Dihydropyrimidine dehydrogenase gene as a major predictor of severe 5-fluorouracil toxicity

Clinical relevance of DPYD variants c.1679T>G, c.1236G>A/HapB3, and c.1601G>A as predictors of severe fluoropyrimidine-associated toxicity: a systematic review and meta-analysis of individual patient data

BACKGROUND

The best-known cause of intolerance to fluoropyrimidines is dihydropyrimidine dehydrogenase (DPD) deficiency, which can result from deleterious polymorphisms in the gene encoding DPD (DPYD), including DPYD*2A and c.2846A>T. Three other variants-DPYD c.1679T>G, c.1236G>A/HapB3, and c.1601G>A-have been associated with DPD deficiency, but no definitive evidence for the clinical validity of these variants is available. The primary objective of this systematic review and meta-analysis was to assess the clinical validity of c.1679T>G, c.1236G>A/HapB3, and c.1601G>A as predictors of severe fluoropyrimidine-associated toxicity.

METHODS

We did a systematic review of the literature published before Dec 17, 2014, to identify cohort studies investigating associations between DPYD c.1679T>G, c.1236G>A/HapB3, and c.1601G>A and severe (grade ≥3) fluoropyrimidine-associated toxicity in patients treated with fluoropyrimidines (fluorouracil, capecitabine, or tegafur-uracil as single agents, in combination with other anticancer drugs, or with radiotherapy). Individual patient data were retrieved and analysed in a multivariable analysis to obtain an adjusted relative risk (RR). Effect estimates were pooled by use of a random-effects meta-analysis. The threshold for significance was set at a p value of less than 0·0167 (Bonferroni correction).

FINDINGS

7365 patients from eight studies were included in the meta-analysis. DPYD c.1679T>G was significantly associated with fluoropyrimidine-associated toxicity (adjusted RR 4·40, 95% CI 2·08-9·30, p<0·0001), as was c.1236G>A/HapB3 (1·59, 1·29-1·97, p<0·0001). The association between c.1601G>A and fluoropyrimidine-associated toxicity was not significant (adjusted RR 1·52, 95% CI 0·86-2·70, p=0·15). Analysis of individual types of toxicity showed consistent associations of c.1679T>G and c.1236G>A/HapB3 with gastrointestinal toxicity (adjusted RR 5·72, 95% CI 1·40-23·33, p=0·015; and 2·04, 1·49-2·78, p<0·0001, respectively) and haematological toxicity (adjusted RR 9·76, 95% CI 3·03-31·48, p=0·00014; and 2·07, 1·17-3·68, p=0·013, respectively), but not with hand-foot syndrome. DPYD*2A and c.2846A>T were also significantly associated with severe fluoropyrimidine-associated toxicity (adjusted RR 2·85, 95% CI 1·75-4·62, p<0·0001; and 3·02, 2·22-4·10, p<0·0001, respectively).

INTERPRETATION

DPYD variants c.1679T>G and c.1236G>A/HapB3 are clinically relevant predictors of fluoropyrimidine-associated toxicity. Upfront screening for these variants, in addition to the established variants DPYD*2A and c.2846A>T, is recommended to improve the safety of patients with cancer treated with fluoropyrimidines.

FUNDING

None.

Phase I study of 5-fluorouracil in children and young adults with recurrent ependymoma

BACKGROUND

We report a phase I study to examine the pharmacokinetics, safety, and recommended dosage of weekly intravenous bolus 5-fluorouracil (5-FU) in children and young adults with recurrent ependymoma.

METHODS

Patients 22 years of age or less with recurrent ependymoma were treated with bolus dosage 5-FU weekly for 4 weeks followed by a 2-week rest period, defining one cycle. Patients could continue on therapy for 16 cycles. The starting 5-FU dosage was 500 mg/m(2). Dose-limiting toxicity was determined after one cycle. Patients were initially enrolled according to a rolling-6 design; subsequent dose re-escalation phase was based on a 3 + 3 design.

RESULTS

We treated patients at 400 (n = 6), 500 (n = 15), and 650 (n = 5) mg/m(2), with de-escalation due to toxicity. Twenty-three of twenty-six patients enrolled were evaluable. Five patients experienced grade 4 neutropenia (n = 2: 650 mg/m(2); n = 3: 500 mg/m(2)). One patient experienced grade 3 diarrhea. At 500 mg/m(2), the median 5-FU maximal concentration, AUC0-∞, and alpha half-life were 825 µM, 205 µM × h, and 9.9 min, respectively. Interim analysis revealed an association between hematologic toxicity and prior number of chemotherapeutic regimens (P = .03). The study was amended to re-escalate the dosage in a less heavily pretreated cohort of patients.

CONCLUSIONS

These phase I clinical data provide initial pharmacokinetic parameters to describe i.v. bolus 5-FU disposition in children with recurrent ependymoma. Tumor exposures effective in preclinical testing can be achieved with tolerable bolus dosages in patients. Bolus 5-FU is well tolerated and possesses antitumor activity.

Beating the odds: efficacy and toxicity of dihydropyrimidine dehydrogenase-driven adaptive dosing of 5-FU in patients with digestive cancer

AIMS

5-FU is the backbone of most regimens in digestive oncology. Administration of standard 5-FU leads to 15-30% of severe side effects, and lethal toxicities are regularly reported with fluoropyrimidine drugs. Dihydropyrimidine dehydrogenase (DPD) deficiency is a pharmacogenetic syndrome responsible for most cases of life-threatening toxicities upon 5-FU intake, and pre-treatment checking for DPD status should help to reduce both incidence and severity of side effects through adaptive dosing strategies.

METHODS

We have used a simple method for rapidly establishing the DPD phenotype of patients with cancer and used it prospectively in 59 routine patients treated with 5-FU-based therapy for digestive cancers. No patient with total DPD deficiency was found but 23% of patients exhibited poor metabolizer phenotype, and one patient was phenotyped as profoundly deficient. Consequently, 5-FU doses in poor metabolizer patients were cut by an average 35% as compared with non deficient patients (2390 ± 1225 mg vs. 3653 ± 1371 mg, P < 0.003, t-test).

