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Abstract
This chapter has been conceived as an introductory text to aid in the understanding of the key design strategies for the development of synthetic analogs of endogenous retinoids as ligands for the retinoic acid receptors (RARs) and retinoid X receptors (RXRs). The structure and binding characteristics of the endogenous retinoids are first explained to put the main chemical design challenges in context. Existing biochemical and structural data is then used to describe the guiding principles used to develop agonists and antagonists of the RARs and RXRs. In light of the increasing proliferation of biophysical methods that employ fluorescence measurements or molecular tags, we also examine the application of retinoids as probes and the chemical principles required to develop these tools.
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Affiliation(s)
| | - Andrew Whiting
- Department of Chemistry, Durham University, Lower Mountjoy, Durham, United Kingdom
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2
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Modulation of RXR function through ligand design. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:57-69. [PMID: 21515403 DOI: 10.1016/j.bbalip.2011.04.003] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Revised: 04/06/2011] [Accepted: 04/07/2011] [Indexed: 12/22/2022]
Abstract
As the promiscuous partner of heterodimeric associations, retinoid X receptors (RXRs) play a key role within the Nuclear Receptor (NR) superfamily. Some of the heterodimers (PPAR/RXR, LXR/RXR, FXR/RXR) are "permissive" as they become transcriptionally active in the sole presence of either an RXR-selective ligand ("rexinoid") or a NR partner ligand. In contrast, "non-permissive" heterodimers (including RAR/RXR, VDR/RXR and TR/RXR) are unresponsive to rexinoids alone but these agonists superactivate transcription by synergizing with partner agonists. Despite their promiscuity in heterodimer formation and activation of multiple pathways, RXR is a target for drug discovery. Indeed, a rexinoid is used in the clinic for the treatment of cutaneous T-cell lymphoma. In addition to cancer RXR modulators hold therapeutical potential for the treatment of metabolic diseases. The modulation potential of the rexinoid (as agonist or antagonist ligand) is dictated by the precise conformation of the ligand-receptor complexes and the nature and extent of their interaction with co-regulators, which determine the specific physiological responses through transcription modulation of cognate gene networks. Notwithstanding the advances in this field, it is not yet possible to predict the correlation between ligand structure and physiological response. We will focus on this review on the modulation of PPARγ/RXR and LXR/RXR heterodimer activities by rexinoids. The genetic and pharmacological data from animal models of insulin resistance, diabetes and obesity demonstrate that RXR agonists and antagonists have promise as anti-obesity agents. However, the treatment with rexinoids raises triglycerides levels, suppresses the thyroid hormone axis, and induces hepatomegaly, which has complicated the development of these compounds as therapeutic agents for the treatment of type 2 diabetes and insulin resistance. The discovery of PPARγ/RXR and LXR/RXR heterodimer-selective rexinoids, which act differently than PPARγ or LXR agonists, might overcome some of these limitations.
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3
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Barnard JH, Collings JC, Whiting A, Przyborski SA, Marder TB. Synthetic retinoids: structure-activity relationships. Chemistry 2010; 15:11430-42. [PMID: 19821467 DOI: 10.1002/chem.200901952] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Retinoid signalling pathways are involved in numerous processes in cells, particularly those mediating differentiation and apoptosis. The endogenous ligands that bind to the retinoid receptors, namely all-trans-retinoic acid (ATRA) and 9-cis-retinoic acid, are prone to double-bond isomerisation and to oxidation by metabolic enzymes, which can have significant and deleterious effects on their activities and selectivities. Many of these problems can be overcome through the use of synthetic retinoids, which are often much more stable, as well as being more active. Modification of their molecular structures can result in retinoids that act as antagonists, rather than agonists, or exhibit a large degree of selectivity for particular retinoid-receptor isotypes. Several such selective retinoids are likely to be of value as pharmaceutical agents with reduced toxicities, particularly in cancer therapy, as reagents for controlling cell differentiation, and as tools for elucidating the precise roles that specific retinoid signalling pathways play within cells.
