The US Food and Drug Administration (FDA) has granted the bispecific antibody blinatumomab breakthrough designation for the treatment of adults with relapsed or refractory B-precursor acute lymphoblastic leukemia (B-ALL).
The decision was based on promising results of a phase 2 trial, which were presented at the 50th Annual Meeting of the American Society of Clinical Oncology (ASCO) and the 19th Congress of the European Hematology Association (EHA).
According to the FDA, breakthrough designation is intended to expedite the development and review of drugs for serious or life-threatening conditions.
For a treatment to receive this designation, there must be preliminary clinical evidence suggesting the drug may offer substantial improvement over currently available therapy on at least one clinically significant endpoint.
Trial results
Nicola Gökbuget, MD, of Goethe University in Frankfurt, Germany, and Max Topp, MD, of the University of Wuerzberg in Germany, presented phase 2 results with blinatumomab at the EHA Congress as abstracts S1314 and S722. The trial was sponsored by Amgen, the company developing blinatumomab.
“Blinatumomab is a bispecific antibody which has two parts,” Dr Gökbuget noted. “With one part—the CD3 part—it attracts T cells, and with the other part, it binds to CD19. And CD19 is a target available on the vast majority of B-precursor ALL blast cells.”
To test this mechanism, Dr Gökbuget and her colleagues evaluated blinatumomab monotherapy in 189 patients with relapsed or refractory B-ALL and a median age of 39 (range, 18-79).
The patients received blinatumomab by continuous intravenous infusion—4 weeks on and 2 weeks off—for up to 5 cycles.
Safety
Dr Gökbuget noted that major toxicities were related to cytokine release syndrome—for example, fever and headache—but cytopenias were also common.
“Another side effect observed with this compound—and this is something seen often with other T-cell therapies—was [central nervous system] events,” she added.
The most frequent adverse events (AEs) were pyrexia (59%), headache (35%) and febrile neutropenia (29%). The most frequent grade 3 or higher AEs were febrile neutropenia (26%), anemia (15%), and neutropenia (15%). Two percent of patients had grade 3 or higher cytokine release syndrome.
The most common grade 3 or higher nervous system AEs were headache (4%), encephalopathy (3%), and ataxia (2%). Three patients (2%) had grade 5 AEs considered treatment-related—2 with sepsis and 1 with Candida infection.
Efficacy
The study’s primary endpoint was complete remission (CR) or CR with partial hematologic recovery (CRh) within the first 2 cycles.
An exploratory endpoint was minimal residual disease (MRD) response (<10-4) within the first 2 cycles. If a patient was MRD-negative, he was classified as having a complete MRD response.
In all, 43% (81/189) of patients achieved a CR/CRh within 2 cycles of therapy. Thirty-three percent (63/189) achieved a CR, and 9% (18/189) achieved a CRh.
Eighty-two percent (60/73) of patients with a CR/CRh who were evaluable for an MRD assessment achieved an MRD response. This included 86% (50/58) of CR patients and 67% (10/15) of CRh patients. Seventy-one percent (51/73) of patients with CR/CRh had a complete MRD response.
The median relapse-free survival was 5.9 months.
“So to conclude, we have observed considerable antileukemic activity for this single-drug therapy,” Dr Gökbuget said. “We have to keep in mind this is a single drug, and, usually, these patients receive many different chemotherapy compounds.”
“Also, although these patients were poorly selected, this is, so far, the largest trial in adult ALL where standardized PCR-based MRD detection was tested in the relapsed setting. So these data will be very important.”
