Functional Gains From Novel Agent for Obstructive HCM, Top-line Results

May 12, 2020

Patients with obstructive hypertrophic cardiomyopathy (HCM) who took an investigational agent that targets cardiac myosin over about 7 months showed across-the-board improvements in functional capacity, symptoms, and left ventricular outflow obstruction in a randomized controlled trial.

Treatment with the oral drug mavacamten (or MYK-461) was well tolerated and showed no untoward safety issues compared with placebo in the phase 3 EXPLORER-HCM trial, its developer, MyoKardia, announced in a press release. The top-line trial results were made public in advance of a more expansive presentation at a later date.

The company describes mavacamten as an allosteric modulator of cardiac myosin that "reduces cardiac muscle contractility by inhibiting excessive myosin-actin cross-bridge formation that results in hypercontractility, left ventricular hypertrophy and reduced compliance."

In the EXPLORER-HCM trial, with its 251 patients with symptomatic obstructive HCM, 37% of those randomly assigned to receive once-daily mavacamten and 17% of those given placebo (P =.0005) reached the functional primary endpoint by 30 weeks, the company reported.

The primary endpoint  was a composite of either a ≥1.5 mL/kg/min improvement in peak VO2 along with symptomatic improvement or ≥3.0 mL/kg/min improvement without deterioration of symptom status.

Patients taking mavacamten also showed significant improvement in the secondary endpoints of left ventricular outflow tract (LVOT) peak gradient after exercise, NYHA functional class, Kansas City Cardiomyopathy Questionnaire Clinical Summary scores, and HCM Symptom Questionnaire Shortness of Breath Domain score, all at P = .0001, and peak VO2 at P = .0006, MyoKardia reported.

The company said beyond its bid to have the drug approved for obstructive HCM, based on its mechanism of action it foresees the drug as a potential treatment for nonobstructive HCM and for some patients with heart failure with preserved ejection fraction.

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