Partial Dihydropyrimidine Dehydrogenase Deficiency Research Articles

Assessing the Hepatotoxic Effects of Fluoropyrimidine Chemotherapy in Male Iraqi Colorectal Cancer Patients.

Colorectal cancer (CRC) is one the most frequently occurring cancer types among various populations. Fluoropyrimidine is the backbone of first-line chemotherapy, the oral capecitabine, or intravenous 5-fluorouracil (5-FU) in various combinations and schedules the chemotherapy regime in the treatment of a wide variety of gastrointestinal cancers. The enzyme dihydropyrimidine dehydrogenase (DPD) functions as the rate-limiting step in the metabolism of fluoropyrimidine chemotherapies, and patients with complete or partial DPD deficiency are at increased risk of severe and fatal toxicity during treatment with fluorouracil. This study aimed to examine thechemotoxicity of the 5-FU drug on hepatocytes in male Iraqi CRC patients. This research is a cross-sectional study conducted between November 2022 and April 2023. The study included 80 male participants who had undergone surgical intervention for stage III CRC under the care of the Misan Health Directorate, Misan Center for Tumors Treatment, located in Misan, Iraq. Based on their subsequent surgical treatment, the participants were divided into two groups. The first group, comprising 45 males aged between 41 and 71 years, experienced a relapse despite receiving adjuvant therapy, which involved a singular cycle of fluoropyrimidine-based chemotherapy (5-FU). The second group consisted of 35 male patients with CRC, aged between 40 and 57 years, who did not experience a relapse post-adjuvant therapy. Their adjuvant therapy involved a single round of fluoropyrimidine-based chemotherapy with 5-FU. Relapse in patients was determined by assessing the white blood cell count(WBC). Liver enzymes were significantly increased after 5-FU treatment, while the concentration of albumin was significantly decreased. The findings of our study clearly indicate that 5-FU induced hepatic injury, lowering the hepatocytefunction with elevated levels of hepatic enzymes and low concentration of albumin in the blood, which is an important predictive marker of chemotherapy toxicity.

Fluoropyrimidine Dose Based on Uracil Plasma Concentration Impairs Survival in Patients

Fluoropyrimidine drugs (5 flurouracil (5 FU) capecitabine) are the backbone of therapeutic regimens for digestive carcinomas and can lead to severe toxicities. To lower that risk, the French health authorities recommend dose adaptation based on plasma uracil concentration. Since dihydro pyrimidine dehydrogenase (DPD) catabolises more than 80% of 5-FU, a uracil threshold of 16 ng/mL has been considered as partial DPD deficiency.

SO-29 Dihydropyrimidine dehydrogenase (DPD) genotype and phenotype among Danish cancer patients: Prevalence and correlation between DPYD-genotype mutations and P-uracil concentrations

Fluoropyrimidines (FP) are the cornerstone of chemotherapy of several, mainly gastrointestinal, solid tumors. FP includes 5-fluorouracil, capecitabine, and tegafur, all metabolized by dihydropyrimidine dehydrogenase (DPD) enzyme. Patients with decreased DPD-activity have a higher risk of getting severe toxicity if treated with standard FP doses. The DPD-activity is currently a standard test in Denmark with a DPYD-genotype-test and/or a measurement of the endogenous compound uracil (DPD-phenotype test). In Denmark, the recommended FP starting dose for patients diagnosed with partial DPD-deficiency is 50%. FP treatment is contraindicated in patients with complete DPD-deficiency due to a high risk of life-threatening adverse effects. Patients with one variant SNP and/or uracil concentrations above 16 ng/ml are categorized as having partial DPD deficiency. However, patients are categorized as having complete DPD deficiency if they are homozygous for one variant SNP or compound heterozygous (patients with≥ 2 different variant SNPs) and/or have uracil concentrations above 150 ng/ml. In France and the Netherlands, the prevalence of clinically relevant DPYD variants was 4.7% and 7.7% respectively. No studies have reported data on the prevalence of DPYD variants or P-uracil in Danish cancer patients. We collected data from all Danish public hospital laboratories performing DPYD-genotype and DPD-phenotype analysis from the 1st of July 2020 to the 31st of December 2021. Patients were genotyped for the four clinically relevant DPYD-variants: rs3918290, rs67376798, rs55886062, and rs56038477/rs75018182. Most of the samples were genotyped using the LAMP (loop-mediated isothermal amplification) technology (Lc-Dpd4mut-Lp-24-Lacar Mdx Technologies). Plasma uracil concentrations were measured using liquid chromatography-mass spectrometry (LC-MS). In total 4228 Danish cancer patients were tested. 1985 of the patients were only tested using one method (P-uracil=17, DPYD-genotype=1968). 2243 patients were tested using P-uracil and DPYD-genotyping. Of the 4215 DPYD-genotyped patients, 3895 (92.4%) was wild type and 316 (7.5%) was heterozygous for one of the tested variants (SNP'S). rs3918290 (1%, n=43), rs67376798 (1.4%, n=57), rs55886062 (0.2%, n=8) and rs56038477/rs75018182 (4.9%, n=208). Four patients (0.1%) were compound heterozygous. Among 2260 patients tested, 2132 (94.3%) had an uracil concentration below 16 ng/ml. The remaining 128 (5.7%) patients had uracil concentrations ≥ 16 ng/mL and < 150 ng/ml. No values above 150 ng/ml was found. Median uracil concentration was 8 ng/ml (range 5-82 ng/ml). Both geno- and phenotype were available for 2243 of the patients. Uracil concentrations among wild type patients were lower (mean 8.6 ng/ml) compared to patients with DPYD-variants (mean 11.2 ng/ml), mean difference of 2.7 ng/ml. (95% CI; 1.9-3.4 ng/ml). In 4.8% (n=99) of wild type patients, the uracil concentration was ≥ 16 ng/ml compared to 16.8% (n=29) in the group with DPYD-mutations. The prevalence of clinically relevant DPYD-mutations in Danish cancer patients is 7.6% and is in line with results from similar studies of other European populations. 5.7% of phenotyped patients had uracil concentrations ≥ 16 ng/ml. Patients with DPYD-variants had higher mean uracil concentrations compared to wild type, but the uracil concentrations varied substantially in both groups. Data regarding adverse events are needed to conclude on the clinical implications.

