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Keita M, McIntyre K, Rodden LN, Schadt K, Lynch DR. Friedreich ataxia: clinical features and new developments. Neurodegener Dis Manag 2022; 12:267-283. [PMID: 35766110 PMCID: PMC9517959 DOI: 10.2217/nmt-2022-0011] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 06/15/2022] [Indexed: 11/21/2022] Open
Abstract
Friedreich's ataxia (FRDA), a neurodegenerative disease characterized by ataxia and other neurological features, affects 1 in 50,000-100,000 individuals in the USA. However, FRDA also includes cardiac, orthopedic and endocrine dysfunction, giving rise to many secondary disease characteristics. The multifaceted approach for clinical care has necessitated the development of disease-specific clinical care guidelines. New developments in FRDA include the advancement of clinical drug trials targeting the NRF2 pathway and frataxin restoration. Additionally, a novel understanding of gene silencing in FRDA, reflecting a variegated silencing pattern, will have applications to current and future therapeutic interventions. Finally, new perspectives on the neuroanatomy of FRDA and its developmental features will refine the time course and anatomical targeting of novel approaches.
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Affiliation(s)
- Medina Keita
- Departments of Pediatrics & Neurology, Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Kellie McIntyre
- Departments of Pediatrics & Neurology, Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Layne N Rodden
- Departments of Pediatrics & Neurology, Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Kim Schadt
- Departments of Pediatrics & Neurology, Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - David R Lynch
- Departments of Pediatrics & Neurology, Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
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2
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Schreiber AM, Li Y, Chen YH, Napierala JS, Napierala M. Selected Histone Deacetylase Inhibitors Reverse the Frataxin Transcriptional Defect in a Novel Friedreich's Ataxia Induced Pluripotent Stem Cell-Derived Neuronal Reporter System. Front Neurosci 2022; 16:836476. [PMID: 35281493 PMCID: PMC8904878 DOI: 10.3389/fnins.2022.836476] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Accepted: 01/12/2022] [Indexed: 11/23/2022] Open
Abstract
Friedreich's ataxia (FRDA) is a neurodegenerative disorder caused by the expansion of guanine-adenine-adenine repeats within the first intron of the frataxin (FXN) gene. The location and nature of the expansion have been proven to contribute to transcriptional repression of FXN by decreasing the rate of polymerase II (RNA polymerase II) progression and increasing the presence of histone modifications associated with a heterochromatin-like state. Targeting impaired FXN transcription appears as a feasible option for therapeutic intervention, while no cure currently exists. We created a novel reporter cell line containing an FXN-Nanoluciferase (FXN-NLuc) fusion in induced pluripotent stem cells (iPSCs) reprogrammed from the fibroblasts of patients with FRDA, thus allowing quantification of endogenous FXN expression. The use of iPSCs provides the opportunity to differentiate these cells into disease-relevant neural progenitor cells (NPCs). NPCs derived from the FXN-NLuc line responded to treatments with a known FXN inducer, RG109. Results were validated by quantitative PCR and Western blot in multiple FRDA NPC lines. We then screened a commercially available library of compounds consisting of molecules targeting various enzymes and pathways critical for silencing or activation of gene expression. Only selected histone deacetylase inhibitors were capable of partial reactivation of FXN expression. This endogenous, FRDA iPSC-derived reporter can be utilized for high-throughput campaigns performed in cells most relevant to disease pathology in search of FXN transcription activators.
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Affiliation(s)
- Anna M. Schreiber
- Department of Biochemistry and Molecular Genetics, Stem Cell Institute, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Yanjie Li
- Department of Biochemistry and Molecular Genetics, Stem Cell Institute, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Yi-Hsien Chen
- Genome Engineering and iPSC Center, Washington University, St. Louis, MO, United States
| | - Jill S. Napierala
- Department of Biochemistry and Molecular Genetics, Stem Cell Institute, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Marek Napierala
- Department of Biochemistry and Molecular Genetics, Stem Cell Institute, University of Alabama at Birmingham, Birmingham, AL, United States
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3
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Rodden LN, Gilliam KM, Lam C, Lynch DR, Bidichandani SI. Epigenetic Heterogeneity in Friedreich Ataxia Underlies Variable FXN Reactivation. Front Neurosci 2021; 15:752921. [PMID: 34899161 PMCID: PMC8655727 DOI: 10.3389/fnins.2021.752921] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Accepted: 11/01/2021] [Indexed: 11/13/2022] Open
Abstract
Friedreich ataxia (FRDA) is typically caused by homozygosity for an expanded GAA triplet-repeat in intron 1 of the FXN gene. The expanded repeat induces repressive histone changes and DNA hypermethylation, which result in epigenetic silencing and FXN transcriptional deficiency. A class I histone deacetylase inhibitor (HDACi-109) reactivates the silenced FXN gene, although with considerable inter-individual variability, which remains etiologically unexplained. Because HDAC inhibitors work by reversing epigenetic silencing, we reasoned that epigenetic heterogeneity among patients may help to explain this inter-individual variability. As a surrogate measure for epigenetic heterogeneity, a highly quantitative measurement of DNA hypermethylation via bisulfite deep sequencing, with single molecule resolution, was used to assess the prevalence of unmethylated, partially methylated, and fully methylated somatic FXN molecules in PBMCs from a prospective cohort of 50 FRDA patients. Treatment of the same PBMCs from this cohort with HDACi-109 significantly increased FXN transcript to levels seen in asymptomatic heterozygous carriers, albeit with the expected inter-individual variability. Response to HDACi-109 correlated significantly with the prevalence of unmethylated and partially methylated FXN molecules, supporting the model that FXN reactivation involves a proportion of genes that are amenable to correction in non-dividing somatic cells, and that heavily methylated FXN molecules are relatively resistant to reactivation. FXN reactivation is a promising therapeutic strategy in FRDA, and inter-individual variability is explained, at least in part, by somatic epigenetic heterogeneity.
