13C-uracil breath test to predict 5-fluorouracil toxicity in gastrointestinal cancer patients

Testing for Dihydropyrimidine Dehydrogenase Deficiency to Individualize 5-Fluorouracil Therapy

Simple Summary

5-Fluorouracil (5-FU) is a chemotherapy drug that is commonly used to treat multiple cancers. Many people who are treated with 5-FU experience severe toxicity to the drug, and in severe cases, patients can die. This review discusses current methods for identifying people who are at high risk for severe side effects to 5-FU therapy.

Abstract

Severe adverse events (toxicity) related to the use of the commonly used chemotherapeutic drug 5-fluorouracil (5-FU) affect one in three patients and are the primary reason cited for premature discontinuation of therapy. Deficiency of the 5-FU catabolic enzyme dihydropyrimidine dehydrogenase (DPD, encoded by DPYD) has been recognized for the past 3 decades as a pharmacogenetic syndrome associated with high risk of 5-FU toxicity. An appreciable fraction of patients with DPD deficiency that receive 5-FU-based chemotherapy die as a result of toxicity. In this manuscript, we review recent progress in identifying actionable markers of DPD deficiency and the current status of integrating those markers into the clinical decision-making process. The limitations of currently available tests, as well as the regulatory status of pre-therapeutic DPYD testing, are also discussed.

A narrative review of genetic factors affecting fluoropyrimidine toxicity

OBJECTIVE

Our objective is to document progress in developing personalized therapy with fluoropyrimidine drugs (FPs) to improve outcomes for cancer patients and to identify areas requiring further investigation.

BACKGROUND

FPs including 5-fluorouracil (5-FU), are among the most widely used drugs for treating colorectal cancer (CRC) and other gastrointestinal (GI) malignancies. While FPs confer a survival benefit for CRC patients, serious systemic toxicities, including neutropenia, occur in ~30% of patients with lethality in 0.5-1% of patients. While serious systemic toxicities may occur in any patient, patients with polymorphisms in DPYD, which encodes the rate-limiting enzyme for pyrimidine degradation are at very high risk. Other genetic factors affecting risk for 5-FU toxicity, including miR-27a, are under investigation.

METHODS

Literature used to inform the text of this article was selected from PubMed.gov from the National Library of Medicine while regulatory documents were identified via Google search.

CONCLUSIONS

Clinical studies to date have validated four DPYD polymorphisms (DPYD*2A, DPYD*13, c.2846A>T, HapB3) associated with serious toxicities in patients treated with 5-FU. Genetic screening for these is being implemented in the Netherlands and the UK and has been shown to be a cost-effective way to improve outcomes. Factors other than DPYD polymorphisms (e.g., miR-27a, TYMS, ENOSF1, p53) also affect 5-FU toxicity. Functional testing for deficient pyrimidine catabolism {defined as [U] >16 ng/mL or [UH2]:[U] <10} is being implemented in France and has demonstrated utility in identifying patients with elevated risk for 5-FU toxicity. Therapeutic drug monitoring (TDM) from plasma levels of 5-FU during first cycle treatment also is being used to improve outcomes and pharmacokinetic-based dosing is being used to increase the percent of patients within optimal area under the curve (AUC) (18-28 mg*h/L) values. Patients maintained in the optimal AUC range experienced significantly reduced systemic toxicities. As understanding the genetic basis for increased risk of 5-FU toxicity becomes more refined, the development of functional-based methods to optimize treatment is likely to become more widespread.

Novel models for the prediction of drug-gene interactions

INTRODUCTION

Adverse drug reactions (ADRs) are among the leading causes of death, and frequently associated with drug-gene interactions (DGIs). In addition to pharmacogenomic programs for implementation of genetic preemptive testing into clinical practice, mathematical modeling can help to understand, quantify and predict the effects of DGIs in vivo. Moreover, modeling can contribute to optimize prospective clinical drug trial activities and to reduce DGI-related ADRs.

AREAS COVERED

Approaches and challenges of mechanistical DGI implementation and model parameterization are discussed for population pharmacokinetic and physiologically based pharmacokinetic models. The broad spectrum of published DGI models and their applications is presented, focusing on the investigation of DGI effects on pharmacology and model-based dose adaptations.