Joint Belgian recommendation on screening for DPD-deficiency in patients treated with 5-FU, capecitabine (and tegafur)

ABSTRACT Objectives Fluoropyrimidines such as 5-Fluorouracil (5-FU), capecitabine and tegafur are drugs that are often used in the treatment of maliginancies. The enzyme dihydropyrimidine dehydrogenase (DPD) is the first and rate limiting enzyme of 5-FU catabolism. Genetic variations within the DPYD gene (encoding for DPD protein) can lead to reduced or absent DPD activity. Treatment of DPD deficient patients with fluoropyrimidines can result in severe and, rarely, fatal toxicity. Screening for DPD deficiency should be implemented in practice. Methods The available methods in routine to screen for DPD deficiency were analyzed and discussed in several group meetings involving members of the oncological, genetic and toxicological societies in Belgium: targeted genotyping based on the detection of 4 DPYD variants and phenotyping, through the measurement of uracil and dihydrouracil/uracil ratio in plasma samples. Results The main advantage of targeted genotyping is the existence of prospectively validated genotype-based dosing guidelines. The main limitations of this approach are the relatively low sensitivity to detect total and partial DPD deficiency and the fact that this approach has only been validated in Caucasians so far. Phenotyping has a better sensitivity to detect total and partial DPD deficiency when performed in the correct analytical conditions and is not dependent on the ethnic origin of the patient. Conclusion In Belgium, we recommend phenotype or targeted genotype testing for DPD deficiency before starting 5-FU, capecitabine or tegafur. We strongly suggest a stepwise approach using phenotype testing upfront because of the higher sensitivity and the lower cost to society.

A comprehensive population-based study comparing the phenotype and genotype in a pretherapeutic screen of dihydropyrimidine dehydrogenase deficiency

BackgroundPretherapeutic screening for dihydropyrimidine dehydrogenase (DPD) deficiency is recommended or required prior to the administration of fluoropyrimidine-based chemotherapy. However, the best strategy to identify DPD-deficient patients remains elusive.MethodsAmong a nationwide cohort of 5886 phenotyped patients with cancer who were screened for DPD deficiency over a 3 years period, we assessed the characteristics of both DPD phenotypes and DPYD genotypes in a subgroup of 3680 patients who had completed the two tests. The extent to which defective allelic variants of DPYD predict DPD activity as estimated by the plasma concentrations of uracil [U] and its product dihydrouracil [UH2] was evaluated.ResultsWhen [U] was used to monitor DPD activity, 6.8% of the patients were classified as having DPD deficiency ([U] > 16 ng/ml), while the [UH2]:[U] ratio identified 11.5% of the patients as having DPD deficiency (UH2]:[U] < 10). [U] classified two patients (0.05%) with complete DPD deficiency (> 150 ng/ml), and [UH2]:[U] < 1 identified three patients (0.08%) with a complete DPD deficiency. A defective DPYD variant was present in 4.5% of the patients, and two patients (0.05%) carrying 2 defective variants of DPYD were predicted to have low metabolism. The mutation status of DPYD displayed a very low positive predictive value in identifying individuals with DPD deficiency, although a higher predictive value was observed when [UH2]:[U] was used to measure DPD activity. Whole exon sequencing of the DPYD gene in 111 patients with DPD deficiency and a “wild-type” genotype (based on the four most common variants) identified seven heterozygous carriers of a defective allelic variant.ConclusionsFrequent genetic DPYD variants have low performances in predicting partial DPD deficiency when evaluated by [U] alone, and [UH2]:[U] might better reflect the impact of genetic variants on DPD activity. A clinical trial comparing toxicity rates after dose adjustment according to the results of genotyping or phenotyping testing to detect DPD deficiency will provide critical information on the best strategy to identify DPD deficiency.

