The dihydrouracil/uracil ratio in plasma, clinical and genetic analysis for screening of dihydropyrimidine dehydrogenase deficiency in colorectal cancer patients treated with 5-fluorouracil

DPYD genetic polymorphisms in non-European patients with severe fluoropyrimidine-related toxicity: a systematic review

BACKGROUND

Pre-treatment DPYD screening is mandated in the UK and EU to reduce the risk of severe and potentially fatal fluoropyrimidine-related toxicity. Four DPYD gene variants which are more prominently found in Europeans are tested.

METHODS

Our systematic review in patients of non-European ancestry followed PRISMA guidelines to identify relevant articles up to April 2023. Published in silico functional predictions and in vitro functional data were also extracted. We also undertook in silico prediction for all DPYD variants identified.

RESULTS

In 32 studies, published between 1998 and 2022, 53 DPYD variants were evaluated in patients from 12 countries encompassing 5 ethnic groups: African American, East Asian, Latin American, Middle Eastern, and South Asian. One of the 4 common European DPYD variants, c.1905+1G>A, is also present in South Asian, East Asian and Middle Eastern patients with severe fluoropyrimidine-related toxicity. There seems to be relatively strong evidence for the c.557A>G variant, which is found in individuals of African ancestry, but is not currently included in the UK genotyping panel.

CONCLUSION

Extending UK pre-treatment DPYD screening to include variants that are present in some non-European ancestry groups will improve patient safety and reduce race and health inequalities in ethnically diverse societies.

Individualized Dosing of Fluoropyrimidine-Based Chemotherapy to Prevent Severe Fluoropyrimidine-Related Toxicity: What Are the Options?

Fluoropyrimidines are widely used in the treatment of several types of solid tumors. Although most often well tolerated, severe toxicity is encountered in ~ 20-30% of the patients. Individualized dosing for these patients can reduce the incidence of severe fluoropyrimidine-related toxicity. However, no consensus has been achieved on which dosing strategy is preferred. The most established strategy for individualized dosing of fluoropyrimidines is upfront genotyping of the DPYD gene. Prospective research has shown that DPYD-guided dose-individualization significantly reduces the incidence of severe toxicity and can be easily applied in routine daily practice. Furthermore, the measurement of the dihydropyrimidine dehydrogenase (DPD) enzyme activity has shown to accurately detect patients with a DPD deficiency. Yet, because this assay is time-consuming and expensive, it is not widely implemented in routine clinical care. Other methods include the measurement of pretreatment endogenous serum uracil concentrations, the uracil/dihydrouracil-ratio, and the 5-fluorouracil (5-FU) degradation rate. These methods have shown mixed results. Next to these methods to detect DPD deficiency, pharmacokinetically guided follow-up of 5-FU could potentially be used as an addition to dosing strategies to further improve the safety of fluoropyrimidines. Furthermore, baseline characteristics, such as sex, age, body composition, and renal function have shown to have a relationship with the development of severe toxicity. Therefore, these baseline characteristics should be considered as a dose-individualization strategy. We present an overview of the current dose-individualization strategies and provide perspectives for a future multiparametric approach.

Pharmacokinetics of continuous transarterial infusion of 5-fluorouracil in patients with advanced hepatocellular carcinoma

Numerous studies concerning hepatic arterial infusion chemotherapy (HAIC) have been conducted by adopting regimens containing 5-fluorouracil (FU), with a favourable efficacy compared with conventional transcatheter arterial chemoembolisation (TACE) treatment; however, the detailed mechanism of HAIC remains unclear. The present study aimed to evaluate peripheral concentration time curves of 5-FU administered through the hepatic artery, which may additionally explain the mechanism of action of HAIC. A total of 10 eligible patients underwent transcatheter arterial embolization and a 2-day HAIC treatment regimen using a folinic acid, fluorouracil and oxaliplatin regimen. Peripheral venous blood sampling was performed in each patient prior to infusion, and at 0, 0.5, 1, 1.5, 2, 5, 10, 15, 22 and 23 h following the start of infusion. The blood sample at 0 h was analysed for dihydropyrimidine dehydrogenase (DPD) levels by high performance liquid chromatography, and the rest of the samples were analysed for 5-FU by optimised liquid chromatography-mass spectrometry (LC-MS). The lower limit of quantification of optimised LC-MS for 5-FU was 5 ng/ml. The steady-state plasma concentration of 5-FU administered through the hepatic artery was achieved after 15 h. This concentration largely varied, ranging from 8.64-152.00 ng/ml. Optimised LC-MS may detect low concentrations of 5-FU. The steady-state concentration of 5-FU administered through the hepatic artery was achieved after 15 h. DPD levels were analysed through determining the ratio of plasma uracil (U) and dihydrouracil (UH2) by HPLC, and the results indicated a mild DPD deficiency in the patients with HCC. These results may provide a basis for the explanation of the clinical efficacy of HAIC, and to additionally optimise its efficacy.

