Background/Aim: Programmed death-1 (PD-

Background Low-density granulocytes (LDGs) have been shown to be increased in the peripheral blood of patients with inflammatory and malignant diseases. This study evaluated LDGs in patients who underwent radical surgery for colorectal cancer (CRC) and their impact on survival. Methods Patients who underwent radical colectomy between 2017 to 2021 were screened for enrolment in the study. Peripheral blood was obtained in the operating room before and after surgery and cells were recovered from the mononuclear layer after density gradient preparations. The ratio of CD66b(+) LDG to CD45(+) leukocytes was determined with flow cytometry, and the association of the ratios with patient outcomes was examined. The main outcome of interest was recurrence-free survival (RFS). Results Out of 228 patients treated, 176 were enrolled, including 108 colonic and 68 rectal cancers. Overall, 38 patients were stage I, 30 were stage II, 72 were stage 3, and 36 were stage IV. The number of LDGs was markedly increased immediately after surgery and the proportion of LDGs correlated positively with operating time (r = 0.2806, P < 0.001) and intraoperative blood loss (r = 0.1838, P = 0.014). Purified LDGs produced high amounts of neutrophil extracellular traps after short-term culture and efficiently trapped tumour cells in vitro. The proportion of postoperative LDGs was significantly higher in 13 patients who developed recurrence (median 9 (range 1.63–47.0)) per cent versus median 2.93 ((range 0.035–59.45) per cent, P = 0.013). When cut-off values were set at 4.9 per cent, a higher proportion of LDGs was strongly and independently associated with decreased RFS (P = 0.005). In patients with stage III disease, adjuvant chemotherapy significantly improved RFS of patients with high ratios of LDGs, but not low LDGs. Conclusion LDGs are recruited to circulating blood by surgical stress early in the postoperative interval after colectomy for colonic cancer and their postoperative proportion is correlated with recurrence.

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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<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<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<0.01), and tumor-associated NETs/TANs ratio significantly decreased in Met-intake group (29.9% vs 19.8%, p<0.01). The number of CD3(+) TILs significantly increased in Met intake group (M=122 (28-257)/mm2 vs 142 (48-386)/mm2, p<0.05). The number of CD8(+) TILs significantly increased in Met-intake group (M=60 (14-180)/mm2 vs 99 (52-318)/mm2, p<0.01), and CD8/CD3 ratio significantly increased in Met-intake group (51.2% vs 72.1%, p<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<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.

Background: Mesothelial cells play tumor-promoting roles in the development of peritoneal metastasis (PM) through mesothelial-mesenchymal transition (MMT). We reported miR-29b suppressed MMT of human peritoneal mesothelial cell (HPMC). Methods: MiR-29b mimics and negative control miRNA (NC) were transfected to human bone marrow derived MSC by lipofection method. Exosomes were purified from the culture supernatants of the MSC with ultracentrifugation, and added to HPMC. Proliferation and migration of HPMC were examined with MTT assay and transwell assay, respectively. MMT of HPMC induced by 10 ng/ml TGF-β, and evaluated with immunofluorescence staining. Results: MSC transfected with miR-29b mimics produced significantly increased amounts of miR-29b-containing exosomes (p<0.0001, n=3) as compared with negative control. After 24h-culture with PKH-26 stained exosomes, HPMC actively took the exosomes. After 48 hr-culture with TGF-β, HPMC apparently changed the morphology from round to spindle shape. The expression level of E-cadherin and Calretinin in HPMC was decreased while vimentin and Fibronectin tended to be upregulated by TGF-β. However, exosomes from miR-29b transfected MSC significantly suppressed the morphological changes and reduced the expression levels of vimentin and Fibronectin with restored expression of E-cadherin and Calretinin, suggesting the inhibition of MMT in HPMC. The exosome inhibited the proliferation and migration of HPMC by 31±14% (p<0.01, n=5) and 67±9% (p<0.01, n=3), and inhibited the adhesion of NUGC by 90±3% (p<0.001, n=5) as compared with NC exosome. Conclusion: Exosomes from MSC transfected with miR-29b mimic efficiently suppresses MMT. Replacement of the miR-29b in peritoneal cavity might be used for the treatment of PM partially via the effects on mesothelial cell. Citation Format: Yuki Kimura, Hideyuki Ohzawa, Yuki Kaneko, Kohei Tamura, Yurie Futoh, Kazuya Takahashi, Akira Saito, Mineyuki Tojo, Hideyo Miyato, Joji Kitayama. Exosomal miR-29b derived from mesenchymal stem cell (MSC) may suppress peritoneal metastasis via the effects on peritoneal mesothelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6284.