Identifying BRCA1 protein variants that provide resistance to therapy

 描述（由申请人提供）：我们工作的目标是确定最有可能从铂或PARP抑制剂治疗中获得治疗获益的BRCA 1患者，并了解最初对药物敏感的肿瘤如何产生耐药性。在美国，每年约有55，000人死于乳腺癌和卵巢癌，其中5%至7%的乳腺癌和6%至15%的卵巢癌病例中发现了BRCA突变。利用与BRCA病变相关的DNA修复缺陷的聚（ADP-核糖）聚合酶（PARP）抑制剂疗法的出现有望延长携带BRCA突变的患者的生命。我们的初步研究使我们假设，一个常见的癌症易感生殖系BRCA 1突变的子集产生半功能截短的亚型，有助于耐药性。选择性剪接的BRCA 1亚型的表达在细胞系和肿瘤中已有很好的记录，但由于亚型缺乏被认为是必需的全长蛋白质的区域，因此一直认为这些蛋白质在哺乳动物细胞生物学中的作用有限。在对PARP抑制剂获得性耐药的BRCA 1突变细胞系的研究中，我们发现了特定BRCA 1蛋白亚型在DNA修复和耐药性中的重要作用。我们的初步数据表明，在选择PARP抑制剂耐药后，BRCA 1外显子11移码突变的细胞优先表达外显子11缺失的BRCA 1亚型（BRCA 1 - 11）。BRCA 1 - 11蛋白保留了N-末端RING和C-末端BRCT结构域，这对同源重组（HR）DNA修复很重要。此外，BRCA 1 - 11蛋白表达升高对于PARP抑制剂和铂类耐药至关重要。在本申请中，我们将进一步鉴定和表征能够促进DNA修复和耐药性的BRCA 1亚型。在目标1中，将克隆并过表达在BRCA 1突变患者肿瘤中表达的同种型。在目标2中，我们将评估从BRCA 1亚型中删除的肽区对DNA损伤反应的影响及其提供耐药性的能力。我们的工作将为目前对BRCA 1突变型疾病耐药性的理解提供新的见解，并可能有助于预测哪些患者对PARP抑制剂或铂类药物治疗有持久的反应。

 DESCRIPTION (provided by applicant): The goal of our work is to identify BRCA1 patients most likely to gain therapeutic benefit from platinum or PARP inhibitor therapy, and understand how tumors that are initially drug sensitive develop resistance. There are approximately 55,000 deaths from breast and ovarian cancer annually in the United States, with BRCA mutations found in 5% to 7% of breast and 6% to 15% of ovarian cancer cases. The emergence of poly(ADP- ribose) polymerase (PARP) inhibitor therapies that exploit DNA repair defects associated with BRCA lesions promises to extend the lives of BRCA mutation-carrying patients. Our preliminary studies have led us to hypothesize that a subset of common cancer-predisposing germline BRCA1 mutations produce semi-functional truncated isoforms that contribute to drug resistance. The expression of alternatively spliced BRCA1 isoforms has been well documented in cell lines and tumors, but because isoforms lack regions of the full-length protein thought to be essential, it has been assumed that these proteins have a limited role in mammalian cell biology. In studies of BRCA1 mutation bearing cell lines that have acquired resistance to PARP inhibitors, we have discovered important roles for specific BRCA1 protein isoforms in DNA repair and drug resistance. Our preliminary data suggest that after selection for PARP inhibitor resistance, cells with BRCA1 exon 11 frameshift mutations preferentially express exon 11-deleted BRCA1 isoforms (BRCA1- 11). BRCA1- 11 proteins retain the N-terminal RING and C-terminal BRCT domains that are important for homologous recombination (HR) DNA repair. Furthermore, elevated expression of BRCA1- 11 protein is crucial for PARP inhibitor and platinum resistance. In this application, we will further identify and characterize BRCA1 isoforms that are capable of contributing to DNA repair and drug resistance. In Aim 1, isoforms that are expressed in BRCA1 mutant patient tumors will be cloned and over-expressed. In Aim 2, we will assess the impact of peptide regions deleted from BRCA1 isoforms on the DNA damage response and their ability to provide therapy resistance. Our work will provide new insights into the current understanding of drug resistance in BRCA1 mutant disease and could be useful for predicting which patients will have lasting responses to PARP inhibitor or platinum therapy.