Background: Pyruvate kinase M2 (PKM2) is a key glycolytic enzyme that regulates the Warburg effect and is necessary for tumor growth. However, its role in chemoresistance has not been fully elucidated. Methods: PKM2 expression was examined by immunohistochemistry in 205 tissue samples from thoracic esophageal squamous cell carcinoma patients who had undergone curative surgery (100 patients with surgery alone and 105 patients with preoperative chemotherapy). The relationship between PKM2 expression and clinicopathological factors, including chemotherapy response was examined. In vitro assays were performed to determine the mechanism of PKM2-related chemoresistance, using esophageal squamous cell carcinoma cell lines. Results: PKM2 expression significantly correlated with tumor cell differentiation, tumor depth, and tumor stage. Strong PKM2 expression significantly correlated with decreased survival rates and poor response to chemotherapy. In vitro assays showed that PKM2 inhibition significantly decreased cisplatin resistance and increased apoptosis. In siPKM2-transfected cells, pyruvate kinase activity paradoxically increased, followed by increased intracellular reactive oxygen species levels. The ratio of NADPH/NADP, which is an indicator of glucose influx into pentose phosphate pathway (PPP), significantly decreased in siPKM2-transfected cells upon cisplatin treatment compared with control cells. Conclusions: PKM2 expression is associated with esophageal squamous cell carcinoma chemoresistance. PKM2 inhibition can restore cisplatin sensitivity by inactivating PPP.
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