Abstract 2167: Efficacy assessment of BTK inhibitor ibrutinib in de novo and viral-induced B cell lymphoma

Bruton9s tyrosine kinase (BTK) is crucial for B cell maturation. Its activation has also been considered as a major oncogenic driver for various B cell-derived lymphoid cancers. A BTK inhibitor, Ibrutinib, has been approved for mantle cell lymphoma, chronic lymphocytic leukemia, and Waldenstrom9s macroglobulinemia, a form of non-Hodgkin9s lymphoma (NHL). Ibrutinib has also shown encouraging efficacies in defuse large B cell lymphoma (DLBCL), specifically in activated B cell-like (ABC) subtype, but not in germinal center B cell-like (GCB) subtype. We have established a series of patient derived xenograft (PDX) models, recapitulating diverse genotypes of de novo DLBCL patients, including two MYD88 L265P /CD79B Y197N double mutants (LY2298, LY2264), one MYD88 L265P single mutant (LY0257), and a variety of wild-types (LY2214, LY3604, and LY6934, etc.). This cohort of PDX models serve as perfect preclinical tools to investigate Ibrutinib responses in different genotypes. Our studies demonstrated a moderate to robust efficacies of Ibrutinib in the MYD88/CD79B double mutants, suggesting that CD79B mutation is the predictive biomarker for chronic activation of B cell receptor (BCR) signaling, as well as generally good responses to BTK inhibitor. Interestingly, the MYD88 single mutant model LY0257, where the disease is likely driven by constitutive activation of MYD88 signaling, also showed response to Ibrutinib when dosed in drinking water. In the wild type PDXs, two of seven models tested so far are either partially responsive or sensitive to Ibrutinib, while the others are resistant to the treatment. It seems that Ibrutinib response does not always require CD79B mutation, and BCR pathway addiction may occur by other means in DLBCL, even when MYD88 signaling is constitutively active. Notably, all 5 wild type DLBCL PDXs that are non-responsive to Ibrutinib are EBV positive verified by RNAseq. These EBV-transformed B lymphoma PDX models, which share the similar histopathology as de novo DLBCL, but have distinct molecular pathology signatures and different pathogenesis. In efficacy studies, none of the transformed B lymphoma PDXs showed response to Ibrutinib. Taken together, our DLBCL and EBV-induced lymphoma PDX models provide a valuable preclinical platform for evaluating BTK inhibitors, as well as future drug discovery efforts on other targets in the BCR and MYD88 pathways, such as PI3K, SYK, and IRAK4. Citation Format: Jessie Jingjing Wang, Meiling Zheng, Xuesong Huang, Yanrui Song, Wubin Qian, Likun Zhang, Jie Cai, Sheng Guo, Henry Qixiang Li, Davy Xuesong Ouyang. Efficacy assessment of BTK inhibitor ibrutinib in de novo and viral-induced B cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2167.