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Allosteric Antagonism of the Pregnane X Receptor (PXR): Current-State-of-the-Art and Prediction of Novel Allosteric Sites. Cells 2022; 11:cells11192974. [PMID: 36230936 PMCID: PMC9563780 DOI: 10.3390/cells11192974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 09/20/2022] [Accepted: 09/20/2022] [Indexed: 11/26/2022] Open
Abstract
The pregnane X receptor (PXR, NR1I2) is a xenobiotic-activated transcription factor with high levels of expression in the liver. It not only plays a key role in drug metabolism and elimination, but also promotes tumor growth, drug resistance, and metabolic diseases. It has been proposed as a therapeutic target for type II diabetes, metabolic syndrome, and inflammatory bowel disease, and PXR antagonists have recently been considered as a therapy for colon cancer. There are currently no PXR antagonists that can be used in a clinical setting. Nevertheless, due to the large and complex ligand-binding pocket (LBP) of the PXR, it is challenging to discover PXR antagonists at the orthosteric site. Alternative ligand binding sites of the PXR have also been proposed and are currently being studied. Recently, the AF-2 allosteric binding site of the PXR has been identified, with several compounds modulating the site discovered. Herein, we aimed to summarize our current knowledge of allosteric modulation of the PXR as well as our attempt to unlock novel allosteric sites. We describe the novel binding function 3 (BF-3) site of PXR, which is also common for other nuclear receptors. In addition, we also mention a novel allosteric site III based on in silico prediction. The identified allosteric sites of the PXR provide new insights into the development of safe and efficient allosteric modulators of the PXR receptor. We therefore propose that novel PXR allosteric sites might be promising targets for treating chronic metabolic diseases and some cancers.
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Ondansetron, a highly selective 5-HT3 receptor antagonist, reduces L-DOPA-induced dyskinesia in the 6-OHDA-lesioned rat model of Parkinson's disease. Eur J Pharmacol 2020; 871:172914. [DOI: 10.1016/j.ejphar.2020.172914] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 12/12/2019] [Accepted: 01/07/2020] [Indexed: 01/06/2023]
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Lummis SCR, Thompson AJ. Agonists and antagonists induce different palonosetron dissociation rates in 5-HT₃A and 5-HT₃AB receptors. Neuropharmacology 2013; 73:241-6. [PMID: 23747573 PMCID: PMC3778450 DOI: 10.1016/j.neuropharm.2013.05.010] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Revised: 04/19/2013] [Accepted: 05/08/2013] [Indexed: 11/30/2022]
Abstract
Palonosetron is a potent 5-HT3 receptor antagonist with a unique structure and some unusual properties. Here we explore the properties of palonosetron at heterologously expressed 5-HT3A and 5-HT3AB receptors. We used receptors expressed in HEK293 cells, and functionally analysed them using a membrane potential sensitive dye in a Flexstation, which revealed IC50s of 0.24 nM and 0.18 nM for 5-HT3A and 5-HT3AB receptors respectively. Radioligand binding studies with [3H]palonosetron revealed similar Kds: 0.34 nM for 5-HT3A and 0.15 nM for 5-HT3AB receptors. Kinetic studies showed palonosetron association and dissociation rates were slightly faster in 5-HT3AB than 5-HT3A receptors, and for both subtypes dissociation rates were ligand-dependent, with antagonists causing more rapid dissociation than agonists. Similar ligand effects were not observed for [3H]granisetron dissociation studies. These data support previous studies which show palonosetron has actions distinct to other 5-HT3 receptor antagonists, and the slow rates observed for agonist induced dissociation (t1/2 > 10 h) could at least partly explain the long duration of palonosetron effects in vivo. Palonosetron IC50s and Kds for 5-HT3A and 5-HT3AB receptors in HEK293 cells are similar. Palonosetron association and dissociation rates are slower at 5-HT3A than 5-HT3AB receptors. Agonist-induced palonosetron dissociation rates are slower than those for antagonists in both 5-HT3A and 5-HT3AB receptors. Agonist- and antagonist-induced granisetron dissociation rates are similar in both 5-HT3A and 5-HT3AB receptors. Palonosetron and granisetron have distinct actions.
