Dihydropyrimidine dehydrogenase polymorphisms and fluoropyrimidine toxicity: ready for routine clinical application within personalized medicine?

Abstract

Fluoropyrimidines, including 5-fluorouracil (5-FU), are widely used in the treatment of solid tumors and remain the backbone of many combination regimens. Despite their clinical benefit, fluoropyrimidines are associated with gastrointestinal and hematologic toxicities, which often lead to treatment discontinuation. 5-FU undergoes complex metabolism, dihydropyrimidine dehydrogenase (DPD) being the rate-limiting enzyme of inactivation of 5-FU and its prodrugs. Several studies have demonstrated significant associations between severe toxicities by fluoropyrimidines and germline polymorphisms of DPD gene. To date, more than 30 SNPs and deletions have been identified within DPD, the majority of these variants having no functional consequences on enzymatic activity. However, the identification of deficient DPD genotypes may help identify poor-metabolizer patients at risk of developing potentially life-threatening toxicities after standard doses of fluoropyrimidines.

Fig. 1

Metabolic pathway of of 5-FU. 5-FdUMP/UDP/UTP: 5-fluorodeoxyuridine-mono/di/triphosphate; 5-FUMP/UDP/UTP: 5-fluorouridine-mono/di/triphosphate; 5-FUH₂: 5,6-dihydro-5-fluorouracil FUPA: α-fluoro-β-ureidopropionic acid; FBAL: α-fluoro-β-alanine; DPD: dihydropyrimidine dehydrogenase; TP: thymidine phosphorylase; TS: thymidylate synthase

Fig. 2

DPD-dependent inactivation of 5-FU and effects of DPD deficiency. For abbreviations, see Fig. 1

Fig. 3

Macroscopic appearance of a palmar region of a patient with severe hand foot syndrome

Fig. 4

Schematic representation of DPD gene structure and polymorphisms

Fig. 5

Proposed algorithm for screening DPD deficiency and dose adjustment in patients