Discovery of Highly Functionalized 5-hydroxy-2H-pyrrol-2-ones That Exhibit Antiestrogenic Effects in Breast and Endometrial Cancer Cells and Potentiate the Antitumoral Effect of Tamoxifen

SIMPLE SUMMARY: About 70% of the breast tumors diagnosed are estrogen receptor (ER)-positive and depend on estrogens and the interactions with their ER to grow and survive; their therapeutic treatment has a good clinical prognosis and effectiveness, but antitumoral treatment resistances and undesirable side effects (ovarian cysts, endometrial cancer, or blood clots) remain clinically challenging. This justifies the development of new drugs that modulate ER activity since it is considered a clinically validated therapeutic target. The goal of this study was the identification and the preclinical pharmacological evaluation of new structures with antitumoral and/or antiestrogenic properties with alternative or complementary mechanisms of action to the endocrine therapy used in the gold-standard treatment of ER-positive breast cancer. Thus, we identified two leading compounds (highly-functionalized 5-hydroxy-2H-pyrrol-2-ones) with potential antitumoral effects and scarce estrogenic activity, which offers a pharmacological opportunity to progress in the study of ER-positive breast cancer treatment. ABSTRACT: Tamoxifen improves the overall survival rate in hormone receptor-positive breast cancer patients. However, despite the fact that it exerts antagonistic effects on the ERα, it can act as a partial agonist, resulting in tumor growth in estrogen-sensitive tissues. In this study, highly functionalized 5-hydroxy-2H-pyrrol-2-ones were synthesized and evaluated by using ERα- and phenotype-based screening assays. Compounds 32 and 35 inhibited 17β-estradiol (E2)-stimulated ERα-mediated transcription of the luciferase reporter gene in breast cancer cells without inhibition of the transcriptional activity mediated by androgen or glucocorticoid receptors. Compound 32 regulated E2-stimulated ERα-mediated transcription by partial antagonism, whereas compound 35 caused rapid and non-competitive inhibition. Monitoring of 2D and 3D cell growth confirmed potent antitumoral effects of both compounds on ER-positive breast cancer cells. Furthermore, compounds 32 and 35 caused apoptosis and blocked the cell cycle of ER-positive breast cancer cells in the sub-G1 and G0/G1 phases. Interestingly, compound 35 suppressed the functional activity of ERα in the uterus, as demonstrated by the inhibition of E2-stimulated transcription of estrogen and progesterone receptors and alkaline phosphatase enzymatic activity. Compound 35 showed a relatively low binding affinity with ERα. However, its antiestrogenic effect was associated with an increased polyubiquitination and a reduced protein expression of ERα. Clinically relevant, a possible combinatory therapy with compound 35 may enhance the antitumoral efficacy of 4-hydroxy-tamoxifen in ER-positive breast cancer cells. In silico ADME predictions indicated that these compounds exhibit good drug-likeness, which, together with their potential antitumoral effects and their lack of estrogenic activity, offers a pharmacological opportunity to deepen the study of ER-positive breast cancer treatment.