The interface of transcription, DNA damage and epigenetics: A therapeutic vulnerability of the EWS-FLI1 transcription factor

目前迫切需要开发新的靶向致癌转录因子的方法。尤因 肉瘤（ES）是这种需要的象征。25年来人们都知道ES绝对是 依赖于EWS-FLI 1转录因子的细胞存活。EWS-FLI 1是唯一的复发性突变， ES（>20%的肿瘤）和细胞对这种蛋白质的依赖性已经通过多项研究建立。 独立研究。我们的首要目标是识别和临床翻译抑制EWS的化合物- FLI 1改善尤文肉瘤患者的预后。为了实现这一目标，我们确定了 小沟DNA结合化合物trabectedin作为EWS-FLI 1的抑制剂。我们把这个 将该化合物与低剂量伊立替康组合应用于临床，并已观察到显著的临床反应。 然而，一些患者在治疗期间进展。其他患者由于以下原因需要降低剂量： 限制治疗效果的毒性。因此，在本研究中，我们建议更深入地了解 对活性和耐药机制的研究将有助于提高治疗效果。我们假设这些 化合物通过我们已经定义的机制毒害EWS-FLI 1，它们也改变染色质结构， 以这种方式平衡细胞的恢复状态。更准确地说，我们已经证明， 将细胞核中的EWS-FLI 1重新分配到核仁中，以触发表观遗传开关来改变染色质 EWS-FLI 1驱动的GGAA微卫星增强子的可及性。然而，我们在此建议， 表观遗传DNA损伤反应机制，通过无偏的方法确定，留下染色质 准备好恢复了此外，我们已经证明EWS-FLI 1重新分布到核仁中可以稳定细胞核， 融合蛋白，从而提供促进转录恢复的储备库。因此，这一目标 研究的目的是直接靶向这些平衡状态，以提高化合物的活性，限制毒性， 抵抗机制。重要的是，这些方法应该改善毒性特征，因为它们 重点关注EWS-FLI 1及其下游GGAA微卫星，EWS-FLI 1仅存在于尤文肉瘤细胞中 在正常细胞中没有已知功能的增强子。如果成功，这项研究将产生一部小说， 针对复发性尤文肉瘤患者的机制性集中联合治疗， trabectedin/irinotecan的初步成功。此外，这项研究将提供重要的见解， 作为致癌转录因子抑制剂的DNA结合化合物.最后，它将产生一个新颖的“陷阱” 方法来靶向相变转录因子。

There is an urgent need to develop novel approaches to target oncogenic transcription factors. Ewing sarcoma (ES) is emblematic of this need. It has been known for more than 25 years that ES is absolutely dependent on the EWS-FLI1 transcription factor for cell survival. EWS-FLI1 is the only recurrent mutation of ES (>20% of tumors) and the dependence of the cells on this protein has been established by multiple independent studies. Our overarching goal is to identify and clinically translate compounds that inhibit EWS- FLI1 to improve outcomes for patients with Ewing sarcoma. Consistent with this goal, we have identified the minor groove DNA binding compound trabectedin as an inhibitor of EWS-FLI1. We have moved this compound into the clinic in combination with low dose irinotecan and have seen striking clinical responses. However, some patients progress while on therapy. Other patients have required dose reductions due to toxicity that limits the efficacy of the therapy. Therefore, in this study, we propose that a deeper understanding of the mechanisms of activity and drug resistance will improve the therapy. We hypothesize that while these compounds poison EWS-FLI1 by mechanisms that we have defined, they also alter chromatin structure and cellular state in such a way that poises the cell for recovery. More precisely, we have shown that trabectedin redistributes EWS-FLI1 in the nucleus to the nucleolus to trigger an epigenetic switch to alter chromatin accessibility at the EWS-FLI1 driven GGAA microsatellite enhancer. However, here we propose that additional epigenetic DNA damage response mechanisms, identified by unbiased approaches, leaves the chromatin poised for recovery. Additionally, we have shown that redistribution of EWS-FLI1 to the nucleolus stabilizes the fusion protein thus providing a reserve pool that facilitates transcriptional recovery. Therefore, the goal of this study is to directly target these poised states to improve the activity of the compound, limit toxicity, and restrict mechanisms of resistance. Importantly, these approaches should improve the toxicity profile because they focus on EWS-FLI1 which is only found in Ewing sarcoma cells and its downstream GGAA microsatellite enhancer which has no known function in normal cells. If successful, the study will yield a novel mechanistically focused combination therapy for relapsed Ewing sarcoma patients that will build on the preliminary success of trabectedin/irinotecan. In addition, the study will provide important insight into the use of DNA binding compounds as inhibitors of oncogenic transcription factors. Finally, it will yield a novel “trapping” approach to target phase transitioned transcription factors.