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Affiliation(s)
- Jonathan H Barnard
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK
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4
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Büttner MW, Burschka C, Daiss JO, Ivanova D, Rochel N, Kammerer S, Peluso-Iltis C, Bindler A, Gaudon C, Germain P, Moras D, Gronemeyer H, Tacke R. Silicon Analogues of the Retinoid Agonists TTNPB and 3-Methyl-TTNPB, Disila-TTNPB and Disila-3-methyl-TTNPB: Chemistry and Biology. Chembiochem 2007; 8:1688-99. [PMID: 17768726 DOI: 10.1002/cbic.200700182] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Twofold sila-substitution (C/Si exchange) in the saturated ring of the tetrahydronaphthalene skeleton of the retinoid agonists TTNPB (1 a) and 3-methyl-TTNPB (2 a) leads to disila-TTNPB (1 b) and disila-3-methyl-TTNPB (2 b), respectively. The silicon compounds 1 b and 2 b were synthesized in multiple steps, and their identities were established by elemental analyses, multinuclear NMR experiments, and single-crystal X-ray diffraction studies. Like TTNPB (1 a) and 3-methyl-TTNPB (2 a), the analogous silicon-based arotinoids 1 b and 2 b are strong pan-RAR agonists and display the same strong differentiation and apoptosis-inducing activity in NB4 promyelocytic leukemia cells as the parent carbon compounds. These results are in keeping with the nearly isomorphous structures of 1 a and 1 b bound to the complex of the RARbeta ligand-binding domain with the nuclear receptor (NR) box 2 peptide of the SRC-1 coactivator. The contacts within the ligand-binding pocket are identical except for helix H11, for which two turns are shifted in the disila-TTNPB (1 b) complex. This study represents the first comprehensive structure-function analysis of a carbon/silicon switch in a signaling molecule and demonstrates that silicon analogues can have the same biological functionalities and conserved structures as their parent carbon compounds, and it illustrates at the same time that silicon analogues of biologically active compounds have the potential to induce alternative allosteric effects, as in the case of helix H11, which might allow for novel options in drug design.
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Affiliation(s)
- Matthias W Büttner
- Universität Würzburg, Institut für Anorganische Chemie, Am Hubland, 97074 Würzburg, Germany
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5
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Hughes PJ, Zhao Y, Chandraratna RA, Brown G. Retinoid-mediated stimulation of steroid sulfatase activity in myeloid leukemic cell lines requires RARalpha and RXR and involves the phosphoinositide 3-kinase and ERK-MAP kinase pathways. J Cell Biochem 2006; 97:327-50. [PMID: 16178010 DOI: 10.1002/jcb.20579] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
All-trans retinoic acid and 9-cis-retinoic acid stimulate the activity of steroid sulfatase in HL60 acute myeloid leukemia cells in a concentration- and time-dependent manner. Neither of these 'natural retinoids' augmented steroid sulfatase activity in a HL60 sub-line that expresses a dominant-negative retinoic acid receptor alpha (RARalpha). Experiments with synthetic RAR and RXR agonists and antagonists suggest that RARalpha/RXR heterodimers play a role in the retinoid-stimulated increase in steroid sulfatase activity. The retinoid-driven increase in steroid sulfatase activity was attenuated by inhibition of phospholipase D (PLD), but not by inhibitors of phospholipase C. Experiments with inhibitors of protein kinase C (PKC) show that PKCalpha and PKCdelta play an important role in modulating the retinoid-stimulation of steroid sulfatase activity in HL60 cells. Furthermore, we show that pharmacological inhibition of the RAF-1 and ERK MAP kinases blocked the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells and, by contrast, inhibition of the p38-MAP kinase or JNK-MAP kinase had no effect. Pharmacological inhibitors of the phosphatidylinositol 3-kinase, Akt, and PDK-1 also abrogated the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells. These results show that crosstalk between the retinoid-stimulated genomic and non-genomic pathways is necessary to increase steroid sulfatase activity in HL60 cells.
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Affiliation(s)
- Philip J Hughes
- Division of Immunity and Infection, The Medical School, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom.
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6
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Vuligonda V, Thacher SM, Chandraratna RA. Enantioselective syntheses of potent retinoid X receptor ligands: differential biological activities of individual antipodes. J Med Chem 2001; 44:2298-303. [PMID: 11428923 DOI: 10.1021/jm0100584] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The synthesis and characterization of chiral RXR selective ligands are described. The enantiomeric acids 2 and 3 were synthesized employing an enantioselective cylopropanation procedure as the key step. Compound 2, with an S,S configuration at C-9 and C-10, is a potent RXR agonist devoid of any RAR activity. The R,R enantiomer 3 is a weak RXR agonist and has demonstrable RAR activity in the receptor transactivation assays. The potent RXR activity of 2 was further confirmed in a hyperglycemic animal model (db/db mice). Compound 2 lowered glucose by 50% by day 7 at 2 mg/kg, whereas 3 had no effect at the same dosage. This further supports the contention that RXR mediated gene transcription is involved in the antidiabetic effects of RXR ligands.