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Affiliation(s)
- Layne N Rodden
- Department of Pediatrics, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States.,Oklahoma Center for Neuroscience, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States
| | - Kaitlyn M Gilliam
- Department of Pediatrics, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States
| | - Christina Lam
- Department of Pediatrics, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States
| | - David R Lynch
- Division of Neurology, The Children's Hospital of Philadelphia, Philadelphia, PA, United States
| | - Sanjay I Bidichandani
- Department of Pediatrics, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States.,Oklahoma Center for Neuroscience, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States.,Department of Biochemistry and Molecular Biology, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States
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4
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Yang W, Thompson B, Kwa FAA. Molecular approaches for the treatment and prevention of Friedreich's ataxia. Drug Discov Today 2021; 27:866-880. [PMID: 34763067 DOI: 10.1016/j.drudis.2021.11.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 10/01/2021] [Accepted: 11/01/2021] [Indexed: 12/11/2022]
Abstract
Friedreich's ataxia (FRDA) is caused by an intronic guanine-adenine-adenine (GAA) trinucleotide expansion in the gene encoding the frataxin protein (FXN). This triggers the transcriptional silencing of the fratxin gene (FXN) and subsequent FXN deficiency in affected cells, which accounts for the multisystemic symptoms of this condition. Current management strategies aim for symptomatic relief and no treatments can prevent disease onset or progression. Thus, research efforts have focused on targeting the molecular pathways that silence FXN and downstream pathological processes. However, progression of potential therapies into clinical use has been hindered by inconclusive clinical trials because of the small patient sample size associated with the low prevalence of this condition. Here, we discuss various molecular approaches and explore their therapeutic potential to alter the course of this progressive condition.
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Affiliation(s)
- Wenyao Yang
- School of Health Sciences, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
| | - Bruce Thompson
- School of Health Sciences, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
| | - Faith A A Kwa
- School of Health Sciences, Swinburne University of Technology, Hawthorn, VIC 3122, Australia.
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5
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Bondarev AD, Attwood MM, Jonsson J, Chubarev VN, Tarasov VV, Schiöth HB. Recent developments of HDAC inhibitors: Emerging indications and novel molecules. Br J Clin Pharmacol 2021; 87:4577-4597. [PMID: 33971031 DOI: 10.1111/bcp.14889] [Citation(s) in RCA: 167] [Impact Index Per Article: 55.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Revised: 04/23/2021] [Accepted: 05/01/2021] [Indexed: 02/06/2023] Open
Abstract
The histone deacetylase (HDAC) enzymes, a class of epigenetic regulators, are historically well established as attractive therapeutic targets. During investigation of trends within clinical trials, we have identified a high number of clinical trials involving HDAC inhibitors, prompting us to further evaluate the current status of this class of therapeutic agents. In total, we have identified 32 agents with HDAC-inhibiting properties, of which 29 were found to interact with the HDAC enzymes as their primary therapeutic target. In this review, we provide an overview of the clinical drug development highlighting the recent advances and provide analysis of specific trials and, where applicable, chemical structures. We found haematologic neoplasms continue to represent the majority of clinical indications for this class of drugs; however, it is clear that there is an ongoing trend towards diversification. Therapies for non-oncology indications including HIV infection, muscular dystrophies, inflammatory diseases as well as neurodegenerative diseases such as Alzheimer's disease, frontotemporal dementia and Friedreich's ataxia are achieving promising clinical progress. Combinatory regimens are proving to be useful to improve responsiveness among FDA-approved agents; however, it often results in increased treatment-related toxicities. This analysis suggests that the indication field is broadening through a high number of clinical trials while several fields of preclinical development are also promising.
