Enhanced Gene Transfer to Rabbit Jugular Veins by an Adenovirus Containing a Cyclic RGD Motif in the HI Loop of the Fiber Knob

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Abstract
Gene therapy using recombinant adenoviral vectors represents a promising therapeutic tool to prevent vein graft stenosis, the main complication of coronary artery bypass grafting. However, the low transduction efficiency of vascular smooth muscle cells and endothelial cells (EC) is a potential limitation, presumably due to the low levels of functional adenovirus receptor (coxsackie:adenovirus receptor; CAR). Designing vectors specifically targeted to alpha(v) integrins is a strategy that might overcome the poor expression of CAR in vascular smooth muscle cells and EC. RGD, a receptor-binding motif that can interact with alpha(v) integrins, was inserted into the HI loop and at the C-terminus of the adenoviral fiber protein in two separate adenovirus vectors encoding a beta-galactosidase reporter gene. Av1nBgCRGD (C-terminus) and Av1nBgHIRGD (HI loop) were evaluated in EC in culture and in jugular vein organ culture. Transduction of primary rat and rabbit EC with Av1nBgHIRGD was significantly more efficient when compared to Av1nBgCRGD or Av1nBg. Transduction of mouse, rat and rabbit jugular veins in organ culture using Av1nBg showed that adenovirus-mediated gene expression was greatest in rabbit jugular veins compared to rat and mouse veins. Av1nBgHIRGD augmented gene expression approximately four-fold in rabbit jugular veins when compared to Av1nBg. Histochemical analysis showed that numerous EC but few smooth muscle cells were transduced at all vector concentrations. A substantial number of adventitial fibroblasts were transduced only at the highest vector concentrations of Av1nBgHIRGD. These findings demonstrate that integrin-targeted vectors allow for enhanced gene delivery to veins and strengthen the viability of adenoviral-mediated gene transfer of therapeutic transgenes to human veins prior to vein grafting.