Improved Gene Delivery and In Vivo Imaging

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Gene therapy is currently limited by the lack of a non-invasive and clinically useful means to monitor vector persistence and biodistribution and transgene expression in vivo. The goal of the current project is to test strategies devised to improve the spatial distribution of gene expression following the local administration of adenovirus-mediated gene therapy so that the entire organ receives a viral dose sufficient for clinical efficacy with as little virus as possible (to limit toxicity). A new reporter gene based on the sodium iodide symporter (NIS) will be characterized with regard to its ability to monitor therapeutic gene expression and contrasted with other measurements of catalytic activity under development. There are three specific aims of the proposed studies. 1. Compare the distribution of NIS reporter gene expression to that of CD/HSV-1 TK therapeutic gene expression. If it can be shown that NIS activity is a surrogate marker of therapeutic gene expression, NIS imaging could eliminate the biopsy currently used to assess transgene expression and allow for dynamic and whole body monitoring of transgene expression. 2. Evaluate new vector formulations and injections conditions designed to optimize placement of the adenovirus within the prostate to obtain maximal organ coverage. This work will provide the scientific basis for a clinical trial described in Project 3. 3. Contrast the prodrug-labeled approach of monitoring transgene expression to the NIS approach. This aim tests the hypothesis that the bystander effect can be measured and exceeds the area of gene expression. Bystander effect will be measured using autoradiography of bound radiolabeled prodrugs ([3H]-ganciclovir-MP, [14C]-5-FdUMP) and compared to iodide localization following transduction of NIS. Finally the measurements will be extended to non-invasive techniques using [19F]-MR chemical shift imaging of 5-FU and 123(I)uptake using SPECT imaging of NIS activity. A large animal model is needed for the proposed studies. We plan to use the prostates of large, mongrel dogs. The studies described represent "proof of principle" and will generate significant new knowledge that will benefit the gene therapy and medical communities.