Dihydropyrimidine Dehydrogenase Deficiency Research Articles

A Facile Method for the Quantification of Urinary Uracil Concentration by a Uracil-Specific Fluorescence Derivatization Reaction.

A facile and reliable fluorescence method for the quantification of urinary uracil concentration is proposed herein. The assay utilizes a specific fluorescence (FL) derivatization reaction for uracil using 3-methylbenzamidoxime as a fluorogenic reagent. Although the presence of urine inhibited the FL reaction, 10 µL of urine was sufficient for the detection of urinary uracil. The uracil derivative was successfully separated from other fluorescent impurities using simple reversed-phase LC with FL detection. Urinary uracil concentrations from 16 people were compared with the concentrations obtained by the traditional column-switching liquid chromatographic analysis with UV detection. The FL derivative of uracil appeared as a single peak in the chromatograms of all samples. However, several samples showed an additional peak overlapping the uracil peak when using the column-switching method because of UV-active impurities. These results indicated that that the present method is not affected by interfering substances in urine and affords a precise determination of urinary uracil. We expect the proposed method to be applicable for diagnosing dihydropyrimidine dehydrogenase deficiency in 5-fluorouracil chemotherapy.

P-297 Upfront dihydropyrimidine dehydrogenase deficiency detection to secure 5-FU or capecitabine administration: Application to colorectal cancer patients

Fluorouracil (5-FU) is rapidly degraded by dihydropyrimidine dehydrogenase (DPD). Therefore, a DPD deficiency can lead to severe toxicity or even death after treatment with 5-FU or capecitabine. Various tests based on the evaluation of the DPD enzymatic activity have been studied for screening for DPD deficiency in order to avoid this toxicity. Testing includes phenotyping (direct or indirect measurement of enzyme activity) or genotyping (detection of inactivating polymorphisms) of the DPD gene.

Eastern Canadian Gastrointestinal Cancer Consensus Conference 2019.

The annual Eastern Canadian Gastrointestinal Cancer Consensus Conference 2019 was held in Morell, Prince Edward Island, 19–21 September 2019. Experts in medical oncology, radiation oncology, and surgical oncology who are involved in the management of patients with gastrointestinal malignancies participated in presentations and discussion sessions for the purpose of developing the recommendations presented here. This consensus statement addresses multiple topics in the management of anal, colorectal, biliary tract, and gastric cancers, including: radiotherapy and systemic therapy for localized and advanced anal cancer; watch and wait strategy for the management of rectal cancer; role of testing for dihydropyrimidine dehydrogenase (DPD) deficiency prior to commencement of fluoropyrimidine therapy; radiotherapy and systemic therapy in the adjuvant and unresectable settings for biliary tract cancer; and radiotherapy and systemic therapy in the perioperative setting for early-stage gastric cancer.

Dihydropyrimidine dehydrogenase deficiency in patients treated with 5FU or capecitabine based regimens: A single center experience from South India.

