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益处的BRCA1患者，并了解最初对药物敏感的肿瘤如何发展耐药。在美国，每年大约有55,000人死于乳腺癌和卵巢癌，其中5%到7%的乳腺癌和6%到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BRCA突变患者的生命。我们的初步研究使我们假设，常见的致癌种系BRCA1突变的子集产生半功能截断的异构体，从而导致耐药性。BRCA1亚型的选择性剪接在细胞系和肿瘤中的表达已经得到了很好的证明，但由于亚型缺乏被认为是必需的全长蛋白质区域，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。在对对PARP抑制剂产生耐药性的BRCA1突变细胞株的研究中，我们发现了特定的BRCA1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抑制剂抗性后，BRCA1外显子11移码突变的细胞优先表达外显子11缺失的BRCA1亚型(BRCA1-11)。BRCA1-11蛋白保留N-末端环和C-末端BRCT结构域，这对同源重组(HR)DNA修复是重要的。此外，BRCA1-11蛋白的高表达在PARP抑制剂和铂耐药中起关键作用。在这一应用中，我们将进一步鉴定和鉴定能够促进DNA修复和耐药的BRCA1亚型。在目标1中，在BRCA1突变患者肿瘤中表达的异构体将被克隆和过度表达。在目标2中，我们将评估BRCA1亚型缺失的多肽区对DNA损伤反应的影响及其提供治疗抵抗的能力。我们的工作将为目前对BRCA1突变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将对PARP抑制剂或铂类药物产生持久反应。

 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.