Predicting 5-fluorouracil toxicity: DPD genotype and 5,6-dihydrouracil:uracil ratio

AIM

Decreased DPD activity is a major cause of 5-fluorouracil (5-FU) toxicity, but known reduced-function variants in the DPD gene (DPYD) explain only a part of DPD-related 5-FU toxicities. Here, we evaluated the baseline (pretherapeutic) plasma 5,6-dihydrouracil:uracil (UH2:U) ratio as a marker of DPD activity in the context of DPYD genotypes.

MATERIALS & METHODS

DPYD variants were genotyped and plasma U, UH2 and 5-FU concentrations were determined by liquid chromatography-tandem mass spectrometry in 320 healthy blood donors and 28 cancer patients receiving 5-FU-based chemotherapy.

RESULTS

Baseline UH2:U ratios were strongly correlated with generally low and highly variable U concentrations. Reduced-function DPYD variants were only weakly associated with lower baseline UH2:U ratios. However, the interindividual variability in the UH2:U ratio was reduced and a stronger correlation between ratios and 5-FU exposure was observed in cancer patients during 5-FU administration.

CONCLUSION

These results suggest that the baseline UH2:U plasma ratio in most individuals reflects the nonsaturated state of DPD and is not predictive of decreased DPD activity. It may, however, be highly predictive at increased substrate concentrations, as observed during 5-FU administration.

Translating DPYD genotype into DPD phenotype: using the DPYD gene activity score

The dihydropyrimidine dehydrogenase enzyme (DPD, encoded by the gene DPYD) plays a key role in the metabolism of fluoropyrimidines. DPD deficiency occurs in 4-5% of the population and is associated with severe fluoropyrimidine-related toxicity. Several SNPs in DPYD have been described that lead to absent or reduced enzyme activity, including DPYD*2A, DPYD*13, c.2846A>T and c.1236G>A/haplotype B3. Since these SNPs differ in their effect on DPD enzyme activity, a differentiated dose adaption is recommended. We propose the gene activity score for translating DPYD genotype into phenotype, accounting for differences in functionality of SNPs. This method can be used to standardize individualized fluoropyrimidine dose adjustments, resulting in optimal safety and effectiveness.

Indirect assessment of dihydropyrimidine dehydrogenase activity in cats

Use of 5-fluoropyridimine antimetabolite drugs, specifically 5-fluorouracil (5-FU), has been discouraged in cats because of adverse events including neurotoxicity and death. Causes of toxicity have never been elucidated. In humans, toxicity has been associated with ineffective metabolism secondary to deficiencies in dihydropyrimidine dehydrogenase (DPD). Direct assessment of DPD activity is challenging; determination of uracil:dihydrouracil (U:UH2 ) in plasma using high performance liquid chromatography (HPLC) has been reported as an indirect measurement. U:UH2 was measured in the plasma of 73 cats. Mean U:UH2 for all cats was 1.66 ± 0.11 (median 1.53, range 0.24-7.00). Seventeen (23%) cats had U:UH2 >2, a value associated with decreased DPD activity in humans. Spayed female cats had significantly lower U:UH2 as compared with intact females, and age and U:UH2 were weakly but significantly negatively correlated (r = -0.26). Studies correlating U:UH2 and 5-FU tolerability are required to further determine the validity and use of this test in cats.

Evaluation of predictive tests for screening for dihydropyrimidine dehydrogenase deficiency

5-Fluorouracil (5-FU) is rapidly degraded by dihyropyrimidine dehydrogenase (DPD). Therefore, DPD deficiency can lead to severe toxicity or even death following treatment with 5-FU or capecitabine. Different tests based on assessing DPD enzyme activity, genetic variants in DPYD and mRNA variants have been studied for screening for DPD deficiency, but none of these are implemented broadly into clinical practice. We give an overview of the tests that can be used to detect DPD deficiency and discuss the advantages and disadvantages of these tests.

The upregulation of dihydropyrimidine dehydrogenase in liver is involved in acquired resistance to 5-fluorouracil

BACKGROUND

Acquired resistance to 5-fluorouracil (5-FU) is one of the important reasons for failure in 5-FU-based chemotherapy. The upregulation of dihydropyrimidine dehydrogenase (DPD) in tumours was reported as an important factor for acquired 5-FU resistance. The aim of this study is to examine whether intra-hepatic DPD was involved in acquired 5-FU resistance.

