Drug Development · global
Not a Safety Signal: Sanofi Pauses Bronchiectasis Antibody Trial
SAR445399, designed to simultaneously block three inflammatory signals, was intended to assess its potential to clear mucus plugs using lung imaging; shortly after the trial began, it was paused for strategic business considerations, leaving both efficacy and safety unanswered.
Non-cystic fibrosis bronchiectasis causes damaged, widened airways to repeatedly accumulate mucus, creating a cycle in which infection and inflammation exacerbate each other. Sanofi had hoped to intervene in this cycle with SAR445399, an antibody targeting multiple inflammatory pathways, but has now paused the Phase 2 trial before obtaining evidence of efficacy in humans, temporarily removing the opportunity to determine whether this mechanism can improve mucus obstruction in the lungs.
According to Fierce Biotech, Sanofi attributed the pause to strategic business considerations rather than a safety signal in the trial. This explanation suggests that the decision may have resulted from resource prioritization within the research and development portfolio, and cannot be used to infer that the drug is ineffective or toxic; however, the company has not disclosed more specific grounds for the assessment, the number of participants enrolled, or a timeline for next steps.
SAR445399 is an antibody that can block the IL-1, IL-33, and IL-36 signaling pathways. All three pathways are involved in inflammatory responses, and the rationale for broadly blocking them is to suppress multiple, intertwined drivers of inflammation in the airways. Conversely, the actual benefits, the types of patients most suitable for treatment, and the risks of inhibiting multiple pathways must still be answered by controlled trials.
ClinicalTrials.gov data show that the Phase 2a trial, numbered NCT07547436 and coded PDY19372, is sponsored by Sanofi and uses a randomized, double-blind, placebo-controlled design. It originally planned to enroll 70 adults aged 18 to 80. The primary endpoint is not a direct count of hospitalizations or disease exacerbations, but a comparison of changes in mucus plug scores seen on high-resolution computed tomography after 24 weeks of treatment.
The mucus plug score is calculated according to whether a mucus plug completely obstructing an airway is present in each bronchopulmonary segment, allowing the degree of obstruction on imaging to be converted into a quantitative measure. This design is suitable for smaller exploratory trials seeking early signals of drug activity. Even if the score improves, that does not automatically mean patients will experience less coughing, improved lung function, or fewer acute exacerbations; confirmation through clinical endpoints would still be required.
The EU Clinical Trials Register lists the same study as EUCT 2025-523403-29-00 and records trial sites in France, Germany, the Netherlands, Poland, and Spain. Before the pause described in the report, the latest public update on ClinicalTrials.gov still listed the study as recruiting, indicating that the registry information may not yet have caught up with the company’s decision. Because there are currently no efficacy results, safety data, or complete reasons for discontinuation, this event is more indicative of a change in Sanofi’s research and development priorities than a definitive conclusion about the scientific value of SAR445399.