Merck Presents New Analyses Supporting the Promising Potential of Sotatercept, its Investigational Medicine for Adults with Pulmonary Arterial Hypertension (PAH)

Merck (NYSE: MRK), known as MSD outside of the United States and Canada, today announced new analyses from studies of sotatercept, Merck’s novel investigational activin signaling inhibitor biologic, for adults with pulmonary arterial hypertension (PAH) (WHO Group 1) at the European Respiratory Society (ERS) International Congress 2023. A new exploratory post-hoc analysis of right heart catheterization and echocardiography data from patients in the Phase 3 STELLAR study showed treatment with sotatercept for 24 weeks on top of background therapy reduced right heart size and improved right-ventricular (RV) function and hemodynamic status. This analysis was featured in an oral presentation, with simultaneous publication in the European Respiratory Journal. An interim analysis of the Phase 3 SOTERIA open-label extension study was also presented, representing the longest safety and efficacy analysis of sotatercept to date.

“There is an urgent need for new approaches to manage PAH, a rare, progressive, and ultimately life-threatening disease,” said Dr. Eliav Barr, senior vice president and head of global clinical development, chief medical officer, Merck Research Laboratories. “These latest data build on the clinically meaningful efficacy results from the STELLAR trial and support our belief that sotatercept has the potential to transform the treatment of PAH. PAH can strain the heart and lead to eventual right heart failure, so we are particularly encouraged by the exploratory analysis from STELLAR suggesting that treatment with sotatercept improved right heart size and function.”

Primary efficacy results from STELLAR, in which sotatercept on top of background therapy demonstrated a statistically significant and clinically meaningful improvement in 6-minute walk distance (6MWD) at 24 weeks and eight of nine secondary outcome measures, were presented at ACC.23/WCC and published in The New England Journal of Medicine. Merck submitted an application for regulatory approval of sotatercept to the U.S. Food and Drug Administration and plans to submit applications to additional regulatory agencies worldwide.

At ERS 2023, nine Merck-sponsored studies in PAH were presented. These include an oral presentation of a population health model predicting the long-term impact of sotatercept on morbidity and mortality in patients with PAH (#OA740).

Results from STELLAR hemodynamics and echocardiography analysis (Abstract #3111)

An exploratory post-hoc analysis from the STELLAR trial evaluated the effects of sotatercept on select hemodynamic parameters and right-ventricle (RV) function. The STELLAR trial enrolled 323 adults with PAH, randomized to receive sotatercept (n=163) or placebo (n=160), on top of background therapy. Participants with available data at screening and week 24 visits were included in this post-hoc analysis, which reported hemodynamic data from 298 participants and echocardiography data from 275 participants, representing 92% and 85% of total participants respectively. In the analysis, after 24 weeks, sotatercept was associated with meaningful improvements in certain measures of hemodynamic status and RV function.

Results from this exploratory analysis showed treatment with sotatercept compared to placebo, on top of background therapy, led to improvements from baseline in mean pulmonary arterial (PA) pressure (−13.9 mmHg), PA compliance (0.58 mL mmHg−1), pulmonary vascular resistance (−254.8 dyn·s·cm−5), mean right atrial pressure (−2.7 mmHg), mixed venous oxygen saturation (3.84%), PA elastance (−0.42 mmHg mL−1 beat−1), cardiac efficiency (0.48 mL beat−1 mmHg−1), RV work (−0.85 g·m) and RV power (−32.70 mmHg·L min−1). Echocardiography data showed improvements in the ratio of tricuspid annular plane systolic excursion to systolic pulmonary artery pressure (TAPSE/sPAP; 0.12 mm mmHg−1), end-systolic and end-diastolic RV areas (−4.39 cm2 and −5.31 cm2, respectively), tricuspid regurgitation and RV fractional area change (2.04% p<0.050). No significant between-group changes from baseline were seen for TAPSE, heart rate, cardiac output/index or stroke volume/stroke volume index.

