Section Review: Retinoids: Biological Function and Use in the Treatment of Dermatological Diseases: Pulmonary-Allergy, Dermatological, Gastrointestinal & Arthritis

Treatments for AIDS/HIV-related Kaposi sarcoma: A systematic review of the literature

BACKGROUND

Treatment guidelines are not well established in AIDS-related Kaposi sarcoma (KS).

OBJECTIVE

We aim to review the evidence on efficacy of treatments for AIDS-related Kaposi sarcoma.

METHODS

We searched the Cochrane Library, PubMed, and Embase Database from date of database inception till July 2020. Randomized controlled trials reporting intervention consisting of any type of treatment compared to control/placebo to a different treatment modality or different combination of treatment/treatment doses with a diagnosis of AIDS-related KS are selected.

MAIN OUTCOMES AND MEASURES

Primary outcomes were response rates defined as complete response (CR), partial response (PR), stable disease (SD), or progressive disease (PD). Secondary outcomes were cosmesis and adverse outcomes such as pain and erythema.

RESULTS

Thirteen out of 536 articles met our eligibility criteria. Three studies reported the efficacy of chemotherapy, two studies looked at different doses of radiotherapy regimes, and three studies compared different antiretroviral therapy (ART) and chemotherapy regimens. Other studies reported topical therapies such as alitretinoin gel, IM862, and bHCG injection which showed varied efficacies.

LIMITATIONS

Lack of standardization classification of disease activity and clinical outcomes and treatment modalities precluded meaningful comparison of studies.

CONCLUSION

The evidence of efficacy of any particular intervention is overall varied and there was insufficient evidence to recommend any particular intervention. We have provided an overview of treatments for KS but larger studies need to be carried out to verify the efficacy of treatment options reported in the literature.

Tazarotene-induced gene 2 is associated with poor survival in non-small cell lung cancer

The aim of the present study was to investigate the expression of tazarotene-induced gene 2 (TIG2) and evaluate the clinicopathological variables and prognostic value for non-small cell lung cancer (NSCLC) patients. Reverse transcription-polymerase chain reaction and western blotting were utilized to detect TIG2 expression in NSCLC specimens and adjacent noncancerous tissue. Furthermore, the present study investigated the protein expression and the clinicopathological significance of TIG2 in 98 paraffin-embedded NSCLC samples by using immunohistochemistry. The results of the present study demonstrated that the expression of TIG2 mRNA (P=0.003) and protein (P=0.0024) was significantly reduced in NSCLC compared with corresponding noncancerous tissue. TIG2 protein expression in NSCLC was significantly associated with lymph node metastasis (P=0.006), Tumor-Node-Metastasis stage (P=0.021) and degree of differentiation (P=0.025). The Kaplan-Meier method and log-rank test revealed that high TIG2 expression was significantly associated with increased survival of NSCLC patients (P=0.003). Multivariate analysis revealed that TIG2 expression was an independent prognostic factor of the overall survival of NSCLC patients. Decreased expression of TIG2 may be useful as a biomarker for poor prognosis in NSCLC carcinogenesis and may act as a target for gene therapy for the treatment of NSCLC patients.

Retinoids: new use by innovative drug-delivery systems

BACKGROUND

Retinoids represent an old class of bioactives used in the treatment of different skin pathologies (such as acne and psoriasis) and in the treatment of many tumors. Unfortunately, they present several side effects, i.e., burning of skin and general malaise after systemic administration and they are very unstable after exposition to light.

METHODS

One of the most promising new approaches for reducing the side effects of retinoids while improving their pharmacological effect is the use of drug-delivery devices. This review explains the current status of retinoid drug transport, which has been developing over the last few years, explaining the modification of their biopharmaceutical properties in detail after encapsulation/inclusion in vesicular and polymeric systems.

RESULTS/CONCLUSION

Different colloidal and micellar systems containing retinoid drugs have been realized furnishing important potential advancements in traditional therapy.

Marked improvement induced in photoaged skin of hairless mouse by ER36009, a novel RARgamma-specific retinoid, but not by ER35794, an RXR-selective agonist

BACKGROUND

Photoaging (premature skin aging) results largely from repeated exposure of the skin to ultraviolet (UV) radiation from the sun. Topical all-trans retinoic acid (RA), the only agent that has been approved for the treatment of photoaging, has been shown to reverse this process. In this study, we evaluated the pharmacologic effects of novel synthetic retinoids, ER36009 and ER35794, on murine wrinkles induced by UVB. ER36009 is a specific agonist of retinoic acid receptor (RAR)gamma, the most abundant RAR subtype in the skin, while ER35794 is a potent retinoid X receptor (RXR)-selective agonist.

METHOD

After a 10-week exposure to escalating doses of UVB irradiation, the animals were treated three times per week with ER36009 (0.0001%, 0.00025%, 0.0005%), ER35794 (0.025%, 0.05%, 0.1%), RA (0.05%) or acetone (control) for 3 weeks.

RESULTS

ER36009 exerted a dose-dependent wrinkle-effacing effect, and 0.0005% ER36009-treated skin was significantly different from the control. ER36009 also significantly and dose-dependently increased both epidermal thickness and the area of the dermal repair zone defined by newly synthesized collagen. The effect of 0.0005% ER36009 on photodamaged skin was superior to that of 0.05% RA. In contrast, ER35794 was inactive in this model, though this compound exhibited lower local toxicity than other retinoids.

