Figure 2.

Strategies to enhance antisense oligonucleotide (ASO) intracellular delivery. ASOs may be conjugated to a fatty acid chain, enhancing its affinity to albumin and other serum proteins, to a cell-penetrating peptide (CCP), or to an anti-transferrin receptor 1 (TfR1) monoclonal antibody to promote cell uptake. (1) Conjugated ASOs are localized at the cell membrane, either because of the conjugate binding to specific cell receptors or because of interactions of the CCP with the cell membrane. (2) ASOs are then internalized in early endosomes by endocytosis. (3) An increase in pH in endosomes promotes cleavage of the ASOs’ linker and their release from the conjugates. (4) A small portion of ASOs escape the endocytic vesicles and cross the nuclear pores to the nucleus, (5) where they can target CUG-expanded RNAs.