Therapeutics, Targets, and Chemical Biology MEK1/2 Inhibition Decreases Lactate in BRAF-Driven Human Cancer Cells

The RAS/BRAF/MEK/ERK signaling pathway is a central driver in cancer withmany BRAF andMEK inhibitors being evaluated in clinical trials. Identifying noninvasive biomarkers of early pharmacodynamic responses is important for development of these targeted drugs. As increased aerobic glycolysis is often observed in cancer, we hypothesized that MEK1/2 (MAP2K1/MAP2K2) inhibitors may reduce lactate levels as detected by magnetic resonance spectroscopy (MRS), as a metabolic biomarker for the pharmacodynamic response. MRS was used to monitor intracellular and extracellular levels of lactate in human cancer cells in vitro and inmelanoma tumors ex vivo. In addition, we used H MRS and a fluorescent glucose analog to evaluate the effect of MEK inhibition on glucose uptake. MEK1/2 signaling inhibition reduced extracellular lactate levels in BRAF-dependent cells but not BRAF-independent cells. The reduction in extracellular lactate in BRAF-driven melanoma cells was timedependent and associated with reduced expression of hexokinase-II driven by c-Myc depletion. Taken together, these results reveal how MEK1/2 inhibition affects cancer cell metabolism in the context of BRAF oncogene addiction. Furthermore, they offer a preclinical proof-of-concept for the use of MRS to measure lactate as a noninvasive metabolic biomarker for pharmacodynamic response toMEK1/2 inhibition in BRAF-driven cancers. Cancer Res; 73(13); 4039–49. 2013 AACR.