Malfunctioning DNA Damage Response (DDR) Leads to the Degeneration of Nigro-Striatal Pathway in Mouse Brain

Safety and efficacy of intra-erythrocyte dexamethasone sodium phosphate in children with ataxia telangiectasia (ATTeST): a multicentre, randomised, double-blind, placebo-controlled phase 3 trial

BACKGROUND

Ataxia telangiectasia is a multisystem disorder with progressive neurodegeneration. Corticosteroids can improve neurological functioning in patients with the disorder but adrenal suppression and symptom recurrence on treatment discontinuation has limited their use, prompting the development of novel steroid delivery systems. The aim of the ATTeST study was to evaluate the efficacy and safety of intra-erythrocyte delivery of dexamethasone sodium phosphate compared with placebo in children with ataxia telangiectasia.

METHODS

This multicentre, randomised, double-blind, placebo-controlled, phase 3 trial was done at 22 centres in 12 countries (Australia, Belgium, Germany, India, Israel, Italy, Norway, Poland, Spain, Tunisia, the UK, and the USA). Eligible participants were children aged 6 years or older weighing more than 15 kg who met clinical criteria for ataxia telangiectasia but who had preserved autonomous gait. Participants were randomly assigned (1:1:1) to low-dose (approximately 5-10 mg), or high-dose (approximately 14-22 mg) intra-erythrocyte dexamethasone sodium phosphate, or placebo, using an independent interactive web response system, with minimisation for sex and age (6-9 years vs ≥10 years). Intravenous intra-erythrocyte dexamethasone sodium phosphate was administered once a month for 6 months. Participants, employees of the sponsor, investigators, all raters of efficacy endpoints, and central reviewers were masked to treatment assignment and dose allocations. The primary efficacy endpoint was change in the modified International Cooperative Ataxia Rating Scale (mICARS) from baseline to month 6, assessed in the modified intention-to-treat (mITT) population, which included all randomly assigned participants who received at least one dose of study drug and had at least one post-baseline efficacy assessment. This trial is registered with Clinicaltrials.gov (NCT02770807) and is complete.

FINDINGS

Between March 2, 2017, and May 13, 2021, 239 children were assessed for eligibility, of whom 176 were randomly assigned. One patient assigned to high-dose intra-erythrocyte dexamethasone sodium phosphate did not initiate treatment. 175 patients received at least one dose of treatment (59 patients received the low dose and 57 received the high dose of intra-erythrocyte dexamethasone sodium phosphate, and 59 received placebo). The mITT population comprised 164 participants (56 children in the low-dose group, 54 children in the high-dose group, and 54 in the placebo group). Compared with the placebo group, no differences were identified with regard to change in mICARS score from baseline to 6 months in the low-dose group (least squares mean difference -1·37 [95% CI -2·932 to 0·190]) or the high-dose group (-1·40 [-2·957 to 0·152]; p=0·0765). Adverse events were reported in 43 (73%) of 59 participants in the low-dose group, 47 (82%) of 57 participants in the high-dose group, and 43 (73%) of 59 participants in the placebo group. Serious adverse events were observed in six (10%) of 59 participants in the low-dose group, seven (12%) of 57 participants in the high-dose group, and seven (12%) of 59 participants in the placebo group. There were no reports of hyperglycaemia, hypertension, hirsutism, or Cushingoid appearance in any of the treatment groups, nor any treatment-related deaths.

INTERPRETATION

Although there were no safety concerns, the primary efficacy endpoint was not met, possibly related to delays in treatment reducing the number of participants who received treatment as outlined in the protocol, and potentially different treatment effects according to age. Studies of intra-erythrocyte delivery of dexamethasone sodium phosphate will continue in participants aged 6-9 years, on the basis of findings from subgroup analyses from this trial.

FUNDING

EryDel and Quince Therapeutics.

Ataxia-telangiectasia clinical trial landscape and the obstacles to overcome

INTRODUCTION

Ataxia telangiectasia (A-T) is a life-limiting autosomal recessive disease characterized by cerebellar degeneration, ocular telangiectasias, and sinopulmonary disease. Since there is no cure for A-T, the standard of care is primarily supportive.

