Dihydropyrimidine dehydrogenase gene variants for predicting grade 4-5 fluoropyrimidine-induced toxicity: FUSAFE individual patient data meta-analysis

BACKGROUND

Dihydropyrimidine dehydrogenase (DPD) deficiency is the main known cause of life-threatening fluoropyrimidine (FP)-induced toxicities. We conducted a meta-analysis on individual patient data to assess the contribution of deleterious DPYD variants *2A/D949V/*13/HapB3 (recommended by EMA) and clinical factors, for predicting G4-5 toxicity.

METHODS

Study eligibility criteria included recruitment of Caucasian patients without DPD-based FP-dose adjustment. Main endpoint was 12-week haematological or digestive G4-5 toxicity. The value of DPYD variants *2A/p.D949V/*13 merged, HapB3, and MIR27A rs895819 was evaluated using multivariable logistic models (AUC).

RESULTS

Among 25 eligible studies, complete clinical variables and primary endpoint were available in 15 studies (8733 patients). Twelve-week G4-5 toxicity prevalence was 7.3% (641 events). The clinical model included age, sex, body mass index, schedule of FP-administration, concomitant anticancer drugs. Adding *2A/p.D949V/*13 variants (at least one allele, prevalence 2.2%, OR 9.5 [95%CI 6.7-13.5]) significantly improved the model (p < 0.0001). The addition of HapB3 (prevalence 4.0%, 98.6% heterozygous), in spite of significant association with toxicity (OR 1.8 [95%CI 1.2-2.7]), did not improve the model. MIR27A rs895819 was not associated with toxicity, irrespective of DPYD variants.

CONCLUSIONS

FUSAFE meta-analysis highlights the major relevance of DPYD *2A/p.D949V/*13 combined with clinical variables to identify patients at risk of very severe FP-related toxicity.

[A Case of Colon Cancer with Suspected DPD Deficiency Causing Severe Adverse Effects following Adjuvant Chemotherapy with Capecitabine]

The present study reports a case of colon cancer in a 76-year-old female who underwent laparoscopic right colectomy. Pathological findings revealed pT3(SS), pN2a, cM0, and pStage Ⅲb. Hence, we administered adjuvant chemotherapy with capecitabine. On day 18, she was urgently hospitalized because of severe oral mucositis(grade 3), diarrhea(grade 3), and leukocytopenia(grade 4). Furthermore, the patient experienced DIC, which gradually improved through intensive conservative treatment. From the clinical course, we suspected that the severe adverse effects were caused due to a deficiency of DPD. We were able to save the patient through early treatment.

Molecular basis of 5-fluorouracil-related toxicity: lessons from clinical practice

We aim to present a comprehensive review of the molecular basis of 5-fluorouracil (5-FU) toxicity, of which dihydropyrimidine dehydrogenase (DYPD) deficiency is a well-known mechanism. The prevalence of partial DYPD deficiency is fairly common, ranging between 3-5% in the general population, whereas it can be as high as 12% in African-American females. More than 50 genetic polymorphisms have been described as being associated with decreased enzymatic activity, whereas the c.1905+1G>A point mutation is the most commonly found (52% of cases), with a prevalence of heterozygosity in the general population ranging between 1-2%. Several methods have been utilized to identify reduced DYPD activity; functional tests are expensive and only available in specialized centers. Genotyping alone is not reliable enough, as some of the polymorphisms may not result in significantly reduced DYPD activity. The rate of cardiotoxicity associated with 5-FU or capecitabine does not seem to be related to DYPD deficiency, and has been estimated to range between 1.2-8%. Several pathophysiological mechanisms seem to contribute to 5-FU cardiotoxicity, including coronary spasm, increased endothelial thrombogenicity and myocardial inflammation. Tegafur/uracil and raltitrexed may be alternative options for patients with partial DYPD deficiency and previous manifested 5-FU cardiotoxicity, respectively. Pharmacogenetics is expected to further identify and clarify the mechanisms associated with 5-FU-related toxicity, thus aiding the oncology societies to formulate specific guidance on pre-treatment testing.

Lethal Toxicity After 5-Fluorouracil Chemotherapy and Its Possible Relationship to Dihydropyrimidine Dehydrogenase Deficiency: A Case Report and Review

5-fluorouracil (5-FU) is a chemotherapeutic agent widely used in the treatment of solid malignancies, especially in colorectal cancer. A characteristic note seen with its use is the considerable interindividual variation in the incidence and severity of the toxicities seen among patients. We report the case of a 55-year old woman who presented with severe, lethal toxicity to standard doses of 5-fluorouracil (5-FU) and folinic acid. We discuss the known clinical determinants of toxicity. We also discuss the possible molecular factors implicated in the variable toxicity seen to 5-FU, especially in regards to dihiyropyrimidine dehydrogenase, a pivotal enzyme in the metabolism of 5-FU.

[Severe bone marrow suppression during adjuvant chemotherapy for gastric cancer by S-1 and its possible relationship to dihydropyrimidine dehydrogenase deficiency]

The patient was a 70-year-old woman, who had undergone total gastrectomy and splenectomy with D2 lymph node dissection, for stage II gastric cancer. We admitted S-1 of 80 mg/day in adjuvant chemotherapy on postoperative day 28. There were no adverse events for one week, and she was discharged. Severe diarrhea occurred 6 days following discharge, but she continued to take S-1. Two weeks after discharge, she visited our hospital, suffering from severe dehydration (grade 4), leucopenia (grade 4)and thrombocytopenia (grade 3). Unfortunately, she died of lung edema and multiple organ failure 28 days after chemotherapy. We measured the mRNA expression level of dihydropyrimidine dehydrogenase (DPD) of the patient's liver by the Dannenberg Tumor Profile method. The expression level of DPD was significantly low, so we suggested that the severe bone marrow suppression might have been caused by the disordered metabolism of 5-FU.

Screening for Dihydropyrimidine Dehydrogenase Deficiency: To Do or Not To Do, That's The Question

The treatment of cancer patients with 5-fluorouracil (5FU)-based chemotherapy can be accompanied by severe and sometimes lethal toxicity. Dihydropyrimidine dehydrogenase (DPD) plays a pivotal role in the metabolism of 5FU and as such, a deficiency of DPD has been recognized as an important risk factor, predisposing patients to the development of severe 5FU-associated toxicity. To date, screening of patients for the presence of a DPD deficiency prior to the treatment is not yet routinely performed. Taking into account the relatively small impact of adjuvant 5FU-based chemotherapy on survival, patients should be informed about the risks of the therapy and should be offered the possibility of testing for the presence of a DPD deficiency in advance of receiving such treatment.

