ABSTRACT
Monocarboxylate transporter 1 (MCT1) inhibition is thought to block tumor growth through disruption of lactate transport and glycolysis. Here, we show MCT1 inhibition impairs proliferation of glycolytic breast cancer cells co-expressing MCT1 and MCT4 via disruption of pyruvate rather than lactate export. MCT1 expression is elevated in glycolytic breast tumors, and high MCT1 expression predicts poor prognosis in breast and lung cancer patients. Acute MCT1 inhibition reduces pyruvate export but does not consistently alter lactate transport or glycolytic flux in breast cancer cells that co-express MCT1 and MCT4. Despite the lack of glycolysis impairment, MCT1 loss-of-function decreases breast cancer cell proliferation and blocks growth of mammary fat pad xenograft tumors. Our data suggest MCT1 expression is elevated in glycolytic cancers to promote pyruvate export that when inhibited, enhances oxidative metabolism and reduces proliferation. This study presents an alternative molecular consequence of MCT1 inhibitors, further supporting their use as anti-cancer therapeutics.
Subject(s)
Breast Neoplasms/metabolism , Gene Expression Regulation, Neoplastic , Monocarboxylic Acid Transporters/genetics , Muscle Proteins/genetics , Pyruvic Acid/metabolism , Symporters/genetics , Animals , Antineoplastic Agents/pharmacology , Biological Transport , Breast Neoplasms/genetics , Breast Neoplasms/pathology , Cell Line, Tumor , Cell Proliferation/drug effects , Citric Acid Cycle/drug effects , Citric Acid Cycle/genetics , Epithelial Cells/drug effects , Epithelial Cells/metabolism , Epithelial Cells/pathology , Female , Gene Expression Profiling , Glycolysis/drug effects , Glycolysis/genetics , Humans , Lung Neoplasms/genetics , Lung Neoplasms/metabolism , Lung Neoplasms/pathology , Mice , Monocarboxylic Acid Transporters/antagonists & inhibitors , Monocarboxylic Acid Transporters/metabolism , Muscle Proteins/metabolism , Oxidative Phosphorylation/drug effects , Pyrimidinones/pharmacology , Signal Transduction , Symporters/antagonists & inhibitors , Symporters/metabolism , Thiophenes/pharmacology , Tumor Burden/drug effects , Xenograft Model Antitumor AssaysABSTRACT
OBJECTIVES: Dichloroacetate (DCA) is a highly bioavailable small molecule that inhibits pyruvate dehydrogenase kinase, promoting glucose oxidation and reversing the glycolytic phenotype in preclinical cancer studies. We designed this open-label phase II trial to determine the response rate, safety, and tolerability of oral DCA in patients with metastatic breast cancer and advanced stage non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: This trial was conducted with DCA 6.25 mg/kg orally twice daily in previously treated stage IIIB/IV NSCLC or stage IV breast cancer. Growth inhibition by DCA was also evaluated in a panel of 54 NSCLC cell lines with and without cytotoxic chemotherapeutics (cisplatin and docetaxel) in normoxic and hypoxic conditions. RESULTS AND CONCLUSIONS: Under normoxic conditions in vitro, single-agent IC50 was >2 mM for all evaluated cell lines. Synergy with cisplatin was seen in some cell lines under hypoxic conditions. In the clinical trial, after seven patients were enrolled, the study was closed based on safety concerns. The only breast cancer patient had stable disease after 8 weeks, quickly followed by progression in the brain. Two patients withdrew consent within a week of enrollment. Two patients had disease progression prior to the first scheduled scans. Within 1 week of initiating DCA, one patient died suddenly of unknown cause and one experienced a fatal pulmonary embolism. We conclude that patients with previously treated advanced NSCLC did not benefit from oral DCA. In the absence of a larger controlled trial, firm conclusions regarding the association between these adverse events and DCA are unclear. Further development of DCA should be in patients with longer life expectancy, in whom sustained therapeutic levels can be achieved, and potentially in combination with cisplatin.