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Affiliation(s)
- Andrey D Bondarev
- Department of Pharmacology, Institute of Pharmacy, I. M. Sechenov First Moscow State Medical University, Moscow, Russia.,Department of Neuroscience, Functional Pharmacology, Uppsala University, Uppsala, Sweden
| | - Misty M Attwood
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Uppsala, Sweden
| | - Jörgen Jonsson
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Uppsala, Sweden
| | - Vladimir N Chubarev
- Department of Pharmacology, Institute of Pharmacy, I. M. Sechenov First Moscow State Medical University, Moscow, Russia
| | - Vadim V Tarasov
- Department of Pharmacology, Institute of Pharmacy, I. M. Sechenov First Moscow State Medical University, Moscow, Russia.,Institute of Translational Medicine and Biotechnology, I. M. Sechenov First Moscow State Medical University, Moscow, Russia
| | - Helgi B Schiöth
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Uppsala, Sweden.,Institute of Translational Medicine and Biotechnology, I. M. Sechenov First Moscow State Medical University, Moscow, Russia
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6
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Rodden LN, Chutake YK, Gilliam K, Lam C, Soragni E, Hauser L, Gilliam M, Wiley G, Anderson MP, Gottesfeld JM, Lynch DR, Bidichandani SI. Methylated and unmethylated epialleles support variegated epigenetic silencing in Friedreich ataxia. Hum Mol Genet 2021; 29:3818-3829. [PMID: 33432325 PMCID: PMC7861014 DOI: 10.1093/hmg/ddaa267] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Revised: 12/01/2020] [Accepted: 12/09/2020] [Indexed: 12/20/2022] Open
Abstract
Friedreich ataxia (FRDA) is typically caused by homozygosity for an expanded GAA triplet-repeat in intron 1 of the FXN gene, which results in transcriptional deficiency via epigenetic silencing. Most patients are homozygous for alleles containing > 500 triplets, but a subset (~20%) have at least one expanded allele with < 500 triplets and a distinctly milder phenotype. We show that in FRDA DNA methylation spreads upstream from the expanded repeat, further than previously recognized, and establishes an FRDA-specific region of hypermethylation in intron 1 (~90% in FRDA versus < 10% in non-FRDA) as a novel epigenetic signature. The hypermethylation of this differentially methylated region (FRDA-DMR) was observed in a variety of patient-derived cells; it significantly correlated with FXN transcriptional deficiency and age of onset, and it reverted to the non-disease state in isogenically corrected induced pluripotent stem cell (iPSC)-derived neurons. Bisulfite deep sequencing of the FRDA-DMR in peripheral blood mononuclear cells from 73 FRDA patients revealed considerable intra-individual epiallelic variability, including fully methylated, partially methylated, and unmethylated epialleles. Although unmethylated epialleles were rare (median = 0.33%) in typical patients homozygous for long GAA alleles with > 500 triplets, a significantly higher prevalence of unmethylated epialleles (median = 9.8%) was observed in patients with at least one allele containing < 500 triplets, less severe FXN deficiency (>20%) and later onset (>15 years). The higher prevalence in mild FRDA of somatic FXN epialleles devoid of DNA methylation is consistent with variegated epigenetic silencing mediated by expanded triplet-repeats. The proportion of unsilenced somatic FXN genes is an unrecognized phenotypic determinant in FRDA and has implications for the deployment of effective therapies.
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Affiliation(s)
- Layne N Rodden
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
- Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - Yogesh K Chutake
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - Kaitlyn Gilliam
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - Christina Lam
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - Elisabetta Soragni
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
| | - Lauren Hauser
- Division of Neurology, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Matthew Gilliam
- Department of Electrical and Computer Engineering, University of Oklahoma, Norman, OK, USA
| | - Graham Wiley
- Arthritis and Clinical Immunology Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
| | - Michael P Anderson
- Department of Biostatistics and Epidemiology, Hudson College of Public Health, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - Joel M Gottesfeld
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, USA
| | - David R Lynch
- Division of Neurology, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Sanjay I Bidichandani
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
- Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
- Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
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7
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Vilema-Enríquez G, Quinlan R, Kilfeather P, Mazzone R, Saqlain S, Del Molino Del Barrio I, Donato A, Corda G, Li F, Vedadi M, Németh AH, Brennan PE, Wade-Martins R. Inhibition of the SUV4-20 H1 histone methyltransferase increases frataxin expression in Friedreich's ataxia patient cells. J Biol Chem 2020; 295:17973-17985. [PMID: 33028632 PMCID: PMC7939392 DOI: 10.1074/jbc.ra120.015533] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Indexed: 12/11/2022] Open
Abstract
The molecular mechanisms of reduced frataxin (FXN) expression in Friedreich's ataxia (FRDA) are linked to epigenetic modification of the FXN locus caused by the disease-associated GAA expansion. Here, we identify that SUV4-20 histone methyltransferases, specifically SUV4-20 H1, play an important role in the regulation of FXN expression and represent a novel therapeutic target. Using a human FXN-GAA-Luciferase repeat expansion genomic DNA reporter model of FRDA, we screened the Structural Genomics Consortium epigenetic probe collection. We found that pharmacological inhibition of the SUV4-20 methyltransferases by the tool compound A-196 increased the expression of FXN by ∼1.5-fold in the reporter cell line. In several FRDA cell lines and patient-derived primary peripheral blood mononuclear cells, A-196 increased FXN expression by up to 2-fold, an effect not seen in WT cells. SUV4-20 inhibition was accompanied by a reduction in H4K20me2 and H4K20me3 and an increase in H4K20me1, but only modest (1.4-7.8%) perturbation in genome-wide expression was observed. Finally, based on the structural activity relationship and crystal structure of A-196, novel small molecule A-196 analogs were synthesized and shown to give a 20-fold increase in potency for increasing FXN expression. Overall, our results suggest that histone methylation is important in the regulation of FXN expression and highlight SUV4-20 H1 as a potential novel therapeutic target for FRDA.
