Project 1 - PARP Project

项目概要-项目1 高级别浆液性卵巢癌（HGSOC）是最常见和最致命的亚型， 基因组的不稳定性。肿瘤抑制因子TP 53在95%以上的病例中失活;范可尼贫血， IA/同源重组（FA/HR）途径在30- 40%中突变失活，导致进一步的基因突变。 原子不稳定性DNA修复蛋白聚（ADP-核糖）聚合酶（PARP）的抑制剂已显示出良好的生物相容性。 在HR缺陷的临床前模型中具有活性，导致广泛努力开发PARP抑制剂， HGSOC和其他HR缺陷癌症。尽管II期临床试验表明PARP抑制剂可促进 i）在BRCA 1或BRCA 2（BRCA 1/2）突变携带者中，铂类药物的客观缓解率为30-45%， 敏感的复发性卵巢癌和ii）在维持性卵巢癌中无进展生存期的显著延长， 在BRCA 1或BRCA 2突变型HGSOC对含铂治疗产生应答后，FDA 强调了需要更好地识别最有可能对PARP抑制剂有反应的卵巢癌。 在上一个供资期所取得成果的基础上，本研究旨在 更好地理解为什么一些HR缺乏的卵巢癌对PARP抑制剂有反应，而另一些则有反应。 没有我们的初步结果表明，在HR缺陷的卵巢癌中，PARP抑制剂的细胞毒性作用 反映了非同源末端连接（NHEJ）的激活，这是一种易错修复途径，而不是中断 单链断裂修复的可能性。重要的是，抑制NHEJ相关的 激酶DNA-PK或下调多种NHEJ蛋白中的任何一种同时抑制这种易错的 修复并减少PARP抑制剂的细胞毒性作用。对PARP抑制剂作用的新认识 提出了这样的假设，即卵巢癌只有在HR有缺陷时才会对PARP抑制剂有反应， NHEJ通路保持完整。与这一假设一致，我们对BRCA 2突变体的进一步研究 临床前卵巢癌模型显示，对PARP抑制剂耐药的选择导致 NHEJ蛋白的下调或Rad 51（BRCA 2下游的HR蛋白）的过表达， 认为通过BRCA 1/2突变以外的方式使NHEJ失能或恢复HR可赋予PARP抑制剂 阻力为了建立在这些发现的基础上，我们现在提出：i）确定Rad 51过表达如何贡献 ii）鉴定赋予HR缺陷型小鼠PARP抑制剂抗性的变化， 患者来源的卵巢癌异种移植物，和iii）开发多参数分类器，其包括 Rad 51和NHEJ蛋白表达的测定、修复基因的测序和基因组DNA的测量。 瘢痕形成，以预测PARP抑制剂rucaparib在患者中的大型多中心II期试验的反应 复发的卵巢癌影响：总的来说，这些研究将提供新的见解机制， PARP抑制剂的耐药性，同时测试的概念，修复路径的多方面评估- 完整的方式将确定卵巢癌患者最有可能受益于这类有前途的新药。

PROJECT SUMMARY – Project 1 High grade serous ovarian cancer (HGSOC), the most common and most lethal subtype, is largely a disease of genomic instability. The tumor suppressor TP53 is inactivated in over 95% of cases; and the Fanconi anem- ia/homologous recombination (FA/HR) pathway is mutationally inactivated in 30-40%, leading to further gen- omic instability. Inhibitors of the DNA repair protein poly(ADP-ribose) polymerase (PARP) have exhibited prom- ising activity in HR-deficient preclinical models, leading to extensive efforts to develop PARP inhibitors for HGSOC and other HR-deficient cancers. Although phase II clinical trials have shown that PARP inhibitors pro- duce i) objective response rates of 30-45% in BRCA1 or BRCA2 (BRCA1/2) mutation carriers with platinum- sensitive relapsed ovarian cancer and ii) substantial prolongation of progression-free survival in the mainten- ance setting after response of BRCA1- or BRCA2-mutant HGSOCs to platinum-containing therapy, the FDA has highlighted the need to better identify ovarian cancers that are most likely to respond to PARP inhibitors. Building on results generated during the previous funding period, the present studies are designed to better understand why some HR-deficient ovarian cancers respond to PARP inhibitors and others do not. Our preliminary results show that the cytotoxic effects of PARP inhibitors in HR-deficient ovarian cancer reflect activation of nonhomologous end-joining (NHEJ), an error-prone repair pathway, rather than interruption of single-strand break repair as originally postulated by others. Importantly, inhibition of the NHEJ-associated kinase DNA-PK or downregulation of any of a number of NHEJ proteins simultaneously inhibits this error-prone repair and diminishes the cytotoxic effects of PARP inhibitors. This new understanding of PARP inhibitor action suggests the hypothesis that ovarian cancers will respond to PARP inhibitors only if HR is defective and the NHEJ pathway remains intact. Consistent with this hypothesis, our further studies in a BRCA2-mutant preclinical ovarian cancer model have revealed that selection for PARP inhibitor resistance results in either downregulation of NHEJ proteins or overexpression of Rad51, an HR protein downstream of BRCA2, sug- gesting that disabling NHEJ or restoring HR by means other than BRCA1/2 mutations confers PARP inhibitor resistance. To build on these findings we now propose to: i) determine how Rad51 overexpression contributes to PARP inhibitor resistance, ii) identify the changes that confer PARP inhibitor resistance in HR-deficient patient-derived ovarian cancer xenografts in vivo and iii) develop a multi-parameter classifier that includes assays of Rad51 and NHEJ protein expression, sequencing of repair genes and measurements of genomic scarring, to predict responses to the PARP inhibitor rucaparib in a large multicenter phase II trial in patients with relapsed ovarian cancer. Impact: Collectively, these studies will provide new insight into mechanisms of PARP inhibitor resistance and simultaneously test the concept that a multifaceted assessment of repair path- way integrity will identify ovarian cancer patients most likely to benefit from this promising new class of drugs.