Patients homozygous for DPYD c.1129-5923C>G/haplotype B3 have partial DPD deficiency and require a dose reduction when treated with fluoropyrimidines.

Dihydropyrimidine dehydrogenase (DPD) is a critical determinant of 5-fluorouracil pharmacology, and reduced activity of DPD as a result of deleterious polymorphisms in the gene encoding DPD (DPYD) can result in severe treatment-related toxicity. Dosing recommendations to individualize treatment have been provided for three DPYD variants (DPYD*2A, c.2846A>T, and c.1679T>G). A fourth variant, c.1129-5923C>G/HapB3, has been shown to increase the risk of fluoropyrimidine-associated toxicity, but little is known about the functional effects of this variant. By performing a large retrospective screen for DPYD variants, we identified three patients who were homozygous for c.1129-5923C>G/HapB3. We describe their clinical course of treatment and analyzed DPD activity and DPYD gene expression, to provide insight into the phenotypic effects of c.1129-5923C>G/HapB3. DPD activity could be measured in two patients and was 4.1 and 5.4nmol/mg/h (DPD activity 41 and 55% compared to controls, respectively). The fluoropyrimidine dose had to be reduced during treatment in both patients. In line with partial DPD deficiency in both patients, sequence analysis of DPD cDNA demonstrated a normal-sized (wild type) cDNA fragment of 486 bp, as well as a larger-sized (mutant) 530-bp fragment containing an aberrant 44-bp insertion in intron 10. Patient three tolerated treatment well, but DPD activity measurement was not possible as the patient had deceased at the time of performing the study. The presented functional and clinical data indicate that the c.1129-5923C>G variant is both functionally and clinically relevant, and support an upfront dose reduction of the fluoropyrimidine starting dose in patients carrying c.1129-5923C>G homozygously.

Tegafur-uracil (UFT) in lower doses is safe for the treatment of colorectal cancer in patients with partial dihydropyrimidine dehydrogenase deficiency: a proof of principle

To the editor, We appreciate the comments from Dr Deenen and colleagues regarding their concerns on the management of dihydropyrimidine dehydrogenase (DPD)-deficient patients [Deenen et al. 2013], in response to our article [Cubero et al. 2012]. In fact, we agree that standard-dose tegafur-uracil (UFT) is not safe as a starting dose for those patients experiencing severe toxicity after receiving 5-fluorouracil (5-FU). However, the aim of our article is to clarify that UFT can still be an option for selected patients if a careful dosing schedule is employed. The statement that the presence of uracil in UFT creates an artificial DPD activity deficiency is a theoretical hypothesis mentioned by other authors [Niederhuber et al. 2004], including Dr Deenen in his previous case report [Deenen et al. 2010]. Interestingly, there seems to be a difference in safety profiles between 5-FU and UFT as it was demonstrated in at least two other randomized controlled trials. In the first, Douillard and colleagues described a multicenter phase III trial comparing UFT plus leucovorin (UFT/LV) and fluorouracil plus leucovorin (5-FU/LV) in previously untreated metastatic colorectal cancer. After including 380 patients (147 patients in each arm without prior adjuvant therapy), they found that there was statistically significantly less severe leukopenia (2% versus 12%; p < 0.001), less severe mucositis (2% versus 16%; p < 0.001) and lower rates of febrile neutropenia (1% versus 8%; p < 0.001) in the UFT/LV arm as compared with the 5-FU/LV arm [Douillard et al. 2002]. Likewise, Carmichael and colleagues presented similar results in a study including 816 patients (652 patients without previous chemotherapy), also in untreated metastatic colorectal cancer. Once again, but in a much larger sample size, there was less severe leukopenia (<1% versus 19%; p < 0.001), less severe mucositis (1% versus 19%; p < 0.001) and lower rates of febrile neutropenia (0% versus 13%; p < 0.001) in UFT/LV arm in comparison with the 5-FU/LV arm [Carmichael et al. 2002]. Considering that the prevalence of partial DPD deficiency in the White population is approximately 3–5% [Lu et al. 1993, 1998; Etienne et al. 1994], reaching up to 12.3% in specific groups such as African-American women [Mattison et al. 2006], the lower percentages of severe side effects in studies of Douillard and colleagues and Carmichael and colleagues raise the possibility that some of the patients with partial DPD deficiency are not experiencing severe toxicity. Checking for mutations and polymorphisms in the coding region of the DPD gene is only a surrogate of DPD activity. Even patients heterozygote for some known mutations can have very low activity of DPD because there are other mechanisms involved in gene expression (epigenetic mechanisms). In our pilot study [Cubero et al. 2012], in order to corroborate the DPD-gene sequencing, we selected only patients presenting severe toxicity (grade 3 and 4) after the first cycle of 5-FU-based chemotherapy, another surrogate of DPD deficiency. The fact that not one patient developed any severe toxicity in any of the UFT cycles is a proof-of-principle that this drug is still feasible for some patients with partial DPD deficiency. However, after a severe toxicity due to 5-FU and a DPD-gene polymorphism is identified, if UFT is still considered, we strongly recommend an empirical reduction in UFT dose in the first cycle of chemotherapy. We do not recommend the use of UFT for those patients proven homozygote for DPD-gene mutation.