CONCLUSIONS

These data indicate that RARgamma, but not RXR, plays an important role in the improvement of the signs of photoaging, and so a specific RARgamma agonist might be superior to an RAR pan-agonist for clinical treatment. We conclude that ER36009 is a candidate for a potent anti-skin-aging agent.

Effect of retinoids on LPS-induced COX-2 expression and COX-2 associated PGE(2) release from mouse peritoneal macrophages and TNF-alpha release from rat peripheral blood mononuclear cells

Anti-inflammatory activity of retinoids has been demonstrated earlier, but their mechanism is poorly understood. In this study, we examined the effects of retinoids on lipopolysaccharide (LPS)-induced prostaglandin (PG) E(2) production, an indicator of cyclooxygenase (COX) activity, and COX-2 protein expression in mouse peritoneal macrophages, and tumor necrosis factor (TNF)-alpha release in rat peripheral blood mononuclear cell (PBMC) to elucidate their possible mechanism for anti-inflammation. All-trans retinoic acid (t-RA) and all-trans retinol significantly inhibited a LPS-induced PGE(2) production as assessed by enzyme-linked immunosorbant assay (ELISA) and COX-2 protein expression as assessed by Western blot assay in mouse peritoneal macrophages, after knocking out the COX-1 activity by aspirin. All-trans retinoic acid, but not all-trans retinol, inhibited LPS-induced TNF-alpha release as assessed by ELISA in rat PBMC. These findings suggest that the modulation of COX-2 and TNF-alpha release could be one of the possible pathways by which retinoids function as anti-inflammatory agents.

Hypermethylation and Silencing of the Putative Tumor Suppressor Tazarotene-Induced Gene 1 in Human Cancers

A variety of tumor suppressor genes are down-regulated by hypermethylation during carcinogenesis. Using methylated CpG amplification-representation difference analysis, we identified a DNA fragment corresponding to the Tazarotene-induced gene 1 (TIG1) promoter-associated CpG island as one of the genes hypermethylated in the leukemia cell line K562. Because TIG1 has been proposed to act as a tumor suppressor, we tested the hypothesis that cytosine methylation of the TIG1 promoter suppresses its expression and causes a loss of responsiveness to retinoic acid in some neoplastic cells. We examined TIG1 methylation and expression status in 53 human cancer cell lines and 74 primary tumors, including leukemia and head and neck, breast, colon, skin, brain, lung, and prostate cancer. Loss of TIG1 expression was strongly associated with TIG1 promoter hypermethylation (P < 0.001). There was no correlation between TIG1 promoter methylation and that of retinoid acid receptor beta2 (RARbeta2), another retinoic-induced putative tumor suppressor gene (P = 0.78). Treatment with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine for 5 days restored TIG1 expression in all eight silenced cell lines tested. TIG1 expression was also inducible by treatment with 1 micro M all-trans-retinoic acid for 3 days except in densely methylated cell lines. Treatment of the K562 leukemia cells with demethylating agent combined with all-trans-retinoic acid induced apoptosis. These findings indicate that silencing of TIG1 promoter by hypermethylation is common in human cancers and may contribute to the loss of retinoic acid responsiveness in some neoplastic cells.

Design, synthesis and structure–activity relationship of novel RXR-selective modulators

The synthesis and in vitro characterization of novel RXR-selective ligands possessing various substituted 1-benzofuran or 1-benzothiophene moieties are described.

Characterization of human circulating TIG2 as a ligand for the orphan receptor ChemR23

The orphan receptor ChemR23 is a G-protein coupled receptor (GPCR) with homology to neuropeptide and chemoattractant receptors. Tazarotene, a synthetic retinoid activating retinoic acid receptor (RAR), up-regulates tazarotene-induced gene-2 (TIG2). The function and molecular target of this protein are now described. By means of reverse pharmacology screening using a peptide library generated from human hemofiltrate, we have isolated and identified TIG2 as the natural ligand of ChemR23 and report the specific molecular form of the bioactive, circulating TIG2, representing the amino-acid residues 21 to 154 of the 163 amino acid-containing prepropeptide. Based on the expression pattern of ChemR23 and TIG2, the physiological role in bone development, immune and inflammatory responses and the maintenance of skin is now being investigated.

Design, synthesis, and structure-activity relationship studies of novel 6,7-locked-[7-(2-alkoxy-3,5-dialkylbenzene)-3-methylocta]-2,4,6-trienoic acids

Retinoid X receptor:peroxisome proliferative-activated receptor (RXR:PPAR) heterodimers play a critical role in the regulation of glucose (RXR/PPARgamma) and lipid metabolism (RXR/PPARalpha). Previously, we described a concise structure-activity relationship study of selective RXR modulators possessing a (2E,4E,6Z)-3-methyl-7-(3,5-dialkyl-6-alkoxyphenyl)-octa-2,4,6-trienoic acid scaffold. These studies were focused on the 2-position alkoxy side chain. We describe here the design and synthesis of a novel series of RXR selective modulators possessing the same aromatic core structure with the addition of a ring locked 6-7-Z-olefin on the trienoic acid moiety. The synthesis and structure-activity relationship studies of these 6,7-locked cyclopentenyl, phenyl, thienyl, furan, and pyridine-trienoic acid derivatives is presented herein.

