Virtual and biomolecular screening converge on
a selective agonist for GPR30
Cristian G Bologa1,7, Chetana M Revankar2,3,7...
master plate for their ability to inhibit binding of fluorescent estrogen
to GPR30; this revealed that only compound 92, a ...
accumulation of phosphatidylinositol 3,4,5-triphosphate (PIP3)
(ref. 4). This is shown by the translocation of a reporter,...
function of GPR30 using G-1, we examined cell migration in response
to estrogen and G-1 (Fig. 4c). Using a Transwell migra...
superstructure) coefficients were given a 6.66% contribution each, for both
Daylight and MDL fingerprints, and a 13.33% cont...
6. Filardo, E.J., Quinn, J.A., Bland, K.I. & Frackelton, A.R., Jr. Estrogen-induced
activation of Erk-1 and Erk-2 requires...
of 6


Published on: Mar 3, 2016

Transcripts - Nat_Chem_Biol_GPR30_2006

  • 1. Virtual and biomolecular screening converge on a selective agonist for GPR30 Cristian G Bologa1,7, Chetana M Revankar2,3,7, Susan M Young3, Bruce S Edwards3,4, Jeffrey B Arterburn5, Alexander S Kiselyov6, Matthew A Parker6, Sergey E Tkachenko6, Nikolay P Savchuck6, Larry A Sklar3,4, Tudor I Oprea1 & Eric R Prossnitz2,3 Estrogen is a hormone critical in the development, normal physiology and pathophysiology1 of numerous human tissues2. The effects of estrogen have traditionally been solely ascribed to estrogen receptor a (ERa) and more recently ERb, members of the soluble, nuclear ligand–activated family of transcription factors3. We have recently shown that the seven- transmembrane G protein–coupled receptor GPR30 binds estrogen with high affinity and resides in the endoplasmic reticulum, where it activates multiple intracellular signaling pathways4. To differentiate between the functions of ERa or ERb and GPR30, we used a combination of virtual and biomolecular screening to isolate compounds that selectively bind to GPR30. Here we describe the identification of the first GPR30-specific agonist, G-1 (1), capable of activating GPR30 in a complex environment of classical and new estrogen receptors. The development of compounds specific to estrogen receptor family members provides the opportunity to increase our understanding of these receptors and their contribution to estrogen biology. With our recent description of an intracellular transmembrane estro- gen receptor that initiates multiple signaling pathways4, some in common with the traditional estrogen receptors, it is clear that dissecting GPR30-specific cellular and physiological responses is essential to understanding the fundamental mechanisms of estrogen action. To this end, we sought to identify compounds that show highly selective binding to GPR30 as compared with the classical estrogen receptors (ERa and ERb). As GPR30 is known to bind many of the same ligands as classical estrogen receptors (for example, 17b-estradiol (2), 4-hydroxytamoxifen (3), ICI182,780 (4))4–6, though with differing cellular effects (for example, ICI182,780 is an ER antagonist but a GPR30 agonist), we screened a library of diverse chemical compounds to identify GPR30-specific ligands. To minimize the biomolecular screening required, we first used virtual screening7, which has recently become increasingly recognized as a complement to bioactivity screening8. Virtual screening aims to sift through vast numbers of structures to rapidly identify those of interest for biological screening. Its experimental counterpart, high- throughput screening, is also aimed at sifting through large numbers of compounds, often based on single-point, single-experiment results. Both procedures rely on the ability to process a large number of structures or compounds9. We therefore began by virtually screening a library of 10,000 molecules (preoptimized to be enriched in G protein–coupled receptor (GPCR)-binding ligands based on the con- cept of the GPCR-privileged substructure10) using a combination of 2D- and 3D-similarity approaches. Our combined similarity score attributed 40% weight to 2D fingerprints, 40% to shape-based similarities and 20% to pharmacophore-based similarity. Given this composite score, the top 100 ranked molecules were selected for biomolecular screening. To accomplish the biomolecular screening, we used a fluorescently labeled estrogen derivative (an Alexa633 conjugate of 17a-[4- aminomethyl-phenylethynyl]-estra-1,3,5(10)-triene-3,17b-diol (5), E2- Alexa633) that we have recently developed and shown to bind GPR30 as well as ERa and ERb (ref. 