Abstract 502: Characterizing breast cancer subtype-specific responses to macrophages.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Breast cancer is a multi-faceted disease giving rise to five distinct subtypes. Emerging data show that each of these subtypes has distinct interactions with the surrounding stroma and immune cell populations present in the microenvironment. We hypothesized that macrophages have distinct interactions with breast cancer in a subtype-dependent manner. Using a coculture system, we evaluated changes in THP-1 differentiation, morphology and gene expression during the monocyte-to-macrophage transition in response to cell lines representing the basal-like (HCC1937, MDA-MB-468, SUM149), luminal (MCF-7, T47D, ZR-75-1), epidermal growth factor receptor/HER2-enriched (BT474, SKBR3) and claudin-low (Hs578T, MDA-MB-231, SUM159) breast cancer subtypes. Macrophage polarization phenotypes were validated by immunofluorescence staining for M1 (CD163) and M2 (CD36) macrophage markers in normal tissue sections adjacent to representative breast tumors. We further investigated differences in genomic and cytokine expression profiles, proliferation, and chemosensitivity (to Doxorubicin) of the breast cancer cell lines in response to THP-1 coculturing. Greatest levels of THP-1 differentiation was induced in basal-like cocultures (mean differentiation 79%, compared to differentiation <42% for all other cell lines). Additionally, all basal-like breast cancers strongly induced macrophage polarization to a mixed M1 and M2 phenotype, however, one cell line from both the claudin-low (SUM159) and HER2-enriched (SKBR3) subtypes also elicited this response. The impact on THP-1 differentiation was clearly visualized by morphological changes after 48 hours of coculturing with these cell lines. Similar macrophage polarization phenotypes were predominantly observed in the triple negative breast cancer, normal-adjacent human tissues. Basal-like breast cancers underwent equally dramatic gene expression changes in response to macrophages compared to luminal cell lines, and demonstrated a more highly differential milieu of secreted cytokines. Ingenuity Pathway Analysis (IPA) revealed significant upregulation of DNA damage and repair pathways in the basal-like subtype under coculture conditions. Interestingly, luminal breast cancer cell lines exhibited increased proliferation as a result of macrophage interaction, while the growth of all basal-like lines was diminished in the presence of THP-1 macrophages. Consistent with alterations in DNA damage response, basal-like breast cancers (SUM149) displayed reduced chemosensitivity after coculturing. These results define subtype-specific interactions between breast cancers and macrophages, and suggest a possible mechanism by which macrophages may promote chemoresistance in more aggressive basal-like breast cancers. Citation Format: Delisha A. Stewart, Yinmeng Yang, Xuezheng Sun, Liza Makowski, Kristen Brantley, Jean Gowen Cook, Melissa A. Troester. Characterizing breast cancer subtype-specific responses to macrophages. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 502. doi:10.1158/1538-7445.AM2013-502