Engineering polypeptide-coated adenoviral gene delivery vectors for systemic cancer therapy

We sought to modify adenoviral (Ad) particles by incorporating the advantageous characteristics of non-viral gene delivery vehicles to complement the viral vectors. alpha-Amino acid-N-carboxyanhydride chemistry was used to synthesize homopolypeptides and diblock copolypeptides that possess well-defined secondary structures. Using cryoelectron, confocal and fluorescence microscopy, we showed that these polypeptides can coat the surfaces of Ad particles in a non-covalent manner to modify their transduction properties. The coated Ad particles were found to bind to and be internalized by cells. In contrast to reports using covalently PEGylated Ad particles, we found that our physically coated Ad hybrid complexes facilitate gene transfer both in vitro and in vivo. We showed that our polypeptide coating was able to shield the Ad particles from the neutralizing effect of antibodies and mitigate the binding of blood coagulation factor (Factor X) in vitro. We also showed that the association of Ad and coated Ad vectors with erythrocytes was not deleterious to the infectivity of the vectors. The biodistribution of the systemically administered hybrid complexes mirrored the behavior of non-viral vectors, where the hybrid complexes were found to divert partially away from the liver and accumulate in the lungs. These data demonstrated that our non-covalent modification of Ad was able to alter its interactions with cells and organs with retention of transduction efficiency. Combined with the transcriptional regulation of the two-step transcriptional amplification (TSTA) system, our hybrid complexes were found to exhibit tumor-specificity with enhanced transduction of lung tissue. The persistence of our hybrid complexes in mediating transgene expression in immune-competent mice indicated a delayed clearance by innate immune mechanisms. Advantages such as facile coating of the Ad vector, design flexibility and ease of attaching ligands to the polypeptides make this system potentially useful as a platform for adding functionalities to Ad to target cancer metastasis.