Obesity contributes to 20% of US female cancer deaths and is linked to increased risk for triple negative breast cancer (TNBC), as well as increased risk of vascular invasion, metastasis, and mortality in breast cancer patients. We previously showed that obesity-induced elevation of hepatocyte growth factor (HGF) signaling through its receptor, cMET, accelerated development of tumors in the C3(1)-TAg GEMM of TNBC compared to low fat diet (LFD)-fed lean controls. Weight loss significantly reduced HGF/cMET signaling in normal mammary glands and cMET in tumors, and reversed high fat diet (HFD)-driven tumor progression, while crizotinib-mediated cMET inhibition limited tumor development and microvascular density in both lean and obese C3(1)-TAg mice. To differentiate tumor-intrinsic versus microenvironment-associated mechanisms, we employed an orthotopic transplant model of a C3(1)-TAg TNBC cell line to investigate tumor growth dynamics in lean, obese, or formerly obese (FOb) microenvironments. We hypothesized that TNBC tumors derived from lean C3(1)-TAg mice and transplanted into obese mice would grow more rapidly, contain more macrophages (MFs) and exhibit greater blood vessel density than tumors in lean or FOb mice due to obesity-induced MF and/or endothelial secretion of HGF. At 8 weeks of age, female FVB/NJ mice were randomized to diet groups (N=20/diet): 1) lean (LFD, 10% kcal from fat), 2) obese (HFD, 60% kcal from fat) 3) or FOb (HFD, 5 weeks; LFD, 5 weeks). Following 10 weeks on diets mice were injected with 2x105 luciferase-tagged C3(1)-TAg cells. Tumor volume was measured by calipers. At 21 days post-injection mice were sacrificed for tissue collection. Normal mammary gland, tumors, and tumor-adjacent adipose + tumor-draining lymph node were collected for histological examination and gene expression analysis. Mammary fat pad mass in obese FVB/NJ mice (0.27 g) was significantly greater than lean (0.14 g) or FOb animals (0.11 g) (P<0.0001). Tumor volume at sacrifice was significantly greater in obese vs lean animals (190 mm3 vs 89.96 mm3, respectively; P<0.05). However, mean final tumor volume in FOb animals (148.0 mm3) did not differ significantly from either lean or obese mice. Our findings show that obesity accelerated tumor progression relative to lean mice. C3(1)-TAg cells transplanted into FOb mice resulted in an intermediate rate of tumor growth, suggesting that obesity-mediated changes to the microenvironment were not fully corrected by weight loss despite normalization of body weight and adiposity. To elucidate how the FOb mammary microenvironment persists in driving TNBC tumor promotion, planned analyses include histological examination of candidate mediators, including MF infiltration and regional lymph node metastasis by diet group, as well as quantification of pro-growth and pro-angiogenic signaling molecules (e.g., HGF, VEGF, Ang2) in lysates of tumors and tumor-adjacent adipose.

Citation Format: Alyssa J. Cozzo, Ottavia Zattra, Alex J. Freemerman, Liza Makowski. Obesity-induced modifications in the mammary gland microenvironment promote TNBC progression even after weight loss [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2974. doi:10.1158/1538-7445.AM2017-2974