Abstract 2211: A novel combined immunotherapy of gut microbial metabolite butyrate and oncolytic adenovirus in colorectal cancer

Abstract Butyrate, a short-chain fatty acid (SCFA) produced by gut bacteria in the colon, serves as a critical energy source for colonocytes. Gut microbiota and its primary metabolite, butyrate, have been reported to potentially modulate tumor sensitivity to chemotherapy or immunotherapy, although the underlying mechanisms remain unclear. Oncolytic virotherapy is a promising antitumor treatment that selectively induces oncolytic cell death in tumor cells. Previously, we developed OBP-702, a telomerase-specific oncolytic adenovirus armed with the p53 tumor suppressor gene, which demonstrated potent antitumor effects across various cancer types. Oncolytic virotherapy is also known to stimulate antitumor immunity. In this study, we investigated the combined effects of OBP-702 and butyrate on colorectal cancer and elucidated the underlying mechanisms. In vitro, the combination of OBP-702 and butyrate exhibited synergistic cytotoxicity against various human and murine colorectal cancer cell lines. In vivo, the combination therapy significantly suppressed tumor growth in HCT116 and CT26 subcutaneous tumor models compared to monotherapy with either OBP-702 or butyrate alone. These synergistic effects were mediated by butyrate enhancing OBP-702's efficacy through the upregulation of coxsackievirus and adenovirus receptor (CAR) and integrin expression on tumor cells, improving viral infection efficiency. Butyrate also increased MHC-I expression on tumor cells through activation of the cGAS-STING pathway, leading to enhanced CXCL10 expression. This, in turn, activated antitumor immunity by recruiting CD8-positive T cells to the tumor microenvironment. The synergistic effects of butyrate and OBP-702 were further confirmed in an orthotopic colorectal tumor model with liver metastases using luciferase-expressing CT26 cells. In this model, the combination therapy not only reduced tumor growth but also improved survival by enhancing antitumor immunity mediated by CD8-positive T cells. To translate these findings into a more clinically relevant approach, butyrate-producing bacteria, Clostridium butyricum Miyairi 588 (CBM588), were used in place of butyrate. The combination therapy of CBM588 and OBP-702 demonstrated similar synergistic antitumor effects in mouse subcutaneous and rectal tumor models. In conclusion, the combination of OBP-702 and butyrate shows promise as a synergistic antitumor strategy and may represent a novel therapeutic approach for colorectal cancer. Citation Format: Tetsuya Katayama, Shinji Kuroda, Masaki Sakamoto Sakamoto, Eri Takeda, Yu Mikane, Shunya Hanzawa, Daisuke Kadowaki, Yusuke Yoshida Yoshida, Masashi Hashimoto, Nobuhiko Kanaya, Yoshihiko Kakiuchi, Satoru Kikuchi, Shunsuke Kagawa, Hiroshi Tazawa, Yasuo Urata, Toshiyoshi Fujiwara. A novel combined immunotherapy of gut microbial metabolite butyrate and oncolytic adenovirus in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2211.