Abstract P6-06-12: Upregulation of beige adipocytes in African-American triple negative breast tumors induce tumorigenesis by promoting anti-inflammatory microenvironment

Background: The complexity of breast cancer (BC) development and progression is heavily influenced by the cross-talk of critical cell types within the tumor microenvironment. While there have been many advancements in BC treatment, triple negative breast cancer (TNBC) still exhibits the lowest rate of response and the nature of its aggressive properties remain poorly understood. African American (AA) women are disproportionally affected and have worse overall survival. Our lab previously reported important role of beige adipocytes in breast tumor growth. Interestingly, we found beige adipocytes were highly up regulated in AA TN breast tumors when compared to TNBC from Caucasian (CA) women. In this study, we have further investigated the mechanisms that increase beige adipocytes in AA TN breast tumors and their influence on breast tumor growth. Methods: Human tumor samples provided by Cooperative Human Tissue Network and National Disease Research Institute were subjected to immunohistochemistry (IHC) and western blot analysis to examine key beige adipocyte markers. To further investigate the mechanisms by which beige adipocytes may contribute tumor growth, xenografts were established from AA TNBC cell lines HCC70, HCC1806 and MDA-MB 468. Tumors excised at various time points were examined for beige adipocyte markers and their key regulators using validated species specific primers to distinguish between host and tumor cell contributions. Boyden chamber assays and ex-vivo experiments were performed to examine whether beige adipocytes were recruited from the host or induced in xenografts, and test whether paracrine secretion of cytokines or contact between various cell types were necessary for adipose browning in these tumors. Possible involvement of lactic acid-mediated adipose browning in these tumors was tested by inhibiting lactate dehydrogenase using sodium oxamate. We further examined whether increased browning in these tumors was associated with increase in anti-inflammatory cytokines that promote M2 macrophage phenotype and angiogenesis, both of which are highly implicated in tumor progression. Results: Both quantitative IHC and western blot analysis showed higher expression of beige adipocyte markers CD137 and TMEM26 in AA TNBC compared to CA TNBC. Expression of beige marker CD137 was detected in all xenografts from AA TNBC by IHC. Quantitative gene expression analysis (qPCR) revealed that host contributed to the origin of beige adipocytes in these tumors. We demonstrate using Boyden Chamber assay that contact between tumor cells and host adipocytes was important for adipose browning. Ex-vivo experiments also showed that breast cancer cells in contact with either host adipocytes or 3T3-L1 mouse adipocyte cell line increased the expression of beige markers that could be attenuated by lactate dehydrogenase inhibitor. We further show that increase in beige adipocytes in AA TNBC was associated with high anti-inflammatory cytokines IL13/IL4 expression, as well as anti-inflammatory pro-tumorigenic M2 macrophages and high angiogenesis. Conclusion: Key beige markers CD137 and TMEM26 are significantly upregulated in AA TNBC compared to the CA TNBC. Host microenvironment contributed to beige adipocyte characteristics in response to lactic acid-mediated adipose browning of tumor cells. Furthermore, beige adipocytes increased anti-inflammatory cytokines that facilitate accumulation of M2 macrophages and promote angiogenesis. Our results implicate that beige adipocytes are key mediators of aggressive tumor development in AA TNBC and could potentially be targeted for therapeutic purposes. Citation Format: Brandis A. Moore, Briana Osorio, Rajan Singh, Shehla Pervin. Upregulation of beige adipocytes in African-American triple negative breast tumors induce tumorigenesis by promoting anti-inflammatory microenvironment [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-06-12.