Modeling, synthesis and biological evaluation of potential retinoid X receptor-selective agonists: novel halogenated analogues of 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (bexarotene)

The synthesis of halogenated analogues of 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)ethynyl]benzoic acid (1), known commonly as bexarotene, and their evaluation for retinoid X receptor (RXR)-specific agonist performance is described. Compound 1 is FDA approved to treat cutaneous T-cell lymphoma (CTCL); however, bexarotene treatment can induce hypothyroidism and elevated triglyceride levels, presumably by disrupting RXR heterodimer pathways for other nuclear receptors. The novel halogenated analogues in this study were modeled and assessed for their ability to bind to RXR and stimulate RXR homodimerization in an RXRE-mediated transcriptional assay as well as an RXR mammalian-2-hybrid assay. In an array of eight novel compounds, four analogues were discovered to promote RXR-mediated transcription with EC(50) values similar to that of 1 and are selective RXR agonists. Our approach also uncovered a periodic trend of increased binding and homodimerization of RXR when substituting a halogen atom for a proton ortho to the carboxylic acid on 1.

Ten-year experience of bexarotene therapy for cutaneous T-cell lymphoma in Finland

Bexarotene is an oral retinoid shown to be active against the cutaneous manifestations of cutaneous T-cell lym-phoma (CTCL). Literature on the efficacy, dosing and side-effects of bexarotene is sparse. We present here data on 37 Finnish patients with CTCL treated with bexarotene during the last 10 years. Bexarotene was equally effective as monotherapy or when combined with other treatment modalities, resulting in overall responses of approximately 75%. Early-stage CTCL responded better than advanced-stage CTCL (83% vs. 33%). The mean time to observable response was 3 months and the mean duration of the response was 21 months. The dose of bexarotene was generally lower than recommended due to side-effects. Abrupt elevation of liver transaminases, resulting in cessation of treatment, was observed in 4 (11%) patients. We conclude that the dose of bexarotene should be titrated individually to achieve optimal results. Maintenance therapy with low-dose bexarotene is a feasible alternative.

Advances in medical therapies for Cushing's syndrome

Cushing's syndrome (CS) is a heterogeneous disorder of diverse etiologies, leading to cortisol excess. Endogenous CS is caused by tumors secreting adrenocorticotropin (ACTH) (either eutopically or ectopically), cortisol, or very rarely corticotropin-releasing hormone (CRH). Definitive therapy of endogenous CS optimally involves tumor resection. Indications for medical therapy include acutely ill patients in preparation for surgery, those for whom surgery is not indicated (such as patients with unknown tumor location or unresectable lesions, and patients unfit for surgery for medical reasons), or patients who remain hypercortisolemic postoperatively. In the current article, the published literature has been reviewed to summarize data on medical therapies used in CS. Several agents are either used "off label" or being studied as potential therapies for CS. Medications suppressing adrenal steroidogenesis currently in use include ketoconazole, metyrapone, mitotane, or etomidate. In addition, the investigational agent LCI699 is under study. Centrally acting agents, which suppress ACTH secretion, include cabergoline, octreotide, as well as the investigational agents pasireotide, bexarotene, and lapatinib, which are being studied in patients with pituitary tumors. Mifepristone, a type 2 glucocorticoid receptor antagonist, was recently approved by the FDA as a new therapy for CS. Although not definitive at present, medical therapies have an important role in the management of CS patients. It is anticipated that understanding the pathogenesis of these tumors at a molecular level may spawn the development of rationally designed, highly efficacious medical therapies for CS in the future.

