<p>The ability of tissue engineered constructs to replace diseased or damaged organs is limited without the incorporation of a functional vascular system. To design microvasculature that recapitulates the vascular niche functions for each tissue in the body, we investigated the following hypotheses: (1) cocultures of human umbilical cord blood-derived endothelial progenitor cells (hCB-EPCs) with mural cells can produce the microenvironmental cues necessary to support physiological microvessel formation in vitro; (2) poly(ethylene glycol) (PEG) hydrogel systems can support 3D microvessel formation by hCB-EPCs in coculture with mural cells; (3) mesenchymal cells, derived from either umbilical cord blood (MPCs) or bone marrow (MSCs), can serve as mural cells upon coculture with hCB-EPCs. Coculture ratios between 0.2 (16,000 cells/cm2) and 0.6 (48,000 cells/cm2) of hCB-EPCs plated upon 3.3 µg/ml of fibronectin-coated tissue culture plastic with (80,000 cells/cm2) of human aortic smooth muscle cells (SMCs), results in robust microvessel structures observable for several weeks in vitro. Endothelial basal media (EBM-2, Lonza) with 9% v/v fetal bovine serum (FBS) could support viability of both hCB-EPCs and SMCs. Coculture spatial arrangement of hCB-EPCs and SMCs significantly affected network formation with mixed systems showing greater connectivity and increased solution levels of angiogenic cytokines than lamellar systems. We extended this model into a 3D system by encapsulation of a 1 to 1 ratio of hCB-EPC and SMCs (30,000 cells/µl) within hydrogels of PEG-conjugated RGDS adhesive peptide (3.5 mM) and PEG-conjugated protease sensitive peptide (6 mM). Robust hCB-EPC microvessels formed within the gel with invasion up to 150 µm depths and parameters of total tubule length (12 mm/mm2), branch points (127/mm2), and average tubule thickness (27 µm). 3D hCB-EPC microvessels showed quiescence of hCB-EPCs (<1% proliferating cells), lumen formation, expression of EC proteins connexin 32 and VE-cadherin, eNOS, basement membrane formation by collagen IV and laminin, and perivascular investment of PDGFR-β+/α-SMA+ cells. MPCs present in <15% of isolations displayed >98% expression for mural markers PDGFR-β, α-SMA, NG2 and supported hCB-EPC by day 14 of coculture with total tubule lengths near 12 mm/mm2. hCB-EPCs cocultured with MSCs underwent cell loss by day 10 with a 4-fold reduction in CD31/PECAM+ cells, in comparison to controls of hCB-EPCs in SMC coculture. Changing the coculture media to endothelial growth media (EBM-2 + 2% v/v FBS + EGM-2 supplement containing VEGF, FGF-2, EGF, hydrocortisone, IGF-1, ascorbic acid, and heparin), promoted stable hCB-EPC network formation in MSC cocultures over 2 weeks in vitro, with total segment length per image area of 9 mm/mm2. Taken together, these findings demonstrate a tissue engineered system that can be utilized to evaluate vascular progenitor cells for angiogenic therapies.</p> / Dissertation

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Gap junctions are intercellular channels that permit passage of electrical and chemical signals between neighbouring cells. Vascular endothelium typically co-expresses Cx37 and Cx40, but may downregulate its expression of Cx37 (and upregulate Cx43) in response to changes in flow. The specific regulatory roles mediated by vascular endothelial connexins, and the consequences of altered connexin expression, remain unclear. In this study, we hypothesized that Cx37 and Cx40 regulate distinct vascular responses. We further hypothesize that Cx37 is predominantly involved in vascular growth control, whereas vascular growth is not affected by ablation of Cx40 expression. We show herein that Cx37, but not Cx40 or Cx43, suppresses growth of a highly-proliferative cancer cell line by inducing G1 cell cycle accumulation. We further show that Cx37-deficient mice, lacking Cx37's putative growth inhibitory effect on the vasculature, exhibit a more extensive native and post-ischemic collateral circulation, and greater ischemia-induced microvascular density. In addition, Cx37-/- mice demonstrate a functional improvement in recovery over wild-type animals in two models of hindlimb ischemia. By contrast, Cx40-/- mice fail to recover distal limb flow following unilateral hindlimb ischemia, resulting in necrosis. Long-term angiotensin II antagonism normalized post-ischemic hindlimb bloodflow, reduced macrophage infiltration, and delayed (but did not reverse) the necrotic phenotype of these animals. In summary, we show a distinct role for each of the endothelial connexins, Cx37 and Cx40, in regulating post-ischemic vascular responses.

