Journal of Antimicrobial Chemotherapy doi:10.1093/jac/dkl444 Antisense peptide-phosphorodiamidate morpholino oligomer conjugate: dose–response in mice infected with Escherichia coli

translation by an antisense mechanism. Membrane-penetrating peptides attached to PMOs increase PMO efficacy by enhancing penetration through bacterial membranes. The objectives of these experiments are to demonstrate gene-specific efficacy and establish a dose–response relationship of a peptide-PMO conjugate. Methods: An 11-base PMO (AcpP) targeted at acpP (an essential gene) of Escherichia coli was synthesized and conjugated with the cell-penetrating peptide RFFRFFRFFRXB (X is 6-aminohexanoic acid and B is b-alanine). Mice were infected by intraperitoneal (ip) injection with K-12 E. coli W3110, and treated ip at 15 min and 12 h post-infection with various amounts of AcpP peptide-PMO conjugate, AcpP PMO without attached peptide, scrambled base sequence PMOs or ampicillin. A strain (LT1) of E. coli was constructed by replacing acpP with an allele that has four wobble base substitutions in the region targeted by the PMO. Results: Twelve hours after a single treatment, 30 mg of AcpP peptide-PMO or 3 mg of AcpP PMO reduced bacteraemia by 3 orders of magnitude compared with treatment with water. Neither scrambled base sequence PMO controls nor 30 mg of ampicillin reduced bacteraemia. Two treatments with 30 mg of AcpP peptide-PMO reduced cfu significantly more than four treatments with 15 mg at 15 min, 4, 8 an