A Novel Molecular Therapy Using Bioengineered Adenovirus for Human Gastrointestinal Cancer

Replication-selective tumor-specific viruses constitute a novel approach for treatment of neoplastic disease. These vectors are designed to induce virus-mediated lysis of tumor cells after selective viral propagation within the tumor. Human telomerase is highly active in more than 85ｵ of primary cancers, regardless of their tissue origins, and its activity correlates closely with human telomerase reverse transcriptase (hTERT) expression. We constructed an attenuated adenovirus 5 vector (Telomelysin, OBP-301), in which the hTERT promoter element drives expression of E1 genes. Since only tumor cells that express telomerase activity would activate this promoter, the hTERT proximal promoter would allow for preferential expression of viral genes in tumor cells, leading to selective viral replication and oncolytic cell death. Lymphatic invasion is a major route for cancer cell dissemination, and adequate treatment of locoregional lymph nodes is required for curative treatment in patients with gastrointestinal tumors. We demonstrated that intratumoral injection of Telomelysin mediates effective in vivo purging of metastatic tumor cells from regional lymph nodes. Moreover, using noninvasive whole-body imaging, we found that intratumoral injection of Telomelysin followed by regional irradiation induces a substantial antitumor effect, resulting from tumor cell-specific radiosensitization, in an orthotopic human esophageal cancer xenograft model. These results illustrate the potential of oncolytic virotherapy as a promising strategy in the management of human gastrointestinal cancer.