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.

The novel function of bexarotene for neurological diseases.

Bexarotene, a retinoid X receptor (RXR) agonist, is approved by FDA to treat cutaneous T-cell lymphoma. However, it has also demonstrated promising therapeutic potential for neurological diseases such as stroke, traumatic brain injury, Parkinson's disease, and particularly Alzheimer's disease(AD). In AD, bexarotene inhibits the production and aggregation of amyloid ß (Aß), activates Liver X Receptor/RXR heterodimers to increase lipidated apolipoprotein E to remove Aß, mitigates the negative impact of Aß, regulates neuroinflammation, and ultimately improves cognitive function. For other neurological diseases, its mechanisms of action include inhibiting inflammatory responses, up-regulating microglial phagocytosis, and reducing misfolded protein aggregation, all of which aid in alleviating neurological damage. Here, we briefly discuss the characteristics, applications, and adverse effects of bexarotene, summarize its pharmacological mechanisms and therapeutic results in various neurological diseases, and elaborate on the problems encountered in preclinical research, with the aim of providing help for the further application of bexarotene in central nervous system diseases.

Cost-Effectiveness of Brentuximab Vedotin Versus Physician's Choice of Methotrexate or Bexarotene for the Treatment of Cutaneous T-cell Lymphoma in Canada.

INTRODUCTION: Brentuximab vedotin versus physician's choice of methotrexate (MTX) or bexarotene (BEX) significantly improved progression-free survival (PFS) (median PFS, 16.7 vs. 3.5 months) and delayed time to subsequent treatment (8.4 vs. 3.7 months), with similar overall survival in patients with CD30-expressing mycosis fungoides (MF) or primary cutaneous anaplastic large cell lymphoma (pcALCL), two types of cutaneous T-cell lymphomas. We assessed the cost-effectiveness of brentuximab vedotin versus MTX or BEX from a Canadian healthcare payer perspective in the indicated population. METHODS: A 5-state partitioned survival model [pre-progression, non-stem cell transplant (SCT) post-progression, SCT, SCT relapse, death] with a weekly cycle length and 45-year lifetime horizon has been developed. Health-state occupancies, utility estimates, and treatment duration were informed by ALCANZA. Other inputs and costs came from the literature or clinician experts. Scenario analyses varied key parameters and tested assumptions. RESULTS: Brentuximab vedotin versus MTX or BEX was cost-effective; the incremental cost-effectiveness ratio was CAN$43,790 per quality-adjusted life year (QALY) gained. Brentuximab vedotin was more effective (incremental life years: 0.15; QALYs: 0.25) and total treatment costs were slightly higher (incremental costs: $11,105) than MTX or BEX. Key model drivers included end-stage care duration, SCT eligibility, and brentuximab vedotin retreatment rates. CONCLUSION: Brentuximab vedotin compared with MTX or BEX was cost-effective for CD30-expressing MF and pcALCL. Brentuximab vedotin's higher drug costs versus MTX or BEX were offset by decreased post-progression and end-stage management costs, and showed a 0.25 QALY gain versus MTX or BEX, and increased the proportion of patients eligible for potentially curative SCT.

Mogamulizumab and bexarotene are a promising association for the treatment of advanced cutaneous T-cell lymphomas: a case series.

BACKGROUND: Treatment choices for patients with advanced-stage mycosis fungoides (MF) or Sézary syndrome (SS) who have failed first-line systemic therapies can be challenging, as several options are available. However, most evidence is based on observational and early phase studies due to the rarity of the disease. Mogamulizumab has recently been approved for the treatment of adult patients with MF or SS who have received at least one prior systemic therapy; it has a good tolerability profile prompting its use in combination with other agents. This article aims at describing the role of the concomitant use of bexarotene with mogamulizumab in this setting. CASES PRESENTATION: To add information in the field, we describe our experience with four patients with MF/SS who failed first- and second-line treatments and started the combination mogamulizumab in addition to bexarotene. The combination of bexarotene with mogamulizumab in patients with advanced MF/SS after the failure of bexarotene alone obtained a response in all the four patients observed. The response was maintained longer than expected. CONCLUSIONS: The combination is promising and deserves further study.

Bexarotene enhances astrocyte phagocytosis via ABCA1-mediated pathways in a mouse model of subarachnoid hemorrhage.

