Histone Deacetylase Inhibitor Research Articles

Low-Dose Treatment with Epirubicin, a Novel Histone Deacetylase 1 Inhibitor, Exerts Anti-leukemic Effects by Inducing Ferroptosis

AimsLeukemia is hematopoietic stem cell malignant tumor with poor outcomes. Histone deacetylase 1 (HDAC1) is highly expressed in leukemia and current HDAC1 inhibitors have clinical limitations in leukemia therapy. Therefore, novel HDAC1 inhibitor is imperative to being found and its mechanism needs to be further explored. Materials and methodsNovel HDAC1 inhibitors were discovered through drug virtual screening. CCK-8, EdU and soft agar assay were used to assess the anti-leukemic effect of the candidate HDAC1 inhibitor. ROS, lipid peroxidation, intracellular Fe2+ and LIP assay were employed to verify cell ferroptosis. Additionally, a xenograft model was performed to explore the efficacy and safety of candidate HDAC1 inhibitor in vivo. ResultsHDAC1 might be a promising therapeutic target for leukemia and Epirubicin (Epi) could be used as a potential HDAC1 inhibitor. Low-dose Epi exhibited good anti-leukemic effects by inhibiting cell proliferation, DNA synthesis and colony formation. Low-dose Epi could induce ferroptosis by triggering lipid peroxidation, which was better than that treated with current HDAC1 inhibitors Chidamide or Vorinostat, ROS generation and Fe2+ overload in leukemia cells. Mechanistically, low-dose Epi induced ferroptosis by targeting amino acid metabolism and iron metabolism. Similar results were found in a xenograft model in NOG mice with a good safety profile. ConclusionOur study demonstrated that Epi might be used as a HDAC1 inhibitor. Low-dose Epi could inhibit tumor progression by inducing cell ferroptosis in vitro and in vivo. Thus, Epi administration with lower concentration may be much more favorable and safer in the treatment with leukemia.

Emerging Neuroprotective Strategies: Unraveling the Potential of HDAC Inhibitors in Traumatic Brain Injury Management.

Traumatic brain injury (TBI) is a significant global health problem, leading to high rates of mortality and disability. It occurs when an external force damages the brain, causing immediate harm and triggering further pathological processes that exacerbate the condition. Despite its widespread impact, the underlying mechanisms of TBI remain poorly understood, and there are no specific pharmacological treatments available. This creates an urgent need for new, effective neuroprotective drugs and strategies tailored to the diverse needs of TBI patients. In the realm of gene expression regulation, chromatin acetylation plays a pivotal role. This process is controlled by two classes of enzymes: histone acetyltransferase (HAT) and histone deacetylase (HDAC). These enzymes modify lysine residues on histone proteins, thereby determining the acetylation status of chromatin. HDACs, in particular, are involved in the epigenetic regulation of gene expression in TBI. Recent research has highlighted the potential of HDAC inhibitors (HDACIs) as promising neuroprotective agents. These compounds have shown encouraging results in animal models of various neurodegenerative diseases. HDACIs offer multiple avenues for TBI management: they mitigate the neuroinflammatory response, alleviate oxidative stress, inhibit neuronal apoptosis, and promote neurogenesis and axonal regeneration. Additionally, they reduce glial activation, which is associated with TBI-induced neuroinflammation. This review aims to provide a comprehensive overview of the roles and mechanisms of HDACs in TBI and to evaluate the therapeutic potential of HDACIs. By summarizing current knowledge and emphasizing the neuroregenerative capabilities of HDACIs, this review seeks to advance TBI management and contribute to the development of targeted treatments.

Upregulated spinal histone deacetylases induce nociceptive sensitization by inhibiting the GABA system in chronic constriction injury-induced neuropathy in rats.

