SUMMARY The rate of glycolytic metabolism changes during differentiation of human embryonic stem cells (hESCs) and reprogramming of somatic cells to pluripotency. However, the functional contribution of glycolytic metabolism to the pluripotent state is unclear. Here we show that naive hESCs exhibit increased glycolytic flux, MYC transcriptional activity, and nuclear N-MYC localization relative to primed hESCs. This status is consistent with the inner cell mass of human blastocysts, where MYC transcriptional activity and nuclear N-MYC levels are also higher than in primed hESCs. Reduction of glycolysis decreases self-renewal of naive hESCs and feeder-free primed hESCs, but not primed hESCs grown in feeder-supported conditions. Reduction of glycolysis in feeder-free primed hESCs also enhances neural specification. These findings reveal associations between glycolytic metabolism and human naive pluripotency and differences in the metabolism of feeder-/feeder-free cultured hESCs. They may also suggest methods for regulating self-renewal and initial cell fate specification of hESCs.

SUMMARY Differences in global levels of histone acetylation occur in normal and cancer cells, although the reason why cells regulate these levels has been unclear. Here we demonstrate a role for histone acetylation in regulating intracellular pH (pHi). As pHi decreases, histones are globally deacetylated by histone deacetylases (HDACs), and the released acetate anions are coexported with protons out of the cell by monocarboxylate transporters (MCTs), preventing further reductions in pHi. Conversely, global histone acetylation increases as pHi rises, such as when resting cells are induced to proliferate. Inhibition of HDACs or MCTs decreases acetate export and lowers pHi, particularly compromising pHi maintenance in acidic environments. Global deacetylation at low pH is reflected at a genomic level by decreased abundance and extensive redistribution of acetylation throughout the genome. Thus, acetylation of chromatin functions as a rheostat to regulate pHi with important implications for mechanism of action and therapeutic use of HDAC inhibitors.

SUMMARY 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, which 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.

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 NSCLC. Materials and Methods This trial was conducted with DCA 6.25 mg/kg orally twice daily in previously treated stage IIIB/IV non-small cell lung cancer (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 one 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.