4). Competitive ligand binding was assessed in transiently transfected COS7 cells, which do not show detectable specific binding of the fluorescent estrogen in the absence of exogenous receptors. Binding was measured with a high-throughput flow cytometric platform (HyperCyt) capable of sampling rates of approximately 1 per s from microplate wells11,12. To maximize the bound fluorescent signal, a GPR30-GFP fusion protein was expressed and cells were gated for high levels of green (FL1) fluorescence (that is, GPR30 expression). Biomolecular screening was carried out with 17b-estradiol as a positive control to block specific binding of E2-Alexa633 to GPR30. Calculation of the Z¢ factor, a measure of screening assay quality that reflects both assay signal dynamic range and data variation of the signal13, yielded a value of 0.5–0.7, indicating the robustness of the assay. From the primary screen performed at a compound concentra- tion of 10 mM, three compounds resulted in inhibition of fluorescent estrogen binding greater than 60%. These compounds, as well as numerous intermediate-quality hits, were retested manually from the ©2006NaturePublishingGroup Received 23 December 2005; accepted 9 February 2006; published online 05 March 2006; doi:10.1038/nchembio775 1Division of Biocomputing, 2Department of Cell Biology & Physiology, 3Cancer Research and Treatment Center and 4Department of Pathology, University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131, USA. 5Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, USA. 6Chemical Diversity Labs Inc., 11558 Sorrento Valley Road, San Diego, California 92121, USA. 7These authors contributed equally to this work. Correspondence should be addressed to E.R.P. ( or T.I.O. ( NATURE CHEMICAL BIOLOGY ADVANCE ONLINE PUBLICATION 1 L E T T E R S
  • 2. master plate for their ability to inhibit binding of fluorescent estrogen to GPR30; this revealed that only compound 92, a substituted dihydroquinoline (Fig. 1a), consistently inhibited binding. This com- pound will be referred to henceforth as G-1 (GPR30-specific compound 1). Its structure, which was subsequently reconfirmed by LC-MS and 1H-NMR, is racemic but diasteromerically pure (see Methods). To characterize the binding properties of G-1 in greater depth, we determined the binding affinity to GPR30 and the binding specificity with respect to ERa and ERb. Competition binding of the fluorescent estrogen by 17b-estradiol in GPR30-expressing cells yielded a Ki of 5.7 nM (similar to the value of 6.6 nM we reported previously), whereas the Ki for G-1 was 11 nM (Fig. 1b). Competition binding in ERa- and ERb-expressing cells yielded Ki values for 17b-estradiol of 0.30 and 0.38 nM, respectively, with no substantial binding of G-1 at concentrations up to 1 mM (Fig. 1c,d). The Hill coefficients for the estrogen-competition binding curves were approximately 1.0 (1.2, 0.9 and 0.9 for GPR30, ERa and ERb, respectively), whereas for G-1, the Hill coefficient was 0.6, suggesting that there could be two binding sites of similar but not identical affinity. These results indicate that G-1 has not only very high affinity for GPR30 but also great selectivity toward GPR30 as compared with ERa and ERb. We next examined the functional cap- abilities of G-1 versus estrogen with respect to the rapid mobilization of intracellular cal- cium. Whereas 17b-estradiol initiates a very rapid (t1/2 o 2 s) rise in intracellular calcium concentrations, G-1 produces a slower (t1/2 B 30 s) but ultimately comparable calcium increase (Fig. 2a). The specificity of the response is shown by the fact that neither 17b-estradiol nor G-1 has an effect on control COS7 cells (not expressing GPR30) and that 17a-estradiol (6) has no effect on GPR30-expressing COS7 cells. To confirm the selectivity of G-1 toward GPR30 as compared with ERa and ERb (as suggested by the binding assays), we also examined calcium mobilization in COS7 cells expressing either ERa or ERb. In neither case did G-1 elicit a calcium response (Fig. 2b,c). This is in contrast to 17b-estradiol, which yields a rapid response with both ERa and ERb. As observed with GPR30, 17a-estradiol had no effect on ERa or ERb. Dose- response determinations showed that the mobilization of intracellular calcium initiated by G-1 in the presence of GPR30 was concentration dependent, with a half-maximal effector concentration (EC50) of about 2 nM (Fig. 2d,e), similar to the binding affinity of G-1 for GPR30, compared