Takeda may have pruned back the potential indications for mezagitamab, but the latest raft of phase 2 data suggests the anti-CD38 antibody could still “transform treatment” of primary immune thrombocytopenia (ITP).
Last month, the Japanese pharma deprioritized the development of mezagitamab, also known as TAK-079, in myasthenia gravis and systemic lupus erythematosus as part of a wider pipeline shake-up. But the team said at the time that it was still planning to continue to clinically evaluate the antibody in ITP.
At the International Society on Thrombosis and Haemostasis Congress on June 22, Takeda unveiled late-breaking data from a 41-patient phase 2b trial assessing three doses of mezagitamab for the immune-mediated bleeding disorder. The trial’s primary endpoint was the percentage of patients with at least one grade 3 or higher treatment-emergent adverse event (TEAE), serious adverse event (SAE) and adverse events (AEs) leading to discontinuation of treatment.
The company reported that the antibody had a favorable safety profile with no new safety signals discovered.
The rate of TEAEs leading to discontinuation was 14.3% across the three dose cohorts compared to 0% for the placebo group, Takeda said. The number of TEAEs at grade 3 or above was lower, at 17.9%, in the mezagitamab cohorts compared to 23.1% in the placebo cohort while 14.3% of the mezagitamab patients experienced a SAE compared to 7.7% on placebo.
ITP involves the accelerated destruction of platelets in blood, resulting in a decreased platelet count and an increase of bleeding that can be debilitating. All three doses of mezagitamab were shown to improve platelet response compared to placebo, with “rapid and sustained increases in platelet counts” above the 50,000/μL therapeutic threshold that persisted for eight weeks after the eight-week course of weekly doses.
This illustrated “the rapid and post-therapy effects of mezagitamab on platelet response,” Takeda said.
When assessing various measures of platelet response, the company noted that these were all highest in patients who received the highest, 600 mg, dose of mezagitamab. Takeda highlighted an 81.8% complete platelet response, a 90.9% clinically meaningful platelet response and a 100% hemostatic platelet response among these patients.
Novartis’ Promacta, Amgen’s Nplate and Sobi’s Doptelet are all approved for ITP. Argenx had been aiming Vyvgart at the condition but the FcRn drug flunked primary and secondary endpoints in a phase 3 study in November 2023.
Around 20% of patients with ITP don’t achieve a platelet count above 50,000/uL despite receiving the available first- and second-line treatments, Takeda explained in the release. This means that maintaining a platelet count of 50,000/uL or more for a sustained period has become the precedent for getting a new drug approved in the indication.
“Despite treatment with currently available therapies, there is still a significant disease burden and need for a disease-modifying treatment that people living with ITP can tolerate,” David Kuter, M.D., who presented the findings at the congress, said in an accompanying press release.