Structural Features of Small Molecules Targeting the RNA Repeat Expansion That Causes Genetically Defined ALS/FTD.

Genetically defined amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), collectively named c9ALS/FTD, are triggered by hexanucleotide GGGGCC repeat expansions [r(GC)] within the gene. In these diseases, neuronal loss occurs through an interplay of deleterious phenotypes, including r(GC) RNA gain-of-function mechanisms. Herein, we identified a benzimidazole derivative, CB096, that specifically binds to a repeating 1 × 1 GG internal loop structure, 5'CG/3'GC, that is formed when r(GC) folds. Structure-activity relationship (SAR) studies and molecular dynamics (MD) simulations were used to define the molecular interactions formed between CB096 and r(GC) that results in the rescue of disease-associated pathways. Overall, this study reveals a unique structural feature within r(GC) that can be exploited for the development of lead medicines and chemical probes.