Citation

All breast cancer subtypes, except triple negative breast cancer (TNBC), possess at least one of the targetable receptors: estrogen receptor ? (ER?), progesterone receptor (PR), and/or human epidermal growth factor receptor 2 (HER2). Having none of these biomarkers, TNBC patients face poor prognoses, especially those suffering from obesity. Obesity is associated with upregulated IGF signalling and hypercholesterolemia. Deregulated cholesterol metabolism is a hallmark of cancer. 27-OHC is the most abundant cholesterol metabolite. Notably, 30%-60% of TNBC express estrogen receptor ? (ER?) to which 27-OHC binds preferentially. This project investigates whether ER? and deregulated cholesterol metabolism, interlinked by a positive feedback loop with EGFR and IGF1 R signalling, drive TNBC progression. Western blotting and qPCR were used to assess the abundance of ER? proteins and mRNA in normal and cancerous breast cells, and the impact of estradiol (E2), 27- OHC, and IGF-I on MDA-MB 231, MCF-7 and BT-20 cells. Subsequently, the effect of ER? silencing by siRNA, and ER? inhibition by 4-[2-Phenyl-5,7-bis(trifluoromethyl) pyrazolo[1,5-a] pyrimidin-3-yl] phenol (PHTPP) on ER?, EGFR, and IGF1 R levels was assessed. Tritiated thymidine incorporation assay and quantitative phase imaging (HoloMonitor) were used to investigate changes in cell proliferation upon simvastatin treatment. Additionally, HoloMonitor was used to investigate the impact of simvastatin on motility, and cell fate. This project found that MDA-MB 231 and BT-20 cells have high levels of ER? protein and mRNA. Upon ER? stimulation by E2, EGFR, and IGF1 R levels increase. In line with that ER? silencing results in a dose-dependent decrease in EGFR and IGF1 R proteins in TNBC cells. Simvastatin significantly decreases proliferation in ER?+ER?- MCF-7 cells and in ER?+ER?- TNBC cells, being cytotoxic at 8µM doses. Due to unsuccessful ER? silencing/inhibition and data inconsistencies stemming from the use of phenol-containing cell culture media, the data does not support the hypothesis where ER? and deregulated cholesterol metabolism drive TNBC progression.