Retinoic Acid Receptor Agonist Research Articles

Neuroprotective effects of ellorarxine in neuronal models of degeneration.

Retinoic acid (RA) was first recognised to be important for the central nervous system (CNS) in its developmental regulatory role and, given this action, it has been proposed in the adult CNS to regulate plasticity and promote regeneration. These types of roles have included support of neurogenesis, induction of neurite outgrowth, and protection from neuronal death. These functions are predominantly mediated by the retinoic acid receptor (RAR) transcription factor, and hence agonists for the RARs have been tested in a variety of models of neurodegeneration. This present study employs several in vitro models less explored for the action of RAR agonists to reverse neurodegeneration. A series of assays are used in which neuronal cells are placed under the types of stress that have been linked to neurodegeneration, in particular amyotrophic lateral sclerosis (ALS), and the neuroprotective influence of a new potent agonist for RAR, ellorarxine, is tested out. In these assays, neuronal cells were subjected to excitotoxic stress induced by glutamate, proteostasis disruption caused by epoxomicin, and oxidative stress leading to stress granule formation triggered by sodium arsenite. Ellorarxine effectively reversed neuronal death in excitotoxic and proteostasis disruption assays and mitigated stress granule formation induced by sodium arsenite. This study also highlights for the first time the novel observation of RAR modulation of stress granules, although it is unknown whether this change in stress granules will be neuroprotective or potentially regenerative. Furthermore, the distribution of RAR agonists following intraperitoneal injection was assessed in mice, revealing preferential accumulation in the central nervous system, particularly in the spinal cord, compared to the liver. Gene expression studies in the spinal cord demonstrated that ellorarxine induces transcriptional changes at a low dose (0.01 mg/kg). These findings underscore the therapeutic potential of RAR agonists, such as ellorarxine, for ALS and potentially other neurodegenerative diseases.

Abstract P396: A Selective Agonist of the Beta 2 Retinoic Acid Receptor Reduces Necrosis, Lipid Peroxidation, and Oxidative Stress in Doxorubicin-induced Cardiotoxicity

Objective: Doxorubicin (Doxo) is used as an antiproliferative agent to treat various cancers. However, a significant limitation of Doxo is cardiotoxicity, that can induce heart failure in patients. Mounting evidence indicates that an increased generation of reactive oxygen species (ROS), lipid peroxidation, and necrosis, are major causes of Doxo-induced heart failure. Recently, we reported that a highly selective and potent agonist of the b2 retinoic acid receptor (RARb2), improved cardiac dysfunction in mice model of myocardial infarction by inhibiting oxidative stress. In this study we investigated cardioprotective effects of RARb2 stimulation on Doxo-induced heart failure. Methods: We performed in vitro and in vivo experiments on an established murine model of Doxo-induced heart failure. Necrosis, oxidative stress, and lipid peroxidation were evaluated, assessing both the prevention and the rescue capacities of RARb2 stimulation. Results: An increased ROS production both at the mitochondrial and cellular level was observed in cardiomyocytes isolated from Doxo-treated mice. RARb2 stimulation significantly attenuated Doxo-induced ROS production. In addition, this treatment mitigated lipid peroxidation induced by Doxo in the left ventricle, marked by 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA). RARb2 stimulation also mitigated the increased expression of High Mobility Group Box 1 (HMGB1), a necrosis marker, in the heart and in the serum of Doxo-treated mice. Conclusion: Our data demonstrate that RARb2 stimulation can attenuate necrosis, lipid peroxidation, and ROS production in a mouse model of Doxo cardiotoxicity.

Dual and opposing role of retinoic acid receptor signaling in mesenchymal stem cells for tendon ossification in mice.