BACKGROUND AND PURPOSE: Enhancing phagocytosis can facilitate the removal of inflammatory molecules, limit the toxicity of dead cells and debris, and promote recovery after brain injury. In this study, we aimed to explore the role of bexarotene (Bex), a retinoid X receptor (RXR) agonist, in promoting astrocyte phagocytosis and neurobehavioral recovery after subarachnoid hemorrhage (SAH). METHODS: Mice SAH model was induced by pre-chiasmatic injection of blood. Modified Garcia score, novel object recognition, rotarod test, and Morris water maze were performed to assess neurological function. Immunofluorescence and electron microscopy were used to evaluate astrocyte phagocytosis in vivo. In addition， ABCA1/MEGF10&GULP1, the primary astrocyte phagocytosis pathway, were stimulated by Bex or suppressed by HX531 (a RXR antagonist) to evaluate their impacts on astrocyte phagocytosis and neurological recovery. RESULTS: Astrocytes phagocytosis of blood components were observed in mice after SAH induction, which is further increased by Bex treatment. Bex dramatically attenuated neuroinflammation, reduced brain edema, improved early neurological performance and promoted neurocognitive recovery. Meanwhile, Bex decreased neurotoxic reactive astrocytes and preserved neurogenesis after SAH. Bex increased the expression of astrocyte phagocytosis-related proteins ABCA1, MEGF10, and GULP1. Bex also increased the lysosomal processing of engulfed blood components in astrocytes. Moreover, Bex significantly promoted astrocytes to phagocytize debris in vitro by increasing the expression of ABCA1, MEGF10 and GULP1, while HX531 inhibited astrocyte phagocytosis and decreased these protein levels. CONCLUSIONS: Bex enhanced astrocyte phagocytosis through the ABCA1-mediated pathways, and promoted neurobehavior recovery in mice after SAH induction.

Inhibition of Integrin αVß3 Signaling Improves the Antineoplastic Effect of Bexarotene in Cutaneous T-Cell Lymphoma.

Bexarotene is a specific retinoid X receptor agonist that has been used for the treatment of cutaneous T-cell lymphoma (CTCL). Because bexarotene causes hypothyroidism, it requires the administration of levothyroxine. However, levothyroxine, in addition to its ubiquitous nuclear receptors, can activate the αVß3 integrin that is overexpressed in CTCL, potentially interfering the antineoplastic effect of bexarotene. We thus investigated the biological effect of levothyroxine in relation to bexarotene treatment. Although in isolated CTCL cells levothyroxine decreased, in an αVß3-dependent manner, the antineoplastic effect of bexarotene, levothyroxine supplementation in preclinical models was necessary to avoid suppression of lymphoma immunity. Accordingly, selective genetic and pharmacologic inhibition of integrin αVß3 improved the antineoplastic effect of bexarotene plus levothyroxine replacement while maintaining lymphoma immunity. Our results provide a mechanistic rationale for clinical testing of integrin αVß3 inhibitors as part of CTCL regimens based on bexarotene administration. TEASER: Inhibiting αVß3 integrin improves the antineoplastic effect of bexarotene while maintaining lymphoma immunity.

Remyelination in humans due to a retinoid-X receptor agonist is age-dependent.

Remyelination efficiency declines with advancing age in animal models, but this has been harder to demonstrate in people with multiple sclerosis. We show that bexarotene, a putatively remyelinating retinoid-X receptor agonist, shortened the visual evoked potential latency in patients with chronic optic neuropathy aged under 42 years only (with the effect diminishing by 0.45 ms per year of age); and increased the magnetization transfer ratio of deep gray matter lesions in those under 43 years only. Addressing this age-related decline in human remyelination capacity will be an important step in the development of remyelinating therapies that work across the lifespan.

Low-dose total skin electron beam therapy plus oral bexarotene maintenance therapy for cutaneous T-cell lymphoma.

BACKGROUND: Total skin electron beam therapy (TSEBT) combined with systemic therapy or maintenance treatment is a reasonable approach to enhance the remission rate and duration in mycosis fungoides (MF) and Sézary syndrome (SS). This study assesses the efficacy of oral bexarotene therapy after low-dose TSEBT for patients with MF and SS. METHODS: In this prospective observational study, we recruited MF/SS patients for treatment with low-dose total skin electron beam therapy (TSEBT) with or without bexarotene therapy to describe outcomes and toxicities. RESULTS: Forty-six subjects with MF or SS underwent TSEBT between 2016 and 2021 at our institute. Following TSEBT, 27 patients (59 %) received oral bexarotene treatment. The median follow-up was 13 months. The overall response rate (ORR) for the cohort was 85 %. The response rate was significantly higher with combined modality (CM) than TSEBT alone (96 % vs. 68 %, p = 0.03). Median progression-free survival (PFS) for the CM was 17 months versus five months following TSEBT alone (p = 0.001). One patient (4 %) in the retinoid group discontinued the bexarotene therapy because of adverse events. The administration of bexarotene therapy did not increase radiation-related toxicities. CONCLUSIONS: Response rate and progression-free survival might be improved with TSEBT in combination with oral bexarotene compared to TSEBT alone.