“Despite available therapies, PAH remains incurable, with high morbidity and mortality, highlighting the urgent need for novel treatments that target new pathways,” said Dr. Vallerie McLaughlin*, professor of medicine and director, Pulmonary Hypertension Program, Division of Cardiovascular Medicine, University of Michigan in Ann Arbor. “Sotatercept is the first activin signaling inhibitor therapy and is proposed to modulate the vascular proliferation underlying PAH. Acknowledging the exploratory nature of these findings, this is the first clinical evidence suggesting that sotatercept may positively impact certain measures of right heart function and dimensions. This is encouraging and further supports the primary results from the STELLAR analysis, underscoring the potential of sotatercept to play a critical role in the treatment of PAH.”

Results from SOTERIA study (Abstract #OA739)

SOTERIA (NCT04796337) is an ongoing open-label extension study evaluating the long-term safety, tolerability and efficacy of sotatercept when added to background therapy for the treatment of PAH in patients who have completed previous sotatercept studies without early discontinuation. The primary objective of SOTERIA is to evaluate long-term safety and tolerability. The secondary objective is to assess the continued efficacy of sotatercept, as measured by 6MWD, N-terminal pro-B-type natriuretic peptide (NT-proBNP), WHO functional class (FC), pulmonary vascular resistance, overall survival, and simplified French risk score.

“The SOTERIA study provides us with important insight into the longer-term safety and efficacy of sotatercept,” said Dr. Ioana Preston, director of the Pulmonary Hypertension Center and associate professor at Tufts University School of Medicine. “These results support the potential durability of clinical benefit and safety of sotatercept for the treatment of PAH.”

At the data cutoff of April 20, 2023, there were 409 participants enrolled in SOTERIA. All participants were evaluated for safety. The median duration of exposure to sotatercept was 462 days (range: 21-1,762 days), including any exposure to sotatercept during the parent study. One hundred forty-three participants rolled over from placebo. The median duration of exposure to sotatercept in SOTERIA was 189 days.

Sotatercept was well-tolerated and the safety profile was similar to previous studies. 98.5% of participants were on treatment at the time of the interim analysis. Treatment-emergent adverse events (TEAEs) occurred in 81.7% (n=334/409) of participants. Serious TEAEs occurred in 19.3% of participants but only a small proportion lead to treatment discontinuation (1.5%; n=6/409) or death (1.0%; n=4/409). Additionally, 22.7% (n=93/409) of participants experienced a telangiectasia event, 0% had a serious telangiectasia event, 0% discontinued treatment and 1% experienced dose reductions or holds due to telangiectasia. Clinical worsening events were documented. Seven participants (1.7%) experienced nine clinical worsening events.

Improvements in clinical efficacy measures measured at week 24 in SOTERIA were maintained at one year during the open-label period. One hundred thirty-one participants who reached one year of therapy in SOTERIA were evaluated for efficacy at one year; most of these participants rolled over from the Phase 2 sotatercept studies, PULSAR and SPECTRA trials. Mean change (SD) from baseline at week 24 in 6MWD (20.2 ±66.5 m) and NT-proBNP (−374.9 ±1479.4 pg/mL) were largely maintained at one year (10.9 ±73.6 m and −227.2 ±1580.1 pg/mL, respectively). The proportion of participants who improved or maintained WHO FC II from baseline at week 24 (77.2%) was similar to that at one year (76.3%). 30.1% of participants achieved low French risk score (WHO-FC I/II, 6MWD >440 m, NT-proBNP <300 pg/mL) at week 24, and 37.4% at one year.

Changes in background PAH therapy were also documented for all participants. Of participants on any prostacyclin, 29/272 (10.7%) had prostacyclin dose decreases. Of participants on infusion prostacyclin, 22/154 (14.3%) had prostacyclin dose decreases. Of participants on other PAH therapy, 21/406 (5.2%) had other PAH therapy dose decreases and 19/406 (4.6%) had other PAH therapy dose increased. As of April 20, 2023, 8 participants had discontinued prostacyclins entirely.

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