Cholesterol biosynthesis pathway as a novel mechanism of resistance to estrogen deprivation in estrogen receptor-positive breast cancer

• Published in: Breast cancer research : BCR 2016-06, Vol.18 (1), p.58-58, Article 58
• Main Authors: Simigdala, Nikiana, Gao, Qiong, Pancholi, Sunil, Roberg-Larsen, Hanne, Zvelebil, Marketa, Ribas, Ricardo, Folkerd, Elizabeth, Thompson, Andrew, Bhamra, Amandeep, Dowsett, Mitch, Martin, Lesley-Ann
• Format: Article
• Language: English
• Subjects: Antineoplastic Agents, Hormonal - pharmacology; Antineoplastic Agents, Hormonal - therapeutic use; Biomarkers; Biosynthetic Pathways; Breast cancer; Breast Neoplasms - drug therapy; Breast Neoplasms - genetics; Breast Neoplasms - metabolism; Breast Neoplasms - mortality; Cell Line, Tumor; Cell Proliferation - drug effects; Cholesterol; Cholesterol - biosynthesis; Cholesterol Esters - metabolism; Diagnosis; Drug Resistance, Neoplasm - genetics; Estrogen; Estrogens - metabolism; Female; Gene Expression Profiling; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Health aspects; Humans; Phenotype; Physiological aspects; Prognosis; Proteome; Proteomics - methods; Receptors; Receptors, Estrogen - metabolism; RNA Interference; Transcriptome; Treatment Outcome
• ISSN: 1465-542X; 1465-5411; 1465-542X
• DOI: 10.1186/s13058-016-0713-5

Therapies targeting estrogenic stimulation in estrogen receptor-positive (ER+) breast cancer (BC) reduce mortality, but resistance remains a major clinical problem. Molecular studies have shown few high-frequency mutations to be associated with endocrine resistance. In contrast, expression profiling of primary ER+ BC samples has identified several promising signatures/networks for targeting. To identify common adaptive mechanisms associated with resistance to aromatase inhibitors (AIs), we assessed changes in global gene expression during adaptation to long-term estrogen deprivation (LTED) in a panel of ER+ BC cell lines cultured in 2D on plastic (MCF7, T47D, HCC1428, SUM44 and ZR75.1) or in 3D on collagen (MCF7) to model the stromal compartment. Furthermore, dimethyl labelling followed by LC-MS/MS was used to assess global changes in protein abundance. The role of target genes/proteins on proliferation, ER-mediated transcription and recruitment of ER to target gene promoters was analysed. The cholesterol biosynthesis pathway was the common upregulated pathway in the ER+ LTED but not the ER- LTED cell lines, suggesting a potential mechanism dependent on continued ER expression. Targeting the individual genes of the cholesterol biosynthesis pathway with siRNAs caused a 30-50 % drop in proliferation. Further analysis showed increased expression of 25-hydroxycholesterol (HC) in the MCF7 LTED cells. Exogenous 25-HC or 27-HC increased ER-mediated transcription and expression of the endogenous estrogen-regulated gene TFF1 in ER+ LTED cells but not in the ER- LTED cells. Additionally, recruitment of the ER and CREB-binding protein (CBP) to the TFF1 and GREB1 promoters was increased upon treatment with 25-HC and 27-HC. In-silico analysis of two independent studies of primary ER+ BC patients treated with neoadjuvant AIs showed that increased expression of MSMO1, EBP, LBR and SQLE enzymes, required for cholesterol synthesis and increased in our in-vitro models, was significantly associated with poor response to endocrine therapy. Taken together, these data provide support for the role of cholesterol biosynthesis enzymes and the cholesterol metabolites, 25-HC and 27-HC, in a novel mechanism of resistance to endocrine therapy in ER+ BC that has potential as a therapeutic target.