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Affiliation(s)
- Sarah C R Lummis
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK.
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Chung HH, Dai ZK, Wu BN, Yeh JL, Chai CY, Chu KS, Liu CP, Chen IJ. KMUP-1 inhibits pulmonary artery proliferation by targeting serotonin receptors/transporter and NO synthase, inactivating RhoA and suppressing AKT/ERK phosphorylation. Vascul Pharmacol 2010; 53:239-49. [DOI: 10.1016/j.vph.2010.09.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2010] [Revised: 09/10/2010] [Accepted: 09/17/2010] [Indexed: 11/24/2022]
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Rojas C, Thomas AG, Alt J, Stathis M, Zhang J, Rubenstein EB, Sebastiani S, Cantoreggi S, Slusher BS. Palonosetron triggers 5-HT3 receptor internalization and causes prolonged inhibition of receptor function. Eur J Pharmacol 2010; 626:193-9. [DOI: 10.1016/j.ejphar.2009.10.002] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Accepted: 10/07/2009] [Indexed: 10/20/2022]
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Aapro M, Blower P. 5-hydroxytryptamine type-3 receptor antagonists for chemotherapy-induced and radiotherapy-induced nausea and emesis: can we safely reduce the dose of administered agents? Cancer 2005; 104:1-18. [PMID: 15929119 DOI: 10.1002/cncr.21141] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND Nausea and emesis as a consequence of chemotherapy or radiotherapy can have an adverse effect on patients' quality of life during cancer treatment and may last for > 5 days after administration. Guidelines suggest that, used at appropriate doses, the 5-hydroxytryptamine type-3 (5-HT3) receptor antagonists--which are considered the antiemetic "gold standard" when they are administered in combination with corticosteroids--demonstrate equivalent efficacy and safety. However, due to financial considerations, these agents often are used at lower doses than recommended. METHODS A literature review of relevant publications pertaining to the control of chemotherapy-induced nausea and emesis and dosing issues of the 5-HT3 receptor antagonists was undertaken to provide a comprehensive review of dosing issues relevant to the 5-HT3 receptor antagonists. RESULTS The issue of "down dosing" was particularly pertinent because of the nature of the 5-HT3 receptor antagonist dose-response curve: A steep dose-response profile within a narrow dose range suggests that antiemetic control will be lost suddenly after dose deescalation. However, the array of predisposing and confounding patient factors indicates that it is unlikely that a loss of antiemetic control will be apparent across a population; rather, individuals will experience loss of control as the dose is reduced below threshold. Of the 4 5-HT3 receptor antagonists currently licensed in the United States (granisetron, ondansetron, dolasetron, and palonosetron), ondansetron is used sometimes at lower than optimal doses, and there is evidence to suggest that even the approved oral dose of dolasetron may be suboptimal. CONCLUSIONS Suboptimal dosing not only will be detrimental to patients' quality of life but, ultimately, will prove counterproductive in terms of hospital resources, and it will add to the already significant socioeconomic burden associated with cancer therapy. Therefore, the dose of antiemetic agent administered should be sufficiently high to ensure good emesis control across the whole patient population.
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Affiliation(s)
- Matti Aapro
- Clinique de Genolier, Genolier, Switzerland.