Thymidylate synthase and dihydropyrimidine dehydrogenase levels are associated with response to 5-fluorouracil in Caenorhabditis elegans

5-Fluorouracil (5-FU), a pyrimidine antagonist, has a long history in cancer treatment. The targeted pyrimidine biosynthesis pathway includes dihydropyrimidine dehydrogenase (DPD), which converts 5-FU to an inactive metabolite, and thymidylate synthase (TS), which is a major target of 5-FU. Using Caenorhabditis elegans as a model system to study the functional and resistance mechanisms of anti-cancer drugs, we examined these two genes in order to determine the extent of molecular conservation between C. elegans and humans. Overexpression of the worm DPD and TS homologs (DPYD-1 and Y110A7A.4, respectively) suppressed germ cell death following 5-FU exposure. In addition, DPYD-1 depletion by RNAi resulted in 5-FU sensitivity, while treatment with Y110A7A.4 RNAi and 5-FU resulted in similar patterns of embryonic death. Thus, the pathway of 5-FU function appears to be highly conserved between C. elegans and humans at the molecular level.

Atypical toxicity associated with 5-Fluororacil in a DPD-deficient patient with pancreatic cancer. Is ethnicity a risk factor?

CONTEXT

Fluoropyrimidines constitute the backbone of chemotherapy regimens for GI tumors, including pancreatic cancer where it is used either as a radiosensitizer or as second-line after failing gemcitabine. While normal dihydropyrimidine dehydrogenase (DPD) enzyme activity is rate limiting in 5-fluorouracil (5-FU) catabolism, its deficiency could increase concentrations of bioavailable 5-FU anabolic products leading to 5-FU related toxicity syndrome. The most common toxicities include myelosuppression, stomatitis, neuropathy, and diarrhea. The prevalence of this autosommal codominently inherited pharmacogenetic syndrome is approximately 3-5% in the Caucasian population and 8% in the African-American population.

CASE REPORT

We present here a case of an African-American patient with pancreatic cancer who developed a desquamative skin rash on the face, trunk, and forearms as the worst rash (grade 3) following 5-FU bolus that led to the investigation of DPD enzyme. Measurement of DPD activity by radioisotopic assay methods described previously revealed an abnormally low level of 0.087 nmol/min/mg protein (reference range: 0.182-0.688 nmol/min/mg protein). She was treated toxicity with intravenous steroids and antihistamine therapy. Further 5-FU therapy was discontinued.

CONCLUSIONS

This case suggest that the pattern of toxicities associated with 5-FU can vary, especially in patients with different ethnic backgrounds (whites versus non-whites). These findings become of further importance as our recent study suggests that DPD deficiency may be more common among African-Americans.

[A case of dihydropyrimidine dehydrogenase (DPD) deficiency with severe side effects from UFT/Uzel administration]

5-FU is among the drugs most frequently used in the treatment of gastrointestinal malignancies. Also, it has been reported to reveal severe side effects in the case of a dihydropyrimidine dehydrogenase (DPD) deficiency. A 75-year-old man showed severe nausea and vomiting after administration of UFT/Uzel as adjuvant chemotherapy. Because of severe thrombocytopenia and grade 4 neutropenia, platelet transfusion and G-CSF administration were performed. With time, the leukocyte, neutrophil and platelet count recovered to normal level. We strongly suspected a DPD deficiency from the result of urinary pyrimidine analysis.

[Pharmacogenetic studies on the prediction of efficacy and toxicity of fluoropyrimidine-based adjuvant therapy in colorectal cancer]

The cytotoxic effect of 5-fluorouracil (5-FU) is mediated by the inhibition of thymidylate synthase (TS), however, at the same time 5-FU is catabolized by dihydropyrimidine dehydrogenase (DPD). Efficacy of 5-FU may therefore depend on the TS and DPD activity and on pharmacogenetic factors influencing these enzymes. Our aims were (1) to determine the distribution of DPD activity, the frequency of DPD deficiency and the DPD (IVS14+1G>A) mutation in the peripheral blood mononuclear cells of colorectal cancer (CRC) patients, and study the relationship between DPD deficiency and toxicity of 5-FU; (2) to investigate the influence of TS polymorphisms and DPD activity on the survival of CRC patients receiving 5-FU-based adjuvant therapy. The frequency of DPD deficiency was determined by radiochemical methods in the peripheral blood mononuclear cells (PBMCs) of 764 CRC patients treated with 5-FU. The relationship between the TS polymorphisms, DPD activity and the disease-free and overall survival was studied in 166 CRC patients receiving 5-FU-based adjuvant therapy. TS polymorphisms were determined in the DNA samples separated from the PBMCs, by PCR-PAGE and PCR-RFLP-PAGE (restriction fragment length polymorphism) methods. Low DPD values (<10 pmol/min/106 PBMCs) were demonstrated in 160/764 patients (20.9%), and of those DPD deficiency (<5 pmol/min/106 PBMCs) was verified in 38 patients (4.9%). In the latter group severe (>Gr 3) toxicity was found in 87%. The prevalence of the DPD IVS14+1G>A mutation among the 38 DPD-deficient patients was 7.8% (3/38) and was accompanied by severe Gr 4 toxic symptoms (neutropenia, mucositis, diarrhea). TS polymorphisms showed a relationship with the survival of CRC patients. It is important to mention that by combining the 3-3 genotypes of 5'-TSER and 3'-TSUTR polymorphisms the obtained 8 genotype combinations showed significantly different Kaplan-Meier survival curves. The evaluation of these curves with Cox regression analysis resulted in two prognostically different groups: "A" good prognosis (RR<1) and "B" bad prognosis (RR>1). The disease-free- and overall survival of these two groups were significantly different. DPD activity also showed correlation with the survival; patients with DPD activity <10 pmol/min/106 PBMCs showed significantly longer disease-free and overall survival. The determination of DPD activity proved to be a more valuable parameter in the evaluation of serious 5-FU-related toxicity compared to the IVS14+1G>A mutation analysis. According to the Cox multivariate analysis the combination of germline TS polymorphisms and DPD activity is/an independent prognostic marker of survival in CRC patients treated with adjuvant 5-FU therapy.

