Role of HDAC6 in platinum resistance of non-small cell lung cancer

描述(申请人提供)：本项目的长期目标是阐明组蛋白脱乙酰酶6(HDAC6)在非小细胞肺癌(NSCLC)铂耐药中的作用。美国每年新增肺癌患者约22万人，这使得肺癌成为男性和女性癌症相关死亡的主要原因。肺癌治疗的两种一线方案是铂加紫杉烷和铂加吉西他滨。这些治疗的主要障碍之一是患者往往对铂产生抗药性。HDAC是一种去除组蛋白和非组蛋白中的乙酰基的酶，从而参与了广泛的生物学过程，包括转录调节、细胞生长/分化、细胞凋亡等。目前，HDAC抑制剂在肺癌治疗中具有很大的前景，部分原因是它们能够恢复化疗的敏感性。然而，HDAC抑制剂增强化疗敏感性的机制在很大程度上尚不清楚。我们的初步数据表明，其中一种HDACs，称为HDAC6，既是脱乙酰酶又是泛素E3连接酶，促进关键的DNA错配修复(MMR)蛋白MSH2的脱乙酰化、多泛素化和降解。我们的结果还表明，MSH2的脱乙酰基下调了MSH2的MMR活性。此外，在15个非小细胞肺癌细胞系中，我们发现HDAC6蛋白水平与顺铂耐药性呈正相关。鉴于MSH2是顺铂诱导的DNA加合物的感受器，MSH2的缺失会导致顺铂耐药，我们推测，HDAC6介导的脱乙酰化和泛素化导致MSH2蛋白水平的下调及其MMR活性的下调与铂耐药有关。因此，在这个方案中，我们将首先表征HDAC6泛素E3连接酶对MSH2降解的活性，并研究HDAC6介导的MSH2脱乙酰基对其MMR活性的影响。然后，我们将在小鼠异种移植模型和非小细胞肺癌患者的组织标本中验证HDAC6在顺铂耐药中的作用。我们的研究结果将使HDAC6成为肺癌治疗的新靶点，并表明HDAC6和MSH2可能作为非小细胞肺癌患者铂耐药的生物标志物。我们的结果将提示临床上相关的抑制HDAC6脱乙酰酶和E3连接酶活性的HDAC6选择性抑制剂用于非小细胞肺癌的治疗。 公共卫生相关性：拟议的研究与公共卫生和NCI的使命相关。化疗耐药性是癌症治疗面临的主要挑战，因为许多癌症患者在一段时间的化疗后复发。尽管临床试验中使用的组蛋白脱乙酰酶(HDAC)抑制剂有望恢复化疗敏感性，但它们抑制了许多HDAC(HDAC1-11)，其中可能并不是所有的HDAC都与化疗耐药有关。我们的研究首次将特定的HDAC6与化疗耐药联系起来，并表明抑制HDAC6脱乙酰酶和E3连接酶活性的HDAC6选择性抑制剂将比PAN HDAC抑制剂获得更高的恢复化疗敏感性的效果。一旦确定了HDAC6在化疗耐药中的作用，治疗肿瘤学家将筛查癌症患者的组织样本中HDAC6的水平，并相应地进行化疗。

DESCRIPTION (provided by applicant): The long-term goal of this project is to elucidate the role of histone deacetylase 6 (HDAC6) in platinum resistance of non-small cell lung cancer (NSCLC). There are about 220,000 new lung cancer patients in the US annually which makes lung cancer the leading cause of cancer-related mortality in both men and women. Two first line regimens of lung cancer treatment are platinum with taxane and platinum with gemcitabine. One of the major obstacles of these treatments is that patients often develop resistance to platinum. HDACs are enzymes which remove acetyl moiety from histone and non-histone proteins, thereby being involved in a wide variety of biological processes including transcription regulation, cell growth/differentiation, apoptosis, etc. HDAC inhibitors now hold great promises in lung cancer treatment partly in that they are able to restore chemosensitivity. However, the mechanisms by which HDAC inhibitors enhance chemosensitivity are largely unknown. Our preliminary data has shown that one of the HDACs, termed HDAC6, acts as both a deacetylase and a ubiquitin E3 ligase to promote a key DNA mismatch repair (MMR) protein MSH2 deacetylation, polyubiquitination and degradation. Our results also indicate that deacetylation of MSH2 down-regulates MSH2 MMR activity. Moreover, we have shown that HDAC6 protein levels positively correlate with cisplatin resistance in a panel of 15 NSCLC cell lines. Given the fact that MSH2 serves as a sensor for cisplatin-induced DNA adducts and loss of MSH2 causes cisplatin resistance, we hypothesize that down-regulation of MSH2 protein level and its MMR activity governed by HDAC6-mediated deacetylation and ubiquitination contributes to platinum resistance. Therefore, in this proposal, we will first characterize HDAC6 ubiquitin E3 ligase activity towards MSH2 degradation and investigate how HDAC6-mediated deacetylation of MSH2 affects its MMR activity. We will then validate the role of HDAC6 in cisplatin resistance in a mouse xenograft model as well as in NSCLC patients' tissue specimens. The results of our research will identify HDAC6 as a novel therapeutic target in lung cancer treatment and show that HDAC6 and MSH2 may serve as biomarkers for platinum resistance in NSCLC patients. Our results will suggest the application of clinically relevant HDAC6-selective inhibitors which suppress HDAC6 deacetylase and E3 ligase activity for the treatment of NSCLC. PUBLIC HEALTH RELEVANCE: The proposed research has relevance to public health and NCI's mission. Chemo-resistance is the major challenge facing cancer treatment since many cancer patients relapse after a period of chemotherapy. Although, the pan histone deacetylase (HDAC) inhibitors used in clinical trials have shown promises to restore chemo-sensitivity, they suppress numerous HDACs (HDAC1-11) of which may not all be involved in chemo-resistance. Our study, for the first time, has linked a specific HDAC, HDAC6, to chemo-resistance and suggested that HDAC6-selective inhibitors which suppress HDAC6 deacetylase and E3 ligase activity will achieve higher efficacy to restore the chemo-sensitivity than that of pan HDAC inhibitors. Once the role of HDAC6 in chemo-resistance has been established, the treating oncologists will screen cancer patients' tissue specimens for levels of HDAC6 and tailor chemotherapy accordingly.