Cytotoxicity of VEGF121/rGel on vascular endothelial cells resulting in inhibition of angiogenesis is mediated via VEGFR-2
1 Departments of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA
2 Departments of Neuro-Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA
3 Departments of Experimental Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA
4 Departments of Pathology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA
5 Department of Medical Microbiology and Immunology, Southern Illinois University, School of Medicine, Springfield, IL, USA
6 Department of Cardiology and Angiology, University Hospital Münster, Münster, Germany
7 Simmons Comprehensive Cancer Center, The University of Texas Southwestern Medical Center, Dallas, TX, USA
8 The University of Texas Southwestern Medical Center, Dallas, TX, USA
9 GlycoFi/Merck & Co., Inc., Lebanon, NH, USA
BMC Cancer 2011, 11:358 doi:10.1186/1471-2407-11-358Published: 17 August 2011
The fusion protein VEGF121/rGel composed of the growth factor VEGF121 and the plant toxin gelonin targets the tumor neovasculature and exerts impressive anti-vascular effects. We have previously shown that VEGF121/rGel is cytotoxic to endothelial cells overexpressing VEGFR-2 but not to endothelial cells overexpressing VEGFR-1. In this study, we examined the basis for the specific toxicity of this construct and assessed its intracellular effects in vitro and in vivo.
We investigated the binding, cytotoxicity and internalization profile of VEGF121/rGel on endothelial cells expressing VEGFR-1 or VEGFR-2, identified its effects on angiogenesis models in vitro and ex vivo, and explored its intracellular effects on a number of molecular pathways using microarray analysis.
Incubation of PAE/VEGFR-2 and PAE/VEGFR-1 cells with 125I-VEGF121/rGel demonstrated binding specificity that was competed with unlabeled VEGF121/rGel but not with unlabeled gelonin. Assessment of the effect of VEGF121/rGel on blocking tube formation in vitro revealed a 100-fold difference in IC50 levels between PAE/VEGFR-2 (1 nM) and PAE/VEGFR-1 (100 nM) cells. VEGF121/rGel entered PAE/VEGFR-2 cells within one hour of treatment but was not detected in PAE/VEGFR-1 cells up to 24 hours after treatment. In vascularization studies using chicken chorioallantoic membranes, 1 nM VEGF121/rGel completely inhibited bFGF-stimulated neovascular growth. The cytotoxic effects of VEGF121/rGel were not apoptotic since treated cells were TUNEL-negative with no evidence of PARP cleavage or alteration in the protein levels of select apoptotic markers. Microarray analysis of VEGF121/rGel-treated HUVECs revealed the upregulation of a unique "fingerprint" profile of 22 genes that control cell adhesion, apoptosis, transcription regulation, chemotaxis, and inflammatory response.
Taken together, these data confirm the selectivity of VEGF121/rGel for VEGFR-2-overexpressing endothelial cells and represent the first analysis of genes governing intoxication of mammalian endothelial cells by a gelonin-based targeted therapeutic agent.