title: MIBE acts as antagonist ligand of both estrogen receptor α and GPER in breast cancer cells.
abstract: BACKGROUND
  The multiple biological responses to estrogens are mainly mediated by the classical estrogen receptors ERα and ERβ, which act as ligand-activated transcription factors. ERα exerts a main role in the development of breast cancer; therefore, the ER antagonist tamoxifen has been widely used although its effectiveness is limited by de novo and acquired resistance. Recently, GPR30/GPER, a member of the seven-transmembrane G protein-coupled receptor family, has been implicated in mediating the effects of estrogens in various normal and cancer cells. In particular, GPER triggered gene expression and proliferative responses induced by estrogens and even ER antagonists in hormone-sensitive tumor cells. Likewise, additional ER ligands showed the ability to bind to GPER eliciting promiscuous and, in some cases, opposite actions through the two receptors. We synthesized a novel compound (ethyl 3-[5-(2-ethoxycarbonyl-1-methylvinyloxy)-1-methyl-1H-indol-3-yl]but-2-enoate), referred to as MIBE, and investigated its properties elicited through ERα and GPER in breast cancer cells.
  
  
  METHODS
  Molecular modeling, binding experiments and functional assays were performed in order to evaluate the biological action exerted by MIBE through ERα and GPER in MCF7 and SkBr3 breast cancer cells.
  
  
  RESULTS
  MIBE displayed the ability to act as an antagonist ligand for ERα and GPER as it elicited inhibitory effects on gene transcription and growth effects by binding to both receptors in breast cancer cells. Moreover, GPER was required for epidermal growth factor receptor (EGFR) and ERK activation by EGF as ascertained by using MIBE and performing gene silencing experiments.
  
  
  CONCLUSIONS
  Our findings provide novel insights on the functional cross-talk between GPER and EGFR signaling. Furthermore, the exclusive antagonistic activity exerted by MIBE on ERα and GPER could represent an innovative pharmacological approach targeting breast carcinomas which express one or both receptors at the beginning and/or during tumor progression. Hence, the simultaneous inhibition of both ERα and GPER may guarantee major therapeutic benefits in respect to the use of a selective estrogen receptor antagonist.
authors.affiliation: Dipartimento Farmaco-Biologico, Università della Calabria, via Bucci, 87036 Rende, Italy.
authors.forename: Rosamaria
authors.initials: R
authors.lastname: Lappano
authors.forename: Maria Francesca
authors.initials: MF
authors.lastname: Santolla
authors.forename: Marco
authors.initials: M
authors.lastname: Pupo
authors.forename: Maria Stefania
authors.initials: MS
authors.lastname: Sinicropi
authors.forename: Anna
authors.initials: A
authors.lastname: Caruso
authors.forename: Camillo
authors.initials: C
authors.lastname: Rosano
authors.forename: Marcello
authors.initials: M
authors.lastname: Maggiolini
mesh_terms: D020816:Amino Acid Motifs; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D001665:Binding Sites; D001667:Binding, Competitive; D001943:Breast Neoplasms / Q000188:drug therapy*; D049109:Cell Proliferation / Q000187:drug effects; D066246:ErbB Receptors / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology / Q000502:physiology; D004965:Estrogen Antagonists / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000037:antagonists & inhibitors* / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D061986:MCF-7 Cells; D062105:Molecular Docking Simulation; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D017434:Protein Structure, Tertiary; D020239:Receptor Cross-Talk; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors*; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors*; D015398:Signal Transduction; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: D018931:Antineoplastic Agents, Hormonal; C506487:ESR1 protein, human; D004965:Estrogen Antagonists; D047628:Estrogen Receptor alpha; C109584:GPER1 protein, human; D007211:Indoles; D011960:Receptors, Estrogen; D043562:Receptors, G-Protein-Coupled; C578102:ethyl 3-(5-(2-ethoxycarbonyl-1-methylvinyloxy)-1-methyl-1H-indol-3-y)but-2-enoate; D004958:Estradiol; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases