The Bruton tyrosine kinase (BTK) inhibitor zanubrutinib appears safe and effective for patients with B-cell malignancies, according to results from a phase 1 trial.
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Among patients with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL), the overall response rate was 96.2%, reported Constantine Si Lun Tam, MD, of Peter MacCallum Cancer Centre in Melbourne and colleagues.
“Zanubrutinib (BGB-3111) is a highly specific next-generation BTK inhibitor with favorable oral bioavailability, as shown in preclinical studies,” the investigators wrote in Blood. “Compared with ibrutinib, zanubrutinib has shown greater selectivity for BTK and fewer off-target effects in multiple in vitro enzymatic and cell-based assays.”
The current, open-label trial involved 144 patients with B-cell malignancies. To determine optimal dosing, the investigators recruited 17 patients with relapsed/refractory B-cell malignancies who had received at least one prior therapy. The dose expansion part of the study assessed responses in multiple cohorts, including patients with CLL/SLL, mantle cell lymphoma, and Waldenström macroglobulinemia. The primary endpoints were safety and tolerability, including maximum tolerated dose. Efficacy findings were also reported.
During dose escalation, no dose-limiting toxicities were observed, so the highest dose – 320 mg once daily or 160 mg twice daily – was selected for further testing.
The investigators highlighted efficacy and safety findings from 94 patients with CLL/SLL who were involved in dose expansion. Although nearly one-quarter (23.4%) were treatment-naive, the median number of prior therapies was two, and some patients had high-risk features, such as adverse cytogenetics, including 19.1% with a TP53 mutation and 23.3% with a 17p deletion. After a median follow-up of 13.7 months, 94.7% of these patients were still undergoing treatment.
Out of the initial 94 patients with CLL/SLL, 78 were evaluable for efficacy. The overall response rate was 96.2%, including two (2.6%) complete responses, 63 (80.8%) partial responses, and 10 (12.8%) partial responses with lymphocytosis. The median progression-free survival had not been reached, and the 12-month estimated progression-free survival was 100%.
In regard to safety, the most common adverse events were contusion (35.1%), upper respiratory tract infection (33.0%), cough (25.5%), diarrhea (21.3%), fatigue (19.1%), back pain (14.9%), hematuria (14.9%), headache (13.8%), nausea (13.8%), rash (12.8%), arthralgia (11.7%), muscle spasms (11.7%), and urinary tract infection (10.6%).
A number of other adverse events were reported, although these occurred in less than 10% of patients.
More than one-third of patients (36.2%) experienced grade 3 or higher adverse events, with neutropenia being most common (6.4%), followed by pneumonia , hypertension, and anemia, which each occurred in 2.1% of patients, and less commonly, back pain, nausea, urinary tract infection, purpura, cellulitis, and squamous cell carcinoma of the skin, which each occurred in 1.1% of patients.
“In this first-in-human study, zanubrutinib demonstrated encouraging activity in patients with relapsed/refractory and treatment-naive CLL/SLL, with good tolerability,” the investigators concluded. “Two ongoing randomized studies of zanubrutinib versus ibrutinib (NCT03053440 and NCT03734016) aim to determine whether consistent, continuous BTK blockade with a selective inhibitor results in fewer off-target effects and translates into improvements in disease control.”
The study was funded by BeiGene USA, which is developing the drug. The investigators reported relationships with the study sponsor, as well as Janssen, Pharmacyclics, AbbVie, and others.
SOURCE: Tam CSL et al. Blood. 2019 Jul 24. doi: 10.1182/blood.2019001160.