[Pro or con the phenotyping/genotyping of patients treated by 5-Fluorouracil to prevent adverse drug reactions?]

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.

Should DPD analysis be required prior to prescribing fluoropyrimidines?

Dihydropyrimidine dehydrogenase (DPD) is a key enzyme in the metabolic catabolism of chemotherapeutic agent 5-fluorouracil (5FU) and its derivatives, including capecitabine. Numerous genetic mutations have been identified in the DPD gene locus (DPYD), with a few key variants having functional consequences on enzymatic activity. Deficiencies in DPD activity have been shown to cause 5FU-treated cancer patients to experience severe drug-related toxicities, often requiring extensive medical intervention. We review the performance of assays that assess DPD and DPYD status, with an emphasis on the robustness for routine clinical applications. None of the current strategies are adequate to mandate routine DPD testing prior to starting a fluoropyrimidine-based therapy. However, further research and technological improvements will hopefully allow prospective identification of potentially toxic patients, in order to reduce the number of patients with severe, life-threatening side effects to 5FU treatment.

Dépistage des patients déficitaires en dihydropyrimidine déhydrogénase avant traitement par fluoropyrimidines

Numerous toxic side-effects, sometimes severe, are regularly reported in patients treated with 5-fluorouracil, and oral fluoropyrimidines, UFT and capecitabine, in metastatic and adjuvant setting. These toxic effects are due to a large interindividual variability of the metabolism, mainly depending on dihydropyrimidine dehydrogenase activity (DPD), the major enzyme of the catabolism of fluoropyrimidines. Thus, the patients with a DPD deficiency are at high risk of early severe acute toxicity, with this kind of drug. These toxic side-effects are potentially lethal. DPD deficiency frequencies, partial or complete, are about 3-5% and 0.2% respectively. They are most often due to a gene polymorphism. Different techniques for the detection of DPD deficiency before treatment have been reported: phenotypic, such as the plasma ratio of dihydrouracil/uracil, or genotypic, such as the detection of DPD gene variants, deleterious for enzyme activity. The pretherapeutic detection of DPD deficiency would permit to avoid almost every early acute toxic side-effects. We must emphasize that it is not merely a genetic result, since the detection of a deficiency most often does not contra-indicate the use of a fluoropyrimidine, but it must be combined with therapeutic advice.

Profiling dihydropyrimidine dehydrogenase deficiency in patients with cancer undergoing 5-fluorouracil/capecitabine therapy

Fluoropyrimidine drugs such as 5-fluorouracil (5-FU) and capecitabine are a mainstay in the treatment of numerous solid tumors, including colorectal cancers, alone or as part of combination therapies. Cytotoxic drugs such as 5-FU and oral capecitabine display narrow therapeutic indexes combined with high interpatient pharmacokinetic variability. As a result, severe toxicities often limit or delay the administration of successive, optimal chemotherapeutic courses, leading to unfavorable clinical outcome in patients with cancer. Catabolism and deactivation of fluoropyrimidine drugs depend on a single and exclusive enzymatic step driven by dihydropyrimidine dehydrogenase (DPD). Dihydropyrimidine dehydrogenase is prone to marked circadian rhythms, drug-drug interactions, and genetic polymorphisms; influence of its erratic activity on 5-FU pharmacokinetics and toxicity profile has been extensively investigated, and it is now well known that DPD deficiency leads to severe toxicities with 5-FU or possibly capecitabine exposure. With the ever-increasing number of patients with cancer likely to be treated with fluoropyrimidines, predicting and preventing the occurrence of such toxicities is now a major issue in clinical oncology. Early determination of DPD status in patients with cancer would allow identification of those at risk and help in subsequent dose adjustment or selection of other treatment modalities. Numerous methods, either genotypic or phenotypic, have been proposed to achieve this goal. This review covers a wide range of techniques available to establish DPD status in patients with cancer.

A pivotal role for beta-aminoisobutyric acid and oxidative stress in dihydropyrimidine dehydrogenase deficiency?

Dihydropyrimidine dehydrogenase (DPD) constitutes the first step of the pyrimidine degradation pathway in which the pyrimidine bases uracil and thymine are catabolised to beta-alanine and beta-aminoisobutyric acid (beta-AIB), respectively. The mean concentration of beta-AIB was approximately 5- to 8-fold lower in urine of patients with a DPD deficiency, when compared to age-matched controls. Comparable levels of 8-hydroxydeoxyguanosine (8-OHdG) were present in urine from controls and DPD patients at the age <2 year. In contrast, slightly elevated levels of 8-OHdG were detected in urine from DPD patients with an age >2 year, suggesting the presence of increased oxidative stress.

Pharmacokinetic modelling of [2-13C]uracil metabolism in normal and DPD-deficient dogs

A physiologically based pharmacokinetic (PBPK) model to simulate the plasma concentration and 13CO2 exhalation after [2-13C]uracil administration to DPD-suppressed dogs was developed. Simulation using this PBPK model should be useful in clinical situations where DPD-deficient patients at risk are to be detected with [2-13C]uracil as an in vivo probe.

A rapid and inexpensive method for anticipating severe toxicity to fluorouracil and fluorouracil-based chemotherapy

Dihydropyrimidine dehydrogenase (DPD) deficiency leads to dramatic overexposure to fluorouracil (5-FU), resulting in a potentially lethal outcome in patients treated with standard doses. The aim of this study was to validate, in a routine clinical setting, a simple and rapid method to determine the DPD status in a subset of cancer patients, all presenting with life-threatening toxicities following 5-FU or capecitabine intake. In this study, 80 out of 615 patients (13%) suffered severe toxicities, including 5 lethal ones (0.8%), during or after chemotherapy with a fluoropyrimidine drug. Patients with severe toxicities were treated with 5-FU (76 patients) or capecitabine-containing protocols (4 patients). Simplified uracil to di-hydrouracil (U/UH2) ratio determination in plasma was retrospectively performed in these 80 patients, as a surrogate marker of DPD activity. When possible, 5-FU Css determination was performed, and screenings for the canonical IVS14+1G>A mutation were systematically carried out. Comparison of the U/UH2 ratios with a reference, non-toxic population, showed abnormal values suggesting impaired DPD activity in 57 out of the 80 toxic patients (71%) included in this study, and in 4 out of 5 patients (80%) with a fatal outcome. Similarly, drug exposures up to 15 times higher than the range observed in the non-toxic population were also observed. Importantly, no IVS14+1G>A mutation was found in these patients, including those displaying the most severe or lethal toxicities. These data warrant systematic detection of DPD-deficient patients prior to fluoropyrimidine administration, including when oral capecitabine (Xeloda) is scheduled. Finally, the simplified methodology presented here proved to be a low cost and rapid way to identify routinely patients at risk of toxicity with 5-FU or capecitabine.

