Intratumoral spread and increased efficacy of a p53-VP22 fusion protein expressed by a recombinant adenovirus

In vitro experiments have demonstrated intercellular trafficking of the VP2 2 tegument protein of herpes simplex virus type 1 from infected cells to ne ighboring cells, which internalize VP22 and transport it to the nucleus. VP 22 also can mediate intercellular transport of fusion proteins, providing a strategy for increasing the distribution of therapeutic proteins in gene t herapy. Intercellular trafficking of the p53 tumor suppressor protein was d emonstrated in vitro using a plasmid expressing full-length p53 fused in-fr ame to full-length VP22. The p53-VP22 chimeric protein induced apoptosis bo th in transfected tumor cells and in neighboring cells, resulting in a wide spread cytotoxic effect. To evaluate the anti-tumor activity of p53-VP22 in vivo, we constructed recombinant adenoviruses expressing either wild-type p53 (FTCB) or a p53-VP22 fusion protein (FVCB) and compared their effects i n p53-resistant tumor cells. In vitro, treatment of tumor cells with FVCB r esulted in enhanced p53-specific apoptosis compared to treatment with equiv alent doses of FTCB. However, in normal cells there was no difference in th e dose-related cytotoxicity of FVCB compared to that of FTCB. In vivo, trea tment of established tumors with FVCB was more effective than equivalent do ses of FTCB. The dose-response curve to FVCB was flatter than that to FTCB; maximal antitumor responses could be achieved using FVCB at doses I log lo wer than those obtained with FTCB. Increased antitumor efficacy was correla ted with increased distribution of p53 protein in FVCB-treated tumors. This study is the first demonstration that VP22 can enhance the in vivo distrib ution of therapeutic proteins and improve efficacy in gene therapy.