Novel (2E,4E,6Z)-7-(2-alkoxy-3,5-dialkylbenzene)-3-methylocta-2,4,6-trienoic acid retinoid X receptor modulators are active in models of type 2 diabetes

Previous data have shown that RXR-selective agonists (e.g., 3 and 4) are insulin sensitizers in rodent models of non-insulin-dependent diabetes mellitus (NIDDM). Unfortunately, they also produce dramatic increases in triglycerides and profound suppression of the thyroid hormone axis. Here we describe the design and synthesis of new RXR modulators that retain the insulin-sensitizing activity of RXR agonists but produce substantially reduced side effects. These molecules bind selectively and with high affinity to RXR and, unlike RXR agonists, do not activate RXR homodimers. To further evaluate the antidiabetic activity of these RXR modulators, we have designed a concise and systematic structure-activity relationship around the 2E,4E,6Z-7-aryl-3-methylocta-2,4,6-trienoic acid scaffold. Selected compounds have been evaluated using insulin-resistant rodents (db/db mice) to characterize effects on glucose homeostasis. Our studies demonstrate the effectiveness of RXR modulators in lowering plasma glucose in the db/db mouse model.

RXR activators molecular signalling: involvement of a PPAR alpha-dependent pathway in the liver and kidney, evidence for an alternative pathway in the heart

(1) In this study we compared the molecular signalling elicited by rexinoids, selective retinoid X receptor (RXR)-activators, in several organs (i.e. liver, kidney, heart) and in hepatocytes of various species. (2) RXR plays the pivotal role of a hetero-dimerization partner for the members of the class II subset of nuclear receptors which regulate the transcription of numerous target genes, following chemical activation. Several of these selective activators are currently used to treat hyperlipidaemia (fibrates), type II diabetes (glitazones), or skin disorders (retinoic acid). Although these therapeutic pathways are not fully elucidated, receptor activation is considered a pre-requisite for efficacy. Therefore RXR, which accepts numerous dimeric partners, is considered a worthwhile pharmacological target. (3) We analysed a number of biochemical and molecular responses to rexinoids which were given orally to mice. Our results showed a prominent involvement of the peroxisome proliferator-activated receptor (PPARalpha) as a majority of the observed hepatic and renal regulations were abolished in PPARalpha-knockout animals. Therefore we documented the species-specificity of these rexinoid actions which were reproduced in rat primary hepatocyte cultures but not in cultures of rabbit or human origin. Conversely, we established that the regulation of the pyruvate dehydrogenase kinase (PDK4) gene in the heart, by rexinoids, is independent of PPARalpha expression. (4) Our results support the obligatory expression of the active, although quiescent, PPARalpha to sustain a subset of relevant regulations attributable to rexinoids in the liver and kidney. Their cardiac molecular signalling unveiled an alternate transduction pathway and therefore opens new prospects in the therapeutic potential of rexinoids.

Topical retinoic acid alters the expression of cellular retinoic acid-binding protein-I and cellular retinoic acid-binding protein-II in non-lesional but not lesional psoriatic skin

Therapeutic retinoids have profound effects on psoriatic skin pathology but their interactions with various retinoid-binding proteins in lesional vs non-lesional skin have not been investigated. Using quantitative real-time PCR the mRNA expression of cellular retinol-binding protein I (CRBPI) and retinoic acid-binding protein I/II (CRABPI/CRABPII) was studied in psoriatic and healthy control (=normal) skin after 4 days of occlusive RA/vehicle treatment (n=6). Untreated psoriatic lesions showed a markedly elevated CRABPII/CRABPI ratio, while the CRBPI level was reduced in lesional and non-lesional skin as compared to normal skin. In RA-treated normal and non-lesional skin, the mRNA expression of CRBPI was unaltered while that of CRABPI and CRABPII was reduced by approximately 80% and increased approximately 5-fold, respectively, as compared to vehicle-treated skin. In contrast, lesional skin exposed to RA showed an almost 90% increase in CRBPI transcripts but unaltered expression of CRABPI and CRABPII, yet, the mRNA expression of several inflammatory mediators, e.g. inducible nitric oxide synthase, interferon-gamma and interleukin-1beta, was clearly reduced. Immunohistochemistry localized CRABPII to suprabasal keratinocytes in normal skin and revealed markedly elevated levels in lesional skin. RA treatment induced CRABPII protein expression in normal and non-lesional skin, to similar levels as in untreated lesions. The results indicate that the effects of RA differ in normal/non-lesional psoriatic skin and lesional skin. Whether the high expression of CRABPII in psoriatic skin lesions is due to increased amounts of endogenous retinoids in lesional skin or reflects an abnormal regulation of the CRABPII gene in psoriasis remains to be studied.

Phase III vehicle-controlled, multi-centered study of topical alitretinoin gel 0.1% in cutaneous AIDS-related Kaposi's sarcoma

OBJECTIVE

This randomized, double-blind and vehicle-controlled phase III study was conducted to evaluate the efficacy and safety of alitretinoin gel 0.1% for the topical treatment of the cutaneous lesions of AIDS-related Kaposi's sarcoma (KS).

METHODS

Patients received treatment with alitretinoin gel (n = 62) or vehicle gel (n = 72) twice daily for 12 weeks. The primary efficacy endpoint was the cutaneous KS tumor response rate according to AIDS Clinical Trials Group (ACTG) objective criteria applied to topical therapy, with the patient as the unit of analysis.