e15517 Background: DPYD deficiency is present in 3-5% of patients. The risk of treatment-related death in DPYD mutation carriers who receive fluoropyrimidine chemotherapy has been estimated at 3-10%. There is growing data in support of widespread screening for DPYD deficiency prior to fluoropyrimidine chemotherapy. The purpose of our study was to identify the prevalence of DPYD deficiency among patients receiving 5-fluorouracil (5FU) or capecitabine based combination chemotherapy, and to analyse the toxicity profile among the DPYD deficient group. Methods: The study involved patients who have received 5FU and capecitabine based chemotherapy for the treatment for gastrointestinal, breast and head and neck cancers between 2019-2020. Four DPYD variants were checked using real-time PCR based Genotyping assay. Three common DPYD variants recommended by the CPIC guidelines (IVS14+1 G>A (*2A), c.1679T>G (*13), c.2846A>T) and a common variant in Asian population (c.496A>G), based on previous studies, was included in our analysis. These variants were assessed prior to the initiation of the chemotherapy and dose was modified based on the activity score and the toxicity profile was assessed. Descriptive statistics was performed using SPSS version 20. Results: 375 patients were included in this analysis. The median age of the cohort was 61years (21-84 years). 51.3% were males and 49.7% females. Among the 375 patients, 47 patients had DPYD mutation (12.5%). The median age of the DPYD mutated patients were 68 years; 29 (61.7%) males and 18 (38.2%) females. 32 (68.8%) had deleterious mutation in DPYD variant c.496A>G (rs2297595) and 15 (31.9%) showed mutation IVS14+1 G>A (rs3918290). 35 out 47 patients had grade II-III toxicity even after dose reduction during the first cycle of chemotherapy. The commonly seen adverse events were hand and foot syndrome in 18 (38.3%), mucositis in 7 (14.9%), diarrrhoea in 15 (31.9%) and neutropenia in 25 (31.9%) patients. Four patients had febrile neutropenia. One patient experience myocardial infarction. There was no mortality. Chi square analysis showed DPYD mutation had significant association with presence of severe adverse reaction (74.5%, p-value. 0.002). Conclusions: Prevalence of DPYD mutation in our patients was 12.5%. They experienced more toxicities while receiving 5-FU/Capecitabine even after dose modification. c.496A>G (rs2297595) was the most common variant seen in our patients. Screening of patients for DPYD mutations prior to administration of 5-FU/capecitabine using pharmacogenetic methods may help identify those patients who are at risk for adverse effects, allowing a more individualized approach to their chemotherapy management. c.496A>G (rs2297595) variant should also be in included routinely in DPYD screening among South Asian population.

Neoadjuvant chemotherapy for locally advanced colon cancer patients: Long-term results from a single institutional experience.

e15598 Background: Neoadjuvant chemotherapy (NAC) is an emerging alternative in the management of patients with locally advanced colorectal cancer (LACRC), with promising results in terms of R0 resection rates, compliance, postoperative morbidity and a trend towards reduced risk of relapse. However, more mature data are required. We evaluated the long-term outcome of this strategy in our institution. Methods: We retrospectively analysed LACRC patients treated preoperatively with either biweekly FOLFOX or XELOX at standard doses as a follow-up of our previous experience with this neoadjuvant approach. Patients were identified from a prospectively collected tumor registry database from our institution. Clinical staging was based on colonoscopy and CT-scan. Only patients with radiological signs of lymph node involvement and/or extramural invasion > 5 mm were included. The uracil/dihidrouracil ratio was calculated at baseline as a surrogate marker of DPD deficiency. Pathological tumor regression was graded according to the MSKCC and toxicity with the NCI-CTCAE 4.0. Results: From February 2006 to November 2019 91 pts with MSS LACRC (M/F: 62/29; median age 66. Clinical stage; T3: 60.4%, T4: 37.4%, N+: 75.8%; Sideness: 82.4% left located were analysed. Preoperative chemo was FOLFOX in 46 pts and CAPOX in 45 pts. Median number of preoperative cycles was 4 (range 1-10). Side effects profile included G3-4 diarrhea (3.3%), G2 sensitive neuropathy (12.1%) and G2 neutropenia (4.4%). 9 pts had a treatment delay due to haematological toxicity. No progressive disease was noted during neoadjuvant chemotherapy. All patients underwent surgery, most of them (63.7%) by a laparoscopic approach. pCR was found in 11 pts (12.1%). Grade 3, 3+ and 4 tumor regression according to MSKCC score was reached in 50.5% of the patients (Median number of harvested nodes was 17 (range 7-51), with 75.8% being ypN0. Lymphovascular and perineural invasion were found in 7.7% and 6.6% of the patients, respectively. The median hospital stay was 7 days (3-36) and 13 pts develop any surgical complication. 37.4% received adjuvant treatment. After a median follow-up of 63 months, median progression-free (PFS) and overall survival (OS) have not been reached. 5-year actuarial PFS for right and left LACRC was 77 and 87%, respectively. Conclusions: Our data add to the growing evidence suggesting that NAC may play a meaningful role in LACRC patients

Leukoencephalopathy with transient splenial lesions related to 5-fluorouracil or capecitabine.

