Efficacy and safety results of long-term extension trial with cardiac myosin inhibitor in HCM

Updated Cumulative Results Of Treatment With Mavacamten From The EXPLORER-LTE Cohort Of The MAVA-LTE Study In Patients With Obstructive Hypertrophic Cardiomyopathy

Presented at ACC.22 by Florian Rader, MD (Los Angeles, CA, USA)

Introduction and methods

Background

Mavacamten is a selective cardiac myosin inhibitor that reduces cardiac muscle contractility by inhibiting excessive myosin-actin cross-bridge formation. The EXPLORER-HCM phase 3 study has previously shown that mavacamten significantly reduced LVOT gradient and improved symptoms, functional capacity, and health status after 30 weeks compared to placevo in patients with symptomatic obstructive hypertrophic cardiomyopathy (HCM). The observed safety profile was similar compared to placebo.

MAVA-LTE is an ongoing, 5-year study of mavacamten in obstructive HCM. 231 of 244 patients who completed EXPLORER-HCM enrolled in MAVA-LTE. Florian Rader, MD presented the updated interim results on the long-term safety and efficacy with mavacamten from the EXPLORER-LTE cohort of the MAVA-LTE study at ACC.22.

Methods

All Patients received a starting dose of 5 mg mavacamten after a wash out period. The dose was titrated at weeks 4, 8 and 12 based on site-read echocardiography measures of Valsalva LVOT gradient and LVEF. The dose could also be adjusted at week 24 based on echocardiography measures of post-exercise LVOT gradient. Possible doses were 2.5, 5, 10 or 15 mg. LVEF <50% is a prespecified criterion for temporary discontinuation of the drug. Median follow-up was 62 weeks in the current analysis.

Main results

Efficacy outcomes

• Resting and Valsalva LVOT improved rapidly within 4 weeks after onset of treatment with mavacamten. This improvement was sustained until 84 weeks (resting LVOT gradient: mean change from baseline at week 48: -35.6 [SD 32.6] mmHg and at week 84: -32.8 [SD 30.8] mmHg; Valsalva LVOT gradient: mean change from baseline at week 48: -45.3 [SD 35.9] mmHg and at week 84: -46.4 [SD 35.8] mmHg).
• A reduction in LVEF was observed. This reduction was expected and consistent with the known mechanism of action of mavacamten. Mean change (SD) in LVEF from baseline was -7.0% (8.3%) at week 48 and -9.0% (8.1%) at week 84.
• A steep drop in serum NT-proBNP was observed at week 4 and this reduction was sustained through week 84 (Median change from baseline to week 48: -480 ng/L, IQR -1104 to -179 ng/L; Median change from baseline to week 84: -488 ng/L, IQR -1098 to -166 ng/L).
• At week 48, 67.5% of patients improved by ≥1 NYHA class (60.2% improved 1 NYHA class and 7.3% improved 2 NYHA classes).

Safety outcomes

• In total, 34 patients (14.7%) experienced an serious adverse event (drug-related and unrelated). Drug-related serious adverse events occurred in 5 patients (2.2%).
• There were 3 deaths reported, none of the deaths were deemed to be related to mavacamten.
• 26 patients (11%) had to temporary stop treatment. Of those, 20 patients could restart therapy with mavacamten. 10 patients (4.3%) had to permanently discontinue treatment.

Conclusion

Interim results of long-term extension study of EXPLORER-HCM showed that treatment with mavacamten resulted in improvements in LVOT gradients, NYHA class, and NT proBNP levels at and beyond 48 weeks in patients with symptomatic obstructive HCM. Rader said that mavacamten was generally well tolerated, and no new safety signals were observed during the longer term follow up.

-Our coverage of ACC.22 is based on the information provided during the congress-

Watch the video with Florian Rader about this study