RESULTS

Treatment of patients with alitretinoin gel resulted in a significant antitumor effect. The overall patient response rate (complete plus partial response) was 37% (23 of 62) for the alitretinoin-treated patients and 7% (5 of 72) for the vehicle-treated patients (p = 0.00003). The difference in response rates for the 2 treatment groups remained significant even after taking into consideration numerous variables, including age (p = 0.00001), Eastern Cooperative Oncology Group (ECOG) status (p = 0.00002), CD4+ cell count (p = 0.00002), history of opportunistic infection (p = 0.00002), aggregate area of indicator lesions (p = 0.00005), number of raised indicator lesions (p = 0.00002), prior therapy for KS (p = 0.00003), and number of drugs (p = 0.00002) used in concomitant antiretroviral therapy. Generally, treatment with alitretinoin gel was well tolerated. The overall incidence of adverse events was similar for the 2 treatment groups. Adverse events related to treatment with alitretinoin gel tended to be mild to moderate in severity and limited to the site of application. The most frequent adverse event occurring at the application site following alitretinoin gel treatment was irritation coded as rash (32%).

CONCLUSIONS

The results of this study provide convincing evidence of the superiority of alitretinoin gel over vehicle gel for the treatment of the cutaneous lesions of AIDS-related KS.

Synthesis of novel retinoid X receptor-selective retinoids

Retinoids 1-5 have been identified as potent RXR agonists for evaluation in the treatment of non-insulin-dependent (type II) diabetes mellitus (NIDDM). Highly convergent syntheses of 1-5 have been developed. The core tetrahydronaphthalene 7, employed in the synthesis of 1 and 2, was prepared in 98% yield using an AlCl(3)-catalyzed (0.03 equiv) Friedel-Crafts alkylation of toluene with 2,5-dichloro-2,5-dimethylhexane 6. A nitromethane-mediated Fridel-Crafts acylation of 7 with chloromethylnicotinate 9 was developed to prepare ketone 10 in 68% yield. Chelate-controlled addition of MeMgCl to 10 followed by dehydration afforded olefin 11 in 65% yield. Cyclopropanation of 11 with trimethylsulfoxonium ylide, followed by saponification, completed a five-step synthesis of 1 in 33% yield. FeCl(3)-catalyzed (0.05 equiv) Friedel-Crafts acylation of 7 with chloromethylterephthalate 14 afforded ketone 15 in 81% yield. Saponification of 15 and reaction with 50% aqueous NH(2)OH in AcOH afforded a 9:1 mixture of cis and trans oximes, from which the desired cis-oxime 2 was isolated in 43% yield. The core bromo-dihydronaphthalene 29 required for the synthesis of 3-5 was prepared by a Shapiro reaction. Transmetalation of 29 and reaction with Weinreb amides 30b or 36 afforded ketones 32 and 37, which were converted into 3-5 using chemistry comparable to the tetrahydronaphthylene series. Suzuki coupling of boronic acids 41 and 42 with vinyl triflate 43 provided an alternative approach to the synthesis of this class of compounds.

Bexarotene

Bexarotene is a selective retinoid X receptor (RXR) agonist. It binds to, and activates RXRs which function as ligand-activated transcription factors that control gene expression. This leads to modulation of cell growth, apoptosis, and differentiation. In patients with refractory or persistent early stage cutaneous T cell lymphoma (CTCL), the overall response rate was 54% after oral bexarotene 300 mg/m2/day. The overall response rate in patients with refractory or persistent advanced stage CTCL was 45% at the same dosage. An overall response rate of 63% was reported after topical bexarotene 0.1 to 1% twice daily in patients with early stage CTCL. Another trial reported an overall response rate of 44% after topical bexarotene 1% once daily escalated up to 4 times daily. Plaque elevation was significantly reduced, and the severity of moderate to severe psoriasis was substantially improved in patients receiving oral bexarotene 0.5 to 2 mg/kg/day. At clinically relevant oral dosages, bexarotene significantly decreases levels of serum thyrotropin and free thyroxine. The most common adverse events associated with oral bexarotene are hypertriglyceridemia, hypercholesterolemia, central hypothyroidism and headache. Reversible acute pancreatitis has occurred during oral bexarotene therapy. Adverse events associated with the topical formulation are limited to rash, pruritus, and pain.

RAR gamma agonists inhibit proliferation of vascular smooth muscle cells

The multifactorial and unpredictable nature of human restenosis will probably necessitate interventional strategies that target multiple processes involved in neointimal proliferation. Retinoids represent a growing class of pleiotropic biologic response modifiers with demonstrable efficacy in managing several pathologic conditions pertaining to neointimal proliferation. However, retinoid treatment is associated with a high incidence of adverse effects. The action of all-trans-retinoic acid is mediated by two families of nuclear receptors, RARs and RXRs, each containing three isoforms alpha, beta, and gamma. Because synthetic retinoids that are receptor and function specific have been shown to differ from each other by several orders of magnitude in their potencies and are associated with limited adverse effects, we examined the effect of synthetic retinoids on serum- and serotonin-induced vascular smooth muscle cell (VSMC) proliferation. Naturally occurring retinoids were used as controls. All-trans-retinoic acid at nanomolar concentrations inhibited smooth muscle cell proliferation. In this study, we report that RAR gamma subgroup-specific agonists are the most potent inhibitors of serum and serotonin VSMC proliferation, as compared with other RAR pan-agonists and naturally occurring retinoids tested. Our results indicate that RAR gamma subgroup-specific agonists should be assessed further in in vivo models of neointimal proliferation.