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Affiliation(s)
| | - Robert Quinlan
- Structural Genomics Consortium, University of Oxford, Oxford, United Kingdom; Alzheimer's Research UK Oxford Drug Discovery Institute, Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - Peter Kilfeather
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Roberta Mazzone
- Structural Genomics Consortium, University of Oxford, Oxford, United Kingdom; Alzheimer's Research UK Oxford Drug Discovery Institute, Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - Saba Saqlain
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | | | - Annalidia Donato
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Gabriele Corda
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Fengling Li
- Structural Genomics Consortium, University of Toronto, Toronto, Ontario, Canada
| | - Masoud Vedadi
- Structural Genomics Consortium, University of Toronto, Toronto, Ontario, Canada; Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada
| | - Andrea H Németh
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom; Oxford Centre for Genomic Medicine, Oxford University Hospitals National Health Service Trust, Oxford, United Kingdom
| | - Paul E Brennan
- Structural Genomics Consortium, University of Oxford, Oxford, United Kingdom; Alzheimer's Research UK Oxford Drug Discovery Institute, Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - Richard Wade-Martins
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
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8
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Sherzai M, Valle A, Perry N, Kalef-Ezra E, Al-Mahdawi S, Pook M, Anjomani Virmouni S. HMTase Inhibitors as a Potential Epigenetic-Based Therapeutic Approach for Friedreich's Ataxia. Front Genet 2020; 11:584. [PMID: 32582297 PMCID: PMC7291394 DOI: 10.3389/fgene.2020.00584] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Accepted: 05/14/2020] [Indexed: 12/17/2022] Open
Abstract
Friedreich's ataxia (FRDA) is a progressive neurodegenerative disorder caused by a homozygous GAA repeat expansion mutation in intron 1 of the frataxin gene (FXN), which instigates reduced transcription. As a consequence, reduced levels of frataxin protein lead to mitochondrial iron accumulation, oxidative stress, and ultimately cell death; particularly in dorsal root ganglia (DRG) sensory neurons and the dentate nucleus of the cerebellum. In addition to neurological disability, FRDA is associated with cardiomyopathy, diabetes mellitus, and skeletal deformities. Currently there is no effective treatment for FRDA and patients die prematurely. Recent findings suggest that abnormal GAA expansion plays a role in histone modification, subjecting the FXN gene to heterochromatin silencing. Therefore, as an epigenetic-based therapy, we investigated the efficacy and tolerability of two histone methyltransferase (HMTase) inhibitor compounds, BIX0194 (G9a-inhibitor) and GSK126 (EZH2-inhibitor), to specifically target and reduce H3K9me2/3 and H3K27me3 levels, respectively, in FRDA fibroblasts. We show that a combination treatment of BIX0194 and GSK126, significantly increased FXN gene expression levels and reduced the repressive histone marks. However, no increase in frataxin protein levels was observed. Nevertheless, our results are still promising and may encourage to investigate HMTase inhibitors with other synergistic epigenetic-based therapies for further preliminary studies.
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Affiliation(s)
- Mursal Sherzai
- Ataxia Research Group, Division of Biosciences, Department of Life Sciences, College of Health and Life Sciences, Brunel University London, Uxbridge, United Kingdom
| | - Adamo Valle
- Energy Metabolism and Nutrition, Research Institute of Health Sciences (IUNICS) and Health Research Institute of Balearic Islands (IdISBa), University of Balearic Islands, Palma de Mallorca, Spain.,Biomedical Research Networking Center for Physiopathology of Obesity and Nutrition (CIBERobn), Instituto de Salud Carlos III, Madrid, Spain
| | - Nicholas Perry
- Division of Cancer Biology, The Institute of Cancer Research, London, United Kingdom
| | - Ester Kalef-Ezra
- Ataxia Research Group, Division of Biosciences, Department of Life Sciences, College of Health and Life Sciences, Brunel University London, Uxbridge, United Kingdom
| | - Sahar Al-Mahdawi
- Ataxia Research Group, Division of Biosciences, Department of Life Sciences, College of Health and Life Sciences, Brunel University London, Uxbridge, United Kingdom
| | - Mark Pook
- Ataxia Research Group, Division of Biosciences, Department of Life Sciences, College of Health and Life Sciences, Brunel University London, Uxbridge, United Kingdom
| | - Sara Anjomani Virmouni
- Ataxia Research Group, Division of Biosciences, Department of Life Sciences, College of Health and Life Sciences, Brunel University London, Uxbridge, United Kingdom
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9
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Kuta R, Larochelle N, Fernandez M, Pal A, Minotti S, Tibshirani M, St Louis K, Gentil BJ, Nalbantoglu JN, Hermann A, Durham HD. Depending on the stress, histone deacetylase inhibitors act as heat shock protein co-inducers in motor neurons and potentiate arimoclomol, exerting neuroprotection through multiple mechanisms in ALS models. Cell Stress Chaperones 2020; 25:173-191. [PMID: 31900865 PMCID: PMC6985055 DOI: 10.1007/s12192-019-01064-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Revised: 12/12/2019] [Accepted: 12/20/2019] [Indexed: 12/13/2022] Open
Abstract
Upregulation of heat shock proteins (HSPs) is an approach to treatment of neurodegenerative disorders with impaired proteostasis. Many neurons, including motor neurons affected in amyotrophic lateral sclerosis (ALS), are relatively resistant to stress-induced upregulation of HSPs. This study demonstrated that histone deacetylase (HDAC) inhibitors enable the heat shock response in cultured spinal motor neurons, in a stress-dependent manner, and can improve the efficacy of HSP-inducing drugs in murine spinal cord cultures subjected to thermal or proteotoxic stress. The effect of particular HDAC inhibitors differed with the stress paradigm. The HDAC6 (class IIb) inhibitor, tubastatin A, acted as a co-inducer of Hsp70 (HSPA1A) expression with heat shock, but not with proteotoxic stress induced by expression of mutant SOD1 linked to familial ALS. Certain HDAC class I inhibitors (the pan inhibitor, SAHA, or the HDAC1/3 inhibitor, RGFP109) were HSP co-inducers comparable to the hydroxyamine arimoclomol in response to proteotoxic stress, but not thermal stress. Regardless, stress-induced Hsp70 expression could be enhanced by combining an HDAC inhibitor with either arimoclomol or with an HSP90 inhibitor that constitutively induced HSPs. HDAC inhibition failed to induce Hsp70 in motor neurons expressing ALS-linked mutant FUS, in which the heat shock response was suppressed; yet SAHA, RGFP109, and arimoclomol did reduce loss of nuclear FUS, a disease hallmark, and HDAC inhibition rescued the DNA repair response in iPSC-derived motor neurons carrying the FUSP525Lmutation, pointing to multiple mechanisms of neuroprotection by both HDAC inhibiting drugs and arimoclomol.
