DNA Methylation and Ovarian Cancer

描述（由申请人提供）：卵巢癌导致的死亡比任何其他女性生殖道恶性肿瘤都要多。在过去的三十年中，五年生存率保持相对不变，耐药性仍然是主要的治疗障碍。在最初的资助期间，我们证明了DNA甲基化的增加和组蛋白甲基化的改变与卵巢癌化疗耐药密切相关。一个流行的化疗耐药模型，以及一般的癌症发生，是基于异常干细胞的行为导致的肿瘤生长，并且假设标准卵巢癌治疗的不足很大程度上是由于它们未能靶向卵巢肿瘤干细胞（导致不可避免的复发）。抑制表观遗传修饰（非编码）在正常和癌症干细胞/起始细胞的建立和维持中发挥着越来越明显的关键作用，我们实验室的长期目标是阐明表观遗传学在卵巢肿瘤形成和进展中的作用。通过利用最近描述的癌症干细胞的特征，我们现在已经从人类卵巢肿瘤中分离并证实了卵巢癌起始细胞。要验证的总体假设是卵巢癌启动细胞中的表观遗传事件控制肿瘤的耐药性和对化疗的反应。虽然表观遗传修饰可能影响癌症干细胞的多种途径，包括自我更新、增殖和分化，但我们将专门研究卵巢癌起始细胞中有助于耐药的表观遗传事件；逆转这些事件可能允许化疗耐药肿瘤干细胞的“表观遗传再敏化”。Aim 1的目标是鉴定卵巢癌起始细胞中与化疗耐药相关的DNA“甲基化特征”。我们将使用DNA甲基化全基因组谱进一步检查我们小组先前鉴定的与无病生存相关的40个甲基化基因。在Aim 2中，高通量表观遗传学分析，染色质免疫沉淀-微阵列杂交，将用于鉴定卵巢癌起始细胞中具有特定激活和抑制组蛋白标记的基因。将组蛋白修饰数据与Aim 1的DNA甲基化数据相结合，将有助于确定卵巢癌启动细胞化疗耐药的途径。使用表观遗传和常规药物直接靶向卵巢癌起始细胞是Aim 3的目标。我们假设DNA甲基化和组蛋白修饰的抑制剂可以破坏表观遗传抑制修饰，这些修饰是卵巢癌起始细胞致瘤分化所必需的，这些细胞负责整个肿瘤的增殖，从而允许它们直接靶向治疗。了解卵巢癌起始细胞中存在的表观遗传事件将导致对这种毁灭性疾病的更全面了解，并将为新的治疗靶点提供有价值的见解。基于PA-05-086建立卵巢癌干细胞表观遗传型，建立化学耐药通路改变的综合模型，并研究表观遗传疗法可能直接破坏这些细胞活性的总体目标，该提案对PA-05-086具有高度响应性。公共卫生相关性：在所有女性癌症中，卵巢癌是迄今为止最致命的。卵巢癌研究的一个新机遇是，卵巢癌被认为含有一小部分负责整个肿瘤生长的“癌症干细胞”。虽然传统的癌症化疗会杀死肿瘤中的大部分细胞，但它们可能会错过这些癌症干细胞，从而使肿瘤重新生长。“表观遗传”变化（DNA结构的变化）可能是表征卵巢癌干细胞的一种方法，而改变这些DNA结构变化的新药可能代表了一种针对这些细胞的新型治疗方法，可以完全杀死肿瘤。

DESCRIPTION (provided by applicant): Ovarian cancer causes more deaths than any other female tract reproductive malignancy. Five-year survival has remained relatively unchanged for the past three decades, and drug resistance remains a major therapeutic barrier. During the initial funding period, we demonstrated that increased DNA methylation and alterations in histone methylation are strongly associated with ovarian cancer chemoresistance. A prevalent model of chemoresistance, and carcinogenesis in general, is based on tumor growth due to the behavior of abnormal stem cells, and it is hypothesized that the inadequacy of standard ovarian cancer therapies is largely due to their failure to target ovarian tumor stem cells (resulting in inevitable relapse). A critical role for repressive epigenetic (noncoding) modifications has become increasingly evident for the establishment and maintenance of both normal and cancer stem/initiating cells, and the long-term goal of our laboratory is to elucidate the role of epigenetics in ovarian tumor formation and progression. By exploiting recently described characteristics of cancer stem cells, we have now isolated and substantiated ovarian cancer-initiating cells from human ovarian tumors. The overall hypothesis to be tested is that epigenetic events in ovarian cancer- initiating cells govern tumor drug resistance and response to chemotherapy. While epigenetic modifications likely affect multiple pathways in cancer stem cells, including self-renewal, proliferation and differentiation, we will specifically examine the epigenetic events in ovarian cancer-initiating cells that contribute to drug resistance; reversal of such events may allow for the "epigenetic resensitization" of chemoresistant tumor stem cells. The goal of Aim 1 is to identify DNA "methylation signatures" associated with chemoresistance in ovarian cancer-initiating cells. We will further examine 40 methylated genes previously identified by our group as associated with disease-free survival, using genome-wide profiling of DNA methylation. In Aim 2, a high- throughput epigenetic analysis, chromatin immunoprecipitation-to-microarray hybridization, will be used to identify genes possessing specific activating and repressive histone marks in ovarian cancer-initiating cells. Integrating this histone modification data with the DNA methylation data from Aim 1 will facilitate the identification of pathways responsible for ovarian cancer-initiating cell chemoresistance. The direct targeting of ovarian cancer-initiating cells, using epigenetic and conventional agents, is the objective of Aim 3. We hypothesize that inhibitors of DNA methylation and histone modifications can disrupt epigenetic repressive modifications necessary for tumorigenic differentiation of the ovarian cancer-initiating cells responsible for propagating an entire tumor, allowing for their direct therapeutic targeting. Knowledge of the epigenetic events present in ovarian cancer-initiating cells will result in a more complete understanding of this devastating disease and will also provide valuable insight into new therapeutic targets. This proposal is highly responsive to PA-05-086, based on its overall objective to establish ovarian cancer stem cell epigenotypes, develop a comprehensive model of altered pathways responsible for chemoresistance, and examine the possible direct disruption of the activity of these cells by epigenetic therapies. PUBLIC HEALTH RELEVANCE: Of all female cancers, ovarian cancer is by far the deadliest. A new opportunity in ovarian cancer research is that ovarian cancer is believed to contain a small population of "cancer stem cells" responsible for growing an entire tumor. While conventional cancer chemotherapies kill most of the cells in a tumor, they may miss these cancer stem cells, allowing the tumor to re-grow. "Epigenetic" changes (changes in DNA structure) may be a way to characterize ovarian cancer stem cells, and new drugs that alter those DNA structural changes may represent a new type of therapy against those cells, allowing complete killing of the tumor.