Development of heterodimeric estrogen receptor alpha antagonists to target simultaneously the ligand and coactivator...

Area of Science:

• Medicinal Chemistry
• Oncology
• Molecular Biology

Background:

• Endocrine therapy resistance is a major challenge in breast cancer treatment, affecting one-third of patients.
• Tumor growth in hormone-refractory breast cancer relies on estrogen receptor alpha (ERα) and coactivator interactions.
• Targeting both the ligand binding site (LBS) and coactivator binding site (CABS) of ERα offers a novel therapeutic strategy.

Purpose of the Study:

• To design and synthesize novel compounds that simultaneously target ERα's LBS and CABS.
• To evaluate the efficacy of these compounds in overcoming endocrine resistance in breast cancer models.
• To investigate the mechanism of action and structure-activity relationships of the novel ERα inhibitors.

Main Methods:

• Synthesis of two series of compounds covalently linking LBS-binder (E)-3-{4-[8-fluoro-4-(4-hydroxyphenyl)-2,3-dihydrobenzo[b]oxepin-5-yl]phenyl}acrylic acid 8 with coactivator binding site inhibitors (CBIs).
• Luciferase reporter gene assay to assess inhibition of estradiol-induced transactivation of ERα and ERβ.
• Antiproliferative assays using MCF-7 and tamoxifen-resistant MCF-7/TamR breast cancer cell lines.
• Molecular docking studies to predict interactions between compounds and ERα.

Main Results:

• The most active compound, benzoxepine-pyrimidine conjugate 31, demonstrated potent inhibition of ERα transactivation (IC50 = 18.2 nM) and ERβ (IC50 = 61.7 nM).
• Compound 31 exhibited significant antiproliferative effects in both MCF-7 (IC50 = 65.9 nM) and tamoxifen-resistant MCF-7/TamR (IC50 = 88.9 nM) cells.
• The synthesized heterodimers showed superior ER antagonism and antiproliferative activity compared to the precursor 8, with enhanced potency against ERα.
• Compound 31 acted as a pure antiestrogen without downregulating ERα content, as confirmed by cellular assays.
• Molecular docking suggested specific interactions of the CBI moiety at the ERα surface, contributing to enhanced activity.

Conclusions:

• Simultaneous targeting of ERα's LBS and CABS is a promising strategy to overcome endocrine resistance in breast cancer.
• The novel benzoxepine-pyrimidine conjugate 31 is a potent antiestrogen with significant antiproliferative activity against resistant breast cancer cells.
• These findings provide a strong foundation for the development of new therapeutics for hormone-refractory breast cancer.