Targeting Of Tumor Neovasculature Research Articles

Cancer siRNA therapy by tumor selective delivery with ligand-targeted sterically stabilized nanoparticle.

Potent sequence selective gene inhibition by siRNA 'targeted' therapeutics promises the ultimate level of specificity, but siRNA therapeutics is hindered by poor intracellular uptake, limited blood stability and non-specific immune stimulation. To address these problems, ligand-targeted, sterically stabilized nanoparticles have been adapted for siRNA. Self-assembling nanoparticles with siRNA were constructed with polyethyleneimine (PEI) that is PEGylated with an Arg-Gly-Asp (RGD) peptide ligand attached at the distal end of the polyethylene glycol (PEG), as a means to target tumor neovasculature expressing integrins and used to deliver siRNA inhibiting vascular endothelial growth factor receptor-2 (VEGF R2) expression and thereby tumor angiogenesis. Cell delivery and activity of PEGylated PEI was found to be siRNA sequence specific and depend on the presence of peptide ligand and could be competed by free peptide. Intravenous administration into tumor-bearing mice gave selective tumor uptake, siRNA sequence-specific inhibition of protein expression within the tumor and inhibition of both tumor angiogenesis and growth rate. The results suggest achievement of two levels of targeting: tumor tissue selective delivery via the nanoparticle ligand and gene pathway selectivity via the siRNA oligonucleotide. This opens the door for better targeted therapeutics with both tissue and gene selectivity, also to improve targeted therapies with less than ideal therapeutic targets.

Tumor-targeting properties of antibody-vascular endothelial growth factor fusion proteins.

A major problem of antibody-based targeting of solid tumors is the poor penetration of antibodies into tumor tissue. Vasoactive immunoconjugates have been proposed as a means of increasing antibody uptake in tumors. In principle, VEGF (also known as vascular permeability factor) could selectively alter vascular permeability, leading to improved tumor targeting. A possible role for VEGF in the targeting of tumor neovasculature has been postulated, based on the overexpression of VEGF receptors in tumor endothelial cells. However, quantitative biodistribution studies on this topic are not available. In this report, we describe the cloning, expression, characterization and biodistribution in tumor-bearing mice of antibodies fused to either VEGF(120) or VEGF(164) The MAb fragments chosen for analysis were scFv(L19), specific for the ED-B domain of fibronectin, a marker of angiogenesis, and scFv(HyHEL-10), a negative control antibody of irrelevant specificity in mice. Neither unconjugated VEGF nor scFv(HyHEL-10)-VEGF fusion proteins showed accumulation in the tumor (tumor:blood ratios approx. 1 at 4 hr and 24 hr postinjection). By contrast, scFv(L19)-VEGF(120) but not scFv(L19)-VEGF(164) showed significant accumulation in tumors (tumor:blood ratio = 9.3 at 24 hr) but was not superior to unconjugated scFv(L19). Preinjection of unlabeled scFv(L19)-VEGF(120) prior to administration of radiolabeled fusion protein led to increased accumulation of radiolabeled scFv(L19)-VEGF(120) in the tumor but only at very high concentrations (20 microg/mouse).