DPYD*2A mutation: the most common mutation associated with DPD deficiency

BACKGROUND

Dihydropyrimidine dehydrogenase (DPD) enzyme is responsible for the elimination of approximately 80% of administered dose of 5-FU. DPD deficiency has been associated with severe 5-FU toxicity. Syndrome of DPD deficiency manifests as diarrhea, stomatitis, mucositis, and neurotoxicity and in some cases death. This is a true pharmacogenetic syndrome, with symptoms being unrecognizable until exposure to the drug.

PATIENTS AND METHODS

A 75-year-old patient with metastatic pancreatic adenocarcinoma developed grade 4 thrombocytopenia, grade 3 coagulopathy, and grade 3 neurologic toxicity with a fatal outcome following administration of 5-FU. Due to pancytopenia, DPD activity could not be determined in peripheral blood mononuclear cells (PBMC) using a previously described radioassay. Therefore, screening and genotypic analysis of homozygous and heterozygous, known and unknown sequence variants, in the DPYD gene were performed using DHPLC as previously described. All DPYD sequence variants identified by DHPLC were confirmed by DNA sequencing using a dideoxynucleotide chain termination method and capillary electrophoresis on an ABI 310 Automated DNA Sequencer.

RESULTS

Genotyping analysis of the DPYD gene revealed the presence of the heterozygous mutation, IVS14 + 1 G > A, DPYD*2A.

CONCLUSION

Genotypic analysis using DHPLC can be employed to screen DPD deficiency in a patient with severe neutropenia. The mutation IVS14 + 1 G > A, DPYD*2A, is the most common mutation associated with DPD deficiency. A G > A base change at the splice recognition sequence of intron 14, leads to exon skipping and results in a 165-bp deletion in the DPD mRNA. We have previously demonstrated that a homozygote DPYD*2A genotype results in complete deficiency while the heterozygous DPYD*2A genotype results in partial deficiency of DPD.

Increased prevalence of dihydropyrimidine dehydrogenase deficiency in African-Americans compared with Caucasians

PURPOSE

African-American patients with colorectal cancer were observed to have increased 5-fluorouracil (5-FU)-associated toxicity (leukopenia and anemia) and decreased overall survival compared with Caucasian patients. One potential source for this disparity may be differences in 5-FU metabolism. Dihydropyrimidine dehydrogenase (DPD), the initial and rate-limiting enzyme of 5-FU catabolism, has previously been shown to have significant interpatient variability in activity. Several studies have linked reduced DPD activity to the development of 5-FU toxicity. Although the distribution of DPD enzyme activity and the frequency of DPD deficiency have been well characterized in the Caucasian population, the distribution of DPD enzyme activity and the frequency of DPD deficiency in the African-American population are unknown.

EXPERIMENTAL DESIGN

Healthy African-American (n=149) and Caucasian (n=109) volunteers were evaluated for DPD deficiency using both the [2-(13)C]uracil breath test and peripheral blood mononuclear cell DPD radioassay.

RESULTS

African-Americans showed significantly reduced peripheral blood mononuclear cell DPD enzyme activity compared with Caucasians (0.26+/-0.07 and 0.29+/-0.07 nmol/min/mg, respectively; P=0.002). The prevalence of DPD deficiency was 3-fold higher in African-Americans compared with Caucasians (8.0% and 2.8%, respectively; P=0.07). African-American women showed the highest prevalence of DPD deficiency compared with African-American men, Caucasian women, and Caucasian men (12.3%, 4.0%, 3.5%, and 1.9%, respectively).

CONCLUSION

These results indicate that African-Americans, particularly African-American women, have significantly reduced DPD enzyme activity compared with Caucasians, which may predispose this population to more 5-FU toxicity.

5-Fluorouracil-related severe toxicity: a comparison of different methods for the pretherapeutic detection of dihydropyrimidine dehydrogenase deficiency

5-Fluorouracil (5-FU)-related early toxicity, due to a metabolic deficiency, is rare but is potentially severe and even lethal (0.1%). It is due to dihydropyrimidine dehydrogenase (DPYD) gene polymorphism or some epigenetic factors. The detection of metabolic change could prevent severe toxicity, but until now it has not been carried out in clinical practice.

PURPOSE

To find the simplest and most accurate pretherapeutic test to predict DPD deficiency in patients treated with 5-FU by comparing different approaches.

RESULTS

Two hundred and fifty two French Caucasian patients treated by 5-FU infusion were studied. A two-step strategy, combining firstly SNP detection and uracil plasma measurement, followed, in cases where metabolic deficiency was suspected, by dihydrouracil/uracil ratio determination to confirm deficiency and to determine the optimum 5-FU dosage, appeared the best approach, with 83% and 82% sensitivity and specificity, respectively.

CONCLUSION

These data support the future use of this approach, suitable to clinical practice, as screening test to identify DPD deficiency before 5-FU-based therapy.

Peripheral neuropathy exacerbation associated with topical 5-fluorouracil

Peripheral neuropathy secondary to 5-flourouracil and capecitabine (Xeloda) has been reported. We report the first case of exacerbation of peripheral neuropathy related to topical 5-flourouracil (Efudex). A 70-year-old Caucasian male with a history of actinic keratosis for 15 years was treated intermittently with topical application of 5-flourouracil. He also developed sensory peripheral neuropathy around the same time, but extensive work-up disclosed no clear etiology. In early 2005, he developed an exacerbation of his peripheral neuropathy following a 21-day course of topical 5-flourouracil for actinic keratosis, especially pain and parasthesias. Dihydropyrimidine dehydrogenase activity was evaluated in the peripheral mononuclear cells both by radioassay and by [2-C] uracil breath test. Dihydropyrimidine dehydrogenase activity was within the normal range by both methods. Stopping topical 5-flourouracil resolved the symptoms to baseline. Instead of topical 5-flourouracil, topical imiquimod was used which did not exacerbate his neuropathy. He was not re-challenged with topical 5-flourouracil. Topical 5-flourouracil has been known to cause mainly dermatological adverse effects, but systemic effects because of absorption are possible, especially in dihydropyrimidine dehydrogenase-deficient patients. As our patient had no other cause responsible for his neuropathy, the onset of symptoms coincided historically with topical application of 5-flourouracil and the 5-flourouracil usage preceded an exacerbation of sensory symptoms, we conclude that this drug was responsible for his polyneuropathy.