Chemopreventive effects of RXR-selective rexinoid bexarotene on intestinal neoplasia of Apc(Min/+) mice

Retinoid X receptor (RXR) has been implicated in several neoplastic diseases. Previously, we have shown that RXR-α is downregulated in human and rodent colonic tumors, suggesting a potential target for colon cancer prevention (http://www.cancer.org/Cancer/ColonandRectumCancer/DetailedGuide/colorectal-cancer-key-statistics). Experiments were designed to assess the chemopreventive efficacy of the selective RXR agonist bexarotene for the suppression of intestinal tumorigenesis in Apc(Min/+) mice. Before the efficacy studies, we determined that the maximal tolerated dose in C57BL/6J mice was less than 400 ppm. For the efficacy study, 6-week-old male and female C57BL/6J-Apc(Min/+) mice (nine mice per group) were fed diets containing 0, 30, and 60 ppm of bexarotene or 200 ppm of bexarotene for 80 days before intestinal tumors were evaluated. Dietary administration of 30 and 60 ppm of bexarotene suppressed the intestinal polyp formation by 38% (P < .015) and 60% (P < .0001) in males, respectively, and by 8.5% and 37% (P < .007) in females, respectively. Also, significant inhibition (50%-100%) of colonic tumor formation was observed in both male and female mice with bexarotene treatment. Administration of 200 ppm of bexarotene showed significant suppression of tumor formation (66%, P < .0001); however, it had significant toxicity. Intestinal tumors of bexarotene-fed mice showed significantly reduced expression of proliferating cell nuclear antigen (60%, P < .0001), cyclin D1, and cyclooxygenase 2 and increased RXR-α messenger RNA and uptake of oleate (34%, P < .01). Also, bexarotene-fed mice showed dose-dependent suppression of serum triglycerides (25%-72%, P < .0001) and inflammatory cytokines.

Mycosis fungoides stage IB progressing to cutaneous tumors

A 44-year-old African American woman presented with well-demarcated, pruritic and intermittently painful plaques and subsequently a diagnosis of mycosis fungoides stage IB was made. Six months after diagnosis, cutaneous tumors developed despite treatment with narrow-band ultraviolet B phototherapy. The patient failed low-dose methotrexate treatment and is now slowly improving on combination therapy with subcutaneous interferon alfa and oral bexarotene. This patient demonstrates the progression of patch/plaque stage disease to cutaneous tumors. Her case highlights the use of interferon and combination therapies in more advanced mycosis fungoides and demonstrates potential difficulties encountered in treating skin of color.

Recurrent localized primary cutaneous marginal-zone B cell lymphoma

A 36-year-old man with a prior diagnosis of primary cutaneous marginal-zone B cell lymphoma presented with newly-developed, small, erythematous papules and nodules on his upper left arm and pink-to-skin-colored, clustered papules on his left forearm. A biopsy specimen and immunohistochemical analysis of the left arm lesions showed a lymphocytic infiltrate which stained positively for CD20 and Bcl-2 and negatively for CD10. A PET-CT scan was negative for any extra-cutaneous manifestations of disease. These clinicopathologic findings are indicative of recurrent localized primary cutaneous marginal-zone B cell lymphoma.

Prevention of mouse lung tumors by combinations of chemopreventive agents using concurrent and sequential administration

BACKGROUND

Concurrent and sequential administration of combinations of budesonide, bexarotene, suberoylanilide hydroxamic acid (SAHA) and atorvastatin were evaluated in A/J mice for prevention of lung tumors initiated by 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanol, NNK).

MATERIALS AND METHODS

Individual drugs and their combinations were administered for 26 weeks after NNK initiation. For sequential administration, budesonide was given for 21 weeks followed by a second drug.

RESULTS

Alone, budesonide, bexarotene, and SAHA caused a significant decrease in total and large tumors at 21 and 26 weeks. Concurrent treatment with budesonide and bexarotene or SAHA caused a significantly greater decrease in total tumors and large tumors than either drug administered alone. Sequential administration of all combinations (except budesonide/atorvastatin) gave a significant reduction in total and large tumors. Budesonide followed by SAHA and SAHA with atorvastatin yielded a greater reduction in large tumors.

CONCLUSION

Combinations of drugs demonstrated a greater efficacy in preventing mouse lung tumors than did the individual agents.

