Pre-therapeutic assessment of plasma dihydrouracil/uracil ratio for predicting the pharmacokinetic parameters of 5-fluorouracil and tumor growth in a rat model of colorectal cancer.

We investigated the correlation between plasma ratio of dihydrouracil/uracil (UH2/Ura), a possible surrogate biomarker of hepatic dihydropyrimidine dehydrogenase (DPD) activity, and 5-fluorouracil (5-FU) treatment efficacy in rats with colorectal cancer (CRC). 5-FU pharmacokinetic and pharmacodynamic studies were performed using DPD circadian variation in rats with 1,2-dimethylhydrazine-induced CRC. By plotting tumor volume after 5-FU treatment against pre-therapeutic plasma UH2/Ura, we inferred a linear relationship (r(2)=0.988). 5-FU concentration fluctuations induced by DPD activity variation affected tumor volume. In CRC patients receiving proper dosing regimens, plasma UH2/Ura could be an indirect biomarker for predicting 5-FU treatment efficacy, tumor growth, and 5-FU doses.