‘Unheard of’ PAH Improvement With Novel Drug: STELLAR

‘Unheard of’ PAH Improvement With Novel Drug: STELLAR

NEW ORLEANS – An investigational, first-in-class agent that delivers a completely new type of intervention to patients with pulmonary arterial hypertension (PAH) scored a clear win in the STELLAR trial, the first to complete among three phase 3 trials that are testing this agent.

Sotatercept, administered subcutaneously every 3 weeks for 24 weeks, improved from baseline average 6-minute walk distance (6MWD) by a significant and clinically meaningful 40.8 meters, compared with placebo, for the trial’s primary efficacy endpoint (P < .001). The treatment also “delivered broad clinical benefit across multiple domains including hemodynamics, World Health Organization functional class, disease biomarkers, risk scores and patient-reported outcomes,” Marius M. Hoeper, MD, said at the joint scientific sessions of the American College of Cardiology and the World Heart Federation.

“These results establish the clinical utility of sotatercept, administered in combination with approved PAH therapies, as a new treatment for PAH,” added Dr. Hoeper, professor and deputy director of the department of respiratory medicine at Hannover (Germany) Medical School,

“The most important aspect was the hemodynamic improvement,” with sotatercept treatment, which led to an average 235 dyn/sec per cm−5 reduction in pulmonary vascular resistance from baseline and an average cut in pulmonary artery pressure of 13.9 mm Hg from baseline, compared with placebo, a result that’s “unheard of,” Dr. Hoeper said in a press conference during the meeting.

“With other tested agents we usually see very little improvement in pulmonary artery pressure. This is a signal that we achieved some reversing of the pathological changes in the pulmonary vessels that lead to” PAH, he added.

Simultaneously with his report the findings also appeared online in the New England Journal of Medicine.

A new hope for patients with PAH

Based on the reported findings, sotatercept is a “very exciting boutique molecule” that will “offer patients with PAH a very exciting new treatment,” commented Rhonda Cooper-DeHoff, PharmD, a designated discussant and a researcher at the University of Florida, Gainesville.

“This study is a new hope for patients with PAH. Until now, they’ve had really bad outcomes, but [in this study] we see significant differences in 6MWD, hemodynamics, and risk factors. Overall, I think the benefit is greater than the risk” it may pose to patients through potential adverse effects, commented Julia Grapsa, MD, PhD, a cardiologist at St. Thomas Hospital in London, and another discussant at the meeting.

“The results are impressive” and “encouraging,” and “suggest that sotatercept may represent a new and clinically consequential addition to current medications for PAH,” wrote three clinicians from Canyons Region Intermountain Medical Center in Murray, Utah, in an editorial that accompanied the published report.

But the authors of the editorial also raised several cautions and concerns. They questioned the generalizability of the findings, noting that the patients with PAH enrolled in the study were all adults who were clinically stable and an average of more than 8 years out from their initial PAH diagnosis, and more than 90% were on stable treatment for PAH with two or three agents specific for treating the disorder. The study cohort also had a disproportionately high enrollment of patients with idiopathic (59%) or heritable (18%) forms of PAH, and the 15% of patients in the trial with connective tissue disease represented a disproportionately low prevalence of this PAH subtype.

The editorialists also called for “ongoing vigilance” for adverse effects from sotatercept treatment, although they acknowledged that the adverse effects reported to date from sotatercept are “largely reassuring.”

Death or clinical worsening cut by 84%

STELLAR randomized 323 patients at 91 sites in 21 countries with WHO Group 1 PAH and with WHO functional class II or III disease to receive either sotatercept or placebo for 24 weeks, with an option for treatment to continue beyond that until the last patient in the study reached 24 weeks on treatment, resulting in an overall median treatment duration of nearly 33 weeks.

In addition to the significant result for the primary endpoint, the 163 patients who received sotatercept had significant improvements, compared with 160 placebo-treated patients, for eight of nine secondary endpoints. The only secondary endpoint with a neutral result was for a measure of cognitive and emotional wellbeing, a parameter that was already at a normal level at baseline in most enrolled patients, Dr. Hoeper explained.

The incidence of either death or an event indicative of clinical worsening during the overall median follow-up of almost 33 weeks was 26.3% among the control patients and 5.5% among those who received sotatercept. This translated into a significant reduction for this endpoint of 84% with sotatercept treatment, compared with placebo.

The rates of treatment-emergent adverse events leading to discontinuation were roughly the same in the control and sotatercept arms, and the incidence of severe or serious treatment-emergent adverse events was higher among the control patients.

The most common adverse event on sotatercept was bleeding events, which occurred in 32% of those on sotatercept and in 16% of the control patients, but the events in the sotatercept arm were “mostly mild,” said Dr. Hoeper. The next most frequent adverse event during sotatercept treatment was appearance of telangiectasias, which occurred in 14% of those on sotatercept and in 4% of control patients.

“It’s an uncommon adverse event profile, but not unexpected for a drug with its mechanism of action,” he said.

Drug binds activin, a pathologic driver of PAH

Sotatercept is an engineered molecule that combines a section of a human immunoglobulin G molecule with a portion of the receptor for activin. This structure allows sotatercept to bind free activin molecules in a patient’s blood, thereby removing a key driver of the pulmonary vascular wall remodeling that is at the pathologic root of PAH.

“Hyperproliferation of blood vessel–wall cells” caused by activin signaling “is perhaps the most important driver of PAH,” Dr. Hoeper said. “Sotatercept allows us for the first time to target the underlying mechanism behind PAH.”

Still ongoing are the HYPERION and ZENITH phase 3 trials of sotatercept. HYPERION is enrolling patients with newly diagnosed or high-risk PAH and is expected to complete in 2028. ZENITH is enrolling patients with more advanced PAH and a higher mortality risk, with results expected in 2026.

Sotatercept has received “Breakthrough Therapy” designation and “Orphan Drug” designation by the Food and Drug Administration, and “Priority Medicines” designation and “Orphan Drug” designation by the European Medicines Agency for the treatment of PAH. One recent review estimated a worldwide PAH prevalence of about 3-4 cases/100,000, which for the United States translates into a total prevalence of perhaps 10,000-15,000 affected people.

STELLAR was funded by Acceleron Pharma, a subsidiary of Merck. Dr. Hoeper is a consultant to Acceleron. Dr. Cooper-DeHoff, Dr. Grapsa, and the authors of the editorial on STELLAR have no relevant disclosures.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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