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Affiliation(s)
- V Vuligonda
- Retinoid Research, Departments of Chemistry and Biology, Allergan Inc., 2525 Dupont Drive, Irvine, California 92623, USA.
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7
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Bachmair F, Hoffmann R, Daxenbichler G, Langer T. Studies on structure-activity relationships of retinoic acid receptor ligands by means of molecular modeling. VITAMINS AND HORMONES 2000; 59:159-215. [PMID: 10714240 DOI: 10.1016/s0083-6729(00)59007-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Vitamin A and its biologically active derivatives, retinal and retinoic acid, play an important role in vision, are required for reproduction, act as morphogenic agents during embryonic development, and regulate the growth and differentiation of a wide variety of cell types throughout the life of an organism. The biological action of retinoic acid and synthetic analogs, referred to as retinoids, is mediated by RAR alpha, RAR beta, or RAR gamma and/or by RXR alpha, RXR beta, or RXR gamma, all being nuclear receptors. Since retinoids exert profound effects on cell proliferation, differentiation, and apoptosis, these compounds seem to be promising agents for the treatment of cancer. Consequently, a large number of retinoids have been synthesized and examined to determine if they exert their biological activity according to retinoic acid receptor interaction. These screening methods are often expensive, time-consuming, and labor-intensive procedures. Since one can construct the pharmacophores of congeneric groups of drug molecules, molecular modeling techniques offer a new way to determine the binding abilities of different agents. We examined the structural properties of retinoids, which allow them to specifically bind to the different receptor subtypes. The thus-generated 3D pharmacophore models were used to predict the binding affinities of several retinoids to the retinoic receptor subtypes. Finally, the 3D models served as criteria for searching the Derwent World Drug Index for compounds that possess the features necessary for favorable ligand receptor interaction. The search resulted in a "hit list" containing 323 compounds, some of which are worth further investigation to determine if they act via retinoic acid receptor binding or not.
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Affiliation(s)
- F Bachmair
- Department of Obstetrics and Gynecology, University Hospital, Innsbruck, Austria
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8
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Darro F, Cahen P, Vianna A, Decaestecker C, Nogaret JM, Leblond B, Chaboteaux C, Ramos C, Pétein M, Budel V, Schoofs A, Pourrias B, Kiss R. Growth inhibition of human in vitro and mouse in vitro and in vivo mammary tumor models by retinoids in comparison with tamoxifen and the RU-486 anti-progestagen. Breast Cancer Res Treat 1998; 51:39-55. [PMID: 9877028 DOI: 10.1023/a:1006098124087] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Retinoids constitute a very promising class of agents for the chemoprevention or treatment of breast cancer. These retinoids exert their biological activity through two distinct classes of retinoic acid (RA) receptors (R), the RAR isotypes (alpha, beta, and gamma) and the three RXR isotypes (alpha, beta, and gamma) and their numerous isoforms which bind as RXR/RAR heterodimers to the polymorphic cis-acting response elements of RA target genes. With respect to these numerous receptor sub-types, the retinoid-induced effects at the biological level include marked modifications with respect to both cell proliferation and cell death (apoptosis), and also in the induction of differentiation processes. The present study aims to characterize the effect which four retinoids (TTNPB, 9-cis-RA, LGD 1069, 4-HPR) with distinct RAR/RXR binding properties induced on various in vitro and in vivo mouse and human breast cancer models. The experiments with the retinoids were carried out in comparison with the anti-estrogen