Application of generalized concentration addition to predict mixture effects of glucocorticoid receptor ligands.
ABSTRACT: Environmental exposures often occur in complex mixtures and at low concentrations. Generalized concentration addition (GCA) is a method used to estimate the joint effect of receptor ligands that vary in efficacy. GCA models have been successfully applied to mixtures of aryl hydrocarbon receptor (AhR) and peroxisome proliferator-activated receptor gamma (PPARγ) ligands, each of which can be modeled as a receptor with a single binding site. Here, we evaluated whether GCA could be applied to homodimer nuclear receptors, which have two binding sites, to predict the combined effect of full glucocorticoid receptor (GR) agonists with partial agonists. We measured transcriptional activation of GR using a cell-based bioassay. Individual concentration-response curves for dexamethasone (full agonist), prednisolone (full agonist), and medroxyprogesterone 17-acetate (partial agonist) were generated and applied in three additivity models, GCA, effect summation (ES), and relative potency factor (RPF), to generate response surfaces. GCA and RPF yielded adequate predictions of the experimental data for two full agonists. However, GCA fit experimental data significantly better than ES and RPF for all other binary mixtures. This work extends the application of GCA to homodimer nuclear receptors and improves prediction accuracy of mixture effects of GR agonists.
Project description:Many glucocorticoid receptor (GR) agonists have been detected in waste and surface waters domestically and around the world, but the way a mixture of these environmental compounds may elicit a total glucocorticoid activity response in water samples remains unknown. Therefore, we characterized 19 GR ligands using a CV1 cell line transcriptional activation assay applicable to water quality monitoring. Cells were treated with individual GR ligands, a fixed ratio mixture of full or partial agonists, or a nonequipotent mixture with full and partial agonists. Efficacy varied (48.09%-102.5%) and potency ranged over several orders of magnitude (1.278 × 10-10 to 3.93 × 10-8 M). Concentration addition (CA) and response addition (RA) mixtures models accurately predicted equipotent mixture responses of full agonists (r2 = 0.992 and 0.987, respectively). However, CA and RA models assume mixture compounds produce full agonist-like responses, and therefore they overestimated observed maximal efficacies for mixtures containing partial agonists. The generalized concentration addition (GCA) model mathematically permits < 100% maximal responses, and fell within the 95% confidence interval bands of mixture responses containing partial agonists. The GCA, but not CA and RA, model predictions of nonequipotent mixtures containing both full and partial agonists fell within the same statistical distribution as the observed values, reinforcing the practicality of the GCA model as the best overall model for predicting GR activation. Elucidating the mechanistic basis of GR activation by mixtures of previously detected environmental GR ligands will benefit the interpretation of environmental sample contents in future water quality monitoring studies.
Project description:Concentration/dose addition is widely used for compounds that act by similar mechanisms. But it cannot make predictions for mixtures of full and partial agonists for effect levels above that of the least efficacious component. As partial agonists are common, we developed generalized concentration addition, which has been successfully applied to systems in which ligands compete for a single binding site. Here, we applied a pharmacodynamic model for a homodimer receptor system with 2 binding sites, the androgen receptor, that acts according to the classic homodimer activation model: Each cytoplasmic monomer protein binds ligand, undergoes a conformational change that relieves inhibition of dimerization, and binds to DNA response elements as a dimer. We generated individual dose-response data for full (dihydroxytestosterone, BMS564929) and partial (TFM-4AS-1) agonists and a competitive antagonist (MDV3100) using reporter data generated in the MDA-kb2 cell line. We used the Schild method to estimate the binding affinity of MDV3100. Data for individual compounds fit the homodimer pharmacodynamic model well. In the presence of a full agonist, the partial agonist had agonistic effects at low effect levels and antagonistic effects at high levels, as predicted by pharmacological theory. The generalized concentration addition model fits the empirical mixtures data-full/full agonist, full/partial agonist, and full agonist/antagonist-as well or better than relative potency factors or effect summation. The ability of generalized concentration addition to predict the activity of mixtures of different types of androgen receptor ligands is important as a number of environmental compounds act as partial androgen receptor agonists or antagonists.
