Rare Disease Report

Promising Results from Phase 3 aTTP Clinical Trial

OCTOBER 02, 2017
James Radke
This morning, European-based company Ablynx announced their Phase 3 clinical trial testing caplacizumab in patients with acquired thrombotic thrombocytopenic purpura (aTTP) met its primary and secondary endpoints.

aTTP is a rare, life-threatening, autoimmune bleeding disorder that leads to severe thrombocytopenia as well as blood clots in smaller blood vessels. If not treated properly, ischemia and widespread organ damage can occur. In most cases, plasmapheresis is the treatment of choice but it is not effective in all patients and aTTP still has a mortality rate of 20%.

Caplacizumab is an anti-von Willebrand factor antibody designed to block platelet aggregation.

The Phase 3 study, known as the HERCULES study recruited 145 patients with aTTP that were randomized to receive either caplacizumab (10 mg daily) or placebo in addition to standard-of-care treatment (i.e. daily plasmapheresis and immunosuppression).

Patients receiving caplacizumab showed a statistically significant reduction in time to platelet count response compared to placebo (P < .01).

Image courtesy Ablynx investor call held October 2, 2017.

Several secondary endpoints were also met. Treatment with caplacizumab had a 74% reduction in the percentage of patients with aTTP-related death, recurrence of aTTP, or at least 1 major thromboembolic event during study drug treatment (P <.0001).  Further, recurrence of aTTP was 67% lower in the caplacizumab-treated group compared to the placebo –treated group (P <.001).

With regard to safety, there were 3 deaths in the placebo-treated group and none in the caplacizumab-treated group during the study. After the study, 1 person from the caplacizumab-treated group died but it was not related to the drug. Most bleeding-related adverse events were mild or moderate in severity.

In a news release, Robert K. Zeldin, M.D, Chief Medical Officer at Ablynx, said, "Patients with aTTP are at risk for significant morbidity and early death. We believe these positive Phase III study results confirm the potential for caplacizumab to address the high unmet medical need in the treatment of aTTP and to have a meaningful impact on the lives of affected patients. We continue to analyze the data and look forward to sharing the results with regulatory authorities and the scientific community."

Marie Scully, M.D., of the University College Hospital in London and lead investigator in the HERCULES study said, "The results of this landmark trial constitute a complete game changer for patients with aTTP. They will revolutionize how we manage the acute phase of the disease, which is when patients are at highest risk for organ damage, recurrence and death."

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