The Role of Selective HDAC Enzymes in Drug Sensitivity

描述（由申请人提供）：组蛋白脱乙酰酶（HDAC）酶在癌症的发生和进展中起重要作用，HDAC抑制剂（HDACi）目前正在作为抗癌剂进行测试。早期临床试验表明，这些药物具有抗肿瘤活性，但反应率较低，目前尚不清楚哪些患者可能受益于HDACi。至少有17个HDAC家族成员，但对单个HDAC的功能及其作为特异性治疗靶点的相关性知之甚少。已经显示HDACi引起癌细胞的细胞周期停滞和分化。HDACi进一步促进染色质去凝聚并增强由细胞毒性剂（例如拓扑异构酶（topo）抑制剂）诱导的DMA损伤。然而，HDACi对肿瘤组织的作用取决于药物治疗的剂量和持续时间，并且不同肿瘤类型之间的作用差异很大。我们假设HDACi的作用，如染色质去凝聚、生长抑制和对化疗的敏感性，可能不仅取决于对特定HDAC酶的抑制，而且还取决于靶组织中特定HDAC酶的表达。这得到了我们的初步数据的支持，初步数据显示主要HDAC 2参与染色质去缩合。我们发现，通过选择性siRNA耗竭对HDAC 2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，也没有观察到对拓扑异构酶抑制剂的敏化。相比之下，虽然与染色质去凝聚无关，但HDAC6参与细胞周期调控，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HDACi，患者的选择以及这些药物单独或组合的临床试验的最佳设计。因此，在具体目标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和在具有变体HDAC表达的细胞系统中选择性抑制的结果。在特定目标2中，患有早期乳腺癌的患者将在暴露于topo II抑制剂之前用HDACi治疗。在治疗前和治疗后的肿瘤样品中，我们将确定哪些HDAC参与HDACi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.