title: Measuring VEGF-Flk-1 activity and consequences of VEGF-Flk-1 targeting in vivo using intravital microscopy: clinical applications.
abstract: Vascular endothelial growth factor (VEGF)-Flk-1/KDR tyrosine kinase signaling pathway plays a pivotal role in tumor angiogenesis. Targeting this angiogenic signaling pathway presents a promising alternative for the treatment of neoplasms. However, recent experimental and clinical studies have suggested that VEGF-Flk-1/KDR activity is unevenly distributed throughout the tumor microvasculature. To further evaluate this phenomenon, the regional differences in VEGF-Flk-1/KDR signaling activities in vivo were studied using intravital fluorescence videomicroscopy in an experimental murine brain tumor model. Regional VEGF-Flk-1/KDR was assessed using the small molecule inhibitor SU5416, which selectively inhibits the tyrosine kinase receptor Flk-1. C(6) glioblastoma cells were implanted into the dorsal skinfold chamber preparation of nude mice. The process of tumor vascularization was repeatedly assessed over 22 days. SU5416 treatment resulted in a significant reduction in tumor vascular density (p<0.05). Regional microvascular evaluation indicated that the magnitude of this antiangiogenic effect was pronounced in the more angiogenic and better vascularized peritumoral areas than in the intratumoral areas of the tumor microvasculature. These results demonstrate regional differences in Flk-1 activity in vivo that may have significant impact on the susceptibility of tumors to compounds that target VEGF-Flk-1/KDR. This finding should be considered in upcoming clinical trials targeting individual signal transduction systems in cancer patients.
authors.affiliation: Department of Neurosurgery, Klinikum Mannheim, University of Heidelberg, Mannheim, Germany. peter.vajkoczy@nch.ma.uni.heidelberg.de
authors.forename: P
authors.initials: P
authors.lastname: Vajkoczy
authors.forename: A
authors.initials: A
authors.lastname: Thurnher
authors.forename: K P
authors.initials: KP
authors.lastname: Hirth
authors.forename: L
authors.initials: L
authors.lastname: Schilling
authors.forename: P
authors.initials: P
authors.lastname: Schmiedek
authors.forename: A
authors.initials: A
authors.lastname: Ullrich
authors.forename: M D
authors.initials: MD
authors.lastname: Menger
mesh_terms: D000704:Analysis of Variance; D020533:Angiogenesis Inhibitors / Q000627:therapeutic use; D000818:Animals; D004195:Disease Models, Animal; D016228:Endothelial Growth Factors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000627:therapeutic use; D005909:Glioblastoma / Q000098:blood supply / Q000188:drug therapy / Q000378:metabolism; D007211:Indoles / Q000008:administration & dosage / Q000627:therapeutic use; D008222:Lymphokines / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008833:Microcirculation / Q000187:drug effects; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000378:metabolism; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011758:Pyrroles / Q000008:administration & dosage / Q000627:therapeutic use; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017978:Receptors, Growth Factor / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011975:Receptors, Mitogen / Q000037:antagonists & inhibitors / Q000378:metabolism*; D040262:Receptors, Vascular Endothelial Growth Factor; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D012878:Skin Neoplasms / Q000098:blood supply / Q000188:drug therapy / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
chemical_list: D020533:Angiogenesis Inhibitors; D016228:Endothelial Growth Factors; D004791:Enzyme Inhibitors; D007211:Indoles; D008222:Lymphokines; D020033:Protein Isoforms; D011758:Pyrroles; D017978:Receptors, Growth Factor; D011975:Receptors, Mitogen; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; C116890:Semaxinib; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases; D040262:Receptors, Vascular Endothelial Growth Factor