Heterotopic ossification is abnormal bone formation in soft tissues that occurs primarily after injury and major surgery. This condition often causes local pain and limits joint motion in the affected limb. Currently, there is no effective treatment or prophylaxis for this condition other than surgical removal of the lesion. Recent studies suggest that retinoic acid receptor (RAR) agonists are effective in suppressing heterotopic ossification in patients with Fibrodysplasia Ossificans Progressiva, a congenital disorder characterized by progressive ossification of soft tissue, by suppressing the aberrant differentiation of mesenchymal stem cells in muscle. In this study, we aimed to elucidate the potential use of RAR agonists in suppressing injury-induced ectopic tendon ossification using a mouse Achilles tenotomy model. Contrary to our initial hypothesis, administration of RAR agonists throughout the experimental period (5 weeks) accelerated ectopic tendon ossification in our model. Of note, in vitro differentiation experiments using tendon-derived mesenchymal stem cells revealed that RAR agonists play opposing roles in osteogenic and chondrogenic differentiation, promoting the former and suppressing the latter. Indeed, we found that RAR agonists suppressed tendon ossification when administered before cartilage nodule formation, but promoted it when administered after. These results suggest that RAR agonists have a dual and opposing effect on tendon ectopic ossification, depending on the duration and timing of their administration. Our data may provide a basis for further investigation of the potential use of RAR agonists in the treatment of injury-induced heterotopic ossification.

Организация профилактики и терапии угревой болезни у подростков на современном этапе.

The organization of prevention and treatment of acne in adolescents, necessary to improve the quality of medical dermatological care, has not been studied enough. The purpose of the study: аnalysis of current and potential opportunities for organizing the prevention and treatment of acne in adolescents. Results. The pathophysiological mechanisms of acne development are being reviewed, considering the characteristics of the puberty period, however, the trends in introducing new approaches to the organization of prevention and treatment of acne in adolescents are not expressed, with the exception of antiandrogen therapy. The official organization of treatment for adolescents with acne considers that any stage of acne development is multifactorial and is based on an inflammatory process. The officially recommended main method of treating acne in adolescents is the combined use of topical agents, especially the combination of benzoyl peroxide and the retinoid adapalene. In complex cases, topical treatment is supplemented with systemic therapy with retinoids (isotretinoin). Prevention of side effects of topical treatment (dry skin, hyperemia or cheilitis) is achieved through the use of moisturizing cosmetics or cream with dexpanthenol, respectively. Officially, in the field of acne prevention and therapy, such methods of influencing acne vulgaris as dermatocosmetics and corneo-or enzyme therapy are not used. The use of local and systemic pre- and probiotics for the treatment of acne has not been introduced. This reveals a connection between the development of acne and the intestinal microbiome. The use of local antiandrogens and insulin-like growth factor 1 inhibitors to control sebum production, as well as selective retinoic acid receptor agonists with a better safety profile compared to retinoid therapy for acne, may be promising for the prevention and treatment of acne in adolescents. Findings. Organization of effective treatment of acne in adolescents should include their clear instructions and correction of dietary habits. Prevention of acne today is practically not organized in the field of medical services.

Human iPSC-derived renal collecting duct organoid model cystogenesis in ADPKD

In autosomal dominant polycystic kidney disease (ADPKD), renal cyst lesions predominantly arise from collecting ducts (CDs). However, relevant CD cyst models using human cells are lacking. Although previous reports have generated invitro renal tubule cyst models from human induced pluripotent stem cells (hiPSCs), therapeutic drug candidates for ADPKD have not been identified. Here, by establishing expansion cultures of hiPSC-derived ureteric bud tip cells, an embryonic precursor that gives rise to CDs, we succeed in advancing the developmental stage of CD organoids and show that all CD organoids derived from PKD1-/- hiPSCs spontaneously develop multiple cysts, clarifying the initiation mechanisms of cystogenesis. Moreover, we identify retinoic acid receptor (RAR) agonists as candidate drugs that suppress invitro cystogenesis and confirm the therapeutic effects on an ADPKD mouse model invivo. Therefore, our invitro CD cyst model contributes to understanding disease mechanisms and drug discovery for ADPKD.

Retinoic Acid Receptor Is a Novel Therapeutic Target for Postoperative Cognitive Dysfunction.

