Kinetics of hyperpolarized ¹³C₁-pyruvate transport and metabolism in living human breast cancer cells
2009
Harris, Talia | Eliyahu, Galit | Frydman, Lucio | Degani, Hadassa
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.
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