SY-1530, a highly selective BTK inhibitor, effectively treats B-cell malignancies by blocking B-cell activation

Objective: B-cell antigen receptor (BCR) signaling is required to maintain the physiological functions of normal B cells and plays animportant pathogenic role in B-cell malignancies. Bruton tyrosine kinase (BTK), a critical mediator of BCR signaling, is an attractivetarget for the treatment of B-cell malignancies. This study aimed to identify a highly potent and selective BTK inhibitor. Methods: Homogeneous time-resolved fluorescence assays were used to screen BTK inhibitors. Typhoon fluorescence imagingand Western blot analysis were used to confirm the effects of SY-1530 on the BCR signaling pathway. Additionally, the anti-tumoractivities of SY-1530 were evaluated in TMD8 xenografts and spontaneous canine B-cell lymphoma. Results: We found a novel irreversible and non-competitive inhibitor of BTK, SY-1530, which provided dose-dependent and timedependentinhibition. SY-1530 selectively bound to BTK rather than inducible T-cell kinase; consequently, it did not significantlyaffect T-cell receptor signaling and caused limited off-target effects. SY-1530 blocked the BCR signaling pathway through downregulationof BTK activity, thus leading to impaired phosphorylation of BTK and its downstream kinases. Moreover, SY-1530induced apoptosis in a caspase-dependent manner and efficaciously inhibited tumor growth in mouse xenograft models of B-cellmalignancy (P < 0.001). SY-1530 also induced positive clinical responses in spontaneous canine B-cell lymphoma. Conclusions: SY-1530 is an irreversible and selective BTK inhibitor that shows inhibitory effects on B-cell malignancies by blockingthe BCR signaling pathway. Therefore, it may be a promising therapeutic approach for the treatment of B-cell malignancies.