Triple-negative breast cancer (TNBC) patients have the poor prognosis due to their high metastatic potential and lack of targeted therapies. Emerging epidemiological data suggest that obesity is associated with increased incidence of more aggressive triple-negative breast cancer; however, mechanisms are unclear. During obesity, adipocytes within breast tissues recruit macrophages. M2-like macrophages can exacerbate TNBC progression; however, obese breast tissue is reported to be enriched with M1-like adipose tissue macrophages (ATMs), which are anti-tumorigenic. These results raise a paradox: how does obesity promote tumor progression if it activates an anti-tumorigenic macrophage phenotype?

Here we show that obesity promotes a distinct pro-inflammatory phenotype (metabolically activated macrophages; MMe) in breast ATMs, which promotes TNBC progression. We showed that ATMs isolated from obese women express cell surface markers of MMe (CD36, ABCA1) but not M1 (CD38, CD319) macrophages. We further found that pretreating TNBC cells with MMe (but not M1) derived conditioned media increase tumorsphere growth, and frequency of tumor-incidence when injected into mice in limited dilutions. Remarkably, we saw the same effect with obesity on tumor-incidence in both spontaneous and syngeneic TNBC mouse models. Moreover, blocking cytokine expression specifically in MMe using myeloid specific genetic knockout mice diminishes the effect of obesity on tumor-incidence. Interestingly, a subset of these MMe-secreted cytokines shared a common signal transducer, gp130, which led us to investigate the role of gp130 in tumors. Knocking down gp130 in cancer cells inhibits the MMe-induced stat-3 phosphorylation and tumorsphere growth in vitro, and diminishes the MMe-mediated effect of obesity on tumor-incidence in mice. Together these findings suggest that obesity-induced metabolically activated macrophages (MMe) in breast adipose tissue secrete inflammatory cytokines that promotes the TNBC tumor-progression by activating gp130 in cancer cells.

A comprehensive understanding of the signaling mechanism(s) involved in metabolic activation of mammary ATMs would enable development of targeted therapies towards this specific pro-tumorigenic macrophage phenotype, thereby leaving the immune system of cancer patients intact.

Citation Format: Payal Tiwari, Ariane Blank, Chang Cui, Kelly Schoenfelt, Seema A. Khan, Marsha R. Rosner, Lev Becker. Metabolically activated macrophages mediate obesity-driven TNBC progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4964.