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In a significant setback for the fight against sickle cell disease (SCD), Pfizer announced that its experimental drug, inclacumab, failed to meet its main efficacy goal in a large Phase 3 clinical trial. The company revealed Friday that the THRIVE-131 study, which tested whether inclacumab could significantly reduce the rate of painful vaso-occlusive crises (VOCs) compared to placebo over a 48-week period, did not achieve its primary endpoint.
The trial enrolled 241 participants aged 16 and older who had experienced between two and ten VOC episodes in the year before enrollment. These painful episodes, caused by the blockage of blood flow due to sickle-shaped red blood cells, represent a dangerous and common complication of the inherited disorder. Despite hopes that inclacumab—a P-selectin inhibitor acquired through Pfizer’s $5.4 billion purchase of Global Blood Therapeutics (GBT) in 2022—would help reduce these crises, the late-stage results were disappointing.
The drug was generally well tolerated, with the most frequent side effects including anemia, joint pain, and back pain. However, the lack of effectiveness in reducing VOCs follows a string of setbacks for Pfizer in the rare blood disease space. In September 2024, Pfizer withdrew the GBT-developed drug Oxbryta from global markets after emerging safety concerns and an imbalance of serious events in clinical studies.
Pfizer noted it remains committed to developing better therapies for sickle cell disease and will continue to advance other drugs in its pipeline, including osivelotor. The company acknowledged the persistent unmet need in the sickle cell community, especially as progress on new treatments remains challenging.
Sickle cell disease impacts an estimated 100,000 Americans and millions globally. While a handful of disease-modifying drugs and newly approved gene therapies offer hope, many patients still endure chronic pain and life-threatening complications tied to their condition.
Disclaimer: This article is for informational purposes only and should not be considered medical advice. Patients are advised to consult their healthcare providers for guidance on treatment and clinical options.
Reference: Reuters, 15-Aug-2025.