AREAS COVERED

We review clinical trials available in PubMed from 1990 to 2023 focused on lessening A-T disease burden. These approaches include genetic interventions, such as antisense oligonucleotides, designed to ameliorate disease progression in patients with select mutations. These approaches also include pharmacologic treatments that target oxidative stress, inflammation, and mitochondrial exhaustion, to attenuate neurological progression in A-T. Finally, we discuss the use of biological immunotherapies for the treatment of malignancies and granulomatous disease, along with other supportive therapies being used for the treatment of pulmonary disease and metabolic syndrome.

EXPERT OPINION

Barriers to successful genetic and pharmacologic interventions in A-T include the need for personalized treatment approaches based on patient-specific ATM mutations and phenotypes, lack of an animal model for the neurologic phenotype, and extreme rarity of disease making large-scale randomized trials difficult to perform. Ongoing efforts are needed to diagnose patients earlier, discover more effective therapies, and include more individuals in clinical trials, with the goal to lessen disease burden and to find a cure for patients with A-T.

Nuclear DJ-1 Regulates DNA Damage Repair via the Regulation of PARP1 Activity

DNA damage and defective DNA repair are extensively linked to neurodegeneration in Parkinson's disease (PD), but the underlying molecular mechanisms remain poorly understood. Here, we determined that the PD-associated protein DJ-1 plays an essential role in modulating DNA double-strand break (DSB) repair. Specifically, DJ-1 is a DNA damage response (DDR) protein that can be recruited to DNA damage sites, where it promotes DSB repair through both homologous recombination and nonhomologous end joining. Mechanistically, DJ-1 interacts directly with PARP1, a nuclear enzyme essential for genomic stability, and stimulates its enzymatic activity during DNA repair. Importantly, cells from PD patients with the DJ-1 mutation also have defective PARP1 activity and impaired repair of DSBs. In summary, our findings uncover a novel function of nuclear DJ-1 in DNA repair and genome stability maintenance, and suggest that defective DNA repair may contribute to the pathogenesis of PD linked to DJ-1 mutations.

DNA Damage-Mediated Neurotoxicity in Parkinson’s Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease around the world; however, its pathogenesis remains unclear so far. Recent advances have shown that DNA damage and repair deficiency play an important role in the pathophysiology of PD. There is growing evidence suggesting that DNA damage is involved in the propagation of cellular damage in PD, leading to neuropathology under different conditions. Here, we reviewed the current work on DNA damage repair in PD. First, we outlined the evidence and causes of DNA damage in PD. Second, we described the potential pathways by which DNA damage mediates neurotoxicity in PD and discussed the precise mechanisms that drive these processes by DNA damage. In addition, we looked ahead to the potential interventions targeting DNA damage and repair. Finally, based on the current status of research, key problems that need to be addressed in future research were proposed.

Decoding the Role of Familial Parkinson's Disease-Related Genes in DNA Damage and Repair

Parkinson's disease (PD) is a neurodegenerative disease characterized by the degeneration of midbrain substantia nigra pars compacta dopaminergic neurons and the formation of Lewy bodies. Over the years, researchers have gained extensive knowledge about dopaminergic neuron degeneration from the perspective of the environmental and disease-causing genetic factors; however, there is still no disease-modifying therapy. Aging has long been recognized as a major risk factor for PD; however, little is known about how aging contributes to the disease development. Genome instability is the main driving force behind aging, and has been poorly studied in patients with PD. Here, we summarize the evidence for nuclear DNA damage in PD. We also discuss the molecular mechanisms of nuclear DNA damage and repair in PD, especially from the perspective of familial PD-related mutant genes. Understanding the significance of DNA damage and repair may provide new potential intervention targets for treating PD.

Analysis of Clinical and Genetic Characterization of Three Ataxia-Telangiectasia Pedigrees With Novel ATM Gene Mutations

OBJECTIVE

The clinical manifestations of ataxia-telangiectasia (AT) are very complex and are easily misdiagnosed and missed. The purpose of this study was to explore the clinical characteristics and genetic features of five pediatric patients with AT from three pedigrees in china.

METHODS

Retrospectively collected and analyzed the clinical data and genetic testing results of five AT patients diagnosed by the Whole-exome sequencing followed by Sanger sequencing. The five patients with AT were from three pedigrees, including two female patients (case 1 and case 2) in pedigree I, one male patient (case 3) in pedigree II, and two male patients (case 4 and case 5) in pedigree III. According to the United Kingdom Association for Clinical Genomic Science Best Practice Guidelines for Variants Classification in Rare Disease 2020 to grade the genetic variants.