Postoperative cognitive dysfunction (POCD) is a clinical syndrome characterizing by cognitive impairments in the elderly after surgery. There is limited effective treatment available or clear pathological mechanisms known for this syndrome. In this study, a Connectivity Map (CMap) bioinformatics model of POCD was established by using differently expressed landmark genes in the serum samples of POCD and non-POCD patients from the only human transcriptome study. The predictability and reliability of this model were further supported by the positive CMap scores of known POCD inducers and the negative CMap scores of anti-POCD drug candidates. Most retinoic acid receptor (RAR) agonists were negatively associated with POCD in this CMap model, suggesting that RAR might be a novel target for POCD. Most importantly, acitretin, a clinically used RAR agonist, significantly inhibited surgery-induced cognitive impairments and prevented the reduction in RARα and RARα-target genes in the hippocampal regions of aged mice. The study denotes a reliable CMap bioinformatics model of POCD for future use and establishes that RAR is a novel therapeutic target for treating this clinical syndrome.

A novel retinoic acid receptor-γ agonist antagonizes immune checkpoint resistance in lung cancers by altering the tumor immune microenvironment

All-trans-retinoic acid (ATRA), the retinoic acid receptors (RARs) agonist, regulates cell growth, differentiation, immunity, and survival. We report that ATRA-treatment repressed cancer growth in syngeneic immunocompetent, but not immunodeficient mice. The tumor microenvironment was implicated: CD8+ T cell depletion antagonized ATRA’s anti-tumorigenic effects in syngeneic mice. ATRA-treatment with checkpoint blockade did not cooperatively inhibit murine lung cancer growth. To augment ATRA’s anti-tumorigenicity without promoting its pro-tumorigenic potential, an RARγ agonist (IRX4647) was used since it regulates T cell biology. Treating with IRX4647 in combination with an immune checkpoint (anti-PD-L1) inhibitor resulted in a statistically significant suppression of syngeneic 344SQ lung cancers in mice—a model known for its resistance to checkpoints and characterized by low basal T cell and PD-L1 expression. This combined treatment notably elevated CD4+ T-cell presence within the tumor microenvironment and increased IL-5 and IL-13 tumor levels, while simultaneously decreasing CD38 in the tumor stroma. IL-5 and/or IL-13 treatments increased CD4+ more than CD8+ T-cells in mice. IRX4647-treatment did not appreciably affect in vitro lung cancer growth, despite RARγ expression. Pharmacokinetic analysis found IRX4647 plasma half-life was 6 h in mice. Yet, RARα antagonist (IRX6696)-treatment with anti-PD-L1 did not repress syngeneic lung cancer growth. Together, these findings provide a rationale for a clinical trial investigating an RARγ agonist to augment check point blockade response in cancers.

Discovery of novel RARα agonists using pharmacophore-based virtual screening, molecular docking, and molecular dynamics simulation studies.

Nuclear retinoic acid receptors (RARs) are ligand-dependent transcription factors involved in various biological processes, such as embryogenesis, cell proliferation, differentiation, reproduction, and apoptosis. These receptors are regulated by retinoids, i.e., retinoic acid (RA) and its analogs, as receptor agonists. RAR agonists are promising therapeutic agents for the treatment of serious dermatological disorders, including some malignant conditions. By inducing apoptosis, they are able to inhibit the proliferation of diverse cancer cell lines. Also, RAR agonists have recently been identified as therapeutic options for some neurodegenerative diseases. These features make retinoids very attractive molecules for medical purposes. Synthetic selective RAR agonists have several advantages over endogenous ones, but they suffer poor pharmacokinetic properties. These compounds are normally lipophilic acids with unfavorable drug-like features such as poor oral bioavailability. Recently, highly selective, potent, and less toxic RAR agonists with proper lipophilicity, thus, good oral bioavailability have been developed for some therapeutic applications. In the present study, ligand and structure-based virtual screening technique was exploited to introduce some novel RARα agonists. Pharmacokinetic assessment was also performed in silico to suggest those compounds which have optimized drug-like features. Finally, two compounds with the best in silico pharmacological features are proposed as lead molecules for future development of RARα agonists.

Am80, a retinoic acid receptor agonist, activates the cardiomyocyte cell cycle and enhances engraftment in the heart.