5-Fluorouracil (5-FU) and its oral prodrug capecitabine have been rarely but consistently associated with acute central nervous system toxicity, including transient leukoencephalopathies involving the splenium of the corpus callosum. We performed a retrospective search in the French Pharmacovigilance database (FPDB) (January 1985-July 2020) for adult patients affected by solid cancers who developed acute toxic leukoencephalopathies with splenial lesions following treatment with 5-FU or capecitabine. A comprehensive review of the literature helped to circumstantiate our findings. Our research in the FPDB identified six patients who, within 3days from their first cycle of 5-FU or capecitabine, developed acute neurological symptoms, including gait ataxia (n=4), dysarthria (n=3), dysmetria (n=2), headache (n=2), and confusion (n=2). Brain magnetic resonance imaging (MRI) showed T2/FLAIR (fluid-attenuated inversion recovery) hyperintensities in the corpus callosum, with diffusion restriction and no contrast enhancement, generally accompanied by additional alterations in the bilateral supratentorial white matter (n=5). All patients discontinued the agent supposedly responsible for the toxicity and experienced full recovery after a median of 8.5days from symptom onset. Control MRI showed a progressive normalization of acute MRI abnormalities. Literature review identified 26 cases with similar clinical and paraclinical characteristics. A single patient from the literature resumed 5-FU at a lower dose, with no recurrent toxicity. 5-FU and capecitabine might be responsible for acute leukoencephalopathies with transient splenial lesions that are generally reversible upon drug discontinuation. Resuming the agent responsible for toxicity might be feasible in selected cases, after having excluded dihydropyrimidine dehydrogenase deficiency, if expected benefits outweigh the risks.

Role of microRNAs in fluoropyrimidine-related toxicity: what we know.

Although more than half a century has passed since the discovery of fluoropyrimidines, they are still used in the treatment of many types of cancer, and it is estimated that annually two million patients undergo fluoropyrimidine-based chemotherapy. The toxicity resulting from the use of fluoropyrimidines affects about 30-40% of patients, which in some cases may prove to be lethal. The key player in fluoropyrimidine toxicity is DPD activity, and patients with deficits are more likely to develop significant adverse events. In addition to genotyping DPYD variants associated with DPD deficiency, overexpression of miR-27 has also been shown to be a predictive factor for fluoropyrimidine toxicity. This review aims to relate what we know so far about the involvement of miRNA in fluoropyrimidine toxicity and to open new perspectives in this field.

An Evaluation of the Diagnostic Accuracy of a Panel of Variants in DPYD and a Single Variant in ENOSF1 for Predicting Common Capecitabine Related Toxicities.