Melflufen (melphalan flufenamide, chemical name L-melphalanyl-p-L-fluorophenylalanine ethyl ester hydrochloride, previously called J1) is a derivative of the classical alkylating agent melphalan. Melflufen is potentiated by hydrolytic cleavage by aminopeptidase N (APN), leading to high intracellular concentrations of alkylating moieties and subsequent cell death. Increased APN expression is associated with the malignant phenotype of several human cancers, including acute myeloid leukemia, lymphoma and ovarian cancer, and plays a functional role in tumor angiogenesis. Therefore investigations of melflufen activity in these malignancies as well as detailed studies of inhibition of angiogenesis are interesting. The aim of this project was to investigate the cytotoxic and antiangiogenic effect, in vitro and in vivo, of melflufen, compared to melphalan and other cytotoxic drugs used in the clinic. We showed that melflufen was more effective than its parental drug melphalan in lymphoma, AML and ovarian cancer in cell lines as well as in primary patient samples. An improved in vitro therapeutic index was demonstrated by an increased cytotoxic activity in the patient samples compared to normal peripheral blood mononuclear cells (PBMCs). Furthermore, melflufen in combination with cytarabine was synergistic in an AML cell line in a sequence-dependent manor. Melflufen was shown effective in several animal models using lymphoma, AML and ovarian cell xenografts (single drug or in combination), including an intraperitoneal ovarian xenograft. Finally, we demonstrated that melflufen had antiangiogenic properties in several different models.

Endometriosis is a common cause of subfertility and pelvic pain, affecting up to 10% of women of reproductive age. It is characterised by the presence of endometrial-like tissue outside the uterus. The development of the disease is still poorly understood and, currently, the diagnosis relies on visualisation of typical lesions during surgery. There is great interest in identifying biomarkers to assist in diagnosis and disease management. Blood vessel development is known to be a crucial feature of endometriosis, but the mechanisms involved in angiogenesis are not well described for this disease. Most vessel development relies on the proliferation and migration of pre-existing endothelial cells. However, there may also be roles for cells derived from peripheral blood (circulating angiogenic cells) and surrounding stromal cells. In this thesis, the contribution of these different cell types to vessel development in endometriosis is assessed. In chapter 2, a robust protocol was optimised to identify circulating angiogenic cells (CACs) with flow cytometry. The reliability of the protocol was verified, and the level of these cells was found not to fluctuate with the menstrual cycle in healthy women (P=0.279, F=1.359, 3 d.f.). In chapter 3, levels of CACs in women with and without endometriosis were found to be equivalent (0.0835% ± 0.0422 compared to 0.0724% ± 0.0414), demonstrating that they have no use as a disease biomarker. In chapter 4, isolation and culture of endothelial cells from the endometrium was attempted. However, a pure culture of endometrial endothelial cells could not be obtained, which may be due to contamination by other cell types or cellular transdifferentiation. Finally, in chapter 5, the contribution of endometrial stromal cells to vessel development was considered. Stromal cells were found not to differentiate towards an endothelial cell phenotype, but were able to participate in tube formation assays. However, the presence of endometriosis did not influence this behaviour.

This thesis considers aspects of modelling solid tumours. We begin by considering the common assumption that nutrient or drug concentrations in avascular tumour spheroids are radially symmetric. We derive a simple Poisson equation for biomolecular diffusion into an avascular tumour, but with highly oscillatory boundary conditions due to the surrounding capillary network. We find that the assumption of radial symmetry is legitimate for biomolecules that are taken up in sufficient quantities by proliferating cancer cells; however radially symmetric profiles need not be observed otherwise. We then investigate how the gap between an avascular tumour and the neighbouring vasculature varies as the tumour grows. This is explored by (i) using scaling arguments based on ordinary differential equations, (ii) coupling the rate of oxygen flux from the vasculature to oxygen evolution within the tumour, and (iii) deriving a system of six coupled non-linear partial differential equations modelling the tumour evolution. It is found that as the tumour grows any initial gap between the tumour and neighbouring vasculature closes since there is no mechanism which would sufficiently up-regulate non-cancerous cell proliferation. This is in contrast to the intra-cornea implantation observations, upon which several mathematical models are based. Finally, we study the growth and treatment of a vascular tumour subjected to chemotherapies, particularly when the therapies can exhibit an anti-angiogenic effect and resistance to the therapy is incorporated. A multi-compartment model is derived for the evolution of a tumour undergoing treatment and parameters are estimated, with extensions to incorporate numerous different therapy protocols in the literature. We find that anti-angiogens can be effective, though the appropriate scheduling is counter-intuative and contradicts many standard therapy rules. We conclude that chemotherapy protocol design is very sensitive to the mode of action of the drug and simple general strategies will, in many cases, not be the most effective.

