Biological Effects of Bexarotene in Cutaneous T-Cell Lymphoma

Immunobiology and treatment of cutaneous T-cell lymphoma

INTRODUCTION

Primary cutaneous T cell lymphomas (CTCL) are a heterogenous group of non-Hodgkin lymphomas derived from skin-homing T cells. These include mycosis fungoides and its leukemic variant Sezary syndrome, as well as the CD30+ lymphoproliferative disorders.

AREAS COVERED

In this review, we provide a summary of the current literature on CTCL, with a focus on the immunopathogenesis and treatment of mycosis fungoides and Sezary syndrome.

EXPERT OPINION

Recent advances in immunology have provided new insights into the biology of malignant T cells. This in turn has led to the development of new therapies that modulate the immune system to facilitate tumor clearance or target specific aspects of tumor biology.

Retinoid X Receptor agonists as selective modulators of the immune system for the treatment of cancer

Upon heterodimerizing with other nuclear receptors, retinoid X receptors (RXR) act as ligand-dependent transcription factors, regulating transcription of critical signaling pathways that impact numerous hallmarks of cancer. By controlling both inflammation and immune responses, ligands that activate RXR can modulate the tumor microenvironment. Several small molecule agonists of these essential receptors have been synthesized. Historically, RXR agonists were tested for inhibition of growth in cancer cells, but more recent drug discovery programs screen new molecules for inhibition of inflammation or activation of immune cells. Bexarotene is the first successful example of an effective therapeutic that molecularly targets RXR; this drug was approved to treat cutaneous T cell lymphoma and is still used as a standard of care treatment for this disease. No additional RXR agonists have yet achieved FDA approval, but several promising novel compounds are being developed. In this review, we provide an overview of the multiple mechanisms by which RXR signaling regulates inflammation and tumor immunity. We also discuss the potential of RXR-dependent immune cell modulation for the treatment or prevention of cancer and concomitant challenges and opportunities.

Development of Bexarotene Analogs for Treating Cutaneous T-Cell Lymphomas

Bexarotene, a drug approved for treatment of cutaneous T-cell lymphoma (CTCL), is classified as a rexinoid by its ability to act as a retinoid X receptor (RXR) agonist with high specificity. Rexinoids are capable of inducing RXR homodimerization leading to the induction of apoptosis and inhibition of proliferation in human cancers. Numerous studies have shown that bexarotene is effective in reducing viability and proliferation in CTCL cell lines. However, many treated patients present with cutaneous toxicity, hypothyroidism, and hyperlipidemia due to crossover activity with retinoic acid receptor (RAR), thyroid hormone receptor (TR), and liver X receptor (LXR) signaling, respectively. In this study, 10 novel analogs and three standard compounds were evaluated side-by-side with bexarotene for their ability to drive RXR homodimerization and subsequent binding to the RXR response element (RXRE). In addition, these analogs were assessed for proliferation inhibition of CTCL cells, cytotoxicity, and mutagenicity. Furthermore, the most effective analogs were analyzed via qPCR to determine efficacy in modulating expression of two critical tumor suppressor genes, ATF3 and EGR3. Our results suggest that these new compounds may possess similar or enhanced therapeutic potential since they display enhanced RXR activation with equivalent or greater reduction in CTCL cell proliferation, as well as the ability to induce ATF3 and EGR3. This work broadens our understanding of RXR-ligand relationships and permits development of possibly more efficacious pharmaceutical drugs. Modifications of RXR agonists can yield agents with enhanced biological selectivity and potency when compared to the parent compound, potentially leading to improved patient outcomes.

Harnessing the immune system in the treatment of cutaneous T cell lymphomas

Cutaneous T cell lymphomas are a rare subset of non-Hodgkin's lymphomas with predilection for the skin with immunosuppressive effects that drive morbidity and mortality. We are now appreciating that suppression of the immune system is an important step in the progression of disease. It should come as no surprise that therapies historically and currently being used to treat these cancers have immune modulating functions that impact disease outcomes. By understanding the immune effects of our therapies, we may better develop new agents that target the immune system and improve combinatorial treatment strategies to limit morbidity and mortality of these cancers. The immune modulating effect of therapeutic drugs in use and under development for cutaneous T cell lymphomas will be reviewed.

The Microenvironment's Role in Mycosis Fungoides and Sézary Syndrome: From Progression to Therapeutic Implications

BACKGROUND

Mycosis fungoides (MF) and Sezary Syndrome (SS) are the most common cutaneous T-cell lymphomas. It has been hypothesized that the interaction between the immune system, cutaneous cells, and neoplastic elements may play a role in MF/SS pathogenesis and progression.

METHODS

This paper aims to revise in a narrative way our current knowledge of the microenvironment's role in MF/SS.

RESULTS AND CONCLUSIONS

Literature data support a possible implication of microenvironment cells in MF/SS pathogenesis and progression, opening up new therapeutic avenues.

A Retinoid X Receptor Agonist Directed to the Large Intestine Ameliorates T-Cell-Mediated Colitis in Mice

Retinoid X receptor (RXR) is a nuclear receptor that heterodimerizes with several nuclear receptors, integrating ligand-mediated signals across the heterodimers. Synthetic RXR agonists have been developed to cure certain inflammatory diseases, including inflammatory bowel diseases (IBDs). However, pre-existing RXR agonists, which are lipophilic and readily absorbed in the upper intestine, cause considerable adverse effects such as hepatomegaly, hyperlipidemia, and hypothyroidism. To minimize these adverse effects, we have developed an RXR agonist, NEt-3IB, which has lipophilic and thus poorly absorptive properties. In this study, we evaluated the effects of NEt-3IB in an experimental murine colitis model induced through the adoptive transfer of CD45RB^highCD4⁺ T cells. Pharmacokinetic studies demonstrated that the major portion of NEt-3IB was successfully delivered to the large intestine after oral administration. Notably, NEt-3IB treatment suppressed the development of T cell-mediated chronic colitis, as indicated by improvement of wasting symptoms, inflammatory infiltration, and mucosal hyperplasia. The protective effect of NEt-3IB was mediated by the suppression of IFN-γ-producing Th1 cell expansion in the colon. In conclusion, NEt-3IB, a large intestine-directed RXR agonist, is a promising drug candidate for IBDs.