EXPERT OPINION

Mathematical modeling provides an opportunity to investigate complex DGI scenarios and can facilitate the development process of safe and efficient personalized dosing regimens. However, reliable DGI model input data from in vivo and in vitro measurements are crucial. For this, collaboration among pharmacometricians, laboratory scientists and clinicians is important to provide homogeneous datasets and unambiguous model parameters. For a broad adaptation of validated DGI models in clinical practice, interdisciplinary cooperation should be promoted and qualification toolchains must be established.

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.

A review on the importance of genotyping and phenotyping in fluoropyrimidine treatment

Fluoropyrimidines, after more than 50 years from their discovery, are still the treatment of many types of cancer, and it is estimated that two million patients receive fluoropyrimidine therapy annually. The toxicity associated with fluoropyrimidines affects 30–40% of patients and some adverse effects can be lethal.

Dihydroypyrimidine dehydrogenase is the main enzyme in the catabolism of 5-FU and DPD activity deficiency can cause important toxicity. This is an important reason to determine DPD activity in order to improve patient safety and to limit potential life-threating toxicity.

At presentmultiple phenotypic and genotypic methods are available for the determination of DPD activity, some of these methods have proven their usefulness in practice, and yet they are not routinely recommended in clinical practice.

This review is another statement of the importance of the determination of DPD status, the phenotypic and genotypic methods that are available and can be used.

Implementation of a pharmacogenomic program in a Brazilian public institution

This narrative review describes implementation, current status and perspectives of a pharmacogenomic (PGx) program at the Brazilian National Cancer Institute (INCA), targeting the cancer chemotherapeutic drugs – fluoropyrimidines, irinotecan and thiopurines. This initiative, designed as a research project, was supported by a grant from the Brazilian Ministry of Health. A dedicated task force developed standard operational procedures from recruitment of patients to creating PGx reports with dosing recommendations, which were successfully applied to test 100 gastrointestinal cancer INCA outpatients and 162 acute lymphoblastic leukemia pediatric patients from INCA and seven other hospitals. The program has been subsequently expanded to include gastrointestinal cancer patients from three additional cancer treatment centers. We anticipate implementation of routine pre-emptive PGx testing at INCA but acknowledge challenges associated with this transition, such as continuous financing support, availability of trained personnel, adoption of the PGx-informed prescription by the clinical staff and, ultimately, evidence of cost–effectiveness.

A case-control study to assess the ability of the thymine challenge test to predict patients with severe to life threatening fluoropyrimidine-induced gastrointestinal toxicity

AIMS

A previous study suggested that a thymine (THY) challenge dose could detect aberrant pharmacokinetics in known cases of fluoropyrimidine toxicity compared with healthy volunteers. The preliminary data suggested that urine sampling also could detect this aberrant disposition. The aim of this case-control study was to assess the ability of the urinary THY challenge test to discriminate cases of severe gastrointestinal toxicity in a cohort of patients treated with 5-fluorouracil or capecitabine.

METHODS

Patients (n = 37) received a 250 mg (per os) dose of THY and a cumulative urine sample was collected for 0-4 h. The urinary amounts of THY and metabolite dihydrothymine (DHT) were determined by liquid chromatography/mass spectrometry. Genomic DNA was analysed for DPYD gene variants. Renal function was estimated from blood creatinine levels. Cases (n = 9) and noncases (n = 23) of severe (grade ≥ 3) gastrointestinal toxicity were defined based on Common Terminology Criteria for Adverse Events.

RESULTS

The median THY/DHT ratios were 6.2 (interquartile range 2.9-6.4) in cases, including the 2 patients who were DPYD heterozygous carriers. However, this was not significantly different (P = .07) from the THY/DHT in noncases (median 2.6, interquartile range 2.8-4.2). Although creatinine clearance was lower (P = .001) in cases, renal function could not discriminate cases from noncases. However, logistic regression analysis using both of these explanatory variables could discriminate most cases (receiver operating characteristic area 0.8792, 95% confidence interval 0.72-1.00).

CONCLUSIONS

The THY challenge test combined with a patient's renal function may be useful as a phenotypic diagnostic test to detect risk of life-threatening fluoropyrimidine gastrointestinal toxicity.

Therapeutic Drug Monitoring in Oncology: International Association of Therapeutic Drug Monitoring and Clinical Toxicology Recommendations for 5-Fluorouracil Therapy

5-Fluorouracil (5-FU) is dosed by body surface area, a practice unable to reduce the interindividual variability in exposure. Endorsed by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT), we evaluated clinical evidence and strongly recommend TDM for the management of 5-FU therapy in patients with colorectal or head-and-neck cancer receiving common 5-FU regimens. Our systematic methodology provides a framework to evaluate published evidence in support of TDM recommendations in oncology.

