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R A Chandraratna

Publications and source records attributed to R A Chandraratna.

At least 19 recordsLinked to original sources
PubMed2001

Retinoid X receptor agonist elevation of serum triglycerides in rats by potentiation of retinoic acid receptor agonist induction or by action as single agents.

Hypertriglyceridemia is a major side-effect of retinoid therapy in humans. We previously reported that agonists for the retinoic acid receptors (RARs), but not the retinoid X receptors (RXRs), elevate serum triglycerides in male Fischer rats, and that, surprisingly, the RAR/RXR pan-agonists 9-cis-retinoic acid and AGN 191659 [(E)-5-[2-(5,6,7,8-tetrahydro-3,5,5,8,8-pentamethyl-2-naphthyl)propen-1-yl]-2-thiophenecarboxylic acid] induce 2- to 3-fold higher levels of serum triglycerides than the RAR-selective agonists alone. We have now demonstrated that hypertriglyceridemia induced by an RAR agonist, AGN 190121 [4-[4-(2',6',6'-trimethylcyclohex-1-enyl)-but-1-yne-3-enyl]benzoic acid], is substantially potentiated by the RXR-selective agonists AGN 191701 [(E) 2-[2-(5,6,7,8-tetrahydro-3,5,5,8,8-pentamethyl-2-naphthyl)propen-1-yl]-4-thiophene-carboxylic acid] and AGN 192849 [(3,5,5,8,8,-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl) (5 carboxypyrid-2-yl)sulfide] in a dose-dependent manner. RXR-specific retinoids, as previously reported, had no independent effect on serum triglycerides when tested at 24 hr after final dosing, but did elicit a reversible hypertriglyceridemia at 2.5 and 5 hr. This induction of serum triglycerides could not be blocked by the potent RAR-specific antagonist AGN 193109 [4-[(5,6-dihydro-5,5-dimethyl-8-(4-methylphenyl)-2-naphthalenyl)-ethynyl] benzoic acid]. The RXR ligand-induced hypertriglyceridemia was independent of the effect of feeding or fasting. The relative potencies of RXR-specific retinoids for acute triglyceride elevation (AGN 194204 [3,7-dimethyl-6S,7S-methano-7-[1,1,4,4-tetramethyl-1,2,3,4-tetrahydronaphth-7-yl] 2(E),4(E) heptadienoic acid] > AGN 192849 approximately AGN 191701) approximately correlated with potencies in the activation of the RXR receptors. The RAR/RXR pan-agonist effect included >50% inhibition of total heparin-releasable lipase activity in serum, consistent with inhibition of lipase-mediated triglyceride disposal. These data also indicate that RAR and RXR ligands can act synergistically to induce hypertriglyceridemia through distinct mechanisms of action.

Animals↗
PubMed2001

Active repression of RAR signaling is required for head formation.

The retinoic acid receptors (RARs) recruit coactivator and corepressor proteins to activate or repress the transcription of target genes depending on the presence of retinoic acid (RA). Despite a detailed molecular understanding of how corepressor complexes function, there is no in vivo evidence to support a necessary function for RAR-mediated repression. Signaling through RARs is required for patterning along the anteroposterior (A-P) axis, particularly in the hindbrain and posterior, although the absence of RA is required for correct anterior patterning. Because RARs and corepressors are present in regions in which RA is absent, we hypothesized that repression mediated through unliganded RARs might be important for anterior patterning. To test this hypothesis, specific reagents were used that either reduce or augment RAR-mediated repression. Derepression of RAR signaling by expressing a dominant-negative corepressor resulted in embryos that exhibited phenotypes similar to those treated by RA. Anterior structures such as forebrain and cement gland were greatly reduced, as was the expression of molecular markers. Enhancement of target gene repression using an RAR inverse agonist resulted in up-regulation of anterior neural markers and expansion of anterior structures. Morpholino antisense oligonucleotide-mediated RARalpha loss-of-function phenocopied the effects of RA treatment and dominant-negative corepressor expression. Microinjection of wild-type or dominant-negative RARalpha rescued the morpholino phenotype, confirming that RAR is functioning anteriorly as a transcriptional repressor. Lastly, increasing RAR-mediated repression potentiated head-inducing activity of the growth factor inhibitor cerberus, whereas releasing RAR-mediated repression blocked cerberus from inducing ectopic heads. We conclude that RAR-mediated repression of target genes is critical for head formation. This requirement establishes an important biological role for active repression of target genes by nuclear hormone receptors and illustrates a novel function for RARs during vertebrate development.

