INDIANAPOLIS – Eli Lilly and Company (NYSE: LLY) today announced updated clinical data from the international Phase 1/2 BRUIN trial of pirtobrutinib, a non-covalent (reversible) Bruton’s tyrosine kinase (BTK) inhibitor, in adult patients with a range of B-cell malignancies. These data, which were presented in oral and poster presentations at the 65th American Society of Hematology (ASH) Annual Meeting and Exposition, continue to support the role of pirtobrutinib in the treatment of chronic lymphocytic leukemia or small lymphocytic lymphoma (CLL/SLL) and mantle cell lymphoma (MCL).
“With longer follow-up, we continue to observe efficacy and tolerability data that support the potential utility of pirtobrutinib in CLL and B-cell lymphomas in the post-covalent BTK inhibitor setting,” said Matthew S. Davids, M.D., M.M.Sc., Dana-Farber Cancer Institute. “These data demonstrate the ability of pirtobrutinib to potentially lengthen the time patients may benefit from inhibiting BTK, a key target in these diseases. It is also encouraging to see the promising initial data for pirtobrutinib combined with venetoclax, which has the possibility to allow for a time-limited regimen for patients with CLL.”
“Following the two FDA accelerated approvals for pirtobrutinib in 2023, we are excited to present these data at ASH, further building the body of evidence for this medicine in CLL, SLL, MCL, and other B-cell malignancies,” said David Hyman, M.D., chief medical officer, Lilly. “These data support the potential role that pirtobrutinib, the first and only FDA-approved non-covalent BTK inhibitor, can play in extending the time patients may benefit from BTK inhibition therapy and provide additional efficacy data in patients previously treated with a covalent BTK inhibitor.
We look forward to expanding our understanding of the broader potential clinical utility of pirtobrutinib as we continue to progress our series of randomized Phase 3 studies in CLL, SLL, and MCL.”The labeling for pirtobrutinib contains warnings and precautions for infections, hemorrhage, cytopenias, cardiac arrhythmias, second primary malignancies, and embryo-fetal toxicity.
Data from the BRUIN Phase 1/2 Study
The BRUIN Phase 1/2 clinical trial is evaluating pirtobrutinib in patients previously treated for MCL, CLL/SLL, or other non-Hodgkin lymphomas (NHL). The efficacy data presented at ASH for CLL/SLL and MCL are based on independent review committee (IRC) assessment. All presentations of safety and efficacy data from the BRUIN Phase 1/2 trial utilized a cutoff date of May 5, 2023.
Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma
An oral presentation (Abstract #325) detailed updated, long-term follow-up data in patients with CLL/SLL. This data set consisted of 282 patients who had received a prior BTK inhibitor. Patients had received a median of four prior lines of therapy (range: 1-11). Efficacy results showed an overall response rate (ORR), including partial response with lymphocytosis (PR-L), of 81.6% (95% CI: 76.5, 85.9) for patients treated with pirtobrutinib. Response rates were consistent across all subgroups analyzed regardless of previous therapies, age, or mutation status. With a median follow-up of 27.5 months, median progression-free survival (PFS) was 19.4 months (95% CI: 16.6, 22.1). With a median follow-up of 29.3 months, median overall survival (OS) was not estimable.
In patients treated with both a prior covalent BTK inhibitor and BCL-2 inhibitor (n=128, median of five prior lines of therapy, range: 1-11), pirtobrutinib demonstrated an ORR, including PR-L, of 79.7% (95% CI: 71.7, 86.3). With a median follow-up of 22.2 months, median PFS was 15.9 months (95% CI: 13.6, 17.5). With a median follow-up of 27.4 months, the median OS was not estimable.
In BCL-2-naïve patients (n=154, median of three prior lines of therapy, range: 1-9), pirtobrutinib demonstrated an ORR, including PR-L, of 83.1% (95% CI: 76.2, 88.7). With a median follow-up of 27.6 months, median PFS was 23.0 months (95% CI: 19.6, 28.4). With a median follow-up of 31.6 months, the median OS was not estimable.
