Tracking leucine metabolism in prostate cancer cells via $^{\mathrm{13}}$C NMR spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy is relatively insensitive due to the weak magnetic moments of nuclei, especially those with low gyromagnetic ratio ($\gamma )$ such as $^{\mathrm{13}}$C ($\gamma =$ 10.705 MHz/T). Fortunately, a technique known as dynamic nuclear polarization (DNP) enhances the NMR signals by transferring the much higher electron ($\gamma =$ 28,000 MHz/T) polarization to nuclei. Furthermore, the invention of dissolution DNP in 2003 has expanded DNP's large signal enhancement (more than 10,000-fold) to the biomedical realm. Significantly, dissolution DNP allows real-time tracking of metabolism via labeling the relevant substrate with $^{\mathrm{13}}$C. This study examined the real-time prostate cancer cell enzyme kinetics involved in the metabolism of [1-$^{\mathrm{13}}$C] alpha-ketoisocaproate [$\alpha $-KIC] into [1-$^{\mathrm{13}}$C] leucine and vice versa. Results of \textit{in vitro} conventional 13C NMR of cell extracts and hyperpolarized 13C NMR of living prostate cancers cells will be discussed in the context of biochemical kinetics and possible diagnostic application.