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

New Fluorescent Synthetic Retinoids as Potential RAR Agonists with Anticancer, Molecular Docking and ADME Assessments

Natural and synthetic retinoids are derivatives of vitamin A that mediate different transcriptional activities. Synthesis of fluorescent probes can be a useful tool in cellular imaging and understanding different regulatory signaling pathways. In this study, new fluorescent synthetic retinoid analogues (3a, 3b, 4a, and 4b) were prepared and biologically screened against six different cancer and normal cell lines for assessment of their anticancer and fluorescent activities. A combination of biological assays, such as MTT, flow cytometry, gene and protein expression analysis, DNA fragmentation, and ATPase activity assays, as well as in-silico and ADME studies, was performed. All new compounds showed anti-proliferative activity (2.09-132.70 µM) against different cancer cell types with minimal cytotoxicity (SI > 1), and the Caco-2 cancer cell line was selected for further in vitro investigation. All compounds showed cell cycle arrest at the SubG0-G1 phase with induction of early apoptosis and necrosis. Compound 4b showed a significant apoptotic effect by overexpression of Caspase-3 and Cyt-c genes, followed by compound 3a. All compounds showed anti-inflammatory activity by significantly down-regulating the IL-10 pro-inflammatory marker, while compounds 3b, 4a, and 4b specifically down-regulated IL-6. Retinoic acid receptors (RARs) were suggested as molecular targets confirmed by their overexpression of both gene and protein levels with molecular docking and molecular dynamic simulation studies. All fluorescent compounds showed intracellular fluorescent emission spectra with intracellular lipophilic properties. The new fluorescent synthetic retinoids showed dual activities as anticancer agents with fluorescence properties and can be used as useful probes in a variety of cellular imaging investigations.

CDK9 recruits HUWE1 to degrade RARα and offers therapeutic opportunities for cutaneous T-cell lymphoma

Cutaneous T-cell lymphoma (CTCL) is a heterogeneous non-Hodgkin lymphoma originating in the skin and invading the systemic hematopoietic system. Current treatments, including chemotherapy and monoclonal antibodies yielded limited responses with high incidence of side effects, highlighting the need for targeted therapy. Screening with small inhibitors library, herein we identify cyclin dependent kinase 9 (CDK9) as a driver of CTCL growth. Single-cell RNA-seq analysis reveals a CDK9high malignant T cell cluster with a unique actively proliferating feature. Inhibition, depletion or proteolysis targeting chimera (PROTAC)-mediated degradation of CDK9 significantly reduces CTCL cell growth in vitro and in murine models. CDK9 also promotes degradation of retinoic acid receptor α (RARα) via recruiting the E3 ligase HUWE1. Co-administration of CDK9-PROTAC (GT-02897) with all-trans retinoic acid (ATRA) leads to synergistic attenuation of tumor growth in vitro and in xenograft models, providing a potential translational treatment for complete eradication of CTCL.

Halogenated retinoid derivatives as dual RARα and RXRα modulators for treating acute promyelocytic leukemia cells

Acute promyelocytic leukemia (APL), a distinctive subtype of acute myeloid leukemia (AML), is characterized by the t(15; 17) translocation forming the PML-RARα fusion protein. Recent studies have revealed a crucial role of retinoid X receptor α (RXRα) in PML-RARα's tumorigenesis. This necessitates the development of dual RARα and RXRα targeting compounds for treating APL. Here, we developed a pair of brominated retinoid isomers, 5a and 5b, exhibiting RARα agonistic selectivity among the RAR subtypes and RXRα partial agonistic activities. In the treatment of APL cells, low doses (RARα activation range) of 5a and 5b degrade PML-RARα and strongly induce differentiation, while higher doses (RXRα activation range) induce G2/M arrest and apoptosis in both all-trans retinoic acid (ATRA)-sensitive and resistant cells. We replaced the bromine in 5a with chlorine or iodine to obtain compounds 7 or 8a. Interestingly, the chlorinated compound 7 tends to activate RXRα and induce G2/M arrest and apoptosis, while the iodinated compound 8a tends to activate RARα and induce differentiation. Together, our work underscores several advantages and characteristics of halogens in the rational design of RARα and RXRα ligands, offering three promising drug candidates for treating both ATRA-sensitive and resistant APL.

