A Noncompetitive Small Molecule Inhibitor of Estrogen-regulated Gene Expression and Breast Cancer Cell Growth That Enhances Proteasome-dependent Degradation of Estrogen Receptor α

• Published in: The Journal of biological chemistry Vol. 285; no. 53; pp. 41863 - 41873
• Main Authors: Kretzer, Nicole M., Cherian, Milu T., Mao, Chengjian, Aninye, Irene O., Reynolds, Philip D., Schiff, Rachel, Hergenrother, Paul J., Nordeen, Steven K., Wilson, Elizabeth M., Shapiro, David J.
• Format: Journal Article
• Language: English
• Published: 9650 Rockville Pike, Bethesda, MD 20814, U.S.A Elsevier Inc 31.12.2010; American Society for Biochemistry and Molecular Biology
• Subjects: Breast Cancer; ER Inhibitor; ER-dependent Cell Growth; Estrogen; Estrogen Receptor; Ligand Binding Protein; Molecular Bases of Disease; Receptors; Steroid Hormone Receptor; TPSF; Ligand Binding Protein; Receptors; ER Inhibitor; Estrogen Receptor; Estrogen; Steroid Hormone Receptor; TPSF; ER-dependent Cell Growth; Breast Cancer
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.183723

The mechanisms responsible for 17β-estradiol (E2)-stimulated breast cancer growth and development of resistance to tamoxifen and other estrogen receptor α (ERα) antagonists are not fully understood. We describe a new tool for dissecting ERα action in breast cancer, p-fluoro-4-(1,2,3,6,-tetrahydro-1,3-dimethyl-2-oxo-6-thionpurin-8-ylthio) (TPSF), a potent small-molecule inhibitor of estrogen receptor α that does not compete with estrogen for binding to ERα. TPSF noncompetitively inhibits estrogen-dependent ERα-mediated gene expression with little inhibition of transcriptional activity by NF-κB or the androgen or glucocorticoid receptor. TPSF inhibits E2-ERα-mediated induction of the proteinase inhibitor 9 gene, which is activated by ERα binding to estrogen response element DNA, and the cyclin D1 gene, which is induced by tethering ERα to other DNA-bound proteins. TPSF inhibits anchorage-dependent and anchorage-independent E2-ERα-stimulated growth of MCF-7 cells but does not inhibit growth of ER-negative MDA-MB-231 breast cancer cells. TPSF also inhibits ERα-dependent growth in three cellular models for tamoxifen resistance; that is, 4-hydroxytamoxifen-stimulated MCF7ERαHA cells that overexpress ERα, fully tamoxifen-resistant BT474 cells that have amplified HER-2 and AIB1, and partially tamoxifen-resistant ZR-75 cells. TPSF reduces ERα protein levels in MCF-7 cells and several other cell lines without altering ERα mRNA levels. The proteasome inhibitor MG132 abolished down-regulation of ERα by TPSF. Thus, TPSF affects receptor levels at least in part due to its ability to enhance proteasome-dependent degradation of ERα. TPSF represents a novel class of ER inhibitor with significant clinical potential.