The inhibitor SerpinPC is biologically based on the serpin family of proteins and could rebalance coagulation in hemophilia patients. SerpinPC is well tolerated, according to topline data from a phase 1/2a proof of concept study announced by Centessa Pharmaceuticals.

In patients taking the highest dose, 1.2 mg/kg, SerpinPC led to an 88% reduction in the median annualized bleeding rate for all bleeds and a 94% reduction in the median annualized bleeding rate for spontaneous joint bleeds, according to a press release from the company.

“The results of this Phase 2a study of SerpinPC continue to show an excellent tolerability profile for this molecule, and the exploratory efficacy results seen in this study of severe hemophilia A and B patients are also very promising,” said David Lillicrap, MD, professor of pathology and molecular medicine at Queen’s University, Kingston in Ontario, Canada.

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SerpinPC inhibits activated protein C (APC) thereby allowing more thrombin to be generated. It has the potential to treat all types of hemophilia regardless of severity or inhibitor status, according to the Centessa.

The aim of the phase 1/2a trial was to investigate the safety and tolerability of SerpinPC in healthy men and women with hemophilia A or B. The study also evaluated the pharmacokinetics of the 3 doses (0.3 mg/kg, 0.6 mg/kg and 1.2 mg/kg) of the treatment.

The results showed that SerpinPC was well tolerated, with only 1 participant with a history of a skin disorder having an injection site reaction.

The trial is ongoing but no longer recruiting participants. It is estimated to be completed in April 2022. In an open-label extension portion, it will assess the effect of a single flat 60 mg subcutaneous dose of SerpinPC every 4 weeks over 48 weeks. Results from this portion of the study are expected in the second half of 2022.


Centessa Pharmaceuticals announces positive topline data from proof-of-concept study of SerpinPC in severe hemophilia A and B patients not on prophylaxis. News release. Centessa Pharmaceuticals; September 9, 2021.

The safety and tolerability of SerpinPC in healthy men and in men with severe blood disorders (haemophilia A and B). US National Library of Medicine. Last updated April 22, 2021. Accessed September 16, 2021.