Novel Bruton's Tyrosine Kinase Inhibitor Bgb-3111 Demonstrates Potent Activity in Mantle Cell Lymphoma

Background:

Aberrant B-cell receptor signaling is an important contributor to lymphomagenesis in mantle cell lymphoma (MCL). Bruton's Tyrosine Kinase (BTK), a component of the BCR signaling axis, has been validated as a clinically relevant target, and BTK inhibitor ibrutinib received FDA approval for treatment of MCL in 2013. Growing concerns that single agent ibrutinib exerts off-target effects that interfere with other treatments such as rituximab-induced antibody-dependent cell cytotoxicity limit its utility in combination treatments. In this study, we assessed the in vitro and in vivo effects of BGB-3111in MCL models.

Methods:

We performed cell viability assays with BGB-3111 treated MCL cell lines to determine inhibition of cellular proliferation. The same assays were conducted on primary human MCL cells and patient-derived xenograft (PDX) tumor samples. Dose-dependent inhibition of BTK auto-phosphorylation and inhibition of downstream targets such as PLC-γ were determined by phospho-protein immunoblotting and immunoprecipitation. A reverse-phase protein assay (RPPA) was conducted on BGB-3111-treated Mino cells to evaluate changes in MCL oncogenic signaling. Induction of apoptosis in MCL cells treated with increasing doses of BGB-3111 was quantified using flow cytometry. For in vivo experiments, an ibrutinib-sensitive MCL PDX mouse model was treated with 50 mg/kg/day BGB-3111 and monitored for mean tumor burden and survival.

Results:

BGB-3111 potently inhibited cell viability in a panel of MCL cell lines, with an activity range of 1-10 uM, and induced apoptosis in a dose-dependent manner in several MCL cell lines.BGB-3111 treatment of MCL cells demonstrated a dose-dependent decrease in p-BTK (Y223) and inhibition of downstream effectors without impacting total protein levels, while RPPA revealed upregulation of the PI3K-Akt signaling axes. In addition, BGB-3111 treatment did not impact phosphorylation of off-target kinases affected by ibrutinib treatment. In vivo, BGB-3111 suppressed tumor growth and prolonged tumor survival in BGB-3111 treated mice.

Conclusion:

The second generation BTK inhibitor BGB-3111 demonstrates selectivity for BTK in vitro and BTK inhibition in vivo. BGB-3111-treated PDX mouse models examining survival, tumor growth, and other factors point to BGB-3111 as an effective single agent BGB-3111 is being investigated in Phase I clinical trials.