Abstract:
Background and Purpose
Bruton's tyrosine kinase (BTK) plays a key role in B‐cell receptor signalling by regulating cell proliferation and survival in various B‐cell malignancies. Covalent low‐MW BTK kinase inhibitors have shown impressive clinical efficacy in B‐cell malignancies. However, the mutant Btk C481S poses a major challenge in the management of B‐cell malignancies by disrupting the formation of the covalent bond between BTK and irreversible inhibitors, such as ibrutinib. The present studies were designed to develop novel BTK inhibitors targeting ibrutinib‐resistant Btk C481S mutation.

Experimental Approach
BTK‐Ba/F3, BTK(C481S)‐Ba/F3 cells, and human malignant B‐cells JeKo‐1, Ramos, and NALM‐6 were used to evaluate cellular potency of BTK inhibitors. The in vitro pharmacological efficacy and compound selectivity were assayed via cell viability, colony formation, and BTK‐mediated signalling. A tumour xenograft model with BTK‐Ba/F3, Ramos and BTK(C481S)‐Ba/F3 cells in Nu/nu BALB/c mice was used to assess in vivo efficacy of XMU‐MP‐3.

Key Results
XMU‐MP‐3 is one of a group of low MW compounds that are potent non‐covalent BTK inhibitors. XMU‐MP‐3 inhibited both BTK and the acquired mutant BTKC481S, in vitro and in vivo. Further computational modelling, site‐directed mutagenesis analysis, and structure–activity relationships studies indicated that XMU‐MP‐3 displayed a typical Type‐II inhibitor binding mode.

Conclusion and Implications
XMU‐MP‐3 directly targets the BTK signalling pathway in B‐cell lymphoma. These findings establish XMU‐MP‐3 as a novel inhibitor of BTK, which could serve as both a tool compound and a lead for further drug development in BTK relevant B‐cell malignancies, especially those with the acquired ibrutinib‐resistant C481S mutation.

Link:https://bpspubs.onlinelibrary.wiley.com/doi/full/10.1111/bph.14809