Quantitative impact of pre-analytical process on plasma uracil when testing for dihydropyrimidine dehydrogenase deficiency

DPYD genotype should be extended to rare variants: report on two cases of phenotype / genotype discrepancy

The enzyme dihydropyrimidine dehydrogenase (DPD) is the primary catabolic pathway of fluoropyrimidines including 5 fluorouracil (5FU) and capecitabine. Cases of lethal toxicity have been reported in cancer patients with complete DPD deficiency receiving standard dose of 5FU or capecitabine. DPD is encoded by the pharmacogene DPYD in which more than 200 variants have been identified. Different approaches have been developed for screening DPD-deficiency, including DPYD genotyping and phenotyping. Plasma uracil ([U]) and dihydrouracil ([UH2]) concentrations are routinely used as surrogate markers for systemic DPD activity: [U] ≥ 16 ng/ml and < 150 ng/ml, and [U] ≥ 150 ng/mL indicate partial and complete DPD deficient phenotype, respectively, while values of 5 or 10 for [UH2]/([U] ratio are often cited. Four clinically relevant DPYD defective variants (DPYD*13, DPYD*2A, p.Asp949Val and haplotype B3), are targeted in genetic testing via PCR. In practice, pretreatment [U], alone or combined with these 4 recommended DPYD alleles guides individual dosage selection, though this approach has limitations. This is illustrated by two cases showing discrepancy between DPD deficient phenotype and normal standard genotype. In these two cases, DPYD exome sequencing with Next Generation Sequencing identified rare inactive variants, establishing concordance between phenotype and genotype. In patient 1, [U] levels of 21.1 and 25.5 ng/mL, indicated partial deficiency though the targeted genotype was normal and 5FU dose was adjusted based on the phenotype. In patient 2, [U] levels of 16.2 and 15.2 ng/mL were near the 16 ng/ml threshold. With a normal genotype, he as considered non-deficient as targeted genotype was normal and the standard dose was administered. These two cases underscore the need to pair DPD phenotyping with whole DPYD gene sequencing, due to the frequent discrepancies between these pharmacogenetic tools, the burden of rare variants and ethnic differences in variant frequencies.

Plasma clearance of 5-fluorouracil is more influenced by variations in glomerular filtration rate than by uracil concentration

OBJECTIVES

The use of plasma uracil measurements to detect dihydropyrimidine dehydrogenase (DPD) deficiency is one of the methods for preventing toxicities associated with fluoropyrimidines, including 5-Fluorouracil (5-FU). Unfortunately, this measurement is subject to variations, that may lead to unnecessary dosage reductions and therefore to a reduced efficacy of treatment. Recently, new factors such as hepatic and renal impairment have been proposed as also influencing uracil concentration. The aim of our study was therefore to study the influence of renal or hepatic function on 5-FU clearance.

PATIENTS AND METHODS

This was a retrospective study, using patients treated with 5-FU between September 1, 2018 to December 1, 2022 in a French Clinical Cancer Center. Patients were included after treatment with 5FU and therapeutic monitoring of 5FU concentrations after each course of chemotherapy. For each patient, DPD phenotyping by uracil concentration measurement was determined before the first course of 5FU. Blood samples were then taken the day after the start of the 5-FU infusion, between 8 and 10 am, for the first three cycles of 5-FU. With the exception of uracil concentration, which was determined only once, the various data were recorded for each course of 5FU chemotherapy performed. Patients with incomplete information (missing one of the above parameters) were excluded from the database.

RESULTS

We included 227 patients, corresponding to 227 uracil concentrations and 575 5-FU concentrations. In an original development, our results show for the first time that 5-FU clearance was proportionally correlated with eGFR (calculated according to CKD-EPI formula). Although we failed to demonstrate this hypothesis significantly, we observed that 5-FU clearance may be more dependent on eGFR than on uracil concentration for low uracil concentrations values.

CONCLUSION

Our study reinforces the still poorly accepted idea of the value of focusing on eGFR in 5-FU dose adjustment.

Can we identify patients carrying targeted deleterious DPYD variants with plasma uracil and dihydrouracil? A GPCO-RNPGx retrospective analysis

OBJECTIVES

Dihydropyrimidine dehydrogenase (DPD) deficiency is the main cause of severe fluoropyrimidine-related toxicities. The best strategy for identifying DPD-deficient patients is still not defined. The EMA recommends targeted DPYD genotyping or uracilemia (U) testing. We analyzed the concordance between both approaches.

METHODS

This study included 19,376 consecutive French patients with pre-treatment plasma U, UH2 and targeted DPYD genotyping (*2A, *13, D949V, *7) analyzed at Eurofins Biomnis (2015-2022).

