Abstract 2593: Telomerase-specific oncolytic virotherapy for osteosarcoma

Abstract

Abstract Oncolytic adenoviruses are being developed as novel antitumor therapeutics and currently undergoing clinical trial. Telomelysin (OBP-301) is a type 5 adenovirus that contains the replication cassette in which the human telomerase reverse transcriptase promoter drives expression of the E1 genes, and shows telomerase specific replication and cell killing effect. We previously demonstrated that the expression of coxsackie-adenovirus receptor (CAR) is high in osteosarcoma compared with the other mesenchymal tumors, and moreover, many investigators have been reported that telomerase expression predicts the unfavorable outcome in osteosarcoma. The present investigation analyzed that the selective replication and antitumor effects of Telomelysin using 8 osteosarcoma and 1 normal dermal fibroblast cell lines in vitro as well as in vivo by using athymic mice carrying xenografts. At first, all cell lines were used to examine the mRNA expression of CAR and hTERT, and 3 osteosarcoma cell lines and 1 normal fibroblast cell were chosen for Telomelysin infection. Selective E1A and E1B expression were shown in osteosarcoma cells by quantitative real-time RT-PCR and Western blot analysis, but not in normal cells such as human dermal fibroblasts. Telomelysin replicated efficiently and induced marked cell death in osteosarcoma cells, whereas replication as well as cytotoxicity was highly attenuated in normal fibroblast cells lacking telomerase activity. Expression of cleaved caspase, PARP and LC-3 I, II after Telomelysin infection was tested by Western blot, however the mechanism of induction of cell death could not be revealed in this time. For in vivo evaluation, nu/nu mice xenografted with NOS10 human osteosarcoma cell received intratumoral injection of 107 plaque-forming units of Telomelysin, and resulted in a significant inhibition of tumor growth and long-term survival in all treated mice. Moreover, selective replication of Telomelysin in tumor cell was also demonstrated by anti-E1A immunohistochemistly, and induction of apoptosis was observed by TUNEL staining. Our results suggest that the hTERT promoter confers competence for selective replication of Telomelysin in osteosarcoma cells, and the outcome has important implications for tumor-specific oncolytic chemovirotherapies for human osteosarcomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2593.