Abstract 380: BaF3-BTK engineering cell lines as a useful platform for novel BTK inhibitor discovery

Abstract

Abstract Introduction: Bruton's tyrosine Kinase (Btk) plays an essential role in BCR signaling and has been a hot new target in molecular targeted therapy in the past few years, led by the clinical success of ibrutinib and acalabrutinib, two first approved BTK inhibitors, that greatly improved the outcome of patients with relapsed chronic lymphocytic leukemia (CLL). Currently, there are 5 approved BTK inhibitors including additionally zanubrutinib, orelabrutinib and velexbru. Up to 24 BTK inhibitors are under active clinical evaluation as antineoplastic drugs against chronic lymphocytic leukemia (CLL), small lymphocytic lymphoma (SLL), B-cell malignancies and mantle cell lymphoma (MCL) in different countries. However, the acquired resistance due to the C481S mutation in BTK remains an essential challenge to improve the poor prognosis of the patient. Subsequently, several next-generation BTK inhibitors are under clinical evaluation targeting the BTK-C481S mutation, such as LOXO-305, a highly selective and non-covalent BTK inhibitor which potently inhibits the cellular activity of BTK C481S/T/R mutations. Methods: Our group has generated 9 Ba/F3-BTK engineering cell lines as useful cell line and xenograft models for novel BTK inhibitor discovery and development. They harbor wild type BTK or ibrutinib resistance BTK mutations such as the C481S and C481S-double mutations, and the T474M/I mutations. Moreover, we generated Ba/F3-ETV6-BTK-F517L and Ba/F3-ETV6-BTK-C481S-F517L cell lines using a dose-escalation method after treating cells with a mutagenic agent. The BTK-F517L mutation is highly resistant to both ibrutinib and LOXO-305 treatment. Crystal structure analysis and 3D modeling revealed that the F517L mutation may affect the conformation of the BTK binding pocket to ibrutinib, indicating novel BTK inhibitors may be needed to overcome this resistance mutation. Conclusion: The Ba/F3-BTK engineering cell lines can be a useful tool to develop and evaluate next-generation BTK inhibitors and to explore new acquired resistance BTK mutations. Citation Format: Guoqian Wang, Hongling Chen, Yu Wang, Jingxiao Xu, Lin Zhou, Yao Tang, Jinying Ning, Feng Hao. BaF3-BTK engineering cell lines as a useful platform for novel BTK inhibitor discovery [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 380.