RESULTS

Mean U was 9.9 ± 10.1 ng/mL (median 8.7, range 1.6-856). According to French recommendations, 7.3 % of patients were partially deficient (U 16-150 ng/mL) and 0.02 % completely deficient (U≥150 ng/mL). DPYD variant frequencies were *2A: 0.83 %, *13: 0.17 %, D949V: 1.16 %, *7: 0.05 % (2 homozygous patients with U at 22 and 856 ng/mL). Variant carriers exhibited higher U (median 13.8 vs. 8.6 ng/mL), and lower UH2/U (median 7.2 vs. 11.8) and UH2/U2 (median 0.54 vs. 1.37) relative to wild-type patients (p<0.00001). Sixty-six% of variant carriers exhibited uracilemia <16 ng/mL, challenging correct identification of DPD deficiency based on U. The sensitivity (% patients with a deficient phenotype among variant carriers) of U threshold at 16 ng/mL was 34 %. The best discriminant marker for identifying variant carriers was UH2/U2. UH2/U2<0.942 (29.7 % of patients) showed enhanced sensitivity (81 %) in identifying deleterious genotypes across different variants compared to 16 ng/mL U.

CONCLUSIONS

These results reaffirm the poor concordance between DPD phenotyping and genotyping, suggesting that both approaches may be complementary and that targeted DPYD genotyping is not sufficiently reliable to identify all patients with complete deficiency.

Case report: A case of severe capecitabine toxicity due to confirmed in trans compound heterozygosity of a common and rare DPYD variant

Variations in the activity of the enzyme dihydropyrimidine dehydrogenase (DPD) are associated with toxicity to fluoropyrimidine-containing chemotherapy. Testing of DPD deficiency either by targeted genotyping of the corresponding DPYD gene or by quantification of plasma concentration of uracil and dihydrouracil (phenotyping approach) are the two main methods capable of predicting reduced enzymatic activity in order to reduce adverse reactions after fluoropyrimidine treatment. In this paper, we describe a patient with locally advanced colon carcinoma with severe toxicity following capecitabine therapy. Whereas targeted genotyping for the 4 most common DPYD variants analysis revealed heterozygous presence of the c.2846A>T variant, which is a relatively common variant associated with a partial deficiency, additional phenotyping was compatible with a complete DPD deficiency. Subsequent sequencing of the whole DPYD gene revealed the additional presence of the rare c.2872A>G variant, which is associated with a total loss of DPD activity. A clinical case of in trans compound heterozygosity of a common and a rare DPYD variant (c.2846A>T and c.2872A>G) has, to the best of our knowledge, not been previously described. Our case report shows the importance of performing either preemptive phenotyping or preemptive complete genetic analysis of the DPYD gene for patients planned for systemic fluoropyrimidines to identify rare and low frequency variants responsible for potentially life-threatening toxic reactions.

Complete DPYD genotyping combined with dihydropyrimidine dehydrogenase phenotyping to prevent fluoropyrimidine toxicity: A retrospective study

INTRODUCTION

In April 2019, French authorities mandated dihydropyrimidine dehydrogenase (DPD) screening, specifically testing uracilemia, to mitigate the risk of toxicity associated with fluoropyrimidine-based chemotherapy. However, this subject is still of debate as there is no consensus on a standardized DPD deficiency screening test. We conducted a real-life retrospective study with the aim of assessing the impact of DPD screening on the occurrence of severe toxicity and exploring the potential benefits of complete genotyping using next-generation sequencing.

METHODS

All adult patients consecutively treated with 5-fluorouracil (5-FU) or its oral prodrug at six cancer centers between March 2018 and February 2019 were considered for inclusion. Dihydropyrimidine dehydrogenase deficiency screening included gene encoding DPD (DPYD) genotyping using complete genome sequencing and DPD phenotyping (uracilemia or dihydrouracilemia/uracilemia ratio) or both tests. Associations between each DPD screening method and (i) severe (grade ≥3) early toxicity and (ii) fluoropyrimidine dose reduction in the second chemotherapy cycle were evaluated using multivariable logistic regression analysis. Furthermore, we assessed the concordance between DPD genotype and phenotype using Cohen's kappa.

RESULTS

A total of 551 patients were included. Most patients were tested for DPD deficiency (86%) including DPYD genotyping only (6%), DPD phenotyping only (8%), or both (72%). Complete DPD deficiency was not detected in the study population. Severe early toxicity events were observed in 73 patients (13%), with two patients (0.30%) presenting grade 5 toxicity. Despite the numerically higher toxicity rate in untested patients, the occurrence of severe toxicity was not significantly associated with the DPD screening method (p = 0.69). Concordance between the DPD genotype and phenotype was weak (Cohen's kappa of 0.14).

CONCLUSION

Due to insufficient numbers, our study was not able to demonstrate any added value of DPYD genotyping using complete genome sequencing to prevent 5-FU toxicity. The optimal strategy for DPD screening before fluoropyrimidine-based chemotherapy requires further clinical evaluation.