Project description:Histamine H1 receptor (H1R) antagonists and glucocorticoid receptor (GR) agonists are used to treat inflammatory conditions such as allergic rhinitis, atopic dermatitis and asthma. Consistent with the high morbidity levels of such inflammatory conditions, these receptors are the targets of a vast number of approved drugs, and in many situations their ligands are co-administered. However, this drug association has no clear rationale and has arisen from clinical practice. We hypothesized that H1R signaling could affect GR-mediated activity, impacting on its transcriptional outcome. Indeed, our results show a dual regulation of GR activity by the H1R: a potentiation mediated by G-protein ?? subunits and a parallel inhibitory effect mediated by G?q-PLC pathway. Activation of the H1R by its full agonists resulted in a composite potentiating effect. Intriguingly, inactivation of the G?q-PLC pathway by H1R inverse agonists resulted also in a potentiation of GR activity. Moreover, histamine and clinically relevant antihistamines synergized with the GR agonist dexamethasone to induce gene transactivation and transrepression in a gene-specific manner. Our work provides a delineation of molecular mechanisms underlying the widespread clinical association of antihistamines and GR agonists, which may contribute to future dosage optimization and reduction of well-described side effects associated with glucocorticoid administration.
Project description:The vast array of potential environmental toxicant combinations necessitates the development of efficient strategies for predicting toxic effects of mixtures. Current practices emphasize the use of concentration addition to predict joint effects of endocrine disrupting chemicals in coexposures. Generalized concentration addition (GCA) is one such method for predicting joint effects of coexposures to chemicals and has the advantage of allowing for mixture components to have differences in efficacy (ie, dose-response curve maxima). Peroxisome proliferator-activated receptor gamma (PPAR?) is a nuclear receptor that plays a central role in regulating lipid homeostasis, insulin sensitivity, and bone quality and is the target of an increasing number of environmental toxicants. Here, we tested the applicability of GCA in predicting mixture effects of therapeutic (rosiglitazone and nonthiazolidinedione partial agonist) and environmental PPAR? ligands (phthalate compounds identified using EPA's ToxCast database). Transcriptional activation of human PPAR?1 by individual compounds and mixtures was assessed using a peroxisome proliferator response element-driven luciferase reporter. Using individual dose-response parameters and GCA, we generated predictions of PPAR? activation by the mixtures, and we compared these predictions with the empirical data. At high concentrations, GCA provided a better estimation of the experimental response compared with 3 alternative models: toxic equivalency factor, effect summation and independent action. These alternatives provided reasonable fits to the data at low concentrations in this system. These experiments support the implementation of GCA in mixtures analysis with endocrine disrupting compounds and establish PPAR? as an important target for further studies of chemical mixtures.
Project description:1. The tachykinin receptor present in the guinea-pig oesophageal mucosa that mediates contractile responses of the muscularis mucosae has been characterized, using functional in vitro experiments. 2. The NK(1) receptor-selective agonist, [Sar(9)(O(2))Met(11)]SP and the NK(3) receptor-selective agonists, [MePhe(7)]-NKB and senktide, produced no response at submicromolar concentrations. The NK(2) receptor-selective agonists, [Nle(10)]-NKA(4 - 10), and GR 64,349 produced concentration-dependent contractile effects with pD(2) values of 8.20+/-0.16 and 8.30+/-0.15, respectively. 3. The concentration-response curve to the non-selective agonist, NKA (pD(2)=8.13+/-0.04) was shifted significantly rightwards only by the NK(2) receptor-selective antagonist, GR 159,897 and was unaffected by the NK(1) receptor-selective antagonist, SR 140,333 and the NK(3) receptor-selective antagonist, SB 222,200. 4. The NK(2) receptor-selective antagonist, GR 159,897, exhibited an apparent competitive antagonism against the NK(2) receptor-selective agonist, GR 64,349 (apparent pK(B) value=9.29+/-0.16) and against the non-selective agonist, NKA (apparent pK(B) value=8.71+/-0.19). 5. The NK(2) receptor-selective antagonist, SR 48,968 exhibited a non-competitive antagonism against the NK(2) receptor-selective agonist, [Nle(10)]-NKA(4 - 10). The pK(B) value was 10.84+/-0.19.6. It is concluded that the guinea-pig isolated oesophageal mucosa is a useful preparation for studying the effects of NK(2) receptor-selective agonists and antagonists as the contractile responses to various tachykinins are mediated solely by NK(2) receptors.
