The Role of Selective HDAC Enzymes in Drug Sensitivity

描述（由申请人提供）：组蛋白去乙酰化酶（HDAC）酶在癌症的发生和进展中起着重要作用，HDAC抑制剂（HDACi）目前正在作为抗癌药物进行测试。早期临床试验表明，这些药物具有抗肿瘤活性，但反应率很低，并且尚不清楚哪些患者可能从HDACi中受益。至少有17个HDAC家族成员，但对单个HDAC的功能及其作为特定治疗靶点的相关性知之甚少。研究表明，HDACi可引起癌细胞的细胞周期阻滞和分化。HDACi进一步促进染色质去浓缩，并增强细胞毒性药物（如拓扑异构酶抑制剂）诱导的DMA损伤。然而，HDACi对肿瘤组织的作用依赖于药物治疗的剂量和持续时间，不同肿瘤类型的作用差异很大。我们假设HDAC的作用，如染色质去浓缩、生长抑制和化疗致敏，可能不仅取决于对特定HDAC酶的抑制，而且还取决于特定HDAC酶在靶组织中的表达。我们的初步数据表明HDAC2主要参与了染色质的脱凝。我们发现选择性siRNA缺失对HDAC2的抑制足以引起染色质去浓缩。此外，在缺乏HDAC2的细胞中，既没有观察到hdaci诱导的染色质去浓缩，也没有观察到对topo抑制剂的敏化。相比之下，虽然与染色质去浓缩无关，但HDAC6参与细胞周期调节，并可能决定细胞周期停滞的阶段。这些发现表明，将单个HDAC酶的作用定义为特定的治疗靶点，可以极大地改善下一代HDAC，患者的选择，以及这些药物单独或联合临床试验的最佳设计。因此，在Specific Aim 1中，我们将定义特定HDAC酶作为治疗靶点的作用，以及它们在细胞培养模型中通过使用siRNA消耗特定HDAC和在具有变异HDAC表达的细胞系统中选择性抑制的后果。在Specific Aim 2中，早期乳腺癌患者将在接受topo II抑制剂治疗之前接受HDACi治疗。在治疗前和治疗后的肿瘤样本中，我们将确定哪些hdac参与了hdac诱导的细胞效应，哪些hdac可以预测反应。

DESCRIPTION (provided by applicant): Histone deacetylase (HDAC) enzymes play an important part in the development and progression of cancer and HDAC inhibitors (HDACi) are currently being tested as anti-cancer agents. Early clinical trials show that these drugs have anti-tumor activity, but the response rates are low and it is unclear which patients may benefit from HDACi. There are at least 17 HDAC family members, yet very little is known about the function of individual HDACs and their relevance as specific therapeutic targets. It has been shown that HDACi cause cell cycle arrest and differentiation in cancer cells. HDACi further promote chromatin decondensation and potentiate DMA damage induced by cytotoxic agents (such as topoisomerase (topo) inhibitors). However, the effects of HDACi on tumor tissues are dependent on the dose and duration of drug treatment and the effects vary greatly between different tumor types. We hypothesized that the effects of HDACi such as chromatin decondensation, growth inhibition and sensitization to chemotherapy may not only depend on the inhibition of specific HDAC enzymes, but is also determined by the expression of specific HDAC enzymes in the target tissue. This is supported by our preliminary data showing that mainly HDAC2 was involved in chromatin de- condensation. We found that the inhibition of HDAC2 by selective siRNA depletion was sufficient to cause chromatin decondensation. Furthermore, neither HDACi-induced chromatin decondensation nor sensitization to topo inhibitors was seen in cells lacking HDAC2. In contrast, while not associated with chromatin decondensation, HDAC6 was involved in cell cycle regulation and may determine the phase of the cell cycle arrest. These findings suggest that defining the roles of individual HDAC enzymes as specific therapeutic targets could vastly improve the next generation of HDACi, the selection of patients, and the optimal design of clinical trials for these drugs either alone or in combination. In Specific Aim 1, we will therefore define the roles of specific HDAC enzymes as therapeutic targets and the consequence of their selective inhibition in cell culture models by the depletion of specific HDACs using siRNA and in cell systems with variant HDAC expression. In Specific Aim 2, patients with early stage breast cancer will be treated with an HDACi, prior to exposure to a topo II inhibitor. In pre- and post-treatment tumor samples, we will determine which HDACs are involved in the cellular effects induced by the HDACi and which HDACs may predict response.