Pharmacogenomics research and clinical implementation in Brazil

We searched PubMed entries and the Lattes database of Brazilian Pharmacogenetics Network investigators, for pharmacogenetic/genomic (PGx) studies in the Brazilian population, focusing on the drugs and genes included in the Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines. Warfarin was the most extensively studied drug in a PGx context: a genomewide association study targeting warfarin stable dose identified significant signals in VKORC1 and CYP2C9, several PGx dosing algorithms were developed based on these and other genes, and the implications of population admixture on extrapolation of dosing recommendations in the CPIC guidelines were examined. A study in renal transplanted patients disclosed association of CYP3A5*6 and CYP3A5*7 with tacrolimus dosing, which led to addition of these variants to CYP3A5*3 in the CPIC tacrolimus guideline. Studies verified predisposition of HIV-positive carriers of UGT1A1*28 to severe atazanavir-induced hyperbilirubinaemia, intolerance to 5-fluorouracyl in gastrointestinal cancer patients with deleterious DPYD variants, failure of HCV-infected carriers of IFNL3 rs12979860 to obtain a sustained viral response to PEG-IFN-α, and hypersensitivity reactions to abacavir in HIV-positive carriers of HLA-B*57:01. No prospective analyses of drug therapy outcomes or cost-effectiveness assessments of PGx-guided therapy were found. In conclusion, the limited adoption of PGx-informed drug prescription in Brazil reflects combination of recognized barriers to PGx implementation worldwide plus factors specific to the Brazilian population. The latter include rarity/absence of genetic variants on which international PGx guidelines are based (eg HLA-B*15.02 for phenytoin and carbamazepine) and the caveat of extrapolating to the admixed Brazilian population, guidelines based on categorical variables, such as continental ancestry (eg warfarin guidelines), "race" or ethnicity.

Pharmacogenetic testing in oncology: a Brazilian perspective

Pharmacogenetics, a major component of individualized or precision medicine, relies on human genetic diversity. The remarkable developments in sequencing technologies have revealed that the number of genetic variants modulating drug action is much higher than previously thought and that a true personalized prediction of drug response requires attention to rare mutations (minor allele frequency, MAF<1%) in addition to polymorphisms (MAF>1%) in pharmacogenes. This has major implications for the conceptual development and clinical implementation of pharmacogenetics. Drugs used in cancer treatment have been major targets of pharmacogenetics studies, encompassing both germline polymorphisms and somatic variants in the tumor genome. The present overview, however, has a narrower scope and is focused on germline cancer pharmacogenetics, more specifically, on drug/gene pairs for which pharmacogenetics-informed prescription guidelines have been published by the Clinical Pharmacogenetics Implementation Consortium and/or the Dutch Pharmacogenetic Working Group, namely, thiopurines/TPMT, fluoropyrimidines/UGT1A1, irinotecan/UGT1A1 and tamoxifen/CYP2D6. I begin by reviewing the general principles of pharmacogenetics-informed prescription, pharmacogenetics testing and the perceived barriers to the adoption of routine pharmacogenetics testing in clinical practice. Then, I highlight aspects of the pharmacogenetics testing of the selected drug-gene pairs and finally present pharmacogenetics data from Brazilian studies pertinent to these drug-gene pairs. I conclude with the notion that pharmacogenetics testing has the potential to greatly benefit patients by enabling precision medicine applied to drug therapy, ensuring better efficacy and reducing the risk of adverse effects.

Improving safety of fluoropyrimidine chemotherapy by individualizing treatment based on dihydropyrimidine dehydrogenase activity - Ready for clinical practice?