Case report: 5-Fluorouracil treatment in patient with an important partial DPD deficiency

Esophageal cancer is a cancer with poor prognosis and the standard 1^st line treatment for metastatic or recurrent EC is systemic chemotherapy with doublet chemotherapy based on platinum and 5-fluorouracil (5-FU). However, 5-FU could be a source of severe treatment-related toxicities due to deficiency of dihydropyrimidine dehydrogenase (DPD). In this case report, a 74-year-old man with metastatic esophageal cancer was found to have partial DPD deficiency based on uracilemia measurements (about 90 ng/mL). Despite this, 5-FU was safely administered thanks to therapeutic drug monitoring (TDM). The case report highlights the importance of TDM in administering 5-FU to patients with partial DPD deficiency, as it allows individualized dosing and prevents severe toxicity.

Impact of renal impairment on dihydropyrimidine dehydrogenase (DPD) phenotyping

BACKGROUND

The chemotherapeutic agent 5-fluorouracil (5-FU) is catabolized by dihydropyrimidine dehydrogenase (DPD), the deficiency of which may lead to severe toxicity or death. Since 2019, DPD deficiency testing, based on uracilemia, is mandatory in France and recommended in Europe before initiating fluoropyrimidine-based regimens. However, it has been recently shown that renal impairment may impact uracil concentration and thus DPD phenotyping.

PATIENTS AND METHODS

The impact of renal function on uracilemia and DPD phenotype was studied on 3039 samples obtained from three French centers. We also explored the influence of dialysis and measured glomerular filtration rate (mGFR) on both parameters. Finally, using patients as their own controls, we assessed as to what extent modifications in renal function impacted uracilemia and DPD phenotyping.

RESULTS

We observed that uracilemia and DPD-deficient phenotypes increased concomitantly to the severity of renal impairment based on the estimated GFR, independently and more critically than hepatic function. This observation was confirmed with the mGFR. The risk of being classified 'DPD deficient' based on uracilemia was statistically higher in patients with renal impairment or dialyzed if uracilemia was measured before dialysis but not after. Indeed, the rate of DPD deficiency decreased from 86.4% before dialysis to 13.7% after. Moreover, for patients with transient renal impairment, the rate of DPD deficiency dropped dramatically from 83.3% to 16.7% when patients restored their renal function, especially in patients with an uracilemia close to 16 ng/ml.

CONCLUSIONS

DPD deficiency testing using uracilemia could be misleading in patients with renal impairment. When possible, uracilemia should be reassessed in case of transient renal impairment. For patients under dialysis, testing of DPD deficiency should be carried out on samples taken after dialysis. Hence, 5-FU therapeutic drug monitoring would be particularly helpful to guide dose adjustments in patients with elevated uracil and renal impairment.

Current diagnostic and clinical issues of screening for dihydropyrimidine dehydrogenase deficiency

Fluoropyrimidine drugs (FP) are the backbone of many chemotherapy protocols for treating solid tumours. The rate-limiting step of fluoropyrimidine catabolism is dihydropyrimidine dehydrogenase (DPD), and deficiency in DPD activity can result in severe and even fatal toxicity. In this review, we survey the evidence-based pharmacogenetics and therapeutic recommendations regarding DPYD (the gene encoding DPD) genotyping and DPD phenotyping to prevent toxicity and optimize dosing adaptation before FP administration. The French experience of mandatory DPD-deficiency screening prior to initiating FP is discussed.

Assay performance and stability of uracil and dihydrouracil in clinical practice

PURPOSE

Measurement of endogenous uracil (U) is increasingly being used as a dose-individualization method in the treatment of cancer patients with fluoropyrimidines. However, instability at room temperature (RT) and improper sample handling may cause falsely increased U levels. Therefore we aimed to study the stability of U and dihydrouracil (DHU) to ensure proper handling conditions.

METHODS

Stability of U and DHU in whole blood, serum, and plasma at RT (up to 24 h) and long-term stability (≥ 7 days) at - 20 °C were studied in samples from 6 healthy individuals. U and DHU levels of patients were compared using standard serum tubes (SSTs) and rapid serum tubes (RSTs). The performance of our validated UPLC-MS/MS assay was assessed over a period of 7 months.

RESULTS

U and DHU levels significantly increased at RT in whole blood and serum after blood sampling with increases of 12.7 and 47.6% after 2 h, respectively. A significant difference (p = 0.0036) in U and DHU levels in serum was found between SSTs and RSTs. U and DHU were stable at - 20 °C at least 2 months in serum and 3 weeks in plasma. Assay performance assessment fulfilled the acceptance criteria for system suitability, calibration standards, and quality controls.

CONCLUSION

A maximum of 1 h at RT between sampling and processing is recommended to ensure reliable U and DHU results. Assay performance tests showed that our UPLC-MS/MS method was robust and reliable. Additionally, we provided a guideline for proper sample handling, processing and reliable quantification of U and DHU.