ATLANTA—Caplacizumab can improve outcomes in patients with acquired thrombotic thrombocytopenic purpura (aTTP), according to research presented at the 2017 ASH Annual Meeting.
In the phase 3 HERCULES trial, researchers compared caplacizumab, an anti-von Willebrand factor nanobody, plus standard care (plasma exchange and immunosuppression) to placebo plus standard care in patients with aTTP.
Patients who received caplacizumab were significantly more likely to achieve platelet normalization and significantly less likely to experience aTTP-related death, aTTP recurrence, and major thromboembolic events.
Patients in the caplacizumab arm also required plasma exchange less frequently and spent less time in the hospital and intensive care unit (ICU).
Bleeding-related adverse events (AEs) were more common among patients who received caplacizumab than those who received placebo.
Marie Scully, MD, of the University College London Hospitals in London, UK, presented these results from HERCULES as a late-breaking abstract at the ASH Annual Meeting (abstract LBA-1). HERCULES was supported by Ablynx.
Patients and treatment
The study enrolled patients with an acute episode of aTTP. They were randomized to receive either caplacizumab (n=72) or placebo (n=73) in addition to standard care, which consisted of plasma exchange and immunosuppression.
Patients received a single intravenous bolus of 10 mg of caplacizumab or placebo followed by a daily subcutaneous dose of 10 mg of caplacizumab or placebo until 30 days after the last daily plasma exchange. If patients had a recurrence during the 30-day treatment period, they could go on to receive open-label caplacizumab.
If, at the end of the 30-day treatment period, there was evidence of persistent underlying disease activity indicative of an imminent risk for recurrence, caplacizumab or placebo could be extended for additional 7-day periods up to a maximum of 28 days. Patients were followed for a further 28 days after discontinuation of treatment.
In all, 71 patients received caplacizumab, and 58 (80.6%) of them completed the treatment. Seventy-three patients received placebo, and 50 of these patients (68.5%) completed treatment. Twenty-six patients in the placebo arm and 2 patients in the caplacizumab arm received open-label caplacizumab.
“If we look at the demographics, they’re relatively comparable to any data we normally see in patients with immune-mediated TTP,” Dr Scully said.
At baseline, the mean age was 44.9 in the caplacizumab arm and 47.3 in the placebo arm. Most patients in both arms were female—68.1% and 69.9%, respectively.
The proportion of patients with an initial aTTP episode was 66.7% in the caplacizumab arm and 46.6% in the placebo arm. The proportion with a recurrent episode was 33.3% and 53.4%, respectively.
Most patients in both arms had ADAMTS13 activity below 10% at baseline—81.7% in the caplacizumab arm and 90.3% in the placebo arm.
The mean platelet count at baseline was 32.0 x 109/L in the caplacizumab arm and 39.1 x 109/L in the placebo arm.
The study’s primary endpoint was the time to normalization of platelet count response, which was defined as initial platelet count of at least 150 x 109/L with subsequent stop of daily plasma exchange within 5 days.
There was a significant reduction in time to platelet count response in the caplacizumab arm compared to the placebo arm. The platelet normalization rate ratio was 1.55 (P<0.01).
“Patients were 55% more likely to achieve normalization of their platelet count at any time in the caplacizumab group, and this was highly significant,” Dr Scully said.
A secondary endpoint was the combination of aTTP-related death, aTTP recurrence, and at least 1 major thromboembolic event during study treatment. The incidence of this combined endpoint was 12.7% (n=9) in the caplacizumab arm and 49.3% (n=36) in the placebo arm (P<0.0001).
The incidence of aTTP-related death was 0% (n=0) in the caplacizumab arm and 4.1% (n=3) in the placebo arm. The incidence of aTTP recurrence was 4.2% (n=3) and 38.4% (n=28), respectively. And the incidence of at least 1 major thromboembolic event was 8.5% (n=6) and 8.2% (n=6), respectively.
The researchers also assessed aTTP recurrence during the overall study period, which occurred in 12.7% (n=9) of patients in the caplacizumab arm and 38.4% (n=28) in the placebo arm (P<0.001).
During the follow-up period, there were 6 relapses (9.1%) in the caplacizumab arm but none in the placebo arm.
“This tells us something about the pathophysiology of TTP and the role of caplacizumab,” Dr Scully said. “All of these patients, on stopping caplacizumab, had ADAMTS13 levels less than 5%. Therefore, it was important that their treatment was continued to ensure removal of antibody.”
According to the International TTP Working Group consensus definition, none of the patients in the caplacizumab arm and 7.0% (n=5) of patients in the placebo arm had refractory aTTP (P=0.018).
The mean number of days of plasma exchange during the overall treatment period was 5.8 days in the caplacizumab arm and 9.4 days in the placebo arm (a 38% relative reduction). The mean volume of plasma used was 21.3L and 35.9L, respectively (a 41% relative reduction).
The mean duration of hospital stay was 9.9 days in the caplacizumab arm and 14.4 days in the placebo arm (a 31% relative reduction).
For patients admitted to the ICU (28 in the caplacizumab arm and 27 in the placebo arm), the mean number of days in the ICU was 3.4 days in the caplacizumab arm and 9.7 days in the placebo arm (a 65% relative reduction).
“The safety profile [of caplacizumab] was comparable to previous results and in keeping with the mechanism of action,” Dr Scully said.
The proportion of patients with at least 1 treatment-emergent AE was 97.2% in the caplacizumab arm and 97.3% in the placebo arm.
The proportion of patients with at least 1 study-drug-related AE was 57.7% in the caplacizumab arm and 43.8% in the placebo arm. The rate of discontinuation due to at least 1 AE was 7.0% and 12.3%, respectively.
The incidence of bleeding-related AEs was higher in the caplacizumab arm (45.6%) than the placebo arm (23.3%).
Bleeding-related AEs (in the caplacizumab and placebo arms, respectively) included epistaxis (23.9% and 1.4%), gingival bleeding (11.3% and 0%), bruising (7.0% and 4.1%), hematuria (5.6% and 1.4%), vaginal hemorrhage (4.2% and 1.4%), menorrhagia (2.8% and 1.4%), catheter site hemorrhage (2.8% and 4.1%), injection site bruising (2.8% and 2.7%), hematochezia (2.8% and 0%), and hematoma (2.8% and 0%).
The proportion of patients with at least 1 serious AE was 39.4% (n=28) in the caplacizumab arm and 53.4% (n=39) in the placebo arm. The proportion of patients with at least 1 study-drug-related serious AE was 14.1% (n=10) and 5.5% (n=4), respectively.
During the treatment period, there were no deaths in the caplacizumab arm and 3 deaths in the placebo arm. There was 1 death in the caplacizumab arm during the follow-up period, but it was considered unrelated to caplacizumab.