Abstract 1268: The effect of metformin for neutrophil extracellular traps (NETs) on tumor immune microenvironment of colorectal cancer with type 2 diabetes mellitus
Authors: Saito Akira , Ohzawa Hideyuki , Kaneko Yuki , Tamura Kohei , Futoh Yurie , Takahashi Kazuya , Kimura Yuki , Kawashima Rie , Miyato Hideyo , Kitayama Joji , Sata Naohiro 
Published: April 2023

Abstract
Background: Although metformin (Met) is well known to suppress tumor growth, the detailed mechanisms of its anti-tumor effect remain unknown. In recent years, it has been pointed out that tumor-associated neutrophils (TAN) can produce neutrophil extracellular traps (NETs) in the tumor microenvironment (TME) which can tumor invasion and metastasis. Here, in this study, we investigated the effect of Met on tumor-associated NETs and its effect on the prognosis of cancer patients.
Method: We retrospectively examined the outcome of colorectal cancer (CRC) patients with type 2 diabetes mellitus (T2DM) who received curative surgery in Jichi Medical University Hospital and asked the impact of Met intake on their outcome. In addition, we performed multicolor immunohistochemistry to examine the phenotypes of tumor-infiltrating lymphocytes (TIL), TAN and NETs in surgically removed tissues specimens in 40 (colorectal cancer) CRC patients who had taken Met before surgery and propensity score-matched 40 patients who had not.
Results: A total of 1858 patients underwent curative colectomy from April 2010 to March 2021. Among them, 283 patients had T2DM at the time of surgery, and 62 patients had been treated with drugs including Met. The postoperative disease-free survival rate (DFS) was significantly improved in the Met intake group compared with non-intake group (HR=0.21, p&lt;0.01). The number of CD66b(+) TANs significantly decreased in Met-intake group (Median(M)=169 (36-553)/mm2 vs 99 (34-322)/mm2, p&lt;0.01). The number of tumor-associated NETs defined as CD66b(+) cit-H3(+) cells significantly decreased in Met-intake group (M=36 (8-272)/mm2 vs 20 (0-104)/mm2, p&lt;0.01), and tumor-associated NETs/TANs ratio significantly decreased in Met-intake group (29.9% vs 19.8%, p&lt;0.01). The number of CD3(+) TILs significantly increased in Met intake group (M=122 (28-257)/mm2 vs 142 (48-386)/mm2, p&lt;0.05). The number of CD8(+) TILs significantly increased in Met-intake group (M=60 (14-180)/mm2 vs 99 (52-318)/mm2, p&lt;0.01), and CD8/CD3 ratio significantly increased in Met-intake group (51.2% vs 72.1%, p&lt;0.01). In addition, there was a negative correlation between TANs or tumor-associated NETs and CD8 positive TILs in all 80 patients (r=-0.26, p&lt;0.05).
Conclusion: Met can inhibit neutrophil infiltration and NETs formation while promote the infiltration of cytotoxic T cells in TME, which may lead to the improvement of the outcome of the patients with CRC.
Citation Format: Akira Saito, Hideyuki Ohzawa, Yuki Kaneko, Kohei Tamura, Yurie Futoh, Kazuya Takahashi, Yuki Kimura, Rie Kawashima, Hideyo Miyato, Joji Kitayama, Naohiro Sata. The effect of metformin for neutrophil extracellular traps (NETs) on tumor immune microenvironment of colorectal cancer with type 2 diabetes mellitus [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1268.