Results of the Randomized, Double-Blind, Placebo-Controlled, Phase 3 Hercules Study of Caplacizumab in Patients with Acquired Thrombotic Thrombocytopenic Purpura

Abstract

Introduction: Acquired or immune-mediated thrombotic thrombocytopenic purpura (aTTP) is a life-threatening thrombotic microangiopathy characterized by severe thrombocytopenia, microangiopathic hemolytic anemia, and organ ischemia. Inhibitory autoantibodies cause a severe deficiency of the von Willebrand factor (vWF) cleaving enzyme ADAMTS13, leading to intravascular vWF-platelet aggregation and microvascular thrombosis. The mainstays of treatment are plasma exchange (PE) and immunosuppression. Caplacizumab, a bivalent Nanobody, targets the A1 domain of vWF, inhibiting the interaction between ultra-large vWF and platelets. Methods: Patients with an acute episode of aTTP who had received one PE treatment were randomized 1:1 to placebo or 10 mg caplacizumab, in addition to daily PE and corticosteroids. A single IV dose of study drug was given before the first on-study PE and a SC dose was given daily during the PE period and 30 days thereafter. If at the end of this period there was evidence of ongoing disease, such as suppressed ADAMTS13 activity, investigators were encouraged to extend the blinded treatment for a maximum of 4 weeks together with optimization of immunosuppression. All patients entered a 28-day treatment-free follow up period after the last dose of study drug (Figure 1). Primary endpoint was time to platelet count response, defined as platelet count ≥ 150×109/L with stop of daily PE within 5 days. There were 4 key secondary endpoints, hierarchically ranked. The 1st was a composite of aTTP-related death, aTTP recurrence, or major thromboembolic event during the study drug treatment period. A blinded, independent committee adjudicated aTTP-related deaths and major thromboembolic events. The 2nd looked at recurrences during the entire study period, including the follow up period. The 3d evaluated refractoriness to therapy, defined as absence of platelet count doubling after 4 days of treatment and LDH still above normal. The 4th was the time to normalization of 3 organ damage markers: LDH, cardiac troponin I and serum creatinine. Results: 145 patients were randomized, 73 to placebo and 72 to caplacizumab. Demographics and baseline disease characteristics were balanced between groups, except for a higher proportion of initial episodes in the caplacizumab arm. Compared to patients treated with placebo, those on caplacizumab were >50% more likely to achieve a platelet response at any given time point (platelet count normalization rate 1.55, 95% CI 1.10 - 2.20, p Conclusions: Results of the Phase 3 HERCULES study confirm that treatment with caplacizumab reduces the time to platelet count response, resulting in faster resolution of aTTP. Treatment with caplacizumab also resulted in a highly clinically meaningful reduction in aTTP-related death, recurrence of aTTP, or a major thromboembolic event during study drug treatment. The relapses after stop of study drug in patients with ADAMTS13 activity Disclosures Scully:Ablynx: Honoraria, Research Funding; Shire: Honoraria, Research Funding; Novartis: Honoraria; Alexion: Honoraria. Cataland:Ablynx NV: Membership on an entity9s Board of Directors or advisory committees. Peyvandi:Ablynx, Roche: Membership on an entity9s Board of Directors or advisory committees; Ablynx, Bayer, Grifols, Novo Nordisk, Sobi: Speakers Bureau;Freeline, Kedrion, LFB, Octapharma: Consultancy. Coppo:Ablynx: Membership on an entity9s Board of Directors or advisory committees; Alexion: Membership on an entity9s Board of Directors or advisory committees; Octapharma: Membership on an entity9s Board of Directors or advisory committees; Shire: Membership on an entity9s Board of Directors or advisory committees. Knobl:Novo Nordisk: Consultancy, Research Funding; Shire: Consultancy, Research Funding. Kremer Hovinga:Baxalta/Shire: Other: unrestricted grant hereditary TTP registry; Ablynx NV: Membership on an entity9s Board of Directors or advisory committees. Metjian:Ablynx NV, Shire, Omeros: Research Funding; Shire: Membership on an entity9s Board of Directors or advisory committees. de la Rubia:Amgen: Other: Honoraria; Celgene: Other: Honoraria; Janssen: Other: Honoraria. Pavenski:Alexion Pharmaceuticals: Honoraria; Novartis: Honoraria; Ablynx: Other: participation in industry sponsored RCT; CSL Behring: Research Funding. Callewaert:Ablynx NV: Employment. Biswas:Ablynx NV: Employment. De Winter:Ablynx NV: Employment. Zeldin:Ablynx NV: Employment.