Noninvasive assessment of regulable transferred-p53 gene expression and evaluation of therapeutic response with FDG-PET in tumor model

The use of tumor-suppressor gene p53 as an anticancer therapeutic has been vigorously investigated. However, progress has met with limited success to date. Some major drawbacks are the difficulty in achieving controllable and efficient gene transfer as well as in analyzing the transferred gene expression in real time and the treatment response in a timely manner. Thus, development of novel gene transfer vector with a regulative gene expression system coupled with the reporter gene, by which transgene can be monitored simultaneously, is critical. Moreover, noninvasive imaging-based assessment of the therapeutic response to exogenous wild-type p53 gene transfer is crucial for refining treatment protocols. In this study, as a simple preclinical model, we constructed a doxycycline-regulated bidirectional vector harboring a reporter gene encoding red fluorescence protein and p53. Then, we determined the controllable and simultaneously coordinated expression of both proteins and the p53-mediated anticancer effects in vitro and in vivo. Next, we observed that cells or tumors with induced p53 overexpression exhibited decreased uptake of [(14)C]FDG in cellular assay and [(18)F]FDG in positron emission tomography (PET) imaging. Thus, by coupling with bidirectional vector, controllable p53 transfer was achieved and the capability of fluoro-2-deoxy-D-glucose (FDG)-PET to assess the therapeutic response to p53 gene therapy was evidently confirmed, which may have an impact on the improvement of p53 gene therapy.

Visualization of in vivo electroporation-mediated transgene expression in experimental tumors by optical and magnetic resonance imaging

In vivo electroporation (EP) is an efficient method for effective gene transfer and is highly expected for application in anticancer gene therapy. Non-invasive monitoring of gene transfer/expression is critical for optimal gene therapy. Here we report in vivo optical and high-field magnetic resonance imaging (MRI) of EP-mediated transgene expression in a tumor model. Initially, we observed spatio-temporal change in in vivo EP-mediated transgene expression by optical imaging using red fluorescence protein (RFP) as a reporter gene. Next, we constructed a dual-reporter plasmid carrying a gene-encoding MRI reporter ferritin heavy chain and RFP gene to visualize the intratumoral transgene expression by dual modality. Cells transfected with this plasmid showed lower signal intensity on in vitro T(2)-weighted cellular MRI and quantitatively increased the transverse relaxation rate (1/T(2)) compared with control cells. After conducting in vivo EP in an experimental tumor, the plasmid-injected region showed both fluorescent emissions in optical imaging and detectably lowered signal on T(2)-weighted MRI. The correlative immunohistological findings confirmed that both the reporter transgenes were co-expressed in this region. Thus, our strategy provides a platform for evaluating EP-mediated cancer gene therapy easily and safely without administering contrast agent or substrate.