Potential therapeutic uses of rexinoids

The discovery of nuclear receptors, particularly retinoid X receptors (RXR), and their involvement in numerous pathways related to development sparked interest in their immunomodulatory properties. Genetic models using deletion or overexpression of RXR and the subsequent development of several small molecules that are agonists or antagonists of this receptor support a promising therapeutic role for these receptors in immunology. Bexarotene was approved in 1999 for the treatment of cutaneous T cell lymphoma. Several other small molecule RXR agonists have since been synthesized with limited preclinical development, but none have yet achieved FDA approval. Cancer treatment has recently been revolutionized with the introduction of immune checkpoint inhibitors, but their success has been restricted to a minority of patients. This review showcases the emerging immunomodulatory effects of RXR and the potential of small molecules that target this receptor as therapies for cancer and other diseases. Here we describe the essential roles that RXR and partner receptors play in T cells, dendritic cells, macrophages and epithelial cells, especially within the tumor microenvironment. Most of these effects are site and cancer type dependent but skew immune cells toward an anti-inflammatory and anti-tumor effect. This beneficial effect on immune cells supports the promise of combining rexinoids with approved checkpoint blockade therapies in order to enhance efficacy of the latter and to delay or potentially eliminate drug resistance. The data compiled in this review strongly suggest that targeting RXR nuclear receptors is a promising new avenue in immunomodulation for cancer and other chronic inflammatory diseases.

The immunopathogenesis and immunotherapy of cutaneous T cell lymphoma: Current and future approaches

In the past few decades, immunotherapy has emerged as an effective therapeutic option for patients with cutaneous T cell lymphoma (CTCL). CTCL is characterized by progressive impairment of multiple arms of the immune system. Immunotherapy targets these deficits to stimulate a more robust antitumor response, thereby both clearing the malignant T cells and repairing the immune dysfunction. By potentiating rather than suppressing the immune system, immunotherapy can result in longer treatment responses than alternatives such as chemotherapy. In recent years, advances in our understanding of the pathogenesis of CTCL have led to the development of several new agents with promising efficacy profiles. The second article in this continuing medical education series describes the current immunotherapeutic options for treatment of CTCL, with a focus on how they interact with the immune system and their treatment outcomes in case studies and clinical trials. We will discuss established CTCL immunotherapies, such as interferons, photopheresis, and retinoids; emerging therapies, such as interleukin-12 and Toll-like receptor agonists; and new approaches to targeting tumor antigens and checkpoint molecules, such as mogamulizumab, anti-programmed cell death protein 1, anti-CD47, and chimeric antigen receptor T cell therapy. We also describe the principles of multimodality immunotherapy and the use of total skin electron beam therapy in such regimens.

Synergistic effect of a retinoid X receptor-selective ligand bexarotene and docetaxel in prostate cancer

Purpose

To explore if bexarotene (BEX) synergistically enhances docetaxel (DTX) cytotoxicity in castration-resistant prostate cancer cell lines.

Materials and methods

MTT assay was used to measure the cytotoxic effect of DTX and BEX on castration-resistant prostate cancer (CRPC) cell proliferation and the combination index (CI) values calculated to analyze the interaction between DTX and BEX. Flow cytometry and Western blot analysis identified the underlying mechanism for the synergistic effect of BEX and DTX.

Results

When mitotic slippage happens, BEX can synergistically strengthen the anti-proliferation of DTX in a way of significantly down-regulating cyclinB1 and CDK1 expression, and then arresting cells in G2 phase.

Conclusion

Results from this study showed that BEX-induced G2 arrest and DTX-induced mitotic arrest probably contributed to the synergistic effect of BEX and DTX.

Successful Treatment of Advanced Primary Cutaneous Peripheral T-Cell Lymphoma with Oral Bexarotene Monotherapy

Bexarotene is a third-generation retinoid X receptor-selective retinoid that is widely used for the early treatment of advanced-stage cutaneous T-cell lymphomas. In this report, we describe a case of successful treatment of advanced primary cutaneous peripheral T-cell lymphoma not otherwise specified (PTCL-NOS) with oral bexarotene monotherapy. After the administration of oral bexarotene at a dose of 300 mg/m²/day, all skin lesions and lymph nodes regressed, and complete remission was achieved for 1 year. Our case suggested that bexarotene monotherapy could be one of the possible therapies for the treatment of primary cutaneous PTCL-NOS.

Bexarotene Modulates Retinoid-X-Receptor Expression and Is Protective Against Neurotoxic Endoplasmic Reticulum Stress Response and Apoptotic Pathway Activation

Retinoid X-receptors (RXRs) are members of the ligand-dependent transcription factor family of nuclear receptors that have gained recent research focus as potential targets for neurodegenerative disorders. Bexarotene is an RXR pharmacological agonist that is shown to be neuroprotective through its effects in promoting amyloid beta (Aβ) uptake by the glial cells in the brain. This study aimed to evaluate the dose-dependent effects of bexarotene on RXR expression in SH-SY5Y neuroblastoma cells and validate the drug effects in the brain in vivo. The protein expression studies were carried out using a combination of various drug treatment paradigms followed by expression analysis using Western blotting and immunofluorescence. Our study demonstrated that bexarotene promoted the expression of RXR α, β and γ isoforms at optimal concentrations in the cells and in the mice brain. Interestingly, a decreased RXR expression was identified in Alzheimer's disease mouse model and in the cells that were treated with Aβ. Bexarotene treatment not only rescued the RXR expression loss caused by Aβ treatment (p < 0.05) but also protected the cells against Aβ-induced ER stress (p < 0.05) and pro-apoptotic BAD protein activation (p < 0.05). In contrast, higher concentrations of bexarotene upregulated the ER stress proteins and led to BAD activation. Our study revealed that these downstream neurotoxic effects of high drug concentrations could be prevented by pharmacological targeting of the TrkB receptor. The ER stress and BAD activation induced by high concentrations of bexarotene were rescued by the TrkB agonist, 7,8 dihydroxyflavone (p < 0.05) while TrkB inhibitor CTX-B treatment further exacerbated these effects. Together, these findings suggest a cross-talk of TrkB signalling with downstream effects of bexarotene toxicity and indicate that therapeutic targeting of RXRs could prevent the Aβ-induced molecular neurotoxic effects.