with an EC50 for 17b-estradiol of approximately 0.3 nM. In addition to calcium mobilization, we have shown that stimulation of ERa, ERb and GPR30 with estrogen results in phos- phatidylinositol 3-kinase (PI3K) activation, resulting in the nuclear ©2006NaturePublishingGroup 100 E2-Alexa633bound(%) 80 60 40 20 0 100 E2-Alexa633bound(%) 80 60 40 20 0 100 E2-Alexa633bound(%) 80 60 40 20 0 –11 –10 –9 –8 Competitor concentration (log M) –7 –6 –5 –11–12 –10 –9 –8 Competitor concentration (log M) –7 –6 –11–12 –10 –9 –8 Competitor concentration (log M) –7 –6 G-1 17β-estradiol GPR30 G-1 (1) ERα ERβ O H N H H O O Br a c b d Relativecalcium mobilization Relativecalcium mobilization Relativecalcium mobilization Relativecalcium mobilization GPR30 ERα ERβ GPR30 0 50 Time (s) 100 150 0 50 Time (s) 100 150 0 50 0 1,500 1,200 1,000 750 [Ca2+ ]nM 500 250 0 –11 –10 Concentration (log M) –9 –8 –7 –6 20 500 nM 1 nM 0.1 nM 10 nM 100 nM 40 60 80 100120 140 Time (s) Time (s) 100 150 17β-estradiol G-1 17α-estradiol GFP only 17β-estradiol 17β-estradiol G-1 17α-estradiol G-1 G-1 17α-estradiol 17β-estradiol 17α-estradiol d e cba Figure 2 G-1 agonism in the mobilization of intracellular calcium by GPR30. (a–c) We compared the activity of G-1 with that of 17b-estradiol using indo1-AM–loaded COS7 cells transfected with GPR30-GFP (a), ERa-GFP (b) or ERb-GFP (c) or with GFP only (a). Ligand addition was performed at 20 s. G-1 and 17b-estradiol were used at 1 nM; 17a-estradiol was used at 1 mM. The y-axis scales are conserved from a–c. (d) Dose-response profile of GPR30-GFP–transfected COS7 cells to increasing concentrations of G-1. (e) Comparison of G-1 and 17b-estradiol dose-response profiles in GPR30-GFP–transfected COS7 cells. Data in panels a–d are representative of at least three independent experiments. Data in panel e represent the mean ± s.e.m. of three separate experiments. Figure 1 Structure and ligand-binding properties of G-1. (a) Chemical structure of compound G-1. (b–d) Ligand-binding affinities of 17b-estradiol and G-1 for GPR30, ERa and ERb. Results of competitive ligand-binding assays using 2 nM E2-Alexa633 and the indicated concentration of either 17b-estradiol (’) or G-1 (m) in COS7 cells transfected with either GPR30-GFP (b), ERa-GFP (c) or ERb-GFP (d). Data indicate the mean ± s.e.m. of three separate experiments. L E T T E R S 2 ADVANCE ONLINE PUBLICATION NATURE CHEMICAL BIOLOGY
  • 3. accumulation of phosphatidylinositol 3,4,5-triphosphate (PIP3) (ref. 4). This is shown by the translocation of a reporter, the pleckstrin homology (PH) domain of Akt fused to a fluorescent protein, in response to the de novo production of PIP3 by PI3K (ref. 14). To confirm our hypothesis that G-1 activates a similar complement of signaling pathways as estrogen, we examined the activation of PI3K in receptor-transfected COS7 cells. As previously observed, estrogen stimulates the nuclear accumulation of PIP3 through all three recep- tors. However, as observed for calcium signaling, G-1 selectively activated GPR30 and not ERa or ERb (Fig. 3). In total, these results indicate that G-1 binds and activates GPR30 with great specificity over both ER types. These results suggest that we should be able to selectively target GPR30 as opposed to ERs in cells that express both receptors. To test this, we cotransfected cells with GPR30–monomeric red fluorescent protein-1 (GFP30-mRFP1) and ERa-GFP, which localize to distinct subcellular compartments (the nucleus and endoplasmic reticulum, respectively). The receptors were visualized with E2-Alexa633, and cells were incubated in the presence or absence of G-1 (Fig. 4a). In the absence of competitor, fluorescent estrogen staining was seen through- out the cell (nucleus and endoplasmic reticulum), representing the sum of the individual compartments. Competition with 17b-estradiol blocked binding of the E2-Alexa633 to both ERa and GPR30. However, in the presence of G-1, staining in the endoplasmic reticulum was selectively lost over that in the nucleus (for both ERa and ERb). This showed that in the same cell, G-1 selectively binds GPR30 and not ERs. Next, we sought to determine whether G-1 activates endogenously expressed GPR30. We have previously shown that estrogen-mediated activation of PI3K in SKBr3 breast cancer cells, which are ERa and ERb negative, occurs exclusively through GPR30. We therefore tested whether G-1 was able to activate PI3K in SKBr3 cells. We found that G-1, like