bplist00Ñ_WebMainResourceÕ _WebResourceData_WebResourceMIMEType^WebResourceURL_WebResourceFrameName_WebResourceTextEncodingNameOAbstract: Metabolic fluxes can serve as specific biomarkers for detecting malignant transformations, tumor progression and response to microenvironmental changes and treatment procedures. We present non-invasive 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 monocarboxylic 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 upregulation of the MCT1. These results suggest that hyperpolarized 13C1-Pyruvate may be a useful magnetic resonance biomarker of MCT regulation and malignant transformations in breast cancer. Ytext/html_Nfile:///Users/lucio/FilesWebPage/Frydman_group(latest)/Publications/abs94.htmlPUUTF-8 (:P_v”°º