Inhibition of proteolytic and ATPase activities of the proteasome by the BTK inhibitor CGI-1746

Bruton’s tyrosine kinase (BTK) inhibitor, ibrutinib, has been shown to synergize in vitro with proteasome inhibitors (PIs) in reducing the viability of cells derived from B-cell malignancies, but the mechanism is not known. We report here that an off-target effect of ibrutinib causes synergy because not all BTK inhibitors exhibited the synergistic effect, and those that synergized did so even in cells that do not express BTK. The allosteric BTK inhibitor CGI-1746 showed the strongest synergy. Co-treatment of cells with CGI-1746 increased PI-induced accumulation of ubiquitin conjugates, expression of heat shock proteins and NOXA, and decreased a ratio of reduced to oxidized glutathione. CGI-1746, but not other BTK inhibitors inhibited ATPase activity and all three peptidase activities of the 26S proteasomes. The effect demonstrates a conceptually novel mode of proteasome inhibition that may aid the development of more potent proteasome inhibitors.

布鲁顿酪氨酸激酶（BTK）抑制剂伊布替尼在体外研究表明，其与蛋白酶体抑制剂（PIs）协同作用，能够降低源自B细胞恶性肿瘤的细胞存活率，但其作用机制尚不明确。本研究报告指出，伊布替尼的脱靶效应导致了这种协同作用，因为并非所有BTK抑制剂均表现出协同效应，而表现出协同作用的抑制剂即使在未表达BTK的细胞中也同样如此。异构酶型BTK抑制剂CGI-1746表现出最强的协同作用。CGI-1746与细胞的共处理增加了PI诱导的泛素化共轭物的积累、热休克蛋白和NOXA的表达，并降低了还原型谷胱甘肽与氧化型谷胱甘肽的比值。CGI-1746而非其他BTK抑制剂抑制了26S蛋白酶体的ATP酶活性和所有三种肽酶活性。该效应展示了蛋白酶体抑制的一种新颖概念模式，可能有助于开发更有效的蛋白酶体抑制剂。