Animals↗
PubMed2001

Antagonists of retinoic acid receptors (RARs) are potent growth inhibitors of prostate carcinoma cells.

Novel synthetic antagonists of retinoic acid receptors (RARs) have been developed. To avoid interference by serum retinoids when testing these compounds, we established serum-free grown sub-lines (>3 years) of the prostate carcinoma lines LNCaP, PC3 and DU145. A high affinity pan-RAR antagonist (AGN194310, K(d) for binding to RARs = 2-5 nM) inhibited colony formation (by 50%) by all three lines at 16-34 nM, and led to a transient accumulation of flask-cultured cells in G1 followed by apoptosis. AGN194310 is 12-22 fold more potent than all-trans retinoic acid (ATRA) against cell lines and also more potent in inhibiting the growth of primary prostate carcinoma cells. PC3 and DU145 cells do not express RARbeta, and an antagonist with predominant activity at RARbeta and RARgamma (AGN194431) inhibited colony formation at concentrations (approximately 100 nM) commensurate with a K(d)value of 70 nM at RARgamma. An RARalpha antagonist (AGN194301) was less potent (IC(50) approximately 200 nM), but was more active than specific agonists of RARalpha and of betagamma. A component(s) of serum and of LNCaP-conditioned medium diminishes the activity of antagonists: this factor is not the most likely candidates IGF-1 and EGF. In vitro studies of RAR antagonists together with data from RAR-null mice lead to the hypothesis that RARgamma-regulated gene transcription is necessary for the survival and maintenance of prostate epithelium. The increased potencies of RAR antagonists, as compared with agonists, suggest that antagonists may be useful in the treatment of prostate carcinoma.

Antineoplastic Agents↗
PubMed2001

The synthetic retinoid AGN 193109 but not retinoic acid elevates CYP1A1 levels in mouse embryos and Hepa-1c1c7 cells.

The synthetic retinoid AGN 193109 is a potent pan retinoic acid receptor (RAR) antagonist. Treatment of pregnant mice with a single oral 1 mg/kg dose of this antagonist on day 8 postcoitum results in severe craniofacial (median cleft face or frontonasal deficiency) and eye malformations in virtually all exposed fetuses. Using differential display analysis, we have determined that CYP1A1 mRNA levels are elevated in mouse embryos 6 h following treatment with AGN 193109. Similarly, an elevation in CYP1A1 mRNA levels, protein levels, and aryl hydrocarbon hydoxylase activity occurs in Hepa-1c1c7 cells, with the maximal elevation observed when the cells were treated with 10(-5) M AGN 193109 for 4 to 8 h. Elevation in CYP1A1 mRNA levels in mouse embryos and Hepa-1c1c7 cells does not occur upon treatment with the natural retinoid, all-trans-retinoic acid. Finally, elevation in CYP1A1 mRNA levels was not observed when mutant Hepa-1c1c7 cells, which are defective in either the aryl hydrocarbon receptor (AhR) or aryl hydrocarbon receptor nuclear translocator (ARNT), were treated with AGN 193109. This suggests that the AhR/ARNT pathway and not the RAR/RXR pathway is mediating the elevation of CYP1A1 mRNA levels by AGN 193109, at least in the Hepa-1c1c7 cells. This is the first example of a retinoid that displays the abililty to regulate both the RAR/RXR and AhR/ARNT transcriptional regulatory pathways.

Animals↗
PubMed2001

Enantioselective syntheses of potent retinoid X receptor ligands: differential biological activities of individual antipodes.

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.

Animals↗
PubMed2001

Regulation of stearoyl coenzyme A desaturase expression in human retinal pigment epithelial cells by retinoic acid.