Hand-Foot Syndrome Variant in a Dihydropyrimidine Dehydrogenase–Deficient Patient Treated with Capecitabine

We present a case with dihydropyrimidine dehydrogenase (DPD) deficiency that manifested a variant of hand-foot syndrome (HFS). A 52-year-old man received capecitabine for adjuvant treatment of rectal cancer. On the ninth day of the first cycle, he presented to the clinic with a rash on the dorsum of both hands accompanied by symptoms of pain, erythema, swelling, and desquamation consistent with grade 3 HFS. The palms of his hands and soles of his feet were only tender with no apparent rash or discoloration. Dihydropyrimidine dehydrogenase activity was evaluated by radio assay using peripheral blood mononuclear cells. Dihydropyrimidine dehydrogenase activity was below normal: 0.12 nmol/minute/mg protein. Capecitabine was not resumed, and the rash resolved in 3 weeks with the use of pyridoxine and Udderly Smooth balm. Interestingly, HFS is rarely seen with 5-fluorouracil regimens containing selective DPD-inhibitors. This patient with DPD deficiency manifested a variant of HFS. The pharmacologic basis for the development of HFS in DPD-deficient patients warrants further investigation. Dihydropyrimidine dehydrogenase deficiency, if undiagnosed, can lead to death. In addition to severe to life-threatening toxicities akin to 5-fluorouracil, capecitabine can lead to unusual variants of common toxicities, including HFS, in DPD-deficient patients.

[A case of recurrent gastric cancer with dihydropyrimidine dehydrogenase (DPD) deficiency]

Dihydropyrimidine dehydrogenase (DPD) is a reducing enzyme for fluoropyrimidine which is a widely-used anti-cancer agent, and its deficiency leads to serious toxicities. We report a rare patient with a DPD deficiency. A 39-year-old man was suspected to have a gastric cancer recurrence from the elevation of CEA. Although TS-1 was administered for five days, it was stopped due to the development of grade 2 anorexia and nausea. Although we administered UFT at his request after a one-month drug rest, grade 1 stomatorrhagia besides the former adverse events developed after five days. Therefore he discontinued it and was admitted to our hospital. After 19 days, he died from multiple brain hemorrhage despite the intensive therapies. We considered that the congenital DPD deficiency caused the development of these adverse events because the DPD value was less than 5 pmol/mg/min in mononuclear cells of peripheral blood.

Individualizing chemotherapeutic treatment of colorectal cancer

PURPOSE

Patient-specific factors that enter into decisions about the chemotherapy used to treat colorectal cancer are illustrated in several case studies.

SUMMARY

Genetic polymorphisms in genes that encode drug-metabolizing enzymes may affect the disposition and the risk for toxicity from chemotherapy agents used to treat colorectal cancer. Severe toxicity from 5-fluorouracil has been attributed to a deficiency in dihydropyrimidine dehydrogenase (DPD), but currently there is no widely used genetic test for DPD deficiency. An assay is available for genotypic testing of the enzyme UGT1A1, which is predictive of toxicity from irinotecan. Advanced age, prior pelvic or abdominal radiotherapy, a poor performance status, and increased pretreatment total bilirubin concentration also are associated with irinotecan-related toxicity. A reduction in irinotecan dosage or use of an alternative agent may be warranted in patients with risk factors for toxicity. Positive epidermal growth factor receptor (EGFR) expression by immunohistochemical (IHC) staining does not necessarily predict the response to cetuximab, a monoclonal antibody that binds EGFR, possibly because of the low sensitivity of the test. Carcinoembryonic antigen (CEA) is the tumor marker of choice for monitoring for progression of colorectal cancer.

CONCLUSION

Individualizing chemotherapy based on disease stage, pharmacogenetics, prior therapy, patient age, performance status, and CEA level may help to optimize outcomes from chemotherapy for patients with colorectal cancer.

Is capecitabine safe in patients with gastrointestinal cancer and dihydropyrimidine dehydrogenase deficiency?

Patients with cancer with dihydropyrimidine dehydrogenase (DPD) deficiency are at significant risk for severe 5-fluorouracil (5-FU) toxicity, including the risk of death. Data regarding the toxicity of capecitabine, an oral fluoropyrimidine, in patients with DPD deficiency are scarce. From 2004 to 2005, 2 patients with gastrointestinal (GI) malignancies (of the pancreas and liver) experienced severe to even life-threatening toxicities during capecitabine therapy, which resulted in death for 1 patient. A DPD enzyme assay was performed as previously defined in our laboratory. Both patients were DPD deficient upon evaluation for toxicity. Capecitabine can lead to severe and sometimes life-threatening toxicities akin to toxicities caused by 5-FU in patients with DPD deficiency. In cases of unexpected severe toxicity during capecitabine treatment, DPD deficiency should be considered. We suggest that capecitabine should not be used in patients with DPD deficiency. Screening should be considered in view of the widespread use of capecitabine and 5-FU, the severe toxicity that can develop in patients with low DPD activity, and the prevalence of the mutation.

Unpredicted severe toxicity after 5-fluorouracil treatment due to dihydropyrimidine dehydrogenase deficiency

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5-FU). Thus, patients with a DPD deficiency are at risk of developing severe 5-FU-associated toxicity. A 37-year-old female with gastric cancer underwent a curative operation, followed by adjuvant chemotherapy consisting of 5-FU and epirubicin. After the first cycle of chemotherapy, the patient manifested grade 2 mucositis and febrile neutropenia, and when her treatment was subsequently continued with doxifluridine she developed severe mucositis and febrile neutropenia. A PCR study revealed that her DPD mRNA level was lower than that in a control group. Thus, when considering the routine use of 5-FU for the treatment of cancer patients, an analysis of DPD activity or screening for DPD mutations is warranted in confined patients who experience unpredicted severe toxicity after initial 5-FU administration, even though DPD deficiency is a rare metabolic defect.

