Cancer gene therapy using a novel adeno-associated virus vector expressing human wild-type p53

Previous studies have indicated that transfer of wild-type (wt) p53 cDNA into cancer cells can suppress the tumor phenotype in vitro and in vivo. In this study we examined the effects of wt p53 transduction in the human cancer cell line H-358 (that bears a homozygous deletion of p53) using a novel recombinant adeno-associated viral vector engineered to express wt p53 (rAAVp53). Western blot analysis demonstrated the expression of wt p53 in H-358 cells following infection with rAAVp53. Furthermore, rAAVp53 inhibited the growth of the neoplastic cells and also mediated cytotoxicity. Cell cycle analysis of rAAVp53-infected cells showed a significant increase in the percentage of cells arrested at the G1-S checkpoint. H-358 cells infected with rAAVp53 underwent apoptosis as demonstrated by the morphological appearance of DAPI-stained nuclei. Direct injection of rAAVp53 into H-358 tumors implanted subcutaneously in immunodeficient nu/nu mice inhibited tumor growth completely in three of the five animals tested. Mock-infected and rAAV control treated tumors showed no growth inhibition. In situ staining in nu/nu mice detected the presence of wild-type p53 protein in residual tumor cells following rAAVp53 administration. The impressive in vivo efficacy of the rAAVp53 suggests a bystander effect. We conclude that rAAV may be effective as a gene transfer vector in the delivery of p53 to cancer cells.