RESULTS

Despite this marked reduction in 5-FU dosing, similar efficacy was achieved in the two subsets (clinical benefit: 40 vs. 43%, stable disease: 40 vs. 37%, progressive disease: 20% in both subsets, P = 0.893, Pearson's chi-square). No difference in toxicities was observed (P = 0.104, Fisher's exact test). Overall, only 3% of early severe toxicities were recorded, a value markedly lower than the 15-30% ones usually reported with 5-FU.

CONCLUSIONS

This feasibility study shows how simplified DPD-based adaptive dosing of 5-FU can reduce sharply the incidence of treatment-related severe toxicities while maintaining efficacy as part of routine clinical practice in digestive oncology.

Hypermutation of DPYD Deregulates Pyrimidine Metabolism and Promotes Malignant Progression

New strategies are needed to diagnose and target human melanoma. To this end, genomic analyses was performed to assess somatic mutations and gene expression signatures using a large cohort of human skin cutaneous melanoma (SKCM) patients from The Cancer Genome Atlas (TCGA) project to identify critical differences between primary and metastatic tumors. Interestingly, pyrimidine metabolism is one of the major pathways to be significantly enriched and deregulated at the transcriptional level in melanoma progression. In addition, dihydropyrimidine dehydrogenase (DPYD) and other important pyrimidine-related genes: DPYS, AK9, CAD, CANT1, ENTPD1, NME6, NT5C1A, POLE, POLQ, POLR3B, PRIM2, REV3L, and UPP2 are significantly enriched in somatic mutations relative to the background mutation rate. Structural analysis of the DPYD protein dimer reveals a potential hotspot of recurring somatic mutations in the ligand-binding sites as well as the interfaces of protein domains that mediated electron transfer. Somatic mutations of DPYD are associated with upregulation of pyrimidine degradation, nucleotide synthesis, and nucleic acid processing while salvage and nucleotide conversion is downregulated in TCGA SKCM.

IMPLICATIONS

At a systems biology level, somatic mutations of DPYD cause a switch in pyrimidine metabolism and promote gene expression of pyrimidine enzymes toward malignant progression.

Aminopeptidase N inhibitor 4cc synergizes antitumor effects of 5-fluorouracil on human liver cancer cells through ROS-dependent CD13 inhibition

Aminopeptidase N (APN, also known as CD13) is involved in cellular processes of various types of tumors and a potential anti-cancer therapeutic target. Here, we report the effect of an APN inhibitor 4cc in enhancing sensitivity of hepatocellular carcinoma (HCC) cell lines and xenograft model in response to 5-fluorouracil (5-FU) in vivo and in vitro. The treatment of the combination of 4cc with 5-FU, compared to the combination of bestain with 5-FU, markedly suppressed cell growth and induced apoptosis of HCC cells, accompanying the increase in the level of reactive oxygen species (ROS) and followed by a decrease in the mitochondrial membrane potential (ΔΨM). Furthermore, the combination of 4cc and 5-FU showed a significant inhibitory effect on the growth of HCC xenograft tumors. In addition, following the treatment of 4cc, APN activity and clonogenic formation and the number of CD13-positive cells in PLC/PRF/5 cells were significantly decreased, suggesting that 4cc may also inhibit liver cancer stem cells by CD13 inhibition. These results showed that the APN inhibitor 4cc synergizes antitumor effects of 5-FU on human liver cancer cells via ROS-mediated drug resistance inhibition and concurrent activation of the mitochondrial pathways of apoptosis.

Predicting 5-fluorouracil toxicity: DPD genotype and 5,6-dihydrouracil:uracil ratio

AIM

Decreased DPD activity is a major cause of 5-fluorouracil (5-FU) toxicity, but known reduced-function variants in the DPD gene (DPYD) explain only a part of DPD-related 5-FU toxicities. Here, we evaluated the baseline (pretherapeutic) plasma 5,6-dihydrouracil:uracil (UH2:U) ratio as a marker of DPD activity in the context of DPYD genotypes.

MATERIALS & METHODS

DPYD variants were genotyped and plasma U, UH2 and 5-FU concentrations were determined by liquid chromatography-tandem mass spectrometry in 320 healthy blood donors and 28 cancer patients receiving 5-FU-based chemotherapy.

RESULTS

Baseline UH2:U ratios were strongly correlated with generally low and highly variable U concentrations. Reduced-function DPYD variants were only weakly associated with lower baseline UH2:U ratios. However, the interindividual variability in the UH2:U ratio was reduced and a stronger correlation between ratios and 5-FU exposure was observed in cancer patients during 5-FU administration.

CONCLUSION

These results suggest that the baseline UH2:U plasma ratio in most individuals reflects the nonsaturated state of DPD and is not predictive of decreased DPD activity. It may, however, be highly predictive at increased substrate concentrations, as observed during 5-FU administration.

Discovery of novel mutations in the dihydropyrimidine dehydrogenase gene associated with toxicity of fluoropyrimidines and viewpoint on preemptive pharmacogenetic screening in patients

Background

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme of the metabolic pathway of 5-fluorouracil (5-FU) and other fluoropyrimidines to inactive compounds. For this reason, severe, life-threatening toxicities may occur in patients with deficient DPD activity when administered standard doses of 5-FU and its prodrugs.

Materials and methods

We selected three patients with colorectal adenocarcinoma who displayed unexpected severe adverse reactions after treatment with 5-FU and capecitabine. To investigate the possible involvement of deficient variants of the DPD gene (DPYD), a denaturing HPLC (dHPLC) approach followed by target exon sequencing of DPYD was performed on DNA extracted from peripheral blood.

Results

Three novel non-synonymous mutations of DPYD, c.2509-2510insC, c.1801G>C, and c.680G>A, were detected in these subjects. Due to the absence of other deficient variants of DPYD and the compatibility of adverse reactions with fluoropyrimidine treatment, the novel variants were associated with a poor-metabolizer phenotype.

Conclusions

Stratification of patients on the basis of their genotype may help prevent toxicity, and the large body of evidence about the pathogenesis of fluoropyrimidine-induced adverse reactions strongly encourages the adoption of best practice recommendations to appropriately address this important clinical issue. This approach is of utmost importance within a preventive, prognostic, and personalized approach to patient care in the oncology setting.

