Results: We examined whether PEG-PEI copolymers can facilitate ESO-mediated dystrophin expression after
intramuscular injections into tibialis anterior (TA) muscles of mdx mice. We utilized a set of PEG-PEI copolymers
containing 2 kDa PEI and either 550 Da or 5 kDa PEG, both of which bind 2'OMe ESOs with high affinity and form
stable nanoparticulates with a relatively low surface charge. Three weekly intramuscular injections of 5 μg of ESO
complexed with PEI2K-PEG550 copolymers resulted in about 500 dystrophin-positive fibers and about 12% of
normal levels of dystrophin expression at 3 weeks after the initial injection, which is significantly greater than for
injections of ESO alone, which are known to be almost completely ineffective