Determination of plasma uracil as a screening for dihydropyrimidine dehydrogenase deficiency: clinical application in oncological treatments

AIMS

Treatment with dihydropyrimidines poses a significant risk of serious adverse reactions for patients with dihydropyrimidine dehydrogenase (DPD) deficiency. This study seeks to analyse the correlation between DPD deficiency and plasmatic uracil values in patients who are candidates for a fluoropyrimidine scheme. It also studies the incidence of adverse events (AEs) in patients with DPD deficiency established with plasmatic uracil determination.

METHODS

This was a retrospective observational study conducted in a tertiary level establishment from September 2020 to April 2021. Patients included were diagnosed with gastrointestinal tumours, were of good status, and were initiated into a fluoropyrimidine-based regimen. The incidence and grade of AEs, according Common Terminology Criteria for Adverse Events (CTCAE), were collected and compared in patients with and without DPD deficiency.

RESULTS

119 patients diagnosed with gastrointestinal cancer met the inclusion criteria. In 92 (77%) patients there was no DPD deficiency according to plasmatic uracil thresholds. In the group of patients without deficit, dose reductions oscillated between 10-25% (mean 17.4%). In the no DPD deficiency group, 43 (46%) patients experienced AEs. Patients who had a DPD deficiency according to plasmatic uracil measurements were started on a 5-fluorouracil (5-FU) regimen with a dose reduction of 15-50% (mean 35%). In this group, 12 patients (44%) experienced some AEs.

CONCLUSION

New research is needed to clarify the correlation between plasma uracil values and DPD deficiency to achieve an optimal balance between clinical benefit and toxicity.

[Review of methods for determination of dihydropyrimidine dehydrogenase and possible application in screening previous chemotheraphy with 5-fluorouracil]

5-fluorouracil (5-FU) and its prodrug capecitabine are one of the most commonly used chemotherapeutic drugs. DPD-deficient cancer patients may be at risk of severe and sometimes lethal toxicity after the administration of 5-FU. In 39-61% of the cases severe toxicity of 5-FU is caused by decreased DPD acivity. DPD is the initial and rate-limiting enzyme of the metabolism of pyrimidines. 80-90% of the administered 5-FU is catabolised by DPD. Mutation of the DPYD gene encoding DPD result in decreased enzyme activity--total (0.2% of population) or partial (3-5% of population). Determination of DPD activity can be used as a screening procedure to identify patients with a DPD deficiency, before the start of treatment with 5-FU. There are several methods for DPD activity determination: the detection of relevant DPYD gene single-nucleotide polymorphism (SNPs), measurement of the level of DPYDmRNA expression, the evaluation of DPD activity in PBMC, the measurement of uracil in plasma and urea, evaluation of the UH2/U (dihydrouracil/uracil) and THYH2/THY (dihydrothymine/tymine) ratio in plasma and urea, [2-C13]uracil breath test, the analysis of fluorouracil and dihydrofluorouracil in plasma after administered a test dose of fluorouracil and measurement of 2-fluoro-beta-alanine. So far more than 30 mutations of DPYD gene have been identified in patients with cancer. A large number of them limits introduction of simple genetic test, which could be used for detection of DPD deficiency. Therefore scientists in searching of the simplest, the cheapest and the most available technique for detection DPD deficiency, generally use methods associated with measurement of DPD activity.

Mutational spectrum of dihydropyrimidine dehydrogenase gene (DPYD) in the Tunisian population

Dihydropyrimidine dehydrogenase enzyme (DPD) deficiency is a pharmacogenetic syndrome leading to severe side-effects in patients receiving therapies containing the anticancer drug 5-fluorouracil (5-FU). The aim of this population study is to evaluate gene variations in the coding region of the dihydropyrimidine dehydrogenase gene (DPYD) in the Tunisian population. One hundred and six unrelated healthy Tunisian volunteers were genotyped by denaturing HPLC (DHPLC). Twelve variants in the coding region of the DPYD were detected. Allele frequencies of DPYD*5 (A1627G), DPYD*6 (G2194A), DPYD*9A (T85C), A496G, and G1218A were 12.7%, 7.1%, 13.7%, 5.7%, and 0.5%, respectively. The DPYD alleles DPYD*2A (IVS 14+1g>1), DPYD*3 (1897 del C) and DPYD*4 (G1601A) associated with DPD deficiency were absent from the examined subjects. We describe for the first time a new intronic polymorphism IVS 6-29 g>t, found in an allelic frequency of 4.7% in the Tunisian population. Comparing our data with that obtained in Caucasian, Egyptian, Japanese and African-American populations, we found that the Tunisian population resembles Egyptian and Caucasian populations with regard to their allelic frequencies of DPYD polymorphisms. This study describes for the first time the spectrum of DPYD sequence variations in the Tunisian population.