A slipped-CAG DNA-binding small molecule induces trinucleotide-repeat contractions in vivo

Area of Science:

• Genetics
• Molecular Biology
• Neuroscience

Background:

• Repeat expansion diseases, like Huntington's disease (HD), are characterized by increasing repeat lengths in affected tissues, driving disease progression.
• Current therapeutic strategies primarily focus on targeting proteins involved in repeat mutations, with limited success in inducing repeat contractions.
• Targeting DNA structures, such as slipped-CAG intermediates, represents an unexplored avenue for therapeutic intervention.

Purpose of the Study:

• To identify and characterize a novel compound that can induce contractions of expanded DNA repeats.
• To investigate the mechanism of action of this compound on repeat expansion mutations.
• To evaluate the therapeutic potential of repeat contraction in a Huntington's disease model.

Main Methods:

• Screening for small molecules that bind to slipped-CAG DNA intermediates.
• Testing the efficacy of the identified compound (naphthyridine-azaquinolone, NA) in patient-derived cells and HD mouse models.
• Investigating the molecular mechanisms underlying NA-induced repeat contractions, including DNA replication, transcription, and DNA repair pathways.
• Assessing the impact of NA treatment on mutant Huntingtin protein aggregates in vivo.

Main Results:

• Naphthyridine-azaquinolone (NA) specifically binds to slipped-CAG DNA intermediates of expansion mutations.
• NA treatment induces efficient repeat contractions in HD patient cells and in neurons of the HD mouse striatum.
• Repeat contractions are allele-specific, independent of DNA replication, and depend on transcription and MutSβ-mediated repair inhibition.
• NA administration in HD mice reduces levels of mutant Huntingtin protein aggregates.

Conclusions:

• Repeat-structure-specific DNA ligands, like NA, represent a novel therapeutic strategy for contracting expanded repeats.
• Targeting DNA intermediates offers a new approach to disease modification in repeat expansion disorders.
• NA demonstrates potential as a therapeutic agent for Huntington's disease by reducing toxic protein aggregates through repeat contraction.