(Adds background on disease, other ALS treatments; updates shares)
Nov 21 (Reuters) - Cytokinetics Inc will stop developing one of its treatments for ALS, which afflicts Stephen Hawking, after the drug failed in a late-stage trial, the company said on Tuesday, sending its shares tumbling about 35 percent.
The drugmaker said two of the three doses it was testing failed to show a statistically significant difference compared to a placebo when measured by their ability to lower the lungs' 'slow vital capacity', a measure of respiratory function.
Amyotrophic lateral sclerosis (ALS), or Lou Gehrig's disease, is a fatal neuro-degenerative condition that affects nerve cells in the brain and the spinal cord. Deaths and disability in ALS patients are strongly related to respiratory failure, according to Cytokinetics.
More than 6,000 people are diagnosed with the disease in the United States every year, according to the ALS Association.
ALS garnered international attention in 2014 with the "Ice Bucket Challenge," which involved people pouring ice-cold water on themselves, posting a video on social media, and donating funds for research on the disease.
After the failure of its drug tirasemtiv, Cytokinetics said it will focus on its other ALS treatment, CK-2127107, that it is developing in collaboration with Japan's Astellas Pharma Inc .
Cytokinetics' chief executive, Robert Blum, said he believes that the limitations of tirasemtiv will be addressed in the development of CK-2127107.
"We believe CK-2127107 will be better tolerated and potentially more effective than tirasemtiv in patients with ALS," he said.
The U.S. Food and Drug Administration in May approved Mitsubishi Tanabe Pharma Corp's ALS treatment, marking the first regulatory approval in more than two decades.
Drugmakers developing an ALS treatment include France's AB Science SA. Its drug, masitinib, is now under European review after positive data from a late-stage trial earlier this year.
Cytokinetics' shares plummeted 35.14 percent to $7.20 in premarket trading. (Reporting by Divya Grover in Bengaluru; Editing by Savio D'Souza)