Platelets play a crucial role for blood hemostasis, the process that prevents bleeding. In addition, platelets have been demonstrated to promote cancer progression and cancer related complications like metastasis and thrombosis. Platelets can affect cancer related diseases either directly or by interacting with other blood cells or molecules in the circulation of individuals with cancer. The current thesis addresses the role of platelets in tumor progression and tumor-induced systemic effects of cancer, with a special focus on the effects on the vasculature. In the first paper, the role of platelets in tumor progression in histidine-rich glycoprotein (HRG)-deficient mice was addressed. We report that HRG-deficient mice show enhanced tumor growth, epithelial to mesenchymal transition (EMT) and metastasis. The enhanced platelet activity in the absence of HRG is responsible for the accelerated tumor progression. In the second paper, we demonstrate that platelet-derived PDGFB is a central player to keep the tumor vessels functional. Moreover, in a pancreatic neuroendocrine carcinoma model with PDGFB-deficient platelets, spontaneous liver metastasis was enhanced. With this finding we identify a previously unknown role of platelet derived PDGFB. In the third paper, we found that TBK1 mediates platelet-induced EMT by activation of NF-kB signaling, which suggest that TBK1 contributes to tumor invasiveness in mammary epithelial tumors. In the last paper, we report that the vascular function in organs that are neither affected by the primary tumor, nor represent metastatic sites, is impaired in mice with cancer. We show that tumor-induced formation of intravascular neutrophil extracellular traps (NETs), a fibril matrix consisting of neutrophils with externalized DNA and histones, granule proteases and platelets, are responsible for the impaired peripheral vessel function.

Injury to the spinal cord results in partial or complete loss of sensory perception and motor function. After spinal cord injury (SCI), damaged tissue dies and a cavity will form. This cavity prevents the regeneration of tissue and any functional recovery. One way to address the cavity is the insertion of an electrospun scaffold that our lab has created. This provides a substrate for regenerating tissue to grow on, and it is thought that reestablishing the blood supply within the scaffold will allow cells necessary for regeneration to thrive. This could ultimately lead to meaningful recovery for patients who have suffered SCI. Full spinal cord transections were performed on rats, and the scaffolds were inserted into the lesion site. Two different types of scaffold were tested to see if altering the fiber size in the scaffolds produced more blood vessels, and ultimately better regeneration of tissue.

Pathological angiogenesis is an essential component of tumor growth, development, and metastasis for which few effective therapeutic options exist. Though many cancer therapies target the function of cell surface receptors, mechanisms regulating membrane receptor crosstalk remain unclear. Two important families of receptors in angiogenesis, the Ties and Integrins, respond to the extracellular environment via outside-in and, in the case of Integrins, also inside- out signaling. Recent reports showed that the endothelial specific tyrosine kinase receptor, Tie2, forms complexes with two of the endothelial Integrin heterodimers, α5β1 and αVβ3, providing a convenient mechanism for the integration of extracellular stimuli. Our data confirm the interaction between Integrins and Tie2 and additionally indicate an interaction with the orphan co-receptor Tie1. To elucidate the biological role of these macromolecular complexes, biochemical and biophysical methods including co-immunoprecipitation, FRET microscopy, and cellular based assays were used to follow receptor/Integrin association in response to the Tie2 ligands Angiopoietin-1 and -2 as well as the Integrin ligand fibronectin. Furthermore, structural analysis by small angle x-ray scattering of Tie2-ligand complexes and specific Integrin and Tie complexes are being used to identify the basis for growth factor receptor and Integrin signal transduction.

The cardiovascular system develops through two distinct processes in embryogenesis: vasculogenesis, whereby the primary plexus in the heart is formed along with embryonic and extraembryonic vasculature, and angiogenesis, which begins after vasculogenesis and results in the refinement and maturation of the branched vessel system. In pathological angiogenesis, tumors expand by releasing pro-angiogenic factors in response to hypoxic conditions. The Tie receptors, Tie1 and Tie2, are receptor tyrosine kinases that are integral to angiogenic pathways. A family of Angiopoietins, Ang1-4, have been shown to act as ligands for Tie2, of which Ang1 and Ang2 are best characterized. Activation of the receptor causes dimerization and autophosphorylation, whereby adaptor proteins recognizing the phosphorylated tyrosine activate downstream signaling via their Src homology 2 (SH2) domains. Currently there are no phosphospecific antibodies for Tie2, therefore, identifying critical residues responsible for certain pathways remains difficult. In our study, we aim to use purified SH2 domains of known binding partners to Tie2 to assess the phosphorylation state of the receptor under various cellular conditions and settings, utilizing immunoprecipitation and western blotting. Unexpectedly, we found that Tie2 can bind non-specifically to nickel sepharose when the SH2 proteins were used as antibody mimetics, and was unable to be consistently precipitated in Protein A sepharose when used in conjunction with a monoclonal YFP antibody. Under the latter conditions however we were able to precipitate the SH2 protein itself. When immunoprecipitations were used with cobalt activated IMAC beads, we were able to precipitate Tie2 in overexpressed systems using the SH2 domains of Shp2 N-C and Grb2. As expected, phosphorylation of Tie2 in the presence of its orphan receptor Tie1 was attenuated compared to wild-type levels. Based upon available data, we anticipate this method as a useful tool to assess the phosphorylation state of Tie2 and its signaling pathways in the near future.