Targeting of endothelial KDR receptors with 3G2 immunoliposomes in vitro

Immunoliposomes (IL) containing anti-angiogenic drugs directed selectively to the easily accessible kinase insert domain containing receptor (KDR) vas cular endothelial growth factor (VEGF), which is predominantly expressed on tumour vessels are a promising tool to inhibit tumour angiogenesis. To exp lore this strategy, we have prepared fluorescent-labelled IL presenting ant ibodies against the KDR receptor (3G2) on their surface. 3G2-IL were compos ed of egg phosphatidylcholine and cholesterol (6:4), containing 2 mol% of t he new thiol reactive linker lipid O-(3-cholesteryloxycarbonyl)propionyl-O' -maleimido-benzoyl tetraethylene glycol. Specific binding of 3G2-IL to immo bilised recombinant KDR was used to show the maintenance of sufficient immu noreactivity of 3G2 antibodies upon the coupling procedure. 3G2-IL bound to Chinese hamster ovarian (CHO) cells stably transfected to overexpress KDR to a five times higher amount as compared to mock-transfected CHO cells. Su bsequently, specific binding of 3G2-IL to KDR could also be demonstrated on KDR expressing cells, human umbilical vein endothelial cells and human mic rovascular endothelial cells, whereas only low binding of 3G2-IL to NIH-3T3 mouse fibroblast cells, which do not express KDR, was found. The binding o f 3G2-IL to KDR receptors could not be blocked by VEGF, suggesting that the binding site for VEGF is not identical with the epitope recognised by 3G2, We could demonstrate that 3G2-IL is able to bind in vitro even in the pres ence of high levels of VEGF. (C) 2000 Elsevier Science B.V. All rights rese rved.