Development of a Conditional Replication Competent Adenovirus, Controlled by the Human Telomerase Promoter(hTERT)

Abstract

Purpose: This study has been planned to generate a replication-competent adenovirus which replicates in a cancer cell-specific manner, thus minimizing the side effects and toxicity of cancer gene therapy. Materials and Methods: we have generated an E1B 19 kD attenuated recombinant adenoviruses, Ad-TERT-19 and Ad-mTERT-19, which encode E1A gene driven by the wild type hTERT and modified m-hTERT promoter containing additional c-myc and Sp1 binding sites in the backbone of Ad-E1B19. The in vitro efficacy and specificity of the hTERT and m-hTERT promoter have been evaluated by the comparison of viral replication and cytopathic effect in cancer cells and normal cell lines. To assess anti-tumor effect and safety of hTERT or m-hTERT promoter driven replication competent adenoviruses, tumor regression after subcutaneous injection in subcutaneous C33A xenografts and lacZ expression after systemic injection in organs were examined. Results: The activation of hTERT or m-hTERT promoter was significantly up-regulated only in hTERT-positive cells, but not in hTERT-negative cells. Moreover, the activity of m-hTERT promoter was substantially increased in hTERT-positive cancer cells, but not in hTERT-negative cells. While Ad-TERT-19 replicated in and induced cytopathic effect in cancer and in some normal cell lines, Ad-mTERT-19 enhanced viral replication and cytopathic effect in cancer cells only. Furthermore, the growth of established human cervical carcinoma in nude mice was significantly suppressed by intratumoral injection of Ad-mTERT-19. Conclusions: The use of m-hTERT promoter is not only useful in the regulation of therapeutic gene expression but also that replication-competent oncolytic adenovirus under the control of m-hTERT promoter may be a new promising tool for the treatment of human malignancies. (Cancer Res Treat. 2003;35:191-206)