OXYSTEROLS AND PHYTOSTEROLS IN HUMAN PATHOPHYSIOLOGY: Adipocytes in tumour microenvironment promote chemoresistance in triple-negative breast cancer through oxysterols

Graphical abstract Adipocytes-derived oxysterols protect TNBC cells from chemotherapy activating LXRα-Pgp axis. Figure generated with Biorender. Abstract Objective Triple-negative breast cancer (TNBC) patients with excess adipose tissue experience poorer disease-free survival than those with a healthy body mass index. Adipocytes store and release cholesterol, which can be hydroxylated to form oxysterols. These cholesterol derivatives activate the liver X receptor (LXR) pathway. This study tested the hypothesis that adipocytes contribute to an imbalanced tumour microenvironment by exposing cancer cells to elevated oxysterols, mimicking chemotherapy exposure conditions and priming for chemoresistance. Methods Tumour tissue microarray from 148 TNBC patients was assessed using immunohistochemistry for CH25H , CYP46A1 , CYP27A1 , P-glycoprotein ( Pgp/ ABCB1 ) expression and survival outcomes were assessed. Gene expression was compared between tumours from patients (GSE78958) and mouse models (GSE151866) with high versus low adiposity. In vitro , cell lines from lineages found in the tumour microenvironment were evaluated for oxysterol content, secretion, expression of relevant enzymes, and ability to induce ABCB1 expression and drug resistance in TNBC cells. Results In patients, stromal expression of oxysterol-synthesising enzymes correlated with ABCP1 expression in cancer epithelial cells and was associated with shorter disease-free survival. Adipocytes-conditioned media contained significantly higher oxysterol levels than that conditioned by other cell types and induced ABCB1 expression and drug resistance in MDA.MB.468 cells. Obese mice had elevated levels of Abcb1 in tumours compared to lean counterparts. Conclusion Adipocytes secrete oxysterols that promote drug resistance in vitro and correlate with oxysterol: Pgp axis and survival in vivo . Significance statement This study reveals a mechanism by which adipose tissue contributes to drug resistance in ER-negative breast cancers, identifying the oxysterol–Pgp axis as a potential therapeutic target.