In collaboration with Astellas, Cytokinetics is developing reldesemtiv, a fast skeletal muscle troponin activator (FSTA) as a potential treatment for people living with debilitating diseases and conditions associated with neuromuscular or non-neuromuscular dysfunction, muscular weakness, and/or muscle fatigue.

Reldesemtiv is an investigational drug candidate intended to slow the rate of calcium release from the regulatory troponin complex of fast skeletal muscle fibers. Reldesemtiv is a next-generation skeletal muscle compound that may improve muscle function and physical performance in people with SMA and ALS.

Reldesemtiv has been the subject of five completed Phase 1 clinical trials in healthy volunteers, which evaluated safety, tolerability, bioavailability, pharmacokinetics, and pharmacodynamics.

Reldesemtiv was the subject of a Phase 2, hypothesis-generating clinical study in patients with Type II, Type III and Type IV SMA. The study showed dose- and concentration-dependent increases in time to muscle fatigue as measured by changes from baseline in Six Minute Walk Distance (6MWD), a sub-maximal exercise test of aerobic capacity and endurance, and Maximal Expiratory Pressure (MEP), a measure of strength of respiratory muscles, after eight weeks of treatment with reldesemtiv.

Cytokinetics is currently conducting a Phase 2 clinical trial of reldesemtiv in ALS called FORTITUDE-ALS. The trial is expected to enroll 445 patients with ALS and is designed to assess the change from baseline on reldesemtiv versus placebo in the percent predicted slow vital capacity (SVC) and other measures of skeletal muscle function after 12 weeks of treatment.

Reldesemtiv was the subject of a Phase 2 clinical trial designed to assess the potential effect of reldesemtiv compared to placebo on exercise tolerance, assessed as change from baseline in Constant Work Rate endurance time over two weeks, in approximately 40 patients with COPD. In October 2018, Cytokinetics and Astellas announced that the trial did not meet the primary endpoint and did not demonstrate a statistically significant treatment difference in any of secondary endpoints. Adverse events were similar between groups receiving reldesemtiv and placebo.

Astellas also conducted a Phase 1b clinical trial designed to assess the effect of reldesemtiv versus placebo on skeletal muscle fatigue in approximately 60 subjects who are 70 to 89 years of age and who have limited mobility. In October 2018, Cytokinetics and Astellas announced that after an interim analysis of the study was conducted, the Independent Data Monitoring Committee determined that the pre-defined criteria for lack of efficacy of reldesemtiv had been met, and enrollment was halted.