Simple Summary5-Fluorouracil (5-FU) is a chemotherapy drug that can cause severe toxicity in some patients. A protein, an action molecule in our cells, called dihydropyrimidine dehydrogenase, or DPD for short, is important in clearing 5-FU from the body. Some people have versions of DPD that do not clear 5-FU very well. This causes active drug to stay in the body too long, causing toxicities such as diarrhoea or low levels of blood cells important for fighting infections. Current guidelines identify four sequence changes in the gene that encodes DPD with high level evidence of an impact on protein activity. Our study aims to calculate the frequency of a set of variants identified in patients with DPD deficiency in patients that were part of a clinical trial called QUASAR 2. We go on to test how well the DPD deficiency variants and a set of common variants previously shown to be associated with 5-FU toxicity can predict a person’s risk of 5-Fluorouracil induced toxicity. Our research is important for working out the best way to identify patients at risk of toxicity so high risk patients can be given lower doses of 5-Fluorouracil or be treated with a different drug all together.Efficacy of 5-Fluorouracil (5-FU)-based chemotherapy is limited by significant toxicity. Tests based upon variants in the Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines with high level evidence of a link to dihydropyrimidine dehydrogenase (DPD) phenotype and 5-FU toxicity are available to identify patients at high risk of severe adverse events (AEs). We previously reported associations between rs1213215, rs2612091, and NM_000110.3:c.1906-14763G>A (rs12022243) and capecitabine induced toxicity in clinical trial QUASAR 2. We also identified patients with DPD deficiency alleles NM_000110.3: c.1905+1G>A, NM_000110.3: c.2846C>T, NM_000110.3:c.1679T>G and NM_000110.3:c.1651G>A. We have now assessed the frequency of thirteen additional DPYD deficiency variants in 888 patients from the QUASAR 2 clinical trial. We also compared the area under the curve (AUC)—a measure of diagnostic accuracy—of the high-level evidence variants from the CPIC guidelines plus and minus additional DPYD deficiency variants and or common variants associated with 5-FU toxicity. Including additional DPYD deficiency variants retained good diagnostic accuracy for serious adverse events (AEs) and improved sensitivity for predicting grade 4 haematological toxicities (sensitivity 0.75, specificity 0.94) but the improvement in AUC for this toxicity was not significant. Larger datasets will be required to determine the benefit of including additional DPYD deficiency variants not observed here. Genotyping two common alleles statistically significantly improves AUC for prediction of risk of HFS and may be clinically useful (AUC difference 0.177, sensitivity 0.84, specificity 0.31).

Unusual case of colorectal carcinoma with sarcoid-like mediastinal adenopathy and near-fatal DPD deficiency

The liver is the commonest site for metastases in colorectal carcinoma; other isolated sites are considered extremely rare. 5-fluorouracil (5-FU) is the backbone of treatment for metastatic colorectal carcinoma (mCRC) and without it survival may be significantly reduced. It is primarily metabolised by dihydropyrimidine dehydrogenase (DPD). Testing for DPD deficiency is not a routine practice and toxicity will only manifest following drug challenge. There are limited standardised treatment guidelines in managing patients with severe drug reactions following 5-FU exposure. We describe a delayed presentation of life-threatening DPD deficiency in a patient with colorectal carcinoma and mediastinal lymphadenopathy. We describe our experience with chemotherapy in this difficult clinical scenario and highlight the importance of histological confirmation in unusual sites of metastatic disease.

Preemptive screening of DPYD as part of clinical practice: high prevalence of a novel exon 4 deletion in the Finnish population

Capecitabine is a fluoropyrimidine that is widely used as a cancer drug for the treatment of patients with a variety of cancers. Unfortunately, early onset, severe or life-threatening toxicity is observed in 19-32% of patients treated with capecitabine and 5FU. Dihydropyrimidine dehydrogenase (DPD) is the rate-limiting enzyme in the degradation of 5FU and a DPD deficiency has been shown to be a major determinant of severe fluoropyrimidine-associated toxicity. DPD is encoded by the DPYD gene and some of the identified variants have been described to cause DPD deficiency. Preemptive screening for DPYD gene alterations enables the identification of DPD-deficient patients before administering fluoropyrimidines. In this article, we describe the application of upfront DPD screening in Finnish patients, as a part of daily clinical practice, which was based on a comprehensive DPYD gene analysis, measurements of enzyme activity and plasma uracil concentrations. Almost 8% of the patients (13 of 167 patients) presented with pathogenic DPYD variants causing DPD deficiency. The DPD deficiency in these patients was further confirmed via analysis of the DPD activity and plasma uracil levels. Interestingly, we identified a novel intragenic deletion in DPYD which includes exon 4 in four patients (31% of patients carrying a pathogenic variant). The high prevalence of the exon 4 deletion among Finnish patients highlights the importance of full-scale DPYD gene analysis. Based on the literature and our own experience, genotype preemptive screening should always be used to detect DPD-deficient patients before fluoropyrimidine therapy.