Modulation of endothelial cell proliferation by retinoid x receptor agonists

One feature that contraindicates the wide therapeutic use of natural retinoids is their adverse effects during systemic use and the lack of receptor selectivity. In contrast, synthetic retinoids are distinguishable from each other on the basis of their partial or exclusive preference in binding and activation of selective retinoid receptors. We examined the inhibitory activities of natural and synthetic retinoids for their ability to reverse basic fibroblast growth factor-induced endothelial cell proliferation. Both the naturally occurring retinoids at nanomolar concentrations reversed basic fibroblast growth factor-induced endothelial cell proliferation. Among the synthetic retinoids tested, retinoic acid receptor/retinoid x receptor pan-agonist AGN 191659 [(E)-5-[2-(5,6,7, 8-tetrahydro-3, 5,5,8,8-pentamethyl-2-naphtyl) propen-1-yl]-2-thiophenecarboxylic acid] and retinoid x receptor pan-agonist AGN 191701 [(E)-2-[2-(5,6,7,8-tetrahydro-3, 5,5,8, 8-pentamethyl-2-naphthyl) propen-1-yl]-4-thiophenecarboxylic acid] at nanomolar concentrations reversed the basic fibroblast growth factor-induced endothelial cell proliferation. Since none of the retinoic acid receptor agonists tested had any effect, the inhibitory effect of AGN 191659 could be attributed to its retinoid x receptor receptor activity. These results suggest that retinoid x receptor agonists may be more selective anti-angiogenic agents due to their ability to inhibit endothelial cell proliferation.

Psoriasis: current perspectives with an emphasis on treatment

An individualized treatment regimen is necessary for each patient with psoriasis because of the diverse nature of the disease. The manifestation of psoriasis, the severity and extent of the lesions, and the medical history and lifestyle of the patient are important factors that determine the selection of treatment, but in general therapies with the fewest side effects are preferred. First-line topical treatments are corticosteroids, calcipotriene, and tazarotene. If topical treatments are unsuccessful, phototherapy with ultraviolet B or photochemotherapy with psoralens plus ultraviolet A (PUVA) are the next choices. If psoriasis fails to respond to an adequate trial of topical therapy or phototherapy, systemic therapies including methotrexate, acitretin, or cyclosporin should be initiated. Because the regimens involved in systemic and phototherapy are complex and require frequent dose adjustments and specialized equipment, the patient should be referred to a dermatologist when topical therapy is not effective.

Treatment of AIDS-related cutaneous Kaposi's sarcoma with topical alitretinoin (9-cis-retinoic acid) gel. Panretin Gel North American Study Group

BACKGROUND

Kaposi's sarcoma (KS) is the most frequent malignancy in patients with HIV. Given the promise that retinoids show in the treatment of various hyperproliferative skin disorders and in vitro evidence of inhibition of proliferation of KS cells, a randomized, controlled clinical trial was conducted.

METHODS AND RESULTS

A 12-week, multicenter, randomized, double-blind, vehicle-controlled safety and efficacy evaluation of topical alitretinoin 0.1% gel applied to cutaneous KS lesions was conducted in HIV-infected patients. The primary efficacy endpoint was the patient's response rate, as determined by evaluating six index lesions representative of the patient's overall KS cutaneous disease using AIDS Clinical Trials Group (ACTG) response criteria applied to topical therapy. Of 268 patients entered in the blinded treatment phase of the study (alitretinoin group, n = 134; vehicle group, n = 134), 47 patients (35%) treated with alitretinoin 0.1% gel had a positive response, compared with 24 patients (18%) treated with vehicle gel. Of 184 patients receiving open-label alitretinoin treatment following the blinded phase of the trial, 90 patients (49%) met criteria for a positive response. This superior efficacy of alitretinoin gel over vehicle gel was maintained when the data were adjusted or analyzed for age, race, Kamofsky scores, baseline CD4+ lymphocyte counts, number of raised lesions at baseline, and aggregate area of index lesions. Alitretinoin 0.1% gel was superior to vehicle gel regardless of the number of concurrent antiretroviral therapies. Most adverse events were mild to moderate in severity, limited to the application site, and reversible on reduction in frequency or suspension of application. Relatively few patients (7%) discontinued alitretinoin therapy because of to related adverse events.

CONCLUSIONS

The results show that alitretinoin gel application is safe and generally well tolerated, and they indicate the superiority of alitretinoin 0.1% gel over vehicle gel in the treatment of cutaneous AIDS-related KS lesions.

Effect of topical tazarotene in the treatment of congenital ichthyoses

The clinical efficacy and tolerability of the topical receptor-selective retinoid tazarotene in the treatment of congenital ichthyoses was investigated. Twelve consecutive patients with different forms of congenital ichthyosis were enrolled in an open, non-randomized, intraindividually controlled, half-side pilot study. Diagnoses were X-linked recessive ichthyosis, non-erythrodermic autosomal recessive lamellar ichthyosis, autosomal dominant ichthyosis vulgaris and ichthyosis bullosa of Siemens (IBS). Tazarotene 0.05% gel was applied unilaterally daily on a defined body area measuring 10% of the body surface area. The contralateral side was treated with an ointment containing 10% urea. After 14 days, application frequency was reduced to three times a week, and stopped after another 2 weeks. The follow-up period was 3 months. Reduction in scaling and roughness was used to assess the clinical response in the tazarotene-treated area compared with the control area. Clinical and laboratory assessments were performed every 14 days during the trial. Unilateral improvement in favour of the tazarotene-treated side was observed in nine of 12 patients (75%). Four patients (33%) achieved an excellent response and four (33%) achieved a good response. No therapeutic effect was seen in patients with IBS. The remission persisted during the reduction phase and after discontinuation for up to 2 months. Local irritation in three patients was the only side-effect detectable. Short-term topical application of tazarotene 0.05% gel is a very effective and well-tolerated treatment modality in different forms of congenital ichthyoses and may be an alternative to systemic retinoid therapy.