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Affiliation(s)
- Rachel Kuta
- Department of Neurology and Neurosurgery and Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC, H3A 2B4, Canada
| | - Nancy Larochelle
- Department of Neurology and Neurosurgery and Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC, H3A 2B4, Canada
| | - Mario Fernandez
- Department of Neurology and Neurosurgery and Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC, H3A 2B4, Canada
| | - Arun Pal
- Department Neurology, Technische Universität Dresden, Fetscherstr. 74, 01307, Dresden, Germany
| | - Sandra Minotti
- Department of Neurology and Neurosurgery and Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC, H3A 2B4, Canada
| | - Michael Tibshirani
- Department of Neurology and Neurosurgery and Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC, H3A 2B4, Canada
| | - Kyle St Louis
- Department of Neurology and Neurosurgery and Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC, H3A 2B4, Canada
| | - Benoit J Gentil
- Department of Neurology and Neurosurgery and Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC, H3A 2B4, Canada
| | - Josephine N Nalbantoglu
- Department of Neurology and Neurosurgery and Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC, H3A 2B4, Canada
| | - Andreas Hermann
- Translational Neurodegeneration Section "Albrecht-Kossel", Department of Neurology and Center for Transdisciplinary Neuroscience (CTNR), University Medical Center Rostock, University of Rostock, Rostock, Germany and German Center for Neurodegenerative Diseases (DZNE) Rostock, Rostock, Germany
| | - Heather D Durham
- Department of Neurology and Neurosurgery and Montreal Neurological Institute, McGill University, 3801 University St., Montreal, QC, H3A 2B4, Canada.
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10
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Gottesfeld JM. Molecular Mechanisms and Therapeutics for the GAA·TTC Expansion Disease Friedreich Ataxia. Neurotherapeutics 2019; 16:1032-1049. [PMID: 31317428 PMCID: PMC6985418 DOI: 10.1007/s13311-019-00764-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Friedreich ataxia (FRDA), the most common inherited ataxia, is caused by transcriptional silencing of the nuclear FXN gene, encoding the essential mitochondrial protein frataxin. Currently, there is no approved therapy for this fatal disorder. Gene silencing in FRDA is due to hyperexpansion of the triplet repeat sequence GAA·TTC in the first intron of the FXN gene, which results in chromatin histone modifications consistent with heterochromatin formation. Frataxin is involved in mitochondrial iron homeostasis and the assembly and transfer of iron-sulfur clusters to various mitochondrial enzymes and components of the electron transport chain. Frataxin insufficiency leads to progressive spinocerebellar neurodegeneration, causing symptoms of gait and limb ataxia, slurred speech, muscle weakness, sensory loss, and cardiomyopathy in many patients, resulting in death in early adulthood. Numerous approaches are being taken to find a treatment for FRDA, including excision or correction of the repeats by genome engineering methods, gene activation with small molecules or artificial transcription factors, delivery of frataxin to affected cells by protein replacement therapy, gene therapy, or small molecules to increase frataxin protein levels, and therapies aimed at countering the cellular consequences of reduced frataxin. This review will summarize the mechanisms involved in repeat-mediated gene silencing and recent efforts aimed at development of therapeutics.
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Affiliation(s)
- Joel M Gottesfeld
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California, 92037, USA.
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11
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Delatycki MB, Bidichandani SI. Friedreich ataxia- pathogenesis and implications for therapies. Neurobiol Dis 2019; 132:104606. [PMID: 31494282 DOI: 10.1016/j.nbd.2019.104606] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Revised: 08/08/2019] [Accepted: 09/04/2019] [Indexed: 01/01/2023] Open
Abstract
Friedreich ataxia is the most common of the hereditary ataxias. It is due to homozygous/compound heterozygous mutations in FXN. This gene encodes frataxin, a protein largely localized to mitochondria. In about 96% of affected individuals there is homozygosity for a GAA repeat expansion in intron 1 of the FXN gene. Studies of people with Friedreich ataxia and of animal and cell models, have provided much insight into the pathogenesis of this disorder. The expanded GAA repeat leads to transcriptional deficiency of the FXN gene. The consequent deficiency of frataxin protein leads to reduced iron-sulfur cluster biogenesis and mitochondrial ATP production, elevated mitochondrial iron, and oxidative stress. More recently, a role for inflammation has emerged as being important in the pathogenesis of Friedreich ataxia. These findings have led to a number of potential therapies that have been subjected to clinical trials or are being developed toward human studies. Therapies that have been proposed include pharmaceuticals that increase frataxin levels, protein and gene replacement therapies, antioxidants, iron chelators and modulators of inflammation. Whilst no therapies have yet been approved for Friedreich ataxia, there is much optimism that the advances in the understanding of the pathogenesis of this disorder since the discovery its genetic basis, will result in approved disease modifying therapies in the near future.