tamoxifen and the anti-progestagen RU-486 compounds. The results show that the 6 compounds under study were markedly more efficient in terms of growth inhibition in the human T-47D cell line when maintained under anchorage-independent culture conditions than when maintained under anchorage-dependent ones. While RU-486 exhibited a weak statistically significant (p < 0.05) influence on the growth of the T-47D stem cells, tamoxifen had a marked inhibitory influence on the growth of these cells. Of the four retinoids, 4-HPR was the least effective since the lowest doses tested (1 and 0.1 nM) exhibited no statistically (p > 0.05) significant influence on the growth of the stem cells. The most efficient retinoid was TTNPB. It was only at the highest dose (10 microM) that tamoxifen and RU-486 showed a weak inhibitory influence on the growth of the T-47D non-stem cells while all 4 retinoids exerted a significant inhibitory influence on the growth of these non-stem cells, with 4-HPR being the most efficient (P < 0.001) at the highest dose, but ineffective (P > 0.05) at the lowest. Tamoxifen and TTNPB were tested in vivo on hormone-sensitive (HS) and hormone-insensitive (HI) strains of the MXT murine mammary carcinoma. While TTNPB appeared to be equally efficient in terms of growth inhibition in both MXT-HS and MXT-HI models, tamoxifen had only a marginal inhibitory influence on the growth of the MXT-HI strain but did inhibit growth in the case of the MXT-HS one. TTNPB was markedly more efficient than tamoxifen in terms of both inhibiting the cell proliferation level (measured by means of computer-assisted microscopy applied to Feulgen-stained nuclei, a method which enables the percentage of cells in the S phase of the cell cycle to be determined) and triggering cell death (measured by means of the determination of the transglutaminase activity) in both the MXT-HI and MXT-HS models. The very significant TTNPB-induced inhibition of the macroscopic MXT-HS growth rate relates to the triggering of cell death (apoptosis) rather than to an inhibition of cell proliferation. All these results clearly indicate that retinoids are very efficient agents against breast cancer, at least as efficient as tamoxifen.
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Affiliation(s)
- F Darro
- Laboratoire d'Histologie, Faculté de Médicine, Université Libre de Bruxelles, Brussels, Belgium
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9
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Umemiya H, Fukasawa H, Ebisawa M, Eyrolles L, Kawachi E, Eisenmann G, Gronemeyer H, Hashimoto Y, Shudo K, Kagechika H. Regulation of retinoidal actions by diazepinylbenzoic acids. Retinoid synergists which activate the RXR-RAR heterodimers. J Med Chem 1997; 40:4222-34. [PMID: 9435893 DOI: 10.1021/jm9704309] [Citation(s) in RCA: 154] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In human HL-60 promyelocytic leukemia cells, diazepinylbenzoic acid derivatives can exhibit either antagonistic or synergistic effects on the differentiation-inducing activities of natural or synthetic retinoids, the activity depending largely on the nature of the substituents on the diazepine ring. Thus, a benzolog of the retinoid antagonist LE135 (6), 4-(13H-10,11,12,13-tetrahydro-10, 10,13,13,15-pentamethyldinaphtho[2,3-b][1,2-e]diazepin-7-yl) benzoic acid (LE540, 17), exhibits a 1 order of magnitude higher antagonistic potential than the parental LE135 (6). In contrast, 4-[5H-2,3-(2,5-dimethyl-2,5-hexano)-5-methyldibenzo[b,e] [1,4]diazepin-11-yl]-benzoic acid (HX600, 7), a structural isomer of the antagonistic LE135 (6), enhanced HL-60 cell differentiation induced by RAR agonists, such as Am80 (2). This synergistic effect was further increased for a thiazepine, HX630 (29), and an azepine derivative, HX640 (30); both synergized with Am80 (2) more potently than HX600 (7). Notably, the negative and positive effects of the azepine derivatives on retinoidal actions can be related to their RAR-antagonistic and RXR-agonistic properties, respectively, in the context of the RAR-RXR heterodimer.
