A new drug for the muscle-wasting disease Duchenne muscular dystrophy has shown significant benefits in mice, opening the door for clinical trials
AVI-4658 is a phosphorodiamidate morpholino oligomer (PMO) designed to induce skipping of dystrophin exon 51 and restore its expression in patients with Duchenne muscular dystrophy (DMD). Preclinically, restoration of dystrophin in the dystrophic mdx mouse model requires skipping of exon 23, achieved with the mouse-specific PMO, AVI-4225. Herein, we report the potential toxicological consequences of exon skipping and dystrophin restoration in mdx mice using AVI-4225. We also evaluated the toxicological effects of AVI-4658 in both mdx and wild-type mice. In both studies, animals were dosed once weekly for 12 weeks up to the maximum feasible dose of 960 mg/kg per injection. Both AVI-4658 and AVI-4225 were well-tolerated at all doses. Findings in AVI-4225-treated animals were generally limited to mild renal tubular basophilia/vacuolation, without any significant changes in renal function and with evidence of reversing. No toxicity associated with the mechanism of action of AVI-4225 in a dystrophic animal was observed.
AVI-4658 is a phosphorodiamidate morpholino oligomer (PMO) drug designed to restore dystrophin expression in a subset of patients with Duchenne muscular dystrophy (DMD). Previous reports demonstrated this clinical proof-of-principle in patients with DMD following intramuscular injection of AVI-4658. This preclinical study evaluated the toxicity and toxicokinetic profile of AVI-4658 when administered either intravenously (IV) or subcutaneously (SC) to cynomolgus monkeys once weekly over 12 weeks, at doses up to the maximum feasible dose of 320 mg/kg per injection. No drug-related effects were noted on survival, clinical observations, body weight, food consumption, opthalmoscopic or electrocardiographic evaluations, hematology, clinical chemistry, urinalysis, organ weights, and macroscopic evaluations. Drug-related microscopic renal effects were dose-dependent, apparently reversible, and included basophilic granules (minimal), basophilic tubules (minimal to moderate), and tubular vacuolation (minimal to mild). These data establish the tolerability of AVI-4658 at doses up to and including the maximum feasible dose of 320 mg/kg by IV bolus or SC injection.