Although the systemic administration of a number of different gene products has been shown to result in the inhibition of angiogenesis and tumor growth in different animal tumor models, the relative potency of those gene products has not been studied rigorously. To address this issue, recombinant adenoviruses encoding angiostatin, endostatin, and the ligand-binding ectodomains of the vascular endothelial growth factor receptors Flk1, Flt1, and neuropilin were generated and used to systemically deliver the different gene products in several different preexisting murine tumor models. Single i.v. injections of viruses encoding soluble forms of Flk1 or Flt1 resulted in Ϸ80% inhibition of preexisting tumor growth in murine models involving both murine (Lewis lung carcinoma, T241 fibrosarcoma) and human (BxPC3 pancreatic carcinoma) tumors. In contrast, adenoviruses encoding angiostatin, endostatin, or neuropilin were significantly less effective. A strong correlation was observed between the effects of the different viruses on tumor growth and the activity of the viruses in the inhibition of corneal micropocket angiogenesis. These data underscore the need for comparative analyses of different therapeutic approaches that target tumor angiogenesis and provide a rationale for the selection of specific antiangiogenic gene products as lead candidates for use in gene therapy approaches aimed at the treatment of malignant and ocular disorders.

Spatio-temporal studies on the growth of capillary blood vessels and capillary lymphatic vessels in tissue remodeling have suggested that lymphangiogenesis is angiogenesis-dependent. We revisited this concept by using fibroblast growth factor 2 (FGF-2) (80 ng) to stimulate the growth of both vessel types in the mouse cornea. When we lowered the dose of FGF-2 in the cornea 6.4-fold (12.5 ng), the primary response was lymphangiogenic. Further investigation revealed that vascular endothelial growth factor-C and -D are required for this apparent lymphangiogenic property of FGF-2, and when the small amount of accompanying angiogenesis was completely suppressed, lymphangiogenesis remained unaffected. Our findings demonstrate that there is a dose-dependent response of FGF-2 for lymphangiogenesis, and lymphangiogenesis can occur in the absence of a preexisting or developing vascular bed, i.e., in the absence of angiogenesis, in the mouse cornea.

Abstract-Notch signaling is critically important for proper architecture of the vascular system, and mutations in NOTCH3 are associated with CADASIL, a stroke and dementia syndrome with vascular smooth muscle cell (VSMC) dysfunction.In this report, we link Notch signaling to platelet-derived growth factor (PDGF) signaling, a key determinant of VSMC biology, and show that PDGF receptor (PDGFR)-␤ is a novel immediate Notch target gene. PDGFR-␤ expression was upregulated by Notch ligand induction or by activated forms of the Notch receptor. Moreover, upregulation of PDGFR-␤ expression in response to Notch activation critically required the Notch signal integrator CSL. In primary VSMCs, PDGFR-␤ expression was robustly upregulated by Notch signaling, leading to an augmented intracellular response to PDGF stimulation. In newborn Notch3-deficient mice, PDGFR-␤ expression was strongly reduced in the VSMCs that later develop an aberrant morphology. In keeping with this, PDGFR-␤ upregulation in response to Notch activation was reduced also in Notch3-deficient embryonic stem cells. Finally, in VSMCs from a CADASIL patient carrying a NOTCH3 missense mutation, upregulation of PDGFR-␤ mRNA and protein in response to ligand-induced Notch activation was significantly reduced. In sum, these data reveal a hierarchy for 2 important signaling systems, Notch and PDGF, in the vasculature and provide insights into how dysregulated Notch signaling perturbs VSMC differentiation and function. Key Words: PDGF Ⅲ VSMC Ⅲ CADASIL Ⅲ vasculogenesis Ⅲ angiogenesis T he vasculature is formed by an initial aggregation of angioblasts during vasculogenesis, followed by remodeling of the primitive vascular plexus through angiogenesis. 1,2 Recruitment of mural cells, which differentiate to vascular smooth muscle cells (VSMCs) and pericytes, to the endothelial tube is required for stabilization of the vessels. 3 Endothelial and mural cell differentiation is controlled by several key signaling pathways, including PDGF and Notch signaling, 2 and, in this study, we addressed the interrelationship between Notch and PDGF signaling in VSMCs.PDGF signaling is critical for several steps in vascular development and for the homeostasis of blood vessels. There are 4 different genes encoding PDGF ligands (PDGFA through -D), and 2 genes encoding PDGF receptors (PDGFRs) (PDGFR-␣ and -␤). PDGFRs are receptor tyrosine kinases that, on interaction with ligand, activate several intracellular signaling pathways, including phosphatidylinositol 3-kinase and mitogen-activated protein kinase signaling. 4 Loss-of-function analysis has revealed the importance for PDGF-BB/ PDGFR-␤ signaling in vascular development. Mice in which the PDGF-B or PDGFR-␤ gene has been targeted are embryonic lethal, and the phenotypes support a model where endothelial cells, through secretion of PDGF-BB, stimulate proliferation and recruitment of PDGFR-␤ positive mural cells during embryonic development. 5,6 PDGF signaling plays an important role also in restenosis in response to angioplasty. 7 N...