Disease characteristics, prognosis, and response to therapy in patients with large-cell transformed mycosis fungoides: A single-center retrospective study.

BACKGROUND: Mycosis fungoides with large-cell transformation (MF-LCT) is associated with an aggressive clinical course, yet data comparing treatment outcomes in MF-LCT are sparse. OBJECTIVE: To compare treatment outcomes and to determine disease prevalence and characteristics associated with survival in MF-LCT. METHODS: A retrospective review was conducted of mycosis fungoides patients from 2012 to 2020 treated at Thomas Jefferson University. Patients with histopathologic diagnosis of MF-LCT were included. Treatment outcomes were assessed by mean changes in the modified Severity Weighted Assessment Tool (mSWAT) and stage. RESULTS: Of 171 patients with mycosis fungoides, 23 (13.4%) had histologic diagnosis of MF-LCT. The overall 5-year survival rate for MF-LCT was 74% and was not significantly associated with sex, age, or initial stage at the time of MF-LCT diagnosis. Brentuximab vedotin showed the greatest mean decrease in mSWAT (-20.53) and stage progression (change in Δ stage: -0.4) in MF-LCT compared to oral bexarotene (ΔmSWAT: +4.51; Δstage: +0.27), skin-directed therapy (ΔmSWAT: -5.93; Δstage: -0.08), and chemotherapy (ΔmSWAT: +4.97; Δstage: +0.85). LIMITATIONS: Single-center retrospective design, and patients often on multiple treatment modalities. CONCLUSIONS: We report superior treatment outcomes for brentuximab vedotin compared to oral bexarotene, skin-directed therapy, and chemotherapy in MF-LCT in both early and advanced disease.

Alitretinoin in the treatment of cutaneous T-cell lymphoma.

INTRODUCTION: In this survey, we analyzed data from patients suffering from the most common cutaneous T-cell lymphomas (CTCLs) subtypes mycosis fungoides (MF) and Sézary syndrome (SS), treated with the retinoid alitretinoin during a 7-year period at our outpatient department between 2015 and 2020. MATERIALS AND METHODS: We analyzed patient medical records including TNMB stage, side effects under therapy with alitretinoin, time to next treatment (TTNT), and previous photo documentation. RESULTS: A total of 35 patients with MF (n = 28) and SS (n = 7) were included in the study, of whom 69% were male and 31% were female. The mean age of onset was 56 ± 15 years in MF and 65.4 ± 10.8 years in SS with 51.4% having early stage (IA-IIA) and 48.6% having advanced stage (IIB-IVA) CTCL. Of these patients 37.2% responded to alitretinoin, 28.6% had a stable course, and 34.3% experienced progression. Alitretinoin was administered as a monotherapy (25.7%) or combined with five concomitant therapies (74.2%), most frequently with ECP (31.4%) and PUVA (11.4%). 63% did not report any side effects, most often hypertriglyceridemia (20%) was described. CONCLUSION: Considering that nearly two thirds of the CTCL patients treated with alitretinoin showed a response or stable disease, together with a low number of side effects and low cost compared to bexarotene, alitretinoin may be a potential alternative in the treatment of less advanced CTCLs. This survey represents the largest number of recorded therapies with the retinoid alitretinoin in CTCLs in a European patient collective.

Novel Inflammatory Biomarkers in Patients with Mycosis Fungoides Treated with Bexarotene.