METHODS

HT-29 human colorectal xenograft tumours were established in nude mice. After long-term exposure to 5-FU, some of the tumour became "resistant" and the others remained "sensitive" to 5-FU. DPD expression levels in the livers and tumours of "resistant", "sensitive" or untreated mice were examined, and pharmacokinetics of 5-FU in rats' plasma were investigated. Gimeracil, a DPD inhibitor, was checked whether it could reverse the reduced bioavailability of 5-FU.

RESULTS

DPD expression was upregulated obviously in tumours of "resistant" mice as reported previously. Importantly, DPD expression was also upregulated significantly in livers of "resistant" mice, compared with those of "sensitive" or untreated mice. Furthermore, the upregulation of DPD expression in livers led to accelerated metabolism of 5-FU. Gimeracil was found to reverse the reduced serum 5-FU concentration. The cultured tumour cells from 5-FU treated mice showed relative sensitivity to higher concentration of 5-FU, even the "resistant" tumour cells.

CONCLUSION

Our study suggested that the upregulation of DPD in liver may be involved in acquired resistance to 5-FU, and DPD inhibitors or increasing 5-FU dosage may have potential application in overcoming 5-FU acquired resistance.

A rapid HPLC-ESI-MS/MS method for determination of dihydrouracil/uracil ratio in plasma: evaluation of toxicity to 5-flurouracil in patients with gastrointestinal cancer

BACKGROUND

A liquid chromatography-tandem mass spectrometry method for the simultaneous quantitation of endogenous uracil (U) and dihydrouracil (UH2) was developed and tested in a Brazilian population of patients with gastrointestinal cancer previously exposed to 5-fluorouracil (5FU).

METHODS

The analytes were extracted by a liquid-liquid method using 5-clorouracil as internal standard. The separation was performed on a reversed-phase XTerra C18 column with a mobile phase composed of methanol and aqueous 0.1% ammonium hydroxide (15:85). Mass spectrometry detection was carried out using negative electrospray ionization and selected reaction monitoring. Bovine serum albumin was employed as an alternative matrix to prepare the calibration standards, aiming to avoid the measurement of physiologic U and UH2. Calibration curves were constructed over the range of 5-200 ng/mL for U and 10-500 ng/mL for UH2.

RESULTS

The mean RSD values in the intrarun precision were 6.5% and 10.0% and in the interrun precision were 7.8% and 9.0% for U and UH2, respectively. The mean accuracy values were within the range of 90%-110% for both analytes. The analytes were stable in plasma under different conditions of temperature and time. The validated method was successfully applied to determine the plasma concentrations of U and UH2 in patients with gastrointestinal cancer (n = 32) previously treated with 5FU and for whom clinical toxicity was well documented. U concentrations varied from 21.8 to 56.6 ng/mL, whereas UH2 concentrations varied from 57.7 to 271.5 ng/mL. UH2/U ratio ranged from 1.56 to 6.18.

CONCLUSIONS

The method has proved to provide a quick, reliable, and reproducible quantitation of the plasma concentrations of U and its metabolite UH2. The UH2/U ratios did not discriminate patients previously exposed to 5FU with and without severe toxicities, possibly due to the small sample. Further studies in a larger population are desirable.

Assessment of plasma uracil-to-dihydrouracil concentration ratio as an indicator of dihydropyrimidine dehydrogenase activity in clinically normal dogs and dogs with neoplasia or renal insufficiency

OBJECTIVE

To determine and compare the ratio of uracil (U) to dihydrouracil (UH(2)) concentrations in plasma as an indicator of dihydropyrimidine dehydrogenase activity in clinically normal dogs and dogs with neoplasia or renal insufficiency.

ANIMALS

101 client- and shelter-owned dogs.

PROCEDURES

Study dogs included 74 clinically normal dogs, 17 dogs with neoplasia, and 10 dogs with renal insufficiency. For each dog, a blood sample was collected into an EDTA-containing tube; plasma U and UH(2) concentrations were determined via UV high-performance liquid chromatography, and the U:UH(2) concentration ratio was calculated. Data were compared among dogs grouped on the basis of sex, clinical group assignment, reproductive status (sexually intact, spayed, or castrated), and age.

RESULTS

Mean ± SEM U:UH(2) concentration ratio for all dogs was 1.55 ± 0.08 (median, 1.38; range, 0.4 to 7.14). In 14 (13.9%) dogs, the U:UH(2) concentration ratio was considered abnormal (ie, > 2). Overall, mean ratio for sexually intact dogs was significantly higher than that for neutered dogs; a similar difference was apparent among males but not females. Dogs with ratios > 2 and dogs with ratios ≤ 2 did not differ significantly with regard to sex, clinical group, reproductive status, or age.

CONCLUSIONS AND CLINICAL RELEVANCE

Determination of the U:UH(2) concentration ratio was easy to perform. Ratios were variable among dogs, possibly suggesting differences in dihydropyrimidine dehydrogenase activity. However, studies correlating U:UH(2) concentration ratio and fluoropyrimidine antimetabolite drug tolerability are required to further evaluate the test's validity and its appropriate use in dogs.

