Adenovirus vectors targeting α_v integrin or heparan sulfate receptors display different distribution of transgene activity after intramuscular injection

Background: Modification of the fiber proteins in replication-deficient adenoviral (Ad) vectors through incorporation of specific receptor-binding motifs may represent a strategy to enhance their tissue targeting capabilities. Methods: In this study, we compared an unmodified Ad (GV10) with two mutated vectors obtained by insertion of specific target sequences that redirect binding, either toward α_V integrin (RGD) or heparan sulfate (UTV) cellular receptors, for reporter gene expression spatial distribution in the rabbit skeletal muscle. In a first series of experiments, injection volume was kept constant and activity of a lacZ transgene was evaluated 48 h after injection of the Ad vectors at different doses. In separate experiments, the effects of different volumes of injection at a constant dose of Ad vector were monitored. Results: All vectors evaluated showed a significant increase in the number of lacZ-positive muscle segments, with increasing vector dose. However, in muscles treated with the UTV vector, fewer muscle fibers were β-gal-positive than in GV10 or RGD vector treated animals. In fact, total β-gal activity increased in a dose-dependent fashion in the GV10- and RGD-treated muscles, but not in the UTV-treated ones. Remarkably, in samples from UTV-treated animals, a volume-dependent enhancement of transgene expression was observed during experiments performed at the same dose and different injection volumes. Conclusions: The results of the present study demonstrate that altering Ad affinity for cellular receptors modulates the level and distribution of transgene activity, conferring characteristics that may allow for treatment customization.