Purpose: To explore the effect of dihydropyrimidine dehydrogenase (DPD) single nucleotide polymorphisms (SNP) and haplotypes on outcome of capecitabine.Experimental Design: Germline DNA was available from 568 previously untreated patients with advanced colorectal cancer participating in the CAIRO2 trial, assigned to capecitabine, oxaliplatin, and bevacizumab AE cetuximab. The coding region of dihydropyrimidine dehydrogenase gene (DPYD) was sequenced in 45 cases with grade 3 or more capecitabine-related toxicity and in 100 randomly selected controls (cohort). Most discriminating (P < 0.1) or frequently occurring (>1%) nonsynonymous SNPs were analyzed in all 568 patients. SNPs and haplotypes were associated with toxicity, capecitabine dose modifications, and survival.Results: A total of 29 SNPs were detected in the case-cohort analysis, of which 8 were analyzed in all 568 patients. Of the patients polymorphic for DPYD IVS14þ1G>A, 2846A>T, and 1236G>A, 71% (5 of 7), 63% (5 of 8), and 50% (14 of 28) developed grade 3 to 4 diarrhea, respectively, compared with 24% in the overall population. All patients polymorphic for IVS14þ1G>A developed any grade 3 to 4 toxicity, including one possibly capecitabine-related death. Because of toxicity, a mean capecitabine dose reduction of 50% was applied in IVS14þ1G>A and 25% in 2846A>T variant allele carriers. Patients were categorized into six haplotype groups: one predicted for reduced (10%), and two for increased risks (41% and 33%) for severe diarrhea. Individual SNPs were not associated with overall survival, whereas one haplotype was associated with overall survival [HR (95% CI) ¼ 0.57 (0.35-0.95)].Conclusions: DPYD IVS14þ1G>A and 2846A>T predict for severe toxicity to capecitabine, for which patients require dose reductions. Haplotypes assist in selecting patients at risk for toxicity to capecitabine.

AIMSThe enzymatic activity of dihydropyrimidine dehydrogenase (DPD) and thymidylate synthase (TS) are important for the tolerability and efficacy of the fluoropyrimidine drugs. In the present study, we explored between-subject variability (BSV) and circadian rhythmicity in DPD and TS activity in human volunteers. METHODSThe BSVs in DPD activity (n = 20) in peripheral blood mononuclear cells (PBMCs) and in plasma, measured by means of the dihydrouracil (DHU) and uracil (U) plasma levels and DHU : U ratio (n = 40), and TS activity in PBMCs (n = 19), were examined. Samples were collected every 4 h throughout 1 day for assessment of circadian rhythmicity in DPD and TS activity in PBMCs (n = 12) and DHU : U plasma ratios (n = 23). In addition, the effects of genetic polymorphisms and gene expression on DPD and TS activity were explored. RESULTSPopulation mean (± standard deviation) DPD activity in PBMCs and DHU : U plasma ratio were 9.2 (±2.1) nmol mg À1 h À1 and 10.6 (±2.4), respectively. Individual TS activity in PBMCs ranged from 0.024 nmol mg À1 h À1 to 0.596 nmol mg À1 h À1 . Circadian rhythmicity was demonstrated for all phenotype markers. Between 00:30 h and 02:00 h, DPD activity in PBMCs peaked, while the DHU : U plasma ratio and TS activity in PBMCs showed trough activity. Peak-to-trough ratios for DPD and TS activity in PBMCs were 1.69 and 1.62, respectively. For the DHU : U plasma ratio, the peak-to-trough ratio was 1.43. WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• Fluoropyrimidine anticancer drugs target thymidylate synthase (TS) and are metabolized by dihydropyrimidine dehydrogenase (DPD).• Circadian rhythms in DPD and TS could provide a rationale for fluoropyrimidine chronotherapy.• However, fluoropyrimidine chronotherapy remains controversial because convincing pharmacological data supporting chronotherapy are lacking. WHAT THIS STUDY ADDS• Using mixed-effect modelling, a circadian rhythm of TS activity in peripheral blood mononuclear cells (PBMCs), with peak activity during the afternoon, was demonstrated.• DPD activity in PBMCs clearly showed circadian rhythmicity, with peak activity during the night. The DPD phenotype in human plasma revealed an opposite, but weak, circadian rhythm.