Dyclonine rescues frataxin deficiency in animal models and buccal cells of patients with Friedreich's ataxia

Abstract

Inherited deficiency in the mitochondrial protein frataxin (FXN) causes the rare disease Friedreich's ataxia (FA), for which there is no successful treatment. We identified a redox deficiency in FA cells and used this to model the disease. We screened a 1600-compound library to identify existing drugs, which could be of therapeutic benefit. We identified the topical anesthetic dyclonine as protective. Dyclonine increased FXN transcript and FXN protein dose-dependently in FA cells and brains of animal models. Dyclonine also rescued FXN-dependent enzyme deficiencies in the iron–sulfur enzymes, aconitase and succinate dehydrogenase. Dyclonine induces the Nrf2 [nuclear factor (erythroid-derived 2)-like 2] transcription factor, which we show binds an upstream response element in the FXN locus. Additionally, dyclonine also inhibited the activity of histone methyltransferase G9a, known to methylate histone H3K9 to silence FA chromatin. Chronic dosing in a FA mouse model prevented a performance decline in balance beam studies. A human clinical proof-of-concept study was completed in eight FA patients dosed twice daily using a 1% dyclonine rinse for 1 week. Six of the eight patients showed an increase in buccal cell FXN levels, and fold induction was significantly correlated with disease severity. Dyclonine represents a novel therapeutic strategy that can potentially be repurposed for the treatment of FA.

Stable Isotopes and LC–MS for Monitoring Metabolic Disturbances in Friedreich’s Ataxia Platelets

“…The lack of a compensatory pathway to acetyl-CoA from fatty acid β-oxidation suggests that decreased histone acetylation could occur in FRDA through decreased cofactor availability similar to our recent observation in tumor cells [40]. This finding is also consistent with epigenetic silencing of frataxin expression that occurs in FRDA [41] as a result of the GAA expansion [4,42], which results in increased DNA [43,44] and histone methylation [45] at the expense of histone acetylation. Decreased glucose utilization in FRDA platelets also results in decreased labeling of succinyl-CoA, suggesting that without some compensatory metabolic change there could be down-regulation of protein succinylation in FRDA through decreased cofactor availability.…”

“…One pathway of epigenetic silencing arises through upregulation of histone lysine methyltransferases resulting in increased methylation of specific lysine residues on histone tails (e.g., H3K9) and inhibition of frataxin gene transcription [45]. Cosilencing of the nrf-2 gene in FRDA could potentially result from a similar pathway.…”

“…Cosilencing of the nrf-2 gene in FRDA could potentially result from a similar pathway. This would then explain the paradoxical finding that nrf-2 expression is reduced in FRDA [45]. The reduction in nrf-2 protein expression in FRDA suggests that there would be a reduced ability to mount an antioxidant response.…”

The role of Nrf2 signaling in counteracting neurodegenerative diseases

“…) is currently in a Phase 2 clinical trial in FRDA patients (ClinicalTrials.gov). Interestingly, Nrf2 binds an upstream response element in the frataxin locus, and the anesthetic dyclonine has been shown to activate Nrf2, increase the mRNA and protein levels of frataxin and rescue frataxin‐dependent enzyme deficiencies in the iron‐sulfur enzymes aconitase and succinate dehydrogenase .…”

Translating HDAC inhibitors in Friedreich’s ataxia

“…A number of laboratories have reported identification of small molecule activators of FXN mRNA synthesis or frataxin protein in patient cells. These include histone deacetylase inhibitors [3, 20], erythropoietin alpha [21], dyclonine [22], gamma-interferon [23], SRC inhibitors [24], short oligonucleotides [25], and inhibitors of frataxin degradation [26]. With the exception of HDAC inhibitors and frataxin stabilizers, the mechanism of action of these compounds has yet to be elucidated.…”