RARα/RXR synergism potentiates retinoid responsiveness in cutaneous T-cell lymphoma cell lines

Retinoids, natural and synthetic derivatives of vitamin A, induce cellular changes by activating nuclear retinoic acid receptors (RAR) and retinoid X receptors (RXR). Although the ability of retinoids to govern gene expression is exploited clinically for cancer therapeutics, the full benefit of retinoid-based strategies is unrealized due to detrimental side effects. Delineating the receptors that prompt cellular outcomes is critical to advancing retinoid-based approaches. Here, we identify the receptors that evoke multiple responses in cutaneous T-cell lymphoma (CTCL). The data demonstrate that RARα drives integrin β7-dependent adhesion and CCR9-mediated chemotaxis in CTCL cells. Of note, concomitant activation of RARα and RXR nuclear receptors yielded synergistic increases in adhesion and migration at concentrations where single agents were ineffective. As the established paradigm of retinoid action in CTCL is apoptosis and growth arrest, the role of RARα/RXR in these events was studied. As with adhesion and migration, RARα/RXR synergism prompted apoptosis and dampened CTCL cell proliferation. Strikingly, RARα/RXR synergism induced responses from CTCL cell lines previously reported to be unresponsive to retinoids. These data provide a novel framework that may further refine a proven CTCL therapy.

Successful Treatment of Primary Cutaneous Peripheral T-Cell Lymphoma Presenting Acquired Ichthyosis with Oral Bexarotene Monotherapy

Acquired ichthyosis (AI) is a reactive cutaneous manifestation that can be associated with malignant hematological disease, including cutaneous T-cell lymphoma (CTCL). Since it is difficult to distinguish AI from ichthyosiform mycosis fungoides, to select the treatment for CTCL with ichthyosis-like appearance and to evaluate its efficacy is sometimes challenging. In this report, we describe a case of primary cutaneous peripheral T-cell lymphoma not otherwise specified presenting AI successfully treated with oral bexarotene. In the present case, the administration of oral bexarotene was not only effective for lymphoma cells infiltrating ulcers and nodules, but it also eliminated AI.

Pharmacological Modulation of Lung Carcinogenesis in Smokers: Preclinical and Clinical Evidence

Many drugs in common use possess pleiotropic properties that make them capable of interfering with carcinogenesis mechanisms. We discuss here the ability of pharmacological agents to mitigate the pulmonary carcinogenicity of mainstream cigarette smoke. The evaluated agents include anti-inflammatory drugs (budesonide, celecoxib, aspirin, naproxen, licofelone), antidiabetic drugs (metformin, pioglitazone), antineoplastic agents (lapatinib, bexarotene, vorinostat), and other drugs and supplements (phenethyl isothiocyanate, myo-inositol, N-acetylcysteine, ascorbic acid, berry extracts). These drugs have been evaluated in mouse models mimicking interventions either in current smokers or in ex-smokers, or in prenatal chemoprevention. They display a broad spectrum of activities by attenuating either smoke-induced preneoplastic lesions or benign tumors and/or malignant tumors. Together with epidemiological data, these findings provide useful information to predict the potential effects of pharmacological agents in smokers.

Alitretinoin in Dermatology-An Update

Alitretinoin is a pan retinoic acid agonist. It was initially used as 0.1% gel in the management of localized Kaposi's sarcoma. At present, the use of systemic alitretinoin has proved extremely efficacious in the management of recalcitrant chronic hand eczema. Furthermore, there have been other retinoid responsive dermatosis that have demonstrated remission post usage of systemic alitretinoin. With a better toxicity profile, compared to the other systemic retinoids, alitretinoin could be considered a valuable treatment option in the near future for the treatment of these dermatologic disorders.

The Role of Systemic Retinoids in the Treatment of Cutaneous T-Cell Lymphoma

Retinoids are natural and synthetic vitamin A analogs with effects on cell proliferation, differentiation, and apoptosis. They have significant activity in hematologic malignancies and have been studied extensively in cutaneous T-cell lymphoma. Retinoids bind to nuclear receptors and exert their effects through moderation of gene expression. Retinoic acid receptor and retinoic X receptor exert regulatory activity in vivo, binding to distinct ligands. Studies investigating systemic retinoids as monotherapy and in combination with other agents active against cutaneous lymphoma are reviewed. Side effects associated with retinoids include teratogenicity, dyslipidemias, and hypothyroidism, which should be carefully monitored in patients receiving treatment.

Retinoids Bias Integrin Expression and Function in Cutaneous T-Cell Lymphoma

Cutaneous T-cell lymphoma (CTCL) is a heterogeneous group of malignancies characterized by accumulation of malignant T-cells within the skin. Retinoids, metabolic derivatives, and synthetic analogs of vitamin A embody an effective CTCL therapy with over three decades of clinical use. The established mechanism of action is induction of growth arrest and apoptosis. However, the natural role of retinoids in T-cell biology is imprinting gut-homing properties by inducing integrin α4β7 expression. How the natural role of retinoids relates to therapeutic effectiveness in CTCL has not been addressed and merits investigation. Here we provide evidence that retinoids, including Bexarotene, selectively induce CTCL lineages to increase integrin β7 expression and function prior to growth arrest and apoptosis. Interestingly, augmented CTCL cell adhesion obtained with retinoid exposure was potently attenuated by 1,25-dihydroxyvitamin D3, a metabolic vitamin derivative involved in prompting immune cell skin homing. The integrin-dependent adhesion changes in CTCL cells occurred through synergistic activation of RAR and RXR nuclear receptors. These data explore the early cellular changes induced by retinoids that may be pivotal to sensitizing CTCL cells to growth arrest and apoptosis.