Standard-dose tegafur-uracil (UFT) is not a safe alternative in partial dihydropyrimidine dehydrogenase-deficient patients

To the editor, With interest we read the article by Dr Cubero and colleagues, in which they evaluated the safety of tegafur-uracil (UFT®) in five cases with partial dihydropyrimidine dehydrogenase (DPD) deficiency [Cubero et al. 2012]. Based on our previous experience [Deenen et al. 2010], however, we would like to express our concern about their conclusion that UFT is a safe alternative for the treatment of patients with partial DPD deficiency. Cubero and colleagues make the erroneous and unproven statement that the presence of uracil in UFT creates an artificial DPD deficiency, and that the DPD activity in patients with normal DPD activity would then be similarly as low as in DPD-deficient patients. This assumption, however, is incorrect. As uracil is a competitive inhibitor of DPD, it competes with 5-fluorouracil (5-FU) for DPD-mediated metabolism. This does not mean that the activity of DPD is depleted, as suggested by Cubero and colleagues, in contrast, its activity is fully utilized, as well as for the metabolism of uracil, as for the metabolism of 5-FU. We would like to caution that treating patients with partial DPD deficiency with the standard dose of UFT may unnecessarily lead to severe, potentially lethal toxicity. Unlike the cases described by Cubero and colleagues, we could previously describe four cases presenting with comparable severe toxicity profiles upon treatment with UFT as had previously occurred during treatment with capecitabine or 5-FU. In all subjects an underlying partial DPD deficiency was identified by genotype and phenotype analyses [Deenen et al. 2010]. Furthermore, there are several pharmacological lines of argument that support our clinical observation, i.e. that the standard dose of UFT is not safe in (partial) DPD-deficient patients. First, pharmacokinetic studies have shown that DPD remains essential for the metabolism of UFT, with significantly longer half-lives of 5-FU after administration of UFT compared with 5-FU administered intravenously [Ho et al. 1998]. This is due to the presence of uracil in UFT. Since DPD-deficient patients already have longer half-lives of 5-FU than other patients [Mattison et al. 2006], presence of uracil increases its half-life even further. This in turn leads to prolonged and elevated circulating levels of 5-FU, with a subsequently increased risk of 5-FU-induced severe toxicity. Another argument underscoring the importance of normal DPD function in the safe application of UFT, is the experience with S-1. S-1 is another drug combination of tegafur, consisting of tegafur, 5-chloro-2,4-dihydroxypyridine (CDHP) and potassium oxonate in a molar ratio of 1:0.4:1. CDHP inhibits DPD 200-fold more potently than does uracil [Shirasaka et al. 1996a, 1996b]. Even after administration of S-1, the primary 5-FU metabolite formed by DPD is observed in significant concentrations in plasma [Kim et al. 2007]. Thus, DPD remains an essential detoxification enzyme of 5-FU, even when its activity is strongly inhibited. The ultimate proof of theory is the occurrence of 18 treatment-related deaths in patients with cancer and herpes zoster given UFT plus the antiviral drug sorivudine [Pharmaceutical Affairs Bureau, 1994]. Subsequent studies in rats showed that a metabolite of sorivudine, (E)-5-(2-bromovinyl)uracil, instantly and irreversibly inactivates DPD by covalent binding, which has been identified as the underlying mechanism of these toxic deaths [Ogura et al. 1998; Okuda et al. 1998]. It is for these arguments that the Summary of Product Characteristics of UFT notes a known DPD deficiency as a contra-indication [Merck Serono, 2011]. The fact that the patients described by Cubero and colleagues did not develop significant toxicity might be due to patient selection, the slightly decreased dose intensity of 90%, or despite their DPYD*2A genotype a DPD enzyme activity within the (lower) range of normal. We are not aware of this, because DPD enzyme activity was not determined in these patients. In summary, we would like to state that standard-dose UFT is not a safe treatment in (partial) DPD-deficient patients. Instead, dose reductions of on average 50% of either capecitabine, 5-FU or UFT with careful monitoring of safety and further dose titration are proposed as the standard of care [Deenen et al. 2011].

