CD 2665

CD 2665 is a retinoic acid receptor β (RARβ) / RARγ antagonist [1] [2] [3] with binding Kd values of 306 nM and 110 nM to RARβ and RARγ, respectively [3].

Retinoic acid receptors include RARα, RARβ and RARγ. They are able to bind 9-cis and all-trans stereoisomers of retinoic acid (RA) [1], and mediate RA signal as transcription factors [2].

CD 2665 (1 µM) did not antagonize the luciferase activity induced by 9-cis- or all-trans-RA in HiB5 cells, but partially blocked the luciferase activity in 3XbRARE-Luc-transfected cells induced by CD 666 (a RARγ-selective agonist, 100 nM). CD 2665 at 1 µM reduced the viable cell number to about 60% level of vehicle-treated cells. CD 2665 (1 µM) clearly antagonized the increase in cell number resulted from the treatment with CD 666 (100 nM) [4].

The biosynthesis of retinoic acid can also be disordered by chronic ethanol consumption. CD 2665 administration did not modify blood alcohol levels in alcohol-treated mice, but totally reversed the impairment of spontaneous alternation rates resulted from alcohol consumption. Administration with CD2665 for 22 days in alcohol-treated mice significantly decreased both mRNA expression and enzymatic activity of tTG (a retinoic acid-target gene) and normalized the expression levels to the level in control mice [2].

References:
[1].  Yasmin Marikar, ZengQuan Wang, Elizabeth A. Duell, et al. Retinoic Acid Receptors Regulate Expression of Retinoic Acid 4-Hydroxylase that Specifically Inactivates All-Trans Retinoic Acid in Human Keratinocyte HaCaT Cells. The Journal of Investigative Dermatology, 1998, 111(3):434-439.
[2].  Serge Alfos, Catherine Boucheron, Véronique Pallet, et al. A Retinoic Acid Receptor Antagonist Suppresses Brain Retinoic Acid Receptor Overexpression and Reverses a Working Memory Deficit Induced by Chronic Ethanol Consumption in Mice. Alcohol Clin Exp Res., 2001, 25(10): 1506-1514.
[3].  Zsuzsa Szondy, Uwe Reichert, Jean-Michel Bernardon, et al. Inhibition of activation-induced apoptosis of thymocytes by all-trans- and 9-cis-retinoic acid is mediated via retinoic acid receptor α. Biochem. J., 1998, 331:767-774.
[4].  Jean-Ju Chung, Sehyung Cho, Yunhee Kim Kwon, et al. Activation of retinoic acid receptor γ induces proliferation of immortalized hippocampal progenitor cells. Molecular Brain Research, 2000, 83:52-62.

Retinoic acid upregulates ret and induces chain migration and population expansion in vagal neural crest cells to colonise the embryonic gut.[Pubmed:23717535]

PLoS One. 2013 May 22;8(5):e64077.

Vagal neural crest cells (VNCCs) arise in the hindbrain, and at (avian) embryonic day (E) 1.5 commence migration through paraxial tissues to reach the foregut as chains of cells 1-2 days later. They then colonise the rest of the gut in a rostrocaudal wave. The chains of migrating cells later resolve into the ganglia of the enteric nervous system. In organ culture, E4.5 VNCCs resident in the gut (termed enteric or ENCC) which have previously encountered vagal paraxial tissues, rapidly colonised aneural gut tissue in large numbers as chains of cells. Within the same timeframe, E1.5 VNCCs not previously exposed to paraxial tissues provided very few cells that entered the gut mesenchyme, and these never formed chains, despite their ability to migrate in paraxial tissue and in conventional cell culture. Exposing VNCCs in vitro to paraxial tissue normally encountered en route to the foregut conferred enteric migratory ability. VNCC after passage through paraxial tissue developed elements of retinoic acid signalling such as Retinoic Acid Binding Protein 1 expression. The paraxial tissue's ability to promote gut colonisation was reproduced by the addition of retinoic acid, or the synthetic retinoid Am80, to VNCCs (but not to trunk NCCs) in organ culture. The retinoic acid receptor antagonist CD 2665 strongly reduced enteric colonisation by E1.5 VNCC and E4.5 ENCCs, at a concentration suggesting RARalpha signalling. By FACS analysis, retinoic acid application to vagal neural tube and NCCs in vitro upregulated Ret; a Glial-derived-neurotrophic-factor receptor expressed by ENCCs which is necessary for normal enteric colonisation. This shows that early VNCC, although migratory, are incapable of migrating in appropriate chains in gut mesenchyme, but can be primed for this by retinoic acid. This is the first instance of the characteristic form of NCC migration, chain migration, being attributed to the application of a morphogen.

The role of specific retinoid receptors in sebocyte growth and differentiation in culture.[Pubmed:10651997]

J Invest Dermatol. 2000 Feb;114(2):349-53.

