The findings were reported in a study titled “Long-Term Pulmonary Function in Duchenne Muscular Dystrophy: Comparison of Eteplirsen-Treated Patients to Natural History,” published in The Journal of Neuromuscular Diseases.
Exondys 51 is the only drug approved by the U.S. Food and Drug Administration (FDA) for the treatment of DMD. It was developed by Sarepta Therapeutics to bind to exon 51 in the mRNA sequence of dystrophin, promoting the skipping of the DMD-causing genetic mutation that is amenable with this strategy.
Results of the Phase 2 201 study (NCT01396239) and its follow-up 202 trial (NCT01540409) have revealed that Exondys 51 is safe and well-tolerated by patients, while it can increase the amount of dystrophin protein up to 0.44% of normal levels after 48 weeks of treatment. However, a full analysis of Exondys 51’s therapeutic impact had not been performed.
As DMD progresses due to the lack of functioning dystrophin, several muscles of the body are affected, including the diaphragm and the heart, which can lead to death. Finding therapeutic strategies that can delay or prevent respiratory and cardiac function decline is critically important.
A research team led by Thomas B. Kinane, MD, chief of the Pediatric Pulmonary Unit at Massachusetts General Hospital for Children, evaluated the impact of treatment with Exondys 51 in pulmonary function.
The team analyzed clinical data collected from 12 patients with Duchenne who participated in the 201 and 202 clinical trials of Exondys 51, and compared them with DMD natural history data that had been previously published. The patients received weekly intravenous administrations of 30 mg per kg body weight, or 50 mg/kg of the treatment.
This post-hoc analysis revealed that treated patients experienced a statistically significant and clinically meaningful reduction in pulmonary function decline.
Natural history data collected from the United Dystrophinopathy Project (UDP) showed that for Duchenne patients ages 7 to 15.5 — the same age range of the participants in the clinical trials — the values of mean predictive forced vital capacity (FVC%p), a commonly used measure of respiratory function, decrease 4.1% annually. Comparatively, patients treated with Exondys 51 were found to experience only a 2.8% decrease in FVC%p per study year.
“Patients treated with eteplirsen [Exondys 51] in Study 201/202 experienced significantly less deterioration of respiratory muscle function than natural history would predict,” Douglas Ingram, president and CEO of Sarepta, said in a press release.
In addition, Exondys 51 was also found to delay the annual decline of predictive maximum expiratory pressure (MEP%p) and maximum inspiratory pressure (MIP%p) compared to natural history.
“This demonstrates the potential of [Exondys 51] in preserving respiratory function in patients with DMD,” the researchers stated.