Exploring the nexus of nuclear receptors in hematological malignancies

Hematological malignancies (HM) represent a subset of neoplasms affecting the blood, bone marrow, and lymphatic systems, categorized primarily into leukemia, lymphoma, and multiple myeloma. Their prognosis varies considerably, with a frequent risk of relapse despite ongoing treatments. While contemporary therapeutic strategies have extended overall patient survival, they do not offer cures for advanced stages and often lead to challenges such as acquisition of drug resistance, recurrence, and severe side effects. The need for innovative therapeutic targets is vital to elevate both survival rates and patients' quality of life. Recent research has pivoted towards nuclear receptors (NRs) due to their role in modulating tumor cell characteristics including uncontrolled proliferation, differentiation, apoptosis evasion, invasion and migration. Existing evidence emphasizes NRs' critical role in HM. The regulation of NR expression through agonists, antagonists, or selective modulators, contingent upon their levels, offers promising clinical implications in HM management. Moreover, several anticancer agents targeting NRs have been approved by the Food and Drug Administration (FDA). This review highlights the integral function of NRs in HM's pathophysiology and the potential benefits of therapeutically targeting these receptors, suggesting a prospective avenue for more efficient therapeutic interventions against HM.

Impact of VDR and RXR expression in non-melanoma skin cancer pathogenesis

1,25(OH)₂ D₃ , the active form of vitamin D, has been extensively studied for its putative protective activities against tumors. It does biological work by connecting to a nuclear receptor called VDR, which heterodimerizes itself to another nuclear receptor, RXR. The study observed differences in VDR and RXR expression in nonmelanoma skin cancer and actinic keratosis and compared it to normal skin. We performed VDR and RXR immunohistochemistry of 76 controls (normal skin), 49 actinic keratosis, 99 basal cell carcinomas and 96 squamous cell carcinomas from formalin-fixed paraffin-embedded, resulting from surgical procedures. There was a clear pattern in the control group (p<0.001), with the positivity of both receptors, VDR and RXR. Actinic keratosis differed from the basal cell carcinoma and control groups concerning RXR expression (p<0.001). SCC was negative for both receptors, differing in all groups (p<0.001). The site of positivity (nuclear, cytoplasmatic, or both) of VDR differed between all groups (p<0.001). To date, our series is the largest of VDR and RXR immunohistochemistry concerning non-melanoma skin cancer. Our findings reinforce the need to understand the pathways involving VDR and RXR to direct therapies and prevention maneuvers.

The role of resveratrol, Sirtuin1 and RXRα as prognostic markers in ovarian cancer

Objective

Ovarian cancer is the most lethal gynecologic cancer. Resveratrol (RSV) is known to alter metabolism in cancer. It affects the nuclear retinoid-X-receptor (RXR), which implies a modulating effect of RXR to gynaecologic cancers. Furthermore, RSV targets Sirtuin1 (Sirt1), a histone deacetylase.

Study design

123 tissue samples of patients with serous or mucinous ovarian cancer were examined for expression of Sirt1 and RXR. Ovarian cell lines were treated with RSV and consequences on viability and apoptosis were evaluated. The influence of RSV to Sirt1 and RXR expression was analyzed by western blotting

Results

A correlation of nuclear Sirt1 and RXRα expression could be detected (p = 0.006). Co-expression of nuclear RXRα and cytoplasmic (p = 0.026) or nuclear (p = 0.041) Sirt1 was associated with significantly increased overall survival in advanced tumour stages. Viability was decreased in all cell lines after stimulation with resveratrol, while cell apoptosis was increased. RSV treatment led to significant lower Sirt1 expression in A2780 cells (p = 0.025) and significant increased RXR expression in cisA2780 cells (p = 0.012)

Conclusion

In order to use RSV as medical target, studies could be developed to improve the understanding of drug resistance mechanisms and consequently improve treatment outcome.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00404-021-06262-w.

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.

Retinoic acid receptor agonist as monotherapy for early-stage mycosis fungoides: does it work?

BACKGROUND

Retinoids exert their biologic effects by binding to intracellular retinoic-acid receptors (RARs) and/or retinoid X receptors (RXRs). Early-stage mycosis fungoides (MF) has been effectively treated with bexarotene, an RXR-agonist, with overall response (OR) rates 54-67% and complete response (CR) rates 7-27%. Data on RAR-agonist monotherapy are limited.

OBJECTIVE

To analyze the effectiveness of RAR-agonist monotherapy for early-stage MF.

METHODS

Data on patients with early-stage MF treated with acitretin/isotretinoin monotherapy at a tertiary cutaneous lymphoma clinic in 2010-2017 were collected retrospectively from the medical files.

RESULTS

Thirty-five patients (26 males) of median age 50 years (range 8-83) with early-stage MF (IA 9, IB 26) underwent 37 treatment events: 25 acitretin and 12 isotretinoin at a median dosages of 0.3 mg/kg (range 0.2-0.9) and 0.2 mg/kg (range 0.1-0.7), respectively. Median time to maximal response was 6 months for both (range 1-10 for acitretin, 3-16 for isotretinoin); median treatment duration was 10 months (range 3-46) for acitretin, and 9 months (range 3-55) for isotretinoin. OR was 64% for acitretin and 80% for isotretinoin, and CR, 4% and 8%, respectively. Side-effect profiles were as previously reported for retinoids.

CONCLUSIONS

Early-stage MF patients may benefit from low dose RAR-agonist monotherapy, although the CR rate is low.