To enhance delivery of phosphorodiamidate morpholino oligomer (PMO) to target tissues, we developed a family of therapeutics consisting of Endosomal Escape Vehicle (EEV™) cyclic cell-penetrating peptides conjugated to exon skipping PMOs. ENTR-601-44 is an EEV-PMO construct developed for the treatment of exon 44 skip-amenable Duchenne muscular dystrophy (DMD). Preclinical studies demonstrated that ENTR-601-44 produced robust exon skipping and dystrophin protein in vitro and in vivo, indicating its therapeutic potential.
ENTR-601-44-101 was a single-center, phase 1, double-blind, placebo-controlled trial to evaluate safety, pharmacokinetics (PK), and pharmacodynamics in healthy adult male volunteers. Randomized participants were administered a single intravenous dose of ENTR-601-44 (0.75 [n=6], 1.5 [n=6], 3.0 [n=7], or 6.0 [n=6] mg/kg) or placebo [n=8] and assessed up to 41 days post-administration. All randomized volunteers completed dosing and 6-week follow-up except for one in the 3 mg/kg group who withdrew from the study prior to receiving treatment (physician’s decision).
ENTR-601-44 was well tolerated in all dose groups. No adverse events (AE) were deemed related to study drug by the investigator. The most common AE was headache (n=7; 5 were mild and 2 were moderate). All AEs resolved by study completion and no severe or serious AEs were reported in any dose group throughout the study. Notably, no clinically significant adverse findings were observed with renal function. Dose-dependent PK was observed as assessed by plasma concentration and urinary excretion. Additionally, dose-dependent concentration of the final metabolite and significant exon 44 skipping were observed in skeletal muscle following administration of 6 mg/kg ENTR-601-44 at 72 hours post dose.
These results demonstrate, for the first time, that the EEV platform can safely and effectively deliver oligonucleotide therapeutics to skeletal muscle with significant target engagement in human volunteers. Furthermore, these findings support the evaluation of ENTR-601-44 in patients with DMD amenable to exon 44 skipping.