5-Fluorouracil "Chemowraps" in the Treatment of Multiple Actinic Keratoses: A Norwich Experience

Introduction

Topical 5-fluorouracil (5-FU) has been used to treat actinic keratosis for decades. It has been an important and effective treatment which the patient can self-administer, but is limited by the surface area of skin to be treated (according to the manufacturer’s guidelines) of 500 cm². Other topical treatments can be painful, or require hospital/health care professional input. The use of 5-FU under occlusion (chemowraps) for large areas of sun-damaged skin on the arms or legs has been described and is a potentially useful treatment option. We describe our experiences with this technique in the Norfolk and Norwich University Hospital Dermatology Department (Norwich, UK).

Methods

Five patients were recruited into this pilot study. Topical 5-FU was applied to sun-damaged limbs under occlusion, and reviewed weekly for response, and local or systemic side effects. Treatment duration was 12–14 weeks. Clinical photography was undertaken prior to, during, and after treatment to document response.

Results

We show that there was substantial clinical improvement in the treated skin in our patients. Experienced dermatologists reviewed all the patients, and documented the changes photographically, and by counting lesions. All patients were satisfied with their treatment regimen, and also with the end result; although two did not complete the treatment regimen due to complications not directly attributable to the treatment.

Conclusion

Topical 5-FU under occlusion (chemowraps) may be a valid treatment option for large areas of sun-damaged skin with field cancerization changes, due to low systemic and local toxicity, and acceptability to patients.

Electronic supplementary material

The online version of this article (doi:10.1007/s13555-015-0082-5) contains supplementary material, which is available to authorized users.

Translating DPYD genotype into DPD phenotype: using the DPYD gene activity score

The dihydropyrimidine dehydrogenase enzyme (DPD, encoded by the gene DPYD) plays a key role in the metabolism of fluoropyrimidines. DPD deficiency occurs in 4-5% of the population and is associated with severe fluoropyrimidine-related toxicity. Several SNPs in DPYD have been described that lead to absent or reduced enzyme activity, including DPYD*2A, DPYD*13, c.2846A>T and c.1236G>A/haplotype B3. Since these SNPs differ in their effect on DPD enzyme activity, a differentiated dose adaption is recommended. We propose the gene activity score for translating DPYD genotype into phenotype, accounting for differences in functionality of SNPs. This method can be used to standardize individualized fluoropyrimidine dose adjustments, resulting in optimal safety and effectiveness.

Dihydropyrimidinase and β-ureidopropionase gene variation and severe fluoropyrimidine-related toxicity

Aims: To assess the association of DPYS and UPB1 genetic variation, encoding the catabolic enzymes downstream of dihydropyrimidine dehydrogenase, with early-onset toxicity from fluoropyrimidine-based chemotherapy. Patients & methods: The coding and exon-flanking regions of both genes were sequenced in a discovery subset (164 patients). Candidate variants were genotyped in the full cohort of 514 patients. Results & conclusions: Novel rare deleterious variants in DPYS (c.253C > T and c.1217G > A) were detected once each in toxicity cases and may explain the occurrence of severe toxicity in individual patients, and associations of common variants in DPYS (c.1–1T > C: padjusted = 0.003; OR = 2.53; 95% CI: 1.39–4.62, and c.265–58T > C: padjusted = 0.039; OR = 0.61; 95% CI: 0.38–0.97) with 5-fluorouracil toxicity were replicated.

Actionable pharmacogenetic markers for prediction and prognosis in breast cancer

Breast cancer is a heterogeneous disease that necessitates proper patient classification to direct surgery, pharmacotherapy, and radiotherapy. Despite patients within the same subgroup receiving similar pharmacotherapy, substantial variation in clinical outcomes is observed. Pharmacogenetic variations with direct effect on pharmacokinetics and pharmacodynamics play a central role in clinical outcomes. Pharmacogenetic markers associated with clinical outcome are known as biomarkers. They are termed prognostic biomarkers when their presence is associated with a specific clinical outcome. If the presence of such biomarkers guides treatment, they are termed predictive biomarkers. A number of pharmacogenetic markers have been described in relation to breast cancer pharmacotherapy both in the adjuvant and neoadjuvant setting. CYP2D6 allelic variants produce variable rates of tamoxifen metabolism and are associated with survival outcomes. Other biomarkers have been described in relation to other forms of endocrine therapy and trastuzumab. In neoadjuvant and adjuvant breast cancer chemotherapy, specific biomarkers were correlated with clinical outcomes and risk of drug toxicity. This review highlights key biomarkers in breast cancer pharmacotherapy with the potential of translating such study outcomes into clinical practice.

Undetected toxicity risk in pharmacogenetic testing for dihydropyrimidine dehydrogenase

Fluoropyrimidines, the mainstay agents for the treatment of colorectal cancer, alone or as a part of combination therapies, cause severe adverse reactions in about 10%–30% of patients. Dihydropyrimidine dehydrogenase (DPD), a key enzyme in the catabolism of 5-fluorouracil, has been intensively investigated in relation to fluoropyrimidine toxicity, and several DPD gene (DPYD) polymorphisms are associated with decreased enzyme activity and increased risk of fluoropyrimidine-related toxicity. In patients carrying non-functional DPYD variants (c.1905+1G>A, c.1679T>G, c.2846A>T), fluoropyrimidines should be avoided or reduced according to the patients’ homozygous or heterozygous status, respectively. For other common DPYD variants (c.496A>G, c.1129-5923C>G, c.1896T>C), conflicting data are reported and their use in clinical practice still needs to be validated. The high frequency of DPYD polymorphism and the lack of large prospective trials may explain differences in studies’ results. The epigenetic regulation of DPD expression has been recently investigated to explain the variable activity of the enzyme. DPYD promoter methylation and its regulation by microRNAs may affect the toxicity risk of fluoropyrimidines. The studies we reviewed indicate that pharmacogenetic testing is promising to direct personalised dosing of fluoropyrimidines, although further investigations are needed to establish the role of DPD in severe toxicity in patients treated for colorectal cancer.

