Tirasemtiv is a fast skeletal muscle troponin activator (FSTA) that selectively activates the fast skeletal muscle troponin complex by increasing its sensitivity to calcium and, in preclinical studies and early clinical trials, demonstrated increases in skeletal muscle force in response to neuronal input and delays in the onset and reductions in the degree of muscle fatigue. Tirasemtiv has been studied in clinical trials that have enrolled over 1000 people internationally.

Tirasemtiv was the subject of VITALITY-ALS, a multi-national, randomized, double-blind, placebo-controlled trial in patients with possible, probable or definite ALS, diagnosed within 24 months, and with SVC at baseline ≥ 70 percent predicted. Unfortunately, VITALITY-ALS did not meet the primary endpoint of change from baseline in slow vital capacity (SVC) which was evaluated at 24 weeks following randomization or any of the secondary endpoints in the trial which were evaluated at 48 weeks. No new safety or tolerability findings related to tirasemtiv were identified in VITALITY-ALS. Serious adverse events were similar between patients who received tirasemtiv or placebo but more patients discontinued double-blind treatment on tirasemtiv than on placebo primarily due to non-serious adverse events related to tolerability.

Due to the suspension of the development of tirasemtiv, patients previously enrolled in VIGOR-ALS, the open-label extension clinical trial following participation in VITALITY-ALS, who have chosen to continue to receive this investigational therapy, have been transitioned to a managed access program. This program is only available for these patients who had been receiving tirasemtiv in VIGOR-ALS.