The Role of Selective HDAC Enzymes in Drug Sensitivity

描述(申请人提供)：组蛋白脱乙酰酶(HDAC)酶在癌症的发生和发展中起着重要作用，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，但应答率较低，目前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。已有研究表明，HDACi可引起癌细胞周期停滞和分化。HDACi进一步促进染色质解缩，并增强细胞毒剂(如拓扑异构酶(TOPO)抑制剂)引起的DMA损伤。然而，HDACi对肿瘤组织的影响依赖于药物治疗的剂量和持续时间，并且不同的肿瘤类型之间的效果差异很大。我们推测，HDACi的作用，如染色质解聚、生长抑制和对化疗的增敏，可能不仅取决于特定的HDAC酶的抑制，而且还取决于特定的HDAC酶在靶组织中的表达。我们的初步数据表明，主要是HDAC2参与了染色质的去缩合。我们发现，选择性耗尽siRNA对HDAC2的抑制足以导致染色质解聚。此外，在缺乏HDAC2的细胞中，既没有观察到HDACi诱导的染色质去凝集，也没有发现对Topo抑制剂的敏化。相反，尽管HDAC6与染色质解聚无关，但它参与了细胞周期的调节，并可能决定细胞周期停滞的时相。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的临床试验的最佳设计，无论是单独使用还是联合使用。因此，在特定的目标1中，我们将确定特定的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耗尽特定的HDAC而选择性抑制的结果，以及在具有不同HDAC表达的细胞系统中的结果。在具体目标2中，早期乳腺癌患者在暴露于Topo II抑制剂之前，将接受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HDACi诱导的细胞效应，以及哪些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.