Hyperpolarized 13C MR spectroscopic imaging can be used to monitor Everolimus treatment in vivo in an orthotopic rodent model of glioblastoma

► We use hyperpolarized 13C MRSI to monitor mTOR-targeted therapy in glioblastoma. ► Hyperpolarized lactate-to-pyruvate ratio drops early following onset of treatment. ► Tumor volume remains unchanged until late time points during treatment. ► The drop in lactate-to-pyruvate ratio is associated with a drop in LDH levels. ► Lactate-to-pyruvate ratio is an early biomarker of drug target modulation.