Aromatase independent estradiol synthesis in triple-negative breast cancer cells.

Abstract

e13110 Background: Breast cancer is a leading cause of cancer related deaths in women in the United States. With advancements in universal screening technology, still one in eight women is likely to be diagnosed in their lifetime. Multiple factors including genetic predispositions (BRAC-1/2, TP53, STK11), environmental exposures (air pollutants, industrial chemicals), and individual risk factors (nulliparity, obesity) are presumed to contribute to the progression of breast cancer. Breast cancers are hormonally regulated signaling to Estrogen (Er + ), Progesterone (Pr + ), or Human Epidermal Growth Factors Receptor (HER 2+ ). Another variant, triple-negative breast cancer (TNBC), minimally expresses hormone receptors and lacks targeted therapy. TNBC typically follows an aggressive course leading to high morbidity and mortality rates. Steroidogenic hormone estradiol plays a key role in promoting breast cell growth and can in turn lead to tumorigenesis. Aromatase is the enzyme that converts androgens to estradiol. In TNBC, aromatase activity is often low or absent leading to TNBC being considered estrogen independent. Using tumorigenic and unaffected breast tissue, our lab has identified a binding partner with aromatase, aromatase interacting parter in breast (AIPB), whose over expression down regulates estradiol synthesis. Use of anti-helminth medications as potential adjunctive treatments for TNBC is an emerging field of investigation. We also observed that AIPB is not acutely regulated, but stimulated by estrogen agonist kinetically. Our current research suggests anti-helminth Pyrvinium pamoate influences expression of AIPB in TNBC cells leading to the down regulation of estradiol synthesis. Methods: Genetically engineered TNBC MDA-MB-231 cells capable of up-regulating expression of AIPB with an addition of tetracycline in a stable fashion were used in the experiment. We compared activity and expression of the stable cells in the presence and absence of tetracycline induced with 50,000-fold (1.0 ng to 50,000 ng) concentration of Pyrvinium pamoate for 48-hours. Estradiol synthesis was measured using radioimmunoassay and protein expression via immunoblotting by a specific antibody. Results: We observed a decrease in estradiol synthesis with increased expression of AIPB when cells were co-induced with tetracycline (Doxycycline). Cells induced with Pyrvinium pamoate showed an increased expression of AIPB by immunoblotting when the concentration of Pyrvinium pamoate was increased more than 20.0 μg. Conclusions: In the absence of aromatase, AIPB is a critical regulator of estradiol synthesis in triple-negative breast cancer appearing early in tumor development and thus serving as a potential biomarker for early prediction of breast cancer.