Abstract 3177: mTOR inhibitor augments the antitumor effect of p53-expressing oncolytic adenovirus in human neuroblastoma cells

Background: Neuroblastoma (NB) is a primary malignant tumor of the peripheral sympathetic nervous system. High-risk NB patients show an unfavorable clinical outcome, even after treatment with intensive chemotherapy and aggressive surgical resection. Therefore, a novel therapeutic strategy is needed for the treatment of high-risk NB patients. We developed a tumor-specific replication-competent oncolytic adenovirus OBP-702, in which the hTERT promoter drives the expression of the viral E1A and E1B genes for tumor-specific viral replication and the Egr-1 promoter induces p53 expression. Preclinical studies demonstrated that OBP-702 induces autophagy-related cell death in human NB cell lines. To enhance OBP-702-induced autophagy-related cell death, we hypothesized that a mTOR inhibitor temsirolimus, which is well-known autophagy inducer, may promote autophagy-related cell death by OBP-702 infection. In this study, we investigated the antitumor effect of OBP-702 in combination with temsirolimus in human NB cell lines. Methods: We used 3 human NB cell lines, including IMR-32, CHP-134 and SK-N-SH. The antitumor effect of OBP-702 and temsirolimus was evaluated using XTT assay. In vitro synergistic effect was calculated with CalcuSyn software (BioSoft, Inc.). Virus-mediated cell death and p53 expression were analyzed by Western blot analysis. Ad-p53, a replication-defective adenovirus expressing p53 gene, was used to assess the effect of p53 in combination with temsirolimus. The combined effect of OBP-702 and temsirolimus was further evaluated using a subcutaneous CHP-134 xenograft tumor model. Results: Combination with OBP-702 and temsirolimus exhibited a synergistic antitumor effect in all NB cell lines in vitro. We confirmed that combination with these drugs enhanced autophagy. In addition, temsirolimus showed an effect to stabilize p53 protein induced by OBP-702. Ad-p53 also showed synergistic effect in combination with temsirolimus. The combination treatment significantly inhibited tumor growth, as compared to monotherapy, in NB xenograft tumor model. Conclusions: These results suggest that p53-expressing oncolytic adenovirus and mTOR inhibitor synergistically induce autophagic cell death and may be a promising strategy in NB patients. Citation Format: Terutaka Tanimoto, Hiroshi Tazawa, Hiroshi Noso, Morimichi Tani, Takanori Oyama, Yasuo Urata, Shunsuke Kagawa, Takuo Noda, Toshiyoshi Fujiwara. mTOR inhibitor augments the antitumor effect of p53-expressing oncolytic adenovirus in human neuroblastoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3177.