Personalized medicine and the clinical laboratory

Personalized medicine is the use of biomarkers, most of them molecular markers, for detection of specific genetic traits to guide various approaches for preventing and treating different conditions. The identification of several genes related to heredity, oncology and infectious diseases lead to the detection of genetic polymorphisms that are involved not only in different clinical progression of these diseases but also in variations in treatment response. Currently, it is possible to detect these polymorphisms using several methodologies: detection of single nucleotide polymorphisms using polymerase chain reaction methods; nucleic acid microarray detection; and nucleic acid sequencing with automatized DNA sequencers using Sanger-derived methods and new generation sequencing. Personalized medicine assays are directed towards detecting genetic variations that alter interactions of drugs with targets or the metabolic pathways of drugs (upstream and downstream) and can be utilized for the selection of drug formulations and detect different immunogenicities of the drug. Personalized medicine applications have already been described in different areas of Medicine and allow specific treatment approaches to be applied to each patient and pathology according to the results of these assays. The application of such a protocol demands an increasing interaction between the clinical laboratory and the clinical staff. For its implementation, a coordinated team composed of basic researchers and physicians highly specialized in their areas supported by a highly specialized team of clinical analysts particularly trained in molecular biology assays is necessary.

Association of new deletion/duplication region at chromosome 1p21 with intellectual disability, severe speech deficit and autism spectrum disorder-like behavior: an all-in approach to solving the DPYD enigma

We describe an as yet unreported neocentric small supernumerary marker chromosome (sSMC) derived from chromosome 1p21.3p21.2. It was present in 80% of the lymphocytes in a male patient with intellectual disability, severe speech deficit, mild dysmorphic features, and hyperactivity with elements of autism spectrum disorder (ASD).

Several important neurodevelopmental genes are affected by the 3.56 Mb copy number gain of 1p21.3p21.2, which may be considered reciprocal in gene content to the recently recognized 1p21.3 microdeletion syndrome. Both 1p21.3 deletions and the presented duplication display overlapping symptoms, fitting the same disorder category. Contribution of coding and non-coding genes to the phenotype is discussed in the light of cellular and intercellular homeostasis disequilibrium. In line with this the presented 1p21.3p21.2 copy number gain correlated to 1p21.3 microdeletion syndrome verifies the hypothesis of a cumulative effect of the number of deregulated genes - homeostasis disequilibrium leading to overlapping phenotypes between microdeletion and microduplication syndromes.

Although miR-137 appears to be the major player in the 1p21.3p21.2 region, deregulation of the DPYD (dihydropyrimidine dehydrogenase) gene may potentially affect neighboring genes underlying the overlapping symptoms present in both the copy number loss and copy number gain of 1p21. Namely, the all-in approach revealed that DPYD is a complex gene whose expression is epigenetically regulated by long non-coding RNAs (lncRNAs) within the locus. Furthermore, the long interspersed nuclear element-1 (LINE-1) L1MC1 transposon inserted in DPYD intronic transcript 1 (DPYD-IT1) lncRNA with its parasites, TcMAR-Tigger5b and pair of Alu repeats appears to be the “weakest link” within the DPYD gene liable to break. Identification of the precise mechanism through which DPYD is epigenetically regulated, and underlying reasons why exactly the break (FRA1E) happens, will consequently pave the way toward preventing severe toxicity to the antineoplastic drug 5-fluorouracil (5-FU) and development of the causative therapy for the dihydropyrimidine dehydrogenase deficiency.

Germline oncopharmacogenetics, a promising field in cancer therapy

Pharmacogenetics (PGx) is the study of the relationship between inter-individual genetic variation and drug responses. Germline variants of genes involved in drug metabolism, drug transport, and drug targets can affect individual response to medications. Cancer therapies are characterized by an intrinsically high toxicity; therefore, the application of pharmacogenetics to cancer patients is a particularly promising method for avoiding the use of inefficacious drugs and preventing the associated adverse effects. However, despite continuing efforts in this field, very few labels include information about germline genetic variants associated with drug responses. DPYD, TPMT, UGT1A1, G6PD, CYP2D6, and HLA are the sole loci for which the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA) report specific information. This review highlights the germline PGx variants that have been approved to date for anticancer treatments, and also provides some insights about other germline variants with potential clinical applications. The continuous and rapid evolution of next-generation sequencing applications, together with the development of computational methods, should help to refine the implementation of personalized medicine. One day, clinicians may be able to prescribe the best treatment and the correct drug dosage based on each patient's genotype. This approach would improve treatment efficacy, reduce toxicity, and predict non-responders, thereby decreasing chemotherapy-associated morbidity and improving health benefits.

Role of ABC transporters in fluoropyrimidine-based chemotherapy response

Since over 50 years, 5-fluorouracil (5-FU) is in use as backbone of chemotherapy treatment regimens for a wide range of cancers including colon, breast, and head and neck carcinomas. However, drug resistance and severe toxicities such as mucositis, diarrhea, neutropenia, and vomiting in up to 40% of treated patients often lead to dose limitation or treatment discontinuation. Because the oral bioavailability of 5-FU is unpredictable and highly variable, 5-FU is commonly administered intravenously. To overcome medical complications and inconvenience associated with intravenous administration, the oral prodrugs capecitabine and tegafur have been developed. Both fluoropyrimidines are metabolically converted intracellularly to 5-FU, which then needs metabolic activation to exert its damaging activity on RNA and DNA. The low response rates of 10-15% of 5-FU monotherapy can be improved by combination regimens of infusional 5-FU and leucovorin together with oxaliplatin (FOLFOX) or irinotecan (FOLFIRI), thereby increasing response rates to 30-40%. The impact of metabolizing enzymes in the development of fluoropyrimidine toxicity and resistance has been studied in great detail. In addition, membrane drug transporters, which are critical determinants of intracellular drug concentrations, may play a role in occurrence of toxicity and development of resistance against fluoropyrimidine-based therapy as well. This review therefore summarizes current knowledge on the role of drug transporters with particular focus on ATP-binding cassette transporters in fluoropyrimidine-based chemotherapy response.

