Investigation of the role of mitochondrial glucose metabolism related with HIF-1a in the hypoxic microenvironment of head and neck cancer cells

Introduction: Oral squamous cell carcinoma, highly aggressive malignant tumor, is sixth cancer worldwide and a subtype of head and neck cancers. The basic treatment methods of oral cavity cancer are surgery, radiotherapy and/or chemotherapy. Drug repositioning is a drug designing method in which available FDA-approved drugs are determined for their potent effects in different diseases especially cancer. In this context, Metformin, used in type 2 diabetes, and Dichloroacetate (DCA), used in lactic acidosis, are FDA approved drugs and have potential in cancer therapy for the effects on tumor metabolism. Objective: The aim of this study is to investigate the effects of Metformin and Dichloroacetate on cell viability, HIF-1α and PDK-1 expressions, and mitochondrial metabolism in the oral squamous cell carcinoma cell line (UPCI-SCC-131). Method: At first, UPCI-SCC-131 cells were treated with Metformin and Dichloroacetate at different concentrations for 72 hours under normoxic (20% O2, 37ﹾC) and hypoxic conditions (1% O2, 37ﹾC) and IC50 values were determined. The synergism of Metformin and DCA were analyzed with CompuSyn software. Gene and protein expression levels of HIF-1α and PDK-1 were examined by Real-Time PCR and Western Blot, respectively. In addition, the effects of drugs on metabolism were evaluated by Seahorse XF Analyzer. Results: The IC50 values of Metformin and Dichloroacetate under normoxic conditions were 4mM and 30mM; under hypoxic conditions were 14mM and 40mM, respectively. Combination index values in all combination groups (0.46-0.80) below 1 showed that Metformin and DCA in UPCI-SCC-131 cells had a synergistic effect on cell viability. After Metformin treatment, HIF-1α and PDK-1 mRNA expression levels did not change and protein expression levels decreased significantly in UPCI-SCC-131 cells. PDK-1 mRNA and protein expressions were significantly decreased in Dichloroacetate-treated cells. In addition, metabolic flow experiments showed that Metformin shifted cellular phenotype into glycolytic pathway and Dichloroacetate into the energetic pathway. Conclusion: We conclude that the data we have obtained will contribute to the development of new therapeutic combinations with anti-tumorigenic properties which targeted the oral squamous cell carcinoma metabolism in the future.