Study Of The Mechanisms Of Chemotherapy Resistance Of Ovarian Cancer

Purpose1. To study the role of microRNAs on BRCAness of ovarian cancer.To validate the impact of miR-9on cisplatin resistance of ovarian cancer.2. To study the association between Dicer1expression and the prognosis of ovarian cancer.3. To investigate the association between ROS pathway and prognosis of serous ovarian cancer. To establish a ROS pathway focused score for prediction of prognosis in serous ovarian cancer.Methods1. microRN A library screening was used to find the exact miRs which could bind directly to the3’UTR of BRCA1. We overexpressed miR-9in vitro and in vivo to study the impacts of miR-9on cellular response to cisplatin. Functional homologous recombination assay was carried out to uncover the underlying mechanism.2. K-M analysis was carried out to discover the relationship between Dicerl expression and the prognosis of ovarian cancer in the public microarray database. IHC was conducted to detected the expression of Dicerl in our ovarian cancers tissue microarrays.3. A literature review was carried out to find all of the genes associated with ROS pathway. Kaplan-Meier log-rank P values were calculated to identify genes whose expression values showed a trend associated with overall survival (OS)(P<.15). A molecular score was generated based on the expression of these genes. Association of the score with OS was analyzed using Cox proportional hazards models. Results were validated in another gene expression microarray datasets. Results1. Through microRNA library screening, we found that miR-9binds directly to the3’UTR of BRCA1and downregulates its expression in ovarian cancer cells. Overexpression of miR-9impacts the cellular response to cisplatin in vitro and in vivo by decreasing the efficiency of homologous recombination. We also showed that the higher levels of miR-9were inversely correlated with BRCA1expression in ovarian cancer patients and were associated with better chemotherapy response and a favourable prognosis. Furthermore, consistent with a BRCA1-deficienct phenotype, miR-9enhanced sensitivity to a poly (ADP-ribose) polymerase (PARP) inhibitor both in vitro and in vivo without significant toxicity.2. Low Dicerl expression was associated with poor outcomes in patients with ovarian cancer. Downregulation of Dicerl expression improved cisplatin resistance in ovarian cancer cell.3. Based on our knowledge of ROS pathways and a literature review, we devised a set of179ROS genes. Kaplan-Meier log-rank P values were calculated and25genes were identified as candidate gens which was associated with ovarian cancer prognosis. Construction of a ROS pathway focused score based on these25genes. Improved survival was associated with higher ROS pathway focused score (P<.001), and result was reproduced in the validation datasets (P=.026). ROC curves indicated that the score outperformed the known clinical factors.Conclusion1. Taken together, our findings indicate that miR-9mediates the downregulation of BRCA1and impedes DNA damage repair. As a candidate therapeutic, miR-9may improve chemotherapeutic efficacy by increasing the sensitivity of cancer cells to DNA damage and may impact ovarian cancer therapy.2. Low Dicerl expression was associated with poor outcomes in patients with ovarian cancer. Downregulation of Dicerl expression improved cisplatin resistance in ovarian cancer cell.3. ROS pathway was associated with prognosis of serous ovarian cancer. The ROS pathway focused score can be used to predict outcomes in ovarian cancer patients.