Abstract 5476: Inhibiting lactate transporters MCT-1 and MCT-4 target hypoxic HNSCC cells and sensitize them to metformin
Authors: Boasquevisque Pedro H. , Schoeneberger Verena , Caporiccio Laura , Vellanki Ravi , Koritzinsky Marianne , Wouters Bradly G. 
Published: August 2018

Abstract
Head and neck squamous cell carcinoma (HNSCC) is treated primarily through a combination of surgery and radiation therapy. The problem of radioresistance, however, persists and requires new approaches to overcome it. Tumor hypoxia has been shown to be a driver of radioresistance, thereby prompting the targeting of the hypoxic niche, known to be highly glycolytic. Two key components of the hypoxic metabolic profile are lactate transporters MCT-1 and MCT-4, which sustain hypoxia-driven lactate production in cells. We hypothesize that inhibition of MCT-1 and MCT-4 will selectively target the growth of hypoxic tumor cells and potentially exert a synergistic effect with the antidiabetic drug metformin, a known inhibitor of mitochondrial respiration that has been shown to improve the radiation response. To study this, we employed CRISPR-Cas9 to genetically ablate both MCT-1 and MCT-4 in an HNSCC cell line. Validation of double knockout (DKO) cells was done through immunoblotting and sequencing. Cells were grown under conditions of 21% O2 (normoxia) in a regular CO2 incubator or 0.2% O2 (hypoxia) in an H45 HypOxystation® hypoxia chamber. Cell proliferation was measured under normoxia and hypoxia through the use of IncuCyte automated imaging while the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) of cells were measured using a Seahorse™ XF analyzer. Metabolic profiling of the DKO cells showed a higher rate of oxygen consumption and a decreased ability of exporting lactate, indicating a metabolic shift when lactate transport is impaired. The loss of MCT-1 and MCT-4 by themselves did not significantly alter cell proliferation under normoxic conditions, but disruption of both transporters concurrently significantly altered growth under normoxia. When exposed to hypoxia, proliferation of the DKO cells was completely halted. In addition, MCT-1/MCT-4 double knockouts showed greater inhibition of cell growth under metformin treatment than either single knockouts or wild-type cells. Significantly lower doses of metformin, which had no effect on the proliferation of wild-type or single knockout cells, were capable of impairing the growth of DKO cells under hypoxia. In conclusion, our study shows that inhibition of lactate export has a profound effect on cell growth under hypoxic conditions in vitro. Moreover, loss of lactate export enhances the sensitivity of HNSCC cells to metformin and could constitute a new way of targeting the hypoxic niche with the purpose of leading to better treatment outcomes.
Citation Format: Pedro H. Boasquevisque, Verena Schoeneberger, Laura Caporiccio, Ravi Vellanki, Marianne Koritzinsky, Bradly G. Wouters. Inhibiting lactate transporters MCT-1 and MCT-4 target hypoxic HNSCC cells and sensitize them to metformin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5476.