Abstract 1095: Macrophage is a novel and rich source of cancer-associated fibroblasts in the tumor microenvironment

Background: Cancer-associated fibroblasts (CAF) are highly heterogeneous and their origins are largely unknown. Recently, we revealed that bone marrow-derived macrophages (BMDM) can further differentiate into myofibroblasts locally at the inflammatory site in a Smad3-dependent manner, but its potential role in the tumor microenvironment (TME) is still unexplored. Thus, we hypothesize that tumor-associated macrophages (TAM) may be able to transit into CAF, termed TAM to CAF transition (TAM-CAF), in TME for cancer promotion. Here, we are the first study to discover TAM-CAF as a common phenomenon in cancer. Methods: The evidence of TAM-CAF was confirmed on tumor biopsies from several cancer types including non-small cell lung carcinoma (NSCLC) tissue microarray. The occurrence pattern of TAM-CAF was determined in LysM-Cre/Rosa26-tdTomato mice with syngeneic lung carcinoma LLC by the fate-mapping study. The pathogenic role of TAM-CAF was examined by adoptive transferring of TAM-CAF cells onto LLC-bearing NOD-SCID mice. The regulatory mechanism was further elucidated on Smad3-WT/KO mice in vivo and BMDM in vitro. Results: Interestingly, we observed myofibroblast marker expressing TAM (α-SMA+CD68+) in the tumor biopsies of liver, kidney and lung cancers, which contributed to ~40% of the total CAF and positively associated with the NSCLC mortality. Fate mapping study confirmed the existence of macrophage-derived CAF (α-SMA+ tdTomato+) in LLC-tumor, where the contribution of TAM-CAF on CAF production was progressively increased throughout the tumorigenesis. Furthermore, adoptive transferring of TAM-CAF cells largely promotes tumor progression in LLC-bearing NOD/SCID mice associated with a marked increase of angiogenesis in the TME. Mechanistically, we found that phosphorylation of Smad3 is significantly associated with CAF production in NSCLC-TME (n=120), supported by the dramatic reduction of TAM-CAF in LLC-tumor and BMDM after deletion of Smad3. More importantly, we identified a conserved Smad3 binding site on the 5’UTR of FAP gene by ECR browser and ChIP assay in vitro; revealing its direct regulation on FAP expression at transcriptional level during TAM-CAF. Conclusion: We are the first study to uncover TAM as a rich source of CAF, which is commonly occurred in TME for cancer promotion via a Smad3-dependent mechanism. Thus, TAM-CAF may represent a novel and precision therapeutic target 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). Citation Format: Philip Chiu-Tsun Tang, Patrick Ming-Kuen Tang, Jeff Yat-Fai Chung, Xiao-Ru Huang, Ka-Fai TO, Hui-Yao LAN. Macrophage is a novel and rich source of cancer-associated fibroblasts 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 1095.