RESULTS

Five patients had mainly clinical presentations including unsteady gait, dysarthria, bulbar conjunctive telangiectasia, cerebellar atrophy, intellectual disability, stunted growth, increase of alpha-fetoprotein in serum, lymphopenia. Notably, one patient with classical AT presented dystonia as the first symptom. One patient had recurrent infections, five patients had serum Immunoglobulin (Ig) A deficiency, and two patients had IgG deficiency. In three pedigrees, we observed five pathogenic variants of the ATM gene, which were c.1339C>T (p.Arg447Ter), c.7141_7151delAATGGAAAAAT (p.Asn2381GlufsTer18), c.437_440delTCAA (p.Leu146GlnfsTer6), c.2482A>T (p.Lys828Ter), and c.5495_5496+2delAAGT (p.Glu1832GlyfsTer4). Moreover, the c.437_440delTCAA, c.2482A>T, and c.5495_5496+2delAAGT were previously unreported variants.

CONCLUSIONS

Pediatric patients with classical AT may present dystonia as the main manifestation, or even a first symptom, besides typical cerebellar ataxia, bulbar conjunctive telangiectasia, etc. Crucially, we also found three novel pathogenic ATM gene variants (c.437_440delTCAA, c.2482A>T, and c.5495_5496+2delAAGT), expanding the ATM pathogenic gene mutation spectrum.

The interplay between mitochondrial functionality and genome integrity in the prevention of human neurologic diseases

As mitochondria are vulnerable to oxidative damage and represent the main source of reactive oxygen species (ROS), they are considered key tuners of ROS metabolism and buffering, whose dysfunction can progressively impact neuronal networks and disease. Defects in DNA repair and DNA damage response (DDR) may also affect neuronal health and lead to neuropathology. A number of congenital DNA repair and DDR defective syndromes, indeed, show neurological phenotypes, and a growing body of evidence indicate that defects in the mechanisms that control genome stability in neurons acts as aging-related modifiers of common neurodegenerative diseases such as Alzheimer, Parkinson's, Huntington diseases and Amyotrophic Lateral Sclerosis. In this review we elaborate on the established principles and recent concepts supporting the hypothesis that deficiencies in either DNA repair or DDR might contribute to neurodegeneration via mechanisms involving mitochondrial dysfunction/deranged metabolism.

Effects of acute noise exposure on DNA damage response genes in the cochlea, cortex, heart and liver

Noise as a systemic stressor induces various organ dysfunctions and the underlying molecular pathology is unknown. Previous studies have shown that noise exposure results in the accumulation of DNA damage in auditory and non-auditory organs. The DNA damage response (DDR) is a global protective mechanism that plays a critical role in maintaining DNA integrity. However, the role of DDR genes in noise induced systemic (non-auditory) pathology has not been investigated. The current pilot study was designed to test the hypothesis that an acute noise exposure would alter the normal expression of DDR genes (e.g., ATM, p53 & XPC) in auditory (cochlea) and non-auditory organs, such as the cortex, heart and liver. Mice were used as subjects in this study and consisted of a baseline group, a one-hour noise exposure (@105 dB) group, and a four-hour noise exposure (@105 dB) group. ATM, p53 and XPC expression levels were quantified through end-point polymerize chain reactions. The current study demonstrated that noise exposure failed to elicit statistically significant changes in DDR genes (relative to baseline) across the various organs. The failure of the cochlea, heart, cortex and liver to upregulate protective DDR genes during acute noise exposure might help to explain their susceptibility to noise-induced DNA damage. This suggests that, biomedical interventions to upregulate DDR genes may need to be implemented before noise exposure or during the early stages of noise exposure.

DNA double-strand breaks: a potential therapeutic target for neurodegenerative diseases

The complexity of neurodegeneration restricts the ability to understand and treat the neurological disorders affecting millions of people worldwide. Therefore, there is an unmet need to develop new and more effective therapeutic strategies to combat these devastating conditions and that will only be achieved with a better understanding of the biological mechanism associated with disease conditions. Recent studies highlight the role of DNA damage, particularly, DNA double-strand breaks (DSBs), in the progression of neuronal loss in a broad spectrum of human neurodegenerative diseases. This is not unexpected because neurons are prone to DNA damage due to their non-proliferative nature and high metabolic activity. However, it is not clear if DSBs is a primary driver of neuronal loss in disease conditions or simply occurs concomitant with disease progression. Here, we provide evidence that supports a critical role of DSBs in the pathogenesis of the neurodegenerative diseases. Among different kinds of DNA damages, DSBs are the most harmful and perilous type of DNA damage and can lead to cell death if left unrepaired or repaired with error. In this review, we explore the current state of knowledge regarding the role of DSBs repair mechanisms in preserving neuronal function and survival and describe how DSBs could drive the molecular mechanisms resulting in neuronal death in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. We also discuss the potential implications of DSBs as a novel therapeutic target and prognostic marker in patients with neurodegenerative conditions.

