KDR/Flk-1 is a major regulator of vascular endothelial growth factor-induced tumor development and angiogenesis in murine hepatocellular carcinoma cells.
Vascular endothelial growth factor (VEGF), which is one of the most potent angiogenic factors, has been shown to play a pivotal role in tumor angiogenesis, including hepatocellular carcinoma (HCC). The effects of VEGF are mediated mainly through two distinct receptors, flt-1 and KDR/Flk-1. It has been suggested that KDR/Flk-1 plays an important role in tumor development. However, the role of KDR/Flk-1 in HCC has not been examined. We previously reported that VEGF tightly regulated murine HCC development, based on the results of a study using a retroviral tetracycline-regulated (Retro-Tet) gene expression system. This system allows VEGF gene expression to be manipulated in vivo by providing tetracycline in the drinking water. In the present study, we combined the KDR/Flk-1-specific neutralizing monoclonal antibody (KDR/Flk-1mAb) and the Retro-Tet system to elucidate the role of KDR/Flk-1 in VEGF-induced tumor development and angiogenesis in a murine HCC experimental model. In a xenograft study, tumor augmentation induced by VEGF overexpression was almost abolished by means of KDR/Flk-1mAb treatment, with accompanying inhibition of angiogenesis, KDR/Flk-1 autophosphorylation, but not interference of flt-1 activation. This inhibitory effect was achieved even on established tumors and regardless of whether the tumor size was small or large. On the contrary, KDR/Flk-1mAb treatment significantly increased the apoptosis in the tumor. With orthotopic transplantation, KDR/Flk-1mAb also inhibited HCC development in the liver. These results suggest that KDR/Flk-1 is a major regulator of VEGF-mediated HCC development and angiogenesis not only at the initial stage, but also after the tumor has fully developed.
Yoshiji
H
H
Third Department of Internal Medicine, Nara Medical University, Nara, Japan. yoshijih@naramed-u.ac.jp
Kuriyama
S
S
Hicklin
D J
DJ
Huber
J
J
Yoshii
J
J
Miyamoto
Y
Y
Kawata
M
M
Ikenaka
Y
Y
Nakatani
T
T
Tsujinoue
H
H
Fukui
H
H
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis; D002455:Cell Division; D016228:Endothelial Growth Factors / Q000235:genetics / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D007074:Immunoglobulin G / Q000494:pharmacology; D008114:Liver Neoplasms, Experimental / Q000098:blood supply* / Q000473:pathology* / Q000503:physiopathology; D008222:Lymphokines / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009389:Neovascularization, Pathologic; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000235:genetics; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D017978:Receptors, Growth Factor / Q000502:physiology*; D011975:Receptors, Mitogen / Q000502:physiology; D040262:Receptors, Vascular Endothelial Growth Factor; D013752:Tetracycline / Q000494:pharmacology; D013753:Tetracycline Resistance / Q000235:genetics; D014162:Transfection; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D001616:beta-Galactosidase / Q000235:genetics
D000911:Antibodies, Monoclonal; D016228:Endothelial Growth Factors; D007074:Immunoglobulin G; D008222:Lymphokines; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D017978:Receptors, Growth Factor; D011975:Receptors, Mitogen; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D020794:Receptor Protein-Tyrosine Kinases; D040262:Receptors, Vascular Endothelial Growth Factor; D001616:beta-Galactosidase; D013752:Tetracycline