Abstract 4851: Involvement of extracellular vesicles in the abscopal effect induced by oncolytic adenovirotherapy
Authors: Kakiuchi Yoshihiko , Kuroda Shinji , Kanaya Nobuhiko , Kumon Kento , Tsumura Tomoko , Kikuchi Satoru , Nishizaki Masahiko , Kagawa Shunsuke , Tazawa Hiroshi , Urata Yasuo , Fujiwara Toshiyoshi 
Published: August 2019

Background: The abscopal effect is a phenomenon that shrinkage of metastatic tumors occurs concurrently with shrinkage of primary tumors by local treatments such as radiotherapy, and is generally considered to be caused through activation of the immune system. Extracellular vesicles (EVs) are recent interesting topics in scientific fields and are known to play important roles in a variety of intercellular communication processes including immune response. We previously developed a telomerase specific oncolytic adenovirus, Telomelysin (OBP-301), which is currently being tested in clinical trials, and have sometimes observed therapeutic effects on metastatic tumors after local injection to primary tumors in immunodeficient mouse models. Here, we hypothesized that EVs derived from OBP-301-treated tumors may be associated with the abscopal effect of OBP-301.

Methods: A human colon carcinoma cell line HCT116 and HCT116 expressing RFP (HCT116-RFP) were used in this study. EVs were isolated by ultracentrifugation from HCT116 cells treated with OBP-301 (Exo-301). Intercellular communication and cytotoxic activity via EVs after OBP-301 treatment were assessed in a non-contact co-culture system in vitro and a bilateral subcutaneous tumor mouse model in vivo.

Results: Exo-301 showed potent cytotoxic effects on HCT116 cells and this cytotoxicity was significantly blocked in the presence of anti-CD9 antibody, which suggested that Exo-301, not OBP-301 itself, was involved in this cytotoxicity. In non-contact co-culture experiments, more RFP was taken up into HCT116 cells after OBP-301 treatment on HCT116-RFP cells than control treatments, which meant that EVs including RFP reached HCT116 cells through membrane after OBP-301 treatment on HCT116-RFP cells. In a HCT116 bilateral subcutaneous tumor model in BALB/c nude mice, intratumoral injection of OBP-301 significantly suppressed the growth of untreated tumors as well as treated tumors, and in a bilateral tumor model with HCT116 on one side and HCT116-RFP on the opposite side, immunohistochemical staining showed the presence of RFP in untreated HCT116 tumors after OBP-301 treatment on HCT116-RFP tumors. These findings suggested that EVs derived from OBP-301-treated tumors was possibly involved in some cytotoxic effects on the opposite untreated tumors.

Conclusion: EVs may be an important factor in the abscopal effect brought by local treatment of OBP-301 besides immune activation.

Citation Format: Yoshihiko Kakiuchi, Shinji Kuroda, Nobuhiko Kanaya, Kento Kumon, Tomoko Tsumura, Satoru Kikuchi, Masahiko Nishizaki, Shunsuke Kagawa, Hiroshi Tazawa, Yasuo Urata, Toshiyoshi Fujiwara. Involvement of extracellular vesicles in the abscopal effect induced by oncolytic adenovirotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4851.