The utility of bexarotene in mycosis fungoides and Sézary syndrome

Cutaneous T-cell lymphoma (CTCL) is an umbrella term that encompasses a group of neoplasms that have atypical T-lymphocytes in the skin. Mycosis fungoides (MF) is the most common type of CTCL and Sézary syndrome (SS) is the leukemic form. Treatment for CTCL is dependent on the stage of disease and response to previous therapy. Therapy is divided into skin-directed treatment, which tends to be first line for early-stage disease, and systemic therapy, which is reserved for refractory CTCL. Bexarotene is a rexinoid and was licensed in Europe in 2002 for use in patients with advanced disease that have been refractory to a previous systemic treatment. We review the use of bexarotene as monotherapy and in combination with other treatments.

Rexinoid inhibits Nrf2-mediated transcription through retinoid X receptor alpha

NF-E2 P45-related factor 2 (Nrf2) is a key transcription factor that controls genes encoding cytoprotective and detoxifying enzymes through antioxidant response elements (AREs) in their regulatory regions. We reported recently that retinoid X receptor alpha (RXRα) inhibits Nrf2 function by direct interaction with the Neh7 domain of Nrf2 in a ligand-independent manner. Here, we provide evidence that an RXRα-specific ligand, bexarotene, dose-dependently inhibits the mRNA expression of ARE-driven genes. Knock-down of RXRα by siRNA abolished the inhibitory effect of bexarotene. Conversely, the over-expression of RXRα enhanced the inhibition by bexarotene, indicating that the effect is mediated by RXRα. The inhibition by bexarotene was also found in the non-small-cell lung cancer cell line A549, which carries a dysfunctional somatic mutation of Kelch-like ECH-associated protein 1 (KEAP1), suggesting that KEAP1 is not involved. Our results demonstrate that rexinoid is able to inhibit the transcriptional activity of Nrf2, and that RXRα can repress the cytoprotection pathway in a ligand-dependent manner.

Topical and oral bexarotene

Bexarotene is a retinoid that specifically binds retinoid X receptors and has numerous effects on cellular growth and differentiation. It is approved for the treatment of cutaneous T cell lymphoma both topically and systemically. Adverse effects include hyperlipidemia, central hypothyroidism, and neutropenia with bexarotene capsules, and an irritant dermatitis with bexarotene gel. With aggressive management of these potential side effects, bexarotene is an additional option in the armamentarium for management of cutaneous T cell lymphoma.

Endocrine side-effects of anti-cancer drugs: the impact of retinoids on the thyroid axis

Bexarotene (Targretin), approved since 1999 as a second-line treatment for late stage cutaneous T-cell lymphomas, has been shown to induce significant hypothyroidism through TSH suppression. This review revisits, through a case report, mechanisms by which rexinoids repress the expression of TSHB gene as well as αTSH and TRH genes. It appears that rexinoids suppress TSH independently from tri-iodothyronine. Bexarotene also differently affects the gene expression of deiodinases 1 and 2 as well as the peripheral clearance of thyroxine. These data might open new ways of research on the potential interaction between thyroid axis and endogenous rexinoids.

Role of bexarotene in the treatment of cutaneous T-cell lymphoma: the clinical and immunological sides

Cutaneous T-cell lymphomas (CTCLs) are a heterogeneous group of lymphoid neoplasms. The incidence of CTCLs has risen over the last three decades. The most common CTCLs are mycosis fungoides and Sèzary syndrome. Therapies for CTCLs are various and range from skin-directed therapy to chemotherapy. Retinoids have been used in CTCL treatment since the 1980s with good results. Bexarotene is the first retinoid approved by the US FDA for CTCL therapy. Since then, numerous experiences of both its efficacy and mechanism of action have been reported. The aim of this paper is to review bexarotene action on CTCLs, as well as to highlight its immunological targets.

Chemopreventive efficacy of raloxifene, bexarotene, and their combination on the progression of chemically induced colon adenomas to adenocarcinomas in rats

Estrogen receptor (ER)-β signaling is associated positively in colon tumor progression, whereas downregulation or loss of function of retinoid X receptor (RXR)-α occurs in colon tumors. The chemopreventive efficacies of the estrogen antagonist raloxifene and the selective RXR agonist bexarotene were tested individually and in combination, during promotion and progression stages of colon tumorigenesis. Colon tumors were induced in male F344 rats with azoxymethane and at early adenoma stage, groups of rats (36 or 45 per group) were fed diets containing raloxifene (1.5 or 3 ppm), bexarotene (50 or 100 ppm), or their low-dose combinations for 40 weeks. Raloxifene or bexarotene alone significantly suppressed colon adenocarcinoma formation in terms of multiplicities (mean ± SE): control, 3.59 ± 0.25; 1.5 ppm raloxifene, 2.51 ± 0.29 (P < 0.004); 3 ppm raloxifene, 2.14 ± 0.28 (P < 0.0001); 50 ppm bexarotene, 2.25 ± 0.32 (P < 0.001); 100 ppm bexarotene, 2.1 ± 0.27 (P < 0.0001); and 1.5 ppm raloxifene + 50 ppm bexarotene, 1.57 ± 0.21 (P < 0.0001). The low-dose combination caused significant (56%) inhibition of adenocarcinomas as compared with control diet fed rats. Tumors exposed to raloxifene, bexarotene and/or the combination showed significant suppression of proliferating cell nuclear antigen, cyclin D1, and β-catenin with an increased apoptotic cells (3-fold) and p21 expression (3.8-fold) as compared tumors of rats fed control diet. The combination of low doses of raloxifene and bexarotene significantly suppressed the progression of colonic adenomas to adenocarcinomas and may be useful for colon cancer prevention and/or treatment in high-risk individuals.

