Tirasemtiv, formerly known as CK-2017357, is a medication that underwent extensive testing for use in ALS/MND by California-based biotechnology company Cytokinetics. Tirasemtiv is a fast skeletal muscle troponin activator, which means that it was developed with the goal of improving muscle function. In addition, it may combat muscle wasting and neuromuscular dysfunction—concerns that are critical for ALS/MND patients.
Skeletal muscles, also known as striated muscles, are voluntarily controlled, but in ALS/MND, the death of motor neurons means that the brain is unable to effectively command the skeletal muscles to move. Troponin, meanwhile, is a protein compound that is essential to skeletal muscle contraction. By activating troponin in the body, Tirasemtiv may result in increased skeletal muscle and slow muscle fatigue.
Tirasemtiv was evaluated for use in ALS/MND via a Phase IIb clinical trial called BENEFIT-ALS (Blinded Evaluation of Neuromuscular Side Effects and Functional Improvement with Tirasemtiv in ALS), which began in October 2012 and ended in April 2014. The Phase I and II trials that preceded the IIb trial demonstrated that Tirasemtiv is safe and generally well-tolerated. While not designed or powered to determine efficacy, a combined analysis from two patient groups were optimistic, showing improved scores on the ALSFRS-R functional rating scale. The results were mixed and generally showed a lack of efficacy.
"We have engaged in an objective and comprehensive review of results from BENEFIT-ALS and have concluded that data favoring the effects of tirasemtiv relative to placebo on Slow Vital Capacity from this large, international Phase IIb trial are robust and warrant further investigation. BENEFIT-ALS is the first clinical trial in patients with ALS to demonstrate a positive and potentially clinically meaningful effect on Slow Vital Capacity, an important measure of disease progression and predictor of survival,” stated Robert I. Blum, Cytokinetics’ President and CEO. “We are encouraged by our initial interactions with the FDA relating to the results of BENEFIT-ALS and believe that our continuing discussions can inform our plans to pursue a potential registration program based on effects observed on respiratory function measured by Slow Vital Capacity in patients with ALS."
In BENEFIT-ALS, treatment with tirasemtiv resulted in a statistically significant and potentially clinically meaningful reduction in the decline of SVC, a measure of the strength of the skeletal muscles responsible for breathing that has been shown to be an important predictor of disease progression and survival in prior trials of patients with ALS. This pre-specified secondary efficacy endpoint in BENEFIT-ALS declined less on tirasemtiv than on placebo at each assessment time point.
Tirasemtiv was granted orphan drug designation and fast track status by the U.S. FDA, as well as orphan medicinal production designation by the European Medicines Agency, for the potential treatment of ALS/MND. This means that the drug was on an accelerated development schedule in the hope of being able to offer it to patients sooner than drugs for which the patient population has a wider range of alternate medication options.
Cytokinetics stated, “Cytokinetics is keenly aware of the urgent treatment needs of today’s ALS patients. [However], we have not yet obtained sufficient evidence to confirm whether any dosing regimen of tirasemtiv is both safe and effective during chronic treatment. We must concentrate our activities on our clinical trials program so that tirasemtiv may have the best chance of regulatory approval as quickly as possible for the potential future benefit of all ALS patients. We pledge that Cytokinetics will continue to revisit options regarding wider access to tirasemtiv if supported by emerging data, as we proceed to later stages of clinical development.”
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