Methylation of the DPYD promoter: an alternative mechanism for dihydropyrimidine dehydrogenase deficiency in cancer patients

PURPOSE

Dihydropyrimidine dehydrogenase (DPD) deficiency, a known pharmacogenetic syndrome associated with 5-fluorouracil (5-FU) toxicity, has been detected in 3% to 5% of the population. Genotypic studies have identified >32 sequence variants in the DPYD gene; however, in a number of cases, sequence variants could not explain the molecular basis of DPD deficiency. Recent studies in cell lines indicate that hypermethylation of the DPYD promoter might down-regulate DPD expression. The current study investigates the role of methylation in cancer patients with an unexplained molecular basis of DPD deficiency.

EXPERIMENTAL DESIGN

DPD deficiency was identified phenotypically by both enzyme assay and uracil breath test, and genotypically by denaturing high-performance liquid chromatography. The methylation status was evaluated in PCR products (209 bp) of bisulfite-modified DPYD promoter, using a novel denaturing high-performance liquid chromatography method that distinguishes between methylated and unmethylated alleles. Clinical samples included five volunteers with normal DPD enzyme activity, five DPD-deficient volunteers, and five DPD-deficient cancer patients with a history of 5-FU toxicity.

RESULTS

No evidence of methylation was detected in samples from volunteers with normal DPD. Methylation was detected in five of five DPD-deficient volunteers and in three of five of the DPD-deficient cancer patient samples. Of note, one of the two samples from patients with DPD-deficient cancer with no evidence of methylation had the mutation DPYD*2A, whereas the other had DPYD*13.

DISCUSSION

Methylation of the DPYD promoter region is associated with down-regulation of DPD activity in clinical samples and should be considered as a potentially important regulatory mechanism of DPD activity and basis for 5-FU toxicity in cancer patients.

Dihydropyrimidine dehydrogenase deficiency in an Indian population

BACKGROUND

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.

PATIENTS AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Toxic death-case after capecitabine + oxaliplatin (XELOX) administration: probable implication of dihydropyrimidine deshydrogenase deficiency

This report here is the case of a 52-year-old male patient who suffered from extremely severe haematological toxicities (G4 neutropenia, G4 thrombocytopenia) while undergoing Xelox (Xeloda + Oxaliplatin) treatment for his multifocal hepatocarcinoma. Despite appropriate supportive treatment, his condition quickly deteriorated and led to death. It was hypothesized that dihydropyrimidine deshydrogenase (DPD) gene polymorphism could be, at least in part, responsible for this fatal outcome. To test this hypothesis, both phenotypic and genotypic studies were undertaken, and fully confirmed the DPD-deficient status of this patient. Uracil to dihydrouracil ratio in plasma was evaluated as a surrogate marker for DPD deficiency, and showed values out of the range previously recorded from a reference, non-toxic population. Interestingly, the canonical IVS14+1G>A single nucleotide polymorphism, usually associated with the most severe toxicities reported with 5-fluorouracil (5-FU), was not found in this patient, but further investigations showed instead a heterozygosity for the 1896C>T mutation located in the exon 14 of the DPYD gene. Taken together, the data strongly suggest for the first time that a toxic-death case after capecitabine-containing protocol could be, at least in part, linked with a DPD-deficiency syndrome. The case reported here warrants therefore systematic detection of patients at risk, including when oral capecitabine is scheduled.

Pseudomembranous colitis associated with chemotherapy with 5-fluorouracil

Pseudomembranous colitis is frequently associated with antibiotics and more rarely with chemotherapeutic agents such as 5-fluorouracil. The objective of this study is to show that it is possible to confuse this infection with chemotherapy associated toxicity. We present a 54 year old woman who underwent surgery for colorectal cancer and in the first cycle of chemotherapy with 5-fluorouracil developed pseudomembranous colitis. We detected the toxin B of Clostridium difficile in stools and we began early antibiotic treatment. Thus, in patients with post chemotherapy neutropenia and diarrhoea that develop negatively, we have to rule out this infection.

A Simple and Sensitive Fully Validated HPLC-UV Method for the Determination of 5-Fluorouracil and Its Metabolite 5,6-Dihydrofluorouracil in Plasma

The authors developed a simple and sensitive, fully validated HPLC-UV method for the determination of both 5-FU and its metabolite DHFU in small-volume plasma samples. The analytes were separated on a 4.6 x 250 mm ID Atlantis dC18 5-microm column with isocratic elution at room temperature. Chlorouracil was used as internal standard. The analytes were detected with an UV diode array detector. DHFU was detected at 205 nm, 5-FU at 266 nm, and chlorouracil at both wavelengths. The limits of quantification in plasma were 0.040 mug /mL for 5-FU and 0.075 microg/mL for DHFU. Linearity, accuracy, precision, recovery, dilution, freeze-thaw stability, and stability in the sample compartment were evaluated. The method appeared linear over a range from 0.04 to 15.90 microg/mL for 5-FU and from 0.075 to 3.84 microg/mL for DHFU. The method appeared very suitable for therapeutic drug monitoring and pharmacokinetic studies of 5-FU because of its simple extraction and small sample volume. Problems in earlier published methods with interfering peaks and variable retention times were overcome. The method appeared also to be suitable for detection of uracil and its metabolite dihydrouracil in plasma.

Dihydropyrimidine dehydrogenase deficiency presenting at birth

Dihydropyrimidine dehydrogenase (DPD) deficiency (McKusick 274270) is a clinically heterogeneous autosomal recessive disorder of pyrimidine metabolism. DPD is the enzyme that catalyses the first and the rate-limiting step in the catabolism of uracil, thymine and the analogue 5-fluorouracil. To date, more than 30 patients have been diagnosed with a complete enzyme deficiency. Here, we describe the fifth case with a complete DPD deficiency presenting at birth with severe neurological abnormalities. The patient was homozygous for the common splice-site mutation IVS14+1G > A.

