MicroRNA-9 promotes tumorigenesis and mediates sensitivity to cisplatin in primary epithelial ovarian cancer cells

MicroRNAs play critical roles in regulating tumor occurrence and drug sensitivity in ovarian cancers. This study aimed to investigate the key members of MicroRNAs (miRNAs) involved in modulating tumor initiation and drug resistance in primary ovarian cancer cells. An in vitro assay based on tumor clonal formation was established to evaluate tumorigenicity and cisplatin sensitivity. By performing real-time polymerase chain reaction, we examined the expression of nine microRNAs associated with the pathology of ovarian cancers in primary ovarian tumor cells, which were surgically resected from 46 patients with distinct sensitivity to platinum-based chemotherapy. MiR-9, miR-145, and miR-429 were expressed significantly higher in drug-sensitive patients (n = 26) than in drug-resistant ones (n = 20), while higher miR-26a expression was found in resistant patients (p < 0.05). In addition, tumor cells from drug sensitive patients were more tumorigenic than those of drug resistance (p = 0.0013). Cisplatin treatment led to a sharp decrease of clonal formation of drug-sensitive cells but showed slight effects on drug resistant cells. Specific anti-miRs were then employed to downregulate the expression of microRNAs in primary tumor cells. Inhibition of miR-9 resulted in decreased clonal formation and sensitivity to cisplatin, while the knockdown of other three microRNAs did not show any influence in tumorigenesis and drug sensitivity. In conclusion, this study showed that in primary ovarian tumor cells, high expression of miR-9 was associated with enhanced tumorigenesis and increased sensitivity of the tumor cells to cisplatin treatment.