Cost effectiveness of DPYD genotyping to screen for dihydropyrimidine dehydrogenase (DPD) deficiency prior to adjuvant chemotherapy for colon cancer.

55 Background: Fluoropyrimidine chemotherapy agents, including 5-fluorouracil and capecitabine, are the backbone of adjuvant treatment for colon cancer, and adjuvant chemotherapy substantially reduces recurrence and mortality after surgical resection of stage 3 colon cancer. While fluoropyrimidine chemotherapy is generally safe, the risk of severe, potentially fatal chemotherapy toxicity is substantially increased for the 2-3% of U.S. patients with DPD deficiency caused by pathogenic variants in the DPYD gene. DPYD genotype testing is readily available in the U.S. but has not been widely adopted. We evaluated the cost effectiveness of DPYD genotyping prior to adjuvant chemotherapy for colon cancer in the U.S. Methods: We constructed a Markov model to simulate screening for DPD deficiency with DPYD genotyping (versus no screening) among patients receiving fluoropyrimidine-based adjuvant chemotherapy for stage 3 colon cancer. Screen-positive patients were modeled to receive dose-reduced fluoropyrimidine chemotherapy. Model transition probabilities for treatment-related toxicities were derived from published clinical trial data with annotation of DPYD genotype and chemotherapy dosing strategy. Our analysis is from the healthcare perspective, with a time horizon of five years and an annual discount rate of 3% for future costs and benefits. Direct healthcare costs and health utilities were estimated from published sources and converted to 2020 US dollars, and post-treatment survival was modeled from SEER data. The primary outcome was the incremental cost-effectiveness ratio (ICER), defined as dollars per quality-adjusted life year (QALY). We used a value of $100,000/QALY as the cost-effectiveness threshold. One-way sensitivity analyses were used to examine model uncertainty. Results: Compared with no screening, screening for DPD deficiency with DPYD genotyping increased per-patient costs by $106 and improved quality-adjusted survival by 0.0028 QALYs, leading to an ICER of $37,300/QALY. In one-way sensitivity analyses, the ICER exceeded $100,000/QALY when the carrier frequency of pathogenic DPYD gene variants was less than 1.17%, and when the specificity of DPYD genotyping was less than 98.9%. Cost-effectiveness estimates were not sensitive to the cost of DPYD genotyping, the cost of toxicity-related hospitalizations, or the health utility associated with grade 3-4 toxicity. Conclusions: Among patients receiving adjuvant chemotherapy for stage 3 colon cancer, screening for DPD deficiency with DPYD genotyping is a cost-effective strategy for preventing infrequent but severe, sometimes fatal toxicities of fluoropyrimidine chemotherapy.

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.

Association of 5-FU Therapeutic Drug Monitoring to DPD Phenotype Assessment May Reduce 5-FU Under-Exposure.

In order to limit 5-fluorouracil (5-FU) toxicity, some health agencies recommend evaluating dihydropyrimidine dehydrogenase (DPD) deficiency before any 5-FU treatment introduction. In our study, we investigated relationships between 5-FU clearance and markers of DPD activity such as uracilemia (U), dihydrouracilemia (UH2)/U ratio, or genotype of the gene encoding DPD (DPYD). All patients with gastrointestinal cancers who received 5-FU-based regimens form March 2018 to June 2020 were included in our study. They routinely benefited of a pre-therapeutic DPYD genotyping and phenotyping. During 5-FU infusion, blood samples were collected to measure 5-FU steady-state concentration in order to adapt 5-FU doses at the following cycles. A total of 169 patients were included. Median age was 68 (40–88) years and main primary tumor sites were colorectal (40.8%) and pancreas (31.4%), metastatic in 76.3%. 5-FU was given as part of FOLFIRINOX (44.4%), simplified FOLFOX-6 (26.6%), or docetaxel/FOLFOX-4 (10.6%). Regarding DPD activity, median U and UH2/U were, respectively, 10.8 ng/mL and 10.1, and almost 15% harbored a heterozygous mutation. On the range of measured U and UH2/U, no correlation was observed with 5-FU clearance. Moreover, in patients with U < 16 ng/mL, 5-FU exposure was higher than in other patients, and most of them benefited of dose increase following 5-FU therapeutic drug monitoring (TDM). If recent guidelines recommend decreasing 5-FU dose in patients harboring U ≥ 16 ng/mL, our study highlights that those patients are at risk of under-exposure and that 5-FU TDM should be conducted in order to avoid loss of efficacy.

