MyoKardia delivers in midstage trial, revs up for phase 3

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The phase 2 data suggest the best dose of mavacamten for obstructive hypertrophic cardiomyopathy is between 5 and 15 mg. (Nadine Doerlé)

MyoKardia’s mavacamten hit its primary and secondary endpoints in a phase 2 trial testing it in patients with symptomatic, obstructive hypertrophic cardiomyopathy (oHCM). The data, which MyoKardia will present this weekend, will inform dosing in the pivotal phase 3 trial for mavacamten.

The 21-patient trial was divided into two cohorts: one received a daily dose of 10, 15 or 20 mg of mavacamten, while the other received a lower daily dose of 2 or 5 mg. The latter group continued to use beta-blockers, which did not affect the safety or action of the drug. At 12 weeks, both cohorts met the primary endpoint, namely a reduction in postexercise left ventricle outflow tract gradient, a measure of heart function.

HCM is an inherited disorder in which a defect in the proteins that help control cardiac contraction cause the muscle wall in the heart to thicken. This usually affects the left ventricle, causing it to become smaller and making it work harder to pump blood. HCM becomes obstructive when the thickened wall blocks blood flow out of the ventricle.

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In addition to hitting its primary endpoint, mavacamten also met its secondary endpoints: Both cohorts showed improvements in New York Heart Association score and dyspnea, or labored or difficult breathing. Additionally, the higher-dose group showed statistically significant gains in peak oxygen consumption, while the lower-dose group had a “positive trend toward improvements.”

“Taken together, data from the PIONEER-HCM study indicate that optimal daily dosing for most patients may be between 5 and 15 mg,” the company said in a statement. These data will inform dosing in the pivotal phase 3 trial of mavacamten, slated to start in the second quarter.

“As we advance into the pivotal phase 3 EXPLORER-HCM trial, we feel confident that we can appropriately treat patients with the aim of optimizing the therapeutic effects of mavacamten to improve patients’ symptoms and functional capacity while preserving left ventricular ejection fraction,” said Marc Semigran, M.D., MyoKardia’s chief medical officer.

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“The lives of symptomatic obstructive HCM patients are limited by the debilitating progression of their condition. Unfortunately, current therapeutic options are either procedurally invasive or have limited effectiveness,” said principal investigator Daniel Jacoby, M.D., director of the cardiomyopathy program and comprehensive heart failure program at the Yale School of Medicine, in the statement. “In the phase 2 PIONEER-HCM study, we are seeing patients on mavacamten feeling better across both quantitative and qualitative measures, including the elimination of their LVOT obstruction, increased functional and exercise capacity and alleviation of shortness of breath."