estrogen, activated PI3K, resulting in the nuclear accumula- tion of PIP3 in both SKBr3 cells (that express only GPR30) as well as in MCF7 cells (which express both GPR30 and classical ERs, with high levels of ERa and low levels of ERb) (Fig. 4b). This latter result in MCF7 cells suggests that the estrogen-mediated response is occurring at least in part through GPR30. To investigate the physiological ©2006NaturePublishingGroup GPR30 Unstimulated PH Merge Merge MergeERα ERβPH PH + 17β-estradiol + G-1 a b c Figure 3 G-1 agonism in PI3K activation by GPR30. We compared the activity of G-1 with that of 17b-estradiol using COS7 cells transfected with Akt-PH- mRFP1 and either GPR30-GFP (a), ERa-GFP (b) or ERb-GFP (c). 17b-estradiol and G-1 were used at 1 nM and 10 nM, respectively. The white bar in upper left panel of a denotes 10 mm. Data are representative of three independent experiments. ERα Unstimulated SKBr3 MCF7 + 17β-estradiol + G-1 ER-GFP E2-Alexa 633GPR30-RFP Merge ERα + G-1 ERβ + G-1 ERα + 17β-E2 a b 100 Cellmigration(%) 60 80 40 20 0 –13 –12 –11 –10 Concentration (log M) –9 –8 –7 –6 ( ) c Figure 4 Selective targeting of GPR30 versus ERa or ERb by G-1. (a) COS7 cells cotransfected with either GPR30-mRFP1 and ERa-GFP or GPR30-mRFP1 and ERb-GFP as indicated and stained with E2-Alexa633 in the absence or presence of excess 17b-estradiol or G-1 (1 mM). Although excess 17b-estradiol prevents binding of E2-Alexa633 to both ER and GPR30, G-1 selectively competes for binding to GPR30 in cells that also express ERs. (b) SKBr3 breast cancer cells, which endogenously express only GPR30, and MCF7 cells, which express GPR30 and ERa/b, after transfection with Akt-PH-mRFP1 and stimulation with either 1 nM 17b-estradiol or 10 nM G-1. White bars denote 10 mm. (c) Cell migration of SKBr3 and MCF7 cells through a Transwell chamber in response to chemoattractant. Cells in the upper chamber were treated with either 17b-estradiol or G-1 as indicated. Data are representative of three independent experiments or represent the mean ± s.e.m. of three separate experiments with all P values o 0.05. L E T T E R S NATURE CHEMICAL BIOLOGY ADVANCE ONLINE PUBLICATION 3
  • 4. function of GPR30 using G-1, we examined cell migration in response to estrogen and G-1 (Fig. 4c). Using a Transwell migration apparatus (Costar), we demonstrated that in response to chemoattractant (serum, EGF and insulin), both estrogen, as previously documented15, and G-1 inhibited migration of SKBr3 cells (with half-maximal inhibitory concentration (IC50) values for estrogen and G-1 of 0.1 and 0.7 nM, respectively) and MCF7 cells (with IC50 values for estrogen and G-1 of 0.4 and 1.6 nM, respectively). The four- to seven-fold greater activity of estrogen as compared with G-1 is consistent with the relative differences between the two compounds in both binding affinity (Fig. 1) and signaling capacity (Fig. 2e). Overall, these results confirm that G-1 can selectively bind GPR30 in the same cell where ERs are present and furthermore that G-1 can activate endogenously expressed GPR30, resulting in physiologic responses even in cells expressing multiple estrogen receptor types. In summary, we have identified a nonsteroidal, high-affinity, highly selective agonist of GPR30. This represents the first description of a compound that can distinguish between GPR30 and the classical estrogen receptors. Superimposition of the structure of 17b-estradiol with G-1 using rapid overlay of chemical structures (ROCS)16 reveals a high degree of shape similarity between both enantiomers of G-1 and 17b-estradiol (Fig. 5a). To examine why G-1 shows such high selectivity for GPR30 over ERs, we performed docking experiments (with AutoDock ( of both enantiomers of G-1 (the structure shown in Fig. 1a as well as its enantiomer) into the ligand-binding pocket of ERa in both its 17b-estradiol- and 4-hydroxytamoxifen-bound crystallographic con- formations (see Methods for Protein Data Bank accession codes). To obtain a computational estimate of the binding affinity, both native ligands were docked into their respective structures as well. Full flexibility for the ligands was assumed, and no initial positioning of the ligand into the binding site was performed. The results of the docking experiment for the enantiomer from Figure 1a are shown in Figure 5b,c, and the computationally predicted binding affinities for both enantiomers are summarized in Supplementary Table 1. When docked into the