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

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

Population-scale predictions of DPD and TPMT phenotypes using a quantitative pharmacogene-specific ensemble classifier

BackgroundInter-individual differences in dihydropyrimidine dehydrogenase (DPYD encoding DPD) and thiopurine S-methyltransferase (TPMT) activity are important predictors for fluoropyrimidine and thiopurine toxicity. While several variants in these genes are known to decrease enzyme activities, many additional genetic variations with unclear functional consequences have been identified, complicating informed clinical decision-making in the respective carriers.MethodsWe used a novel pharmacogenetically trained ensemble classifier to analyse DPYD and TPMT genetic variability based on sequencing data from 138,842 individuals across eight populations.ResultsThe algorithm accurately predicted in vivo consequences of DPYD and TPMT variants (accuracy 91.4% compared to 95.3% in vitro). Further analysis showed high genetic complexity of DPD deficiency, advocating for sequencing-based DPYD profiling, whereas genotyping of four variants in TPMT was sufficient to explain >95% of phenotypic TPMT variability. Lastly, we provided population-scale profiles of ethnogeographic variability in DPD and TPMT phenotypes, and revealed striking interethnic differences in frequency and genetic constitution of DPD and TPMT deficiency.ConclusionThese results provide the most comprehensive data set of DPYD and TPMT variability published to date with important implications for population-adjusted genetic profiling strategies of fluoropyrimidine and thiopurine risk factors and precision public health.

Exposure-response analysis of Raltitrexed assessing liver toxicity.

Raltitrexed (RTX) is a thymidylate synthase inhibitor with large pharmacokinetics (PK) variability that can be administered in case of 5-fluorouracil (5FU) intolerance or dihydropyrimidine dehydrogenase deficiency. While it is a more potent thymidylate synthase inhibitor than 5FU, RTX failed to replace this drug for colorectal cancer patients, mainly due to its toxicity at the recommended dose of 3 mg/m2 every 3 weeks. However, every 2 weeks administration at 2 mg/m2 demonstrated a favourable toxicity profile. We performed a randomized crossover comparative population PK study between every 2 weeks TOMOX (RTX 2 mg/m2 ) and every 3 weeks TOMOX (RTX 3 mg/m2 ). A three-compartment model and a proportional error model best describe the data. Creatinine clearance and sex, but not body surface area (BSA), were covariates of RTX clearance leading to decrease of its interindividual variability of 28%. Weight and body surface area were covariates of central and peripheral volumes of distribution, respectively, leading to decreases of interindividual variability of 34.6% and 100%, respectively. In contrast to the dose, AUC was a good predictor of liver toxicity (P = 0.006, OR = 3.91, 95%CI = [1.48-10.34]). Using covariates to compute individual clearance and a threshold AUC (1.639, determined in this study), a covariates-based dose was calculated, leading to less variability in AUC than observed with the actual BSA-based or fixed doses. These results advocate for the use of creatinine clearance and sex to determine the RTX dose instead of BSA.

