Abstract 5816: Ablation of oncogenic MYCN expression by hTERT-driven oncolytic adenovirus induces cell death in MYCN-amplified neuroblastoma
Authors: Tanimoto Terutaka , Tazawa Hiroshi , Noso Hiroshi , Oyama Takanori , Urata Yasuo , Kagawa Shunsuke , Noda Takuo , Fujiwara Toshiyoshi 
Published: July 2017

Abstract
Background: Neuroblastoma (NB) is a primary malignant tumor of the peripheral sympathetic nervous system. Amplification and overexpression of the MYCN proto-oncogene occur in approximately 20% of NB. Since MYCN activation is highly associated with poor prognosis, MYCN is an attractive target for the treatment of MYCN-amplified NB. MYCN is a transcriptional activator that induces the expression of many down-stream target genes including human telomerase reverse transcriptase (hTERT). We developed two types of hTERT-driven oncolytic adenoviruses, OBP-301 and OBP-702, in which the hTERT promoter drives the expression of the viral E1A and E1B genes for tumor-specific virus replication, and OBP-702 further expresses tumor suppressor p53 protein. Although hTERT-driven oncolytic viruses are expected to be effective against MYCN-amplified NB with hTERT activation, the therapeutic potential of these viruses in MYCN-amplified NB remains unclear. In this study, we investigated whether OBP-301 and OBP-702 induce cell death and modulate MYCN expression in MYCN-amplified NB cells.
Methods: We used 3 human NB cell lines with MYCN amplification, including IMR-32, CHP-134 and LA-N-5. The antitumor effect of OBP-301 and OBP-702 was evaluated using XTT assay. Virus-mediated cell death and modulation of MYCN and E2F1 expression were analyzed by Western blot analysis. The mRNA expression of hTERT and MYCN was analyzed by real-time RT-PCR analysis. To explore the role of E2F1 in the virus-mediated MYCN modulation, Ad-E2F1, a replication-defective adenovirus expressing E2F1 gene, was further used.
Results: All NB cell lines showed high hTERT mRNA expression. OBP-301 and OBP-702 showed profound antitumor effect through autophagy-related cell death in all NB cell lines. Both viruses induced E1A and its target mediator E2F1 expression in these cell lines. Expression of MYCN mRNA and protein was downregulated by these viruses. Replication-deficient Ad-E2F1 infection also downregulated the expression of MYCN.
Conclusions: These results suggest that hTERT-driven oncolytic adenoviruses are promising antitumor agent for the treatment of MYCN-amplified NB. These viruses induce profound autophagy through hTERT-dependent viral replication. E2F1 upregulation by viral infection is supposed to be one of the causes for MYCN downregulation and autophagy-related cell death. In vivo experiments are under way to investigate the antitumor effect of these viruses against xenograft NB tumors.
Citation Format: Terutaka Tanimoto, Hiroshi Tazawa, Hiroshi Noso, Takanori Oyama, Yasuo Urata, Shunsuke Kagawa, Takuo Noda, Toshiyoshi Fujiwara. Ablation of oncogenic MYCN expression by hTERT-driven oncolytic adenovirus induces cell death in MYCN-amplified neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5816. doi:10.1158/1538-7445.AM2017-5816