Comprehensive analysis of pyrimidine metabolism in 450 children with unspecific neurological symptoms using high-pressure liquid chromatography-electrospray ionization tandem mass spectrometry

To evaluate the significance of inborn metabolic disorders of the pyrimidine degradation pathway, 450 children with unspecific neurological symptoms were comprehensively studied; 200 healthy children were recruited as controls. Uracil and thymine as well as their degradation products in urine were determined with an improved method based on reversed-phase HPLC coupled with electrospray ionization tandem mass spectrometry and detection by multiple-reaction monitoring using stable-isotope-labelled reference compounds as internal standards. From the results of the control group we established age-related reference ranges of all pyrimidine degradation products. In the patient group, two children with dihydropyrimidine dehydrogenase (DPYD) deficiency were identified; one of these was homozygous for the exon 14-skipping mutation of the DPYD gene. In addition, two patients with high uracil, dihydrouracil and beta-ureidopropionate were found to have ornithine transcarbamylase deficiency. In the urine of 9 patients, beta-alanine was markedly elevated owing to treatment with vigabatrin, an irreversible inhibitor of GABA transaminase, which interferes with beta-alanine breakdown. Four patients had exclusively high levels of beta-aminoisobutyrate (beta-AIB) due to a low activity of the D-beta-AIB-pyruvate aminotransferase, probably without clinical significance. In conclusion, quantitative investigation of pyrimidine metabolites in children with unexplained neurological symptoms, particularly epileptic seizures with or without psychomotor retardation, can be recommended as a helpful tool for diagnosis in clinical practice. Sensitive methods and age-related reference ranges enable the detection of partial enzyme deficiencies.

Pyrimidine Degradation Defects and Severe 5‐Fluorouracil Toxicity

5-Fluorouracil (5FU) remains one of the most frequently prescribed chemotherapeutic drugs for the treatment of cancer. Recently, the pivotal role of the catabolic pathway of 5FU in the determination of toxicity towards 5FU has been highlighted. Patients with a (partial) dihydropyrimidine dehydrogenase deficiency proved to be at risk of developing severe toxicity after the administration of 5FU. A partial dihydropyrimidinase deficiency proved to be a novel pharmacogenetic disorder associated with severe 5FU toxicity.

RELATIONSHIPS AMONG PLASMA [2-13C]URACIL CONCENTRATIONS, BREATH 13CO2 EXPIRATION, AND DIHYDROPYRIMIDINE DEHYDROGENASE (DPD) ACTIVITY IN THE LIVER IN NORMAL AND DPD-DEFICIENT DOGS

Dihydropyrimidine dehydrogenase (DPD), the first enzyme in the sequential metabolism of pyrimidine, regulates blood concentrations of 5-fluorouracil and is deeply involved in its toxicity. This study was designed to examine the effects of a DPD inhibitor on blood concentrations of [2-(13)C]uracil ([(13)C]uracil) and (13)CO(2) concentration (Delta(13)C) expired in breath after oral or intravenous administration of [(13)C]uracil to DPD-suppressed dogs prepared by pretreatment with 5-(trans-2-bromovinyl)uracil (BVU), a DPD inhibitor. Area under the curve (AUC(t)) of [(13) C]uracil after oral administration at 20 micromol/kg to dogs pretreated with BVU at 2, 5, and 40 mmol/kg were 37-, 88- and 120-fold higher than those of the control dogs, respectively. In contrast, breath AUC(t) values of Delta(13)C were reduced to 0.88-, 0.47- and 0.13-fold the control values, respectively. Upon intravenous administration of [(13)C]uracil at 20 micromol/kg to dogs pretreated with BVU at 0.5, 2, and 40 micromol/kg, blood AUC(t) values of [(13)C]uracil were 1.4-, 4.2-, and 13-fold higher than those of the control group, respectively, whereas breath AUC(t) values were reduced to 1.0-, 0.83-, and 0.07-fold the respective control values. DPD activities in the liver cytosol of dogs pretreated with BVU at 0.5, 2, 5, and 40 micromol/kg were decreased to 0.71-, 0.12-, 0.06-, and 0.04-fold those of the control dogs, respectively. These findings demonstrate that breath output (Delta(13)C) is a good marker of hepatic DPD activity in vivo.

Rapid identification of dihydropyrimidine dehydrogenase deficiency by using a novel 2-13C-uracil breath test

PURPOSE

Dihydropyrimidine dehydrogenase (DPD)-deficient cancer patients have been shown to develop severe toxicity after administration of 5-fluorouracil. Routine determination of DPD activity is limited by time-consuming and labor-intensive methods. The purpose of this study was to develop a simple and rapid 2-(13)C-uracil breath test, which could be applied in most clinical settings to detect DPD-deficient cancer patients.

EXPERIMENTAL DESIGN

Fifty-eight individuals (50 "normal," 7 partially, and 1 profoundly DPD-deficient) ingested an aqueous solution of 2-(13)C-uracil (6 mg/kg). (13)CO(2) levels were determined in exhaled breath at various time intervals up to 180 min using IR spectroscopy (UBiT-IR(300)). DPD enzyme activity and DPYD genotype were determined by radioassay and denaturing high-performance liquid chromatography, respectively.

RESULTS

The mean (+/-SE) C(max), T(max), delta over baseline values at 50 min (DOB(50)) and cumulative percentage of (13)C dose recovered (PDR) for normal, partially, and profoundly DPD-deficient individuals were 186.4 +/- 3.9, 117.1 +/- 9.8, and 3.6 DOB; 52 +/- 2, 100 +/- 18.4, and 120 min; 174.1 +/- 4.6, 89.6 +/- 11.6, and 0.9 DOB(50); and 53.8 +/- 1.0, 36.9 +/- 2.4, and <1 PDR, respectively. The differences between the normal and DPD-deficient individuals were highly significant (all Ps <0.001).

CONCLUSIONS

We demonstrated statistically significant differences in the 2-(13)C-uracil breath test indices (C(max), T(max), DOB(50), and PDR) among healthy and DPD-deficient individuals. These data suggest that a single time-point determination (50 min) could rapidly identify DPD-deficient individuals with a less costly and time-consuming method that is applicable for most hospitals or physicians' offices.

Multiple Organ Failure due to 5-Fluorouracil Chemotherapy in a Patient with a Rare Dihydropyrimidine Dehydrogenase Gene Variant

BACKGROUND

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the metabolism of the chemotherapeutic drug 5-fluorouracil (5-FU). Application of 5-FU is restricted by a narrow therapeutic index because of severe toxicity of WHO grades III-IV. The exon 14-skipping mutation (c.1905+1G>A) accounts for approximately a quarter of all severely toxic cases. However, numerous other polymorphisms have been identified within the DPYD gene in affected patients, and the pathophysiological significance of most of them is unclear.

PATIENT AND METHODS

We report a patient with advanced caecum cancer who twice received 950 mg 5-FU and 45 mg folinic acid as adjuvant by bolus injection. 2 days after onset of chemotherapy, the patient developed a multiple organ dysfunction exhibiting a cardiogenic shock with severe left ventricular insufficiency, marked reduction of renal function, and beginning hepatic encephalopathy with somnolence, myoclonus, and a seizure. In order to investigate a possible defect within the DPYD gene direct sequencing of all 23 exons was carried out.

