Advances in Brief In Vivo Monitoring of Capecitabine Metabolism in Human Liver by Fluorine Magnetic Resonance Spectroscopy at 1.5 and 3 Tesla Field Strength

In metastatic colorectal cancer the oral 5-fluorouracil (5FU) prodrug capecitabine is used with increasing frequency as an alternative to i.v. 5FU administration. The rate of conversion of capecitabine into 5 deoxy-5fluorouridine has been related to tumor response, and 5FU catabolites have been associated with 5FU-related systemic toxicity. Here we demonstrate for the first time that capecitabine, its metabolites 5 deoxy-5-fluorocytidine and 5 deoxy-5-fluorouridine, and its catabolites 5-fluoro-ureido-propionic acid, -fluoro-alanine, and -fluoro-alanine-bile acid conjugate can be monitored in vivo by fluorine magnetic resonance spectroscopy (F MRS) in the liver of patients with metastatic colorectal cancer. Moreover, we demonstrate an improved signal-to-noise ratio and spectral resolution of the F MRS spectra when measurements are performed at 3 T field strength as compared with measurements at the common clinical field strength of 1.5 T. We conclude that assessment of capecitabine metabolism in patients by F MRS is a promising noninvasive tool for the prediction of its efficacy and toxicity, especially at the now currently available clinical field strength of 3 T.