Retinoids are known to inhibit the growth of hormone-dependent but not that of hormone-independent breast cancer cells. We investigated the involvement of retinoic acid (RA) receptors (RARs) in the differential growth-inhibitory effects of retinoids and the underlying mechanism. Our data demonstrate that induction of RAR␤ by RA correlates with the growth-inhibitory effect of retinoids. The hormone-independent cells acquired RA sensitivity when the RAR␤ expression vector was introduced and expressed in the cells. In addition, RA sensitivity of hormone-dependent cells was inhibited by a RAR␤-selective antagonist and the expression of RAR␤ antisense RNA. Introduction of RAR␣ also restored RA sensitivity in hormone-independent cells, but this restoration was accomplished by the induction of endogenous RAR␤ expression. Furthermore, we show that induction of apoptosis contributes to the growth-inhibitory effect of RAR␤. Thus, RAR␤ can mediate retinoid action in breast cancer cells by promoting apoptosis. Loss of RAR␤, therefore, may contribute to the tumorigenicity of human mammary epithelial cells.

Retinoic acid (RA) exerts its pleiotropic effects on cell growth and differentiation through the activation of a family of transcription factors-the RA receptors (RARs). Three subtypes of these receptors exist, RARa, RAR(3, and RARly. The receptors are differentially expressed in different cell types and stages of development, suggesting that they may regulate different sets of genes. We have identified a synthetic retinoid with the characteristics of a selective RARa antagonist. This antagonist counteracts RA effects on HL-60 cell differentiation and on B-lymphocyte polyconal activation.Beyond its potential practical relevance, this and other specific antagonists will be useful to dissect the RAR system and to assign to one given receptor each of the many RA-regulated functions.The natural retinol (vitamin A) derivative retinoic acid (RA) is known to have profound effects on cell growth and differentiation (1) and to be essential for normal embryonic development (2). While RA and some synthetic analogs (retinoids) are useful in the control of some tumors (3) as well as of nonmalignant hyperproliferative conditions of the skin (4), they are, at high concentrations, teratogenic (5).The pleiotropic effects of retinoids are mediated by two known families of nuclear receptors, both belonging to the steroid-thyroid hormone receptor superfamily of ligandinducible transcriptional regulators (6, 7). The RA receptor (RAR) gene family comprises three subtypes-RARa (8, 9), RAR,[8][9][10][11][12], and RAR'y (13, 14)-with each gene encoding a variable number of isoforms arising by differential splicing of two primary . All receptors of the RAR family bind RA with comparable affinity (18). The retinoid receptors of the second family (RXR) do not bind the major form of RA (all-trans-RA) (19). They bind instead the 9-cis stereoisomer of RA (20, 21).Transcription of some RAR genes themselves is RA sensitive (22-25). Also, the expression of some of the cellular retinol-or RA-binding proteins (CRBP and CRABP), putatively involved in the storage, transport, and/or metabolism of retinol and RA, is differentially regulated by RA in a receptor-specific manner (26-28). The RA-related molecules represent, therefore, an autoregulated system. RAR types and isoforms, as well as RXRa and RXRB, are differentially expressed both spatially and temporally (15-18, 29-32). They might therefore regulate different target genes during embryonic and adult life, as well as in specific cell types at different stages of differentiation. RARa is the most ubiquitously expressed, while RAR8 and RARy display a more restricted pattern of distribution, with RARy being predominantly expressed in the skin (31).It seems reasonable to assume that the multiple effects of RA could be dissociated by specific ligands for each of the known receptors, and/or by receptor-specific antagonists, so as to obtain the desired beneficial effects while limiting the unwanted side effects. Retinoids with a good degree of selectivity have been described (33), and we have o...