Molecular markers associated with clinical response to bexarotene therapy in cutaneous T-cell lymphoma

Bexarotene (Targretin(®)), was registered for the treatment of cutaneous T-cell lymphoma (CTCL) in 2002, and has been reported to induce a 45% overall response. Responses are mostly partial or generate a stable, skin-restricted disease. This study explored the usefulness of a novel cancer-associated gene, NAV3 and corresponding chromosome 12 copy numbers as possible biomarkers to monitor the therapeutic response to bexarotene in 21 Finnish patients with CTCL. Six patients (29%) reached complete remission (CR) and 3 of these remained in CR for more than 24 months, 12 (57%) reached a partial response (PR, with one stable disease) and 3 were non-responders. Low-level NAV3 deletions were detected using a fluorescence in-situ hybridization (FISH) assay in the lesions of 5 patients, 4 of whom were non-responders or progressed after short PR. This occurrence of NAV3 deletions was statistically significant compared with non-progressors (p = 0.011, Fisher's exact test). Chromosome 12 tetraploidy was found in the lesions of two of the 3 patients with CR who remained in remission. While such tetraploidy is a feature of proliferating normal T cells, this observation may reflect a favourable anti-tumour immune response among the skin-infiltrating lymphocytes.

Identification of polymorphisms associated with hypertriglyceridemia and prolonged survival induced by bexarotene in treating non-small cell lung cancer

BACKGROUND

Bexarotene was evaluated in treating advanced non small cell lung cancer (NSCLC) in two phase III trials. Although a significant survival benefit was not observed for the overall bexarotene-treated population (617 patients), a third of bexarotene-treated patients who developed high-grade hypertriglyceridemia exhibited significantly longer survival.

PATIENTS AND METHODS

In order to identify genomic polymorphisms that could serve as potential predictive biomarkers for response and improved survival in NSCLC patients, DNA samples extracted from plasma archived from 403 patients were genotyped using Affymetrix 500K whole genome SNP arrays and/or Sequenom iPLEX™ assays.

RESULTS

Fourteen SNPs were identified on nine loci that showed significant associations with high-grade hypertriglyceridemia induced by bexarotene. Four such single nucleotide polymorphisms (SNPs) reside on the region upstream of solute carrier family 10, member 2 (SLC10A2), and one SNP is located close to lymphocyte cytosolic protein 1 (LCP1), whose expression correlated with the activity of bexarotene in tumor cells.

CONCLUSION

We identified novel polymorphisms exhibiting significant association with bexarotene induced hypertriglyceridemia, implicating their potential in predicting bexarotene-improved survival response.

About the cutaneous targets of bexarotene in CTCL patients

There are several approved therapies for cutaneous T-cell lymphoma (CTCL). The retinoids are one of the major biologic response modifiers used in CTCL, producing good response rates but few complete responses. Bexarotene has been demonstrated to act on malignant T-cells by inducing their apoptosis, but nothing is known about its role on keratinocytes and Langerhans cells. Immunohistochemical analysis using CD1a, HLA-DR, ICAM-1 (activation markers), CD95 and CD40 (apoptosis markers) was conducted on frozen sections of bexarotene-exposed cutaneous explants and skin biopsy specimens from patients treated with bexarotene. None of the studied markers was significantly modulated both on cutaneous explants and on skin biopsy specimens after treatment with bexarotene, compared to controls. Langerhans cells and keratinocytes do not appear to play a central role in the therapeutic control of CTCL by bexarotene therapy. The main bexarotene's target thus remains T-cells by inducing their apoptosis, a mechanism that is different from the other retinoids used in CTCL.

Poikilodermatous mycosis fungoides

Poikilodermatous mycosis fungoides is a rare form of cutaneous T-cell lymphoma that is characterized clinically by localized or diffuse patches, which consist of telangiectases, mottled hyper- and hypopigmentation, and atrophy. The immunophenotype of neoplastic cells is similar to that observed in classic mycosis fungoides. Therapeutic options used in poikilodermatous and classic mycosis fungoides include both skin-directed and systemic treatments. We present a case of poikilodermatous mycosis fungoides in a 53-year-old woman, who initially presented with erythroderma and who has failed multiple treatment modalities.

