Lacosamide Interaction with Expanded CGG Repeats RNA and Its Role in Modulating Poly-Glycine Protein-Mediated Toxicity in Fragile-X Tremor/Ataxia Syndrome

Fragile X-associated Tremor/Ataxia Syndrome (FXTAS) is a severe neurodegenerative disorder triggered by expansions of CGG trinucleotide repeats in the <i>FMR1</i> gene. These extended trinucleotide RNA repeats [r-(CGG)_exp] generate toxic homopolymeric poly-Glycine (polyG) proteins in neuronal cells through Repeat-Associated Non-AUG (RAN) translation and are also associated with RNA foci formation. This study examines the neuroprotective potential of Lacosamide, an antiepileptic drug, in targeting CGG repeat expansions associated with FXTAS. We employed a multidimensional approach, combining biophysical techniques, cellular assays, and a <i>Drosophila</i> model, to validate the selective interactions of Lacosamide with toxic CGG repeat RNA through a drug-repurposing strategy. Biophysical analyses, including Circular Dichroism (CD), Isothermal Titration Calorimetry (ITC), Electrophoretic Mobility Shift Assays (EMSA), and Nuclear Magnetic Resonance (NMR) spectroscopy, revealed Lacosamide's binding affinity for GG mismatches within toxic CGG repeat RNA. Furthermore, Lacosamide treatment effectively mitigated polyG toxicity in FXTAS cellular and a <i>Drosophila</i> model of the disease. These affirmed the small molecule's ability to reduce polyG aggregation-associated toxicity, thereby improving the diseased conditions. These findings suggest Lacosamide's potential neuroprotective role in FXTAS, supporting further translational efforts for its clinical application to improve outcomes for patients affected by this debilitating disorder.