At the 70th annual American College of Cardiology (ACC) 2021 meeting, results were presented for the Phase III trial EXPLORE-HCM, demonstrating improvements in health status for patients treated with mavacamten for symptomatic obstructive hypertrophic cardiomyopathy (oHCM) relative to placebo. Mavacamten is currently in pre-registration in the US for the treatment of oHCM and potentially provides physicians with a novel treatment strategy that is disease-specific. EXPLORE-HCM identified that mavacamten leads to a significant improvement in quality of life and health status for patients with oHCM. The quality-of-life and health status improvement was assessed using the Kansas City Cardiomyopathy Questionnaire (KCCQ), a 23-question disease-specific questionnaire quantifying symptoms, physical and social function and quality of life. This quality-of-life improvement, which is often not observed with currently available treatment regimens, drives its likelihood of achieving US Food and Drug Administration (FDA) approval. With the benefits that mavacamten treatment provides, GlobalData predicts that this therapy is likely to achieve a dominant share of the oHCM market, stealing significant market share from the incumbent therapies that have poor long-term outcomes.
HCM is a primary myocardial disorder that results from unexplained left ventricular (LV) hypertrophy that is often caused by pathogenic variants in sarcomeric genes. There are two major types of HCM, oHCM and non-oHCM, with the key difference being that in oHCM blood flow is blocked or severely restricted due to stiffening of the left ventricular wall as a result of HCM. The current treatment regimen for HCM, both types, has a primary goal of improving symptoms and cardiac function using beta-blockers and other cardiovascular drugs such as verapamil, an anti-hypertensive, and disopyramide, an anti-arrhythmic. Mavacamten has a significant advantage in entering the oHCM portion of the cardiovascular disease market as it is a first-in-class cardiac myosin inhibitor, whereas the current pharmacological options are not disease-specific and are inadequate or poorly tolerated.
The EXPLORER-HCM trial, a Phase III, double-blind, randomised, placebo-controlled trial, took place across 68 clinical cardiovascular centres in 13 countries. The study participants were adult patients ages 18 years and older with symptomatic oHCM with left ventricular outflow tract (LVOT) obstruction gradient of ≥50mmHg and New York Heart Association (NYHA) Functional Classification class II-III. The participants were randomly assigned to mavacamten or placebo for 30 weeks, followed by a reassessment after eight weeks of discontinued therapy. EXPLORE-HCM’s primary outcome of a functional composite of improved peak oxygen consumption (pVO2) and NYHA significantly favoured treatment with mavacamten (37% vs. 17%, p<0.01) with a difference in KCCQ-OS score between mavacamten and placebo, favouring mavacamten +9.1 (95% CI: 5.5,12.8).
The trial results from the EXPORE-HCM Phase III trials demonstrate that mavacamten significantly improves the health status and quality of life for patients with symptomatic oHCM. Mavacamten will likely dominate the oHCM market as the first-in-class cardiac myosin inhibitor and rapidly steal market share from the non-specific therapies that are part of the current treatment regimen. There is a clear need for novel therapies to address the symptomatic oHCM market to improve treatment outcomes with drugs that are pharmacologically designed to target the hypercontractility and impaired relaxation that is observed in the HCM sarcomere of this disease. As the new data demonstrates, mavacamten is on course to address this gap in the oHCM market.