Tumor angiogenesis appears to be achieved by the expression of vascular endothelial growth factor (VEGF)
within solid tumors that stimulate host vascular endothelial cell mitogenesis and possibly chemotaxis. VEGF’s
angiogenic actions are mediated through its high-affinity binding to 2 endothelium-specific receptor tyrosine
kinase, Flt-1 (VEGFR1), and Flk-1/KDR (VEGFR2). RNA interference-mediated knockdown of protein expression
at the messenger RNA level provides a new therapeutic strategy to overcome various diseases. To achieve
high efficacy in RNA interference-mediated therapy, it is critical to develop an efficient delivering system to
deliver small interference RNA (siRNA) into tissues or cells site-specifically. We previously reported an angiogenic
endothelial cell-targeted polymeric gene carrier, PEI-g-PEG-RGD. This targeted carrier was developed
by the conjugation of the anb3/anb5 integrin-binding RGD peptide (ACDCRGDCFC) to the cationic polymer,
branched polyethylenimine, with a hydrophilic polyethylene glycol (PEG) spacer. In this study, we used PEI-gPEG-RGD
to deliver siRNA against VEGFR1 into tumor site. The physicochemical properties of PEI-g-PEGRGD/siRNA
complexes was evaluated. Further, tumor growth profile was also investigated after systemic
administration of PEI-g-PEG-RGD/siRNA complexes.