Human induced pluripotent stem cell-derived (hiPSC) cardiomyocytes are a promising source for regenerative therapy. To realize this therapy, however, their engraftment potential after their injection into the host heart should be improved. Here, we established an efficient method to analyze the cell cycle activity of hiPSC cardiomyocytes using a fluorescence ubiquitination-based cell cycle indicator (FUCCI) system. Invitro high-throughput screening using FUCCI identified a retinoic acid receptor (RAR) agonist, Am80, as an effective cell cycle activator in hiPSC cardiomyocytes. The transplantation of hiPSC cardiomyocytes treated with Am80 before the injection significantly enhanced the engraftment in damaged mouse heart for 6months. Finally, we revealed that the activation of endogenous Wnt pathways through both RARA and RARB underlies the Am80-mediated cell cycle activation. Collectively, this study highlights an efficient method to activate cell cycle in hiPSC cardiomyocytes by Am80 as a means to increase the graft size after cell transplantation into a damaged heart.

Optimized Automated Analysis of Live Neuronal Mitochondria Homeostasis Modulation by Isoform-Specific Retinoic Acid Receptors.

The complex mitochondrial network makes it very challenging to segment, follow, and analyze live cells. MATLAB tools allow the analysis of mitochondria in timelapse files, considerably simplifying and speeding up the process of image processing. Nonetheless, existing tools produce a large output volume, requiring individual manual attention, and basic experimental setups have an output of thousands of files, each requiring extensive and time-consuming handling. To address these issues, a routine optimization was developed, in both MATLAB code and live-script forms, allowing for swift file analysis and significantly reducing document reading and data processing. With a speed of 100 files/min, the optimization allows an overall rapid analysis. The optimization achieves the results output by averaging frame-specific data for individual mitochondria throughout time frames, analyzing data in a defined manner, consistent with those output from existing tools. Live confocal imaging was performed using the dye tetramethylrhodamine methyl ester, and the routine optimization was validated by treating neuronal cells with retinoic acid receptor (RAR) agonists, whose effects on neuronal mitochondria are established in the literature. The results were consistent with the literature and allowed further characterization of mitochondrial network behavior in response to isoform-specific RAR modulation. This new methodology allowed rapid and validated characterization of whole-neuron mitochondria network, but it also allows for differentiation between axon and cell body mitochondria, an essential feature to apply in the neuroscience field. Moreover, this protocol can be applied to experiments using fast-acting treatments, allowing the imaging of the same cells before and after treatments, transcending the field of neuroscience.

The Endogenous Dual Retinoid Receptor Agonist Alitretinoin Exhibits Immunoregulatory Functions on Antigen-Presenting Cells.

Retinoids are a frequently used class of drugs in the treatment of inflammatory as well as malignant skin diseases. Retinoids have differential affinity for the retinoic acid receptor (RAR) and/or the retinoid X receptor (RXR). The endogenous dual RAR and RXR agonist alitretinoin (9-cis retinoic acid) demonstrated remarkable efficacy in the treatment of chronic hand eczema (CHE) patients; however, detailed information on the mechanisms of action remains elusive. Here, we used CHE as a model disease to unravel immunomodulatory pathways following retinoid receptor signaling. Transcriptome analyses of skin specimens from alitretinoin-responder CHE patients identified 231 significantly regulated genes. Bioinformatic analyses indicated keratinocytes as well as antigen presenting cells as cellular targets of alitretinoin. In keratinocytes, alitretinoin interfered with inflammation-associated barrier gene dysregulation as well as antimicrobial peptide induction while markedly inducing hyaluronan synthases without affecting hyaluronidase expression. In monocyte-derived dendritic cells, alitretinoin induced distinct morphological and phenotypic characteristics with low co-stimulatory molecule expression (CD80 and CD86), the increased secretion of IL-10 and the upregulation of the ecto-5'-nucleotidase CD73 mimicking immunomodulatory or tolerogenic dendritic cells. Indeed, alitretinoin-treated dendritic cells demonstrated a significantly reduced capacity to activate T cells in mixed leukocyte reactions. In a direct comparison, alitretinoin-mediated effects were significantly stronger than those observed for the RAR agonist acitretin. Moreover, longitudinal monitoring of alitretinoin-responder CHE patients could confirm in vitro findings. Taken together, we demonstrate that the dual RAR and RXR agonist alitretinoin targets epidermal dysregulation and demonstrates strong immunomodulatory effects on antigen presenting cell functions.

Safety, Tolerability, and Pharmacokinetics of IMU-935, a Novel Inverse Agonist of Retinoic Acid Receptor-Related Orphan Nuclear Receptor γt: Results From a Double-Blind, Placebo-Controlled, First-in-Human Phase 1 Study.