The ATM kinase inhibitor KU-55933 provides neuroprotection against hydrogen peroxide-induced cell damage via a γH2AX/p-p53/caspase-3-independent mechanism: Inhibition of calpain and cathepsin D

The role of the kinase ataxia-telangiectasia mutated (ATM), a well-known protein engaged in DNA damage repair, in the regulation of neuronal responses to oxidative stress remains unexplored. Thus, the neuroprotective efficacy of KU-55933, a potent inhibitor of ATM, against cell damage evoked by oxidative stress (hydrogen peroxide, H₂O₂) has been studied in human neuroblastoma SH-SY5Y cells and compared with the efficacy of this agent in models of doxorubicin (Dox)- and staurosporine (St)-evoked cell death. KU-55933 inhibited the cell death induced by H₂O₂ or Dox but not by St in undifferentiated (UN-) and retinoic acid-differentiated (RA)-SH-SY5Y cells, with a more pronounced effect in the latter cell phenotype. Furthermore, this ATM inhibitor attenuated the Dox- but not H₂O₂-induced caspase-3 activity in both UN- and RA-SH-SY5Y cells. Although KU-55933 inhibited the H₂O₂- and Dox-induced activation of ATM, it attenuated the toxin-induced phosphorylation of the proteins H2AX and p53 only in the latter model of cell damage. Moreover, the ATM inhibitor prevented the H₂O₂-evoked increases in calpain and cathepsin D activity and attenuated cell damage to a similar degree as inhibitors of calpain (MDL28170) and cathepsin D (pepstatin A). Finally, we confirmed the neuroprotective potential of KU-55933 against the H₂O₂- and Dox-evoked cell damage in primary mouse cerebellar granule cells and in the mouse hippocampal HT-22 cell line. Altogether, our results extend the neuroprotective portfolio of KU-55933 to a model of oxidative stress, with this effect not involving inhibition of the γH2AX/p-p53/caspase-3 pathway and instead associated with the attenuation of calpain and cathepsin D activity.

Neuroprotective Transcription Factors in Animal Models of Parkinson Disease

A number of transcription factors, including En1/2, Foxa1/2, Lmx1a/b, Nurr1, Otx2, and Pitx3, with key roles in midbrain dopaminergic (mDA) neuron development, also regulate adult mDA neuron survival and physiology. Mouse models with targeted disruption of some of these genes display several features reminiscent of Parkinson disease (PD), in particular the selective and progressive loss of mDA neurons in the substantia nigra pars compacta (SNpc). The characterization of these animal models has provided valuable insights into various mechanisms of PD pathogenesis. Therefore, the dissection of the mechanisms and survival signalling pathways engaged by these transcription factors to protect mDA neuron from degeneration can suggest novel therapeutic strategies. The work on En1/2-mediated neuroprotection also highlights the potential of protein transduction technology for neuroprotective approaches in PD.

The appropriateness of the mouse model for ataxia-telangiectasia: neurological defects but no neurodegeneration

Patients with ataxia-telangiectasia (A-T) are characterised by genome instability, cancer predisposition and a progressive neurodegeneration. A number of model systems have been developed for A-T but none recapitulate all the phenotype. The majority of these models have been generated in mice. While Atm deficient mouse models exhibit much of the phenotype described in patients with A-T, the broad consensus is that they do not display the most debilitating aspect of A-T, i.e. neurodegeneration. Cerebellar atrophy is one of the neuronal characteristics of A-T patients due to defects in neuronal development and progressive loss of Purkinje and granule cells. This is not evident in Atm-deficient mutants but there are multiple reports on neurological abnormalities in these mice. The focus of this review is to evaluate the appropriateness of Atm mutant mouse models for A-T, particularly with reference to neurological abnormalities and how they might relate to neurodegeneration.