Selective tissue targeting of synthetic nucleic acid drugs

Abstract

Antisense oligonucleotides (ASOs) are chemically synthesized nucleic acid analogs designed to bind to RNA by Watson-Crick base pairing. Following binding to the targeted RNA, the ASO perturbs RNA function by promoting selective degradation of the targeted RNA, altering RNA intermediary metabolism, or disrupting function of the RNA. Most antisense drugs are chemically modified to enhance their pharmacological properties and for passive targeting of the tissues of therapeutic interest. Recent advances in selective tissue targeting have resulted in a newer generation of ASO drugs that are more potent and better tolerated than previous generations, spawning renewed interest in identifying selective ligands that enhance targeted delivery of ASOs to tissues.

Figure 1. Chemical modification and formulation strategies for delivery of oligonucleotide drugs.

(A) Chemical modifications commonly used to impart drug-like properties to oligonucleotide drugs. (B) Double-stranded RNA (pink and green carbons illustrate individual strands). (C) Single-stranded PS-modified MOE gapmer ASO (yellow spheres show PS, and pink spheres show MOE modifications). (D and E) LNP-encapsulated double-stranded oligonucleotides (D) versus single-stranded oligonucleotide-coated SNAs (E). cEt, constrained ethyl; F, 2′-fluoro; LNA, locked nucleic acid; LNP, lipid nanoparticle; MOE, 2′-O-methoxyethyl; OMe, 2′-O-methyl; PMO, phosphorodiamidate morpholino; PS, phosphorothioate; SNA, spherical nucleic acid.

Figure 2. Models for interactions of formulated, chemically modified, or ligand-conjugated oligonucleotides with cell surface receptors.

(A) Vitamin A–LNPs interact with retinol-binding proteins (RBPs) in plasma and promote cellular uptake via RBP receptors (RBPRs). (B) SNAs interact with scavenger receptors via multivalent interactions to promote cellular uptake. (C and D) LDLR-mediated uptake of apolipoprotein E–decorated LNPs (C) or cholesterol-conjugated siRNA (D). (E and F) Single-stranded PS ASOs (E) interact with stabilin receptors more efficiently than double-stranded oligonucleotides (F). (G and H) Trivalent GalNAc-modified ASOs (G) and siRNA (H) interact with the ASGR with equal efficiency.

Figure 3. The tissue and cellular barriers an oligonucleotide drug must overcome for effective delivery.

Interaction with plasma proteins facilitates distribution to peripheral tissues from the site of injection. Oligonucleotide drugs can gain access to the tissue interstitium by paracellular or transcellular transport across the capillary endothelium. Upon arrival at the cell surface of interest, oligonucleotide drugs can gain cellular entry by interaction with the targeted cell surface receptor.