RESULTS

Genotyping revealed a rare c.1601G>A polymorphism which causes a change in the protein sequence (S534N). Data regarding the clinical relevance are ambiguous. The polymorphism has been detected together with an intronic mutation and both polymorphisms have consistently been reported with reduced enzyme activity.

CONCLUSION

The present case provides further evidence of an etiologic role of the c.1601G>A mutation for DPD deficiency and the occurrence of severe 5-FU-related toxicity and underlines the value of comprehensive pharmakogenetic diagnostics with respect to the dihydropyrimidine dehydrogenase.

Dihydropyrimidine Dehydrogenase Deficiency, a Pharmacogenetic Syndrome Associated with Potentially Life-Threatening Toxicity Following 5-Fluorouracil Administration

Dihydropyrimidine dehydrogenase (DPD) deficiency is a pharmacogenetic syndrome associated with potentially life-threatening toxicity following the administration of standard doses of 5-fluorouracil. This syndrome derives its importance from the fact that approximately 2 million patients receive the drug worldwide each year. Population studies have suggested that 4%-7% of the American population exhibit dose-limiting toxicity that might be associated with a genetic defect in the DPYD gene that encodes for the DPD enzyme. During the past several years it has become increasingly clear that genetics is a major determinant of the variability in drug response, accounting for the probability of drug efficacy and the likelihood of toxic drug reactions. This article briefly discusses the clinical presentation, laboratory diagnosis, pharmacokinetics, inheritance, and the clinical management options of DPD deficiency. The variability of DPD enzyme activity in population studies and the different DPYD alleles together with new phenotypic and genotypic methods of screening for DPD deficiency will also be reviewed.

Dihydropyrimidine dehydrogenase deficiency: impact of pharmacogenetics on 5-fluorouracil therapy

Through the use of pharmacogenetic studies, interindividual variability in response (efficacy and toxicity) to 5-fluorouracil (5-FU) chemotherapy has been linked to the rate-limiting enzyme in the drug's catabolic pathway, known as dihydropyrimidine dehydrogenase (DPD). This pharmacogenetic syndrome, known as "DPD deficiency," results in excessive amounts of 5-FU available to be anabolized to its active metabolites and is relatively undetectable by clinical observation prior to 5-FU administration. Extensive studies have associated both profound and partial deficiency in DPD activity with severe, unanticipated toxicity after 5-FU administration, while research on the molecular basis behind DPD deficiency has been linked to various sequence variants of the DPYD gene. Due to the widespread use of 5-FU, the severity of toxicity associated with DPD deficiency, and the prevalence of DPD deficiency in the population, extensive research is continually being performed to develop quick and accurate phenotypic and genotypic assays suitable for clinical settings that would allow clinicians to identify patients susceptible to adverse 5-FU reactions.

New insights in dihydropyrimidine dehydrogenase deficiency: a pivotal role for beta-aminoisobutyric acid?

DPD (dihydropyrimidine dehydrogenase) constitutes the first step of the pyrimidine degradation pathway, in which the pyrimidine bases uracil and thymine are catabolized to beta-alanine and the R-enantiomer of beta-AIB (beta-aminoisobutyric acid) respectively. The S-enantiomer of beta-AIB is predominantly derived from the catabolism of valine. It has been suggested that an altered homoeostasis of beta-alanine underlies some of the clinical abnormalities encountered in patients with a DPD deficiency. In the present study, we demonstrated that only a slightly decreased concentration of beta-alanine was present in the urine and plasma, whereas normal levels of beta-alanine were present in the cerebrospinal fluid of patients with a DPD deficiency. Therefore the metabolism of beta-alanine-containing peptides, such as carnosine, may be an important factor involved in the homoeostasis of beta-alanine in patients with DPD deficiency. The mean concentration of beta-AIB was approx. 2-3-fold lower in cerebrospinal fluid and urine of patients with a DPD deficiency, when compared with controls. In contrast, strongly decreased levels (10-fold) of beta-AIB were present in the plasma of DPD patients. Our results demonstrate that, under pathological conditions, the catabolism of valine can result in the production of significant amounts of beta-AIB. Furthermore, the observation that the R-enantiomer of beta-AIB is abundantly present in the urine of DPD patients suggests that significant cross-over exists between the thymine and valine catabolic pathways.

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.

5FU and oxaliplatin-containing chemotherapy in two dihydropyrimidine dehydrogenase-deficient patients

Patients with a germline mutation leading to a deficiency of the dihydropyrimidine dehydrogenase (DPD) enzyme are at risk from developing severe toxicity on the administration of 5FU-containing chemotherapy. We report on the implications of this inborn genetic error in two patients who received 5FU and oxaliplatin. A possible co-medication effect of oxaliplatin is considered, as are the consequences of screening for DPD deficiency.

Mutational analysis of the human dihydropyrimidine dehydrogenase gene by denaturing high-performance liquid chromatography

Mutations in the DPYD gene, which encodes dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme in the catabolism of pyrimidines, are responsible for an inborn error of metabolism associated with thymine-uraciluria and neurological symptoms. Because the antimetabolite 5-fluorouracil (5-FU) is metabolized by the same enzyme, deficient DPYD alleles may also constitute a risk factor for severe toxicity following treatment with this anticancer drug. The aim of this study was to develop a comprehensive and rapid method to detect sequence variations within the DPYD gene. Using polymerase chain reaction (PCR) amplification and denaturing high-performance liquid chromatography (DHPLC), we established a protocol that makes it possible to screen all 23 exons of the DPYD gene and their exon-intron boundaries for both known and unknown mutations under identical conditions. A novel one-step PCR mutagenesis procedure was developed to generate heterozygous mutant amplicons as positive controls to optimize DHPLC detection of any sequence variation. DHPLC analysis was shown to result in mutation-specific elution profiles and to be able to distinguish different base changes within the same exon or different heterozygous combinations of mutations within the same exon. By analyzing the DPYD gene in 16 affected individuals, a total of 47 base changes were detected, representing eight known mutations and three novel intronic base changes. Sequence analysis confirmed all base changes detected. This method will be useful in identifying patients at risk for toxicity prior to 5-FU treatment, as well as in the analysis of individual patients with thymine-uraciluria.