Retinoic acid receptor-related orphan nuclear receptor (ROR)γt regulates the transcription of interleukin-17 and other cytokines implicated in inflammatory and autoimmune diseases. We assessed the safety, tolerability, and pharmacokinetics (PK) of IMU-935, an inverse agonist of RORγt, in a first-in-human phase 1 study. This was a double-blind, placebo-controlled trial that randomly assigned healthy subjects single ascending doses (25-400mg) or multiple ascending doses (150mg once or twice daily for 14days) of IMU-935 or placebo. Dose escalation was determined by the safety, tolerability, and PK. Twenty-four and 70 subjects received placebo or IMU-935, respectively. Of the 70 subjects who received IMU-935, 59 received a single dose and 11 received multiple doses. Treatment-emergent adverse events (TEAEs) occurred in 21 subjects (88%) and 58 (83%) given any dose of placebo or IMU-935, respectively. Treatment-related TEAEs occurred in 6 (30%) and 25 (42%) subjects given a single dose of placebo and IMU-935, respectively. All treatment-related TEAEs were mild except for 2 moderate TEAEs and 1 moderate TEAE in the IMU-935 group and placebo group, respectively. No treatment-related discontinuations or serious adverse events occurred. The PK of IMU-935 were dose proportional with a half-life of ≈24hours. In conclusion, IMU-935 was safe with no dose-limiting toxicities and had a PK profile that supports once-daily dosing.

Prediction and Demonstration of Retinoic Acid Receptor Agonist Ch55 as an Antifibrotic Agent in the Dermis

The prevalence of fibrotic diseases and the lack of pharmacologic modalities to effectively treat them impart particular importance to the discovery of novel antifibrotic therapies. The repurposing of drugs with existing mechanisms of action and/or clinical data is a promising approach for the treatment of fibrotic diseases. One paradigm that pervades all fibrotic diseases is the pathological myofibroblast, a collagen-secreting, contractile mesenchymal cell that is responsible for the deposition of fibrotic tissue. In this study, we use a gene expression paradigm characteristic of activated myofibroblasts in combination with the Connectivity Map to select compounds that are predicted to reverse the pathological gene expression signature associated with the myofibroblast and thus contain the potential for use as antifibrotic compounds. We tested a small list of these compounds in a first-pass screen, applying them to fibroblasts, and identified the retinoic acid receptor agonist Ch55 as a potential hit. Further investigation exhibited and elucidated the antifibrotic effects of Ch55 invitro as well as showing antiscarring activity upon intradermal application in a preclinical rabbit ear hypertrophic scar model. We hope that similar predictions to uncover antiscarring compounds may yield further preclinical and ultimately clinical success.

Suggested Guidelines for the Treatment of Mycosis Fungoides in Countries with Limited Resources.

The treatment options for mycosis fungoides (MF) have been expanding but unfortunately many of the currently used treatment modalities are unavailable in Egypt and other African/Arab countries. In addition, there is a lack of consensus on the treatment of hypopigmented MF (HMF), which is a frequently encountered variant in our population. We aimed to develop regional treatment guidelines based on the international guidelines but modified to encompass the restricted treatment availability and our institutional experience. Special attention was also given to studies conducted on patients with skin phototype (III-IV). Treatment algorithm was formulated at Ain-Shams cutaneous lymphoma clinic through the collaboration of dermatologists, haematologists, and oncologists. Level of evidence is specified for each treatment option. For HMF, phototherapy is recommended as a first line treatment, while low-dose methotrexate is considered a second line. For early classical MF, we recommend Psoralen-ultraviolet A (PUVA), which is a well-tolerated treatment option in dark phenotype. Addition of either retinoic acid receptor (RAR) agonist and/or methotrexate is recommended as a second line. Total skin electron beam (TSEB) is considered a third-line option. For advanced stage, PUVA plus RAR agonist and/or methotrexate is recommended as first line, TSEB or monochemotherapy is considered a second line option. Polychemotherapy is regarded as a final option. All patients with complete response (CR) enter a maintenance and follow-up schedule. We suggest a practical algorithm for the treatment of MF for patients with dark phenotype living in countries with limited resources.

