Kinetics of hyperpolarized 13C1-pyruvate transport and metabolism in living human breast cancer cells

Metabolic fluxes can serve as specific biomarkers for detecting malignant transformations, tumor progression, and response to microenvironmental changes and treatment procedures. We present noninvasive hyperpolarized 13C NMR investigations on the metabolic flux of pyruvate to lactate, in a well-controlled injection/perfusion system using T47D human breast cancer cells. Initial rates of pyruvate-to-lactate conversion were obtained by fitting the hyperpolarized 13C and ancillary 31P NMR data to a model, yielding both kinetic parameters and mechanistic insight into this conversion. Transport was found to be the rate-limiting process for the conversion of extracellular pyruvate to lactate with Km = 2.14 ± 0.03 mM, typical of the monocarboxylate transporter 1 (MCT1), and a Vmax = 27.6 ± 1.1 fmol·min−1·cell−1, in agreement with the high expression level of this transporter. Modulation of the environment to hypoxic conditions as well as suppression of cells' perfusion enhanced the rate of pyruvate-to-lactate conversion, presumably by up-regulation of the MCT1. Conversely, the addition of quercetin, a flavonoidal MCT1 inhibitor, markedly reduces the apparent rate of pyruvate-to-lactate conversion. These results suggest that hyperpolarized 13C1-pyruvate may be a useful magnetic resonance biomarker of MCT regulation and malignant transformations in breast cancer.