Stearoyl-CoA desaturase (SCD) is a regulatory enzyme involved in the synthesis of the monounsaturated fatty acids palmitoleate and oleate. The regulation of SCD is of physiological importance because the ratio of saturated fatty acids to unsaturated fatty acids is thought to modulate membrane fluidity. Differential display analysis of retinal pigment epithelial (ARPE-19) cells identified SCD as a gene regulated by retinoic acid. Two SCD transcripts of 3.9 and 5.2 kilobases in size were found to be expressed in these cells by Northern blot analysis. All-trans-retinoic acid (all-trans-RA) increased SCD mRNA expression in a dose- and time-dependent manner; an approximately 7-fold increase was observed with 1 microm all-trans-RA at 48 h. SCD mRNA expression was also increased by 9-cis-retinoic acid (9-cis-RA) as well as 4-(E-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl)benzoic acid (TTNPB), a retinoic acid receptor (RAR)-specific agonist. AGN194301, a RAR alpha-specific antagonist, suppressed the SCD expression induced by all-trans-RA, TTNPB, and 9-cis-RA. These results indicate the involvement of RAR alpha in the induction of SCD expression by retinoic acid. However, AGN194204, a RXR (retinoid X receptor) pan agonist, also increased SCD mRNA expression. This increase was not blocked by AGN194301, suggesting that an RAR-independent mechanism may also be involved. Thus, SCD expression in retinal pigment epithelial cells is regulated by retinoic acid, and the regulation appears to be mediated through RAR and RXR.

Alitretinoin↗
PubMed2001

Phenylcyclohexene and phenylcyclohexadiene substituted compounds having retinoid antagonist activity.

Retinoids are natural and synthetic analogues of the hormone retinoic acid. Systemic retinoid agonist therapy is usually associated with toxic side effects, such as mucocutaneous toxicity, which may be alleviated by the use of topical retinoid antagonists. We report the synthesis and biological activity of a new series of potent, RAR-specific antagonists substituted with phenylcyclohexene and phenylcyclohexadiene groups.

Animals↗
PubMed2001

Retinoic acid (RA) receptor transcriptional activation correlates with inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced ornithine decarboxylase (ODC) activity by retinoids: a potential role for trans-RA-induced ZBP-89 in ODC inhibition.

Evaluation of retinoic acid receptor (RAR) subtype-selective alpha and gamma agonists and antagonists and a retinoid X receptor (RXR) class-selective agonist for efficacy at inhibiting both induction of ornithine decarboxylase (ODC) by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse epidermis and rat tracheal epithelial cells and the appearance of papillomas in mouse epidermis treated in the 2-stage tumor initiation-promotion model indicated that (i) RXR class-selective transcriptional agonists, such as MM11246, were not involved in ODC inhibition; (ii) RAR-selective agonists that induce gene transcription from RA-responsive elements (RAREs) were active at low concentrations; (iii) RAR-selective antagonists that bind RARs and inhibit AP-1 activation on the collagenase promoter but do not activate RAREs to induce gene transcription were less effective inhibitors; and (iv) RARgamma-selective retinoid agonists were more effective inhibitors of TPA-induced ODC activity than RARalpha-selective agonists. These results suggest that RARE activation has a more important role in inhibition of ODC activity than RXR activation or AP-1 inhibition and that RARgamma-selective agonists would be the most useful inhibitors of epithelial cell proliferation induced by tumor promoters. The natural retinoid all-trans-RA induced expression of transcription factor ZBP-89, which represses activation of the GC box in the ODC promoter by the transcription factor Sp1.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2001

Evidence of a lysosomal pathway for apoptosis induced by the synthetic retinoid CD437 in human leukemia HL-60 cells.

The novel synthetic retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphtalene carboxylic acid (AHPN/CD437) has been proven to be a potent inducer of apoptosis in a variety of tumor cell types. However, the mechanism of its action remains to be elucidated. Recent studies suggest that the lysosomal protease cathepsin D, when released from lysosomes to the cytosol, can initiate apoptosis. In this study, we examined whether cathepsin D and free radicals are involved in the CD437-induced apoptosis. Exposure of human leukemia HL-60 cells to CD437 resulted in rapid induction of apoptosis as indicated by caspase activation, phosphatidylserine exposure, mitochondrial alterations and morphological changes. Addition of the antioxidants alpha-tocopherol acetate effectively inhibited the CD437-induced apoptosis. Measurement of the intracellular free radicals indicated a rise in oxidative stress in CD437-treated cells, which could be attenuated by alpha-tocopherol acetate. Interestingly, pretreatment of cells with the cathepsin D inhibitor pepstatin A blocked the CD437-induced free radical formation and apoptotic effects, suggesting the involvement of cathepsin D. However, Western blotting revealed no difference in cellular quantity of any forms of cathepsin D between control cells and CD437-treated cells, whereas immunofluorescence analysis of the intracellular distribution of cathepsin D showed release of the enzyme from lysosomes to the cytosol. Labeling of lysosomes with lysosomotropic probes confirmed that CD437 could induce lysosomal leakage. The CD437-induced relocation of cathepsin D could not be prevented by alpha-tocopherol acetate, suggesting that the lysosomal leakage precedes free radical formation. Furthermore, a retinoic acid nuclear receptor (RAR) antagonist failed to block these effects of CD437, suggesting that the action of CD437 is RAR-independent. Taken together, these data suggest a novel lysosomal pathway for CD437-induced apoptosis, in which lysosomes are the primary target and cathepsin D and free radicals act as death mediators.