Identification of the Natural Steroid Sapogenin Diosgenin as a Direct Dual-Specific RORα/γ Inverse Agonist.

The steroid sapogenin diosgenin is a well-known natural product with a plethora of described pharmacological activities including the amelioration of T helper 17 (Th17)-driven pathologies. However, the exact underlying mode of action of diosgenin leading to a dampened Th17 response is still largely unknown and specific molecular targets have yet to be identified. Here, we show that diosgenin acts as a direct ligand and inverse agonist of the nuclear receptor retinoic acid receptor (RAR)-related orphan receptor (ROR)α and RORγ, which are key transcription factors involved in Th17 cell differentiation and metabolism. IC50 values determined by luciferase reporter gene assays, employing constructs for either RORγ-Gal4 fusion proteins or full length receptors, were in the low micromolar range at around 2 µM. To highlight the functional consequences of this RORα/γ inverse agonism, we determined gene expression levels of important ROR target genes, i.e., IL-17A and glucose-6-phosphatase, in relevant cellular in vitro models of Jurkat T and HepG2 cells, respectively, by RT-qPCR (reverse transcription quantitative PCR). Thereby, it was shown that diosgenin leads to a dose-dependent decrease in target gene expressions consistent with its potent cellular ROR inverse agonistic activity. Additionally, in silico dockings of diosgenin to the ROR ligand-binding domain were performed to determine the underlying binding mode. Taken together, our results establish diosgenin as a novel, direct and dual-selective RORα/γ inverse agonist. This finding establishes a direct molecular target for diosgenin for the first time, which can further explain reported amendments in Th17-driven diseases by this compound.

A non-retinol retinoic acid receptor-γ (RAR-γ/NR1B3) selective agonist, tectorigenin, can effectively inhibit the ultraviolet A-induced skin damage.

Long-term ultraviolet (UV) exposure can cause inflammation, pigmentation and photoaging. All-trans retinoic acid (ATRA/tretinoin) is a commonly used retinoic acid receptor (RAR) agonist in the clinical treatment of UV-induced skin problems. However, the use of such drugs is often accompanied by systemic adverse reactions caused by nonspecific activation of RARs. Therefore, this study was designed to screen for a novel RAR-γ-selective agonist with high safety. Molecular docking, dynamic simulation and Biacore were used to screen and identify novel RAR-γ-selective agonists. RT-PCR, ELISA, western blotting, immunofluorescence staining, flow cytometry and proteomic analysis were used to detect the effects of these novel RAR-γ selective agonists on UVA-induced inflammation and photoaging cell models. UVA-induced mouse models were used to evaluate the effects of tectorigenin on skin repair, ageing and inflammation. Tectorigenin is a novel RAR-γ-selective agonist, which inhibits UV-induced oxidative damage, inflammatory factor release and matrix metalloproteinase (MMP) production. Tectorigenin can also reverse the UVA-induced loss of collagen. The results of the signalling pathway research showed that tectorigenin mainly affects the MAPK/JNK/AP-1 pathway. In animal experiments, tectorigenin showed better anti-inflammatory and anti-photoaging effects, and caused less skin irritation than ATRA. Nano-particle loaded tectorigenin significantly improved the utilization of tectorigenin. Tectorignen is a non-retinol RAR-γ-selective agonist that can inhibit UV-induced skin damage and could be developed as a safe pharmaceutical component for the prevention of photoaging and skin inflammation.

Pathophysiology and Emerging Molecular Therapeutic Targets in Heterotopic Ossification.

The term heterotopic ossification (HO) describes bone formation in tissues where bone is normally not present. Musculoskeletal trauma induces signalling events that in turn trigger cells, probably of mesenchymal origin, to differentiate into bone. The aetiology of HO includes extremely rare but severe, generalised and fatal monogenic forms of the disease; and as a common complex disorder in response to musculoskeletal, neurological or burn trauma. The resulting bone forms through a combination of endochondral and intramembranous ossification, depending on the aetiology, initiating stimulus and affected tissue. Given the heterogeneity of the disease, many cell types and biological pathways have been studied in efforts to find effective therapeutic strategies for the disorder. Cells of mesenchymal, haematopoietic and neuroectodermal lineages have all been implicated in the pathogenesis of HO, and the emerging dominant signalling pathways are thought to occur through the bone morphogenetic proteins (BMP), mammalian target of rapamycin (mTOR), and retinoic acid receptor pathways. Increased understanding of these disease mechanisms has resulted in the emergence of several novel investigational therapeutic avenues, including palovarotene and other retinoic acid receptor agonists and activin A inhibitors that target both canonical and non-canonical signalling downstream of the BMP type 1 receptor. In this article we aim to illustrate the key cellular and molecular mechanisms involved in the pathogenesis of HO and outline recent advances in emerging molecular therapies to treat and prevent HO that have had early success in the monogenic disease and are currently being explored in the common complex forms of HO.