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Affiliation(s)
- H Umemiya
- Graduate School of Pharmaceutical Sciences, University of Tokyo, Japan
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10
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Standeven AM, Escobar M, Beard RL, Yuan YD, Chandraratna RA. Mitogenic effect of retinoid X receptor agonists in rat liver. Biochem Pharmacol 1997; 54:517-24. [PMID: 9313779 DOI: 10.1016/s0006-2952(97)00209-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
(E)-2-[2-(5,6,7,8-Tetrahydro-3,5,5,8,8-pentamethyl-2-naphthyl) propen-1-yl]-4-thiophenecarboxylic acid (AGN 191701) and other retinoid X receptor (RXR)-selective agonists were observed to cause hepatomegaly in rats. The purpose of the present study was to understand the biochemical basis of RXR agonist-induced hepatomegaly. Male Fischer rats were implanted s.c. with osmotic pumps containing 5-bromo-2'-deoxyuridine (BrdU) and treated by gavage with 0,60, or 180 mumol/kg/day of AGN 191701 for 3 days. AGN 191701 caused dose-dependent hepatomegaly in the absence of hepatic necrosis and necrosis and increased hepatocyte BrdU labeling index (LI). To determine if AGN 191701-induced hepatic hyperplasia was sustained, rats were treated by gavage with 60 mumol/kg of AGN 191701 for up to 7 days and exposed to BrdU via osmotic pump on days 1-3 or on days 6-8. Hepatocyte L1 and mitotic index were increased only in rats exposed to BrdU on days 1-3, indicating that AGN 191701-induced hepatocyte proliferation was transient. The receptor specificity of this mitogenic effect was tested by co-treating rats for 2 days with various retinoids and BrdU. 2-(5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)-2-(4-carboxylph enyl)-1,3-dioxolane (SR11237), an RXR-selective agonist, and (E)-5-[2-(5,6,7,8-tetrahydro-3,5,5,8-pentamethyl-2-naphthyl)propen -1-yl]-2-thiophenecarboxylic acid (AGN 191659), a retinoic acid receptor (RAR)/RXR pan-agonist, both increased hepatocyte LI. Two RAR-selective agonist, all-trans-retinoic acid and (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)propen -1-yl] benzoic acid (TTNPB), did not affect hepatocyte LI. To determine if RXR agonists have biochemical effects in common with a peroxisome proliferator, various endpoints were measured 24 hr after two daily treatments with AGN 191701, SR11237, or clofibrate. While all three compounds induced hepatic acyl CoA oxidase activity, only clofibrate increased hepatic carnitine acyl transferase activity and lowered serum triglycerides. Taken together, these data show that RXR-selective agonists but not RAR-selective agonists cause hepatomegaly accompanied by hepatocyte mitogenesis in rats. The fact that RXR agonist have some biological effects distinct from RAR agonists and clofibrate suggests that RXR-selective agonists may have unique therapeutic applications.
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Affiliation(s)
- A M Standeven
- Department of Biology, Allergan, Irvine, CA 92612, USA
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11
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Johnson AT, Klein ES, Wang L, Pino ME, Chandraratna RA. Identification of retinoic acid receptor beta subtype specific agonists. J Med Chem 1996; 39:5027-30. [PMID: 8978832 DOI: 10.1021/jm960687r] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- A T Johnson
- Department of Chemistry, Allergan Inc., Irvine, California 92623-9534, USA
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12
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Beard RL, Colon DF, Song TK, Davies PJ, Kochhar DM, Chandraratna RA. Synthesis and structure-activity relationships of retinoid X receptor selective diaryl sulfide analogs of retinoic acid. J Med Chem 1996; 39:3556-63. [PMID: 8784454 DOI: 10.1021/jm960386h] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Retinoids exert their biological effects by binding to and activating nuclear receptors that interact with responsive elements on DNA to promote gene transcription. There are two families of retinoid receptors, the retinoic acid receptor (RAR) family and the retinoid X receptor (RXR) family, which are each further divided into three subclasses: RAR alpha, beta, gamma and RXR alpha, beta, gamma. Herein we describe the synthesis and structure-activity relationships of a new series of diaryl sulfide retinoid analogs that specifically bind and transactivate the RXRs. Furthermore, the sulfoxide and sulfone derivatives of these analogs are partial agonists which activate the RXRs only at high concentrations. Thus, these compounds possess a potential site of metabolic deactivation and may have less prolonged systemic effects than other compounds with arotinoid-like structures. We show also that these compounds have activity in nontransfected cells as demonstrated by their ability to induce TGase activity in HL-60 cells. Finally, we corroborate our earlier report that RXR-specific agonists may possess reduced teratogenic toxicity compared to RAR-specific agonists since these compounds are much less potent inhibitors of chondrogenesis than RAR-specific agonists such as TTNPB.
