, Munn LL Simultaneous measurement of RBC velocity, flux, hematocrit and shear rate in vascular networks. Nat Methods. 2010;7(8):655-60 - PMID: 20581828 - PMCID: PMC2921873
Patan S, Tanda S, Roberge S, Jones RC, Jain RK, Munn LL Vascular morphogenesis and remodeling in a human tumor xenograft: blood vessel formation and growth after ovariectomy and tumor implantation. Circ Res. 2001;89(8):732-9 - PMID: 11597997 - PMCID: PMC2752899
View a list of publications by researchers at the Munn Laboratory
Edwin L. Steele Laboratory for Tumor Biology
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