PO-287 ’Annex’in A1 to the breast tumour microenvironment by aiding in macrophage polarisation

Abstract

IntroductionTumor-associated macrophages (TAMs) choreograph various aspects of the tumour microenvironment. Macrophages exhibit cellular plasticity and can be polarised to M1 or M2 subtypes in the presence of different microenvironment ’signals’. Annexin A1 (ANXA1), an anti-inflammatory protein is highly expressed in the metastatic breast cancer. Many studies have found that the TAMs exhibit a higher pro-tumorigenic and anti-inflammatory, M2 phenotype.Material and methodsGene Expression Omnibus (GEO) and ArrayExpress were used to assess the association between TAMs and breast cancer in the patients. Percentage of M2 macrophages was evaluated using flow cytometry in the breast tumours from the MMTV mice and the mammary fat pad of the control mice. Macrophage education by breast cancer was assessed by ex vivo differentiation of bone-marrow derived macrophages (BMDMs) in the presence or absence of breast cancer conditioned media by flow cytometry, ELISA, and mRNA expression.Results and discussionsClinically, we found that the M2 TAMs were highly enriched in the claudin-low breast cancer subtype and was strongly associated with ANXA1 gene expression. In the MMTV mouse model, M2 TAMs were higher in the breast tumours as compared to the mammary tissues along with higher expression of ANXA1 and other M2 markers. Additionally, BMDMs were skewed to a more M2 TAM-like phenotype upon co-culture with the breast cancer cells, with enhanced migratory and invasive properties and phagocytic potential, which was reduced in the ANXAI-deficient BMDMs. In another in vivo mouse model employed in our study, we found that the pro-tumorigenic M2 macrophages were significantly reduced in the breast tumours isolated from the ANXA1-deficient mice as compared to the wild type, when 4 T1 had been injected orthotopically in them.ConclusionCollectively, our data describe a novel regulatory role of Annexin A1 in promoting macrophage polarisation to a more M2 phenotype in the breast tumour microenvironment both ex vivo and in vivo, thus presenting itself and its associated receptor as a potential drug target.Furthermore, our secretome data has also revealed some interesting results and Affymetrix microarray profiling and RNA sequencing studies are underway to explore the unique signature molecules and the signalling mechanism involved in governing this dynamic process.