We have recently reported that cell-penetrating peptides (CPPs) and novel chimeric peptides containing CPP (referred as
B peptide) and muscle-targeting peptide (referred as MSP) motifs significantly improve the systemic exon-skipping activity
of morpholino phosphorodiamidate oligomers (PMOs) in dystrophin-deficient mdx mice. In the present study, the general
mechanistic significance of the chimeric peptide configuration on the activity and tissue uptake of peptide conjugated PMOs
in vivo was investigated. Four additional chimeric peptide-PMO conjugates including newly identified peptide 9 (B-9-PMO and
9-B-PMO) and control peptide 3 (B-3-PMO and 3-B-PMO) were tested in mdx mice. Immunohistochemical staining, RT-PCR and
western blot results indicated that B-9-PMO induced significantly higher level of exon skipping and dystrophin restoration than
its counterpart (9-B-PMO), further corroborating the notion that the activity of chimeric peptide-PMO conjugates is dependent on
relative position of the tissue-targeting peptide motif within the chimeric peptide with respect to PMOs. Subsequent mechanistic
studies showed that enhanced cellular uptake of B-MSP-PMO into muscle cells leads to increased exon-skipping activity in
comparison with MSP-B-PMO. Surprisingly, further evidence showed that the uptake of chimeric peptide-PMO conjugates of
both orientations (B-MSP-PMO and MSP-B-PMO) was ATP- and temperature-dependent and also partially mediated by heparan
sulfate proteoglycans (HSPG), indicating that endocytosis is likely the main uptake pathway for both chimeric peptide-PMO
conjugates. Collectively, our data demonstrate that peptide orientation in chimeric peptides is an important parameter that
determines cellular uptake and activity when conjugated directly to oligonucleotides. These observations provide insight into
the design of improved cell targeting compounds for future therapeutics studies.This is the publisher’s final pdf. The article is copyrighted by the American Society of Gene & Cell Therapy and published by the Nature Publishing Group. It can be found at: http://www.nature.com/mtna/index.html.Keywords: Antisense oligonucleotide, Exon skipping, Chimeric peptide conjugate, Duchenne muscular dystroph