Potentiation of Topo Inhibitors by the HDACi, SAHA

描述(申请人提供)：组蛋白脱乙酰酶抑制剂(HDACi)是一类很有前途的新型抗癌药物。几种HDACi目前正作为单一药物进行临床试验。HDACi处理细胞会导致组蛋白的乙酰化，因此HDACi可能在基因调控和染色质结构中发挥重要作用。来自我们实验室的细胞培养和异种移植模型的机制研究表明，HDACi可能会增强依赖于获得DNA的抗肿瘤药物所引起的DNA损伤。特别令人感兴趣的是拓扑异构酶II抑制剂(TOPO II)。Topo II是在癌细胞分裂中优先表达的重要酶，Topo II抑制剂的疗效与Topo II亚型Topo 11a的表达有关。我们的临床前数据表明，肿瘤细胞暴露在HDACi中会导致组蛋白的超乙酰化。组蛋白的超乙酰化与几种蛋白质的下调有关，这些蛋白质是维持染色质结构和随后的染色质解缩所必需的。HDACi诱导的染色质解缩增加了DNA与Topo II抑制剂的结合。在它们的靶标存在的情况下，这导致了Topo II抑制剂诱导的DNA损伤和凋亡的增强。当细胞被HDACi处理至少48小时时，这些影响最为深刻。随着暴露前时间的缩短，协同作用被取消。协同活性与治疗前Topo II的表达水平密切相关。然而，在HDACi介导的染色质解缩过程中，不仅topo 11a，而且topo Lib似乎是一个重要的靶点。这些观察结果为将HDACi与Topo II抑制剂结合提供了强有力的理由，因为预先暴露于HDACi可能选择性地增强Topo II抑制剂的抗肿瘤活性，同时限制它们对正常组织的毒性。我们将通过以下目的在临床试验和相关研究中验证这些观察结果：特定目的1描述一项序列特异性I期试验，在该试验中将探索Suberoylanilde异羟肟酸(SAHA)和阿霉素的毒性、安全性和药代动力学。特定目的2涉及相关研究，评估SAHA对肿瘤活检组织中组蛋白乙酰化、染色质重塑和阿霉素诱导的DNA损伤的影响。SAHA的早期试验表明，它的耐受性很好，可能具有抗肿瘤活性。阿霉素之所以被选中，是因为它是癌症治疗中最常用和最有效的药物之一。这一建议可能有助于为HDACi和Topo II抑制剂的序列特异性组合建立新的范例，并为协同作用的机制提供进一步的洞察。这些发现可能对未来涉及HDACi的临床试验的合理设计有用。

DESCRIPTION (provided by applicant): Histone deacetylase inhibitors (HDACi) are a promising new class of anti-cancer agents. Several HDACi are currently in clinical trials as single agents. Treatment of cells with HDACi leads to acetylation of histones, therefore HDACi may play an important role in gene regulation and chromatin structure. Mechanistic studies from cell culture and xenograft models from our lab suggest that HDACi may potentiate DNA damage induced by anti-tumor agents that depend on access to the DNA. Of particular interest are the topoisomerase II inhibitors (topo II). Topo II are essential enzymes that are preferentially expressed in dividing cancer cells and the efficacy of topo II inhibitors has been associated with the expression of topo II isoform, topo lla. Our preclinical data indicate that exposure of tumor cells to HDACi resulted in hyperacetylation of histones. Histone hyperacetylation was associated with a down-regulation of several proteins essential for the maintenance of chromatin structure and subsequent chromatin decondensation. The HDACi-induced chromatin decondensation increased the binding of DNA to topo II inhibitors. In the presence of their targets, this resulted in a potentiation of topo II inhibitor-induced DNA damage and apoptosis. These effects were most profound when cells were treated with HDACi for at least 48 hours. Synergy was abrogated with shorter pre-exposure. Synergistic activity strongly correlated with pre-treatment expression levels of topo II. However, in the setting of HDACi-mediated chromatin decondensation, not only topo lla, but also topo lIb appeared to be an important target. These observations provide a strong rationale to combine HDACi with topo II inhibitors, as the pre- exposure to HDACi may selectively enhance the anti-tumor activity of topo II inhibitors while limiting their toxicity to normal tissues. We will test these observations in a clinical trial and its associated correlative studies by the following aims: Specific Aim 1 describes a sequence-specific Phase I trial where the toxicity, safety and pharmacokinetics of suberoylanilide hydroxamic acid (SAHA) and doxorubicin will be explored. Specific Aim 2 involves correlative studies evaluating the effects of SAHA on histone acetylation, chromatin remodeling and DNA damage induced by doxorubicin in tumor biopsies. Early trials with SAHA suggest that it is well tolerated and may have anti-tumor activity. Doxorubicin was chosen as it is one of the most often used and most effective drugs in cancer therapy. This proposal may help to establish a new paradigm for sequence-specific combinations of HDACi and topo II inhibitors and provide further insight into the mechanism of synergy. These findings may be useful in the rational design of future clinical trials involving HDACi.