A short and efficient synthesis of 4-[2,2-dimethyl-4(tol-4-yl)benzochrom-3-en-7-yl]benzoic acid - a potent retinoic acid receptor antagonist

An efficient synthesis of a potent RAR antagonist is described starting from disubstituted beta-naphthol. The functional groups on 2 and 3 positions of the beta-naphthol 5 were elaborated into benzochromanone 8. The title compound was prepared by Suzuki coupling of the left and right hand pieces.

Identification of the AP1-antagonism domain of retinoic acid receptors

Retinoids are therapeutically effective in the treatment of psoriasis, photoaging, acne, and certain cancers. Some of the therapeutic actions of retinoids can be ascribed to retinoic acid receptor (RAR)-mediated antagonism of AP1-dependent gene expression. The increased activity of transcription factor AP1, a complex of oncoproteins Jun and Fos, is associated with cell growth and proliferation. Retinoids, on the other hand, inhibit cell proliferation and affect differentiation, activities that possibly stem from an antagonism of AP1-mediated gene expression by RARs. To gain insight into the molecular mechanism of RAR-AP1 interaction, we have identified the regions of the RAR required for AP1 antagonism. We demonstrate that the AP1 antagonism domain of RAR is a complex of the core of the DNA binding domain and the hydrophobic zipper region. Further, both monomeric RAR and RAR-RXR heterodimers inhibit the expression of an AP1 reporter. CREB binding protein (CBP) has been described as a cofactor for AP1, various nuclear hormone receptor proteins including RARs, and certain other transcription factors and is required for their transactivation properties. Therefore, CBP has been proposed as a common limiting cofactor that can account for inhibition of AP1-dependent gene expression by RARs. Interestingly, however, our results along with previously reported observations suggest that in addition to CBP, there may be other limiting cofactor(s) responsible for mutual transrepression of RAR and AP1.

Optimizing therapy: tazarotene in combination with phototherapy

Phototherapy is often used in combination with other antipsoriatic treatments in an attempt to improve efficacy and reduce patients' cumulative exposure to radiation. Although this aim has been achieved with some combinations, the additional therapies often introduce a potential risk of other tolerability and safety problems. The efficacy of tazarotene reported in clinical trials to date suggest that this drug may help to improve the efficacy of phototherapy, and perhaps reduce the ultraviolet light exposure required without introducing additional, clinically significant problems. Preliminary results from the first 10 patients in a clinical trial investigating such combination therapy are reported here. They demonstrate that the addition of tazarotene to UVB phototherapy increases the percentage of patients achieving treatment success (> or = 50% global improvement in psoriasis) from 60% to 100% at Day 81. The UVB plus tazarotene combination achieved consistently greater reductions in the elevation and scaling of difficult-to-treat psoriatic plaques than UVB phototherapy alone or UVB phototherapy plus vehicle gel. The tazarotene combination therapy also achieved initial treatment success in less than half the time needed with phototherapy alone (median of 32 vs. 67 days). Combining UVB phototherapy with tazarotene treatment appears to offer a valuable therapeutic option that is more efficacious and faster than UVB phototherapy alone.

A new class of potent RAR antagonists: dihydroanthracenyl, benzochromenyl and benzothiochromenyl retinoids

The synthesis and biological activity of a novel series of tricyclic retinoic acid receptor antagonists are described. These compounds bind with high affinity to the RARs and are potent antagonists of retinoid function in in vitro and in vivo systems.

Retinoic acid potentiates TNF-alpha-induced ICAM-1 expression in normal human epidermal keratinocytes

ICAM-1 protein in keratinocytes is thought to contribute to cutaneous inflammatory reactions. Its induction depends-among others-on cytokines such as TNF-alpha, IFN-gamma, IL-1 or on retinoic acid (RA), a key regulator of epidermal homeostasis. We investigated the effect of treatments with TNF-alpha, RA or their combination on ICAM-1 expression on proliferative or differentiating keratinocytes over an 8 day culture period. Basal ICAM-1 levels were undetectable at low (30 microM) and standard (88 microM) Ca2+ and RA alone did not induce ICAM-1. However, at high Ca2+ (1500 microM), ICAM-1 levels were augmented in response to RA-treatment. TNF-alpha induced a transient ICAM-1 increase in NHK, which reached peak-levels 2-4 days post cytokine stimulus. RA potentiated the TNF-alpha-induced ICAM-1 response in all Ca2+-concentrations. This potentiating effect of RA was confirmed at the mRNA level. In summary, our results establish retinoic acid as an enhancer of TNF-alpha-induced ICAM-1 levels in NHK.

