Abstract 4570: Telomerase-specific oncolytic virotherapy promotes therapeuticefficacy of PD-1 blockade in murine osteosarcoma
Authors: Mochizuki Yusuke , Tazawa Hiroshi , Demiya Koji , Komatsubara Tadashi , Sugiu Kazuhisa , Hasei Joe , Kunisada Toshiyuki , Urata Yasuo , Ozaki Toshifumi , Fujiwara Toshiyoshi 
Published: August 2018

Abstract
Background: Treatment with immune checkpoint inhibitor anti-programmed death protein 1 (PD-1) antibody has dramatically improved the clinical outcome in cancer patients. Then immunotherapy is the most exciting field for cancer treatment in recent years. However, PD-1 blockade therapy is limited to certain cancer types. Therefore, the enhancement of therapeutic efficacy in PD-1 blockade therapy is required. Recently, it has been suggested that the effect of PD-1 blockade therapy can be enhanced when combined with immunogenic antitumor therapy including chemotherapy and virotherapy. We recently developed a RGD fiber-modified telomerase-specific oncolytic adenovirus OBP-502, which can enter into tumor cells by binding to cell surface integrin and induce oncolytic cell death in a telomerase-dependent manner. In this study, we assessed the in vitro and in vivo antitumor efficacy of combination therapy with anti-PD-1 antibody and OBP-502 in murine osteosarcoma.
Methods: We used 2 murine osteosarcoma cell lines, K7M2 and NHOS. The expression of PD-L1, coxsackie and adenovirus receptor (CAR), and integrin on the cell surface was analyzed by flow cytometric analysis. The in vitro antitumor effect of OBP-502 was evaluated using a XTT assay. Virus-induced immunogenic cell death was assessed by analyzing the level of extracellular ATP and high-mobility group box protein B1 (HMGB1). To evaluate the therapeutic potential of anti-PD-1 antibody and OBP-502, we assessed the antitumor effect of combination therapy with anti-PD-1 antibody and OBP-502 using a subcutaneous K7M2 xenograft tumor model. Moreover, the number of tumor-infiltrating CD8+ and Foxp3+ T cells was analyzed by immunohistochemistry.
Results: K7M2 and NHOS cells showed the expression of PD-L1 and integrin, but not CAR, in flow cytometric analysis. OBP-502 efficiently suppressed the viability of K7M2 and NHOS cells in a dose-dependent manner. OBP-502 significantly increased the release of HMGB1 in K7M2 cells and the secretion of ATP in NHOS cells. Intratumoral injection of OBP-502 significantly induced the number of tumor-infiltrating CD8+ T cells and enhanced the suppression of tumor growth by PD-1 blockade in a subcutaneous K7M2 xenograft tumor model. Moreover, tumor free was observed in 6 out of 7 mice treated with anti-PD-1 antibody and OBP-502 even at 4 weeks after treatment.
Conclusion: These results suggest that telomerase-specific oncolytic virotherapy is a promising antitumor strategy to promote the therapeutic efficacy of PD-1 blockade therapy in osteosarcoma.
Citation Format: Yusuke Mochizuki, Hiroshi Tazawa, Koji Demiya, Tadashi Komatsubara, Kazuhisa Sugiu, Joe Hasei, Toshiyuki Kunisada, Yasuo Urata, Toshifumi Ozaki, Toshiyoshi Fujiwara. Telomerase-specific oncolytic virotherapy promotes therapeuticefficacy of PD-1 blockade in murine osteosarcoma [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 4570.