~ 88% reduction in median Annualized Bleeding Rate (ABR) for all bleeds and 94% reduction in median ABR for spontaneous joint bleeds in highest dose tested ~

~ SerpinPC observed to be well-tolerated ~

~ Company has initiated planning for global registrational program ~

CAMBRIDGE, MA, USA and LONDON, UK I September 09, 2021 I Centessa Pharmaceuticals plc (“Company”) (Nasdaq: CNTA), together with subsidiary ApcinteX Limited (“ApcinteX”), today announced positive topline results from the Phase 2a part of AP-0101, the six-month repeat dose portion of its ongoing first-in-human proof-of-concept study evaluating SerpinPC in severe hemophilia A and B patients.

AP-0101 is a Phase 1/2a proof-of-concept study evaluating SerpinPC, an inhibitor of activated protein C (“APC”), in 23 male subjects with either severe hemophilia A or B who were not on prophylaxis.1 The Phase 2a part of the study assessed the safety, tolerability and pharmacokinetics across three dose cohorts (0.3 mg/kg, 0.6 mg/kg and 1.2 mg/kg) of SerpinPC administered as a subcutaneous (SC) injection every 4 weeks over a 24-week period (6 total doses). Reduction in the annualized bleeding rates (ABRs) were exploratory outcomes. Although eligible, none of the patients in the study had inhibitors.

SerpinPC was well-tolerated. As previously disclosed, one subject with a history of a skin disorder discontinued treatment on SerpinPC due to an injection site reaction. No other SerpinPC-related adverse events have been recorded. There was no reported sustained elevation in D-dimer, a sensitive measure of excess thrombin generation, throughout the 24-week study. Two subjects had anti-drug antibodies and remained on treatment without apparent impact on ABRs.

In the highest dose cohort, SerpinPC reduced the self-reported all bleeds ABR by 88% during the last 12 weeks of treatment (pre-specified primary assessment period) as compared to the all bleeds ABR prospectively measured during the pre-exposure observation period. In the highest dose cohort, five out of eight subjects had zero or one bleed during the 12-week pre-specified primary assessment period. Self-reported spontaneous joint bleeds ABR was reduced by 94% in the highest dose cohort. ABR reductions were similar between patients with either hemophilia A or hemophilia B.

  Dose Tested
Exploratory Efficacy Endpoints 0.3 mg/kg
0.6 mg/kg
1.2 mg/kg
All Bleeds ABR (median percent change) -80%
Spontaneous Joint Bleeds ABR (median percent change) -76%
Above analyses compared last 12 weeks of treatment (pre-specified primary assessment period) to
pre-exposure baseline measures. Bleeding events were self-reported.
p-values presented are based on small numbers and are exploratory in nature.

The median number of target joints (joint with >3 bleeds in any 6-month period) was reduced to zero at the end of the study from a pre-exposure baseline of 2.5. All subjects had target joints at the start of the study and 15 subjects had zero target joints at the end of the study.

All 22 patients who completed the Phase 2a portion of the study have elected to enroll into the 48-week open label extension (“OLE”) portion of the study in which a single flat 60 mg subcutaneous dose of SerpinPC will be administered every 4 weeks over a period of 48 weeks (13 doses total). Centessa expects to report results from the OLE portion of this study in the second half of 2022.

“The compelling reduction in bleeds and continued tolerability that we observed in both hemophilia A and hemophilia B patients in this proof-of-concept study are very encouraging, and we are eager to move SerpinPC into a global development plan aimed at pursuing one or more registrations. We see broad utility of SerpinPC across the hemophilia landscape and will seek the most rapid path to bring this potential subcutaneous therapy to hemophilia patients,” said Antoine Yver, M.D., M.Sc., Chief Medical Officer of Centessa Pharmaceuticals.

“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. A safe, subcutaneous, prophylaxis option for both hemophilia A and B patients would be an important addition to our treatment choices,” said David Lillicrap, M.D., Professor of Pathology and Molecular Medicine at Queen’s University, Kingston, Ontario, Canada and previously a World Federation of Hemophilia Advisory Board member.

¹ Clinicaltrials.gov identifier: NCT04073498 (https://clinicaltrials.gov/ct2/show/NCT04073498)

Conference Call and Webcast
Centessa Pharmaceuticals will host a webcast and conference call today, September 9, 2021, at 8:30 a.m. EDT to discuss topline data from the proof-of-concept trial. To access the audio webcast with slides, please visit the “Events & Publications” page in the Investors & Media section of the Company’s website at https://investors.centessa.com/events-presentations. The call can also be accessed by dialing (855) 493-3565 (domestic) or (929) 517-9002 (international) with conference ID 8459296. An archive of today’s webcast will be available on the Company’s website.

About Centessa Pharmaceuticals
Centessa Pharmaceuticals plc aims to bring impactful new medicines to patients by combining the strengths of an asset-centric model with the benefits of scale and diversification typical of larger R&D organizations. The asset-centric model refers to a highly specialized, singular-focused company that is led by a team of well-recognized subject matter experts. Centessa’s asset-centric companies’ programs range from discovery-stage to late-stage development and include diverse therapeutic areas such as oncology, hematology, immunology/inflammation, neuroscience, hepatology, pulmonology and nephrology. For more information, visit www.centessa.com.

About ApcinteX Limited
ApcinteX Limited is focused on developing SerpinPC for the treatment of hemophilia A and hemophilia B. Hemophilia is a rare bleeding disorder that is caused by a deficiency of thrombin generation upon vascular damage.

About SerpinPC
SerpinPC, a biologic based on the serpin family of proteins, is designed to allow more thrombin to be generated by inhibiting activated protein C (APC) thus rebalancing coagulation in hemophilia patients. SerpinPC has the potential to treat all types of hemophilia regardless of severity or inhibitor status, and may also prevent bleeding associated with other bleeding disorders.

About AP-0101
AP-0101 is an ongoing Phase 1/2a open-label clinical trial to investigate the safety, tolerability and pharmacokinetics of intravenous and subcutaneous doses of SerpinPC in healthy male volunteers and male persons with severe hemophilia (https://clinicaltrials.gov/ct2/show/NCT04073498).

About Hemophilia A (HA) and Hemophilia B (HB)
HA and HB are X-linked genetic disorders affecting one in 5,000 and one in 20,000 live male births, respectively, resulting in spontaneous internal bleeding that can be life-threatening. More than 70% of bleeds occur into joints (hemarthrosis) causing chronic joint damage (arthropathy) with musculoskeletal destruction. The bleeding associated with these disorders is the result of a defect or deficiency in factor VIII (in the case of HA) or factor IX (in the case of HB), the two components of the intrinsic tenase complex.

Normal blood coagulation (hemostasis) is a crucial part of the physiological response to tissue damage. When blood components come into contact with extravascular cells and proteins, platelets accumulate and ultimately lead to the formation of thrombin, the effector enzyme of blood coagulation. Prothrombinase activity is required for the rapid, localized production of thrombin needed for adequate blood clotting. Prothrombinase is continuously degraded by APC, which is present in the circulation at low concentrations. In the setting of deficient intrinsic tenase activity (hemophilia), the natural anticoagulant activity of the circulating APC results in insufficient prothrombinase activity for normal blood clotting.

SOURCE: Centessa Pharmaceuticals