Abstract
Recombinant adenovirus (Ad) has emerged as the vector system of choice in cancer gene therapy. Its full utility, however, has been limited because of the low efficiency of adenovirus-mediated gene transfer to cancer cells - the main reason being that cancer cells in general express inherently low levels of the coxsackie and adenovirus receptor (CAR) on their surface. Development of novel strategies to achieve adenovirus infection in a CAR-independent manner may help to overcome this limitation. To this end, we have generated a novel recombinant Ad, dl-VSVG-LacZ, that contains a fiber knob with intact CAR entry capability and an additional phosphatidylserine (PS) entry capability. This was achieved by incorporating the vesicular stomatitis virus glycoprotein (VSV-G) epitope onto the C terminus of the fiber knob. VSV-G is an envelope protein that facilitates the specificity for binding of the virus to PS moieties on the cellular plasma membrane. The newly tropism-expanded adenovirus, dl-VSVG-LacZ, showed a remarkable improvement (3- to 20-fold) in the delivery of LacZ to a variety of mammalian cells including those that were CAR deficient. The greatest improvement in gene transfer was observed in cells that were difficult to transduce with an untargeted Ad (wildtype fiber). Furthermore, treatment with dl-VSVG-LacZ significantly enhanced gene transfer in vivo when compared with control adenovirus that lacked the VSV-G epitope. Taken together, these studies demonstrate that the strategy to extend adenovirus tropism may greatly improve the utility of adenovirus in gene therapy applications.
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