Selective C9orf72 G-Quadruplex-Binding Small Molecules Ameliorate Pathological Signatures of ALS/FTD Models

Abstract

The G-quadruplex (G4) forming <i>C9orf72</i> GGGGCC (G4C2) expanded hexanucleotide repeat (EHR) is the predominant genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Developing selective G4-binding ligands is challenging due to the conformational polymorphism and similarity of G4 structures. We identified three first-in-class marine natural products, chrexanthomycin A (<b>cA</b>), chrexanthomycin B (<b>cB</b>), and chrexanthomycin C (<b>cC</b>), with remarkable bioactivities. Thereinto, <b>cA</b> shows the highest permeability and lowest cytotoxicity to live cells. NMR titration experiments and <i>in silico</i> analysis demonstrate that <b>cA</b>, <b>cB</b>, and <b>cC</b> selectively bind to DNA and RNA G4C2 G4s. Notably, <b>cA</b> and <b>cC</b> dramatically reduce G4C2 EHR-caused cell death, diminish G4C2 RNA foci in (G4C2)₂₉-expressing Neuro2a cells, and significantly eliminate ROS in HT22 cells. In (G4C2)₂₉-expressing <i>Drosophila</i>, <b>cA</b> and <b>cC</b> significantly rescue eye degeneration and improve locomotor deficits. Overall, our findings reveal that <b>cA</b> and <b>cC</b> are potential therapeutic agents deserving further clinical study.