Mechanisms of PARP Inhibitor Resistance in Ovarian Cancer

描述（由申请人提供）：Fanconi贫血/同源重组（FA/HR）通路在几种类型的癌症中经常被突变或表观遗传过程沉默，包括高级别浆液性卵巢癌（HGSOC）、基础乳腺癌和一部分胰腺癌和前列腺癌。结果，DNA双链断裂的高保真修复被禁用，导致这些癌症的基因组不稳定。DNA修复蛋白聚（adp -核糖）聚合酶（PARP）抑制剂在hr缺陷的临床前模型中显示出良好的活性，在铂敏感的复发性HGSOC患者中，BRCA1或BRCA2 （BRCA1/2）突变携带者的缓解率为30-45%。该项目旨在更好地理解为什么一些brca1 /2突变型癌症对PARP抑制剂有反应，而另一些则没有。我们的研究小组成员之前的结果不仅在临床前模型和临床样品中确定了BRCA1/2逆转突变是铂耐药的潜在原因，而且还证明了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，这是一种容易出错的DNA双链断裂修复途径，而不是抑制DNA单链断裂修复。重要的是，抑制或下调任何一种NHEJ蛋白都会抑制这种容易出错的修复，并减弱PARP抑制剂的细胞毒性作用。这种对PARP抑制剂作用的新认识导致了一种假设，即brca1 /2突变型癌症对PARP抑制剂的抗性可能是由于逆转突变或DNA修复途径蛋白的变化，从而取消了PARP抑制剂的作用。与这一假设一致，我们在BRCA2突变的临床前卵巢癌模型中的进一步研究表明，选择PARP抑制剂耐药导致NHEJ蛋白下调或Rad51 （BRCA2下游的HR蛋白）过表达。在这些发现的基础上，我们现在建议：i)进一步评估NHEJ蛋白下调对PARP抑制剂体外和体内敏感性的影响，ii)研究Rad51如何上调以诱导PARP抑制剂耐药性；iii)在体外进行全外显子组shRNA筛选，寻找brca1 /2突变卵巢癌系中PARP抑制剂耐药的其他机制；iv)检查接受单药PARP抑制剂治疗的患者的两组独特的癌症活检，以评估这些耐药机制在临床环境中的潜在重要性。总的来说，这些研究将为PARP抑制剂耐药机制提供新的见解，这将使未来卵巢癌患者最有可能从这些有前途的新药中获益。

DESCRIPTION (provided by applicant): The Fanconi anemia/homologous recombination (FA/HR) pathway is frequently silenced by mutations or epigenetic processes in several types of cancer, including high-grade serous ovarian cancer (HGSOC), basal breast cancer, and a subset of pancreatic and prostate cancers. As a result, high fidelity repair of DNA double- strand breaks is disabled, leading to genomic instability in these cancers. Inhibitors of the DNA repair protein poly(ADP-ribose) polymerase (PARP) have shown promising activity in HR-deficient preclinical models and response rates of 30-45% in BRCA1 or BRCA2 (BRCA1/2) mutation carriers with platinum-sensitive relapsed HGSOC. This project is designed to better understand why some BRCA1/2-mutant cancers respond to PARP inhibitors and others do not. Previous results from members of our investigative team have not only identified BRCA1/2 reversion mutations as a potential cause of platinum resistance in preclinical models and clinical samples, but also demonstrated that the cytotoxic effects of PARP inhibitors reflect activation of nonhomologous end-joining (NHEJ), an error-prone DNA double-strand break repair pathway, rather than inhibition of DNA single-strand break repair as originally thought. Importantly, inhibition or downregulation of any of a number of NHEJ proteins inhibits this error-prone repair and diminishes the cytotoxic effects of PARP inhibitors. This new understanding of PARP inhibitor action leads to the hypothesis that resistance of BRCA1/2-mutant cancers to PARP inhibitors can result from either reversion mutations or changes in DNA repair pathway proteins that abrogate the action of the PARP inhibitors. Consistent with this hypothesis, our further studies in a BRCA2-mutant preclinical ovarian cancer model have demonstrated that selection for PARP inhibitor resistance results in either downregulation of NHEJ proteins or overexpression of Rad51, an HR protein downstream of BRCA2. To build on these findings we now propose to: i) further assess the impact of NHEJ protein downregulation on PARP inhibitor sensitivity in vitro and in vivo, ii) examine how Rad51 is upregulated to induce PARP inhibitor resistance; iii) perform a whole-exome shRNA screen looking for additional mechanisms of PARP inhibitor resistance in BRCA1/2-mutant ovarian cancer lines in vitro; and iv) examine two unique sets of cancer biopsies from patients receiving single-agent PARP inhibitor therapy to evaluate the potential importance of these resistance mechanisms in the clinical setting. Collectively, these studies will provide new insight into mechanisms of PARP inhibitor resistance that will enable future selection of ovarian cancer patients most likely to benefit from these promising new drugs.