Retinoic acid derivatives (retinoids) exert their pleiotropic effects on cell development through specific nuclear receptors, the retinoic acid receptors and retinoid X receptors. Despite recent progress in understanding the cellular and molecular mechanisms of retinoid activity, it is unknown which of the retinoid receptor pathways are involved in the specific processes of sebocyte growth and development. In this study, we investigated the roles of specific retinoid receptors in sebocyte growth and differentiation, by testing the effects of selective retinoic acid receptor and retinoid X receptor ligands at concentrations between 10-10 M and 10-6 M in a primary rat preputial cell monolayer culture system. Cell growth was determined by number of cells and colonies, and cell differentiation by analysis of lipid-forming colonies. All-trans retinoic acid and selective retinoic acid receptor agonists (CD271 = adapalene, an RAR-beta,gamma agonist; CD2043 = retinoic acid receptor pan-agonist; and CD336 = Am580, an RAR-alpha agonist) caused significant decreases in numbers of cells, colonies, and lipid-forming colonies, but with an exception at high doses of all-trans retinoic acid (10-6 M), with which only a small number of colonies grew but they became twice as differentiated as controls (42.2 +/- 4.0% vs 22.6 +/- 2.7%, mean +/- SEM, lipid-forming colonies, p < 0.01). Furthermore, the RAR-beta,gamma antagonist CD2665 antagonized the suppressive effects of all-trans retinoic acid, adapalene, and CD2043 on both cell growth and differentiation. In contrast, the retinoid X receptor agonist CD2809 increased cell growth slightly and lipid-forming colonies dramatically in a clear dose-related manner to a maximum of 73.7% +/- 6.7% at 10-6 M (p < 0. 001). Our data suggest that retinoic acid receptors and retinoid X receptors differ in their roles in sebocyte growth and differentiation: (i) retinoic acid receptors, especially the beta and/or gamma subtypes, mediate both the antiproliferative and antidifferentiative effects of retinoids; (ii) retinoid X receptors mediate prominent differentiative and weak proliferative effects; (iii) the antiproliferative and antidifferentiative effects of all-trans retinoic acid are probably mediated by retinoic acid receptors, whereas its differentiative effect at high dose may be mediated by retinoid X receptors via all-trans retinoic acid metabolism to 9-cis retinoic acid, the natural ligand of retinoid X receptors.

Antiproliferative activity and apoptosis induced by retinoic acid receptor-gamma selectively binding retinoids in neuroblastoma.[Pubmed:9673404]

Anticancer Res. 1998 May-Jun;18(3A):1777-86.

Retinoids modulate several cell functions and especially inhibit the growth of tumor cells. Their biological activity is mediated by retinoic acid receptors (RARs), of which three subtypes (alpha, beta, gamma) have been identified. In human neuroblastoma (NB) reduced endogenous RAR-gamma expression was suggested to diminish the sensitivity for retinoids, to promote proliferation, and to contribute to the malignant phenotype. To correlate receptor selectivity with in vitro activity, we analysed the effect of six synthetic retinoids with selectivity for human RAR-alpha/beta/gamma on the human LAN-5 NB cell line and compared it with the natural compound all-trans-retinoic acid (ATRA). Apoptosis was determined by flow-cytometry using terminal-deoxynucleotidyl transferase to end-label DNA fragments in situ in apoptotic cells. The antagonist for RAR-beta/gamma CD2665 as well as the selective agonists for RAR-alpha CD336 and RAR-beta CD2019 were less effective in growth inhibition than ATRA. In contrast, the synthetic RAR-gamma selective agonists CD437 and CD2325 induced a concentration- and time-dependent antiproliferative effect, which was similar or even more pronounced than ATRA. In contrast to ATRA, the adition of CD437 and CD2325 did not induce morphological changes typical of NB cell maturation but resulted in morphological features consistent with the occurrence of programmed cell death. Flow-cytometric analysis showed that in contrast to ATRA the addition of CD 437 and CD 2325 results in progressive time-dependent increase of apoptotic cells (25.9% and 57.7% after 72 hours). In conclusion, our study demonstrates RAR-gamma selectively binding retinoids dramatically suppress NB cell growth, primarily by inducing programmed cell death rather than by cell differentiation. Since advanced or disseminated NB tumors endogenously express low levels of RAR-gamma and lack of apoptosis is involved in tumor progression, RAR-gamma selectively binding retinoids may be more appropriate retinoids for clinical trials in NB.

Induction of apoptosis by retinoids and retinoic acid receptor gamma-selective compounds in mouse thymocytes through a novel apoptosis pathway.[Pubmed:9187263]

Mol Pharmacol. 1997 Jun;51(6):972-82.

Retinoic acids are morphogenic signaling molecules that are derived from vitamin A and involved in a variety of tissue functions. Two groups of their nuclear receptors have been identified: retinoic acid receptors (RARs) and retinoic acid X receptors (RXRs). All-trans retinoic acid is the high affinity ligand for RARs, and 9-cis retinoic acid also binds to RXRs with high affinity. In cells at high concentrations, all-trans retinoic acid can be converted to 9-cis retinoic acid via unknown mechanisms. It was previously shown that retinoic acids prevents activation-induced death of thymocytes. Here, we report that both all-trans and 9-cis retinoic acid induce apoptosis of mouse thymocytes and purified CD4+CD8+ cells in ex vivo cultures, with 9-cis retinoic acid being 50 times more effective. The induction of apoptosis by retinoic acids is mediated by RARgamma because (a) the phenomenon can be reproduced only by RARgamma-selective retinoic acid analogs, (b) the cell death induced by either retinoic acids or RARgamma analogs can be inhibited by RARgamma-specific antagonists, and (c) CD4+CD8+ thymocytes express RARgamma. In vivo administration of an RARgamma analog resulted in thymus involution with the concomitant activation of the apoptosis-related endonuclease and induction of tissue transglutaminase. The RARgamma pathway of apoptosis is RNA and protein synthesis dependent, affects the CD4+CD8+ double positive thymocytes, and can be inhibited by the addition of either Ca2+ chelators or protease inhibitors. Using various RAR- and RXR-specific analogs and antagonists, it was demonstrated that stimulation of RAR alpha inhibits the RARgamma-specific death pathway (which explains the lack of apoptosis stimulatory effects of all-trans retinoic acid at physiological concentrations) and that costimulation of the RXR receptors (in the case of 9-cis retinoic acid) can neutralize this inhibitory effect. It is suggested that formation of 9-cis retinoic acid may be a critical element in regulating both the positive selection and the "default cell death pathway" of thymocytes.