Targeting The Crosstalk Between Tumor Cells And Adipocytes To Block Breast Cancer Progression

It is now well-established that the local microenvironment of an emerging tumor plays a vital role in various steps of tumorigenesis. Stromal cells, such as fibroblasts, endothelial and various inflammatory cells, can contribute to tumor progression, and tumor cells can directly model their microenvironment, influencing host cells to secrete factors that favor cancer cell survival and growth. Recent studies have demonstrated the existence of cross-talk between breast cancer (BC) cells and adipocytes, the most abundant stromal cell in the breast, supporting their involvement in BC and consistent with epidemiological studies reporting the association of obesity and insulin resistance/diabetes with a higher risk and poor prognosis of BC. Based on this evidence, we investigated whether adipocyte de-differentiation is the crucial trigger in inducing pro-tumor microenvironment remodeling and tumor progression. Co-culture of 4T1 mouse mammary tumor cells using Transwell or their conditioned medium with mature adipocytes derived from the 3T3-L1 mouse cells induced adipocyte de-differentiation, observed as a reduced expression of specific differentiation markers (peripilin, adipocyte protein 2 (aP2), PPARa and adiponectin) in Western blots and by qRT-PCR, and a reduced triglyceride content as assessed by oil red O staining compared to mature adipocytes. Strong adipocyte de-differentiation, associated with an increase in pro-inflammatory molecules (IL6 and CCL2), was also induced in vitro by tumor interstitial fluids obtained from MMT-PyMT transgenic mice, but not by plasma of these mice. Preliminary studies to identify molecules involved in the cross-talk indicated that the phenomenon is exosome-unrelated. Based on the relevant role of the PPARa transcription factor in inducing and maintaining adipocyte differentiation, we co-cultured adipocytes with 4T1 BC cells in the presence of several PPARa agonists enriched in the diets of many populations displaying a low incidence of cancer (þ3-fatty acids), and in the presence of glitazones (rosiglitazone and pioglitazone) to force adipocyte stable differentiation. While most of these compounds did not block adipocyte de-differentiation induced by tumor cells, pioglitazone and eicosanoid acid showed some activity in inhibiting this de-differentiation in vitro. Treatment of MMTV-PyMT transgenic mice at tumor onset by oral gavage with pioglitazone did not significantly reduce mammary tumor growth compared to controls, whereas eicosanoid acid treatment significantly reduced tumor multiplicity and tumor burden compared to controls. Overall, our results suggest that tumor-induced adipocyte de-differentiation participates in tumorigenesis and that the blockade of this program can inhibit tumor progression. Supported by AIRC and Fondazione Cariplo. Citation Format: Tiziana Triulzi, Valentina Ciravolo, Viola Regondi, Martina Di Modica, Claudia Chiodoni, Elda Tagliabue. Targeting the crosstalk between tumor cells and adipocytes to block breast cancer progression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 748.