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(G4C2)exp] within the C9orf72 gene. In these diseases, neuronal loss occurs through an interplay of deleterious phenotypes, including r(G4C2)exp 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'CGG/3'GGC, that is formed when r(G4C2)exp folds. Structure-activity relationship (SAR) studies and molecular dynamics (MD) simulations were used to define the molecular interactions formed between CB096 and r(G4C2)exp that results in the rescue of disease-associated pathways. Overall, this study reveals a unique structural feature within r(G4C2)exp that can be exploited for the development of lead medicines and chemical probes.