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Vitális B, Sebestyén L, Sike M, Sólyom S, Hársing LG. Binding characteristics of GYKI-46 903, a non-competitive ligand at 5-HT3 receptors. Pharmacol Res 2001; 43:291-9. [PMID: 11401422 DOI: 10.1006/phrs.2000.0774] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
GYKI-46903 [(+)-(5S,6R)-4-(4-fluorophenyl)-6-propionyloxy-1-aza-bicyclo[3.3.1]-non-3-ene-hydrochloride], a cognition enhancer identified as a non-competitive antagonist of 5-HT3receptors in isolated guinea-pig ileum, was investigated for allosteric action at 5-HT3 receptors in rat cortical membranes by using [3H]granisetron. Equilibrium and kinetic protocols were applied and the competitive antagonist granisetron was included as a negative control. In competition studies, both granisetron and GYKI-46 903 displaced the radioligand with K(i) values of 0.20 +/- 0.02 and 79.84 +/- 0.28 nM, respectively. The inhibition curve for GYKI-46 903 resulted in a Hill slope significantly greater than unity ( 1.37 +/- 0.11), whereas the slope for granisetron was 0.88 +/- 0.08, not different from unity. These results indicate non-competitive and competitive interactions, respectively. Scatchard analysis yielded a linear plot, suggesting a single population of binding sites with a Kd of 0.13 +/- 0.01 nM and a Bmax) of 13.15 +/- 0.34 fmol per mg of protein. Scatchard plots obtained in the absence and presence of granisetron (0.1-3 nM) or GYKI-46 903 (30-1000 nM) revealed a concentration-dependent increase in Kd values by either of these compounds. Granisetron left the Bmax unchanged, but there was a significant increase in the Bmax by GYKI-46 903, which could point to an atypical allosteric interaction. The Schild plot derived from the Kd shifts induced by granisetron was linear with a slope of 1.02, not different from unity, as expected from a competitive interaction. The Schild regression for GYKI-46 903 was linear with a slope of 1.20, deviating significantly from unity, which may also indicate an allosteric interaction. Both the association and dissociation curves of [3H]granisetron were monoexponential. The dissociation rate constant (K(-1)) and the association rate constant (K(+1)) were 0.32 +/- 0.01 min(-1) and 1.15 min(-1) x nM(-1), respectively. The dissociation driven by an excess concentration of ondansetron ( 1 microM) in the absence and presence of granisetron (0.1-3 nM) or GYKI-46 903 (30-10 000 nM) was not influenced by the compounds under study, as compared with the control, indicating the lack of an allosteric effect on the dissociation. Summing up, the binding profile of GYKI-46 903 may reflect a mixed type of action, including a negative allosteric interaction.
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Affiliation(s)
- B Vitális
- Institute for Drug Research Ltd., Budapest, Hungary
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Mochizuki S, Watanabe T, Miyake A, Saito M, Furuichi K. Cloning, expression, and characterization of ferret 5-HT(3) receptor subunit. Eur J Pharmacol 2000; 399:97-106. [PMID: 10884508 DOI: 10.1016/s0014-2999(00)00371-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Ferrets (Mustela putorius furo) are useful animals for determining anti-emetic activity via 5-HT(3) receptors in vivo. We isolated a cDNA encoding the 5-hydroxytryptamine (5-HT) type 3A receptor subunit (5-HT(3A)) from ferret colon, expressed it in a human embryonic kidney cell line and determined its pharmacological properties. The open reading frame of the isolated cDNA encoded a 483-amino acid protein, corresponding to the shorter splice variant of 5-HT(3A) receptors. Splice variants were no longer detected by reverse transcriptase-polymerase chain reaction. The ferret 5-HT(3A) receptor exhibits a high degree of amino acid sequence identity (>/=80%) to that of other species. Binding studies demonstrated the following rank order of potency for agonists: meta-chlorophenylbiguanide (mCPBG)>2-methyl-5-hydroxytryptamine (2-Me-5-HT)=5-HT, and for antagonists: ondansetron=tropisetron>(+)-tubocurarine>metoclopramide. Electrophysiological studies revealed that mCPBG was a partial agonist and 2-Me-5-HT was an almost fully effective agonist compared to 5-HT.