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Affiliation(s)
- Martin B Delatycki
- Bruce Lefroy Centre, Murdoch Children's Research Institute, Parkville, Victoria, Australia; Victorian Clinical Genetics Services, Parkville, Victoria, Australia; Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia.
| | - Sanjay I Bidichandani
- Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA; Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA; Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
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Clay A, Hearle P, Schadt K, Lynch DR. New developments in pharmacotherapy for Friedreich ataxia. Expert Opin Pharmacother 2019; 20:1855-1867. [PMID: 31311349 DOI: 10.1080/14656566.2019.1639671] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Introduction: Friedreich ataxia (FRDA), a rare disease caused by the deficiency of the mitochondrial matrix protein frataxin, affects roughly 1 in 50,000 individuals worldwide. Current and emerging therapies focus on reversing the deleterious effects of such deficiency including mitochondrial augmentation and increasing frataxin levels, providing the possibility of treatment options for this physiologically complex, multisystem disorder. Areas covered: In this review article, the authors discuss the current and prior in vivo and in vitro research studies related to the treatment of FRDA, with a particular interest in future implications of each therapy. Expert opinion: Since the discovery of FXN in 1996, multiple clinical trials have occurred or are currently occurring; at a rapid pace for a rare disease. These trials have been directed at the augmentation of mitochondrial function and/or alleviation of symptoms and are not regarded as potential cures in FRDA. Either a combination of therapies or a drug that replaces or increases the pathologically low levels of frataxin better represent potential cures in FRDA.
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Affiliation(s)
- Alexandra Clay
- Division of Neurology, Children's Hospital of Philadelphia , Philadelphia , PA , USA
| | - Patrick Hearle
- Division of Neurology, Children's Hospital of Philadelphia , Philadelphia , PA , USA
| | - Kim Schadt
- Division of Neurology, Children's Hospital of Philadelphia , Philadelphia , PA , USA
| | - David R Lynch
- Division of Neurology, Children's Hospital of Philadelphia , Philadelphia , PA , USA
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13
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Alfedi G, Luffarelli R, Condò I, Pedini G, Mannucci L, Massaro DS, Benini M, Toschi N, Alaimo G, Panarello L, Pacini L, Fortuni S, Serio D, Malisan F, Testi R, Rufini A. Drug repositioning screening identifies etravirine as a potential therapeutic for friedreich's ataxia. Mov Disord 2019; 34:323-334. [PMID: 30624801 DOI: 10.1002/mds.27604] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Revised: 10/31/2018] [Accepted: 11/05/2018] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Friedreich's ataxia is an autosomal-recessive cerebellar ataxia caused by mutation of the frataxin gene, resulting in decreased frataxin expression, mitochondrial dysfunction, and oxidative stress. Currently, no treatment is available for Friedreich's ataxia patients. Given that levels of residual frataxin critically affect disease severity, the main goal of a specific therapy for Friedreich's ataxia is to increase frataxin levels. OBJECTIVES With the aim to accelerate the development of a new therapy for Friedreich's ataxia, we took a drug repositioning approach to identify market-available drugs able to increase frataxin levels. METHODS Using a cell-based reporter assay to monitor variation in frataxin amount, we performed a high-throughput screening of a library containing 853 U.S. Food and Drug Administration-approved drugs. RESULTS Among the potentially interesting candidates isolated from the screening, we focused our attention on etravirine, an antiviral drug currently in use as an anti-human immunodeficiency virus therapy. Here, we show that etravirine can promote a significant increase in frataxin levels in cells derived from Friedreich's ataxia patients, by enhancing frataxin messenger RNA translation. Importantly, frataxin accumulation in treated patient cell lines is comparable to frataxin levels in unaffected carrier cells, suggesting that etravirine could be therapeutically relevant. Indeed, etravirine treatment restores the activity of the iron-sulphur cluster containing enzyme aconitase and confers resistance to oxidative stress in cells derived from Friedreich's ataxia patients. CONCLUSIONS Considering its excellent safety profile along with its ability to increase frataxin levels and correct some of the disease-related defects, etravirine represents a promising candidate as a therapeutic for Friedreich's ataxia. © 2019 International Parkinson and Movement Disorder Society.