Project description:Human prostate cancer cell lines treated with androgen receptor (AR) agonists/antagonists and concurrent glucocorticoid receptor (GR) agonist/antagonists Overall design: Human prostate cancer cell lines in charcoal-stripped FCS-containing media were treated for 3 days with AR agonists (R1881 1nM) +/-antagonist (enzalutamide 10uM) and then pulsed with 2 or 6 hour treatment with GR agonist (Dex 100nM) +/- antagonist (SGRM, 335 1uM and 297 1uM) after which RNA was collected and sequenced
Project description:The project is directed to the development of selective glucocorticoid receptor agonists for anticancer therapy. Glucocorticoids (GC) are widely used in treatment of many types of cancer due to its ability to induce apoptosis in malignant cells (in blood cancer therapy) and to prevent nausea and emesis (in the chemotherapy of solid tumors). However, severe dose-limiting side effects occur, including osteoporosis, muscle wasting, diabetes and other metabolic complications. Both beneficial and harmful effects of glucocorticoids are due to selective activation or repression of particular genes by glucocorticoid receptor (GR). GR regulates gene expression via transactivation that requires GR homodimer binding to gene promoters and transrepression mediated via negative interaction between GR and other transcription factors as well as binding with negative glucocorticoid response elements (nGRE) in genes. GR transactivation is linked to metabolic side effects, while GR transrepression underlies glucocorticoid therapeutic action. Novel selective GR agonist Compound A (CpdA) prevents GR dimerization and transactivation, specifically activates GR transrepression, and has fewer side effects compared to glucocorticoids. Here we compare the gene expression profiles in lymphoma cells treated with glucocorticoid Dexamethasone (Dex) or CpdA Overall design: B-cell mantle cell lymphoma cells Granta-519 were treated with Dexamethasone (1 uM), Compound A (1 uM) or solvent (Ethanol) for 16 h. Then cells were pelleted and total RNA was isolated with RiboPure kit (Ambion) according to manufacturer's protocol. The RNA samples were treated with TURBOTM DNase (Ambion). Quality control was performed with Agilent Bioanalyser.
Project description:The project is directed to the development of selective glucocorticoid receptor agonists for anticancer therapy. Glucocorticoids (GC) are widely used in treatment of many types of cancer due to its ability to induce apoptosis in malignant cells (in blood cancer therapy) and to prevent nausea and emesis (in the chemotherapy of solid tumors). However, severe dose-limiting side effects occur, including osteoporosis, muscle wasting, diabetes and other metabolic complications. Both beneficial and harmful effects of glucocorticoids are due to selective activation or repression of particular genes by glucocorticoid receptor (GR). GR regulates gene expression via transactivation that requires GR homodimer binding to gene promoters and transrepression mediated via negative interaction between GR and other transcription factors as well as binding with negative glucocorticoid response elements (nGRE) in genes. GR transactivation is linked to metabolic side effects, while GR transrepression underlies glucocorticoid therapeutic action. Novel selective GR agonist Compound A (CpdA) prevents GR dimerization and transactivation, specifically activates GR transrepression, and has fewer side effects compared to glucocorticoids. Here we compare the gene expression profiles in prostate cancer cells treated with glucocorticoid Dexamethasone (Dex) or CpdA Overall design: LNCaP prostrate cancer cells were treated with Dexamethasone (1 uM), Compound A (1 uM) or solvent (Ethanol) for 16 h. Then cells were pelleted and total RNA was isolated with RiboPure kit (Ambion) according to manufacturer's protocol. The RNA samples were treated with TURBOTM DNase (Ambion). Quality control was performed with Agilent Bioanalyser.
