转录因子C/EBPβ调控同源重组修复介导卵巢癌PARP抑制剂耐药的机制研究及靶向阻遏

卵巢癌最难治的高级别浆液性癌患者最终死于耐药，即使最具前景的靶向药物PARP抑制剂的维持治疗改善了患者的预后，但仍存在继发耐药、HRD阴性人群和铂耐药人群疗效欠佳等难题亟待解决。课题组延续前期研究成果，即从表观遗传角度由临床组织标本筛选出的调控一群卵巢癌耐药相关基因的关键调控因子C/EBPβ为科研突破口，大胆提出C/EBPβ调控同源重组修复介导铂耐药和PARP抑制剂交叉耐药的科学假说，系统阐明转录因子C/EBPβ以位点特异性的方式调控一群同源重组修复相关基因的表达，来发挥其作为“带头基因”的上游调控作用，从而为卵巢癌铂耐药和PARP抑制剂耐药的临床难题在理论上引入“无靶造靶”的概念，拓宽PARP抑制剂的适用人群，同时引入选择性复制溶瘤病毒构建技术，从应用角度出发探索一条有效清除卵巢癌耐药病灶的靶向基因治疗新途径，从而达到探索肿瘤耐药治疗新方法及解决腺病毒基因治疗关键技术障碍等多重目的。

High grade serous ovarian cancer (HGSOC), which accounts for 70% of ovarian cancer, is the fundamental cause of the poor prognosis and refractory of ovarian cancer. Although most patients are sensitive to initial platinum-based therapy, they eventually die of platinum resistance due to multiline chemotherapy. As much as half of HGSOC has homologous recombination deficiency (HRD) due to germline or somatic BRCA1 / 2 or associated HRD genes mutations, or epigenetic silence of BRCA1. In response to this feature, a new targeted drug, a poly- (ADP-ribose) polymerase (PARP) inhibitor, is able to induce synthetic lethality in HRD-positive tumors, thereby suppressing tumor recurrence and metastasis safely and effectively for a long term. Thus, PARPi have been approved by several guidelines for maintenance treatment of platinum-sensitive recurrent ovarian cancer. Nevertheless, the clinical application of PARP inhibitors still faces three important issues that need to be resolved: 1. Acquired resistance to PARP inhibitors; 2. Poor efficacy in HRD-negative populations; 3. Lack of efficiency in platinum-resistant populations. We previously put forward a bold idea of searching for the master regulators of chromatin reprogramming in isolated clinical specimens, and identified C/EBPβ, a transcription factor, acting as potential modulators by recruiting the methyltransferase DOT1L, can maintain an open chromatin state by H3K79 methylation of multiple drug-resistance genes, thereby augmenting the platinum resistance of tumor cells. To further identify C/EBPβ-regulated genes genome wide, we performed RNA-seq in two HRD negetive ovarian cancer cell lines upon C/EBPβ knockdown. The differential genes after depletion of C/EBPβ were significantly enriched in the HRR pathway including BRCA2, ATM, ATR and TOPBP1 genes through GO and KEGG pathway analysis, changes in any one of which could cause significant resistance to PARPi. These data suggested that C/EBPβ regulating HRR might be closely related to PARPi responses. Therefore, HRR pathway is a common mechanism which joint platinum resistance with PARP inhibitor resistance. Based on the preliminary unpublished data, we hypothesize that C/EBPβ regulates HRR and mediates the cross-drug resistance of platinum and PARP inhibitors, further illustrate how this transcription factor C/EBPβ plays its upstream regulatory role as a “master gene” to control the expression of a group of HRR related genes in a site-specific manner. If our hypotheses are true, with the C / EBPβ target, it is possible to provide “artificial targets” for clinical solutions of platinum-resistant or HRD-negative patients, and expand the benefits of PARP inhibitors to broader people. Ingeniously, when the results mentioned above is incorporated with the novel oncolysis adenovirus, which combined the characteristics of oncolysis with targeted gene amplication and constructed by ourself previously, tumor-selective replication of the E1A mutant adenovirus would activate the native adenovirus E3 promoters to express the shC/EBPβ preferentially in tumor cells thus shut down the C/EBPβ gene. We believe this targeting C/EBPβ gene therapy of ovarian cancer will shed the new light on the PARP inhibitor resistance of ovarian cancer, span the key technique barrier in adenovirus gene therapy and ultimately provide a new strategy to prevent the drug resistance of cancer.