Abstract 4677: Tumor suppressor p53 reactivation by oncolytic adenovirus reverses chemoresistance in human osteosarcomas
Authors: Sugiu Kazuhisa , Tazawa Hiroshi , Hasei Joe , Osaki Shuhei , Yamakawa Yasuaki , Omori Toshinori , Komatsubara Tadashi , Uotani Kouji , Fujiwara Tomohiro , Kunisada Toshiyuki , Urata Yasuo , Ozaki Toshifumi , Fujiwara Toshiyoshi 
Published: July 2016

Abstract
Background: Osteosarcoma is a primary malignant bone tumor. Despite recent advances in multi-agent chemotherapy and aggressive surgical resection, the poor response to chemotherapy often contributes to poor prognosis in osteosarcoma patients. Therefore, the development of novel strategies for reversing the chemoresistance is a pivotal approach to improve the clinical outcome for osteosarcoma patients. We recently developed a tumor suppressor p53-expressing oncolytic adenovirus, OBP-702, which drives the adenoviral E1 gene under the control of the human telomerase reverse transcriptase promoter for tumor-specific virus replication and induces profound p53 expression for tumor-specific cell death. We recently found that OBP-702 effectively kills human osteosarcoma cells. In this study, we investigated the therapeutic potential of OBP-702 as a chemosensitizing reagent in human osteosarcoma cells with different p53 status.
Methods: We used 4 human osteosarcoma cell lines with different p53 status, including U2OS (p53 wild-type), MNNG/HOS (p53 mutant), 143B (p53 mutant), SaOS2 (p53 null). We also used the doxorubicin (DOX)-resistant U2OS cells, which were established by sequential exposure to DOX over 3 months. We performed the XTT assay to examine the antitumor effects of DOX and OBP-702. Combination efficacy between DOX and OBP-702 was assessed by calculating the combination index using CalcuSyn software (BioSoft, Inc.). We further investigated the DOX- and OBP-702-mediated apoptosis in parental and DOX-resistant U2OS cells using Western blot analysis.
Results: OBP-702 improved the sensitivity to DOX in a dose-dependent manner in all 4 osteosarcoma cell lines. The calculation of combination index revealed the synergistic effect in all 4 osteosarcoma cell lines. Combination with DOX and OBP-702 induced more profound apoptosis than monotherapy in all 4 osteosarcoma cell lines. Moreover, in DOX-resistant U2OS cells, OBP-702 induced the cytopathic effect as well as parental U2OS cells. Synergistic effect was also observed in DOX-resistant U2OS cells when we treated with DOX and OBP-702. Although DOX-resistant U2OS cells was more resistant to the DOX-mediated apoptosis than parental cells, OBP-702 enhanced the DOX-mediated apoptosis in DOX-resistant U2OS cells as well as parental cells.
Conclusions: These results suggest that OBP-702-mediated p53 reactivation reverses the chemoresistance in human osteosarcomas.
Citation Format: Kazuhisa Sugiu, Hiroshi Tazawa, Joe Hasei, Shuhei Osaki, Yasuaki Yamakawa, Toshinori Omori, Tadashi Komatsubara, Kouji Uotani, Tomohiro Fujiwara, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Tumor suppressor p53 reactivation by oncolytic adenovirus reverses chemoresistance in human osteosarcomas. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4677.