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Affiliation(s)
- Giulia Alfedi
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Riccardo Luffarelli
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Ivano Condò
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Giorgia Pedini
- Laboratory of Molecular Neurobiology, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Liliana Mannucci
- Laboratory of Molecular Neurobiology, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Damiano S Massaro
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Monica Benini
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
- Fratagene Therapeutics Srl, Rome, Italy
| | - Nicola Toschi
- Medical Physics Section, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
- Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging and Harvard Medical School, Boston, Massachusetts, USA
| | - Giorgia Alaimo
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
- Fratagene Therapeutics Srl, Rome, Italy
| | - Luca Panarello
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Laura Pacini
- Laboratory of Molecular Neurobiology, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Silvia Fortuni
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Dario Serio
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Florence Malisan
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
| | - Roberto Testi
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
- Fratagene Therapeutics Srl, Rome, Italy
| | - Alessandra Rufini
- Laboratory of Signal Transduction, Department of Biomedicine and Prevention, University of Rome "Tor Vergata", Rome, Italy
- Fratagene Therapeutics Srl, Rome, Italy
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14
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Strawser C, Schadt K, Hauser L, McCormick A, Wells M, Larkindale J, Lin H, Lynch DR. Pharmacological therapeutics in Friedreich ataxia: the present state. Expert Rev Neurother 2017; 17:895-907. [PMID: 28724340 DOI: 10.1080/14737175.2017.1356721] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
INTRODUCTION Friedreich ataxia (FRDA) is a progressive, inherited, neurodegenerative disease for which there is currently no cure or approved treatment. FRDA is caused by deficits in the production and expression of frataxin, a protein found in the mitochondria that is most likely responsible for regulating iron-sulfur cluster enzymes within the cell. A decrease in frataxin causes dysfunction of adenosine triphosphate synthesis, accumulation of mitochondrial iron, and other events leading to downstream cellular dysfunction. Areas covered: Therapeutic development for FRDA currently focuses on improving mitochondrial function and finding ways to increase frataxin expression. Additionally, the authors will review potential approaches aimed at iron modulation and genetic modulation. Finally, gene therapy is progressing rapidly and is being explored as a treatment for FRDA. Expert commentary: The collection of multiple therapeutic approaches provides many possible ways to treat FRDA. Although the mitochondrial approaches are not thought to be curative, as the primary frataxin deficit will remain, they may still produce improvements in quality of life and slowing of progression. Therapies aimed at frataxin restoration are more likely to truly modify the disease, with gene therapy as the best possibility to alter the course of the disease from both a cardiac and neurological perspective.
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Affiliation(s)
| | - Kimberly Schadt
- a Children's Hospital of Philadelphia , Philadelphia , PA , USA
| | - Lauren Hauser
- a Children's Hospital of Philadelphia , Philadelphia , PA , USA
| | | | - McKenzie Wells
- a Children's Hospital of Philadelphia , Philadelphia , PA , USA
| | - Jane Larkindale
- a Children's Hospital of Philadelphia , Philadelphia , PA , USA
| | - Hong Lin
- a Children's Hospital of Philadelphia , Philadelphia , PA , USA
| | - David R Lynch
- a Children's Hospital of Philadelphia , Philadelphia , PA , USA
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15
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Pleasure D. New hearts for Friedreich patients. J Neurol Sci 2017; 375:474-475. [PMID: 28131391 DOI: 10.1016/j.jns.2017.01.035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Accepted: 01/09/2017] [Indexed: 11/27/2022]
Affiliation(s)
- David Pleasure
- Neurology, UC Davis, c/o Shriners Hospital, 2425 Stockton Blvd, Sacramento, CA 95817, United States.
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16
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Bürk K. Friedreich Ataxia: current status and future prospects. CEREBELLUM & ATAXIAS 2017; 4:4. [PMID: 28405347 PMCID: PMC5383992 DOI: 10.1186/s40673-017-0062-x] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 03/24/2017] [Indexed: 01/23/2023]
Abstract
Friedreich ataxia (FA) represents the most frequent type of inherited ataxia. Most patients carry homozygous GAA expansions in the first intron of the frataxin gene on chromosome 9. Due to epigenetic alterations, frataxin expression is significantly reduced. Frataxin is a mitochondrial protein. Its deficiency leads to mitochondrial iron overload, defective energy supply and generation of reactive oxygen species. This review gives an overview over clinical and genetic aspects of FA and discusses current concepts of frataxin biogenesis and function as well as new therapeutic strategies.
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Affiliation(s)
- Katrin Bürk
- University of Marburg, and Paracelsus-Elena Klinik, Klinikstr. 16, 34128 Kassel, Germany
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Design, synthesis and anti-tumor activity study of novel histone deacetylase inhibitors containing isatin-based caps and o-phenylenediamine-based zinc binding groups. Bioorg Med Chem 2017; 25:2981-2994. [PMID: 28511906 DOI: 10.1016/j.bmc.2017.03.036] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2017] [Revised: 03/12/2017] [Accepted: 03/14/2017] [Indexed: 11/23/2022]
Abstract
As a hot topic of epigenetic studies, histone deacetylases (HDACs) are related to lots of diseases, especially cancer. Further researches indicated that different HDAC isoforms played various roles in a wide range of tumor types. Herein a novel series of HDAC inhibitors with isatin-based caps and o-phenylenediamine-based zinc binding groups have been designed and synthesized through scaffold hopping strategy. Among these compounds, the most potent compound 9n exhibited similar if not better HDAC inhibition and antiproliferative activities against multiple tumor cell lines compared with the positive control entinostat (MS-275). Additionally, compared with MS-275 (IC50 values for HDAC1, 2 and 3 were 0.163, 0.396 and 0.605µM, respectively), compound 9n with IC50 values of 0.032, 0.256 and 0.311µM for HDAC1, 2 and 3 respectively, showed a moderate HDAC1 selectivity.
