For decades, difficulties delivering antisense oligos into cells have limited their use in many models, especially in adult animals. Uncharged steric-blocking antisense, such as Morpholino oligos or peptide nucleic acids, are especially suited to delivery by guanidinium-based delivery moieties (such as arginine-rich cell-penetrating peptides) because the oligos and peptides do not form electrostatic complexes. This delivery technology is reviving the use of antisense oligos in adult animal models.

This open-access review considers Morpholinos conjugated with either of two kinds of delivery moieties: arginine-rich cell-penetrating peptides and octa-guanidinium dendrimers, called PPMO and Vivo-Morpholinos respectively. Published reports of work with Vivo-Morpholinos are just starting to appear, so this review focuses on the PPMO, which are now in a clinical trial for prevention of cardiac restenosis after angioplasty and stenting (http://www.avibio.com/pr/pr397.php) and are in late preclinical development for Duchenne muscular dystrophy.

Moulton JD, Jiang S. Gene Knockdowns in Adult Animals: PPMOs and Vivo-Morpholinos. Molecules. 2009 Mar 25;14(3):1304-23.
http://www.mdpi.com/1420-3049/14/3/1304