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 plasmidinjected 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.

Malignant mesothelioma (MM) is a fatal malignancy with a rapidly increasing incidence in industrialized countries because of the widespread use of asbestos in the past centuries. Early diagnosis of MM is critical for a better prognosis, but this is often difficult because of the lack of disease-specific diagnostic imaging. Here, we report that manganese-enhanced magnetic resonance imaging (MEMRI) represents a promising approach for a more selective mesothelioma imaging by monitoring a high-level expression of manganese-superoxide dismutase (Mn-SOD), which is observed in many MM. We found that most human MM cells overexpressed Mn-SOD protein compared with human mesothelial cells and that NCI-H226 human MM cells highly expressed Mn-SOD and augmented Mn accumulation when loaded with manganese chloride (MnCl 2 ). The cells showed marked T 1 -signal enhancement on in vitro MRI after incubation with MnCl 2 because of the T 1 shortening effect of Mn 21 . H226subcutaneous tumor was preferentially enhanced compared with a lung adenocarcinoma cell tumor and another human MM cell tumor in MnCl 2 -enhanced T 1 -weighted MR image (T 1 WI), correlating with their respective Mn-SOD expression levels. Moreover, in a more clinically relevant setting, H226 xenografted pleural tumor was markedly enhanced and readily detected by MEMRI using manganese dipyridoxyl diphosphate (MnDPDP), a clinically used contrast agent, as well as MnCl 2 . Therefore, we propose that MEMRI can be a potentially powerful method for noninvasive detection of MM, with high spatial resolution and marked signal enhancement, by targeting Mn-SOD.Malignant mesothelioma (MM) is an asbestos-related malignant tumor originating from mesothelial cells lining pleural and peritoneal cavities. There is a long latency period (more than 30 years) between the asbestos exposure and the onset of the disease, and the number of patients is now rapidly increasing in industrialized countries because of the widespread use and installation of asbestos fibers in the past centuries. Epidemiological studies indicate that the incidence is rapidly increasing worldwide.

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Purpose: Manganese-enhanced magnetic resonance imaging (MEMRI), used to trace neuronal connections and visualize brain activity, has recently been suggested useful for tumor detection, but the mechanism of tumor enhancement by manganese (Mn) is poorly understood. Our recent report of preferential enhancement of human mesothelioma cells with higher levels of manganese-superoxide dismutase (Mn-SOD) expression may suggest a correlation between Mn-SOD expression and enhancement. We investigate this possibility further using engineered human ovarian cancer cells overexpressing Mn-SOD.Methods: We subcutaneously implanted SK-OV-3 human ovarian cancer cells stably overexpressing Mn-SOD (SK-Mn-SOD) into athymic nude mice and SK-OV-3 cells with plasmid DNAs carrying neomycin-resistant genes (SK-neo) into the same mice for controls. We conducted MEMRI in the tumor-bearing mice and compared enhancement between the 2 tumors.Results: Subcutaneous SK-Mn-SOD tumors were preferentially enhanced in MEMRI compared to SK-neo tumors. After Mn enhancement, the T 1 -relaxation rate (R 1 ＝1/T 1 ) increased signiˆcantly for SK-Mn-SOD but not SK-neo tumors.Conclusion: In some tumors, high expression of Mn-SOD may be a biological factor responsible for enhanced signal in MEMRI.