Neuropathic pain (NP) affects countless people worldwide; however, few effective treatments are currently available. Histone deacetylases (HDACs) participate in epigenetic modifications in neuropathy-induced nociceptive sensitization. Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter that can inhibit NP. The present study aimed to examine the role of spinal HDAC and its isoforms in neuropathy. Male Wistar Rat with chronic constriction injury (CCI)-induced peripheral neuropathy and HDAC inhibitor, panobinostat, was administrated intrathecally. We performed quantitative real-time polymerase chain reaction (RT-qPCR), western blot, and immunohistochemical analysis of lumbar spinal cord dorsal horn and nociceptive behaviors (thermal hyperalgesia and mechanical allodynia) measurements. Herein, RT-qPCR analysis revealed that spinal hdac3, hdac4, and hdac6 were upregulated in CCI rats. Western blotting and immunofluorescence staining further confirmed that HDAC3, HDAC4, and HDAC6 were significantly upregulated, whereas GABA and its synthesis key enzyme glutamic acid decarboxylase (GAD) 65 were dramatically downregulated. Intrathecal panobinostat attenuated nociceptive behavior and restored the downregulated spinal GAD65 and GABA expression in CCI rats. HDAC upregulation might induce nociception through GAD65 and GABA inhibition in CCI-induced neuropathy. These findings strongly suggest that HDACs negatively regulate inhibitory neurotransmitters, constituting a potential therapeutic strategy for an epigenetic approach to manage NP.

A retrospective study of an irradiation-based conditioning regimen and chidamide maintenance therapy in T-ALL/LBL.

T-cell acute lymphoblastic leukemia/lymphoblastic lymphoma (T-ALL/LBL) are highly malignant and aggressive hematologic tumors for which there is no standard first-line treatment. Chidamide, a novel histone deacetylase inhibitor, shows great promise. We assessed the efficacy and safety of an irradiation-containing conditioning regimen for allogeneic hematopoietic stem cell transplantation (allo-HSCT) and post-transplantation chidamide maintenance in patients with T-ALL/LBL. We retrospectively analyzed the clinical data of six patients with T-ALL/LBL who underwent allo-HSCT with a radiotherapy-containing pretreatment regimen and post-transplant chidamide maintenance therapy. The endpoints were relapse, graft-versus-host disease (GVHD), transplant-related mortality (TRM), progression-free survival (PFS), overall survival (OS), and adverse events (AEs). All of the patients had uneventful post-transplant hematopoietic reconstitution, and all achieved complete molecular remission within 30 days. All six patients survived, and two relapsed with a median relapse time of 828.5 (170-1335) days. The 1-year OS rate was 100%, the 2-year PFS rate was 66.7%, and the TRM rate was 0%. After transplantation, two patients developed grade I-II acute GVHD (2/6); grade III-IV acute and chronic GVHD were not observed. The most common AEs following chidamide administration were hematological AEs, which occurred to varying degrees in all patients; liver function abnormalities occurred in two patients (grade 2), and symptoms of malaise occurred in one patient (grade 1). Chidamide maintenance therapy after T-ALL/LBL transplantation is safe, but the efficacy needs to be further investigated.

Insight in Quinazoline-based HDAC Inhibitors as Anti-cancer Agents.

Cancer remains a primary cause of death globally, and effective treatments are still limited. While chemotherapy has notably enhanced survival rates, it brings about numerous side effects. Consequently, the ongoing challenge persists in developing potent anti-cancer agents with minimal toxicity. The versatile nature of the quinazoline moiety has positioned it as a pivotal component in the development of various antitumor agents, showcasing its promising role in innovative cancer therapeutics. This concise review aims to reveal the potential of quinazolines in creating anticancer medications that target histone deacetylases (HDACs).

