Plasma microRNA profiles: identification of miR-744 as a novel diagnostic and prognostic biomarker in pancreatic cancer

Background: This study aims to explore novel microRNAs in plasma for screening cancer and predicting clinical outcomes in pancreatic cancer (PCa) patients using a microRNA array-based approach. Methods: We used the Toray 3D-Gene microRNA array-based approach to compare plasma levels between PCa patients and healthy volunteers. Results: (1) Six oncogenic microRNAs (miR-615-5p, -744, -575, -557, -675, and -550a) with high expression in plasma were selected. (2) By quantitative RT-PCR using plasma samples from 94 PCa patients and 68 healthy volunteers, a significantly higher level of plasma miR-744 in PCa patients than in healthy volunteers was validated in small-scale analysis (P = 0.0038), two independent cohort analyses, and large-scale analysis (Po0.0001, AUC 0.8307). (3) miR-744 expression was significantly higher in PCa tissues (P<0.0069) and PCa cell lines (P = 0.0074) than in normal tissues and fibroblasts, respectively. Preoperative plasma level of miR-744 was significantly reduced in postoperative samples (P = 0.0063). (4) A high level of plasma miR-744, which was correlated with lymph node metastasis (P = 0.0407) and recurrences (P = 0.0376), was an independent poor prognostic factor of PCa patients after pancreatectomy (P = 0.0007, HR 21.2 (3.17-436)). Furthermore, a high level of plasma miR-744 contributed to poorer progression-free survival of non-operable PCa patients who underwent gemcitabine-based chemotherapy (P = 0.0533). Overexpression of miR-744 in PCa cells induced significant chemoresistance to gemcitabine in vitro. Conclusions: Plasma miR-744 might be useful biomarker for screening PCa, monitoring, and predicting poor prognosis and chemoresistance in PCa patients.