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MESH Headings
- Alternative Splicing
- Amino Acid Sequence
- Animals
- Biguanides/pharmacology
- Binding, Competitive
- Cell Line
- Cloning, Molecular
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- Dose-Response Relationship, Drug
- Electrophysiology
- Ferrets
- Gene Expression
- Humans
- Imidazoles/metabolism
- Indoles/metabolism
- Kruppel-Like Factor 6
- Kruppel-Like Transcription Factors
- Membrane Potentials/drug effects
- Molecular Sequence Data
- Ondansetron/pharmacology
- Piperazines
- Proto-Oncogene Proteins
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Radioligand Assay
- Rats
- Receptors, Serotonin/genetics
- Receptors, Serotonin, 5-HT3
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Serotonin/analogs & derivatives
- Serotonin/pharmacology
- Serotonin Antagonists/pharmacology
- Serotonin Receptor Agonists/pharmacology
- Tissue Distribution
- Trans-Activators
- Tritium
- Tubocurarine/pharmacology
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Affiliation(s)
- S Mochizuki
- Molecular Medicine Laboratories, Institute for Drug Discovery Research, Yamanouchi Pharmaceutical Co., Ltd., 21 Miyukigaoka, Tsukuba, 305-8585, Ibaraki, Japan.
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Dubin AE, Huvar R, D'Andrea MR, Pyati J, Zhu JY, Joy KC, Wilson SJ, Galindo JE, Glass CA, Luo L, Jackson MR, Lovenberg TW, Erlander MG. The pharmacological and functional characteristics of the serotonin 5-HT(3A) receptor are specifically modified by a 5-HT(3B) receptor subunit. J Biol Chem 1999; 274:30799-810. [PMID: 10521471 DOI: 10.1074/jbc.274.43.30799] [Citation(s) in RCA: 226] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
While homomers containing 5-HT(3A) subunits form functional ligand-gated serotonin (5-HT) receptors in heterologous expression systems (Jackson, M. B., and Yakel, J. L. (1995) Annu. Rev. Physiol. 57, 447-468; Lambert, J. J., Peters, J. A., and Hope, A. G. (1995) in Ligand-Voltage-Gated Ion Channels (North, R., ed) pp. 177-211, CRC Press, Inc., Boca Raton, FL), it has been proposed that native receptors may exist as heteromers (Fletcher, S., and Barnes, N. M. (1998) Trends Pharmacol. Sci. 19, 212-215). We report the cloning of a subunit 5-HT(3B) with approximately 44% amino acid identity to 5-HT(3A) that specifically modified 5-HT(3A) receptor kinetics, voltage dependence, and pharmacology. Co-expression of 5-HT(3B) with 5-HT(3A) modified the duration of 5-HT(3) receptor agonist-induced responses, linearized the current-voltage relationship, increased agonist and antagonist affinity, and reduced cooperativity between subunits. Reverse transcriptase-polymerase chain reaction in situ hybridization revealed co-localization of both 5-HT(3B) and 5-HT(3A) in a population of neurons in the amygdala, telencephalon, and entorhinal cortex. Furthermore, 5-HT(3A) and 5-HT(3B) mRNAs were expressed in spleen and intestine. Our data suggest that 5-HT(3B) might contribute to tissue-specific functional changes in 5-HT(3)-mediated signaling and/or modulation.
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Affiliation(s)
- A E Dubin
- R. W. Johnson Pharmaceutical Research Institute, San Diego, California 92121, USA.
