DNA Methylation and Ovarian Cancer

描述(申请人提供)：卵巢癌导致的死亡比任何其他女性生殖系统恶性肿瘤都多。在过去的三十年里，五年的存活率相对保持不变，耐药性仍然是一个主要的治疗障碍。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的化疗耐药密切相关。一种流行的化疗耐药和肿瘤发生的模型是基于异常干细胞的行为导致的肿瘤生长，并假设标准的卵巢癌治疗方法的不足在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)。抑制性表观遗传(非编码)修饰在正常和癌症干细胞/起始细胞的建立和维持中的关键作用已经变得越来越明显，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发展中的作用。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启动细胞。有待检验的总体假设是，卵巢癌启动细胞中的表观遗传事件控制着肿瘤的耐药性和对化疗的反应。虽然表观遗传修饰可能会影响癌症干细胞的多条途径，包括自我更新、增殖和分化，但我们将专门研究卵巢癌启动细胞中导致耐药性的表观遗传事件；这些事件的逆转可能允许化疗耐药肿瘤干细胞的表观遗传再敏化。目标1的目标是识别与卵巢癌启动细胞的化疗耐药相关的DNA“甲基化特征”。我们将使用DNA甲基化的全基因组图谱，进一步检查40个以前被我们的团队确定为与无病生存相关的甲基化基因。在目标2中，一种高通量的表观遗传学分析，染色质免疫沉淀到微阵列杂交，将被用来识别卵巢癌启动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来自AIM 1的DNA甲基化数据相结合，将有助于识别导致卵巢癌启动细胞化疗耐药的途径。使用表观遗传学和常规药物直接靶向卵巢癌启动细胞是目标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负责传播整个肿瘤的卵巢癌启动细胞的致癌分化所必需的表观遗传抑制修饰，从而实现它们的直接治疗靶向。了解卵巢癌启动细胞中存在的表观遗传学事件将导致对这种毁灭性疾病的更全面的了解，并将为新的治疗靶点提供有价值的见解。这项建议对PA-05-086高度响应，基于其总体目标：建立卵巢癌干细胞表观类型，开发导致化疗耐药的改变途径的综合模型，并检查表观遗传疗法可能直接干扰这些细胞的活性。与公共健康相关：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会是，人们认为卵巢癌包含一小部分负责生长整个肿瘤的“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，使肿瘤重新生长。“表观遗传学”变化(DNA结构的变化)可能是表征卵巢癌干细胞的一种方式，而改变这些DNA结构变化的新药可能代表着一种针对这些细胞的新型治疗方法，使肿瘤得以完全杀死。

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.