Tumor and Stem Cell Biology Changes in Pyruvate Metabolism Detected by Magnetic Resonance ImagingAre Linked toDNADamage andServe as aSensor of TemozolomideResponse inGlioblastomaCells

Recent findings show that exposure to temozolomide (TMZ), a DNA-damaging drug used to treat glioblastoma (GBM), can suppress the conversion of pyruvate to lactate. To understand themechanistic basis for this effect and its potential utility as a TMZ response biomarker, we compared the response of isogenic GBM cell populations differing only in expression of theDNA repair proteinmethyltransferase (MGMT), a TMZ-sensitivity determinant, after exposure to TMZ in vitro and in vivo. Hyperpolarized [1-C]-pyruvate–based MRI was used to monitor temporal effects on pyruvate metabolism in parallel with DNA-damage responses and tumor cell growth. TMZ exposure decreased conversion of pyruvate to lactate only in MGMT-deficient cells. This effect coincided temporally with TMZ-induced increases in levels of the DNA-damage response protein pChk1. Changes in pyruvate to lactate conversion triggered by TMZ preceded tumor growth suppression and were not associated with changes in levels of NADH or lactate dehydrogenase activity in tumors. Instead, they were associated with a TMZ-induced decrease in the expression and activity of pyruvate kinase PKM2, a glycolytic enzyme that indirectly controls pyruvate metabolism. PKM2 silencing decreased PK activity, intracellular lactate levels, and conversion of pyruvate to lactate in the same manner as TMZ, and Chk1 silencing blocked the TMZ-induced decrease in PKM2 expression. Overall, our findings showed how TMZ-induced DNA damage is linked through PKM2 to changes in pyruvate metabolism, and how these changes can be exploited by MRI methods as an early sensor of TMZ therapeutic response. Cancer Res; 74(23); 1–10. 2014 AACR.