Abstract C051: Epigenetic reprogramming of brain-infiltrating myeloid cells deters brain metastasis outgrowth

Abstract The unique brain immune microenvironment (BrIME) co-evolves with brain metastasis (BrM) and is marked by immune suppression, posing a significant therapeutic challenge. BrIME is dominated by myeloid cells, with monocyte-derived macrophages (MDMs) comprising nearly half of the tumor-infiltrating leukocytes. Targeting MDMs remains challenging due to their inherent heterogeneity and high plasticity, which are regulated by epigenetic modifiers, including histone deacetylases (HDACs). Yet, the impact of HDAC inhibition in BrIME and its implications for BrM immunotherapy remains unclear. Here, we establish BrM syngenetic model by intracarotid artery (ICA) injection. Immune profiling by mass cytometry (CyTOF) analysis shows that selective class I HDAC inhibitor (HDACi) Entinostat (ENT) significantly enriches inflammatory MDMs in E0771 murine mammary tumor BrM model. Additionally, functional assay with bone marrow-derived macrophages (BMDMs) shows that ENT significantly enhances tumor cell phagocytosis and antigen presentation, increasing the proliferation of antigen-specific T cells in vitro. To test whether HDAC inhibition enhances antitumoral response in the BrIME, we designed a novel sequential treatment: with (1) ENT pre-conditioning the BrIME, (2) low- dose whole brain radiotherapy (LD-WBRT) to release tumor antigen followed by (3) anti-PD1 immune checkpoint therapy (ICT) to reinvigorate tumor-infiltrating. Our result shows that sequential triple treatment demonstrates significant BrM deterrence and induce a specific interferon-responsive MDM subset with robust type I interferon response in single-cell RNA sequencing, correlating with improved ICT clinical outcomes. Our data show that selective HDACi treatment reprograms the suppressive BrIME by steering the BrM-infiltrating MDMs toward immuno-stimulatory status. Sequential triple combinatorial therapy impedes BrM by activating innate and adaptive immunity simultaneously and is well tolerated in the animal model. Our findings highlight the potential of HDACi-mediated epigenetic reprogramming of the BrIME to enhance therapeutic efficacy in treating BrM. Citation Format: Shao-Ping Yang, Yimin Duan, Xiangliang Yuan, Lin Zhang, Wendao Liu, Jun Yao, Patrick Zhang, Jason T Huse, Zhongming Zhao, Dihua Yu. Epigenetic reprogramming of brain-infiltrating myeloid cells deters brain metastasis outgrowth [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr C051.

Valproate Administration to Adult 5xFAD Mice Upregulates Expression of Neprilysin and Improves Olfaction and Memory.

It is well known that the development of neurodegeneration, and especially Alzheimer's disease (AD), is often accompanied by impaired olfaction which precedes memory loss. A neuropeptidase neprilysin (NEP)-a principal amyloid-degrading enzyme in the brain-was also shown to be involved in olfactory signalling. Previously we have demonstrated that 5xFAD mice develop olfactory deficit by the age of 6months which correlated with reduced NEP expression in the brain areas involved in olfactory signalling. The aim of this study was to analyse the effect of administration of a histone deacetylase inhibitor, valproic acid (VA), to adult 5xFAD mice on their olfaction and memory as well as on brain morphology and NEP expression in the parietal cortex (PC) and hippocampus (Hip). The data obtained demonstrated that administration of VA to 7-month-old mice (200mg/kg of body weight) for 28days resulted in improvement of their memory in the Morris water maze as well as olfaction in the odor preference and food search tests. This correlated with increased expression of NEP in the PC and Hip as well as a reduced number of amyloid plaques in these brain areas. This strongly suggests that NEP can be considered an important therapeutic target not only in AD but also in olfactory loss.

Sirtuin inhibitors reduce intracellular growth of M. tuberculosis in human macrophages via modulation of host cell immunity.

