Abstract 1081: Smad3 silences neutrophil anticancer activity in the tumor microenvironment

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Abstract Tumor microenvironment (TME) is a new therapeutic target for cancer, however it is highly heterogeneous and still largely unknown. Recently, we revealed that Smad3 is essential for TME-driven cancer progression, better understanding of the underlying mechanism may uncover novel therapeutic targets for cancer. Indeed, Smad3-dependent TME (Smad3-TME) is originated from bone marrow, where neutrophils are the most abundant leukocytes but their role in cancer is still controversial. Here, we are the first study to reveal the regulatory role of Smad3 in tumor-associated neutrophils (TAN). Interestingly, we observed that knockout of Smad3 (Smad3-KO) dramatically increased TAN population in mice bearing syngeneic melanoma B16F10 and lung carcinoma LLC, where the anticancer N1 phenotypes were significantly induced in the SMad3-KO TME-isolated TAN. Unexpectedly, adoptive transfer of Smad3-KO bone marrow-derived neutrophils markedly suppressed the progression of LLC-tumor on Smad3-WT mice in vivo, and their enhanced cancer-killing activity was confirmed by co-culture assay in vitro. Furthermore, microarray analysis identified a total of 4416 differentially expressed genes associated with Smad3-KO neutrophils under cancer condition in vitro, but the presence of Smad3 largely decreased the transcriptome diversity; especially on genes associated with virus defense response including an anticancer cytokine IL-28. Silencing of IL-28 significantly reduced the anticancer efficiency of Smad3-KO TAN on LLC-bearing mice in vivo. Mechanistically, we uncovered that IL-28A serves as a direct Smad3 target gene and specifically down-regulated in neutrophils under TGF-β1 or LLC-secretome stimulations; showing by ChIP and dual-luciferase reporter assays in vitro. Thus, targeting Smad3 precisely on TAN may represent as a novel and effective immunotherapy for cancer. Acknowledgments: This study was supported by Lui Che Woo Institute of Innovative Medicine (CARE program), Research Grants Council of Hong Kong (GRF 14117815, 14121816, 14163317, C7018-16G, TRS T12-402/13N), Health and Medical Research Fund (03140486, 14152321), Innovation and Technology Fund of Hong Kong (ITS/068/18), Direct Grant for Research CUHK (2017.002). Note: This abstract was not presented at the meeting. Citation Format: Patrick Ming-Kuen Tang, Philip Chiu-Tsun Tang, Jeff Yat-Fai Chung, Xiao-Ru Huang, Ka-Fai To, Hui-Yao Lan. Smad3 silences neutrophil anticancer activity in the tumor microenvironment [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 1081.