Hyperthermia combined chemotherapy regulates energy metabolism of cancer cells under hypoxic microenvironment

Abstract

Objective: Oral squamous cell carcinoma (OSCC) represents one of the main types of head and neck malignant tumors with high incidence and mortality as well extremely poor prognosis. Hyperthermia (HT) shows great promises for tumor therapy. However it can promote autophagy in tumor microenvironment, which is found to serve as a surviving mechanism for cancer cells. Inhibiting autophagy has been considered as an adjuvant anti-cancer strategy. The present study investigated the role of HT-induced autophagy, while attempting to combine chemotherapy and autophagy blocking with HT in OSCC cells under hypoxia and starvation microenvironment.Materials and methods: HIF-1α and Beclin-1 expression in tissues was determined by immunohistochemistry in 80 OSCC sample pairs. The IC50 of CoCl2, YC-1 (an inhibitor of HIF-1α) and 3-MA (an inhibitor of autophagy) was detected by CCK-8. CoCl2 and complete culture medium without serum were used to achieve the hypoxic and nutrient deficient microenvironment, respectively. HT was performed by heating in a 42 ℃ water bath. The role of HT and YC-1,3-MA on autophagy in vitro were assessed by qRT-PCR and Western blot, and the secretion of high mobility group box1 (HMGB1) was determined by ELISA. The migration and apoptosis rates of cells were assessed by wound healing assay and flow cytometry.Results: We observed that HIF-1α and Beclin1 were highly expressed in OSCC tissues, which were correlated with more advanced malignancy features. CoCl2 could establish hypoxia microenvironment, induce HIF-1α expression with dose-dependence as well as promote cell migration in Cal-27 and SCC-15 cells. Notably, hyperthermia and hypoxia could activate the HIF-1α/BNIP3/Beclin1 signaling pathway and promote HMGB1 secretion, which triggered cytoprotective autophagy to counteract the hypoxia and starvation cellular stresses, as indicated by downregulation of p62 and light chain 3-II (LC3 II). Furthermore, we found that hyperthermia combined YC-1 and/or 3-MA suppressed autophagy and cell migration whereas facilitated cell apoptosis.Conclusion: The present study demonstrated that combined use of YC-1 and 3-MA might increase death of tumor cells in physiological and hyperthermia conditions, which could be relevant with the inhibition of autophagy in OSCC tumor cells under hypoxia microenvironment in vitro.