Influence of DPYD Genetic Polymorphisms on 5-Fluorouracil Toxicities in Patients with Colorectal Cancer: A Meta-Analysis

Our meta-analysis aggregated existing results from relevant studies to comprehensively investigate the correlations between genetic polymorphisms in dihydropyrimidine dehydrogenase (DPYD) gene and 5-fluorouracil (5-FU) toxicities in patients with colorectal cancer (CRC). The MEDLINE (1966∼2013), the Cochrane Library Database (Issue 12, 2013), EMBASE (1980∼2013), CINAHL (1982∼2013), Web of Science (1945∼2013), and the Chinese Biomedical Database (CBM) (1982∼2013) were searched without language restrictions. Meta-analyses were conducted with the use of STATA software (Version 12.0, Stata Corporation, College Station, TX, USA). Seven clinical cohort studies with a total of 946 CRC patients met our inclusion criteria, and NOS scores of each of the included studies were ≥5. Our findings showed that DPYD genetic polymorphisms were significantly correlated with high incidences of 5-FU-related toxicity in CRC patients. SNP-stratified analysis indicated that there were remarkable connections of IVS14+1G>A, 464T>A, and 2194G>A polymorphisms with the incidence of marrow suppression in CRC patients receiving 5-FU chemotherapy. Furthermore, we found that IVS14+1G>A, 496A>G, and 2194G>A polymorphisms were correlated with the incidence of gastrointestinal reaction. Ethnicity-stratified analysis also revealed that DPYD genetic polymorphisms might contribute to the development of marrow suppression and gastrointestinal reaction among Asians, but not among Caucasians. The present meta-analysis suggests that DPYD genetic polymorphisms may be correlated with the incidence of 5-FU-related toxicity in CRC patients.

Dihydropyrimidine accumulation is required for the epithelial-mesenchymal transition

It is increasingly appreciated that oncogenic transformation alters cellular metabolism to facilitate cell proliferation, but less is known about the metabolic changes that promote cancer cell aggressiveness. Here, we analyzed metabolic gene expression in cancer cell lines and found that a set of high-grade carcinoma lines expressing mesenchymal markers share a unique 44 gene signature, designated the "mesenchymal metabolic signature" (MMS). A FACS-based shRNA screen identified several MMS genes as essential for the epithelial-mesenchymal transition (EMT), but not for cell proliferation. Dihydropyrimidine dehydrogenase (DPYD), a pyrimidine-degrading enzyme, was highly expressed upon EMT induction and was necessary for cells to acquire mesenchymal characteristics in vitro and for tumorigenic cells to extravasate into the mouse lung. This role of DPYD was mediated through its catalytic activity and enzymatic products, the dihydropyrimidines. Thus, we identify metabolic processes essential for the EMT, a program associated with the acquisition of metastatic and aggressive cancer cell traits.

Clinical importance of risk variants in the dihydropyrimidine dehydrogenase gene for the prediction of early-onset fluoropyrimidine toxicity

We investigated the clinical relevance of dihydropyrimidine dehydrogenase gene (DPYD) variants to predict severe early-onset fluoropyrimidine (FP) toxicity, in particular of a recently discovered haplotype hapB3 and a linked deep intronic splice site mutation c.1129-5923C>G. Selected regions of DPYD were sequenced in prospectively collected germline DNA of 500 patients receiving FP-based chemotherapy. Associations of DPYD variants and haplotypes with hematologic, gastrointestinal, infectious, and dermatologic toxicity in therapy cycles 1-2 and resulting FP-dose interventions (dose reduction, therapy delay or cessation) were analyzed accounting for clinical and demographic covariates. Fifteen additional cases with toxicity-related therapy delay or cessation were retrospectively examined for risk variants. The association of c.1129-5923C>G/hapB3 (4.6% carrier frequency) with severe toxicity was replicated in an independent prospective cohort. Overall, c.1129-5923G/hapB3 carriers showed a relative risk of 3.74 (RR, 95% CI = 2.30-6.09, p = 2 × 10(-5)) for severe toxicity (grades 3-5). Of 31 risk variant carriers (c.1129-5923C>G/hapB3, c.1679T>G, c.1905+1G>A or c.2846A>T), 11 (all with c.1129-5923C>G/hapB3) experienced severe toxicity (15% of 72 cases, RR = 2.73, 95% CI = 1.61-4.63, p = 5 × 10(-6)), and 16 carriers (55%) required FP-dose interventions. Seven of the 15 (47%) retrospective cases carried a risk variant. The c.1129-5923C>G/hapB3 variant is a major contributor to severe early-onset FP toxicity in Caucasian patients. This variant may substantially improve the identification of patients at risk of FP toxicity compared to established DPYD risk variants (c.1905+1G>A, c.1679T>G and c.2846A>T). Pre-therapeutic DPYD testing may prevent 20-30% of life-threatening or lethal episodes of FP toxicity in Caucasian patients.

Screening for 392 polymorphisms in 141 pharmacogenes

Pharmacogenomics is the study of the association between inter-individual genetic differences and drug responses. Researches in pharmacogenomics have been performed in compliance with the use of several genotyping technologies. In this study, a total of 392 single-nucleotide polymorphisms (SNPs) located in 141 pharmacogenes, including 21 phase I, 13 phase II, 18 transporter and 5 modifier genes, were selected and genotyped in 150 subjects using the GoldenGate assay or the SNaPshot technique. These variants were in Hardy-Weinberg equilibrium (HWE) (P>0.05), except for 22 SNPs. Genotyping of the 392 SNPs revealed that the minor allele frequencies of 47 SNPs were <0.05, 105 SNPs were monomorphic and 22 variants were not in HWE. Also, based on previous studies, we predicted the association between the polymorphisms of certain pharmacogenes, such as cytochrome P450 2D6, cytochrome P450 2C9, vitamin K epoxide reductase complex, subunit 1, cytochrome P450 2C19, human leukocyte antigen, class I, B and thiopurine S-methyltransferase, and drug efficacy. In conclusion, our study demonstrated the allele distribution of SNPs in 141 pharmacogenes as determined by high-throughput screening. Our results may be helpful in developing personalized medicines by using pharmacogene polymorphisms.

ABCC11/MRP8 polymorphisms affect 5-fluorouracil-induced severe toxicity and hepatic expression

AIM

Because 5-fluorodeoxyuridine monophosphate (5-FdUMP), an anabolic active metabolite of 5-fluorouracil (5-FU), is a substrate of MRP8 (encoded by ABCC11), we investigated whether ABCC11 polymorphisms play a role in severe toxicity of 5-FU.

PATIENTS & METHODS

Genomic DNA from 672 cancer patients treated with 5-FU monotherapy and with documented toxicity according to WHO criteria was genotyped for 12 ABCC11 tag SNPs. Functional impact of polymorphisms was assessed in a Caucasian human liver cohort (n = 150) and by recombinant expression of MRP8 protein variants.

RESULTS

Univariate and multivariate analysis identified rs17822471 (G>A, T546M) as risk factor of severe leukopenia (p = 0.021, odds ratio [95%CI]: 3.31 [1.26-8.66]) but not of other toxicity types. MRP8 protein expression in human liver was 1.7-fold lower in carriers compared with wild-type (p = 0.02). Recombinant expression confirmed the effect of T546M on protein expression.