Host-directed therapies aiming to strengthen the body's immune system, represent an underexplored opportunity to improve treatment of tuberculosis (TB). We have previously shown in Mycobacterium tuberculosis (Mtb)-infection models and clinical trials that treatment with the histone deacetylase (HDAC) inhibitor, phenylbutyrate (PBA), can restore Mtb-induced impairment of antimicrobial responses and improve clinical outcomes in pulmonary TB. In this study, we evaluated the efficacy of different groups of HDAC inhibitors to reduce Mtb growth in human immune cells. A panel of 21 selected HDAC inhibitors with different specificities that are known to modulate infection or inflammation was tested using high-content live-cell imaging and analysis. Monocyte-derived macrophages or bulk peripheral blood cells (PBMCs) were infected with the green fluorescent protein (GFP)-expressing Mtb strains H37Ra or H37Rv and treated with HDAC inhibitors in the micromolar range in parallel with a combination of the first-line antibiotics, rifampicin, and isoniazid. Host cell viability in HDAC inhibitor treated cell cultures was monitored with Cytotox-red. Seven HDAC inhibitors were identified that reduced Mtb growth in macrophages > 45-75% compared to average 40% for PBA. The most effective compounds were inhibitors of the class III HDAC proteins, the sirtuins. While these compounds may exhibit their effects by improving macrophage function, one of the sirtuin inhibitors, tenovin, was also highly effective in extracellular killing of Mtb bacilli. Antimicrobial synergy testing using checkerboard assays revealed additive effects between selected sirtuin inhibitors and subinhibitory concentrations of rifampicin or isoniazid. A customized macrophage RNA array including 23 genes associated with cytokines, chemokines and inflammation, suggested that Mtb-infected macrophages are differentially modulated by the sirtuin inhibitors as compared to PBA. Altogether, these results demonstrated that sirtuin inhibitors may be further explored as promising host-directed compounds to support immune functions and reduce intracellular growth of Mtb in human cells.

Identification of Potential Inhibitors of Histone Deacetylase 6 Through Virtual Screening and Molecular Dynamics Simulation Approach: Implications in Neurodegenerative Diseases

Background: Histone deacetylase 6 (HDAC6) plays a crucial role in neurological, inflammatory, and other diseases; thus, it has emerged as an important target for therapeutic intervention. To date, there are no FDA-approved HDAC6-targeting drugs, and most pipeline candidates suffer from poor target engagement, inadequate brain penetration, and low tolerability. There are a few HDAC6 clinical candidates for the treatment of mostly non-CNS cancers as their pharmacokinetic liabilities exclude them from targeting HDAC6-implicated neurological diseases, urging development to address these challenges. They also demonstrate off-target toxicity due to limited selectivity, leading to adverse effects in patients. Selective inhibitors have thus been the focus of development over the past decade, though no selective and potent HDAC6 inhibitor has yet been approved. Methods: This study involved an integrated virtual screening against HDAC6 using the DrugBank database to identify repurposed drugs capable of inhibiting HDAC6 activity. The primary assessment involved the determination of the ability of molecules to bind with HDAC6. Subsequently, interaction analyses and 500 ns molecular dynamics (MD) simulations followed by essential dynamics were carried out to study the conformational flexibility and stability of HDAC6 in the presence of the screened molecules, i.e., penfluridol and pimozide. Results: The virtual screening results pinpointed penfluridol and pimozide as potential repurposed drugs against HDAC6 based on their binding efficiency and appropriate drug profiles. The docking results indicate that penfluridol and pimozide share the same binding site as the reference inhibitor with HDAC6. The MD simulation results showed that stable protein–ligand complexes of penfluridol and pimozide with HDAC6 were formed. Additionally, MMPBSA analysis revealed favorable binding free energies for all HDAC6–ligand complexes, confirming the stability of their interactions. Conclusions: The study implies that both penfluridol and pimozide have strong and favorable binding with HDAC6, which supports the idea of repositioning these drugs for the management of neurodegenerative disorders. However, further in-depth studies are needed to explore their efficacy and safety in biological systems.

The HDAC6 inhibitor AVS100 (SS208) induces a pro-inflammatory tumor microenvironment and potentiates immunotherapy.