In a prospective, double-blind, randomised placebocontrolled study, we tested the hypothesis that a new formulation consisting of wheat gliadin chemically combined with a vegetal (thus orally effective) preparation of superoxide dismutase (SOD) allows to prevent hyperbaric oxygen (HBO)-induced oxidative cell stress.Twenty healthy volunteers were exposed to 100% oxygen breathing at 2.5 ATA for a total of 60 min. DNA strand breaks (tail moments) were determined using the alkaline version of the comet assay. Whole blood concentrations of reduced (GSH) and oxidised (GSSG) glutathione and F 2 -isoprostanes, SOD, glutathione peroxidase (GPx) and catalase (Cat) activities and red cell malondialdehyde (MDA) content were determined.After HBO exposure the tail moment ðp ¼ 0:03Þ and isoprostane levels ðp ¼ 0:049Þ were significantly lower in the group that received the vegetal formulation. Neither SOD and Cat nor GSH and GSSG were significantly affected by this preparation or HBO exposure. By contrast, blood GPx activity, which tended to be lower in the SODgroup already before the HBO exposure ðp ¼ 0:076Þ; was significantly lower afterwards ðp ¼ 0:045Þ:We conclude that an orally effective SOD-wheat gliadin mixture is able to protect against DNA damage, which coincided with reduced blood isoprostane levels, and may therefore be used as an antioxidant.

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␣, as has been demonstrated through the use of a selective RAR␣ 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␣-selective synthetic retinoid. We also present evidence that these RXR-selective ligands are able to bind to a DNA RXR⅐RAR 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.A subclass of nuclear hormone receptors have been described, termed retinoid X receptors (RXR) 1 (2-4), which are ligand-inducible transcription factors responsive to the 9-cis isomer of retinoic acid (5, 6). A related subclass of receptors, the retinoic acid receptors (RAR) (7-12), also responds to 9-cis retinoic acid (9-cis RA), as well as to the all-trans isomer of retinoic acid (t-RA). A striking feature of RXRs is their ability to heterodimerize with several members of the steroid receptor superfamily, including the RA receptors, thyroid receptors, peroxisome proliferator-activated receptors, vitamin D receptor, and chicken ovalbumin upstream promoter-transcription factor (13-21). Growing evidence suggests that heterodimers are the active species for binding to promoter response elements.In view of the involvement of RXRs in multiple signaling pathways, RXR-selective ligands can possibly be expected to show medical usefulness through their modulation of the above mentioned and perhaps also other hormone-regulated processes. The pharmacological effects of RXR ligands, which are attributable solely to activity on RXRs, are difficult to assess using 9-cis RA as an activating ligand since 9-cis RA also functions as an RAR ligand and consequently elicits the full range of classical retinoid effects. Therefore, to gain deeper insight into RXR function as well as to evaluate their pharmacological usefulness, we have designed and characterized a number of RXR-selective compounds and report on some intriguing pharmacological properties. These compounds are sterically restricted analogues of 9-cis RA, which cannot isomerize. They exhibit high potency and high selectivity for RXRs versus RARs and belong to different structural classes than other RXR-selective compounds r...

Among the many factors regulating Th cell differentiation, some nuclear hormone receptors are emerging as important players. The retinoid X receptor (RXR) functions as heterodimerization partner for a variety of nuclear hormone receptors. We show in this study that RXR is critical for Th2-mediated immunity. An RXR antagonist inhibited Th2 differentiation, resulting in reduced production of IL-4, IL-10, and IL-13, whereas IFN-γ production was enhanced. This effect was dependent on the presence of APCs. In addition, IL-5 production was blocked directly in Th cells. In vivo, inhibition of RXR prevented experimentally induced allergic lung inflammation. Th1-mediated inflammation was not affected. Its specific role in Th2-mediated inflammation makes RXR a promising target for the development of therapies against diseases such as allergic asthma and atopic dermatitis.

No abstract

The effect of structural modifications on the arotinoid molecule, a new class of retinoids, on their teratogenicity in mice was studied. Animals were treated on days 8 and 9 of gestation, the most susceptible stages to retinoid-induced malformations in rodents. The teratogenic potency of the 13 arotinoids tested varied over a dose range of more than five orders of magnitude. Next, we tested whether the quantitative differences in the teratogenicity of these arotinoids correlates with their activity in high density (micromass) cultures of rat embryonic limb bud and midbrain cells. There was a good quantitative correlation between the in vivo teratogenicity and the in vitro activity in limb bud cells but no correlation was found in midbrain cells. Thus, the limb bud cell culture system may be useful for a preliminary testing to select non-teratogenic retinoids. For the risk assessment in humans, however, the in vitro results should be verified in animals studies.