Mycosis fungoides (MF) is a skin lymphoma characterised by atypical T lymphocyte infiltration, which may present with patches and tumors in advanced stages. Treatment options in MF aim to reduce symptoms, since patients usually do not achieve complete cure. Bexarotene is used for treatment-resistant early stage MF and advanced stages of the disease. It has been suggested that white blood cell (WBC)/absolute lymphocyte count, WBC, absolute lymphocyte and eosinophil counts might be prognostic factors in MF. Therefore, we investigated the changes in complete blood count (CBC) parameters and CBC-derived inflammatory biomarkers in patients with MF treated with bexarotene. The results revealed that neutrophil (NE)%, NE numbers, neutrophil/lymphocyte, derived neutrophil/lymphocyte, (neutrophil × monocytes)/lymphocyte and (neutrophils × monocytes × platelets)/lymphocyte counts decreased in all patients three months after bexarotene treatment. We suggest that these inflammatory biomarkers can be used in the follow-up of patients with MF receiving bexarotene treatment. Moreover, these results indicate that decrease in these inflammatory biomarkers may signify improvement of the disease. Key Words: Bexarotene, Inflammatory biomarkers, Mycosis fungoides.

How we treat advanced stage cutaneous T-cell lymphoma - mycosis fungoides and Sézary syndrome.

T-cell lymphomas (TCLs) constitute a rare subset of non-Hodgkin lymphomas, with mycosis fungoides/Sézary syndrome (MF/SS) being the most common subtype of cutaneous TCLs (CTCLs). Considered an incurable but treatable disease, MF/SS management presents several challenges including diagnostic delays, debilitating effect on patients' quality of life, need for several lines of therapies, multidisciplinary care and cumulative drug toxicities limiting duration of use. The present review intends to provide an overview of the recent advances in our understanding of the biology of CTCL and how these are being leveraged to provide additional treatment options for management of advanced and recurrent disease. In addition, the discussion of the different modalities of treatment is summarised to further outline the importance of multidisciplinary care and early referral to CTCL centres.

Suppression of TLR4/MyD88/TAK1/NF-κB/COX-2 Signaling Pathway in the Central Nervous System by Bexarotene, a Selective RXR Agonist, Prevents Hyperalgesia in the Lipopolysaccharide-Induced Pain Mouse Model.

A selective RXR agonist, bexarotene, has been shown to have anti-inflammatory, anti-nociceptive, and neuroprotective effects in several models of numerous neurological diseases characterized by systemic inflammation. The mechanisms underlying these effects remains unknown. To elucidate these mechanisms, we investigated whether the TLR4/MyD88/TAK1/NF-κB/COX-2 signaling pathway in the CNS mediates the effect of bexarotene to prevent hyperalgesia in the LPS-induced inflammatory pain mouse model. The reaction time to thermal stimuli within 30 s was evaluated by the hot plate test in male mice treated with saline, LPS (10 mg/kg), DMSO, and/or bexarotene (0.1, 1, 3, or 10 mg/kg) after 6 h. The latency to the thermal stimulus (18.11 ± 1.36 s) in the LPS-treated mice was significantly decreased by 30% compared with saline-treated mice (25.84 ± 1.99 s). Treatment with bexarotene only at a dose of 10 mg/kg showed a significant increase in the latency by 22.49 ± 1.00 s compared with LPS-treated mice. Bexarotene also prevented the reduction in RXRα protein expression associated with a rise in the expression of TLR4, MyD88, phosphorylated TAK1, NF-κB p65, phosphorylated NF-κB p65, COX-2, and IL-1ß proteins, in addition to COX-2 activity and levels of PGE2 and IL-1ß in the brains and spinal cords of the LPS-treated animals. Likely, decreased activity of TLR4/MyD88/TAK1/NF-κB/COX-2 signaling pathway in addition to increased pro-inflammatory cytokine formation in the CNS of mice participates in the protective effect of bexarotene against hyperalgesia induced by LPS.

Infrared nanospectroscopy reveals the molecular interaction fingerprint of an aggregation inhibitor with single Aß42 oligomers.

Significant efforts have been devoted in the last twenty years to developing compounds that can interfere with the aggregation pathways of proteins related to misfolding disorders, including Alzheimer's and Parkinson's diseases. However, no disease-modifying drug has become available for clinical use to date for these conditions. One of the main reasons for this failure is the incomplete knowledge of the molecular mechanisms underlying the process by which small molecules interact with protein aggregates and interfere with their aggregation pathways. Here, we leverage the single molecule morphological and chemical sensitivity of infrared nanospectroscopy to provide the first direct measurement of the structure and interaction between single Aß42 oligomeric and fibrillar species and an aggregation inhibitor, bexarotene, which is able to prevent Aß42 aggregation in vitro and reverses its neurotoxicity in cell and animal models of Alzheimer's disease. Our results demonstrate that the carboxyl group of this compound interacts with Aß42 aggregates through a single hydrogen bond. These results establish infrared nanospectroscopy as a powerful tool in structure-based drug discovery for protein misfolding diseases.