Project description:Many acute and chronic anaemias, including haemolysis, sepsis and genetic bone marrow failure diseases such as Diamond-Blackfan anaemia, are not treatable with erythropoietin (Epo), because the colony-forming unit erythroid progenitors (CFU-Es) that respond to Epo are either too few in number or are not sensitive enough to Epo to maintain sufficient red blood cell production. Treatment of these anaemias requires a drug that acts at an earlier stage of red cell formation and enhances the formation of Epo-sensitive CFU-E progenitors. Recently, we showed that glucocorticoids specifically stimulate self-renewal of an early erythroid progenitor, burst-forming unit erythroid (BFU-E), and increase the production of terminally differentiated erythroid cells. Here we show that activation of the peroxisome proliferator-activated receptor ? (PPAR-?) by the PPAR-? agonists GW7647 and fenofibrate synergizes with the glucocorticoid receptor (GR) to promote BFU-E self-renewal. Over time these agonists greatly increase production of mature red blood cells in cultures of both mouse fetal liver BFU-Es and mobilized human adult CD34(+) peripheral blood progenitors, with a new and effective culture system being used for the human cells that generates normal enucleated reticulocytes. Although Ppara(-/-) mice show no haematological difference from wild-type mice in both normal and phenylhydrazine (PHZ)-induced stress erythropoiesis, PPAR-? agonists facilitate recovery of wild-type but not Ppara(-/-) mice from PHZ-induced acute haemolytic anaemia. We also show that PPAR-? alleviates anaemia in a mouse model of chronic anaemia. Finally, both in control and corticosteroid-treated BFU-E cells, PPAR-? co-occupies many chromatin sites with GR; when activated by PPAR-? agonists, additional PPAR-? is recruited to GR-adjacent sites and presumably facilitates GR-dependent BFU-E self-renewal. Our discovery of the role of PPAR-? agonists in stimulating self-renewal of early erythroid progenitor cells suggests that the clinically tested PPAR-? agonists we used may improve the efficacy of corticosteroids in treating Epo-resistant anaemias.
Project description:The effect of retinoid X receptor (RXR) antagonists on the conformational exchange of the RXR ligand-binding domain (LBD) remains poorly characterized. To address this question, we used nuclear magnetic resonance spectroscopy to compare the chemical shift perturbations induced by RXR antagonists and agonists on the RXRalpha LBD when partnered with itself as a homodimer and as the heterodimeric partner with the peroxisome proliferator-activated receptor gamma (PPARgamma) LBD. Chemical shift mapping on the crystal structure showed that agonist binding abolished a line-broadening effect caused by a conformational exchange on backbone amide signals for residues in helix H3 and other regions of either the homo- or hetero-dimer, whereas binding of antagonists with similar binding affinities failed to do so. A lineshape analysis of a glucocorticoid receptor-interacting protein 1 NR box 2 coactivator peptide showed that the antagonists enhanced peptide binding to the RXRalpha LBD homodimer, but to a lesser extent than that enhanced by the agonists. This was further supported by a lineshape analysis of the RXR C-terminal residue, threonine 462 (T462) in the homodimer but not in the heterodimer. Contrary to the agonists, the antagonists failed to abolish a line-broadening effect caused by a conformational exchange on the T462 signal corresponding to the RXRalpha LBD-antagonist-peptide ternary complex. These results suggest that the antagonists lack the ability of the agonists to shift the equilibrium of multiple RXRalpha LBD conformations in favor of a compact state, and that a PPARgamma LBD-agonist complex can prevent the antagonist from enhancing the RXRalpha LBD-coactivator binding interaction.