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Abstract
INTRODUCTION Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused by expansion of a GAA·TTC triplet in the first intron of the FXN gene, encoding the essential mitochondrial protein frataxin. Repeat expansion results in transcriptional silencing through an epigenetic mechanism, resulting in significant decreases in frataxin protein in affected individuals. Since the FXN protein coding sequence is unchanged in FRDA, an attractive therapeutic approach for this disease would be to increase transcription of pathogenic alleles with small molecules that target the silencing mechanism. AREAS COVERED We review the evidence that histone postsynthetic modifications and heterochromatin formation are responsible for FXN gene silencing in FRDA, along with efforts to reverse silencing with drugs that target histone modifying enzymes. Chemical and pharmacological properties of histone deacetylase (HDAC) inhibitors, which reverse silencing, together with enzyme target profiles and kinetics of inhibition, are discussed. Two HDAC inhibitors have been studied in human clinical trials and the properties of these compounds are compared and contrasted. Efforts to improve on bioavailability, metabolic stability, and target activity are reviewed. EXPERT OPINION 2-aminobenzamide class I HDAC inhibitors are attractive therapeutic small molecules for FRDA. These molecules increase FXN gene expression in human neuronal cells derived from patient induced pluripotent stem cells, and in two mouse models for the disease, as well as in circulating lymphocytes in patients treated in a phase Ib clinical trial. Medicinal chemistry efforts have identified compounds with improved brain penetration, metabolic stability and efficacy in the human neuronal cell model. A clinical candidate will soon be identified for further human testing.
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Affiliation(s)
- Elisabetta Soragni
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037 USA
| | - Joel M Gottesfeld
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037 USA
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Chutake YK, Costello WN, Lam CC, Parikh AC, Hughes TT, Michalopulos MG, Pook MA, Bidichandani SI. FXN Promoter Silencing in the Humanized Mouse Model of Friedreich Ataxia. PLoS One 2015; 10:e0138437. [PMID: 26393353 PMCID: PMC4579136 DOI: 10.1371/journal.pone.0138437] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 08/31/2015] [Indexed: 11/25/2022] Open
Abstract
BACKGROUND Friedreich ataxia is caused by an expanded GAA triplet-repeat sequence in intron 1 of the FXN gene that results in epigenetic silencing of the FXN promoter. This silencing mechanism is seen in patient-derived lymphoblastoid cells but it remains unknown if it is a widespread phenomenon affecting multiple cell types and tissues. METHODOLOGY / PRINCIPAL FINDINGS The humanized mouse model of Friedreich ataxia (YG8sR), which carries a single transgenic insert of the human FXN gene with an expanded GAA triplet-repeat in intron 1, is deficient for FXN transcript when compared to an isogenic transgenic mouse lacking the expanded repeat (Y47R). We found that in YG8sR the deficiency of FXN transcript extended both upstream and downstream of the expanded GAA triplet-repeat, suggestive of deficient transcriptional initiation. This pattern of deficiency was seen in all tissues tested, irrespective of whether they are known to be affected or spared in disease pathogenesis, in both neuronal and non-neuronal tissues, and in cultured primary fibroblasts. FXN promoter function was directly measured via metabolic labeling of newly synthesized transcripts in fibroblasts, which revealed that the YG8sR mouse was significantly deficient in transcriptional initiation compared to the Y47R mouse. CONCLUSIONS / SIGNIFICANCE Deficient transcriptional initiation accounts for FXN transcriptional deficiency in the humanized mouse model of Friedreich ataxia, similar to patient-derived cells, and the mechanism underlying promoter silencing in Friedreich ataxia is widespread across multiple cell types and tissues.
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Affiliation(s)
- Yogesh K. Chutake
- Department of Pediatrics, University of Oklahoma College of Medicine, Oklahoma City, OK 73104, United States of America
| | - Whitney N. Costello
- Department of Pediatrics, University of Oklahoma College of Medicine, Oklahoma City, OK 73104, United States of America
| | - Christina C. Lam
- Department of Pediatrics, University of Oklahoma College of Medicine, Oklahoma City, OK 73104, United States of America
| | - Aniruddha C. Parikh
- Department of Pediatrics, University of Oklahoma College of Medicine, Oklahoma City, OK 73104, United States of America
| | - Tamara T. Hughes
- Department of Pediatrics, University of Oklahoma College of Medicine, Oklahoma City, OK 73104, United States of America
| | - Michael G. Michalopulos
- Department of Pediatrics, University of Oklahoma College of Medicine, Oklahoma City, OK 73104, United States of America
| | - Mark A. Pook
- Ataxia Research Group, Division of Biosciences, Department of Life Sciences, College of Health & Life Sciences, Brunel University London, Uxbridge, UB8 3PH, United Kingdom
| | - Sanjay I. Bidichandani
- Department of Pediatrics, University of Oklahoma College of Medicine, Oklahoma City, OK 73104, United States of America
- Department of Biochemistry & Molecular Biology, University of Oklahoma College of Medicine, Oklahoma City, OK 73104, United States of America
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