Seralutinib Shows Promise in Pulmonary Arterial Hypertension, Phase III Data Reveal
Berlin, Germany – February 25, 2026 – Gossamer Bio has announced topline results from the Phase III PROSERA study, evaluating the investigational drug seralutinib for the treatment of pulmonary arterial hypertension (PAH). While the study narrowly missed its primary endpoint, findings indicate a clinically meaningful benefit, particularly in patients with intermediate and high-risk disease. The development of seralutinib is a collaborative effort between Gossamer Bio and Chiesi Group, under a global partnership agreement.
Pulmonary arterial hypertension is a progressive and debilitating condition characterized by increased pressure in the pulmonary arteries, leading to shortness of breath, fatigue, and heart failure. Current treatments aim to manage symptoms and improve quality of life, but a significant unmet need remains for therapies that can address the underlying disease pathology and improve long-term outcomes. Seralutinib represents a novel approach, targeting a key pathway involved in the development of PAH.
PROSERA Trial Design and Key Findings
The PROSERA trial enrolled 390 patients diagnosed with PAH, classified as World Health Organization (WHO) Functional Class II or III. These patients were randomly assigned to receive either seralutinib or a placebo, in addition to their existing PAH therapies. The study was designed as a double-blind, placebo-controlled trial, with participants receiving treatment for up to 48 weeks. A significant proportion of participants – 55% – were already receiving triple or quadruple therapy for PAH, and 61% were on prostacyclin therapy, reflecting real-world treatment patterns. Baseline characteristics were generally well-matched between the two groups, minimizing potential bias.
The primary endpoint of the trial was the change in six-minute walk distance (6MWD) from baseline to week 24. 6MWD is a commonly used measure of exercise capacity in PAH patients. The seralutinib group demonstrated a median improvement of +28.2 meters in 6MWD, compared to +13.5 meters in the placebo group. The estimated Hodges-Lehmann treatment effect was +13.3 meters. While this result showed a positive trend, it did not reach the pre-specified statistical significance level required for the primary endpoint. This means that the observed difference could be due to chance.
Despite not meeting the primary endpoint, all four key secondary endpoints favored seralutinib over placebo in the overall study population. However, due to the failure to achieve statistical significance on the primary endpoint, the p-values for these secondary endpoints could not be formally assessed for statistical significance. What we have is a common practice in clinical trials – when the primary endpoint is not met, conclusions about secondary endpoints are limited.
A more pronounced effect was observed in a pre-specified subgroup of patients identified as being at intermediate and high risk for disease progression. This subgroup, comprising 234 patients, was defined by a REVEAL 2 Lite Risk Score greater than six at the start of the study. In this group, seralutinib demonstrated a placebo-adjusted improvement of +20.0 meters in 6MWD. Importantly, three out of four secondary endpoints in this subgroup achieved p-values below 0.0125, indicating a statistically significant benefit.
Expert Commentary and Future Directions
Faheem Hasnain, chairman, co-founder, and CEO of Gossamer Bio, acknowledged the disappointment of narrowly missing the primary endpoint but emphasized the positive signals observed in the data. “While we are disappointed to have narrowly missed the stringent pre-specified statistical threshold for our primary endpoint, the result still clears the traditional 0.05 p-value, and we believe these data clearly demonstrate seralutinib is an active drug in patients with PAH,” Hasnain stated. He further highlighted the clinically meaningful improvements seen in the intermediate- and high-risk patient population, noting that this group faces a higher risk of adverse events and represents a significant unmet medical need.
Hasnain also pointed to the consistency of the findings with the TORREY Study, another clinical trial evaluating seralutinib in PAH patients. The TORREY study, he explained, identified a similar signal of benefit in higher-risk patients, suggesting that seralutinib may be particularly effective in this subgroup. The REVEAL 2 Lite Risk Score is a tool used to assess the risk of mortality in PAH patients, incorporating factors such as functional class, 6MWD, and biomarkers.
The mechanism of action of seralutinib involves selectively modulating the GluN2B subunit of the NMDA receptor. This modulation is intended to address the dysregulation of the receptor, which is believed to contribute to the development and progression of PAH. By targeting this specific pathway, seralutinib offers a potentially more targeted approach compared to currently available non-selective treatments.
Implications for PAH Treatment
The PROSERA trial results offer a nuanced picture of seralutinib’s potential in PAH treatment. While the drug did not meet its primary endpoint in the overall population, the significant benefit observed in the intermediate- and high-risk subgroup suggests that it may be a valuable option for patients who are most vulnerable to disease progression. Further research may be warranted to explore the optimal apply of seralutinib in this specific patient population.
Pulmonary arterial hypertension remains a challenging condition to treat, and new therapies are urgently needed. Current treatment options include vasodilators, diuretics, and oxygen therapy, but these treatments often only manage symptoms and do not address the underlying disease process. Seralutinib, with its novel mechanism of action, represents a potential step forward in the treatment of PAH, offering hope for improved outcomes for patients with this debilitating condition.
The development of new therapies for PAH is an active area of research, with numerous clinical trials underway evaluating a range of novel approaches. These include therapies targeting inflammation, fibrosis, and metabolic dysfunction, all of which are believed to play a role in the pathogenesis of PAH. The ongoing research efforts are aimed at developing more effective and targeted treatments that can improve the lives of patients with PAH.
Next Steps: Gossamer Bio and Chiesi Group are expected to further analyze the PROSERA data and discuss potential regulatory pathways with health authorities. The companies will also likely explore opportunities to conduct additional studies to further evaluate the efficacy and safety of seralutinib in specific patient populations.
This article provides information for general knowledge and informational purposes only, and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.
Do you have thoughts on these findings? Share your comments below, and please share this article with your network.