Recombinant adenovirus is one of the most widely used viral vectors for gene delivery. This study was designed to evaluate the ability of chitosan, a cationic, linear polysaccharide composed of β(1,4) linked glucosamine partly containing N-acetyl-glucosamine, to enhance the in vitro infectivity of adenovirus to mammalian cells. Wild type and a fiber-mutant replication-defective recombinant adenoviruses expressing β-galactosidase were used. In the latter, an RGD peptide, the binding site for αvβ3 and αvβ5 integrin, was introduced in the fiber knob enabling adenovirus receptor-independent viral infection. Enhanced effect of chitosan on the infectivity of both adenoviruses was observed in Chinese hamster ovary cells that do not express the receptor for adenovirus with β-galactosidase activity assay and x-gal staining. These data indicate the receptor-independent mechanism(s) for this enhancement effect. In addition, we found that pH of the culture medium, and molecular mass and concentration of chitosan are also critical factors. Thus, the highest effect was obtained with 0.1-1μg/ml of chitosan with molecular mass of 19K and 40K in the culture medium of pH 6.4; on the other hand, the effect was negligible with the higher chitosan concentrations (10μg/ml or more), lower or higher molecular mass (11K and 110K) of chitosan, or at pH of 7.4. Studies using several cell lines with variable levels of adenoviral infectivity revealed that this enhanced effect is evident in the cells with poor infectivity to adenovirus. Since chitosan is biocompatible and inexpensive, these data indicate that chitosan may be a potential candidate for a non-viral vector to safely increase adenoviral infectivity to mammalian cells, particularly those with poor susceptibility to adenoviral infection.
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