Exploring the Structural Compliancy versus Specificity of the Estrogen Receptor Using Isomeric Three-Dimensional Ligands

Abstract

The estrogen receptors (ER) bind with high affinity to many structurally diverse ligands by significantly distorting the contours of their ligand-binding pockets. This raises a question: To what degree is ER able to distinguish between structurally related regioisomers and enantiomers? We have explored the structural compliance and specificity of ERα with a set of ligands having a 7-oxa-bicyclo[2.2.1]hept-5-ene sulfonate core and basic side chains typical of selective ER modulators (SERMs). These ligands have two regioisomers, each of which is a racemate of enantiomers. Using orthogonal protecting groups and chiral HPLC, we isolated all 4 isomers and assigned their absolute stereochemistry by X-ray analysis. The 1S,2R,4S isomer has a 80–170-fold higher affinity for ERα than the others, and it profiles as a partial agonist/antagonist in cellular reporter gene assays and in suppressing proliferation of MCF-7 breast cancer cells with subnanomolar potency, far exceeding that of the other isomers. It is the only isomer found bound to ERα by X-ray analysis after crystallization with 4-isomer mixtures of closely related analogs. Thus, despite the general compliance of this receptor for binding a large variety of ligand structures, ER demonstrates marked structural- and stereo-specificity by selecting a single component from a mixture of structurally related isomers to drive ER-regulated cellular activity. Our findings lay the necessary groundwork for seeking unique ER-mediated pharmacological profiles by rational structural perturbations of two different types of side chains in this unprecedented class of ER ligands, which may prove useful in developing more effective endocrine therapies for breast cancer.

The SERM/SERD bazedoxifene disrupts ESR1 helix 12 to overcome acquired hormone resistance in breast cancer cells

“…The 6 × His TEV-tagged ERα-L372S, L536S double mutant LBD was expressed in E.coli BL21(DE3) and purified as described (Sharma et al, 2017). LBD (10 mg/mL) and incubated with 1 mM BZA overnight at 4°C.…”

Dual mechanism estrogen receptor inhibitors

“…Datasheet). We previously published 32 crystal structures of ERa bound to compounds in the OBHS series in which we had consistently found all activity in one enantiomer (1S,2R,4S) 6,19,26,27 , but here we found two of the structures with amine side chain compounds, 16 and 18 (out of 16 structures, of which we are reporting 10 here, Supplementary Dataset 1), that displayed the (1R,2R,4S), while the high affinity enantiomer 29 displayed the 1S configuration.…”

“…In all cases, R1 was a trifluoroethyl group. All synthesis involved facile Diels-Alder reactions of various aryl-substituted furans with different vinyl sulfonamide dienophiles, conducted under conditions of thermodynamic control, which favored production of the exo stereoisomers [17][18][19] . Synthetic routes and experimental details are in The DMERIs varied in potency, but they inhibited breast cancer cell proliferation to a degree similar to that of fulvestrant ( Fig.…”

“…The ERα-L372S/L536S double-mutant ligand-binding domain (LBD, amino acid residues 298-554) was expressed in BL21 (DE3) E. coli cells, purified by IMAC using a Ni2+ column, dialysis, TEV digest, ion exchange, and size exclusion chromatography to remove the HA tag, as previously described (22). The purified LBD was co-crystallized with various ligands through sitting drop vapor diffusion method using trial gradients of 20% -25% (w/v) PEG 3350, 200 mM MgCl2, and pH 6.5-8.0, as previously described (37,42). Data was collected at the Stanford Synchrotron Radiation Lightsource (Beamline: 12-2) and…”

One‐Pot Synthesis of Tetrahydropyridine Derivatives: Liquid Salt Catalyst vs Glycolic Acid Promoter. Structure and Antiradical Activity of the New Products

“…Morphine is probably the most famous representative of this class of compounds. Besides the analgesic effect of morphine, they express cytotoxic activity, they are commonly used as neuroleptics, analeptics, selective estrogen receptor modulators, and many other activities.…”