Homologous recombination-based adenovirus vector system for tumor cell-specific gene delivery

Cancer gene therapy requires tumor-specific delivery and expression of a transgene to maximize antitumor efficacy and minimize side effects. In this study, we developed a new tumor-targeting, homologous recombination-based adenovirus vector system, HRAVS. HRAVS is composed of two adenovirus vectors, Ad.CMV.IR containing reverse sequence (IR) and a CMV promoter and Ad.IR.EGFP comprising the report gene EGFP and IR. For improved viral DNA replication and transgene expression, the E1a gene was added to HRAVS to generate the enhanced HRAVS, EHRAVS, which consists of Ad.CMV.IR and Ad.IR.EGFP/E1a. The optimal vector composition ratio of Ad.CMV.IR to Ad.IR.EGFP or Ad.IR.EGFP/E1a was identified as 30:70 based on EGFP expression efficiency in tumor cells. The transgene expression of HRAVS and EHRAVS was efficiently and specifically activated in tumor cells only and not in normal cells. Moreover, compared with HRAVS, EHRAVS infection led to higher virus yields and transgene expression and higher toxicity to tumor cells, and these results could be related to the involvement of E1a genes. The results in present study suggest the need for in vivo antitumor study using these new dual-Ad vector systems based on the homologous recombination.