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Affiliation(s)
- R L Beard
- Department of Chemistry, Allergan, Incorporated, Irvine, California 92715-1599, USA
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13
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Arafa HM, Hamada FM, Elmazar MM, Nau H. Fully automated determination of selective retinoic acid receptor ligands in mouse plasma and tissue by reversed-phase liquid chromatography coupled on-line with solid-phase extraction. J Chromatogr A 1996; 729:125-36. [PMID: 9004933 DOI: 10.1016/0021-9673(95)00980-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
A fully automated reversed-phase HPLC method was developed for the quantitative assay of three retinoids (Am-580, CD-2019 and CD-437) which selectively activate the retinoic acid receptors RAR alpha, RAR beta and RAR gamma, respectively. Mouse plasma, embryo and maternal tissues were prepared for injection by on-line solid-phase extraction (SPE) and valve-switching techniques. Following automatic injection, the sample was loaded on preconditioned disposable cartridges, cleaned-up and then transferred onto the analytical column to be eluted in the backflush mode, separated by gradient elution and detected by UV, while a new cartridge was concomitantly conditioned. The overall recovery was quantitative allowing for external standardization. The calibration curves were linear in all biological samples tested so far, with a correlation coefficient (r) >0.99. The intra-day precision was < or = 7.8% (n = 5-6) and the inter-day variability was < or = 9.4% (n = 3). The lower limit of detection was 2.5 ng/ml or ng/g for CD-2019 and CD-437, and 5 ng/ml for Am-580 with a S/N ratio of 5 using a sample weight of 25 microliters or mg. The method is now in routine use in our laboratory for the assessment of the pharmacokinetic profiles of these retinoids. The small sample size required, the simple sample preparation and the rapid analysis with high degree of automation make this method convenient for microanalysis of biological samples both in animal and human studies.
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Affiliation(s)
- H M Arafa
- Institut für Toxikologie und Embryopharmakologie, Freie Universität Berlin, Germany
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14
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LeMotte PK, Keidel S, Apfel CM. Characterization of synthetic retinoids with selectivity for retinoic acid or retinoid X nuclear receptors. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1289:298-304. [PMID: 8600988 DOI: 10.1016/0304-4165(95)00179-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The broad spectrum of physiological activities of retinoids is mediate d by two types of receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs). Though they have 9-cis retinoic acid as a common ligand, the amino acid sequence of their ligand binding domains is only distantly related (27%). This fact makes it probable that the ligand binding pockets of RARs and RXRs differ significantly with respect to their three dimensional structure. Therefore, one can expect that selective ligands for these receptor subclasses do exit. A clear example of a naturally existing RAR-selective retinoid is all-trans retinoic acid. Here we report on two synthetic retinoids which are very closely related to retinoic acid in structure yet show good receptor subclass selectivity. These compounds have a saturated double bond in the polyene side chain between either the 7, 8 or 9, 10 carbon atoms and are highly RAR or RXR selective, respectively (as shown by receptor binding, transactivation activity and the ability to induce RXR homodimer formation). In addition, we present compounds of the synthetic arotinoid class which are highly RAR selective. Interestingly the corresponding '9-cis analogs' are not able to bind or activate RXR alpha and show greatly reduced activity on the RARs.
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Affiliation(s)
- P K LeMotte
- F. Hoffmann-LaRoche Ltd., Basel, Switzerland
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15
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Kochhar DM, Jiang H, Penner JD, Beard RL. Differential teratogenic response of mouse embryos to receptor selective analogs of retinoic acid. Chem Biol Interact 1996; 100:1-12. [PMID: 8599851 DOI: 10.1016/0009-2797(95)03681-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Early events that initiate teratogenesis by Accutane or other retinoids in mammalian embryos remain unknown. It would be helpful for mechanistic considerations to know whether or not retinoids act through retinoid receptor-dependent pathways, and if they do, which of the two families of receptors (retinoic acid receptors - RARalpha, beta, gamma or retinoid X receptors - RXRalpha, beta, gamma) are more likely involved. We previously used an in vitro bioassay to demonstrate that those retinoid analogs with binding affinity and transactivational activity limited only to the RXRs have a low potential as teratogens. Here, we have extended the study to examine teratogenicity, in pregnant mice, of a number of synthetic retinoids with varying degrees of receptor selectivity. The ability of each compound to induce fetal limb and craniofacial defects after a single exposure on day 11 of gestation was assessed and compared to that of all-trans retinoic acid (RA). The highest dose selected was 100 mg/kg maternal body weight since such a regimen of all-trans RA affects virtually every exposed embryo without any indication of maternal toxicity. We found that although all RAR agonists were strong teratogens, their potencies varied over a wide magnitude. The teratogenic potencies and receptor transactivation profiles of RAR agonists were not directly correlated since compounds with similar receptor activities presented major differences in potencies. Three compounds were exclusively RXR agonists, and these were not teratogenic under our experimental conditions. Two additional compounds which turned out to be non-teratogenic were distinguished by the fact that they activated neither RARs nor RXRs. These data indicate that although RAR-dependent mechanisms are likely involved in retinoid-induced teratogenesis, there are additional factors which determine teratogenic potency. The absence of teratogenic response in the case of RXR agonists suggests that risk-benefit analyses of such receptor-selective compounds may be fruitful in further studies.