agonist-bound conformation of ERa (Fig. 5b), both enantiomers of G-1 are estimated to have an affinity approximately three orders of magnitude worse than that of 17b-estradiol17. For example, in the best-docked poses, both G-1 enantiomers do not present the hydrogen-bonding pattern of 17b-estradiol (that is, no interaction with Glu353 and His524), and moreover they show steric clashes with multiple backbone atoms. The estimated Ki values from Supple- mentary Table 1 appear to suggest that G-1 might bind ERa as a low-affinity antagonist. When docked into the 4-hydroxytamoxifen- bound conformation of ERa (Fig. 5c), both G-1 enantiomers are estimated to have affi- nities approximately two orders of magnitude above that of 4-hydroxytamoxifen. Once again, however, both enantiomers of G-1 fail to interact with key hydrogen bond partners, while showing steric clashes with the receptor ligand-binding site. Thus, we conclude that G-1 cannot be positioned to interact opti- mally with either the agonist- or antagonist- occupied conformations of ERa, a finding consistent with our experimental results. In conclusion, the overall discovery process was facilitated by the preliminary step of virtual or in silico screening combined with technological advances, including the use of a new fluorescent estrogen derivative in the binding assay, a high-throughput flow cytometric platform (HyperCyt) and new assays of estrogen-mediated PI3K activation. The discovery of the first GPR30-specific agonist that does not bind classical ERs should facilitate further physiological experiments to define the role of GPR30 in vivo and open the door to the generation of diagnostics and therapeutics directed at individual estrogen receptors. METHODS Database processing. A database of 10,000 in-house molecules (CDLDB) provided by Chemical Diversity Labs, to which 17b-estradiol was added, was processed according to a procedure detailed elsewhere18. Very briefly, canonical isomeric SMILES (ref. 19, Daylight Toolkit v4.81, Daylight Chemical Informa- tion Systems) were derived from input structures. Smi2fp_ascii (Daylight Chemical Information Systems) and MACCSKeys320 Generator (Mesa Analy- tics and Computing) software was used to compute Daylight and MDL20 fingerprints, respectively, and 3D structures were derived with the OMEGA software from OpenEye Scientific Software. 2D-based similarity. Using 17b-estradiol as a reference point, we computed similarity coefficients using both Daylight and MDL fingerprints for CDLDB using Tanimoto’s symmetric distance-between-patterns21 and Tversky’s asymmetric contrast model22. Tanimoto similarities are symmetric (that is, when molecule A is compared to molecule B and vice versa, the Tanimoto coefficients are identical), whereas Tversky similarity is asymmetric (that is, the two coefficient values differ). In total, six 2D-based similarity coefficients were obtained. 3D-based similarity. Using the 3D structure of 17b-estradiol as a reference point, we obtained shape-similarity coefficients using the Tanimoto21 and Tversky22 formulas using ROCS, rapid overlay of chemical structures16, a Gaussian-shape-volume-overlap filter that identifies shapes that match the query molecule. Another similarity metric, using Euclidian distances in a nine-dimensional principal component analysis (PCA) space23, was derived from ALMOND descriptors24. ALMOND encodes hydrophobic, H-bond donor and H-bond acceptor pharmacophoric elements derived from molecular interaction fields computed with GRID25 into a reduced set of variables. Final similarity score. Our combined similarity score attributed 40% weight to 2D fingerprints, 40% to the shape-based similarities and 20% to pharmaco- phore-based similarity. Thus, Tanimoto and Tversky (substructure and ©2006NaturePublishingGroup a b c Figure 5 G-1 and 17b-estradiol structural overlap and docking to ERa. (a) Overlay of stick-model representations of G-1 and 17b-estradiol to maximize spatial overlap by the shape-matching procedure of ROCS. 17b-estradiol is shown in yellow, G-1 in light gray, oxygen atoms in bright red, nitrogen in blue and bromine in dark red. (b,c) Docking of G-1 into the 17b-estradiol– (b) and 4-hydroxytamoxifen–bound (c) conformations of ERa (1ERE and 3ERT, respectively). The endogenous ligand (17b-estradiol in b and 4-hydroxytamoxifen in c) as found in each crystal structure is shown in red. The optimal shape overlays of G-1 onto 17b-estradiol (as shown in a) and 4-hydroxytamoxifen are shown in blue. The optimally ERa-docked structures of G-1 based on protein interactions as computed using AutoDock are shown in green. L E T T E R S 4 ADVANCE ONLINE PUBLICATION NATURE CHEMICAL BIOLOGY