Tegafur–uracil is a safe alternative for the treatment of colorectal cancer in patients with partial dihydropyrimidine dehydrogenase deficiency: a proof of principle

The objective of this study was to evaluate the safety of using tegafur-uracil (UFT) in colorectal cancer patients with partial dihydropyrimidine dehydrogenase (DPD) deficiency. The study included five colorectal cancer patients who presented with acute toxicity (grades 3 and 4) after being given the first cycle of chemotherapy using 5-fluorouracil. The DPD deficiency was confirmed by gene sequencing. After a full recovery from all side effects, we changed the regimen to UFT (300 mg/m(2)/day) associated with leucovorin (90 mg/day) for 21 days, with an empirical dose reduction of at least 10% in the first cycle. We prospectively analysed 22 UFT cycles in 5 patients. We did not observe any episodes of grade 3 or 4 toxicity. The predominant toxicities were of grades 1 and 2 (nausea, vomiting and diarrhoea). Here, we demonstrate a complete absence of severe toxicity in all patients and cycles analysed. We believe that UFT is a safe alternative for the treatment of patients with partial DPD deficiency.

Evaluation of 5-Fluorouracil Pharmacokinetics in Cancer Patients with a C.1905+1G&gt;A Mutation in DPYD by Means of a Bayesian Limited Sampling Strategy

Dihydropyrimidine dehydrogenase (DPD) is the initial enzyme in the catabolism of 5-fluorouracil (5FU) and DPD deficiency is an important pharmacogenetic syndrome. So far, only very limited information is available regarding the pharmacokinetics of 5FU in patients with a (partial) DPD deficiency and no limited sampling models have been developed taking into account the non-linear pharmacokinetic behaviour of 5FU. The aim of this study was to evaluate the pharmacokinetics of 5FU and to develop a limited sampling strategy to detect decreased 5FU elimination in patients with a c.1905+1G>A-related DPD deficiency. Thirty patients, heterozygous for the c.1905+1G>A mutation in DPYD, and 18 control patients received a dose of 5FU 300 mg/m2 and/or 5FU 450 mg/m2, followed by pharmacokinetic analysis of the 5FU plasma levels. A population pharmacokinetic analysis was performed in order to develop a compartmental pharmacokinetic model suitable for a limited sampling strategy. Clinical aspects of treating DPD-deficient patients with 5FU-based chemotherapy were assessed from the retrospectively collected clinical data. In a two-compartment model with Michaelis-Menten elimination, the mean maximum enzymatic conversion capacity (V(max)) value was 40% lower in DPD-deficient patients compared with controls (p < 0.001). Using a limited sampling strategy, with V(max) values calculated from 5FU concentrations at 30 or 60 minutes, significant differences were observed between DPD-deficient patients and controls at both dose levels (p < 0.001). The positive predictive value and negative predictive value for V(max), calculated from 5FU levels at 60 minutes, were 96% and 88%, respectively, in patients treated with a single dose of 5FU 300 mg/m2. All seven DPD-deficient patients (two males and five females) who had been genotyped prior to initiation of standard 5FU-containing chemotherapy developed grade 3-4 toxicity, with one case of lethal toxicity in a female patient. No grade 4 toxicity or lethal outcome was observed in 13 DPD-deficient patients treated with reduced doses of 5FU. The average dose of 5FU in DPD-deficient patients with mild toxicity (grade ≤2) was 61 ± 16% of the normal 5FU dose (n = 10). Profound differences in the elimination of 5FU could be detected between DPD-deficient patients and control patients. Pharmacokinetic 5FU profiling, using a single 5FU concentration at 60 minutes, may be useful for identification of DPD-deficient patients in order to reduce severe toxicity. Furthermore, treatment of DPD-deficient patients with standard 5FU-containing chemotherapy was associated with severe (lethal) toxicity.

