We have developed a potent, histone deacetylase 8 (HDAC8)-specific inhibitor PCI-34051 with >200-fold selectivity over the other HDAC isoforms. PCI-34051 induces caspase-dependent apoptosis in cell lines derived from T-cell lymphomas or leukemias, but not in other hematopoietic or solid tumor lines. Unlike broad-spectrum HDAC inhibitors, PCI-34051 does not cause detectable histone or tubulin acetylation. Cells defective in T-cell receptor signaling were still sensitive to PCI-34051-induced apoptosis, whereas a phospholipase C-gamma1 (PLCgamma1)-defective line was resistant. Jurkat cells showed a dose-dependent decrease in PCI-34051-induced apoptosis upon treatment with a PLC inhibitor U73122, but not with an inactive analog. We found that rapid intracellular calcium mobilization from endoplasmic reticulum (ER) and later cytochrome c release from mitochondria are essential for the apoptotic mechanism. The rapid Ca(2+) flux was dependent on PCI-34051 concentration, and was blocked by the PLC inhibitor U73122. Further, apoptosis was blocked by Ca(2+) chelators (BAPTA) and enhanced by Ca(2+) effectors (thapsigargin), supporting this model. These studies show that HDAC8-selective inhibitors have a unique mechanism of action involving PLCgamma1 activation and calcium-induced apoptosis, and could offer benefits including a greater therapeutic index for treating T-cell malignancies.

中文翻译：

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一种新型的组蛋白脱乙酰基酶8（HDAC8）特异性抑制剂PCI-34051诱导T细胞淋巴瘤的凋亡。

我们已经开发了一种有效的组蛋白脱乙酰基酶8（HDAC8）特异性抑制剂PCI-34051，其选择性是其他HDAC亚型的200倍以上。PCI-34051在源自T细胞淋巴瘤或白血病的细胞系中诱导caspase依赖性细胞凋亡，但在其他造血或实体瘤细胞系中则不诱导凋亡。与广谱HDAC抑制剂不同，PCI-34051不会引起可检测的组蛋白或微管蛋白乙酰化。T细胞受体信号传导缺陷的细胞仍然对PCI-34051诱导的凋亡敏感，而磷脂酶C-γ1（PLCgamma1）缺陷型则具有抗性。在用PLC抑制剂U73122治疗后，Jurkat细胞在PCI-34051诱导的细胞凋亡中显示出剂量依赖性的降低，但是在无活性的类似物中则没有。我们发现内质网（ER）的快速细胞内钙动员和线粒体中后期细胞色素c的释放对于凋亡机制至关重要。Ca（2+）的快速通量取决于PCI-34051的浓度，并被PLC抑制剂U73122阻止。此外，凋亡被Ca（2+）螯合剂（BAPTA）阻止，并被Ca（2+）效应物（thapsigargin）增强，从而支持了该模型。这些研究表明，HDAC8选择性抑制剂具有涉及PLCgamma1活化和钙诱导的细胞凋亡的独特作用机制，并可能提供益处，包括更大的治疗T细胞恶性肿瘤的治疗指数。凋亡被Ca（2+）螯合剂（BAPTA）阻止，并被Ca（2+）效应物（thapsigargin）增强，支持此模型。这些研究表明，HDAC8选择性抑制剂具有涉及PLCgamma1活化和钙诱导的细胞凋亡的独特作用机制，并可能提供益处，包括更大的治疗T细胞恶性肿瘤的治疗指数。凋亡被Ca（2+）螯合剂（BAPTA）阻止，并被Ca（2+）效应物（thapsigargin）增强，支持此模型。这些研究表明，HDAC8选择性抑制剂具有涉及PLCgamma1活化和钙诱导的细胞凋亡的独特作用机制，并可能提供益处，包括更大的治疗T细胞恶性肿瘤的治疗指数。