Histone deacetylase 6 (HDAC6) inhibition is associated with an increased pro-inflammatory tumor microenvironment and antitumoral immune responses. Here, we show that the HDAC6 inhibitor AVS100 (SS208) had an antitumoral effect in SM1 melanoma and CT26 colon cancer models and increased the efficacy of anti-programmed cell death protein 1 treatment, leading to complete remission in melanoma and increased response in colon cancer. AVS100 treatment increased pro-inflammatory tumor-infiltrating macrophages and CD8 effector T cells with an inflammatory and T cell effector gene signature. Acquired T cell immunity and long-term protection were evidenced as increased immunodominant T cell clones after AVS100 treatment. Last, AVS100 showed no mutagenicity, toxicity, or adverse effects in preclinical good laboratory practice studies, part of the package that has led to US Food and Drug Administration clearance of an investigational new drug application for initiating clinical trials. This would be a first-in-human combination therapy of pembrolizumab with HDAC6 inhibition for locally advanced or metastatic solid tumors.

Discovery of Novel 5-Cyano-3-phenylindole-Based LSD1/HDAC Dual Inhibitors for Colorectal Cancer Treatment.

The dual inhibition of histone lysine-specific demethylase 1 (LSD1) and histone deacetylase (HDAC) has emerged as a promising strategy for cancer therapy. In this study, we report the discovery of novel 5-cyano-3-phenylindole-based LSD1/HDAC dual inhibitors, evaluated through both in vitro and in vivo assays. Among these inhibitors, compound 20c was identified as particularly potent, exhibiting high inhibitory activity against LSD1 (IC50 = 39.0 nM) and HDAC1/2/3/6/8 (IC50 = 1.4, 1.0, 1.3, 2.9, and 16.0 nM, respectively). Compound 20c effectively modulated the expression of biomarkers associated with LSD1 and HDAC inhibition and demonstrated superior antiproliferative activity compared to SAHA and 4SC-202 across multiple colorectal cancer cell lines. Following pharmacokinetic studies, 20c was further assessed in HCT-116 and HT-29 xenograft mouse models. It demonstrated significantly enhanced antitumor efficacy compared to SAHA, without causing observable toxicity. These findings highlight the potential of LSD1/HDAC dual inhibitors for the treatment of malignant cancers.

Discovery of Janus Kinase and Histone Deacetylase Dual Inhibitors as a New Strategy to Treat Psoriasis.

Psoriasis is a common, chronic, recurrent, and inflammatory skin disease, which causes physical and psychological problems in patients and lacks effective and economic therapeutics. Herein, we designed Janus kinase (JAK) and histone deacetylase (HDAC) dual inhibitors as a new strategy for the treatment of psoriasis. In particular, compound 11i was identified with excellent inhibitory activity toward JAKs (JAK2 IC50 = 0.49 nM) and HDACs (HDAC6 IC50 = 12 nM). Moreover, it exhibited potent activities in inhibiting the proliferation of TNF-α-induced HaCAT cells and the production of nitric oxide. Importantly, compound 11i significantly ameliorated psoriasis-like skin lesions in an imiquimod-induced murine model with low toxicity, which was superior to JAK inhibitor momelotinib, HDAC inhibitor vorinostat, and their combination. This work provided a proof-of-concept for JAK/HDAC dual inhibitors as a promising strategy for the treatment of psoriasis.

The Impact of Alcohol-Induced Epigenetic Modifications in the Treatment of Alcohol use Disorders.

