Abstract 5619: An oral BTK degrader TGRX-3911 overcomes resistance conferred by kinase-proficient and kinase-impaired mutations
Authors: Yanxia Shi, Linxin Li, Fengli He, Li Hu, Xiangyu Hong, Tingting Yan, Shuzhen Jiang, Yingying Zuo, Haoran Tang, Yuanpeng Shen, Huanyin Li, Yixin Ai, Yihan Wang
Journal: Cancer Research (2025)

Abstract As a key component of the B-cell receptor (BCR) signaling complex, Bruton’s tyrosine kinase (BTK) plays an essential role in B-cell malignancies via both kinase and non-kinase functions. This was revealed by early genetic studies and the emerging kinase-impaired mutations, which activate BCR signaling via intricate protein-protein interactions, conferring resistance to a range of covalent or non-covalent BTK inhibitors (BTKi). Therefore, a new targeting strategy is urgently needed for patients who acquired kinase-impaired mutations of BTK. Targeted protein degradation is a potential and powerful means to modulate the non-catalytic functions. TGRX-3911 is a heterobifunctional molecule that promotes ubiquitination and proteasomal degradation of BTK. In a diffuse large B cell lymphoma (DLBCL) cell line TMD8 featuring chronic active BCR signaling, TGRX-3911 induced rapid (4h) and potent degradation of wildtype (WT) and knock-in mutant BTK proteins including the kinase-proficient C481S and T474I, the kinase-impaired L528W and V416L, and even the compound mutants C481S/T474I, C481S/L528W and T474I/L528W, with DC50 &amp;lt; 1 nM and near 100% Dmax. Functionally, in Ramos cells expressing WT or knock-in C481S, T474I, V416L or L528W mutant BTK, TGRX-3911 diminished anti-IgM induced phosphorylation of BTK (excluding V416L and L528W) and PLCγ2, and strongly blocked Ca2+ flux. TGRX-3911 also reduced surface CD86 expression in TMD8 cells, as well as in C481S, T474I, V416L and T474I/C481S mutant cells. These results confirm that degradation of BTK induced by TGRX-3911 abolishes the BCR signaling pathway. TGRX-3911 potently inhibited proliferation of TMD8 parental cells and those harboring knock-in BTK mutations that are resistant to currently approved ibrutinib, zanubrutinib and/or pirtobrutinib, including C481S, T474I, L528W, V416L, A428D, T474I/C481S, T474I/L528W and C481S/L528W (IC50 from 0.4 to 9.9 nM). Remarkably, TGRX-3911 potently inhibited the A428D mutant which is still resistant to current BTK degraders, NX-5948, BGB-16673 and ABBV-101. It also demonstrated higher potency against the T474I/L528W compound mutant. In vivo, oral dosing of TGRX-3911 led to tumor shrinkage in a mantle cell lymphoma (MCL) REC-1 xenograft model expressing BTK-C481S, and the effect was superior to pirtobrutinib. No sign of toxicity was observed. In summary, TGRX-3911 has potent and robust degradation activity and effectively suppresses the BCR signaling pathway. It has potent anti-proliferation activity against kinase-proficient, -impaired and even compound mutants of BTK, and has in vivo anti-tumor activity. By eliminating both the catalytic and scaffold functions of BTK, TGRX-3911 has the potential to overcome clinical resistance which can hardly be achieved by conventional BTKi. The potential clinical application of TGRX-3911 for patients with B-cell malignancies is worth exploring. Citation Format: Yanxia Shi, Linxin Li, Fengli He, Li Hu, Xiangyu Hong, Tingting Yan, Shuzhen Jiang, Yingying Zuo, Haoran Tang, Yuanpeng Shen, Huanyin Li, Yixin Ai, Yihan Wang. An oral BTK degrader TGRX-3911 overcomes resistance conferred by kinase-proficient and kinase-impaired mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5619.