Antioxidants↗
PubMed2001

Retinoids inhibit proliferation of human coronary smooth muscle cells by modulating cell cycle regulators.

Retinoids inhibit rat vascular smooth muscle cell (VSMC) proliferation in vitro and intimal hyperplasia in vivo. We examined the mechanism of the antiproliferative effect of retinoids on human coronary artery smooth muscle cells (human CASMCs). The RAR ligands all-trans-retinoic acid (atRA) and ethyl-p-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)-l-propenyl]-benzoic acid (TTNPB); a pan-RXR/RAR agonist, 9-cis-retinoic acid (9cRA); and the RXR-selective ligand AGN4204 all inhibited DNA synthesis stimulated with platelet-derived growth factor and insulin (IC(50): TTNPB 63 nmol/L, atRA 120 nmol/L, AGN4204 460 nmol/L, 9cRA 1.5 micromol/L). All retinoids blocked cell cycle progression as determined by flow cytometry and inhibited retinoblastoma protein (Rb) phosphorylation. TTNPB, atRA, and AGN4204 inhibited the mitogenic induction of cyclin D1, whereas 9cRA had no effect. None of the retinoids affected the expression of CDK 2, 4, or 6 or cyclin E. All retinoids attenuated mitogen-induced downregulation of CDKI p27(Kip1), a major negative regulator of Rb phosphorylation, partly through stabilizing p27(Kip1) turnover. These data demonstrate that retinoids have antiproliferative activity by modulating G(1) --> S cell cycle regulators in human CASMCs through inhibition of Rb phosphorylation and elevation of p27(Kip1) levels.

Cell Cycle Proteins↗
PubMed2000

Retinoic acid receptor-beta: an endogenous inhibitor of the perinatal formation of pulmonary alveoli.

Pulmonary alveoli are formed, in part, by subdivision (septation) of the gas-exchange saccules of the immature lung. Septation is developmentally regulated, and failure to septate at the appropriate time is not followed by delayed spontaneous septation. We report retinoic acid receptor (RAR) beta knockout mice exhibit premature septation; in addition, they form alveoli twice as fast as wild-type mice during the period of septation but at the same rate as wild-type mice thereafter. Consistent with the perinatal effect of RARbeta knockout, RARbeta agonist treatment of newborn rats impairs septation. These results 1) identify RARbeta as the first recognized endogenous signaling that inhibits septation, 2) demonstrate premature onset of septation may be induced, and 3) show the molecular signaling regulating alveolus formation differs during and after the period of septation. Suppressing perinatal RARbeta signaling by RARbeta antagonists may offer a novel, nonsurgical, means of preventing, or remediating, failed septation in prematurely born children.

Animals↗
PubMed2000

Peroxisome proliferator-activated receptor and retinoid X receptor ligands inhibit monocyte chemotactic protein-1-directed migration of monocytes.