Alcohol use disorders are responsible for 5.9% of all death annually and 5.1% of the global disease burden. It has been suggested that alcohol abuse can modify gene expression through epigenetic processes, namely DNA and histone methylation, histone acetylation, and microRNA expression. The alcohol influence on epigenetic mechanisms leads to molecular adaptation of a wide number of brain circuits, including the hypothalamus-hypophysis-adrenal axis, the prefrontal cortex, the mesolimbic-dopamine pathways and the endogenous opioid pathways. Epigenetic regulation represents an important level of alcohol-induced molecular adaptation in the brain. It has been demonstrated that acute and chronic alcohol exposure can induce opposite modifications in epigenetic mechanisms: acute alcohol exposure increases histone acetylation, decreases histone methylation and inhibits DNA methyltransferase activity, while chronic alcohol exposure induces hypermethylation of DNA. Some studies investigated the chromatin status during the withdrawal period and the craving period and showed that craving was associated with low methylation status, while the withdrawal period was associated with elevated activity of histone deacetylase and decreased histone acetylation. Given the effects exerted by ethanol consumption on epigenetic mechanisms, chromatin structure modifiers, such as histone deacetylase inhibitors and DNA methyltransferase inhibitors, might represent a new potential strategy to treat alcohol use disorder. Further investigations on molecular modifications induced by ethanol might be helpful to develop new therapies for alcoholism and drug addiction targeting epigenetic processes.

Autoimmune disease: a view of epigenetics and therapeutic targeting

Autoimmune diseases comprise a large group of conditions characterized by a complex pathogenesis and significant heterogeneity in their clinical manifestations. Advances in sequencing technology have revealed that in addition to genetic susceptibility, various epigenetic mechanisms including DNA methylation and histone modification play critical roles in disease development. The emerging field of epigenetics has provided new perspectives on the pathogenesis and development of autoimmune diseases. Aberrant epigenetic modifications can be used as biomarkers for disease diagnosis and prognosis. Exploration of human epigenetic profiles revealed that patients with autoimmune diseases exhibit markedly altered DNA methylation profiles compared with healthy individuals. Targeted cutting-edge epigenetic therapies are emerging. For example, DNA methylation inhibitors can rectify methylation dysregulation and relieve patients. Histone deacetylase inhibitors such as vorinostat can affect chromatin accessibility and further regulate gene expression, and have been used in treating hematological malignancies. Epigenetic therapies have opened new avenues for the precise treatment of autoimmune diseases and offer new opportunities for improved therapeutic outcomes. Our review can aid in comprehensively elucidation of the mechanisms of autoimmune diseases and development of new targeted therapies that ultimately benefit patients with these conditions.

Effects of a novel HDAC6-selective inhibitor's radiosensitization on cancer cells.

The radiation sensitivity of tumor cells is a critical determinant of their therapeutic response to radiotherapy. Histone deacetylase 6 (HDAC6), beyond its known role in modulating tubulin acetylation and influencing cell motility, is also involved in the DNA damage response, potentially enhancing tumor cell radiosensitivity. Targeted HDAC6 inhibitors have shown substantial promise in preclinical studies aimed at increasing radiosensitivity and inhibiting cellular migration. A new HDAC inhibitor, named OXHA, was designed by substituting the phenyl cap of SAHA with an N,5-diphenyloxazole-2-carboxamide group. The inhibitory activity of OXHA was evaluated via in vitro enzymatic assays. Its effects on tumor cell migration and radiosensitization potential were assessed using scratch wound healing assays, micronucleus formation, and clonogenic survival assays. Enzymatic assays confirmed OXHA's selective inhibition of HDAC6. Compared to SAHA, OXHA significantly increased α-tubulin acetylation while minimally impacting histone H3 acetylation, indicating a high selectivity for HDAC6. In combination with X-ray irradiation, OXHA markedly impaired wound healing in A549 and HepG2 cells, enhanced micronucleus formation, and reduced clonogenic survival across multiple tumor lines. OXHA exhibits potent and selective HDAC6 inhibition, effectively impeding tumor cell migration and enhancing radiosensitivity across multiple cell lines. These findings suggest that OXHA has strong potential as a therapeutic strategy to improve radiotherapy efficacy.

The Impact of the Histone Deacetylase Inhibitor-Sodium Butyrate on Complement-Mediated Synapse Loss in a Rat Model of Neonatal Hypoxia-Ischemia.