Identification and characterization of a retinoid-induced class II tumor suppressor/growth regulatory gene

Retinoids, synthetic and natural analogs of retinoic acid, exhibit potent growth inhibitory and cell differentiation activities that account for their beneficial effects in treating hyperproliferative diseases such as psoriasis, actinic keratosis, and certain neoplasias. Tazarotene is a synthetic retinoid that is used in the clinic for the treatment of psoriasis. To better understand the mechanism of retinoid action in the treatment of hyperproliferative diseases, we used a long-range differential display-PCR to isolate retinoid-responsive genes from primary human keratinocytes. We have identified a cDNA, tazarotene-induced gene 3 (TIG3; Retinoic Acid Receptor Responder 3) showing significant homology to the class II tumor suppressor gene, H-rev 107. Tazarotene treatment increases TIG3 expression in primary human keratinocytes and in vivo in psoriatic lesions. Increased TIG3 expression is correlated with decreased proliferation. TIG3 is expressed in a number of tissues, and expression is reduced in cancer cell lines and some primary tumors. In breast cancer cell lines, retinoid-dependent TIG3 induction is observed in lines that are growth suppressed by retinoids but not in nonresponsive lines. Transient over-expression of TIG3 in T47D or Chinese hamster ovary cells inhibits colony expansion. Finally, studies in 293 cells expressing TIG3 linked to an inducible promoter demonstrated decreased proliferation with increased TIG3 levels. These studies suggest that TIG3 may be a growth regulator that mediates some of the growth suppressive effects of retinoids.

Pharmacokinetics and safety review of tazarotene

The safety profile of tazarotene is superior to that of orally administered retinoids. The limited percutaneous penetration of tazarotene limits its systemic absorption and this, combined with its rapid metabolism in the skin and the plasma to the more water-soluble active metabolite, tazarotenic acid, helps prevent accumulation of the drug in fat containing tissues. Urinary and fecal elimination are virtually complete within 2 to 3 days and 7 days after dosing, respectively. Tazarotene also exhibits no indication of mutagenicity, carcinogenicity, phototoxic potential, photoallergic potential, or contact sensitization.

Rational design of receptor-selective retinoids

Orally administered retinoids can be associated with significant adverse effects because of high systemic exposure and a lack of receptor selectivity. Targeting the diseased tissue and improving the selectivity of the retinoid-receptor interaction to activate only those discrete pathways required for efficacy may minimize adverse effects. First- and second-generation retinoids contain several alternating single and double bonds that confer great conformational flexibility, allowing the molecules to adopt a variety of shapes and creating the potential to interact with multiple receptors. We hypothesized that, by designing a more rigid conformational structure, the receptor selectivity of retinoids could be improved and their therapeutic index enhanced. This strategy has resulted in the development of tazarotene. The receptor selectivity of tazarotene, together with its topical delivery, ensures a targeted action on psoriatic keratinocytes.

Retinoic acid receptor-nuclear factor-interleukin 6 antagonism. A novel mechanism of retinoid-dependent inhibition of a keratinocyte hyperproliferative differentiation marker

Retinoids inhibit the expression of migration inhibitory factor-related protein-8 (MRP-8), a marker of hyperproliferative or abnormal keratinocyte differentiation, in a retinoic acid receptor (RAR)-dependent manner in various cell culture systems. MRP-8 expression is also down-regulated in vivo in psoriatic lesions after topical application of an anti-psoriatic RARbeta/gamma-selective synthetic retinoid, tazarotene. We demonstrate that an MRP-8 promoter linked to a chloramphenicol acetyltransferase reporter (MRP8CAT) faithfully replicates the differentiation-specific regulation of the endogenous keratinocyte MRP-8 gene. Further, interferon gamma and serum-induced expression of MRP8CAT is inhibited by retinoid receptors in a ligand-dependent manner. We also show that NF-IL6 acts as a transcriptional enhancer of MRP-8, and that RARs inhibit MRP8CAT by inhibiting the enhancer action of nuclear factor-interleukin-6 (NF-IL6). The NF-IL6 antagonism function of RAR is a complex of the core of the DNA binding domain and the hydrophobic zipper region. This manuscript identifies NF-IL6 as another transcription factor, in addition to AP1, whose activity is inhibited by RAR in a ligand-dependent manner. The interdiction of NF-IL6-dependent signal transduction pathway by RARs may explain some of the therapeutic effects of retinoids in inflammatory and proliferative diseases.

Lack of involvement of retinoic acid receptor alpha in retinoid-induced skin irritation in hairless mice

It has been proposed that RAR gamma, the major retinoic acid receptor (RAR) subtype in skin, mediates retinoid-induced skin irritation. However, RAR alpha is also found in skin, and its role in retinoid-induced skin irritation has not been tested. In this study, RAR subtype-specific agonists and antagonists were used to test the possible contribution of RAR alpha to retinoid-induced skin irritation. Female hairless mice were treated topically on the dorsal skin for 5 days with various retinoids over a 2-log dose range, and cutaneous toxicity was scored by semiquantitative visual observations of skin flaking and abrasions daily up to 3 days post-treatment. Three RAR alpha-selective agonists were > or = 100-fold less potent as skin irritants than the structurally-related RAR pan-agonist, TTNPB. Skin irritation potency decreased in the following order: TTNPB > > Am580 > AGN 193835 > > 193836 and correlated with RAR beta and/or RAR gamma binding affinity rather than RAR alpha binding affinity. TTNPB-induced skin irritation was blocked in a dose-dependent fashion by co-treatment with the RAR pan-antagonist AGN 193109 but was not blocked by co-treatment with the RAR alpha-specific antagonist AGN 194301. In contrast, skin irritation induced by the RAR alpha-selective agonist AGN 193835 was almost completely blocked by co-treatment with AGN 193644, an RAR beta/gamma-selective antagonist. These data demonstrate that RAR alpha is not significantly involved in mediating retinoid-induced skin irritation in mice and suggest that RAR alpha-selective agonists may have reduced mucocutaneous side effects relative to other retinoids.