  • 5. superstructure) coefficients were given a 6.66% contribution each, for both Daylight and MDL fingerprints, and a 13.33% contribution each for shape. The Euclidian distance in PCA was given a 20% weight to the final score. Given this composite score, the top 100 ranked molecules were selected for physical screening. Ligand overlaying and docking. To overlay the structure of G-1 and 17b- estradiol or 4-hydroxytamoxifen, we used the shape-matching procedure of ROCS with full conformational flexibility and the receptor-bound conforma- tions of 17b-estradiol and 4-hydroxytamoxifen. We performed docking of ligands into ERa using AutoDock 3.0.5 (ref. 26). We selected the 17b-estradiol co-crystallized with ERa in its agonist-bound conformation and 4-hydroxyta- moxifen co-crystallized with ERa in its antagonist-bound conformation. The structure of G-1 was docked in the ligand-binding site of the two conforma- tions of ERa, after extracting 17b-estradiol and 4-hydroxytamoxifen, respec- tively. To get a computational estimate of the binding affinity, both native ligands were docked into their respective receptors as well. We assumed full ligand flexibility, and no initial positioning of the ligand into the binding pocket was performed. Ligand-binding assays. We performed binding assays as described4. Briefly, COS7 cells were transiently transfected with either nuclear estrogen receptor (ERa-GFP or ERb-GFP) or GPR30-GFP and serum starved for 24 h before assay. For HyperCyt screening, cells (B5 Â 104) were incubated with 10 mM compound for 20 min in a final volume of 10 ml before addition of 10 ml 8 nM E2-Alexa633 diluted in saponin-based permeabilization buffer. Following 10 min at 37 1C, cells were washed once with 200 ml PBS in 1% BSA, and 2-ml samples were analyzed on a FACS Calibur. Cell Quest time bin–based data produced by the HyperCyt system were analyzed with IDLQuery software as described27. We analyzed dose responses manually using the indicated con- centration of competitor and 2 nM E2-Alexa633. Nonspecific binding was determined in presence of 100 nM 17b-estradiol. We carried out labeling of cells for microscopy as previously described4 using 1 mM 17b-estradiol or G-1 to determine nonspecific binding. Competition binding studies were analyzed with Prism 4.0 (GraphPad). Intracellular calcium mobilization. Transfected COS7 cells (5 Â 106) were incubated in HBSS containing 5 mM indo1-AM and 0.05% pluronic acid for 30 min at 25 1C. Cells were then washed once with HBSS and resuspended in HBSS at a density of 107 cells per ml. We determined Ca2+ mobilization ratiometrically using lex 340 nm and lem 400/490 nm at 37 1C in a spectro- fluorometer (QM-2000-2, Photon Technology International) equipped with a magnetic stirrer. The relative 490/400 nm ratio was plotted as a function of time. PI3K activation. We used the PIP3 binding domain of Akt fused to mRFP1 (PH-mRFP1) to assess PIP3 production by PI3K. COS7 cells cotransfected with GPR30-GFP or ERa-GFP and PH-mRFP1 were plated on coverslips and serum starved for 24 h, and then they were stimulated with ligands as indicated. The cells on coverslips were fixed with 2% PFA in PBS, washed and mounted in Vectashield (Vector Labs). The cells were analyzed by confocal microscopy with a Zeiss LSM510. Cell migration. Migration assays were carried out with 6.5 mm Transwells with an 8-mm pore size (Costar Corning) as previously described28. The undersur- face of the Transwell was coated overnight at 4 1C with approximately 50 mg ml–1 rat-tail collagen and washed with PBS. DMEM/F12 (600 ml) supplemented with 10% FBS, 10 ng ml–1 of EGF and 10 mg ml–1 of insulin was added to the lower chamber as chemoattractant. SKBr3 or MCF7 cells (75,000 cells) in serum-free DMEM/F12 (150 ml) were treated with ethanol (control), 17b- estradiol or G-1 for 15 min at 37 1C before loading in the upper chamber. After incubation for 48 h at 37 1C, the remaining cells were wiped from the upper surface of the membrane with a damp cotton swab. The migrated cells on the undersurface of the membrane were fixed with 2% paraformaldehyde and stained with 1% crystal violet. Quantification of cells was performed by counting the number of cells per field in five random