Monocyte chemotactic protein-1 (MCP-1)-directed transendothelial migration of monocytes plays a key role in the development of inflammatory diseases. Infiltration of tissues by monocytes requires degradation of extracellular matrices, a process that involves matrix metalloproteinases. We studied the effects of peroxisome proliferator-activated receptor (PPAR) gamma, alpha, and retinoid X receptor alpha (RXRalpha) ligands on MCP-1-directed migration and matrix metalloproteinase expression of a human acute monocytic leukemia cell line (THP-1). PPARgamma ligands attenuated MCP-1-induced migration, with 50% inhibition (IC(50)) at 2.8 microM for troglitazone and 4.8 microM for rosiglitazone. PPARalpha ligands WY-14643 (IC(50): 0.9 microM) and 5,8,11,14-eicosatetranoic acid (IC(50): 9.9 microM), and the potent RXRalpha ligand AGN 4204 (IC(50): 3.6 nM) also blocked monocyte migration. Troglitazone, rosiglitazone, or AGN 4204 inhibited phorbol 12-myristate 13-acetate (PMA)-induced matrix metalloproteinase-9 expression. PPARalpha activators WY-14643 and 5,8,11,14-eicosatetraynoic acid, however, had no inhibitory effect. AGN 4204 increased PMA-induced tissue inhibitor of matrix metalloproteinases-1 (TIMP-1) expression, whereas all PPAR ligands showed no effect. All PPAR and RXRalpha ligands blocked chemotaxis of THP-1 monocytes in the absence of a matrix barrier. This study demonstrates that activated PPARs and RXRalpha, block MCP-1-directed monocyte migration, mediated, at least in part, through their effects on matrix metalloproteinase-9 or TIMP-1 production, or chemotaxis.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed2000

Recruitment of nuclear receptor corepressor and coactivator to the retinoic acid receptor by retinoid ligands. Influence of DNA-heterodimer interactions.

Ligand activation of retinoic acid receptors (RARs) involves coordinated changes in their interaction with coregulatory molecules. Binding of the agonist all-trans-retinoic acid to the RAR results in increased interaction with coactivator molecules as well as a decreased interaction with corepressor molecules. Thus, an all-trans-retinoic acid antagonist might function either by preventing agonist induction of such events or, additionally, by actively increasing repression via corepressor recruitment. We demonstrate that the repression of the transcriptional activity of a constitutively active RARgamma-VP-16 chimeric receptor by the inverse agonist AGN193109 requires a functional Co-R box and that binding of this ligand to RARgamma leads to an increased interaction with the corepressor N-CoR both in glutathione S-transferase pull-down and yeast two-hybrid analyses. Detection of nuclear receptor corepressor (N-CoR) association with RARgamma was greatly facilitated by inclusion of a RARE oligonucleotide in coimmunoprecipitation analyses, a result of an increase in association of the ternary complex consisting of RAR, RXR, and DNA. Similarly, this DNA-dependent increase in heterodimer formation likewise resulted in an increase in agonist-mediated recruitment efficiency of the coactivator SRC-1. Under conditions which favor ternary complex formation, a RAR neutral antagonist is distinguished from an inverse agonist with respect to corepressor recruitment as is a RAR partial agonist distinguished from an agonist with respect to coactivator recruitment. These results indicate that it is possible to design RAR ligands with distinct recruitment capabilities for coregulators, both coactivators as well as corepressors. In addition, using this recruitment assay, we show that SRC-1 and the related coactivator molecule ACTR associate with the ternary complex via utilization of different helical motifs within their conserved receptor interaction domains.

Amino Acid Sequence↗
PubMed2000

Regulation of skeletal progenitor differentiation by the BMP and retinoid signaling pathways.

The generation of the paraxial skeleton requires that commitment and differentiation of skeletal progenitors is precisely coordinated during limb outgrowth. Several signaling molecules have been identified that are important in specifying the pattern of these skeletal primordia. Very little is known, however, about the mechanisms regulating the differentiation of limb mesenchyme into chondrocytes. Overexpression of RARalpha in transgenic animals interferes with chondrogenesis and leads to appendicular skeletal defects (Cash, D.E., C.B. Bock, K. Schughart, E. Linney, and T.M. Underhill. 1997. J. Cell Biol. 136:445-457). Further analysis of these animals shows that expression of the transgene in chondroprogenitors maintains a prechondrogenic phenotype and prevents chondroblast differentiation even in the presence of BMPs, which are known stimulators of cartilage formation. Moreover, an RAR antagonist accelerates chondroblast differentiation as demonstrated by the emergence of collagen type II-expressing cells much earlier than in control or BMP-treated cultures. Addition of Noggin to limb mesenchyme cultures inhibits cartilage formation and the appearance of precartilaginous condensations. In contrast, abrogation of retinoid signaling is sufficient to induce the expression of the chondroblastic phenotype in the presence of Noggin. These findings show that BMP and RAR-signaling pathways appear to operate independently to coordinate skeletal development, and that retinoid signaling can function in a BMP-independent manner to induce cartilage formation. Thus, retinoid signaling appears to play a novel and unexpected role in skeletogenesis by regulating the emergence of chondroblasts from skeletal progenitors.

