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2477 The Role of Antithrombin Lowering in Patients with Hemophilia: Hemostatic Control Pre- and Post-Fitusiran Dosing Interruption

Program: Oral and Poster Abstracts
Session: 322. Disorders of Coagulation or Fibrinolysis: Poster II
Hematology Disease Topics & Pathways:
Diseases, Bleeding Disorders, Hemophilia, Therapies, Non-Biological, Bleeding and clotting, MPN, coagulant drugs, Clinically relevant
Sunday, December 2, 2018, 6:00 PM-8:00 PM
Hall GH (San Diego Convention Center)

Margaret V. Ragni, MD, MPH1, Pencho Georgiev, MD2*, Michael Desmond Creagh3*, Toshko Jelev Lissitchkov, MD4*, Steve K. Austin, BMedSci, MBBS5*, Charles Richard Morris Hay, MD, FRCP, FRCPath6, Inga Hegemann, MD7*, Syed Rashid Saeed Kazmi, MBBS8*, Pratima Chowdary, MD9*, Savita Rangarajan, MBBS, MD10*, Meredith C. Foster, ScD11*, Qifeng Yu, PhD11*, Craig Benson, MD, MS11*, Kate Madigan, MD12*, Huy Van Nguyen, PharmD12*, Shariq Ali, PhD11*, Ketaki Kadam, MS11*, Pallavi Jain, PharmD11* and K. John Pasi, MB, ChB, PhD, FRCP, FRCPath, FRCPCH13

1Department of Medicine and Clinical Translational Science, University of Pittsburgh, Pittsburgh, PA
2University Multiprofile Hospital for Active Treatment “Sveti Georgi”, and Medical University Plovdiv, Plovdiv, Bulgaria
3Royal Cornwall Hospitals NHS Trust, Truro, United Kingdom
4Clinical Haematology Clinic Specialized Hospital for Active Treatment "Joan Pavel", Sofia, Bulgaria
5St. George’s Healthcare NHS Trust Haemophilia Centre, London, United Kingdom
6Manchester Royal Infirmary, Manchester, United Kingdom
7University Hospital, Zurich, CHE
8University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom
9KD Haemophilia and Thrombosis Centre, Royal Free Hospital, London, GBR
10Haemophilia, Haemostasis & Thrombosis Centre, Hampshire Hospital NHS Foundation Trust, Basingstoke, United Kingdom
11Sanofi Genzyme, Cambridge, MA
12Alnylam Pharmaceuticals, Cambridge, MA
13Royal London Haemophilia Centre, Barts and the London School of Medicine and Dentistry, London, United Kingdom

Introduction

Hemophilia A and hemophilia B are rare bleeding disorders characterized by insufficient thrombin generation due to deficiencies in factors VIII or IX, respectively. Standard treatment for hemophilia is currently based on replacement of the deficient factor with factor concentrate. This, unfortunately, subjects the patient to the risk of developing neutralizing antibodies, or inhibitors, against replacement factor VIII or IX. Individuals with inhibitors become refractory to standard replacement therapy, a serious complication for as many as one-third of patients with severe hemophilia A and a lower proportion of patients with hemophilia B. Fitusiran is a once-monthly subcutaneously administered investigational RNA interference therapeutic that targets antithrombin (AT) to improve thrombin generation (TG) and promote hemostasis in patients with hemophilia A or hemophilia B with or without inhibitors. In September 2017, fitusiran dosing in the Phase 2 open-label extension (OLE) study was temporarily suspended to investigate a case of fatal cerebral venous sinus thrombosis. Following this investigation, fitusiran dosing resumed in December 2017 with protocol amendments for bleed management dosing and safety monitoring. During the temporary dosing suspension, AT levels, TG, bleeding events, and frequency of factor replacement and bypassing agents were assessed.

Methods

Before the dosing suspension, 33 patients (hemophilia A=27, hemophilia B=6) were enrolled, of whom 28 patients continued treatment over 20 months in the Phase 2 OLE study, with a median of 11 months on study. As of June 2018, data collected monthly during the clinical hold included AT levels, TG, and description and management of treated bleeding events before and during the clinical hold, which were used to estimate annualized bleeding rates (ABRs) and bleeding rates per month.

Results

AT activity in patients previously receiving fitusiran demonstrated a progressive increase during the interruption of fitusiran dosing. Median %AT increased to >60% after a 5-month period compared with the last data point before dosing interruption. These data confirm our previous findings that discontinuation of fitusiran results in gradual recovery of AT activity over time. Subjects also demonstrated a concomitant steady decrease in TG during the interruption of fitusiran dosing, which occurred over a similar time course to that of AT recovery. Consistent with both the increase in AT activity and decrease in TG, preliminary analysis shows the median overall ABR increased from 1.43 events/year before the dosing interruption to 6.07 events/year during the dosing interruption.

Conclusions

During a period of fitusiran dosing suspension, recovery of AT activity was accompanied by a decrease in TG and an increase in bleeding events. These observations provide support for the therapeutic hypothesis that AT activity lowering by fitusiran leads to an increase in TG and improved hemostasis. Phase 3 studies of fitusiran are ongoing.

Disclosures: Ragni: Bioverativ: Consultancy, Research Funding; MOGAM: Membership on an entity's Board of Directors or advisory committees; CSL Behring: Research Funding; SPARK: Consultancy, Research Funding; Shire: Research Funding; Alnylam: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novo Nordisk: Research Funding; Sangamo: Research Funding; Biomarin: Membership on an entity's Board of Directors or advisory committees, Research Funding. Georgiev: Alnylam: Consultancy. Lissitchkov: Novo Nordisk: Other: Investigator fees as a participant of the clinical trial. Austin: Pfizer: Research Funding. Chowdary: Novo Nordisk: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; CSL Behring: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Freeline: Consultancy; Bayer: Honoraria; Baxalta (Shire): Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Swedish Orphan Biovitrum AB (Sobi): Honoraria; Biogen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Foster: Sanofi Genzyme: Employment. Yu: Sanofi Genzyme: Employment. Benson: Sanofi Genzyme: Employment. Madigan: Alnylam Pharmaceuticals Inc: Employment. Nguyen: Alnylam Pharmaceuticals Inc: Employment. Ali: Sanofi Genzyme: Employment. Kadam: Sanofi Genzyme: Employment. Jain: Sanofi Genzyme: Employment. Pasi: Octapharma: Honoraria; Catalyst Bio: Honoraria; Bayer: Speakers Bureau; Shire: Speakers Bureau; NovoNordisk: Speakers Bureau; Sobi: Honoraria; Apcintex: Honoraria; Biomarin: Honoraria, Research Funding; Pfizer: Speakers Bureau; Alnylam: Honoraria, Research Funding; Bioverativ: Honoraria, Research Funding.

*signifies non-member of ASH