CONCLUSION

Since MRP8 is expressed in bone marrow blasts and leukocytes, lower expression may lead to intracellular accumulation of 5-FdUMP and increased risk of leukopenia.

Evaluation of 5-fluorouracil pharmacokinetic models and therapeutic drug monitoring in cancer patients

5-fluorouracil (5-FU) remains the cornerstone of all currently applied regimens for the treatment of patients with cancers of the gastrointestinal tract, breast, and head and neck. Unfortunately, a large variation in the clearance of 5-FU has been observed between patients, suggesting that some patients might receive nonoptimal 5-FU doses. However, therapeutic drug monitoring of 5-FU has been shown to result in reduced intra- and inter-individual variability in 5-FU plasma levels and pharmacokinetically guided dose adjustments of 5-FU-containing therapy results in a significantly improved efficacy and tolerability. To date, compartmental Michaelis-Menten elimination-based modeling has proven to be a sensitive and accurate tool for analyzing the pharmacokinetics of 5-FU and to identify patients with a dihydropyrimidine dehydrogenase deficiency. These Michaelis-Menten models also allow the use of a limited sampling strategy and offer the opportunity to predict a priori the 5-FU plasma concentrations in patients receiving adapted doses of 5-FU.

DPYD IVS14+1G>A and 2846A>T genotyping for the prediction of severe fluoropyrimidine-related toxicity: a meta-analysis

AIM

In the present study we conducted a systematic review and meta-analysis of published data to quantify the impact of the DPYD IVS14+1G>A and 2846A>T variants on the risk of fluoropyrimidine-related toxicities and to determine sensitivity and specificity testing for DPYD variants.

METHODS

Relevant studies were identified through PubMed and Web of Knowledge databases, studies included were those published up until to May 2012. Study quality was assessed according to the HuGENET guidelines and Strengthening the Reporting of Genetic Association (STREGA) recommendations.

RESULTS

Random-effects meta-analysis provided evidence that carriers of DPYD IVS14+1G>A are at higher risk of ≥3 degrees of overall grade toxicity, hematological toxicity, mucositis and diarrhea. In addition, a strong association was also found between carriers of the DPYD 2846T allele and overall grade ≥3 toxicity or grade ≥3 diarrhea. An inverse linear relationship was found in prospective studies between the odds ratio of DPYD IVS14+1G>A and the incidence of overall grade ≥3 toxicity, indicating an higher impact in cohorts in which the incidence of severe toxicity was lower.

CONCLUSION

The results of this meta-analysis confirm clinical validity of DPYD IVS14+1G>A and 2846A>T as risk factors for the development of severe toxicities following fluoropyrimidine treatment. Furthermore, the sensitivity and specificity estimates obtained could be useful in establishing the cost-effectiveness of testing for DPYD variants.

Predictive testing for DPD deficiency in a patient with familial history of fluoropyrimidine-associated toxicity

Reduced activity of DPD leads to severe toxicity in cancer patients receiving standard doses of fluoropyrimidines, particularly in the case of combination regimens. We describe a 38-year-old man with a resectable metastasis from hereditary nonpolyposis colorectal cancer, with indication of neoadjuvant chemotherapy and a family history of fluoropyrimidine-associated toxicity. We tested our patient for functional DPYD variants, before any choice of the neoadjuvant regimen, including for the c.496A>G, already described in his mother, and a deep intronic variant c.1129-5923C>G recently reported associated to severe toxicity. Our patient was found to be heterozygous for both c.469A>G and c.1129-5923C>G DPYD variants. We thus offered the most active perioperative regimen, capecitabine, oxaliplatin, irinotecan plus bevacizumab by which we reduced the dosing of capecitabine to 50%. Treatment was well tolerated, with grade 2 diarrhea as the most significant adverse event, and led to a complete pathological response after liver resection. We provide a rationale approach to improve the safety of fluoropirimidine-based therapy in a patient with family history of fluoropyrimidine-associated toxicity.

Curcumin reduces cytotoxicity of 5-Fluorouracil treatment in human breast cancer cells

Antimetabolites have proven successful as therapeutics for advanced-stage breast cancers, but are often accompanied by severe side effects that can limit treatment regimens. 5-Fluorouracil (5-FU), an antimetabolite that inhibits cell proliferation, has served an important role in standard chemotherapy protocols for a variety of solid tumors. Although reasonable response rates have been reported for 5-FU, continued exploration is necessary to improve clinical outcomes and reduce cytotoxic side effects that are an inherent problem for chemotherapeutic interventions. Because of its diverse anticancer properties, we explored whether by combining the natural product curcumin with 5-FU, synergistic improvements in preventing breast cancer cell proliferation and/or provide protection against 5-FU-induced cytotoxicity could be achieved. Indeed both curcumin and 5-FU inhibit DNA synthesis in MDA-MB-231 cells using BrdU incorporation assays; however, combined treatment showed no synergistic improvement. We next established the cytotoxicity profile for 5-FU in MDA-MB-231 cells using a tetrazolium-based cell viability assay and obtained an LD50 value of 28 μM. When 5-FU incubations were repeated with the addition of curcumin, the LD50 value increased to 200-300 μM, representing a 7-10-fold protection by curcumin against 5-FU cytotoxicity. These findings suggest that the addition of curcumin as an adjuvant therapy during 5-FU treatment might enhance the chemotherapeutic effectiveness of 5-FU by protecting normal cells from reduced viability and thus permitting higher dosing or longer treatment times. This would be especially important to those individuals who are plagued with severe cytotoxicities and require frequent interruptions, or even early termination of their treatment regimens.

Clinical Pharmacogenetics Implementation Consortium guidelines for dihydropyrimidine dehydrogenase genotype and fluoropyrimidine dosing

The fluoropyrimidines are the mainstay chemotherapeutic agents for the treatment of many types of cancers. Detoxifying metabolism of fluoropyrimidines requires dihydropyrimidine dehydrogenase (DPD, encoded by the DPYD gene), and reduced or absent activity of this enzyme can result in severe, and sometimes fatal, toxicity. We summarize evidence from the published literature supporting this association and provide dosing recommendations for fluoropyrimidines based on DPYD genotype (updates at http://www.pharmgkb.org).