Abstract 1519: ALDH1A1 enhances micro homology-mediated end joining by increasing POLQ expression

Abstract Aldehyde dehydrogenase (ALDH) is a superfamily of 19 known enzymes that participated in the metabolism of endogenous and exogenous aldehydes. ALDH1A1 is a major subtype contributing to high ALDH activity out of all ALDH isoforms and plays a critical role in the maintenance of cancer stem cells. Our previous studies have shown that ALDH1A1 is able to reduce the sensitivity of BRCA2-/- ovarian cancer cells to PARP inhibitors by enhancing microhomology-mediated end joining (MMEJ). MMEJ uses 5-25 base pair micro homologous sequences to align the broken strands before joining, and this repair pathway requires DNA polymerase θ (Pol θ, encoded by POLQ). Here we show that ALDH1A1 can increase the expression of Pol θ, at both mRNA and protein levels, in ovarian cancer cell lines. ALDH1A1 is reported to catalyze the production of all-trans retinoic acid (ATRA), which can bind to the retinoic acid receptor (RAR), and promote transcription of the downstream target genes that possess retinoic acid response element (RARE) in their promoter regions. Interestingly we identified several RAREs in the promoter region of the POLQ gene. Thus, we hypothesized that ALDH1A1 promotes Pol θ expression via activation of the RAR signaling pathway. We found that ATRA and RAR agonist (CH55) increased but pan RAR antagonist (AGN193109) treatment decreased the expression of POLQ, indicating that the RAR pathway is involved in the transcription of POLQ. We also demonstrated that RARα can bind to the promoter region of Pol Q, activation of RAR signaling by treatment with ATRA or CH55 increased the enrichment of K27 acetylated histone H3 in this promoter region. Moreover, we showed that mutated ALDH1A1 lacking the enzyme activity was unable to enhance POLQ transcription. These data suggest that ALDH1A1 enhances the Pol Q expression by increasing the production of ATRA which further activates the RAR signaling pathway. Citation Format: Kousalya Lavudi, Ananya Banerjee, Shurui Cai, Na Li, Xuetao Bai, Wang Qi-En. ALDH1A1 enhances micro homology-mediated end joining by increasing POLQ expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1519.

Parenteral vaccination strategies target protective immunity to the small and large intestine mucosa

Abstract Prophylactic vaccines are most commonly given by a parenteral route. However, this strategy often confers poor protection against GI pathogens because antigens are primarily presented in peripheral lymph nodes, which do not provide the prerequisite ‘tissue imprinting signals’ to target memory T and B cells to the gut. Here, we describe a platform that enables parenteral vaccines to target protection to the GI tract. This was achieved by subcutaneous (s.c.) delivery of compounds known to imprint gut tropism onto lymphocytes. Am80, a retinoic acid receptor agonist, targeted immunity to the small intestine through up-regulation of gut-homing receptors α4β7 and CCR9, and promotion of IgA class-switching. S.c. injection of OVA + CpG combined with repeated injections of Am80 generated significantly higher and durable fecal anti-OVA IgA titers, compared to OVA + CpG without Am80. Vaccination with Am80 also increased antigen-specific CD4 and CD8 T cell trafficking to the small intestine and generated tissue resident memory T (Trm) cells. To overcome the need for multiple doses of Am80, which can cause tissue toxicity at the injection site and hinder clinical translation, we developed a polymeric nanocarrier that showed equivalent imprinting efficacy upon a single injection, lowering the cumulative dose to one-third. Furthermore, we also developed a modified vaccination strategy that could augment effector and memory T cell responses not only in the small intestine, but also in the cecum, colon and rectum, conferring protection to the entire intestinal tract. We conclude that supplementation with mucosal imprinting signals is a promising approach to enhance parenteral vaccines by generating mucosal protection against GI infections. Supported by the Bill & Melinda Gates Foundation