Fluoropyrimidines remain the cornerstone of treatment for different types of cancer, and are used by an estimated two million patients annually. The toxicity associated with fluoropyrimidine therapy is substantial, however, and affects around 30% of the patients, with 0.5-1% suffering fatal toxicity. Activity of the main 5-fluorouracil (5-FU) metabolic enzyme, dihydropyrimidine dehydrogenase (DPD), is the key determinant of 5-FU pharmacology, and accounts for around 80% of 5-FU catabolism. There is a consistent relationship between DPD activity and 5-FU exposure on the one hand, and risk of severe and potentially lethal fluoropyrimidine-associated toxicity on the other hand. Therefore, there is a sound rationale for individualizing treatment with fluoropyrimidines based on DPD status in order to improve patient safety. The field of individualized treatment with fluoropyrimidines is now rapidly developing. The main strategies that are available, are based on genotyping of the gene encoding DPD (DPYD) and measuring of pretreatment DPD phenotype. Clinical validity of additional approaches, including genotyping of MIR27A has also recently been demonstrated. Here, we critically review the evidence on clinical validity and utility of strategies available to clinicians to identify patients at risk of developing severe and potentially fatal toxicity as a result of DPD deficiency. We evaluate the advantages and limitations of these methods when used in clinical practice, and discuss for which strategies clinical implementation is currently justified based on the available evidence and, in addition, which additional data will be required before implementing other, as yet less developed strategies.

Endogenous plasma and salivary uracil to dihydrouracil ratios and DPYD genotyping as predictors of severe fluoropyrimidine toxicity in patients with gastrointestinal malignancies

OBJECTIVE

The aim of this study was to evaluate the use of plasma and saliva uracil (U) to dihydrouracil (UH₂) metabolic ratio and DPYD genotyping, as a means to identify patients with dihydropyrimidine dehydrogenase (DPD) deficiency and fluoropyrimidine toxicity.

METHODS

Paired plasma and saliva samples were obtained from 60 patients with gastrointestinal cancer, before fluoropyrimidine treatment. U and UH₂ concentrations were measured by LC-MS/MS. DPYD was genotyped for alleles *7, *2A, *13 and Y186C. Data on toxicity included grade 1 to 4 neutropenia, mucositis, diarrhea, nausea/vomiting and cutaneous rash.

RESULTS

35% of the patients had severe toxicity. There was no variant allele carrier for DPYD. The [UH₂]/[U] metabolic ratios were 0.09-26.73 in plasma and 0.08-24.0 in saliva, with higher correlation with toxicity grade in saliva compared to plasma (r_s=-0.515 vs r_s=-0.282). Median metabolic ratios were lower in patients with severe toxicity as compared to those with absence of toxicity (0.59 vs 2.83 saliva; 1.62 vs 6.75 plasma, P<0.01). A cut-off of 1.16 for salivary ratio was set (AUC 0.842), with 86% sensitivity and 77% specificity for the identification of patients with severe toxicity. Similarly, a plasma cut-off of 4.0 (AUC 0.746), revealed a 71% sensitivity and 76% specificity.

CONCLUSIONS

DPYD genotyping for alleles 7, *2A, *13 and Y186C was not helpful in the identification of patients with severe DPD deficiency in this series of patients. The [UH₂]/[U] metabolic ratios, however, proved to be a promising functional test to identify the majority of cases of severe DPD activity, with saliva performing better than plasma.

A comparison of cardiomyocyte cytotoxic mechanisms for 5-fluorouracil and its pro-drug capecitabine

1. 5-Fluorouracil (5-FU) and its prodrug capecitabine are key chemotherapeutic agents in the treatment of many gastrointestinal tract adenocarcinomas. In addition to their beneficial antitumor effects, they also possess undesired cardiac toxicity. In the present study, we investigated the cytotoxic mechanisms of 5-FU and capecitabine in freshly isolated rat cardiomyocytes. 2. 5-FU and capecitabine cytotoxicities were associated with reactive oxygen species (ROS) formation, lipid peroxidation and rapid glutathione depletion. Increased intracellular ROS could target mitochondria, and our findings confirmed that the cardiomyocytes mitochondrial membrane potential (ΔΨm) was rapidly decreased by 5-FU and capecitabine. Mitochondrial dysfunction subsequently initiates downstream events that trigger caspase-3 activation, and our results showed that 5-FU and capecitabine activated caspase-3 which leads to apoptosis or necrosis. However, 5-FU acted much more powerful than capecitabine at inducing several cytotoxicity markers in heart cardiomyocytes. In addition, 5-FU but not capecitabine caused lysosomal membrane leakiness when it was incubated with cardiomyocytes. All cytotoxicity markers were prevented by antioxidants, ROS scavengers, mitochondrial permeability transition (MPT) pore sealing agents and lysosomotropic agents. 3. Our findings showed that the cytotoxic action of 5-FU and capecitabine on cardiomyocytes are mediated by oxidative stress and subsequent mitochondrial dysfunction which causes caspase-3 activation and cell death.