Modified adenoviruses for cancer gene therapy

Adenoviral gene therapy is an exciting novel approach for treating cancers resistant to currently available therapies. However, currently there is little evidence supporting significant clinical benefits with replication-incompetent adenoviruses. Recent data suggest that expression of the primary receptor, the coxsackie-adenovirus receptor (CAR), may be highly variable on tumor cells, resulting in resistance to infection. Consequently, various strategies have been evaluated to modify adenovirus tropism in order to circumvent CAR deficiency, including retargeting complexes or genetic capsid modifications. To improve tumor penetration and local amplification on the antitumor effect, selectively oncolytic agents, i.e., conditionally replicating adenoviruses, have been constructed. Infection of tumor cells results in replication, oncolysis and subsequent release of the virus progeny. Normal tissue is spared due to lack of replication. This review focuses on the various modifications that have been investigated for improving the antitumor effect of adenoviral gene therapy. (C) 2004 Wiley-Liss, Inc.