fields per membrane, and migration was calculated as: % migration ¼ (number of cells in treated/ number of cells in ethanol control) Â 100. Chemical synthesis and characterization of G-1. The compound G-1 (1-[4-(6-bromobenzo[1,3]dioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c] quinolin-8-yl]-ethanone) was synthesized through a previously described method29: trifluoroacetic acid (1.52 g, 13.3 mmol) was added dropwise to a solution of 4-aminoacetophenone (7) (2.0 g, 14.8 mmol) in acetonitrile. Freshly distilled cyclopentadiene (8) (3.91 g, 59.2 mmol) was added, followed by 6-bromopiperonal (9) (3.39 g, 14.8 mmol). The mixture was stirred overnight at 25 1C, and the product was isolated from an aliquot of the mixture by preparative HPLC (C18, 5–95% CH3CN in H2O gradient, 0.05% trifluoroacetic acid), with a yield of approximately 70%. Spectroscopic characterization of G-1 yielded the following: 1H NMR (400 MHz, DMSO-d6): d 7.62 (s, 1H), 7.53 (dd, 1H, J ¼ 1.9 Hz, 8.6 Hz), 7.26 (s, 1H), 7.11 (s, 1H), 6.73 (d, 1H, J ¼ 8.4 Hz), 6.47 (s, 1H), 6.09 (d, 2H, J ¼ 9.1 Hz), 5.97 (m, 1H), 5.60 (broad d, 1H, J ¼ 5.7 Hz), 4.78 (d, 1H, J ¼ 3.3 Hz), 4.05 (d, 1H, J ¼ 8.8 Hz), 3.02 (q, 1H, J ¼ 8.4 Hz), 2.41 (s, 3H), 2.36–2.44 (m, 1H), 1.66 (broad dd, 1H, J ¼ 7–9 Hz). 13C NMR (100 MHz, CD3CN): d 25.76, 31.61, 42.33, 45.50, 56.15, 102.69, 108.44, 112.75, 112.84, 115.49, 124.93, 127.57, 128.48, 130.31, 130.33, 134.19, 134.64, 147.95, 148.04, 150.94, 196.33. HRMS (m/z): calcd. C21H18BrNO3 requires MH+, 412.0543; found MH+, 412.0539. G-1 was analyzed by standard LC-MS methods with positive ion detection. The LC-MS chromatogram showed the correct molecular (MH+) ion as well as a single peak by both UV (254 nm) and ELSD detection. Only one diaster- eomer was obtained; examination of the 1H NMR data shows H-4 (4.78 p.p.m.) with a coupling constant of 3.3 Hz, indicating a cis orientation of the cyclopentene ring and phenyl group, in agreement with the all-cis stereo- chemistry determined by other groups for similar imino Diels-Alder reactions using cyclopentadiene30. Thus G-1 is a racemic but diastereomerically pure compound. Accession codes. Protein Data Bank: 17b-estradiol-bound conformation of ERa, 1ERE; 4-hydroxytamoxifen-bound conformation of ERa, 3ERT. Note: Supplementary information is available on the Nature Chemical Biology website. ACKNOWLEDGMENTS This work was supported by US National Institutes of Health (NIH) grant AI36357 and a University of New Mexico Cancer Research and Treatment Center Translational Research Grant to E.R.P., by NIH grant EB00264 to L.A.S., and by support from the New Mexico Tobacco Settlement fund to C.G.B. and T.I.O. Additional support was provided by the New Mexico Cancer Research and Treatment Center (CRTC; NIH 1. P30 CA118100), the New Mexico Molecular Libraries Screening Center (NIH MH074425) and the New Mexico Center for Environmental Health Sciences (NIH ES012072). Flow cytometry data and confocal images in this study were generated in the Flow Cytometry and Fluorescence Microscopy Facilities, respectively, at the University of New Mexico Health Sciences Center, which received support from National Center for Research Resources (NCRR) 1 S10 RR14668, National Science Foundation MCB9982161, NCRR P20 RR11830, National Cancer Institute R24 CA88339, NCRR S10 RR19287, NCRR S10 RR016918, the University of New Mexico Health Sciences Center, and the University of New Mexico CRTC. COMPETING INTERESTS STATEMENT The authors declare that they have no competing financial interests. Published online at Reprints and permissions information is available online at reprintsandpermissions/ 1. Osborne, C.K. & Schiff, R. Estrogen-receptor biology: continuing progress and ther- apeutic implications. J. Clin. Oncol. 23, 1616–1622 (2005). 2. Hall, J.M., Couse, J.F. & Korach, K.S. The multifaceted mechanisms of estradiol and estrogen receptor signaling. J. Biol. Chem. 276, 36869–36872 (2001). 3. Korach, K.S. et al. Update on animal models developed for analyses of estrogen receptor biological activity. J. Steroid Biochem. Mol. Biol. 86, 387–391 (2003). 4. Revankar, C.M., Cimino, D.F., Sklar, L.A., Arterburn, J.B. & Prossnitz, E.R. A transmembrane intracellular estrogen receptor mediates rapid cell signaling. Science 307, 1625–1630 (2005). 5. Thomas, P., Pang, Y., Filardo, E.J. & Dong, J. Identity of an estrogen membrane receptor coupled to a G-protein in human breast cancer cells. Endocrinology 146, 624–632 (2005). ©2006NaturePublishingGroup L E T T E R S NATURE CHEMICAL BIOLOGY ADVANCE ONLINE PUBLICATION 5