Animals↗
PubMed2000

Role of retinoic acid in lens regeneration.

Prompted by the actions of retinoids and their receptors in gene regulation, in the developing eye and especially in the lens, we have undertaken a detailed study to examine the effects of retinoids on urodele lens regeneration. First, we examined the effects of exogenous retinoids. It was found that exogenous retinoids had no significant effect on lens regeneration. However, when synthesis of retinoic acid was inhibited by disulfiram, or when the function of the retinoid receptors was impaired by using a RAR antagonist, the process of lens regeneration was dramatically affected. In the majority of the cases, lens regeneration was inhibited and lens morphogenesis was disrupted. In a few cases, we were also able to observe ectopic lens regeneration from places other than the normal site, which is from the dorsal iris. The most spectacular case was the regeneration of a lens from the cornea, an event possible only in premetamorphic frogs. These data show that inhibition of retinoid receptors is paramount for the normal course and distribution of lens regeneration. We have also examined expression of RAR-delta during lens regeneration. This receptor was expressed highly in the regenerating lens only. Therefore, it seems that this receptor is specific for the regeneration process and consequently such expression correlates well with the effects of RAR inhibition observed in our studies.

Animals↗
PubMed2000

13-cis retinoic acid exerts its specific activity on human sebocytes through selective intracellular isomerization to all-trans retinoic acid and binding to retinoid acid receptors.

Despite its potent biologic effect on human sebocytes, 13-cis retinoic acid exhibits low binding affinity for cellular retinoic acid binding proteins and nuclear retinoid receptors. Hence, 13-cis retinoic acid may represent a pro-drug possibly acting through all-trans isomerization. In this study, marked isomerization of 13-cis retinoic acid has been confirmed in cultured SZ95 sebocytes showing 2- to 15-fold higher levels of all-trans retinoic acid at 12-72 h, as measured by high performance liquid chromatography. In contrast, only low amounts of all-trans retinoic acid were converted intracellularly to its 13-cis isoform. 9-cis retinoic acid was not detected after either 13-cis retinoic acid or all-trans retinoic acid treatment. The rapid isomerization of 13-cis retinoic acid to high levels of all-trans retinoic acid was a sebocyte-specific event, as no significant isomerization of 13-cis retinoic acid to all-trans retinoic acid occurred in HaCaT keratinocytes. De novo mRNA expression of cytochrome P450 1A1, a major xenobiotic metabolizing enzyme, in SZ95 sebocytes was induced by all-trans retinoic acid, but not by 13-cis retinoic acid. In addition, mRNA levels of cellular retinoic acid-binding protein II, which is supposed to regulate the concentration of intracellular all-trans retinoic acid, rapidly increased under all-trans retinoic acid treatment (30 min-6 h), whereas the 13-cis retinoic acid effect was markedly weaker and delayed. Both 13-cis retinoic acid and all-trans retinoic acid suppressed mRNA expression of cytochrome P450 1A2. In parallel experiments, 13-cis retinoic acid significantly reduced SZ95 sebocyte proliferation at 10-7 M, show- ing 30-40% inhibition after 9 d. All-trans retinoic acid and 9-cis retinoic acid exhibited similar anti-proliferative effects. AGN 193109, a pan-antagonist of the retinoic acid receptors, antagonized the anti-proliferative activity of all retinoic acid isomers tested in a concentration-dependent manner with complete abolishment at ratios of 1:10 13-cis retinoic acid and 1:1 all-trans retinoic acid. Coincubation of SZ95 sebocytes with 13-cis retinoic acid and AGN 193109 did not alter the intracellular concentration of 13-cis retinoic acid and its isomerization profile. In contrast, the retinoid X receptor antagonist CD 3507 did not affect the inhibition of SZ95 sebocyte proliferation induced by retinoic acids. Our findings indicate: (i) a selective 13-cis retinoic acid isomerization to all-trans retinoic acid in the intracellular compartment of SZ95 sebocytes; (ii) a reduced all-trans retinoic acid inactivation process after 13-cis retinoic acid treatment as compared with treatment with all-trans retinoic acid; and (iii) a retinoic acid receptor-mediated inhibition of SZ95 sebocyte proliferation. These data explain the sebocyte-specific activity of 13-cis retinoic acid and support a pro-drug/drug relation between 13-cis retinoic acid and all-trans retinoic acid.

Cell Division↗