Abstract P2-13-28: Inhibiting retinoic acid receptor signalling enhances the effect of neratinib in HER2 positive breast cancer cell lines

Abstract Introduction: Treatment strategies for HER2+ breast cancer (BC) involves first line treatment with the monoclonal antibody trastuzumab, however resistance to treatment can occur. The pan-HER tyrosine kinase inhibitor neratinib is an approved adjuvant treatment for early stage HER2+ BC after one year of treatment with trastuzumab. Recent studies have highlighted the potential benefits of using retinoic acid as an adjuvant treatment for BC. The retinoic acid receptor (RAR) family of nuclear transcription factors consists of RARα, RARβ and RARγ. Interestingly ~30% of HER2+ BC have a co-amplification of the RARA gene, which codes for RARα. We examined the effect of RARα agonists (Fenretinide & AM580) and antagonist (AGN194310) in combination with neratinib in two HER2+ cell lines: SKBR3, has co-amplification of ERBB2 and RARA, and HCC1569 has amplified ERBB2 but are not RARA-amplified. Methods: SKBR3 and HCC1569 cell lines were cultured in RPMI/10% FCS at 370C/5% CO2. 10mM stock concentrations of fenretinide (H7779-Sigma), AM580 (A8843-Sigma), AGN194310 (SML2665-Sigma) and neratinib (Puma Biotechnology, Inc) were prepared in DMSO. For proliferation assays, cells were seeded in 96 well plates at a density of 3 X 104 cells per well for 24h. Cells were treated with a drug alone (2X concentration) or combination of drugs (4X concentration) in 100μL of medium. Proliferation was measured using an acid phosphatase-based assay after 5 days as percentage growth versus DMSO control. The half maximal inhibitory concentration (IC50) was calculated for each drug, using CalcuSyn. The combination assays were performed using fixed ratios. The combination index (CI) values were calculated at the effective dose that inhibits 50% growth (ED50), using CalcuSyn. Values < 1 represent a synergistic effect, a value of 1 is additive and values > 1 represent an antagonistic effect. All data presented as the mean of biological triplicate experiments ± standard deviation. Results: This research has found that the synthetic retinoic acid fenretinide, a pan-RAR (α, β and γ) activator, was more potent in the HCC1569 cells compared to the SKBR3 cell line with an IC50 of 0.21 ± 0.03μM compared to 4.55 ± 0.87 μM, respectively. However, when combined with neratinib there was a strong antagonistic effect observed in the HCC1569 cell line (CI value: 15.63 ± 9.5). Conversely, fenretinide enhanced the effect of neratinib in the SKBR3 cell line (CI value: 0.83 ± 0.4). The RARα-specific activator AM580 had an IC50 >10μM for both cell lines. When combined with neratinib there was an additive effect observed in the RARα negative HCC1569 cells (CI value: 0.97 ± 0.4), and a synergistic effect observed in the RARα upregulated SKBR3 cell line (CI value: 0.78 ± 0.08). Next we wanted to determine if inhibiting RAR activity would have any effect on the proliferation of these cell lines. The IC50 for the pan-RAR (α, β and γ) antagonist AGN194310 was >10μM for each cell line. However, when combined with neratinib treatment there was a strong synergistic effect observed in the HCC1569 cell line (CI value: 0.52 ± 0.17) and the SKBR3 cell line (CI value: 0.66 ± 0.19). Conclusions: This study suggests a differential effect of RAR agonists when combined with neratinib in RARα amplified versus non-amplified HER2+ BC. Targeting RAR signalling, particularly with a RAR antagonist, in combination with the pan-HER inhibitor warrants further investigation in HER2+ BC. Citation Format: Debbie O'Reilly, Nicola Gaynor, Neil Conlon, Irmina Diala, Lisa D Eli, John Crown, Denis M Collins. Inhibiting retinoic acid receptor signalling enhances the effect of neratinib in HER2 positive breast cancer cell lines [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-13-28.