Endocrine Abstracts

Breast cancer (BCa) patients who present at clinic with elevated circulating LDL-cholesterol have poor prognosis, whilst pharmacological and lifestyle interventions that lower circulating cholesterol (statins, exercise, low saturated fat intake etc.) are associated with better treatment efficacy. The molecular mechanisms that link cholesterol with chemotherapy resistance (CR) remain unexplored. Hydroxycholesterols (OHCs) activate the transcription factor LXR, and are formed in the liver from cholesterol during bile acids synthesis, or in macrophages, fibroblasts and adipocytes at extra-hepatic sites. Here we explore the hypothesis that hydroxycholesterols induce chemotherapy resistance through activation of non-canonical LXR target genes. The promoters of a panel of chemotherapy resistance genes were assessed for LXR occupancy (LXR-ChIP-Seq) and their expression correlated with LXR expression (BCa RNA-Seq). LXR-specific activation of candidate LXR-regulated chemoresistance markers was confirmed in a panel of BCa cell lines exposed to LXR agonists (hydroxycholesterols and synthetic ligands), and an antagonist (GSK2033) using qPCR. Utilising the natural fluorescence of the BCa chemotherapy agent Epirubicin, we found pre-treatment of BCa cell cultures with LXR agonists enhanced intra-cellular drug efflux (non-linear curve fitting: P<0.0001). Epirubicin cytotoxicity was impaired by LXR activation in colony forming assays (one-tailed t-test MDAMB231: P=0.0049; MDAMB468: P=0.0051; MCF7: P=0.0092); LXR antagonists reversed these affects. Finally we measured endogenous hydroxycholesterol concentrations in the tumours of 28 BCa patients using LC-MS/MS. We observed high intra-tumour variance in OHC concentration, presumably reflecting differences in tumour invasion of OHC synthesising macrophages, fibroblasts and/or adipocytes. Our data support the hypothesis that elevated LDL-C may drive innate chemotherapy resistance in breast tumours through LXR-mediated induction of chemotherapy efflux pumps. This molecular mechanisms represents a metabolic legion that is targetable through existing pharmacological and lifestyle interventions which could allow patients a route to modify the efficacy of their chemotherapy.