ROS/PI3K/Akt and Wnt/beta-catenin signalings activate HIF-1 alpha-induced metabolic reprogramming to impart 5-fluorouracil resistance in colorectal cancer

Background: Acquired resistance of 5-fluorouracil (5-FU) remains a clinical challenge in colorectal cancer (CRC), and efforts to develop targeted agents to reduce resistance have not yielded success. Metabolic reprogramming is a key cancer hallmark and confers several tumor phenotypes including chemoresistance. Glucose metabolic reprogramming events of 5-FU resistance in CRC has not been evaluated, and whether abnormal glucose metabolism could impart 5-FU resistance in CRC is also poorly defined. Methods: Three separate acquired 5-FU resistance CRC cell line models were generated, and glucose metabolism was assessed by measuring glucose and lactate utilization, RNA and protein expressions of glucose metabolism-related enzymes and changes of intermediate metabolites of glucose metabolite pool. The protein levels of hypoxia inducible factor 1 alpha (HIF-1 alpha) in primary tumors and circulating tumor cells of CRC patients were detected by immunohistochemistry and immunofluorescence. Stable HIF1A knockdown in cell models was established with a lentiviral system. The influence of both HIF1A gene knockdown and pharmacological inhibition on 5-FU resistance in CRC was evaluated in cell models in vivo and in vitro. Results: The abnormality of glucose metabolism in 5-FU-resistant CRC were described in detail. The enhanced glycolysis and pentose phosphate pathway in CRC were associated with increased HIF-1 alpha expression. HIF-1 alpha-induced glucose metabolic reprogramming imparted 5-FU resistance in CRC. HIF-1 alpha showed enhanced expression in 5-FU-resistant CRC cell lines and clinical specimens, and increased HIF-1 alpha levels were associated with failure of fluorouracil analog-based chemotherapy in CRC patients and poor survival. Upregulation of HIF-1 alpha in 5-FU-resistant CRC occurred through non-oxygen-dependent mechanisms of reactive oxygen species-mediated activation of PI3K/Akt signaling and aberrant activation of beta-catenin in the nucleus. Both HIF-1 alpha gene knock-down and pharmacological inhibition restored the sensitivity of CRC to 5-FU. Conclusions: HIF-1 alpha is a potential biomarker for 5-FU-resistant CRC, and targeting HIF-1 alpha in combination with 5-FU may represent an effective therapeutic strategy in 5-FU-resistant CRC.