Severe fluoropyrimidine-related toxicity: clinical implications of DPYD analysis and UH2/U ratio evaluation

The fluoropyrimidines are commonly used in chemotherapeutic cancer medicine, but many patients still experience severe adverse side effects from these drugs. We observed a severe toxicity in a 50-year-old woman treated with capecitabine and docetaxel for a metastatic breast cancer. Since dihydropyrimidine dehydrogenase (DPD) is the main candidate for pharmacogenetic studies on 5-FU toxicity, the entire coding sequence and exon-flanking intronic regions of the DPYD gene were sequenced in the patient. None of the previously described deleterious variants were detected. Also, the haplotype-based analysis failed to reveal DPYD variations associated with 5-FU toxicity. We also evaluated the UH2/U ratio in plasma as an index of 5-FU pharmacokinetics. The UH2/U value did not demonstrate low DPD activity in the patient. We discuss the advantages and limitations of this approach, particularly concerning the clinical applications of 5-FU pharmacogenetics in the family setting.

Pharmacokinetics of orally administered uracil in healthy volunteers and in DPD-deficient patients, a possible tool for screening of DPD deficiency

Purpose

Dihydropyrimidine dehydrogenase (DPD) deficiency can lead to severe toxicity in patients treated with standard doses of 5-fluorouracil (5-FU). Oral uracil administration and subsequent measurement of uracil and dihydrouracil (DHU) plasma concentrations might detect patients with DPD deficiency. This study compares the pharmacokinetics of uracil and DHU after oral uracil administration in subjects with normal and deficient DPD status.

Methods

Five hundred milligrams of uracil per metre square was administered orally to 11 subjects with normal DPD status and to 10 subjects with reduced DPD activity. Repeated administration (n = 3) of this dose was performed in 4 subjects, and 1,000 mg uracil/m² was administered to 4 subjects to assess intra-individual variation and linearity of pharmacokinetics.

Results

In subjects with normal DPD status, 500 mg/m² uracil resulted in uracil C_max levels of 14.4 ± 4.7 mg/L at T_max = 30.0 ± 11.6 min, and in DPD-deficient subjects, 20.0 ± 4.5 mg/L at 31.5 ± 1.1 min. The uracil AUC_0>180 was 31.2 ± 5.1 mg L/h in DPD-deficient subjects, which was significantly higher (P < 0.05) than in the subjects with normal DPD status (13.8 ± 3.9 mg L/h). Repeated uracil dosing showed reproducible uracil PK in subjects with normal DPD status, and dose elevation of uracil suggested linear pharmacokinetics.

Conclusion

The pharmacokinetics of uracil differs significantly between subjects with a normal DPD activity and those with a deficient DPD status. The AUC and C_max of uracil can be useful as a diagnostic tool to differentiate patients with regard to DPD status.

Strong association of a common dihydropyrimidine dehydrogenase gene polymorphism with fluoropyrimidine-related toxicity in cancer patients

Background

Cancer patients carrying mutations in the dihydropyrimidine dehydrogenase gene (DPYD) have a high risk to experience severe drug-adverse effects following chemotherapy with fluoropyrimidine drugs such as 5-fluorouracil (5-FU) or capecitabine. The pretreatment detection of this impairment of pyrimidine catabolism could prevent serious, potentially lethal side effects. As known deleterious mutations explain only a limited proportion of the drug-adverse events, we systematically searched for additional DPYD variations associated with enhanced drug toxicity.

Methodology/Principal Findings

We performed a whole gene approach covering the entire coding region and compared DPYD genotype frequencies between cancer patients with good (n = 89) and with poor (n = 39) tolerance of a fluoropyrimidine-based chemotherapy regimen. Applying logistic regression analysis and sliding window approaches we identified the strongest association with fluoropyrimidine-related grade III and IV toxicity for the non-synonymous polymorphism c.496A>G (p.Met166Val). We then confirmed our initial results using an independent sample of 53 individuals suffering from drug-adverse-effects. The combined odds ratio calculated for 92 toxicity cases was 4.42 [95% CI 2.12–9.23]; p (trend)<0.001; p (corrected) = 0.001; the attributable risk was 56.9%. Comparing tumor-type matched sets of samples, correlation of c.496A>G with toxicity was particularly present in patients with gastroesophageal and breast cancer, but did not reach significance in patients with colorectal malignancies.

Conclusion

Our results show compelling evidence that, at least in distinct tumor types, a common DPYD polymorphism strongly contributes to the occurrence of fluoropyrimidine-related drug adverse effects. Carriers of this variant could benefit from individual dose adjustment of the fluoropyrimidine drug or alternate therapies.