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Affiliation(s)
- D M Kochhar
- Department of Pathology, Thomas Jefferson University, Philadelphia, PA 19107 USA
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16
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Nagy L, Saydak M, Shipley N, Lu S, Basilion JP, Yan ZH, Syka P, Chandraratna RA, Stein JP, Heyman RA, Davies PJ. Identification and characterization of a versatile retinoid response element (retinoic acid receptor response element-retinoid X receptor response element) in the mouse tissue transglutaminase gene promoter. J Biol Chem 1996; 271:4355-65. [PMID: 8626785 DOI: 10.1074/jbc.271.8.4355] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Tissue transglutaminase (transglutaminase type II) is an intracellular protein cross-linking enzyme that accumulates in connective tissue and in cells undergoing apoptosis. Retinoids regulate the transcription of the mouse tissue transglutaminase gene via activation of regulatory elements contained within 4 kilobases of the 5'-end of the gene. Co-transfection studies with retinoid receptor expression vectors in CV-1 cells demonstrated that the mouse tissue transglutaminase promoter is activated by ligand activation of either retinoic acid receptor-retinoid X receptor (RAR.RXR) heterodimers or RXR homodimers. Optimal induction is achieved with retinoid receptor panagonists; partial activation can also be achieved with either RAR-specific or RXR-specific retinoids. Retinoid-dependent activation of the tissue transglutaminase promoter depends on both a proximal regulatory region containing sequences highly conserved between the human and the mouse tissue transglutaminase promoters and a distal region that includes a 30-base pair retinoid response element (mTGRRE1). mTGRRE1 contains three hexanucleotide half-sites (two canonical and one non-canonical) in a DR7/DR5 motif that bind both RAR*RXR heterodimers and RXR homodimers. These studies suggest that retinoid-dependent expression of the mouse tissue transglutaminase gene is mediated by a versatile tripartite retinoid response element located 1.7 kilobases upstream of the transcription start site.
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Affiliation(s)
- L Nagy
- Department of Pharmacology, University of Texas-Houston Medical School, 77225, USA
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17
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Vuligonda V, Lin Y, Chandraratna RA. Synthesis of highly potent RXR-specific retinoids: The use of a cyclopropyl group as a double bond isostere. Bioorg Med Chem Lett 1996. [DOI: 10.1016/0960-894x(95)00588-k] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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18
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Apfel CM, Kamber M, Klaus M, Mohr P, Keidel S, LeMotte PK. Enhancement of HL-60 differentiation by a new class of retinoids with selective activity on retinoid X receptor. J Biol Chem 1995; 270:30765-72. [PMID: 8530518 DOI: 10.1074/jbc.270.51.30765] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Cellular responsiveness to retinoic acid and its metabolites is conferred through two distinct families of receptors: the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs). Herein, we report on the identification and characterization of several conformationally restricted retinoids, which selectively bind and activate RX receptors. Under the influence of retinoids, HL-60 myelocytic leukemia cells differentiate into granulocytes. This effect is mediated by RAR alpha, as has been demonstrated through the use of a selective RAR alpha antagonist (Apfel, C., Bauer, F., Crettaz, M., Forni, L., Kamber, M., Kaufmann, F., LeMotte, P., Pirson, W., and Klaus, M. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 7129-7133). Here, we show that conformationally restricted RXR-specific retinoids, at doses that are per se inactive, are able to potentiate by up to one order of magnitude the pro-differentiating effects of all-trans retinoic acid and an RAR alpha-selective synthetic retinoid. We also present evidence that these RXR-selective ligands are able to bind to a DNA RXR.RAR heterodimer complex. This finding demonstrates that agonists for RARs and RXRs can synergistically promote HL-60 differentiation, which could be mediated through a heterodimer of these receptors.
