Reversing the Genomic, Epigenetic, and Triple-Negative Breast Cancer-Enhancing Effects of Obesity.

The reversibility of the procancer effects of obesity was interrogated in formerly obese C57BL/6 mice that lost weight via a nonrestricted low-fat diet (LFD) or 3 distinct calorie-restricted (CR) regimens (low-fat CR, Mediterranean-style CR, or intermittent CR). These mice, along with continuously obese mice and lean control mice, were orthotopically injected with E0771 cells, a mouse model of triple-negative breast cancer. Tumor weight, systemic cytokines, and incidence of lung metastases were elevated in the continuously obese and nonrestricted LFD mice relative to the 3 CR groups. Gene expression differed between the obese and all CR groups, but not the nonrestricted LFD group, for numerous tumoral genes associated with epithelial-to-mesenchymal transition as well as several genes in the normal mammary tissue associated with hypoxia, reactive oxygen species production, and p53 signaling. A high degree of concordance existed between differentially expressed mammary tissue genes from obese versus all CR mice and a microarray dataset from overweight/obese women randomized to either no intervention or a CR diet. Assessment of differentially methylated regions in mouse mammary tissues revealed that obesity, relative to the 4 weight loss groups, was associated with significant DNA hypermethylation. However, the anticancer effects of the CR interventions were independent of their ability to reverse obesity-associated mammary epigenetic reprogramming. Taken together, these preclinical data showing that the procancer effects of obesity are reversible by various forms of CR diets strongly support translational exploration of restricted dietary patterns for reducing the burden of obesity-associated cancers. PREVENTION RELEVANCE: Obesity is an established risk and progression factor for triple-negative breast cancer (TNBC). Given rising global rates of obesity and TNBC, strategies to reduce the burden of obesity-driven TNBC are urgently needed. We report the genomic, epigenetic, and procancer effects of obesity are reversible by various calorie restriction regimens.

The flaxseed lignan secoisolariciresinol diglucoside decreases local inflammation, suppresses NFκB signaling, and inhibits mammary tumor growth.

PURPOSE: Exposure to the polyphenolic plant lignan secoisolariciresinol diglucoside (SDG) and its metabolite enterolactone (ENL) has been associated with reduced breast cancer progression, particularly for estrogen receptor alpha (ERα)-negative disease, and decreased preclinical mammary tumor growth. However, while preclinical studies have established that SDG and ENL affect measures of progression in models of triple-negative breast cancer (TNBC, a subset of ERα-negative disease), the molecular mechanisms underlying these effects remain unclear. METHODS: C57BL/6 mice were fed a control diet (control, 10% kcal from fat) or control diet + SDG (SDG, 100 mg/kg diet) for 8 weeks, then orthotopically injected with syngeneic E0771 mammary tumor cells (a model of TNBC); tumor growth was monitored for 3 weeks. The role of reduced NF-κB signaling in SDG's anti-tumor effects was explored in vitro via treatment with the bioactive SDG metabolite ENL. In addition to the murine E0771 cells, the in vitro studies utilized MDA-MB-231 and MCF-7 cells, two human cell lines which model the triple-negative and luminal A breast cancer subtypes, respectively. RESULTS: SDG supplementation in the mice significantly reduced tumor volume and expression of phospho-p65 and NF-κB target genes (P < 0.05). Markers of macrophage infiltration were decreased in the distal-to-tumor mammary fat pad of mice supplemented with SDG relative to control mice (P < 0.05). In vitro, ENL treatment inhibited viability, survival, and NF-κB activity and target gene expression in E0771, MDA-MB-231, and MCF-7 cells (P < 0.05). Overexpression of Rela attenuated ENL's inhibition of E0771 cell viability and survival. CONCLUSIONS: SDG reduces tumor growth in the E0771 model of TNBC, likely via a mechanism involving inhibition of NF-κB activity. SDG could serve as a practical and effective adjuvant treatment to reduce recurrence, but greater understanding of its effects is needed to inform the development of more targeted recommendations for its use.

Leptin Signaling Mediates Obesity-Associated CSC Enrichment and EMT in Preclinical TNBC Models.

Obesity is associated with poor prognosis in triple-negative breast cancer (TNBC). Preclinical models of TNBC were used to test the hypothesis that increased leptin signaling drives obesity-associated TNBC development by promoting cancer stem cell (CSC) enrichment and/or epithelial-to-mesenchymal transition (EMT). MMTV-Wnt-1 transgenic mice, which develop spontaneous basal-like, triple-negative mammary tumors, received either a control diet (10% kcal from fat) or a diet-induced obesity regimen (DIO, 60% kcal from fat) for up to 42 weeks (n = 15/group). Mice were monitored for tumor development and euthanized when tumor diameter reached 1.5 cm. Tumoral gene expression was assessed via RNA sequencing (RNA-seq). DIO mice had greater body weight and percent body fat at termination than controls. DIO mice, versus controls, demonstrated reduced survival, increased systemic metabolic and inflammatory perturbations, upregulated tumoral CSC/EMT gene signature, elevated tumoral aldehyde dehydrogenase activity (a CSC marker), and greater leptin signaling. In cell culture experiments using TNBC cells (murine: E-Wnt and M-Wnt; human: MDA-MB-231), leptin enhanced mammosphere formation, and media supplemented with serum from DIO versus control mice increased cell viability, migration, invasion, and CSC- and EMT-related gene expression, including Foxc2, Twist2, Vim, Akt3, and Sox2 In E-Wnt cells, knockdown of leptin receptor ablated these procancer effects induced by DIO mouse serum. These findings indicate that increased leptin signaling is causally linked to obesity-associated TNBC development by promoting CSC enrichment and EMT.Implications: Leptin-associated signals impacting CSC and EMT may provide new targets and intervention strategies for decreasing TNBC burden in obese women. Mol Cancer Res; 16(5); 869-79. ©2018 AACR.