Bexarotene in cutaneous T-cell lymphoma: third retrospective study of long-term cohort and review of the literature

BACKGROUND

Bexarotene was approved for cutaneous T-cell lymphoma (CTCL) in 1999. Apart from the two first clinical trials published ten years ago, very few data were published on the long-term use of bexarotene in CTCL patients.

OBJECTIVES

We performed a retrospective review of CTCL patients treated with bexarotene at a single skin Cancer department between 2002 and 2012. We aimed to determine retrospectively the long-term tolerability and outcome of bexarotene in a cohort of CTCL patients and to compare these results with data from the literature.

RESULTS

Thirty-two patients were included (18 men/14 women); 20 patients had a mycosis fungoïdes and 12 a Sézary syndrome. The longest bexarotene treatment duration observed was 65.2 months and 10 patients were treated for more than 24 months. A clinical response was reported in 60% of all patients and in 75% of patients with Sézary syndrome. Most common drug-related adverse events were hypothyroidism (94%), hypertriglyceridemia (78%) and hypercholesterolemia (44%). Most events (84%) were mild to moderate.

CONCLUSIONS

This study with a very long observation time confirms that bexarotene is well tolerated by CTCL patients during long-term use. It is effective in early and advanced stages of CTCL.

Oral retinoids and rexinoids in cutaneous T-cell lymphomas

Retinoids are biologically active derivatives of vitamin A modulating cell proliferation, differentiation, apoptosis and altering the immune response. They have been used for years in therapy of cutaneous T-cell lymphomas (CTCL) but the exact mechanism of retinoids' action is unclear. It is based on the presence of specific receptors' families, mediating the biological effects of retinoids on the tumor cells: retinoic acid receptor (RAR) and retinoic X receptor (RXR). Orally administrated bexarotene, the first synthetic selective RXR retinoid, was revealed to be active against the cutaneous manifestation of CTCL. The toxicity profile caused by bexarotene seems to be more limited to laboratory values and better tolerated than classical retinoids, but generally associated with more severe grades of toxicity. Both selective retinoic acid receptor- and retinoic X receptor-mediated retinoids have modest objective response rates and, therefore, most likely will have limited impact as monotherapeutic agents. However, the immunomodulatory effects of RAR and RXR retinoids provide a rational basis for using retinoids in combination with other biologic immune response modifiers, phototherapy and radiotherapy. The authors reviewed the literature on the results of the use of retinoids and rexinoids in patients with mycosis fungoides and Sézary syndrome.

Cell death signaling and anticancer therapy

For a long time, it was commonly believed that efficient anticancer regimens would either trigger the apoptotic demise of tumor cells or induce a permanent arrest in the G₁ phase of the cell cycle, i.e., senescence. The recent discovery that necrosis can occur in a regulated fashion and the increasingly more precise characterization of the underlying molecular mechanisms have raised great interest, as non-apoptotic pathways might be instrumental to circumvent the resistance of cancer cells to conventional, pro-apoptotic therapeutic regimens. Moreover, it has been shown that some anticancer regimens engage lethal signaling cascades that can ignite multiple oncosuppressive mechanisms, including apoptosis, necrosis, and senescence. Among these signaling pathways is mitotic catastrophe, whose role as a bona fide cell death mechanism has recently been reconsidered. Thus, anticancer regimens get ever more sophisticated, and often distinct strategies are combined to maximize efficacy and minimize side effects. In this review, we will discuss the importance of apoptosis, necrosis, and mitotic catastrophe in the response of tumor cells to the most common clinically employed and experimental anticancer agents.

Investigational histone deacetylase inhibitors for non-Hodgkin lymphomas

IMPORTANCE OF THE FIELD

Histone deacetylase inhibitors (HDIs) have been shown effective as single agents for cutaneous T-cell lymphomas, peripheral T-cell lymphomas, and B-cell lymphomas, such as follicular lymphoma and mantle cell lymphoma. Of interest, HDIs in combination with other drugs can be a treatment for Epstein-Barr virus-associated lymphoproliferative disorders. Our data of gene expression profiles in PBMCs of responders to vorinostat was discussed.

AREAS COVERED IN THIS REVIEW

This review summarizes recent clinical trials of HDIs in non-Hodgkin lymphomas, the effects of HDIs in in vitro and mouse models, and the possibility of future combination treatments.

WHAT THE READER WILL GAIN

The HDI dosing schedule is crucial to optimize outcomes and avoid irreversible adverse effects. Responses to HDIs are slow, highlighting the need to continue treatment until the maximum response is achieved. HDIs cause hyperacetylation of histone and nonhistone proteins, resulting in various effects on neoplastic cells and immune responses in their microenvironment.

TAKE HOME MESSAGE

Even though HDIs are not potent as single agents, they are likely to provide promising therapeutic options when combined with other agents, i.e., BCL2/BCL-XL antagonists and proteasome inhibitors. Future studies should seek to identify biomarkers that predict patient responses to HDIs.

Absence of modulation of CD4+CD25 regulatory T cells in CTCL patients treated with bexarotene

Cutaneous T-cell lymphoma (CTCL) are a heterogeneous group of lymphoproliferative disorders, characterized by the infiltration of the epidermis by mature and activated malignant CD4+ T-lymphocytes. Retinoids such as retinoic acid and synthetic analogues have long been used alone or in combination with other therapies for CTCL. Bexarotene, the first synthetic highly selective RXR retinoid, was approved for the treatment of all stages of CTCL in patients refractory to at least one systemic therapy. Recently, six cases in which the initiation of bexarotene therapy for CTCL was associated with the progression of internal disease despite improvement of cutaneous signs and symptoms were reported. Moreover, it has been established that retinoids promote the generation of CD4+ Foxp3+ regulatory T cells, raising the question of an induction of regulatory T-cells by bexarotene. The aim of this work was to determine if bexarotene induces an increase of functional regulatory T cells which could play a role in the development of secondary extra-cutaneous lymphomas. Regulatory T cells were studied both in cutaneous biopsy specimens using an immunohistochemical analysis of CD4, CD25 and Foxp3 and in blood where proportion and functionality of circulating CD4+CD25(high) T-cells were determined. The study was performed in 10 patients [five patients with Sézary syndrome (SS) and five mycosis fungoïdes (MF)], treated for 6 months with bexarotene. Four healthy donors were used as controls for phenotypic and functional analysis on PBL. We found that the frequency of CD4+CD25(high) Treg cells was not significantly different before starting bexarotene and after 6 months of treatment in CTCL patients. However, we observed that the frequency of CD4+CD25(high) Treg cells before the beginning of the treatment was significantly increased compared to healthy donors. In addition, functional assays demonstrated that Foxp3 expressing CD4+CD25(high) T-cells were capable of suppressing autologous CD4 + CD25- T-cell proliferation. In the present work, we detected the presence of functional circulating CD4+CD25(high) Foxp3+ regulatory T-cells in CTCL patients, with an increased frequency compared to healthy donors. The treatment with bexarotene does not seem to affect the regulatory T-cell compartment.

