The nucleobase guanine at the 3’-terminus of oligonucleotide RGLS4326 drives off-target AMPAR inhibition and CNS toxicity

Designing safe and effective oligonucleotide (ON) therapeutics requires thorough understanding of structural-activity relationship (SAR) with the intended on-target(s) as well as the unintended off-target(s). Despite encouraging pharmacodynamic activity in a Phase 1b study, development of the first-generation anti-miR-17 ON RGLS4326 for the treatment of autosomal dominant polycystic kidney disease was discontinued due to dose-limiting central nervous system (CNS)-related toxicity observed in nonclinical chronic toxicity studies. Here, we provide SAR evidence that the nucleobase guanine at the 3'-terminus of RGLS4326 drives an unexpected off-target aptamer-like direct interaction with α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), thereby causing CNS toxicity. By replacing the 3'-terminal guanine with adenine, we discover the next-generation anti-miR-17 RGLS8429 that is devoid of off-target AMPAR interaction and CNS toxicity while preserving the potency against the on-target miR-17. Here, we show a way to avoid off-target CNS effects and, more importantly, data that support the clinical development of RGLS8429.