Uridine triacetate for prevention of 5FU toxicity due to dihydropyrimidine dehydrogenase (DPD) deficiency.

e19560 Background: Dihydropyrimidine dehydrogenase (DPD) catalyzes degradation of 5-fluorouracil (5FU). Patients with complete or partial DPD deficiency (0.1 and 3% of the population, respectively) can experience severe or lethal toxicities to 5FU, and impaired clearance may underlie many of the 1300 US 5FU toxicity deaths each year. Uridine triacetate prevents or diminishes toxicities when orally administered after 5FU overexposure, and has been used successfully as an investigational antidote in >50 patients following accidental overdoses. Methods: A colorectal cancer patient experienced Grade 3 and 4 GI and hematologic toxicities after a 96 hour infusion of 1000 mg/m2 5FU and was found to be DPD deficient (double mutation). The patient subsequently tolerated 50 and 100 mg 5FU bolus treatments in a modified FOLFOX regimen. However, during the second cycle, this DPD-deficient patient inadvertently received 1000 mg 5FU in 1 minute. Life-threatening toxicity was expected. Treatment with uridine triacetate (10 g q6h for 20 total doses) began within 8 hours. Results: In marked contrast to his first exposure to 5FU, the patient experienced no mucositis or additional cytopenia. Preclinical and mechanistic data predicted and support this observation. In a mouse model of DPD deficiency using ethynyluracil (2 mg/kg i.p.), a standard therapeutic 5FU dose of 100 mg/kg i.p. was lethal. Treatment with oral uridine triacetate (2 g/kg t.i.d. x 5 d) starting 2, 24 or 72 hours after 5FU resulted in 100%, 80% or 70% survival, respectively. Conclusions: Timely treatment with uridine triacetate appeared to prevent severe 5FU toxicity in a DPD-deficient patient and reduced mortality in DPD-inhibited mice receiving 5FU. Uridine triacetate has been shown previously to protect patients (and mice) from 5FU toxicities following 5FU overdose. Therefore, DPD-deficient patients who have received 5FU should also benefit from uridine triacetate treatment if the overexposure is identified soon enough after 5FU dosing. Therapeutic monitoring of 5FU during or after infusions would permit rapid detection of 5FU overexposure due to DPD-deficiency or other clearance defects, enabling the use of uridine triacetate as a potential antidote.

Lethal outcome of 5‐fluorouracil infusion in a patient with a total DPD deficiency and a double DPYD and UTG1A1 gene mutation

5-Fluorouracil (5-FU)-based chemotherapy has been widely used for almost 50 years in the treatment of solid malignancies, especially in digestive cancers. Its main effect consists in the inhibition, via its active metabolite, of thymidylate synthase, a major enzyme involved in DNA synthesis. In normal conditions, less than 20% of the administered 5-FU is used in this anabolic pathway while more than 80% is catabolized via dihydropyrimidine dehydrogenase (DPD) [1]. This is the initial and rate-limiting enzyme in the catabolic pathway and therefore a partial or complete DPD deficiency is associated with different degrees of 5-FU toxicity whose most frequent manifestations include neutropenia, mucositis and diarrhoea [2].

The safety of oral uracil-tegafur plus leucovorin in the treatment of colorectal cancer in patients with partial DPD deficiency.

e13146 Background: Fluoropyrimidines are the cornerstone of chemotherapeutic regimens for most gastrointestinal tract tumors. The metabolization of these drugs depends on an enzyme called dihydropyrimidine dehydrogenase (DPD). The quantitative or qualitative deficiency of this enzyme is responsible for at least 50% of severe toxicity cases. We evaluated the safety of using oral uracil-tegafur (UFT) in patients with a partial deficiency in DPD. Methods: The study included 5 colorectal cancer patients who presented with acute toxicity (grades 3 and 4) after being given the first cycle of chemotherapy using 5-fluorouracil. After a full recovery from all side effects, we changed the regimen to oral uracil-tegafur (300 mg/m2/day) associated with leucovorin (90 mg/day) for 21 days, with an empirical dose reduction of at least 10% in the first cycle. The DPD deficiency status was confirmed by gene sequencing. Results: We analyzed 22 uracil-tegafur cycles in 5 patients. We did not observe any episodes of grades 3 or 4 toxicity. The predominant toxicities were of grades 1 and 2 (nausea, vomiting, and diarrhea). Conclusions: Here, we demonstrate a complete absence of severe toxicity in all patients and cycles analyzed. We believe that oral uracil-tegafur plus leucovorin is a safe alternative for the treatment of patients with partial DPD deficiency. No significant financial relationships to disclose.