[Improvement of medication safety by identification of genetically predisposed subjects. Personalized clinical strategies and regulatory advices]

BACKGROUND

Because adverse drug events (ADEs) have a high socio-economic impact there is an urgent need for effective prevention. In addition to process-related avoidable errors personalised approaches for the prevention of ADEs should also focus on genetic polymorphisms as potential causative agents.

AIM

Using five case reports as examples therapeutic modalities are described to illustrate the clinical impact of prospective testing aimed at estimating the individual risk of susceptible subjects.

MATERIAL AND METHODS

The role of the HLA system, the cytochrome P450 family, other metabolic enzymes and transport proteins are described to illustrate the broad range of genetic susceptibility. It is shown, why, when and for whom pretherapeutic tests on genetic polymorphisms are recommended to reduce the risk of ADEs.

RESULTS

The determination of genetic susceptibility is already implemented in clinical practice prior to (1) carbamazepine therapy in south-east Asians and (2) treatment with abacavir independent of ethnicity. Before prescribing carbamazepine or abacavir, it is recommended that therapeutic decisions be based on these test results.

CONCLUSION

The broad application of personalised medicine used as an effective tool for minimizing ADE risks is limited by the evidence-based benefit for the patient on the one hand and the costs of the test on the other hand.

53BP1 sensitizes breast cancer cells to 5-fluorouracil

Chemoresistance of breast cancer is a worldwide problem for breast cancer and the resistance to chemotherapeutic agents frequently led to the subsequent recurrence and metastasis. In our previous study, we have found that 53BP1 showed a gradual decrease during the progression of breast cancer and loss of 53BP1 was associated with metastasis and poor prognosis in breast cancer. Here we aimed to reveal whether 53BP1 could sensitize breast cancer to 5-Fu. We found that ectopic expression of 53BP1 can significantly sensitize breast cancer cells to 5-Fu while knockdown of 53BP1 conferred the resistance. The in vivo experiments confirmed that overexpression of 53BP1 in combination with 5-Fu markedly inhibited growth of xenotransplanted tumors in nude mice when compared to either agent alone. Furthermore, we demonstrated that 53BP1 regulated the sensitivity to 5-Fu through thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPYD). The present studies provide a new clue that combination of 5-Fu and 53BP1 could be a potential novel targeted strategy for overcoming breast cancer chemoresistance.

A review of pharmacogenetics of adverse drug reactions in elderly people

Older adults are more susceptible to the prevalence of therapeutic failure and adverse drug reactions (ADRs). Recent advances in genomic research have shed light on the crucial role of genetic variants, mainly involving genes encoding drug-metabolizing enzymes, drug transporters and genes responsible for a compound's mechanism of action, in driving different treatment responses among individuals, in terms of therapeutic efficacy and safety. The interindividual variations of these genes may account for the differences observed in drug efficacy and the appearance of ADRs in elderly people. The advent of whole genome mapping techniques has allowed researchers to begin to characterize the genetic components underlying serious ADRs. The identification and validation of these genetic markers will enable the screening of patients at risk of serious ADRs and to establish personalized treatment regimens.The aim of this review was to provide an update on the recent developments in geriatric pharmacogenetics in clinical practice by reviewing the available evidence in the PubMed database to September 2012. A Pubmed search was performed (years 1999-2012) using the following two search strategies: ('pharmacogenomic' OR 'pharmacogenetic ') AND ('geriatric' or 'elderly ') AND 'adverse drug reactions'; [gene name] AND ('geriatric' or 'elderly ') AND 'adverse drug reactions', in which the gene names were those contained in the Table of Pharmacogenomic Biomarkers in Drug Labels published online by the US Food and Drug Administration ( http://www.fda.gov/drugs/scienceresearch/researchareas/pharmacogenetics/ucm083378.htm ). Reference lists of included original articles and relevant review articles were also screened. The search was limited to studies published in the English language.

Pharmacogenetics and pharmacogenomics: a bridge to individualized cancer therapy

In the past decade, advances in pharmacogenetics and pharmacogenomics (PGx) have gradually unveiled the genetic basis of interindividual differences in drug responses. A large portion of these advances have been made in the field of anticancer therapy. Currently, the US FDA has updated the package inserts of approximately 30 anticancer agents to include PGx information. Given the complexity of this genetic information (e.g., tumor mutation and gene overexpression, chromosomal translocation and germline variations), as well as the variable level of scientific evidence, the FDA recommendation and potential action needed varies among drugs. In this review, we have highlighted some of these PGx discoveries for their scientific values and utility in improving therapeutic efficacy and reducing side effects. Furthermore, examples are also provided for the role of PGx in new anticancer drug development by revealing novel druggable targets.

Screening of dihydropyrimidine dehydrogenase genetic variants by direct sequencing in different ethnic groups

Dihydropyrimidine dehydrogenase (DPYD) is an enzyme that regulates the rate-limiting step in pyrimidine metabolism, especially catabolism of fluorouracil, a chemotherapeutic agent for cancer. In order to determine the genetic distribution of DPYD, we directly sequenced 288 subjects from five ethnic groups (96 Koreans, 48 Japanese, 48 Han Chinese, 48 African Americans, and 48 European Americans). As a result, 56 polymorphisms were observed, including 6 core polymorphisms and 18 novel polymorphisms. Allele frequencies were nearly the same across the Asian populations, Korean, Han Chinese and Japanese, whereas several SNPs showed different genetic distributions between Asians and other ethnic populations (African American and European American). Additional in silico analysis was performed to predict the function of novel SNPs. One nonsynonymous SNP (+199381A > G, Asn151Asp) was predicted to change its polarity of amino acid (Asn, neutral to Asp, negative). These findings would be valuable for further research, including pharmacogenetic and drug responses studies.

DMET™ (Drug-Metabolizing Enzymes and Transporters) microarray analysis of colorectal cancer patients with severe 5-fluorouracil-induced toxicity

PURPOSE

5-fluorouracil (5-FU) has been widely used since the 1980s, and it remains the backbone of many chemotherapeutic combination regimens. However, its use is often limited by the occurrence of severe toxicity. Although several reports have shown the detrimental effect of some dihydropyrimidine dehydrogenase (DPYD) and thymidylate synthase (TYMS) gene polymorphisms in patients undergoing 5-FU-based treatment, they account for only a minority of toxicities.