Mitogenic effect of retinoid X receptor agonists in rat liver

(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.

Identification of highly potent retinoic acid receptor alpha-selective antagonists

The syntheses and full retinoid receptor characterization of a novel series of retinoic acid receptor alpha (RAR alpha) antagonists, 1-5, are described. These compounds bind with high affinity to RAR alpha but were completely inactive in gene transactivation. They were also potent and effective antagonists of retinoic acid (RA) induced gene transcription at RAR alpha. Compounds 1-5 exhibited varying degrees of selectivity for RAR alpha relative to RAR beta/gamma, with compound 5 being the most selective in both binding and functional antagonism assays. These compounds will be invaluable tools in delineating the physiological roles of RAR alpha in development and in the adult animal and may themselves be useful therapeutic agents in human diseases associated with RAR alpha.

Tazarotene-induced gene 2 (TIG2), a novel retinoid-responsive gene in skin

Retinoids exert their biologic effects through two families of nuclear receptors, retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which belong to the superfamily of steroid/thyroid hormone nuclear receptors. By using a subtraction hybridization approach, we have identified a cDNA sequence TIG2 (Tazarotene-induced gene 2), whose expression is up-regulated by the treatment of skin raft cultures by an RAR beta/gamma-selective anti-psoriatic synthetic retinoid tazarotene [AGN 190168/ethyl 6-[2-(4,4-dimethylthiochroman-6-yl)-ethynyl] nicotinate]. The retinoid-mediated up-regulation in the expression of TIG2 was confirmed by Northern blot analysis. Upon sequencing, TIG2 was found to be a cDNA whose complete sequence was not in the GenBank and EMBL data bases. The TIG2 cDNA is 830 bp long and encodes a putative protein product of 164 amino acids. TIG2 is neither expressed nor induced by tazarotene in primary keratinocyte and fibroblast cultures. Thus, TIG2 is expressed and induced by tazarotene only when keratinocytes and fibroblasts form a tissue-like 3-dimensional structure. We further demonstrate that RAR-specific retinoids increase TIG2 mRNA levels. In contrast, neither RXR-specific retinoids nor 1,25-dihydroxyvitamin D3 increased TIG2 levels. Finally, we demonstrate that TIG2 is expressed at high levels in nonlesional psoriatic skin but at lower levels in the psoriatic lesion and that its expression is up-regulated in psoriatic lesions after topical application of tazarotene.

Discovery of novel retinoic acid receptor agonists having potent antiproliferative activity in cervical cancer cells

Retinoic acid receptor (RAR) active retinoids have proven therapeutically useful for treating certain cancers and dermatological diseases. Herein, we describe the discovery of two new RAR active trienoic acid retinoids, (2E,4E,6E)-7-(3,5-di-tert-butylphenyl)-3-methylocta-2, 4,6-trienoic acid (10a, ALRT1550) and (2E,4E,6Z)-7-(3,5-di-tert-butylphenyl)-3-methylocta-2, 4,6-trienoic acid (10b, LG100567). ALRT1550 is a RAR selective retinoid which exhibits exceptional potency in both competitive binding and cotransfection assays. Moreover, it is the most potent antiproliferative retinoid described to date and thus has implications for the treatment of certain cancers. LG100567 is a potent panagonist which activates both RARs and retinoid X receptors.

Tazarotene-induced gene 1 (TIG1), a novel retinoic acid receptor-responsive gene in skin

Retinoids exert their effect through ligand-dependent transcription factors, retinoic acid receptors (RARalpha, beta, and gamma) and retinoid X receptor (RXRalpha, beta, and gamma), which belong to the superfamily of steroid/thyroid/vitamin D3, nuclear receptors. Using a subtraction hybridization approach, we have identified a cDNA sequence, Tazarotene Induced Gene 1 (TIG1), which is highly upregulated in skin raft cultures by an RARbeta/gamma -selective retinoid AGN 190168 (tazarotene/ethyl 6-[2-(4,4-dimethylthiochroman-6-yl)-ethynyl]nicotinate), which is effective in the treatment of psoriasis. The retinoid-mediated upregulation in the expression of TIG1 was confirmed by Southern and Northern analyses. Upon sequencing, TIG1 was found to be a novel cDNA which encodes a protein of 228 amino acids whose sequence suggests that is a transmembrane protein with a small N-terminal intracellular region, a single membrane-spanning hydrophobic region, and a large C-terminal extracellular region containing a glycosylation signal. We demonstrate that TIG1 is also upregulated by AGN 190168 in skin raft cultures prepared from psoriatic fibroblasts and normal keratinocytes and in primary fibroblast and keratinocyte cultures. We also show that TIG1 is upregulated by retinoic acid receptor but not by retinoid X receptor-specific synthetic retinoids. Finally, we demonstrate that TIG1 is induced by AGN 190168 in psoriatic lesions during the course of clinical treatment of the disease.