Molecular Fluorescent Imaging of Metastatic Tumors with Conditionally Replication-Selective Adenovirus and GFP Gene

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Currently available methods for detection of tumors in vivo such as X-ray, computed tomography, and ultrasonography are noninvasive and well studied ; the images, however, are not specific for tumors. Direct optical imaging of tumor cells in vivo that can clearly distinguish them from surrounding normal tissues may be clinically useful. Here, we describe a new approach to visualizing tumors whose fluorescence can be detected using tumor-specific replication-competent adenovirus (OBP-301, "Telomelysin") in combination with replication-deficient adenovirus expressing GFP (Ad-GFP). Human telomerase reverse transcriptase (hTERT) is the catalytic subunit of telomerase, which is highly active in cancer cells, but is quiescent in most normal somatic cells. We constructed an adenovirus 5 vector, in which the hTERT promoter element drives expression of E1A and E1B genes linked with an IRES, and showed that OBP-301 replicated efficiently exclusively in human cancer cells, but not in normal cells … More such as human fibroblasts. When the human lung and colon cancer cell lines H1299 and SW620 were infected with Ad-GFP at low multiplicity of infection(MOI), GFP expression could not be detected under a fluorescence microscope ; in the presence of OBP-301, however, Ad-GFP replicated in these tumor cells and showed strong green signals. In contrast, co-infection of OBP-301 and Ad-GFP did not show any signals in normal cells such as WI-38 fibroblasts. We also found that established subcutaneous tumors could be visualized following intratumoral injection of OBP-301 and Ad-GFP. A549 human lung tumors and SW620 human colon tumors transplanted into BALB/c nu/nu mice were intratumorally injected with 8 x 10^5 plaque forming units(PFU) of Ad-GFP in combination with 8 x 10^6 PFU of OBP-301. Within 3 days of treatment, the fluorescence of the expressed GFP became visible by 3CCD camera in these tumors, whereas intratumoral injection of Ad-GFP alone could not induce GFP fluorescence. Moreover, intrathoracic administration of Ad-GFP and OBP-301 could visualize disseminated A549 tumor nodules in mice following intrathoracic implantation. Our results indicate that intratumoral or intrathoracic injection of Ad-GFP in combination with OBP-301 might be a useful diagnostic method that provides a foundation for future clinical application. Less