Dual B-cell receptor pathway blockade was tolerable and efficacious for patients with relapsed or refractory chronic lymphocytic leukemia (CLL) or mantle cell lymphoma (MCL) who participated in a multicenter phase 1-1b clinical study that added umbralisib to ibrutinib.
Dr. Matthew S. Davids
The study “is the first successful combination for two drugs targeting the B-cell receptor pathway,” Matthew S. Davids, MD, of the Dana-Farber Cancer Institute in Boston and his colleagues wrote in the Lancet Haematology.
Of the 21 patients with CLL, 90% (n = 19) achieved an overall response (OR), 62% (n = 13) achieved partial response (PR) or PR with lymphocytosis, and 29% (n = 6) achieved complete response (CR). All patients in complete response still had minimal residual disease (MRD) in bone marrow. No CLL patients had progressive disease.
Of the 21 patients with MCL, 67% (n = 14) had an OR, with 19% (n = 4) showing CR and 48% (n = 10) achieving partial response. Three MCL patients (14%) had progressive disease.
Umbralisib is a next-generation phosphoinositide-3-kinase-delta inhibitor that, when added to the Bruton tyrosine kinase inhibitor (BTKi) ibrutinib, offers once-daily oral dosing. The combination affords the possibility of overcoming the resistance that can come with prolonged ibrutinib monotherapy.
A total of 44 patients were enrolled, and 42 patients (21 with CLL and 21 with MCL) received at least one dose of the study drug and were included in the analysis. At enrollment, patients had received a median of two previous therapies.
Diarrhea was the most frequent adverse event, seen in 22 patients (52%), and half of all patients (n = 21) had infections.
Hematologic toxicities included neutropenia, seen in 9 (43%) of the CLL patients and 8 (38%) of the MCL patients; thrombocytopenia, seen in 6 (29%) of the CLL patients and 10 (48%) of the MCL patients; and anemia, seen in 4 (19%) of the CLL and 9 (43%) of the MCL patients. Grade 3 and 4 hematologic toxicities of any type were less common, occurring in less than 20% of patients. One MCL patient developed febrile neutropenia. According to the study investigators, none of the hematologic toxicities were deemed related to the study drugs.
Adverse events did not appear to be dose-dependent for umbralisib, with the maximum tolerated dose not reached in the study, the investigators wrote. For phase 2 trials, the recommended dose of umbralisib is 800 mg given orally once daily in combination with ibrutinib.
“One unanticipated benefit of doublet B-cell receptor pathway inhibition in this study was the ability to continue one drug when a characteristic toxicity required the other drug to be held,” the investigators wrote.
For MCL patients, 67% achieved OR and 19% achieved CR, figures similar to those reported for ibrutinib monotherapy. However, “the 2-year progression-free survival of 49% and overall survival of 58% suggest that patients who made it to 1 year progression-free had few events during the second year on therapy,” the investigators wrote. They also noted that this MCL population was high risk; more than one-quarter of patients had relapsed after prior autologous stem cell transplantation.
The study was limited by small sample size and a short duration of follow-up, so durability of response can’t yet be assessed. Also, neither pharmacokinetics nor resistance mutations were tracked for participants.
Currently, the doublet regimen is designed to be continuous therapy, and although it’s not known whether this regimen would be effective as time-limited therapy, it’s unlikely because 100% of patients who had CR still had detectable minimal residual disease, the investigators noted.
Umbralisib and ibrutinib are also being explored as part of triplet therapy, with the type 2 CD20 antibody ublituximab, for relapsed or refractory B-cell malignancies (NCT02006485).
“These novel drug-based approaches, along with several others in development, hold promise as highly effective and well-tolerated regimens with the potential to substantially improve outcomes for patients with B-cell malignancies,” the investigators wrote.
The study was supported by TG Therapeutics and the Leukemia and Lymphoma Society Therapy Accelerator Program. The authors reported financial relationships with several pharmaceutical companies, including TG Therapeutics.
SOURCE: Davids MS et al. Lancet Haemtol. 2019;6:e38-47.