Malignant T cells in cutaneous T-cell lymphoma lesions contain decreased levels of the antiapoptotic protein Ku70

BACKGROUND

Malignant T cells in primary cutaneous T-cell lymphoma (CTCL) are genetically unstable and exhibit prolonged lifespans potentially explained by dysregulation of apoptosis, yet are responsive to apoptosis-inducing therapies. The heterodimeric protein Ku70/80 is known to play a role in DNA repair (Ku70 and Ku80) and inhibition of apoptosis (Ku70 only).

OBJECTIVES

To investigate the expression of Ku70/80 in CD3+ T cells derived from skin and blood in patients with CTCL and normal samples, as well as benign dermatoses.

METHODS

Normal (n=10), CTCL (n=9) and benign dermatoses (n=13) skin samples were stained for confocal imaging of Ku70/80 and CD3 and analysed using imaging software. Circulating CD4+ T cells in normal and CTCL peripheral blood were analysed by flow cytometry and Western blot for Ku70/80 expression (n=6).

RESULTS

Ku70 and Ku80 were significantly diminished in T cells of CTCL lesions relative to T cells of control skin. Decreased T-cell Ku70 expression was not a feature of the benign dermatoses psoriasis and contact dermatitis, suggesting that loss of Ku70/80 in CTCL is not simply the result of cutaneous inflammation. Reduced Ku70 was also noted in circulating CD4+ T cells in patients with CTCL with peripheral blood involvement.

CONCLUSIONS

Deficient expression or lack of Ku70/80 may result in genomic instability and play a role in tumorigenesis, as well as account for the increased susceptibility of malignant T cells to apoptosis-inducing treatment modalities in the setting of intrinsic resistance to apoptosis.

Clinical and in vitro resistance to bexarotene in adult T-cell leukemia: loss of RXR-alpha receptor

The oral rexinoid bexarotene (Targretin) is widely used for treatment of cutaneous T-cell lymphomas (CTCL). We recently reported the first case of adult T-cell leukemia/lymphoma (ATLL) that responded rapidly to combination therapy of bexarotene and interferon (IFN)-alpha2b with complete clinical response. We demonstrated that bexarotene induced apoptosis of the patient's malignant peripheral blood T-cells in vitro. However, our patient developed skin and nodal relapse 180 days after starting treatment. We now demonstrate that his peripheral blood malignant T cells became resistant to bexarotene-induced apoptosis. We investigated potential mechanisms that may cause aberrations in the retinoid X receptor (RXR) subunits, RXR-alpha and RXR-beta, to account for these findings. Sequence analysis did not reveal acquisition of mutations in the genes encoding RXR-alpha and RXR-beta by resistant cells. We assessed RXR-alpha and RXR-beta expression by Western blot analysis and found that resistant cells had significantly decreased RXR-alpha expression compared with pretherapy bexarotene-sensitive cells. Our findings indicate that reduced expression of the RXR-alpha receptor subunit may represent a mechanism for resistance to bexarotene in T-cell malignancies.

The optimal use of bexarotene in cutaneous T-cell lymphoma

The management goal in cutaneous T-cell lymphomas (CTCLs) is to improve symptoms and induce remission. Early-stage disease is generally treated with skin-directed therapies. However, if these do not control the disease, systemic therapy becomes necessary. Bexarotene, a novel rexinoid, is an oral, noncytotoxic drug that has been approved in Europe for the treatment of refractory advanced-stage CTCL and in the U.S.A. for refractory CTCL. We provide guidance on the use of bexarotene in the management of CTCL, based on data from phase II/III clinical trials and the authors' clinical experience, and suggest how the potential of the drug can be maximized. The clinical trial results with bexarotene are reviewed, especially in comparison with interferon-alpha, which is the other commonly used noncytotoxic systemic therapy for CTCL. A treatment algorithm for bexarotene in refractory CTCL is suggested. As bexarotene may take time to achieve a maximum response, this algorithm recommends that therapy should be continued for a sufficient period to allow for a delayed onset of action. In addition, possible combination therapies with bexarotene are discussed. We conclude that bexarotene is effective in the management of CTCL, and has the advantage of oral administration. An on-going randomized clinical trial comparing psoralen plus ultraviolet A (PUVA) with PUVA plus bexarotene will provide valuable information about this combination regimen in early-stage disease, but further data are needed on the relative efficacies of other combination therapies with bexarotene in CTCL.

