The US Food and Drug Administration (FDA) has granted Orphan Drug designation to Centessa Pharmaceutical’s SerpinPC , a new activated protein C (APC) inhibitor designed to treat hemophilia B.

The designation, announced by news release, follows the results of a phase 2a study showing that SerpinPC at the highest dose reduced the median annualized bleeding rate for all bleeds by 88% and for spontaneous joint bleeds by 94% in patients with severe hemophilia A and B.

“We believe SerpinPC has the potential to offer patients with hemophilia B a convenient subcutaneous option that is designed to prevent and reduce bleeds without the risk of thrombosis,” Saurabh Saha, MD, PhD, chief executive officer of Centessa, said in the press release.

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Serpins are protease inhibitors that regulate coagulation and fibrinolysis, and they have become an important target in the treatment of hemophilia. SerpinPC is a biological drug candidate that is designed to rebalance coagulation in patients with hemophilia by inhibiting APC and subsequently allowing greater thrombin generation.

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In Centessa’s phase 2a study, part of the AP-0101 proof-of-concept study, SerpinPC was assessed at 3 doses—0.3 mg/kg, 0.6 mg/kg, and 1.2 mg/kg—administered subcutaneously over 24 weeks. It was well tolerated in 23 male patients with severe hemophilia A or B who were not on prophylactic therapy, with no long-term increases in D-dimer levels and no cases of thrombosis.

All 22 patients who completed the study elected to join a 48-week open-label extension study on a flat subcutaneous dose of 60 mg of SerpinPC, which will be administered every 4 weeks. That study is ongoing, and Centessa will report 2-year follow-up data in the fourth quarter of 2022.


Centessa Pharmaceuticals announces Orphan Drug designation granted to SerpinPC for the treatment of hemophilia B. News release. Centessa Pharmaceuticals plc; September 14, 2022.