Abstract 3976: Recurrent BCL10 mutations drive BTK inhibitor resistance in BN2-subtype diffuse large B-cell lymphomas by constitutively activating NF-kB and the MALT1 protease
Authors: Coughlin Caroline A. , Kumar Preet , Roberts Evan R. , Lopez Horacio Gonzalez , Lekakis Marianna , Li Lingxio , Bilbao Daniel , Schatz Jonathan H. 
Published: June 2022

Abstract
Diffuse large B cell lymphoma (DLBCL), the most common lymphoma diagnosis, is a heterogeneous group of sub-entities with differing biology and prognosis. Frontline R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone), used regardless of subtype, cures 60-70%. Patients failed by this combination have poor prognosis. Extensive efforts to improve on R-CHOP in the frontline have failed, but recent post-hoc analysis of one negative trial suggested younger patients with specific DLBCL biologic subtypes may benefit from addition of a Bruton’s Tyrosine Kinase inhibitor (BTKi). These results could inform prospective studies in a small subset of DLBCL cases, but the rest lack biomarker-driven frontline optimizations. Newer classification systems define the BN2 (LymphGen) or Cluster 1 (Chapuy consensus clusters) subtype, characterized by BCL6 translocations and/or NOTCH2 truncations. BN2 cases specifically saw no benefit from adding BTKi to R-CHOP regardless of patient age. BCL10, encoding a key protein promoting NF-kB activation through formation of a signaling complex with CARD11 and MALT1, is recurrently mutated in DLBCL (~5%), clustering strongly in BN2 (30-40%). We hypothesize that activation of NF-kB downstream of BTK due to BCL10 gain of function promotes BTKi resistant lymphomagenesis. Recurrent BCL10 mutations include the R58Q missense mutation in the oncogenic N-terminal CARD domain and frequent truncations of the regulatory C-terminal S/T-rich domain. Overexpression of BCL10 with either mutation type in DLBCL cells promoted strong activation of NF-kB assessed by immunoblotting and EGFP NF-kB reporters. Truncated BCL10 also increased MALT1 protease activity, measured by increased substrate cleavage. BCL10 mutations drove resistance to BTKis as hypothesized, but there was no difference in sensitivity to MALT1 inhibition, revealing that downstream targets overcome drug resistance by BCL10 mutant-mediated activation. Combining MALT1i with BTKi synergistically killed cells, identifying a promising therapeutic strategy for BN2 cases. Delving into the mechanism of BCL10-mutant lymphomagenesis, gene ontology analysis of transcriptome data showed cross-activation of ERK1/2 signaling, confirmed by immunoblotting, and strong induction of cytokine production and related signaling. To fuel future studies, we have established a cre-inducible conditional BCL10-truncation mouse model at the ROSA26 locus in C57BL/6J mice. After crossing into the Mb1-Cre background, these animals showed expansion of the B-cell compartment by three months of age and remain under observation for onset of lymphoma. We therefore define mechanisms and therapeutic consequences of recurrent BCL10 mutations in DLBCL and provide new drug combinations aimed at overcoming them.
Citation Format: Caroline A. Coughlin, Preet Kumar, Evan R. Roberts, Horacio Gonzalez Lopez, Marianna Lekakis, Lingxio Li, Daniel Bilbao, Jonathan H. Schatz. Recurrent BCL10 mutations drive BTK inhibitor resistance in BN2-subtype diffuse large B-cell lymphomas by constitutively activating NF-kB and the MALT1 protease [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3976.