Uridine triacetate for lethal 5-FU toxicity due to dihydropyrimidine dehydrogenase (DPD) deficiency.

e13505 Background: The enzyme dihydropyrimidine dehydrogenase (DPD) catalyzes the first step in degradation of 5-fluorouracil (5FU). Patients with complete or partial DPD deficiency (about 0.1% and 3% of the population, respectively) can experience severe or lethal toxicities after receiving standard doses of 5FU, and impaired clearance may underlie a large fraction of the ∼1,300 deaths per year due to 5FU toxicity in the US. Orally-administered uridine triacetate (vistonuridine) prevents or diminishes toxicities when administered after 5FU overexposure, and has been used successfully as an antidote in more than 28 patients to date who had received accidental overdoses of 5FU. Because DPD deficiency may alter 5FU clearance kinetics (versus 5FU overdoses in the setting of normal DPD activity), studies were conducted on reversal of 5FU toxicity in mice pretreated with the potent DPD inhibitor ethynyluracil (eniluracil; EU) to model DPD deficiency. Methods: Balb/C mice received 2 mg/kg EU i.p., followed by 1...

Uracil pharmacokinetics in a DPD-deficient patient with a novel DPYD mutation compared to volunteers with normal DPD activity.

e13134 Background: Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the metabolism of 5-fluorouracil (5-FU). Patients with a partial or complete DPD deficiency are at risk to develop severe toxicity after 5-FU administration. Uracil (U) is degraded in dihydrouracil (DHU) in a similar way as 5-FU. An oral uracil test dose might be useful to determine the systemic DPD activity by measuring uracil and its metabolite dihydrouracil in plasma. DPD deficiency is hypothesized to result in higher uracil levels and a reduced turnover of uracil into dihydrouracil. Methods: Uracil (500 mg/m2) was administered to 11 healthy volunteers with normal DPD activity (≥ 6 nmol/mg/hour) and 1 patient with colorectal carcinoma with a novel DPYD mutation and decreased DPD activity (4.6 nmol/mg/hour). DPD activity was measured in PBMC, as determined as described earlier. Blood samples were taken at t= 15, 30, 45, 60, 80, 100, 120, 150, 180, and 220 or 240 min after oral uracil intake. U and DHU pla...

A well‐tolerated 5‐FU‐based treatment subsequent to severe capecitabine‐induced toxicity in a DPD‐deficient patient

5-Fluorouracil (5-FU) is widely administered as a continuous infusion to treat gastrointestinal tract or head and neck cancers, and as bolus injections in breast cancer chemotherapy regimens. Grade 3–4 toxicity occurs in about 30% of patients receiving 5-FU as a continuous infusion, and proves lethal in 0.5% of these patients [1]. 5-FU-related toxicity has mostly been reported with intravenous administration [1–3]. However, some cases of severe toxicity, including deaths, have been described after oral administration of 5-FU derivatives, such as capecitabine (Xeloda®) [4, 5]. A polymorphism of the dihydropyrimidine dehydrogenase (DPD) gene has been identified as a frequent cause of such toxicity [6, 7]. DPD catalyses the rate-limiting step of fluoropyrimidine catabolism. Partial or total DPD deficiency therefore leads to substantial overexposure in patients treated with the standard dose, exacerbating drug toxicity. This raises questions about possible screening for DPD deficiency before the administration of fluoropyrimidine drugs, including their oral forms. Patients found to have a deficiency on screening before treatment or following signs of toxicity during a previous course are usually given alternative treatments based on nonfluoropyrimidine compounds. However, 5-FU is highly active and its use may be essential in patients who fail to respond to other treatments. We report the case of a patient with DPD deficiency detected due to severe toxicity during capecitabine treatment, who has since received a continuous infusion of 5-FU at almost the standard dose with no significant signs of toxicity.

Pour ou contre le phénotypage/génotypage des patients traités par le 5-fluorouracile pour prévenir les effets indésirables ?

5-fluorouracil, (5-FU) is an antimetabolite used in many types of cancers. It has a narrow therapeutic index. More than 80% of administered 5-FU is detoxified in 5-fluoro-5,6-dihydrouracil (5-FUH2) by an enzyme: dihydropyrimidine dehydrogenase (DPD). Half life increased with DPD deficiency. Thus, patients presenting a partial or profound DPD deficiency have an increased risk of severe or lethal toxicity. DPD deficiency was estimated between 3 to 5% in the normal population. Different approaches have been developed: Pharmacogenetic on the DPD gene or pharmacologic measuring DPD activity. More than 30 mutations have been reported on this gene. The more common mutation is the slice-site mutation IVS14+1G>A. Analysis of the various mutations allowed to identify a population at risk with a DPD deficiency. DPD activity is determined in peripheral blood mononuclear cells. This assay offers the capability of identifying individuals who are completely deficient in DPD activity and those who are partially deficient. Assays to detect DPD deficiency are not used as a screening test to prevent 5-FU toxicity.