Unter kstimmten GC.-Bcdingungen (z.B. 2 m, 20% C-20-M*, 85"-ZOO') erschien die analysenreine Substanz in Form zweier dicht benachbarter, anniihernd glcich grosscr Pike und girb auch damit des Vorliegcn cines (~/E)-Stereoiaomerengeinisches zu crkcnnen. 1,ZTERATURVERZE'lCH NI S [l] M . Schlosser, U. SiAaub. B. Spakic' L % G.Summary. Using a meso-compound which is asymmetrically substituted with a chiral moiety 8s an intermediate, prostaglandins have becn synthesizcd. Sincc the undesired enantiomer is readily recycled, this approach leads to a synthcsis with high c h i d efficiency. In addition it is possible to prepare both enantionwric configurdions of prostaglandins by simply altcring thc sequence of reactions. This concept should be generally useful in thc synthesis of optically activc molecules. I. Ehnleitung. -Wnseren synthetischen Arbciten zur Offnung eines neuen Zugangs zu den Prostaglandinen [I] war das Postulat der totalen Umsetzung des achiralen Ausgangsmaterials zum gewiinsch ten optiscli aktiven Produkt zugrunde gelegt. Von den moglichen Wegen wurcle derjenige iiber einc asymmetrische Synthesc bereits von anderer Seite xealisiert [Z]; unscr Ziel war der Aufbau einer racemischen Zwischenstufe rnit anschliessendcr Racernatspaltung und Ruckfuhrung des unerwiinschten Enantiomeren. weden, Die Reduktion des kristallinen An'hydrids 3 rnit Natrium-bis-B-mcthoxy-HLLVETICA CRIMICA ACTA -Vol. 58, Fa%. 2 (1975) -Nr. 67 567 Schema 3 t ~~hoxy-alurniniumhydrid (REDAL) lieferte die gcwiinschte kristalline meso-Verbindung 4 in guter Ausbeute. Zur asymmetrischen Acylierung wurde die krist a l h e msso-Verbindung 4 , (vgl. Schema 5) zunachs t mit Phosgen in Toluol LU einem siehengliedrigen, cyclivchen Carbonat I) umgesetzt, das sehr leicht bei Raumtemperatur mit nattirlichem Iso-bornylamin3) ([aJzT* = -42,9", G 3 ; 0,96, EtOH) zum Diastereomerenpaar 5a und 5b geoff net werden konnte. Durch einc frdktionnierte Kristallisation mit Essigester konnten die beiden Diastereomeren 5a und 5b gctrennt werden, wobei das Uiastereomere Sa = -56,2", c = I 1,0, EtOH) in ZU-U% Ausbeute, bezogen auf die Gcsamtmenge dieses Diastereomeren irn Ausgmgsgemisch, isoliert wurde. Die Mutterlaugc, in der sich mchr vom unerwiinsdhten Diastereomeren 5b befand, m i t e rnit l) Diem wurde in der Toluollbung mittels X . / M S . eindcutig nachgcwiewn. *) Hergestellt aua natllrlichem Csmpheroxim durch katalytieche Reduktion mit Pd/C in Mc-than01 bei 90" und YO Atii. _-_---568 HBLWTICA CHIMICA ACTA --Vol. 58, Fasc. 2 (1975) -Nr. 67 Schema 5 \ I \ 1 Kaliumhydroxid verseift. Ilabei wurde dic krjstdline meso-Verbindung 4 in 75-80proz. Ausbcute regeneriert. IXese Hydrolyse erlaubt cine wcitgehende Recyclisicrung des uncrwiinschten Dimtereomeren 5b. Auf diese Weisc wird os m6glicti, bci maxirnalen Ausbeut.cn der chiral asymmctrischen Acylierung , der Diastercomerentrennung und der Recyclisierung, das gcsamte Ausgangsrnaterial zu eitiem eitizigcn Diastcrcomeren (hicr 5 a) umzusetzen.3. Beweis der abaoluten Konfiguration des Hydroxy-urethans 5a. -Urn die