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Mair ID, Lambert JJ, Yang J, Dempster J, Peters JA. Pharmacological characterization of a rat 5-hydroxytryptamine type3 receptor subunit (r5-HT3A(b)) expressed in Xenopus laevis oocytes. Br J Pharmacol 1998; 124:1667-74. [PMID: 9756382 PMCID: PMC1565579 DOI: 10.1038/sj.bjp.0702037] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The present study has utilized the two electrode voltage-clamp technique to examine the pharmacological profile of a splice variant of the rat orthologue of the 5-hydroxytryptamine type 3A subunit (5-HT3A(b)) heterologously expressed in Xenopus laevis oocytes. At negative holding potentials, bath applied 5-HT (300 nM - 10 microM) evoked a transient, concentration-dependent (EC50 = 1.1+/-0.1 microM), inward current. The response reversed in sign at a holding potential of -2.1+/-1.6 mV. The response to 5-HT was mimicked by the 5-HT3 receptor selective agonists 2-methyl-5-HT (EC50= 4.1+/-0.2 microM), 1-phenylbiguanide (EC50=3.0+/-0.1 microM), 3-chlorophenylbiguanide (EC50 = 140+/-10 nM), 3,5-dichlorophenylbiguanide (EC50 = 14.5+/-0.4 nM) and 2,5-dichlorophenylbiguanide (EC50 = 10.2+/-0.6 nM). With the exception of 2-methyl-5-HT, all of the agonists tested elicited maximal current responses comparable to those produced by a saturating concentration (10 microM) of 5-HT. Responses evoked by 5-HT at EC50 were blocked by the 5-HT3 receptor selective antagonist ondansetron (IC50=231+/-22 pM) and by the less selective agents (+)-tubocurarine (IC50=31.9+/-0.01 nM) and cocaine (IC50 = 2.1+/-0.2 microM). The data are discussed in the context of results previously obtained with the human and mouse orthologues of the 5-HT3A subunit. Overall, the study reinforces the conclusion that species differences detected for native 5-HT3 receptors extend to, and appear largely explained by, differences in the properties of homo-oligomeric receptors formed from 5-HT3A subunit orthologues.
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Affiliation(s)
- I D Mair
- Neurosciences Institute, Department of Pharmacology and Neuroscience, The University of Dundee
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5-HT3 receptors. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s0165-7208(97)80016-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Hope AG, Peters JA, Brown AM, Lambert JJ, Blackburn TP. Characterization of a human 5-hydroxytryptamine3 receptor type A (h5-HT3R-AS) subunit stably expressed in HEK 293 cells. Br J Pharmacol 1996; 118:1237-45. [PMID: 8818349 PMCID: PMC1909612 DOI: 10.1111/j.1476-5381.1996.tb15529.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. A cloned cDNA encoding a human 5-hydroxytryptamine3 receptor type A subunit (h5-HT3R-As) was transfected into human embryonic kidney (HEK 293) cells maintained in cell culture and a stable cell line expressing a high density of the recombinant receptor was selected. 2. Membrane homogenates prepared from transfected, but not untransfected, cells exhibited a homogeneous and saturable population (Bmax = 4.49 +/- 0.46 pmol mg-1 protein) of sites that bound the radiolabelled 5-HT3 receptor antagonist, [3H]-granisetron with high affinity (pKD = 8.87 +/- 0.08). Kinetic studies (at 37 degrees C) revealed rapid association (kappa +1 4.76 +/- 0.3 x 10(8) M-1 min-1) and dissociation (kappa -1 = 0.21 +/- 0.003 min-1) of the radioligand. 3. Selective and non-selective 5-HT3 receptor ligands competed for [3H]-granisetron binding with a rank order of potency (granisetron > ondansetron > meta-chlorophenylbiguanide > 5-HT > 2-methyl-5-HT > metoclopramide > > phenylbiguanide > cocaine > (+)-tubocurarine) identical to that established for 5-HT3 receptors endogenous to the human CNS. 4. In electrophysiological recordings performed on transfected cells, voltage-clamped at a holding potential of -60 mV, locally applied 5-HT (10 microM) evoked transient inward current responses that reversed in sign at a potential of -1.0 +/- 1.1 mV. Such responses were antagonized in a reversible manner by granisetron (1 nM). 5. The construction of a stable cell line expressing a high density of recombinant human 5-HT3 receptors which display appropriate pharmacology and function will assist in the further characterization of this receptor subtype and the exploration of species differences in 5-HT3 receptor pharmacology.
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Affiliation(s)
- A G Hope
- Department of Pharmacology and Clinical Pharmacology, Ninewells Hospital and Medical School, Dundee University, U.K
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