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Affiliation(s)
- C M Apfel
- Department of Dermatology, F. Hoffmann-LaRoche, Basel, Switzerland
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19
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Beard RL, Colon DF, Klein ES, Vorse KA, Chandraratna RA. Differential RXR & RAR activity of stilbene retinoid analogs bearing thiazole and imidazole carboxylic acids. Bioorg Med Chem Lett 1995. [DOI: 10.1016/0960-894x(95)00455-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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20
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Jiang H, Penner JD, Beard RL, Chandraratna RA, Kochhar DM. Diminished teratogenicity of retinoid X receptor-selective synthetic retinoids. Biochem Pharmacol 1995; 50:669-76. [PMID: 7669070 DOI: 10.1016/0006-2952(95)00183-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
One feature that contraindicates the wide therapeutic use of retinoids is their teratogenicity. Synthetic retinoids are distinguishable from each other on the basis of their partial or exclusive preference in binding and activation of all-trans retinoic acid receptors (RARs) or retinoid X receptors (RXRs). Using mouse embryo limb bud cells in micromass cultures as a bioassay, we examined the inhibitory activities of a number of standard and novel retinoids on chondrogenic cell differentiation. Transient cotransfection of HeLa cells was used to measure the ability of each retinoid to induce transcription of a reporter gene by activating RAR alpha, RAR beta, RAR gamma, or RXR alpha chimeric constructs. All retinoids in this study that activated RARs to any degree in the cotransfection assay also inhibited chondrogenesis in vitro, whereas retinoids that were either specific for RXR or inactive in the cotransfection assay did not. The activity of RAR-selective agonists and the inactivity of RXR-specific agonists in the cotransfection assay correlated well with the relative teratogenicity of six of the representative retinoids studied when orally administered at day 11 to pregnant ICR mice.
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Affiliation(s)
- H Jiang
- Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA, USA
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21
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Chandraratna RA, Gillett SJ, Song TK, Attard J, Vuligonda S, Garst ME, Arefieg T, Gil DW, Wheeler L. Synthesis and pharmacological activity of conformationally restricted, acetylenic retinoid analogs. Bioorg Med Chem Lett 1995. [DOI: 10.1016/0960-894x(95)00065-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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22
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Nagpal S, Athanikar J, Chandraratna RA. Separation of transactivation and AP1 antagonism functions of retinoic acid receptor alpha. J Biol Chem 1995; 270:923-7. [PMID: 7822331 DOI: 10.1074/jbc.270.2.923] [Citation(s) in RCA: 125] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Retinoic acid receptors (RARs) regulate gene expression either by directly binding to the RAR-responsive elements or by antagonizing the action of c-Jun/c-Fos (AP1). AP1 is involved in the expression of metalloproteases, cytokines and other factors which play critical roles in the turnover of extracellular matrix, inflammation and hyperproliferation in diseases such as psoriasis, rheumatoid arthritis and in tumor metastases. We demonstrate here that synthetic retinoids inhibit 12-O-tetradecanoylphorbol-14-acetate-induced transcription from the stromelysin AP1 motif through RAR alpha, -beta, and -gamma. Interestingly, these diaryl acetylenic retinoids, which are potent agonists only for RAR beta and RAR gamma, but not for RAR alpha, in transactivation assays, are able to inhibit AP1-dependent gene expression through RAR alpha. Thus these analogs can differentially affect the transactivation and AP1 antagonistic functions of RAR alpha. These results demonstrate that the transactivation and AP1 antagonistic functions are separable, and it should be possible to develop retinoids that are completely specific for AP1 antagonism through all RARs. Furthermore, using an RAR-selective ligand, we also demonstrate the separation of ligand binding and AP1 antagonism functions of RARs.
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Affiliation(s)
- S Nagpal
- Department of Biology, Allergan Inc., Irvine, California 92713
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Chandraratna RA, Henry E, Attard J, Gillett SJ, Song T, Garst ME, Nagpal S, Athanikar J, Arefieg T, Gil DW, Wheeler LA, Lew-Kaya D, Sefton J. DEVELOPMENT OF RAR SUBTYPE SELECTIVE RETINOIDS FOR DERMATOLOGICAL DISEASES. Eur J Med Chem 1995. [DOI: 10.1016/s0223-5234(23)00148-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
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