Mutation in fiber of adenovirus serotype 5 gene therapy vector decreases liver tropism

Recombinant adenovirus (Ad) vectors are widely used for both in vitro and in vivo gene transfer. However, intravenous administration of Ad vectors results mainly in hepatocyte transduction and subsequent hepatotoxicity. Coxsackie-adenovirus receptor (CAR) and αvβ integrins, which are functional receptors for the fiber and penton proteins, respectively, are the tropism determinants of Ad type 5 (Ad5). We previously developed a system for rapid construction of fiber-modified Ad5 vectors. We also constructed a fiber-modified Ad5 containing an Arg-Gly-Asp (RGD) motif in the HI-loop and showed that it could enhance anti-tumor effects in vitro and in vivo. Here, we constructed a novel Ad5 vector containing two amino acid mutations in the AB loop of the fiber-modified Ad5 fiber knob and showed that it could significantly reduce liver tropism and increase gene transfer in low-CAR or CAR-deficient cancer cells following intravascular delivery. However, anti-tumor effects of the fiber-mutated Ad5 expressing HSV-TK under control of the hTERT promoter was not found when compared with an unmodified Ad5 vector in cancer lines expressing different levels of CAR, likely due to the activity of the hTERT promoter being lower than that of the CMV promoter. Nevertheless, this study describes an enhanced Ad5 vector for intravascular gene delivery, and further modifications such as changes in the promoter may facilitate the development of this vector for cancer treatment.