Genome-wide microRNA Analysis Identified Over-expression in Pancreatic Cancer Tissues as a Predictor of their Local Invasiveness.

[BACKGROUND/AIM] The severe malignancy of pancreatic ductal adenocarcinoma (PDAC) is mainly due to frequent local invasiveness and distant metastasis. As for local invasiveness, we previously reported that cancer-specific molecular alterations detected on resected PDAC specimen surfaces, so-called molecular surgical margin (MSM) positiveness, were significantly associated with postoperative locoregional recurrence and distant metastasis. However, due to anatomical limitations, achieving adequate surgical margins during pancreatic cancer resection is often challenging. Therefore, predicting local invasiveness based on the primary tumor's gene profile is crucial to avoid positive MSM.

[MATERIALS AND METHODS] Genome-wide miRNA expression profiles were examined and compared between MSM-positive and negative cases. Candidate miRNAs were evaluated in another validation cohort, and their clinicopathological characteristics were examined. Mimic or inhibitor constructs of the candidate miRNA were transfected to PDAC cell lines to evaluate the miRNA function in the pancreatic cancer cell lines and detect the downstream targets.

[RESULTS] Among some candidates with highly expressed miRNAs in MSM-positive cases by miRNA expression array, recurrence-free survival (RFS) was significantly shorter in the miR-210-3p high expression group (p=0.015). High miR-210-3p was significantly associated with large tumor diameter (p=0.001), anterior invasion positive (p=0.010), and positive lymph node metastasis (p<0.001). miR-210-3p inhibition in PDAC cell lines resulted in decreased proliferation and invasiveness. The iron-sulfur cluster assembly enzyme (ISCU) gene was identified as a target of miR-210-3p. ISCU reduction was significantly observed in PDAC primary tumors with high levels of miR-210-3p, leading to mitochondrial dysfunction in miR-210-3p-overexpressing PDAC cell lines, as demonstrated by glycolysis stress tests.

[CONCLUSION] Highly expressed hypoxia-inducible miR-210-3p in primary PDAC tissues induces locally invasive characteristics through mitochondrial dysfunction by suppressing ISCU expression, which may result in poor postoperative RFS outcomes.