Res Sq. 2023 Jun 01. pii: rs.3.rs-2987323. [Epub ahead of print]
Vignesh Narayan Hariharan,
Jillian Caiazzi,
Rachael Miller,
Chantal Ferguson,
Ellen Sapp,
Hassan Fakih,
Qi Tang,
Nozomi Yamada,
Raymond Furgal,
Joseph Paquette,
Brianna Bramato,
Nicholas McHugh,
Ashley Summers,
Clemens Lochmann,
Bruno Godinho,
Samuel Hildebrand,
Dimas Echeverria,
Matthew Hassler,
Julia Alterman,
Marian DiFiglia,
Neil Aronin,
Anastasia Khvorova,
Ken Yamada.
Metabolic stabilization of therapeutic oligonucleotides requires both sugar and backbone modifications, where phosphorothioate (PS) is the only backbone chemistry used in the clinic. Here, we describe the discovery, synthesis, and characterization of a novel biologically compatible backbone, extended nucleic acid (exNA). Upon exNA precursor scale up, exNA incorporation is fully compatible with common nucleic acid synthetic protocols. The novel backbone is orthogonal to PS and shows profound stabilization against 3'- and 5'-exonucleases. Using small interfering RNAs (siRNAs) as an example, we show exNA is tolerated at most nucleotide positions and profoundly improves in vivo efficacy. A combined exNA-PS backbone enhances siRNA resistance to serum 3'-exonuclease by ~ 32-fold over PS backbone and > 1000-fold over the natural phosphodiester backbone, thereby enhancing tissue exposure (~ 6-fold), tissues accumulation (4- to 20-fold), and potency both systemically and in brain. The improved potency and durability imparted by exNA opens more tissues and indications to oligonucleotide-driven therapeutic interventions.