Bexarotene blunts malignant T-cell chemotaxis in Sezary syndrome: reduction of chemokine receptor 4-positive lymphocytes and decreased chemotaxis to thymus and activation-regulated chemokine

The malignant cells in Sezary syndrome express the skin trafficking molecules' cutaneous lymphocyte associated antigen (CLA) and chemokine receptor 4 (CCR4). High levels of the CCR4 ligand, thymus, and activation-regulated chemokine (TARC), have been reported in the blood and skin of patients. The rexinoid X-receptor specific retinoid, bexarotene, has contributed to the resolution of cutaneous disease among patients. To evaluate the effects of bexarotene on skin trafficking molecule expression and chemotaxis, peripheral blood mononuclear cells from Sezary syndrome patients and healthy controls were treated with bexarotene in vitro. CCR4 and CLA expression levels and chemotaxis in response to TARC (6.25 ng/ml) were evaluated among lymphocytes before and after treatment with bexarotene (10 microM). Flow cytometric analysis was performed to evaluate CD4, CD26, CLA, and CCR4 cell surface expression. Transwell migration assays were performed to evaluate chemotaxis to TARC. Prior to treatment, malignant cells exhibited higher CCR4 expression (45-90%) and greater than four times more chemotaxis to TARC compared with healthy controls. After treatment with bexarotene for 36-96 hr, a 28% reduction in CCR4 expression was noted (P < 0.05) among the malignant population with an associated 9% decrease in chemotaxis to TARC (P < 0.05). Our results show that bexarotene may inhibit malignant cell trafficking to the skin through an ability to suppress CCR4 expression among Sezary syndrome lymphocytes.

Results of a Phase II trial of oral bexarotene (Targretin) combined with interferon alfa-2b (Intron-A) for patients with cutaneous T-cell lymphoma

BACKGROUND

Bexarotene is one of the most active single agents for the treatment of recurring or refractory cutaneous T-cell lymphoma (CTCL). Interferon alfa has also been used for many years as an effective treatment for this disease. The results in recent case reports of the combination of bexarotene and interferon alfa have been promising. Based on more extensive results reported with the combination of other retinoids with interferon alfa, the present study attempted to determine the response rate, response duration, and safety of bexarotene (Targretin capsules, Ligand Pharmaceuticals, San Diego, Calif) alone and then with the addition of interferon alfa-2b (Intron-A, Schering-Plough, Kenilworth, NJ).

METHODS

Patients with biopsy-proven CTCL, TNM stages IB, IIA, IIB-IV, were treated with oral bexarotene 300 mg/m2/day for at least 8 weeks. If a complete response was not seen after 8 weeks, interferon alfa-2b 3 million units (MU) subcutaneously was added, and increased to 5 MU if tolerated, 3 times a week.

RESULTS

A total of 22 patients were enrolled at 5 sites, and 18 patients were assessable for response. Overall response rate for combined bexarotene and interferon alfa was 39% (95% confidence interval [CI]: 17%-64%), including 1 patient with a clinical complete response, 6 patients with partial response, 3 patients with stable disease, and 8 patients with progressive disease. Three partial responses were first noted during the bexarotene-alone phase. Adverse events were generally manageable, and only 1 patient was withdrawn from study for hypertriglyceridemia.

CONCLUSIONS

The addition of interferon alfa-2b did not increase the response rate that would have been expected with bexarotene alone.

Juvenile mycosis fungoides treated with bexarotene and PUVA

A 14-year-old Caucasian boy presented with a 4-month history of a slightly pruritic eruption that began on the hips and later extended to the trunk and upper and lower limbs. The patient did not present fever, weight loss, or asthenia. Physical examination revealed multiple, red, desquamative, oval patches with areas of healthy skin between them, which covered nearly 50% of the body surface area. The palms, soles, face, and mucosa were not affected. In addition, he presented two violet-colored infiltrated plaques on the left thigh and right buttock (Fig. 1). There were multiple, > 1 cm, freely mobile, axillary and inguinal nodes. In follow-up, the patient developed two red-colored, mobile, well-delimited cutaneous nodules of 2.5 cm in diameter in the right hemithorax and lumbar area. The lumbar nodule regressed spontaneously before treatment. The clinical diagnosis was mycosis fungoides. We obtained three skin biopsies, one from a patch lesion and the others from a nodule; the third was sent to a reference hospital to determine the rearrangement. Histologic examination was similar in the three biopsies and revealed an atypical lymphoid infiltrate in the superficial dermis with epidermotropism and a tumoral nodule of atypical, small-sized lymphocytes in the deep dermis and subcutaneous level (Fig. 2). The atypical infiltrate was CD3+, CD4+, CD8-, T-cell intracellular antigen (TIA)+/-, Epstein-Barr-encoded RNA (EBER)-, and CD56-. The biopsy of one left axillary adenopathy was compatible with mycosis fungoides (Fig. 3). Amongst the additional tests carried out was a blood analysis showing 5300 leukocytes (neutrophils, 35%; lymphocytes, 40.7%; monocytes, 16.8%; eosinophils, 6.40%) without Sézary cells, normal lactate dehydrogenase (LDH), immunoglobulin E (IgE) of 497 U/mL (normal, 3-100 U/mL), and beta2-microglobulin of 3.09 mg/L (normal, 1.64 +/- 0.58 mg/L). A bone marrow study and a thoraco-abdomino-pelvic scan were normal. The rearrangement in the skin was monoclonal, whereas in peripheral blood and lymph nodes it was polyclonal. With the diagnosis of mycosis fungoides stage IVA (according to the TNM classification), treatment was initiated with psoralen plus ultraviolet light A (PUVA), three times a week, plus oral bexarotene at a dose of 300 mg/m2/day. The parents were informed that this treatment was not approved for this age group and informed consent was obtained. The clinical tolerance to bexarotene was very good, although low doses of atorvastatin (10 mg/day) and 75-100 mg of thyroxine were needed to control the expected adverse reactions to oral retinoid. After 32 sessions of PUVA and 6 months of treatment with oral bexarotene, the skin patches regressed, except for the plaque on the left buttock and the nodule on the right hemithorax (Fig. 4). There was no evidence of lymphadenopathy clinically or via sonographic evaluation. Bexarotene was discontinued after patient clearance and resolution of adenopathies. Nevertheless, 5 months after discontinuation of oral treatment, the patient developed multiple, scaling, nonconfluent macules on the trunk and arms affecting almost 30% of the body surface area, which disappeared with the application of methylprednisolone aceponate. He did not present significant lymphadenopathies.