Pompholyx: a review of clinical features, differential diagnosis, and management

Pompholyx is a vesicobullous disorder of the palms and soles. The condition is hard to treat because of the peculiarities of the affected skin, namely the thick horny layer and richness of the sweat glands. In this article, we review the available therapies, and score the treatments according to the level of evidence. The cornerstones of topical therapy are corticosteroids, although calcineurin inhibitors also seem to be effective. Topical photochemotherapy with methoxsalen (8-methoxypsoralen) is as effective as systemic photochemotherapy or high-dose UVA-1 irradiation. Systemic therapy is often necessary in bullous pompholyx. Corticosteroids are commonly used although no controlled study has been published to date. For recalcitrant cases, corticosteroids are combined with immunosuppressants. Alitretinoin has efficacy in chronic hand dermatitis including pompholyx. Another evolving treatment seems to be the intradermal injection of botulinum toxin. Radiotherapy might be an option for selected patients not responding to conventional treatment. In practice, patients benefit most from a combination of treatments.

Identification of a naturally occurring rexinoid, honokiol, that activates the retinoid X receptor

Screening of a total of 86 crude drugs for retinoid X receptor (RXR) ligands demonstrated that the methanol extract of the bark of Magnolia obovata markedly activated the transcriptional activity of RXRalpha in luciferase reporter assays. Thereafter, honokiol (1) was isolated as a constituent able to activate RXR selectively as a natural rexinoid, but not RARalpha. The activity of 1 was more potent than those of phytanic acid and docosahexaenoic acid, both of which are known to be natural RXR agonists. Honokiol (1) is capable of activating a RXR/LXR heterodimer, resulting in the induction of ATP-binding cassette transporter A1 mRNA and protein expression in RAW264.7 cells, as well as an increase in [(3)H]cholesterol efflux from peritoneal macrophages. These effects of 1 were enhanced synergistically in the presence of an LXR agonist, 22(R)-hydroxycholesterol. The results obtained demonstrate that 1, a newly identified natural rexinoid, regulates the functions of RXR/LXR heterodimer and abrogates foam cell formation by the induction of ABCA1 via activation of the RXR/LXR heterodimer.

Development of Hodgkin's lymphoma under bexarotene treatment for Sézary syndrome and review of the literature

There are several reports of patients who developed extracutaneous lymphoma after they started bexarotene treatment. The authors report a case in which the initiation of bexarotene therapy for Sézary syndrome was temporally associated with the development of Hodgkin's lymphoma despite improvement in cutaneous signs and symptoms. It is possible that bexarotene may contribute to the development of extracutaneous lymphoma. Although bexarotene therapy may relieve symptoms and signs of cutaneous T-cell lymphoma, careful examination of the lymph nodes during treatment is recommended.

Systemic retinoids for chemoprevention of non-melanoma skin cancer in high-risk patients

Patients at high risk for the development of multiple non-melanoma skin cancers, especially those receiving immunosuppressive medications following solid organ transplantation, are candidates for chemoprophylaxis. In patients where photo-protection and topical medications are insufficient to prevent the growth of new cancers, there is considerable evidence that oral retinoids, including vitamin A, and synthetics such as isotretinoin, etretinate and acitretin are efficacious in this regard. This manuscript is a review of the literature regarding the use of these agents for chemoprophylaxis of non-melanoma skin cancer. Also included is anecdotal evidence that bexarotene, a rexinoid, may be as effective as acitretin in terms of chemoprevention, with a comparable side effects at doses recommended for chemoprophylaxis.

Preventive effects of bexarotene and budesonide in a genetically engineered mouse model of small cell lung cancer

In the present study, we examined the effect of bexarotene (Targretin) and budesonide in the chemoprevention of small cell lung carcinoma using a lung-specific knockout model of Rb1 and p53. Upon treatment with bexarotene, tumor incidence, number, and load were significantly reduced (P < 0.05). Budesonide treatment trended to inhibition, but the effect was not statistically significant (P > 0.05). Immunohistochemical staining indicated that bexarotene treatment decreased cell proliferation and increased apoptosis in tumors. The Rb1/p53 gene-targeted mouse seems to be a valuable model for chemopreventive studies on human small cell lung cancer. Our results indicate that the retinoid X receptor agonist bexarotene may be a potent chemopreventive agent in this cancer type.