An in vitro approach to simulate the process of 5-fluorouracil degradation with dihydropyrimidine dehydrogenase: the process in accordance to the first-order kinetic reaction

Partial or complete deficiency in the dihydropyrimidine dehydrogenase (DPD) has been observed in 3%–5% and 0.1% of the general population, respectively. It causes severe toxicity in the context of 5-fluorouracil (5-FU) therapy. However, the current tests for determination of DPD deficiency have limitations in routine clinical usage. Therefore, an in vitro approach for simulating 5-FU degradation was established by mixing 5-FU with blank whole blood matrix in this study. The effects of initial 5-FU concentrations and temperatures on DPD activities were investigated as well. The degradation process followed the first-order kinetic reaction (r2 > 0.98). The degradation rates were determined by temperature and individually different. The DPD inhibitor, gimeracil, could block this degradation, which indicated that DPD was the main factor. The degradation process of 5-FU in patients’ whole blood in vitro was consistent with it after mixing 5-FU with blank whole blood matrix. In conclusion, mixing 5-FU with blank matrix can simulate the process of 5-FU degradation with DPD.

Comparison of 4 Screening Methods for Detecting Fluoropyrimidine Toxicity Risk: Identification of the Most Effective, Cost-Efficient Method to Save Lives.

Background:Fluoropyrimidines (FPs) carry around 20% risk of G3-5 toxicity and 0.2-1% risk of death, due to dihydropyrimidine dehydrogenase (DPD) deficiency. Several screening approaches exist for predicting toxicity, however there is ongoing debate over which method is best. This study compares 4 screening approaches.Method:472 patients treated for colorectal, head-and-neck, breast, or pancreatic cancers, who had not been tested pre-treatment for FP toxicity risk, were screened using: DPYD genotyping (G); phenotyping via plasma Uracil (U); phenotyping via plasma-dihydrouracil/uracil ratio (UH2/U); and a Multi-Parametric Method (MPM) using genotype, phenotype, and epigenetic data. Performance was compared, particularly the inability to detect at-risk patients (false negatives).Results:False negative rates for detecting G5 toxicity risk were 51.2%, 19.5%, 9.8% and 2.4%, for G, U, UH2/U and MPM, respectively. False negative rates for detecting G4-5 toxicity risk were 59.8%, 36.1%, 21.3% and 4.7%, respectively. MPM demonstrated significantly (p < 0.001) better prediction performance.Conclusion:MPM is the most effective method for limiting G4-5 toxicity. Its systematic implementation is cost-effective and significantly improves the risk-benefit ratio of FP-treatment. The use of MPM, rather than G or U testing, would avoid nearly 8,000 FP-related deaths per year globally (500 in France), and spare hundreds of thousands from G4 toxicity.

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.

New DPYD variants causing DPD deficiency in patients treated with fluoropyrimidine.

Several clinical guidelines recommend genetic screening of DPYD, including coverage of the variants c.1905 + 1G>A(DPYD*2A), c.1679T>G(DPYD*13), c.2846A>T, and c.1129-5923C>G, before initiating treatment with fluoropyrimidines. However, this screening is often inadequate at predicting the occurrence of severe fluoropyrimidine-induced toxicity in patients. Using a complementary approach combining whole DPYD exome sequencing and in silico and structural analysis, as well as phenotyping of DPD by measuring uracilemia (U), dihydrouracilemia (UH2), and the UH2/U ratio in plasma, we were able to characterize and interpret DPYD variants in 28 patients with severe fluoropyrimidine-induced toxicity after negative screening. Twenty-five out of 28 patients (90%) had at least 1 variant in the DPYD coding sequence, and 42% of the variants (6/14) were classified as potentially deleterious by at least 2 of the following algorithms: SIFT, Poly-Phen-2, and DPYD varifier. We identified two very rare deleterious mutations, namely, c.2087G>A (p.R696H) and c.2324T>G (p.L775W). We were able to demonstrate partial DPD deficiency, as measured by the UH2/U ratio in a patient carrying the variant p.L775W for the first time. Whole exon sequencing of DPYD in patients with suspicion of partial DPD deficiency can help to identify rare or new variants that lead to enzyme inactivation. Combining different techniques can yield abundant information without increasing workload and cost burden, thus making it a useful approach for implementation in patient care.