RNAi专家Nature揭示白血病新靶点

　　

生物通报道  来自美国冷泉港实验室、奥地利分子病理研究所及美国纽约州立大学石溪分校等处的研究人员利用一种非常规的RNAi筛选策略在急性骨髓性白血病（AML）模型小鼠中筛选了一千余个shRNA，抑制了243个已知染色质的表观遗传学调节蛋白，从而揭示出了AML的关键性作用酶Brd4。

领导这一研究的是冷泉港实验室的Christopher R. Vakocclose教授和沃森生物科学学院Scott W. Lowe教授，Lowe教授是RNAi小鼠模型研究方面的领先科学家。

癌症细胞利用改变表观遗传表现来驱动其细胞生长程序，然而这些表观遗传学改变通常是可逆的，且对药物干预很敏感。于是Lowe等提出了利用这种表观学依赖性来进行干扰的想法。

在这篇文章中，该研究小组基于一种称为RNAi的筛查策略将以核染色质已知的243个表观遗传监管者为目标的1000多个小发夹RNA（shRNA）导入到有白血病致病突变的小鼠体内。从中，他们筛查出了一个以Brd4为目标的shRNA。 研究人员发现用这个shRNA抑制Brd4能够引发一个戏剧性的细胞周期停滞以及标志白血病进程延迟的白血病细胞死亡，从而极大地延迟延长了白血病动物模型的生存期。

这一研究发现促成了冷泉港实验室研究人员与美国哈佛医学院达纳-法伯癌症研究所的肿瘤学家和化学生物学家James Bradner博士的合作。Bradner以前研发了一种针对Brd4的小型分子抑制剂JQ1。通过共同努力，研究人员利用JQ1再现了在Brd4 shRNA试验中观察到的所有抗-白血病的反应。对JQ1在主要人类白血病样本和确立细胞株中的敏感度的大量评估显示，这一化合物对不同的AML亚型都是广泛有效的

进一步的研究证实Brd4抑制有可能是破坏了一个被认为是AML特质的细胞过程— 即白血病干细胞自我更新异常以及无法完成分化、或变异的过程。他们发现，抑制Brd4可能对维持白血病干细胞的Myc的水平及活性造成的影响。研究人员对此感到异常兴奋，因为这表明他们找到了一种能抑制Myc的药理方式。Myc在很多致癌途径中都起作用，且在大多数癌症中Myc都被解除了管制。

新研究揭示了AML的一个潜在的药物靶标Brd4，强调了将RNAi筛查作为药物研发平台来鉴定其它类型癌症的药物靶标的潜在可能性。这一研究成果发布在最新一期（10月27日）的《自然》（Nature）杂志上。

（生物通：何嫱）

生物通推荐原文摘要：

RNAi screen identifies Brd4 as a therapeutic target in acute myeloid leukaemia

Epigenetic pathways can regulate gene expression by controlling and interpreting chromatin modifications. Cancer cells are characterized by altered epigenetic landscapes, and commonly exploit the chromatin regulatory machinery to enforce oncogenic gene expression programs1. Although chromatin alterations are, in principle, reversible and often amenable to drug intervention, the promise of targeting such pathways therapeutically has been limited by an incomplete understanding of cancer-specific dependencies on epigenetic regulators. Here we describe a non-biased approach to probe epigenetic vulnerabilities in acute myeloid leukaemia (AML), an aggressive haematopoietic malignancy that is often associated with aberrant chromatin states2. By screening a custom library of small hairpin RNAs (shRNAs) targeting known chromatin regulators in a genetically defined AML mouse model, we identify the protein bromodomain-containing 4 (Brd4) as being critically required for disease maintenance. Suppression of Brd4 using shRNAs or the small-molecule inhibitor JQ1 led to robust antileukaemic effects in vitro and in vivo, accompanied by terminal myeloid differentiation and elimination of leukaemia stem cells. Similar sensitivities were observed in a variety of human AML cell lines and primary patient samples, revealing that JQ1 has broad activity in diverse AML subtypes. The effects of Brd4 suppression are, at least in part, due to its role in sustaining Myc expression to promote aberrant self-renewal, which implicates JQ1 as a pharmacological means to suppress MYC in cancer. Our results establish small-molecule inhibition of Brd4 as a promising therapeutic strategy in AML and, potentially, other cancers, and highlight the utility of RNA interference (RNAi) screening for revealing epigenetic vulnerabilities that can be exploited for direct pharmacological intervention.