High Clinical Response Rate with Multimodality Immunomodulatory Therapy for Sézary Syndrome

PURPOSE

The goal of this study was to evaluate the clinical response rate of patients with Sézary syndrome (SS) to multimodality immunomodulatory therapy consisting of extracorporeal photopheresis in combination with >/= 2 systemic biologic response modifiers (interferon-, interferon-, retinoids, and/or sargramostim) and psoralen plus UV-A.

PATIENTS AND METHODS

Twenty-eight patients who met established criteria for SS were treated with multimodality immunomodulatory therapy at the Hospital of the University of Pennsylvania between January 2000 and December 2002. All patients received > 6 cycles of extracorporeal photopheresis. Patients were categorized into groups based on their response to therapy.

RESULTS

An overall clinical response of 89% was achieved with multimodality immunomodulatory therapy. Twenty-nine percent of patients exhibited a complete response, characterized by no evidence of cutaneous disease and a Sézary count 5%. Sixty-one percent exhibited a partial response. Eleven percent were nonresponders.

CONCLUSION

Based on our experience, multimodality immunomodulatory therapy is an exceptionally effective treatment for SS. The durability of response and impact on overall survival remains to be determined; however, this approach offers an appealing alternative to treatments associated with higher morbidity rates.

Mycosis fungoides and sezary syndrome: An update

Mycosis fungoides (MF), and the associated leukemic variant Sezary Syndrome (SS), are the most common group of cutaneous T-cell lymphomas. MF/SS is a non-Hodgkin's lymphoma of mature, skin-homing, clonal, malignant T lymphocytes that initially presents in the skin as patches, plaques, tumors, or generalized erythema (erythroderma) and can involve the lymph nodes and peripheral blood. Much progress has been made in recent years in understanding the origin of the malignant T cell in MF/SS and the pathophysiology and immunology of the disease. This recent work has made a great impact on diagnosis, prognostication, and treatment. In this review, we survey the MF/SS published literature over the past year and highlight some of the important advances.

Organ-specific expression profiles of rat mammary gland, liver, and lung tissues treated with targretin, 9-cis retinoic acid, and 4-hydroxyphenylretinamide

A rexinoid, targretin, and two retinoids, 9-cis retinoic acid (9cRA) and 4-hydroxyphenylretinamide (4HPR), were examined for their effects on gene expression in rat mammary gland, liver, and lung tissues. The chemopreventive effects of these agents have largely been attributed to their ability to interact with retinoic acid receptors (RAR) and/or retinoid X receptors (RXR). Targretin interacts with the RXR receptors. 9cRA interacts with both the RAR and RXR receptors, whereas 4HPR has a moderate affinity primarily for RAR gamma. Based on previous studies on mammary chemoprevention, targretin (150 mg/kg diet), 9cRA (100 mg/kg diet), and 4HPR (782 mg/kg diet), were administered to rats continually in their diet for 7 days. Tissue- and agent-specific expression differences were determined by comparing tissues from treated rats with those from rats given a control diet. There were significantly more changes associated with targretin than 9cRA or 4HPR. Only a limited number of expression changes were found with 4HPR treatment. For each organ, targretin- and 9cRA-treated tissues clustered closely together, whereas 4HPR-treated tissues clustered with the tissues from the control diet group. In contrast to 9cRA treatment, targretin treatment altered genes that involved fatty acid metabolism and modulation of various cytochromes P450 in the liver, clearly demonstrating the very disparate nature of these two retinoids. These expression signatures could provide useful pharmacodynamic biomarkers for retinoid treatment and chemoprevention.

Bexarotene in the treatment of cutaneous T-cell lymphoma

Primary cutaneous T-cell lymphomas encompass a spectrum of non-Hodgkin's lymphomas that are characterised by clonal proliferation of skin-homing malignant T lymphocytes. Mycosis fungoides and the leukaemic variant Sézary syndrome, collectively referred to as cutaneous T-cell lymphomas, are the most common entities. No curative therapy exists and patients ultimately develop advanced or relapsed disease that is refractory to standard treatment options. Therefore, there is a great need for the development of novel emerging therapies. Bexarotene is the first synthetic nuclear retinoid X receptor-selective retinoid approved by the FDA for the treatment of refractory cutaneous T-cell lymphoma in all stages, as both an oral capsule and a topical gel formulation. Bexarotene was found to induce apoptosis in a variety of preclinical in vitro and in vivo models including cutaneous T-cell lymphoma cells, and has shown efficacy in two multi-centre, open-label Phase II - III clinical trials for early and advanced stages of cutaneous T-cell lymphoma in patients who have failed or were refractory to standard therapies. New insights into the immunomodulatory function of bexarotene have indicated opportunities for combined treatment with IFN-alpha, denileukin diftitox or phototherapy. This article reviews the biological properties, pharmacokinetics, clinical efficacy, safety and role of bexarotene in the treatment of cutaneous T-cell lymphoma.

The New World Health Organization–European Organization for Research and Treatment of Cancer Classification of Cutaneous Lymphomas

The WHO-EORTC classification of cutaneous lymphomas is a good start to unifying nomenclature, a necessity before coherent consensus diagnoses can be made. There are three provisional diagnoses in this new classification that are not covered in detail in this review because they are rare diseases that still require further study for definitive classification. Much remains to be elucidated about cutaneous lymphomas, but understanding of the major entities within the new classification is an important first step in understanding these diverse diseases.

Immunopathogenesis and therapy of cutaneous T cell lymphoma

Cutaneous T cell lymphomas (CTCLs) are a heterogenous group of lymphoproliferative disorders caused by clonally derived, skin-invasive T cells. Mycosis fungoides (MF) and Sezary syndrome (SS) are the most common types of CTCLs and are characterized by malignant CD4(+)/CLA(+)/CCR4(+) T cells that also lack the usual T cell surface markers CD7 and/or CD26. As MF/SS advances, the clonal dominance of the malignant cells results in the expression of predominantly Th2 cytokines, progressive immune dysregulation in patients, and further tumor cell growth. This review summarizes recent insights into the pathogenesis and immunobiology of MF/SS and how these have shaped current therapeutic approaches, in particular the growing emphasis on enhancement of host antitumor immune responses as the key to successful therapy.