Highlights
- Sotatercept, when added to standard therapy, dramatically lowers the risk of death, lung transplantation, or hospitalization in patients with advanced, high-risk pulmonary arterial hypertension (PAH).
- The ZENITH phase 3 trial shows a hazard ratio of 0.24 for the composite primary endpoint, signaling significant clinical benefit.
- Sotatercept’s efficacy extends to delaying clinical worsening and improving functional outcomes in both intermediate and high-risk PAH populations.
- Adverse events, while notable (epistaxis, telangiectasia), were generally manageable and did not outweigh the clinical benefits.
Clinical Background and Disease Burden
Pulmonary arterial hypertension (PAH) is a progressive, life-threatening disease characterized by elevated pulmonary vascular resistance, right heart failure, and high mortality rates. Despite advancements in targeted vasodilator therapies, patients with advanced PAH, particularly those in World Health Organization (WHO) functional class III or IV, continue to face poor prognoses. The annual mortality for these high-risk populations remains unacceptably high, and there is a substantial unmet need for disease-modifying interventions that improve survival and quality of life beyond symptom control.
Research Methodology
The ZENITH phase 3, multicenter, randomized, double-blind, placebo-controlled trial (NCT04896008) evaluated sotatercept in adults with PAH who were classified as WHO functional class III or IV and had a Registry to Evaluate Early and Long-Term Pulmonary Arterial Hypertension Disease Management Lite 2 (REVEAL Lite 2) risk score of ≥9, indicating high 1-year mortality risk. All patients were on maximal background therapy. Participants (n=172) were randomized 1:1 to receive add-on sotatercept (starting at 0.3 mg/kg, titrated to 0.7 mg/kg) or placebo subcutaneously every 3 weeks. The primary endpoint was a time-to-first-event composite of death from any cause, lung transplantation, or hospitalization (≥24 hours) for worsening PAH. The study was halted early after a prespecified interim analysis showed overwhelming efficacy.
For broader context, the STELLAR phase 3 trial (Hoeper et al., 2023) evaluated sotatercept in WHO functional class II or III PAH patients, using change in 6-minute walk distance and multiple secondary clinical endpoints.
Key Findings
In the ZENITH trial, the risk of the primary composite endpoint was dramatically reduced with sotatercept:
– Events occurred in 17.4% of the sotatercept group versus 54.7% in placebo (hazard ratio [HR], 0.24; 95% CI, 0.13–0.43; P<0.001).
– Death from any cause: 8.1% (sotatercept) vs 15.1% (placebo).
– Lung transplantation: 1.2% vs 7.0%.
– Hospitalization for worsening PAH: 9.3% vs 50.0%.
The trial’s early termination underscores the magnitude of clinical benefit. In the STELLAR trial, sotatercept improved 6-minute walk distance by a median of 34.4 m (vs 1.0 m for placebo; difference 40.8 m, 95% CI, 27.5–54.1; P<0.001) and significantly improved most secondary endpoints, further supporting sotatercept’s efficacy across a spectrum of PAH severity.
Common adverse events included epistaxis and telangiectasia, with some increases in hemoglobin, thrombocytopenia, and blood pressure. These were generally manageable within the clinical trial context.
Mechanistic Insights and Biological Plausibility
Sotatercept is a first-in-class activin signaling inhibitor, functioning as a ligand trap for members of the TGF-β superfamily implicated in vascular remodeling. By rebalancing pro- and anti-proliferative signaling in pulmonary vasculature, sotatercept addresses fundamental pathobiologic drivers of PAH, differentiating it from traditional vasodilators.
Expert Commentary
International PAH experts have hailed sotatercept as a “disease-modifying” addition to the PAH therapeutic armamentarium. The NEJM editorial accompanying ZENITH emphasizes that sotatercept’s impact on clinical events—rather than solely on exercise capacity or surrogate markers—sets a new standard for future PAH trials and highlights the urgent need for guideline integration.
Controversies or Limitations
The ZENITH trial was stopped early, which, while ethically appropriate, can introduce statistical uncertainties and may overestimate effect sizes. The cohort was limited to those already on maximal background therapy and at very high risk, potentially limiting generalizability to lower-risk or treatment-naïve populations. Long-term safety, especially regarding hematologic and vascular complications, requires further surveillance. The high cost and access to sotatercept may also pose challenges for global implementation.
Conclusion
Sotatercept represents a transformative advance for patients with advanced, high-risk PAH, offering significant reductions in mortality, need for transplantation, and hospitalization. Its unique mechanism and robust clinical effect signal a paradigm shift towards disease modification in PAH management. Future research should focus on long-term outcomes, real-world applicability, and cost-effectiveness, while ongoing studies will clarify its role in broader PAH populations.
References
Humbert M, McLaughlin VV, Badesch DB, et al.; ZENITH Trial Investigators. Sotatercept in Patients with Pulmonary Arterial Hypertension at High Risk for Death. N Engl J Med. 2025;392(20):1987-2000. doi:10.1056/NEJMoa2415160.
Hoeper MM, Badesch DB, Ghofrani HA, et al.; STELLAR Trial Investigators. Phase 3 Trial of Sotatercept for Treatment of Pulmonary Arterial Hypertension. N Engl J Med. 2023;388(16):1478-1490. doi:10.1056/NEJMoa2213558.
