Abstract P5-06-07: Selective inhibition of fibroblast-specific domain discoidin receptor 1 (DDR1) results in reduced collagen deposition and immunomodulatory cytokine release: A potential target to modulate the activity of breast cancer associated fibroblasts
Authors: Fein Daniel EC , Traugh Nicole , Rauner Gat , Mal Youssof , Trepicchio Colin , Kuperwasser Charlotte 
Published: March 2022

Abstract
Background: Cancer-Associated Fibroblasts (CAFs) are a major cell type within breast tumor microenvironment (TME) which have emerged as a new target for cancer therapy given their contributions to tumor growth, metastasis, and suppression of the anti-tumor immune response. In the breast, CAFs are predominantly formed from conversion of tissue-resident mammary fibroblasts through mechanisms including increasing extracellular matrix (ECM) stiffness, ECM composition, hypoxia, and activating signals TGFβ and IL-6. Domain Discoidin Receptor 1 (DDR1) is a cell surface tyrosine kinase receptor expressed by epithelial and stromal cells which is activated by collagen within the TME. DDR1 expression and activity has been implicated in the development of fibrosis within the breast as well as chemotherapy resistance in several tumor types. Thus, we set out to examine whether selective inhibition of DDR1 would affect CAF immunomodulatory function to generate an immune-permissive breast microenvironment and result in reduction in stromal desmoplasia. Results: Using a human cell model of CAFs, we studied the effects of DDR1 inhibition (DDR1i) on the expression of immune modulating factors and CAF functions and features. Using a multiplex cytokine array, we observed high expression levels of key immunomodulatory cytokines IL-6, IL-8, and MCP-1 in conditioned media collected from CAF-like cells cultured in 3D collagen gels which were consequently downregulated in the presence of DDR1i. Downregulation of IL-6, IL-8, and MCP-1 induced by DDR1i was also by observed by RT-qPCR, with enhanced downregulation seen in cells cultured with increasing concentrations of collagen. Downregulation of CAF markers αSMA and FAP as well as Collagen type 1 were observed with selective DDR1 inhibition, an effect seen also with CAF-like cells stimulated with recombinant TGFβ1. Additionally, we observed reduced contraction of CAF-like cells in 3D collagen gels in the presence of DDR1i. In vivo DDR1i resulted in tissue remodeling and reduced collagen deposition as well as changes in immunomodulatory cytokine release within the mammary gland in a murine model. We observed downregulation of IL-6, as well as downregulation of Collagens type I, type IV, and MMP9. RT-qPCR also revealed reduced expression of potent chemokines CXCL1 and CXCL12 in mammary gland tissue of mice treated with DDR1i. Consistent with this, multiplexed flow cytometry demonstrated trends of increased CD45.2+ immune cell infiltration within the mammary glands and reduction of Ly6G+/Ly6C- neutrophil infiltration within the mammary gland and spleens in mice treated with DDR1i. Conclusions: Collectively, these findings suggest that breast fibroblast-specific DDR1 mediates collagen deposition and immunomodulatory function within the mammary gland and warrants further investigation as a potential target for CAF-modulating therapy in breast cancer.
Citation Format: Daniel EC Fein, Nicole Traugh, Gat Rauner, Youssof Mal, Colin Trepicchio, Charlotte Kuperwasser. Selective inhibition of fibroblast-specific domain discoidin receptor 1 (DDR1) results in reduced collagen deposition and immunomodulatory cytokine release: A potential target to modulate the activity of breast cancer associated fibroblasts [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-06-07.