Investigating the Effects of Obesity and Therapeutic Intervention on Immune Responses in Breast Cancer

Around 1 in 7 women in the UK are affected by breast cancer in the UK, with both the risk and progression of the disease known to be influenced by a variety of environmental and genetic factors, including obesity. Obesity-induced changes, including increased free fatty acid (FFA) availability, dysregulated inflammation and adipocyte death, all modulate the mammary adipose environment and are hypothesised to drive neoplasia. As the prevalence of obesity continues to rise there is a greater need to understand the relationship between obesity and breast cancer to guide the development novel therapeutics to improve survival outcomes. One promising therapeutic angle involves the repurposing of metformin as retrospective studies have highlighted an association between metformin treatment and improved survival. Here we investigated the metabolic effects of metformin, an inhibitor of mitochondrial respiration, using a metabolic stress test to determine how it modulates both glycolytic and mitochondrial metabolism in breast cancer cells. Alongside this, we assessed the effects of two of the most abundant FFAs in circulation, oleic acid (18:1) and palmitic acid (16:0), on macrophage and breast cancer cell characteristics. Macrophages were cultured with FFAs for 48 hours or 8 days to assess the impact of FFAs on macrophage phenotype. The FFAs were also added into the culture of three breast cancer cell lines, MDA-MB-231, MCF7 and SKBR3 which were chosen to reflect some of the different subtypes of breast cancer, to determine their effects on metabolism and cellular characteristics. Here we have demonstrated that low concentrations of metformin still inhibit OXPHOS but the sensitivity of the cells and the observed effects on glycolysis vary across breast cancer subtypes. The FFAs were shown to alter macrophage phenotype when in culture for prolonged periods, with PA promoting a pro-inflammatory phenotype. Metabolically, OA was observed to increase the rates of mitochondrial respiration whilst glycolysis rates were lowered in its presence. These effects highlight the importance of the interplay between obesity and breast cancer and how the heterogeneity of breast cancer plays a key role in therapeutic response. Further delineation of these effects should clarify how obesity-induced changes drive the poorer survival outcomes associated with obesity.