Low expression of MYCN promotes cisplatin resistance by suppressing cisplatin-induced apoptosis in epithelial ovarian cancer.

Epithelial ovarian cancer (EOC) is the most common cause of gynecological cancer-associated mortality. Cisplatin is one of the most effective chemotherapeutic drugs used in EOC; however, its use can lead to relapse due to cisplatin resistance. MYCN sensitizes neuroblastoma to undergo cisplatin-induced apoptosis. However, to the best of our knowledge, there have been no studies to date on the association between MYCN and cisplatin resistance in EOC. Therefore, the present study assessed this association. Datasets from The Cancer Genome Atlas database were used. The overall survival (OS) of patients receiving platin-based therapy was analyzed using Kaplan-Meier Plotter software. RNA sequencing data of 300 patients with EOC were downloaded from cBioportal. The co-expressed genes were subjected to 'Kyoto Encyclopedia of Genes and Genomes' analysis using DAVID software. For gene set enrichment analysis, the expression matrix was separated according to the median expression of MYCN, which was selected for hallmark gene set enrichment. Immunohistochemistry was used to assess MYCN expression in EOC tissue. Western blotting was used to evaluate MYCN, p53, Bax and Bcl-2 protein expression levels in EOC cells. Cell viability and apoptosis were assessed using Cell Counting Kit-8 and flow cytometry, respectively. The results demonstrated that MYCN upregulation was associated with increased cisplatin sensitivity and prolonged OS of patients with EOC and patients receiving platin-based therapy. Cisplatin downregulated MYCN expression in cisplatin-sensitive, but not resistant, EOC cells. The genes co-expressed with MYCN were primarily involved in pathways involved in 'chemotherapeutic resistance' and 'apoptosis'. MYCN enriched the apoptosis and p53 signaling pathways in hallmark gene sets. Cells in which MYCN was knocked down demonstrated significantly increased cisplatin resistance; however, MYCN overexpression in cisplatin-resistant cells restored cisplatin sensitivity. Collectively, the present study demonstrated that MYCN downregulation promoted cisplatin resistance by suppressing cisplatin-induced apoptosis in EOC.