In the CLL/SLL safety cohort (n=282), the most frequent treatment-emergent adverse events (TEAEs) were fatigue (36.9%), neutropenia (34.4%), diarrhea (28.4%), cough (27.3%), and contusion (26.2%).
A second oral presentation (Abstract #326) detailed updated analyses of genomic evolution and resistance during pirtobrutinib therapy in patients with relapsed covalent BTK inhibitor pre-treated CLL who subsequently developed disease progression on pirtobrutinib monotherapy (n=88). These data showed that although many patients harbored BTK mutations (C481 and non-C481) prior to initiation of pirtobrutinib therapy, these baseline genomic features did not predict response to pirtobrutinib. Moreover, while many patients acquired mutations at progression (68%), fewer than half were in the BTK gene.
A poster presentation (Abstract #3269) detailed updated data from the Phase 1b portion of the BRUIN trial, which investigated pirtobrutinib in combination with venetoclax with or without rituximab as a two-year fixed-duration therapy. This data set consisted of 25 patients, 17 of whom had received a prior BTK inhibitor. Patients were enrolled into sequential cohorts, first in the pirtobrutinib plus venetoclax (PV) cohort (n=15) and then the PV plus rituximab (PVR) cohort (n=10). Efficacy results showed an ORR of 96% (95% CI: 79.6, 99.9), with 40% complete responses (PV, n=7; PVR, n=3) and 56% partial responses (PV, n=7; PVR, n=7) across the two arms. Undetectable minimal residual disease (uMRD) was achieved by 87.5% of patients (PV, n=12; PVR, n=9) at some time during the trial. Across the two arms, the PFS rate at 24 months was 79.5% (95% CI: 52.0, 92.3).
The primary endpoint was safety as assessed by TEAEs graded according to the Common Terminology Criteria for Adverse Events (CTCAE) v5.0. The safety profiles were generally similar among both combination treatment groups, and no dose limiting toxicities were observed. In the PV cohort, the most frequent treatment-related AEs were neutropenia (46.7%), nausea (46.7%), fatigue (33.3%), diarrhea (26.7%), and decreased platelet count (26.7%). In the PVR cohort, the most frequent treatment-related AEs were neutropenia (70.0%), diarrhea (60.0%), nausea (40.0%), infusion-related reactions (40.0%), and chills (30.0%). There were no apparent drug interactions between pirtobrutinib and venetoclax. These efficacy and safety data support the ongoing BRUIN CLL-322 Phase 3 trial evaluating two years of pirtobrutinib plus venetoclax and rituximab versus two years of venetoclax plus rituximab in previously treated CLL/SLL.
Mantle Cell Lymphoma
An oral presentation (Abstract #981) detailed updated efficacy results, including in high-risk subgroups. This data set consisted of 152 patients who had received a prior covalent BTK inhibitor. Patients had received a median of three prior lines of therapy (range: 1-9). Efficacy results showed an ORR of 49.3% (95% CI: 41.1, 57.6), including 15.8% complete responses (n=24) and 33.6% partial responses (n=51) for patients treated with pirtobrutinib. At a median follow-up of 14.7 months, the median duration of response (DOR) was 21.6 months (95% CI: 9.2, 27.2). Median PFS and OS were 5.6 months (95% CI: 5.3, 9.2) and 23.5 months (95% CI: 17.1, not estimable), respectively. Response rates were consistent across subgroups regardless of prior treatment or high-risk molecular features.
In the MCL safety cohort (n=166), the most frequent TEAEs were fatigue (31.9%), diarrhea (22.3%), and dyspnea (17.5%). Additionally, Lilly presented posters highlighting pirtobrutinib in relapsed or refractory follicular lymphoma (FL), relapsed or refractory marginal zone lymphoma (MZL), and Richter transformation (RT). Loxo@Lilly is studying pirtobrutinib in multiple Phase 3 studies. Details on the trials can be found by visiting clinicaltrials.gov.