FDA Grants Orphan Drug Status to SerpinPC for Hemophilia B

Centessa is set to begin registrational studies for the therapy's regulatory approval

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by Steve Bryson, PhD |

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The U.S. Food and Drug Administration (FDA) has granted orphan drug status to SerpinPC for treating hemophilia B.

Orphan drug status is awarded to therapeutics intended to treat rare conditions, defined as those affecting fewer than 200,000 people in the U.S. The designation provides financial incentives to support clinical development and, if approved, up to seven years of marketing exclusivity.

Administered as an under-the-skin (subcutaneous) injection, SerpinPC can potentially treat all types of hemophilia, regardless of disease severity or the presence of inhibitors.

Later this year, Centessa Pharmaceuticals, expects to begin registrational studies to support its bid for SerpinPC’s approval and report two-year data from an ongoing Phase 2a open-label extension study that evaluated the therapy.

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“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, Centessa’s CEO, said in a press release. “This designation from the FDA is an important milestone in the development of SerpinPC and underscores the need for new, innovative treatment options for patients with hemophilia B.”

People with hemophilia lack certain clotting factors, proteins that support blood clot formation and prevent excessive bleeding.

Standard replacement therapy provides patients with the missing clotting factors derived from an external source. Long-term use, however, is associated with developing neutralizing antibodies, or inhibitors, that may lower the clotting factors’ effectiveness.

SerpinPC is a biological therapy designed to elevate thrombin, an enzyme that converts the protein fibrinogen to fibrin, triggering blood clots to form. The goal is to rebalance blood clotting processes regardless of hemophilia type, disease severity, or the presence of inhibitors.

The open-label Phase 1/2a AP-0101 trial (NCT04073498) is evaluating the safety, tolerability, and pharmacological properties of SerpinPC. The Phase 1 part assessed its safety in healthy volunteers, while Phase 2a tested SerpinPC in 23 men with severe hemophilia A or B who were not using preventive treatments.

Top-line Phase 2a data showed that when given once a month, SerpinPC safely reduced overall bleeds by up to 88% and spontaneous joint bleeds by up to 94%. Hemophilia A and B participants saw similar outcomes.

The therapy was well tolerated with no evidence of abnormal blood clot formation or sustained D-dimer elevations (which signal excessive formation and breakdown of blood clots) due to excess thrombin, according to Centessa.

All 22 patients who completed the trial enrolled in a 48-week open-label extension study to continue receiving SerpinPC every four weeks for a total of 13 treatments.

“We look forward to initiating registrational studies for SerpinPC later this year, as well as reporting the two-year follow-up data from the SerpinPC Phase 2a open label extension study in the fourth quarter,” Saha said.