  • 6. 6. Filardo, E.J., Quinn, J.A., Bland, K.I. & Frackelton, A.R., Jr. Estrogen-induced activation of Erk-1 and Erk-2 requires the G protein-coupled receptor homolog, GPR30, and occurs via trans-activation of the epidermal growth factor receptor through release of HB-EGF. Mol. Endocrinol. 14, 1649–1660 (2000). 7. Walters, W.P., Stahl, M.T. & Murcko, M.A. Virtual screening—an overview. Drug Discov. Today 3, 160–178 (1998). 8. Oprea, T.I. & Matter, H. Integrating virtual screening in lead discovery. Curr. Opin. Chem. Biol. 8, 349–358 (2004). 9. Oprea, T.I., Li, J., Muresan, S. & Mattes, K.C. High throughput and virtual screening: choosing the appropriate leads, in EuroQSAR 2002. In Designing Drugs and Crop Protectants: Processes, Problems and Solutions (eds. Ford, M., Livingstone, D., Dearden, J. and Van de Waterbeemd, H.) (Blackwell Publishing, New York, 2003). 10. Savchuk, N.P., Tkachenko, S.E. & Balakin, K.V. Rational design of GPCR-specific combinatorial libraries based on the concept of privileged substructures. in Cheminfor- matics in Drug Discovery (ed. Oprea, T.I.) 287–313 (Wiley VCH, Weinheim, 2005). 11. Edwards, B.S., Oprea, T., Prossnitz, E.R. & Sklar, L.A. Flow cytometry for high- throughput, high-content screening. Curr. Opin. Chem. Biol. 8, 392–398 (2004). 12. Waller, A. et al. Techniques: GPCR assembly, pharmacology and screening by flow cytometry. Trends Pharmacol. Sci. 25, 663–669 (2004). 13. Zhang, J.H., Chung, T.D. & Oldenburg, K.R. A simple statistical parameter for use in evaluation and validation of high throughput screening assays. J. Biomol. Screen. 4, 67–73 (1999). 14. Balla, T. & Varnai, P. Visualizing cellular phosphoinositide pools with GFP-fused protein-modules. Sci. STKE 2002, PL3 (2002). 15. Rochefort, H. et al. Estrogen receptor mediated inhibition of cancer cell invasion and motility: an overview. J. Steroid Biochem. Mol. Biol. 65, 163–168 (1998). 16. Grant, J.A., Pickup, B.T. & Nicholls, A. A smooth permittivity function for Poisson- Boltzmann solvation methods. J. Comput. Chem. 22, 608–640 (2001). 17. Rich, R.L. et al. Kinetic analysis of estrogen receptor/ligand interactions. Proc. Natl. Acad. Sci. USA 99, 8562–8567 (2002). 18. Olah, M., Bologa, C.G. & Oprea, T.I. Strategies for compound selection. Curr. Drug Discov. Technol. 1, 211–220 (2004). 19. Weininger, D. SMILES, a chemical language and information system. 1. Introduction to methodology and encoding rules. J. Chem. Inf. Comput. Sci. 28, 31–36 (1988). 20. Durant, J.L., Leland, B.A., Henry, D.R. & Nourse, J.G. Reoptimization of MDL keys for use in drug discovery. J. Chem. Inf. Comput. Sci. 42, 1273–1280 (2002). 21. Tanimoto, T.T. Non-linear model for a computer assisted medical diagnostic procedure. Trans. NY Acad. Sci. 23, 576–580 (1961). 22. Tversky, A. Features of similarity. Psychol. Rev. 84, 327–352 (1977). 23. Jackson, J.E. A Users Guide to Principal Components (Wiley-VCH, New York, 1991). 24. Pastor, M., Cruciani, G., McLay, I., Pickett, S. & Clementi, S. GRid-INdependent descriptors (GRIND): a novel class of alignment-independent three-dimensional molecular descriptors. J. Med. Chem. 43, 3233–3243 (2000). 25. Goodford, P.J. A computational procedure for determining energetically favorable binding sites on biologically important macromolecules. J. Med. Chem. 28, 849–857 (1985). 26. Morris, G.M. et al. Automated docking using a Lamarckian genetic algorithm and empirical binding free energy function. J. Comp. Chem. 19, 1639–1662 (1998). 27. Ramirez, S., Aiken, C.T., Andrzejewski, B., Sklar, L.A. & Edwards, B.S. High-through- put flow cytometry: validation in microvolume bioassays. Cytometry A 53, 55–65 (2003). 28. Deryugina, E.I. et al. MT1-MMP initiates activation of pro-MMP-2 and integrin alphavbeta3 promotes maturation of MMP-2 in breast carcinoma cells. Exp. Cell Res. 263, 209–223 (2001). 29. Baudelle, R., Melnyk, P., Deprez, B. & Tartar, A. Parallel synthesis of polysubstituted tetrahydroquinolines. Tetrahedron 54, 4125–4140 (1998). 30. Sartori, G., Bigi, F., Maggi, R., Mazzacani, A. & Oppici, G. Clay/water mixtures—a heterogeneous and ecologically efficient catalyst for the three-component stereo- selective synthesis of tetrahydroquinolines. Eur. J. Org. Chem. 2001, 2513–2518 (2001). ©2006NaturePublishingGroup L E T T E R S 6 ADVANCE ONLINE PUBLICATION NATURE CHEMICAL BIOLOGY

Related Documents