PTC Therapeutics slumps on mixed Translarna trial results

US biotech firm PTC Therapeutics (Nasdaq: PTCT) saw its shares plunge 17% to $26.49 on heavy volume in extended trading yesterday, after it announced disappointing results from the Phase III, double-blind, placebo-controlled, 48-week ACT DMD trial of Translarna (ataluren), an oral, first-in-class, protein restoration therapy for the treatment of nonsense mutation Duchenne muscular dystrophy (nmDMD). The shares recovered to $35.36 in pre-market activity today.

Although the trial results showed clinically meaningful benefits for Translarna-treated patients,  in the overall intent-to-treat study population, the primary endpoint of change from baseline in the 6-minute walk test (6MWT) demonstrated a 15 meter benefit (p=0.213), which was not statistically significant.

A highly significant benefit of 47 meters (p=0.007) was demonstrated in the pre-specified patient population of 300-400 meters at baseline as measured by the 6MWT, which is in line with the company's prior experience in its Phase IIb trial and consistent with the evolving understanding of the 6MWT.  Importantly, no patients in this group lost ambulation (0/47) versus four patients in the placebo group (4/52).  Translarna showed a benefit over placebo across key secondary and tertiary endpoints, including timed function tests (10 meter Run/Walk, 4 Stair Climb, 4 Stair Descend) and the North Star Ambulatory Assessment test.  In addition, a pre-specified meta-analysis of the combined placebo-controlled ACT DMD and Phase 2b trials demonstrated a statistically significant benefit of Translarna across the primary (p=0.015) and key secondary endpoints.