Dihydropyrimidine dehydrogenase deficiency in an Indian population

Dihydropyrimidine dehydrogenase (DPD) deficiency is prevalent in 3-5% of the Caucasian population; however, the frequency of this pharmacogenetic syndrome in the Indian population and other racial and ethnic groups remains to be elucidated. We describe an Indian patient who presented to clinic for the treatment of gastric adenocarcinoma with 5-flurouracil (5-FU) therapy who subsequently was diagnosed with DPD deficiency by using the peripheral blood mononuclear cell (PBMC) DPD radioassay. This observation prompted us to examine the data generated from healthy (cancer-free) Indian subjects who were enrolled in a large population study to determine the sensitivity and specificity of the uracil breath test (UraBT) in the detection of DPD deficiency. Thirteen Indian subjects performed the UraBT. UraBT results were confirmed by PBMC DPD radioassay. The Indian cancer patient demonstrated reduced DPD activity (0.11 nmol/min/mg protein) and severe 5-FU toxicities commonly associated with DPD deficiency. Of the 13 Indian subjects [ten men and three women; mean age, 26 years (range: 21-31 years)] enrolled in the UraBT, 12 Indian subjects demonstrated UraBT breath profiles and PBMC DPD activity within the normal range; one Indian subject demonstrated a reduced breath profile and partial DPD deficiency. DPD deficiency is a pharmacogenetic syndrome which is also present in the Indian population. If undiagnosed, the DPD deficiency can lead to death. Future epidemiological studies would be helpful to determine the prevalence of DPD deficiency among racial and ethnic groups, allowing for the optimization of 5-FU chemotherapy.

The Uracil Breath Test in the Assessment of Dihydropyrimidine Dehydrogenase Activity: Pharmacokinetic Relationship between Expired 13CO2 and Plasma [2-13C]Dihydrouracil

Dihydropyrimidine dehydrogenase (DPD) deficiency is critical in the predisposition to 5-fluorouracil dose-related toxicity. We recently characterized the phenotypic [2-(13)C]uracil breath test (UraBT) with 96% specificity and 100% sensitivity for identification of DPD deficiency. In the present study, we characterize the relationships among UraBT-associated breath (13)CO(2) metabolite formation, plasma [2-(13)C]dihydrouracil formation, [2-(13)C]uracil clearance, and DPD activity. An aqueous solution of [2-(13)C]uracil (6 mg/kg) was orally administered to 23 healthy volunteers and 8 cancer patients. Subsequently, breath (13)CO(2) concentrations and plasma [2-(13)C]dihydrouracil and [2-(13)C]uracil concentrations were determined over 180 minutes using IR spectroscopy and liquid chromatography-tandem mass spectrometry, respectively. Pharmacokinetic variables were determined using noncompartmental methods. Peripheral blood mononuclear cell (PBMC) DPD activity was measured using the DPD radioassay. The UraBT identified 19 subjects with normal activity, 11 subjects with partial DPD deficiency, and 1 subject with profound DPD deficiency with PBMC DPD activity within the corresponding previously established ranges. UraBT breath (13)CO(2) DOB(50) significantly correlated with PBMC DPD activity (r(p) = 0.78), plasma [2-(13)C]uracil area under the curve (r(p) = -0.73), [2-(13)C]dihydrouracil appearance rate (r(p) = 0.76), and proportion of [2-(13)C]uracil metabolized to [2-(13)C]dihydrouracil (r(p) = 0.77; all Ps < 0.05). UraBT breath (13)CO(2) pharmacokinetics parallel plasma [2-(13)C]uracil and [2-(13)C]dihydrouracil pharmacokinetics and are an accurate measure of interindividual variation in DPD activity. These pharmacokinetic data further support the future use of the UraBT as a screening test to identify DPD deficiency before 5-fluorouracil-based therapy.

Dihydropyrimidine dehydrogenase and the efficacy and toxicity of 5-fluorouracil

The identification of genetic factors associated with either responsiveness or resistance to 5-fluorouracil (5-FU) chemotherapy, as well as genetic factors predisposing patients to the development of severe 5-FU-associated toxicity, is increasingly being recognised as an important field of study. Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5-FU). Although the role of tumoral levels as a prognostic factor for clinical responsiviness has not been firmly established, there is ample evidence that a deficiency of DPD is associated with severe toxicity after the administration of 5-FU. Patients with a partial DPD deficiency have an increased risk of developing grade IV neutropenia. In addition, the onset of toxicity occurred twice as fast compared with patients with a normal DPD activity. To date, 39 different mutations and polymorphisms have been identified in DPYD. The IVS14+1G>A mutation proved to be the most common one and was detected in 24–28% of all patients suffering from severe 5-FU toxicity. Thus, a deficiency of DPD appears to be an important pharmacogenetic syndrome.