639. In Vivo Imaging of Lymph Node Metastasis with Telomerase-Specific Replication-Competent Adenovirus Containing Green Fluorescent Protein Gene.

Currently available methods for detection of tumors in vivo such as X-ray, computed tomography, ultrasonography, and magnetic resonance imaging are noninvasive and are 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 telomerase-specific replication-competent adenovirus expressing green fluorescent protein (GFP) (OBP-401, Telomelysin- GFP) and a charged-coupled device (CCD) imaging system. Human telomerase reverse transcriptase (hTERT) is the catalytic subunit of telomerase, which is highly active in cancer cells but quiescent in most normal somatic cells. OBP-401 contains the replication cassette, in which the hTERT promoter element drives expression of E1A and E1B genes linked with an IRES, and the GFP gene driven by the cytomegalovirus promoter for monitoring viral replication. Quantitative real time PCR analysis targeting the viral E1A sequence in vitro showed that OBP-401 replicated 5–6 logs by 3 days after infection in human cancer cell lines and coordinately induced GFP expression under fluorescence microscopy; OBP-401 replication, however, was attenuated up to 2 logs in normal human lung fibroblasts without GFP expression. We also found that established subcutaneous tumors could be visualized after intratumoral injection of OBP-401. Three weeks after treatment, tumors expressed strong green signals under a three-chip color cooled charged-coupled device camera. Tumor sections diffusely expressed GFP, suggesting in vivo viral replication and spread throughout the tumors. Finally, we examined whether OBP-401 might be useful for detection of lymph node metastasis in an orthotopic rectal cancer model. OBP-401 was intratumorally injected into HT29 tumors orthotopically implanted into the rectum in BALB/c nu/nu mice. Five days after injection, para-aortic lymph node metastasis could be visualized at laparotomy. Histological examination confirmed that GFP-positive lymph nodes contained microscopic metastasis. Our results indicate that intratumoral injection of OBP-401 causes viral spread into the regional lymphatic area and selectively replicates in neoplastic lesions, resulting in tumor-specific GFP expression. These observations suggest that intratumoral injection of OBP-401 might be a useful diagnostic method that provides a foundation for future clinical application.Molecular Therapy (2006) 13, S246–S246; doi: 10.1016/j.ymthe.2006.08.715 [ABSTRACT FROM AUTHOR]