Perinatal asphyxia is one of the most important causes of morbidity and mortality in newborns. One of the key pathogenic factors in hypoxic-ischemic (HI) brain injury is the inflammatory reaction including complement system activation. Over-activated complement stimulates cells to release inflammatory molecules and is involved in the post-ischemic degradation of synaptic connections. On the other hand, complement is also involved in regenerative processes. The histone deacetylase inhibitor (HDACi)-sodium butyrate (SB)-provides reduction of inflammation by decreasing the expression of the proinflammatory factors. The main purpose of this study was to examine the effect of SB treatment on complement activation and synapse elimination after HI. Neonatal HI was induced in Wistar rats pups by unilateral ligation of the common carotid artery followed by 60-min hypoxia (7.6% O2). SB (300mg/kg) was administered on a 5-day regimen. Our study has shown decreased levels of synapsin I, synaptophysin, and PSD-95 in the hypoxic-ischemic hemisphere, indicating synaptic loss after neonatal HI. Transmission electron microscopy revealed injury of the synaptic structures in the brain after HI. SB treatment increased the level of the synaptic proteins, improved tissue ultrastructure, and reduced degradation of the synapses. Neonatal HI induced mRNA expression of the complement C1q, C3, C5, and C9, and their receptors C3aR and C5aR. The effect of SB was different depending on the time after induction of hypoxic-ischemic damage. Our study demonstrated that neuroprotective effect of SB may be related to the modulation of complement activity after HI brain injury.

Spirotetrahydroisoquinoline-Based Histone Deacetylase Inhibitors as New Antifibrotic Agents: Biological Evaluation in Human Fibroblasts from Bronchoalveolar Lavages of Idiopathic Pulmonary Fibrosis Patients

Spirotetrahydroisoquinoline-Based Histone Deacetylase Inhibitors as New Antifibrotic Agents: Biological Evaluation in Human Fibroblasts from Bronchoalveolar Lavages of Idiopathic Pulmonary Fibrosis Patients

Drug prioritization identifies panobinostat as a tailored treatment element for patients with metastatic hepatoblastoma.

Patients with metastatic hepatoblastoma are treated with severely toxic first-line chemotherapies in combination with surgery. Yet, inadequate response of lung metastases to neo-adjuvant chemotherapy still compromises patient outcomes making new treatment strategies, tailored to more efficient lung clearance, mandatory. We harnessed a comprehensive patient-derived xenograft platform and a variety of in vitro and in vivo assays to establish the preclinical and biological rationale for a new drug for patients with metastatic hepatoblastoma. The testing of a library of established drugs on patient-derived xenografts identified histone deacetylase inhibitors, most notably panobinostat, to be highly efficacious on hepatoblastoma cells, as compared to non-cancerous cells. Molecularly, the anti-tumor effect of panobinostat is mediated by posttranslational obstruction of the MYC oncoprotein as a result of dual specificity phosphatase 1 upregulation, thereby leading to growth inhibition and programmed cell death. Of clinical importance, upregulation of the MYC target gene nucleophosmin 1 is indicative of response to panobinostat and associated with metastatic disease in patients with hepatoblastoma. The combination of panobinostat with the current SIOPEL 4 induction protocol, consisting of cisplatin and doxorubicin, revealed high synergies already at low nanomolar levels. The simulation of a clinical trial, with this combination therapy, in patient-derived xenograft models, and ultimately heterotypic lung metastasis mimics clearly underscored the potency of this approach. Integrated studies define MYC inhibition by panobinostat as a novel treatment element to be introduced into the therapeutic strategy for patients with metastatic hepatoblastoma.

