Mutations in exon 14 of dihydropyrimidine dehydrogenase and 5-Fluorouracil toxicity in Portuguese colorectal cancer patients

Abstract

Purpose: Dihydropyrimidine dehydrogenase is a critical enzyme in the catabolism of 5-Fluorouracil, a drug frequently used in cancer therapy. Patients with deficient dihydropyrimidine dehydrogenase activity are at risk of developing severe 5-Fluorouracil-associated toxicity. Genetic analysis of the gene coding for dihydropyrimidine dehydrogenase has shown that mutations in exon 14, especially the splice-site mutation IVS14ϩ1G3 A, were associated with dihydropyrimidine dehydrogenase enzymatic deficiency. Methods: We evaluated the frequency of mutations in exon 14 of dihydropyrimidine dehydrogenase (DPYD) gene in 73 unselected colorectal cancer patients treated with 5-Fluorouracil after surgery at a Portuguese Cancer Institute. Results: Sequencing the entire exon 14 allowed the detection of mutations in two of the 73 patients (2.7%), namely two of the eight (25%) patients who presented grade 3-4 toxicity after 5-Fluorouracil chemotherapy. One patient was heterozygous for the splice-site mutation IVS14ϩ1G3 A, whereas the second patient was heterozygous for a novel missense mutation 1845G3 T (E615D) in exon 14 of DPYD gene. Conclusion: We conclude that mutations in exon 14 of DPYD gene are responsible for a significant proportion of life-threatening toxicity to 5-Fluorouracil, and should therefore be excluded before its administration to cancer patients. Genet Med 2004:6(2):102-107. Key Words: DPYD mutations, dihydropyrimidine dehydrogenase, 5-FU toxicity, 5-FU catabolism, chemotherapy5-Fluorouracil (5-FU) is one of the most commonly used chemotherapeutic drugs for the treatment of malignant neoplasms, namely colorectal cancer. 5-FU is a pyrimidine analogue, giving rise to cytotoxic metabolites after metabolization by the pyrimidine pathways. One of them, the 5-fluorodUMP, inhibits thymidylate synthase, thus impairing DNA synthesis. Additional cytotoxic effects arise from 5-FU metabolites being incorporated into RNA and DNA. 1 Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-FU. It has been reported that more than 80% of the administered 5-FU is catabolized by DPD, 2-4 so the activity of this enzyme may be of paramount importance to predict the efficacy and toxicity of this drug. Deficiency in DPD enzyme activity has been correlated with considerable delay in 5-FU clearance from plasma. 4,5 The important role of DPD in 5-FU-based chemotherapy has been demonstrated in cancer patients with major deficiency of this enzyme's activity. These patients may present severe toxicity after the administration of 5-FU, including diarrhea, neutropenia, and neurotoxicity, and death may occasionally occur. 6 -9 Population studies suggested that, although total deficiency is rare, as many as 3% to 5% of the population may have low enzyme levels and thus be at increased risk of severe toxicity if treated with 5-FU. 10 Several of these patients are genotypically heterozygous for a mutant DPYD allele. [11][12][13][14][15][16] To date, more than 30 variant DPYD alleles have been identi...

Promoter methylation and large intragenic rearrangements of DPYD are not implicated in severe toxicity to 5-fluorouracil-based chemotherapy in gastrointestinal cancer patients

“…Previous observations confirmed the high specificity, positive and negative predictive values of this genetic analysis[6,14,30]. However, our previous analysis of 73 consecutive colorectal cancer patients detected exon 14 mutations in only two of eight cases with severe toxicity[29]. …”

“…All patients enrolled in this study were screened for DPYD exon 14 mutations by sequencing (including the exon 14 skipping mutation IVS14+1G > A), eight of which were included in a previous publication on unselected colorectal cancer patients[29]. This mutation was found in two patients (one previously reported) and both of them developed severe toxicity following 5-FU administration.…”

Translating DPYD Genotype into DPD Phenotype: Using the DPYD Gene Activity Score

“…Furthermore, a correlation between the DPYD*2A variant and reduced enzyme activity in peripheral blood mononuclear cells (PBMCs) was found in several ex vivo studies that confirmed decreased function of DPYD*2A [26,[28][29][30] and consequently an association was also found between DPYD*2A and reduction in fluoropyrimidine clearance in patients [31,32]. In numerous studies an association between DPYD*2A allele carriership and the increased risk of toxicity related to fluoropyrimidine treatment was confirmed [4,24,31,[33][34][35][36][37][38][39][40][41][42][43][44][45]. For example, in a meta-analysis by Terrazzino et al a strong correlation between the DPYD*2A allele and overall grade ≥3 toxicity was found (odds ratio 5.42, p < 0.001) [33].…”

“…Simultaneously, our work was [4,8,10,11,19,27,[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] DPYD*13 (rs55886062) [4,19,30,32,33,46,49,50] 0.5 c.2846A>T (rs67376798) [4,13,24,33,36,41,42,44,47] c.1236G>A/ HapB3 (rs56038477) [14,15,42,44,46,47,49,50,56] 1 DPYD*1 (wild-type)…”

Pharmacokinetic and Metabolism Determinants of Fluoropyrimidines and Oxaliplatin Activity in Treatment of Colorectal Patients

“…The frequency of low DPD enzymatic activity, indicating partial DPD deficiency, in the general population was initially estimated at between 3% and 5% [62]. Additional studies have shown significant variability among different ethnic subpopulations, showing that the prevalence of partial DPD deficiency is higher in Asian [63], Southwest Asian [64], African [65], American [66] than European and Caucasian Group [67,68].…”