EXTH-47. ENHANCING GD2.CART THERAPY FOR DIFFUSE MIDLINE GLIOMA WITH LSD1 AND HDAC INHIBITORS

Abstract Chimeric antigen receptor T cells against the glycolipid GD2 (GD2.CARTs) are showing promise in diffuse midline glioma (DMG) but are not yet curative. Since low target antigen expression is one potential mechanism by which tumor cells can escape CART therapy, we profiled GD2 expression levels on 9 different H3K27M-mutant DMG cell lines using flow cytometry. This analysis shows that only 5 of the 9 cell lines exhibit high GD2 expression while the remaining 4 lines have low GD2-expressing cells. When treating these cell lines with GD2.CARTs in co-culture assays and xenograft mice, we find that low GD2 expression on DMG cells correlates with tumor cell escape from GD2.CARTs and therapeutic resistance in vivo. Our lab previously found that simultaneous inhibition of histone deacetylases (HDACs) and lysine-demethylase 1 (LSD1) in DMG cells causes synergistic increases in gene expression and tumor cell death. Previous studies in neuroblastoma also demonstrate that HDAC inhibitor (HDACi) treatment can increase GD2 on tumor cells and improve targeting by GD2.CARTs. We therefore decided to assess whether treating GD2-low DMG cell lines with combinations of LSD1 inhibitors (LSD1i) and HDACi improves DMG response to GD2.CARTs. Immunofluorescence and flow cytometric analyses show that GD2 expression is increased on LSD1i+HDACi-treated GD2-low DMG cells and that there is enhanced tumor cell targeting by GD2.CARTs in subsequent co-culture assays. Treating mice transplanted with GD2-low DMG cells with LSD1i+HDACi followed by intravenous GD2.CART infusion also led to reduced tumor growth. These results suggest that LSD1i+HDACi pre-treatment may provide a way to improve DMG patient responses to GD2.CART therapy by increasing target antigen expression.

TMET-22. OVERCOMING RESISTANCE: PANOBINOSTAT SENSITIZES 2DG-RESISTANT PEDIATRIC HIGH-GRADE GLIOMAS WITH H3.3 K27M/G34R MUTATIONS TO APOPTOSIS

Abstract BACKGROUND Pediatric high-grade gliomas (pHGG) harboring H3.3 K27M/G34R mutations present formidable challenges in treatment due to their aggressiveness and resistance to standard chemotherapy. Our preliminary investigations have shown promising results, indicating that combining 2-deoxyglucose (2DG), a glycolytic inhibitor, with DNA-damaging agents synergistically inhibits pHGG growth. However, prolonged exposure to 2DG induces resistance, necessitating the exploration of alternative therapies. This study aims to investigate the potential of panobinostat, a histone deacetylase inhibitor, in sensitizing 2DG-resistant pHGG with H3.3 K27M/G34R mutations to apoptosis. METHODS Transcriptomic analysis via Illumina NovaSeq 6000 and metabolomic profiling employing Liquid Chromatography-High-Resolution Mass Spectrometry was used to delineate the molecular landscape of naive and 2DG-resistant pHGG cell lines. Functional assays, including the Agilent Seahorse Mito Stress Test and flow cytometry, assessed bioenergetics and mitochondrial dynamics. Intracellular NAD+ and NADH levels were quantified utilizing NAD+/NADH Glo assays, while apoptotic markers and metabolic stress were measured using the Annexin V-FITC Conjugates for Apoptosis Detection kit and western blot. RESULTS Comparative analysis revealed increased transketolase activity in 2DG-resistant cells, augmenting the interaction between the pentose phosphate pathway and glycolysis, resulting in elevated levels of NADPH and ATP. Additionally, these resistant cells displayed enhanced reliance on mitochondrial energy metabolism, as evidenced by substantial increases in mitochondrial membrane potential and mass, coupled with elevated NAD+ levels. Subsequent treatment with panobinostat induced a significant decrease in NAD+ biosynthesis and ATP generation. Furthermore, this intervention triggered the upregulation of pro-apoptotic BCL-2 family proteins, particularly BAX and BAK, concomitant with a notable reduction in mitochondrial membrane potential and the accumulation of reactive oxygen species. Consequently, heightened caspase-3 activity ensued, leading to significantly elevated cell death rates in 2DG-resistant gliomas. CONCLUSION Our findings highlight panobinostat as a promising therapy to resensitize 2DG-resistant pHGG cells to apoptosis, offering hope for treating these aggressive tumors with H3.3 K27M/G34R mutations.