METHODS

Looking for new candidate genetic variants associated with 5-FU-induced toxicity, we used the innovative genotyping microarray Affymetrix Drug-Metabolizing Enzymes and Transporters (DMET)™ Plus GeneChip that interrogates 1,936 genetic variants distributed in 231 genes involved in drug metabolism, excretion, and transport. To reduce variability, we analyzed samples from colorectal cancer patients who underwent fairly homogenous treatments (i.e., Machover or Folfox) and experienced G3 or G4 toxicity; control patients were matched for therapy and selected from those who did not disclose toxicity (G0-G1).

RESULTS

Pharmacogenetic genotyping showed no significant difference in DPYD and TYMS genetic variants distribution between cases and controls. However, other polymorphisms could account for 5-FU-induced toxicity, with the CHST1 rs9787901 and GSTM3 rs1799735 having the strongest association.

CONCLUSIONS

Although exploratory, this study suggests that genetic polymorphisms not directly related to 5-FU pharmacokinetics and pharmacodynamics are involved in 5-FU-induced toxicity. Our data also indicates DMET™ microarray as a valid approach to discover new genetic determinants influencing chemotherapy-induced toxicity.

Fluoropyrimidine toxicity in patients with dihydropyrimidine dehydrogenase splice site variant: the need for further revision of dose and schedule

Dihydropyrimidine dehydrogenase (DPD) is a key enzyme in the metabolic catabolism of 5-fluorouracil (5-FU) and its derivatives (capecitabine and tegafur). Complete or partial deficiency of DPD activity has been demonstrated to induce severe toxicities in cancer patients treated with fluoropyrimidine therapy. We analyzed 180 individuals that were candidates for a treatment with 5-FU class drugs for the most common DPD mutation, IVS14+1G>A, and detected four heterozygous patients. We recorded the toxicities for all 180 individuals after the first two chemotherapy cycles and found that three of the four patients, although they were treated with a dose reduction in 50 % on the basis of the genetic analysis, all showed severe toxicities that resulted in hospitalization of patient and premature discontinuation of treatment. One patient with mutated DPD was not treated with chemotherapy upon the clinician's decision because of his DPD mutated genotype and the presence of microsatellite instability. Our data suggest that greater dose reductions or alternative therapies are needed for patients with DPD IVS14+1G>A mutations.

Pharmacogenetic variants in the DPYD, TYMS, CDA and MTHFR genes are clinically significant predictors of fluoropyrimidine toxicity

Background:

Fluoropyrimidine drugs are extensively used for the treatment of solid cancers. However, adverse drug reactions are a major clinical problem, often necessitating treatment discontinuation. The aim of this study was to identify pharmacogenetic markers predicting fluoropyrimidine toxicity.

Methods:

Toxicity in the first four cycles of 5-fluorouracil or capecitabine-based chemotherapy were recorded for a series of 430 patients. The association between demographic variables, DPYD, DPYS, TYMS, MTHFR, CDA genotypes, and toxicity were analysed using logistic regression models.

Results:

Four DPYD sequence variants (c.1905+1G>A, c.2846A>T, c.1601G>A and c.1679T>G) were found in 6% of the cohort and were significantly associated with grade 3–4 toxicity (P<0.0001). The TYMS 3′-untranslated region del/del genotype substantially increased the risk of severe toxicity (P=0.0123, odds ratio (OR)=3.08, 95% confidence interval (CI): 1.38–6.87). For patients treated with capecitabine, a MTHFR c.1298CC homozygous variant genotype predicted hand–foot syndrome (P=4.1 × 10⁻⁶, OR=9.99, 95% CI: 3.84–27.8). The linked CDA c.−92A>G and CDA c.−451C>T variants predicted grade 2–4 diarrhoea (P=0.0055, OR=2.3, 95% CI: 1.3–4.2 and P=0.0082, OR=2.3, 95% CI: 1.3–4.2, respectively).

Conclusion:

We have identified a panel of clinically useful pharmacogenetic markers predicting toxicity to fluoropyrimidine therapy. Dose reduction should be considered in patients carrying these sequence variants.

Determination of common genetic variants in cytidine deaminase (CDA) gene in Indian ethnic population

Cytidine deaminase (CDA) is the major enzyme involved in metabolism of gemcitabine, a pyrimidine analog widely used for chemotherapy of solid tumors. While only low amounts of administered gemcitabine undergo intracellular phosphorylation into active forms and involve in antineoplastic activities, majority of it is rapidly inactivated by CDA and excreted to avoid drug toxicity. Knowledge of the genetic polymorphisms mildly effecting cellular activity of the enzyme CDA is therefore crucial to understanding drug-induced toxicities associated with gemcitabine. Functional significance and allele frequencies for common SNPs including 79A>C (*2) and 208G>A (*3) have been reported in various ethnic populations including Caucasian, African, Korean and Japanese. However, such studies have not been reported in any Indian sub-population. In the present study, conventional polymerase chain reaction (PCR) based amplification using gene specific primers and Sanger sequencing were performed to identify CDA variants in 50 healthy individuals from Indian sub-population. Established common variant 79A>C known to reduce CDA activity was observed at a frequency of 0.14 in the study cohort. In addition to other known variants, one novel variant, c.325-209T>C was detected at a frequency of 0.06. Genetic variants in CDA gene and their frequencies established in our study hold value in pharmacogenetics.

Interference in DNA replication can cause mitotic chromosomal breakage unassociated with double-strand breaks

Morphological analysis of mitotic chromosomes is used to detect mutagenic chemical compounds and to estimate the dose of ionizing radiation to be administered. It has long been believed that chromosomal breaks are always associated with double-strand breaks (DSBs). We here provide compelling evidence against this canonical theory. We employed a genetic approach using two cell lines, chicken DT40 and human Nalm-6. We measured the number of chromosomal breaks induced by three replication-blocking agents (aphidicolin, 5-fluorouracil, and hydroxyurea) in DSB-repair-proficient wild-type cells and cells deficient in both homologous recombination and nonhomologous end-joining (the two major DSB-repair pathways). Exposure of cells to the three replication-blocking agents for at least two cell cycles resulted in comparable numbers of chromosomal breaks for RAD54^−/−/KU70^−/− DT40 clones and wild-type cells. Likewise, the numbers of chromosomal breaks induced in RAD54^−/−/LIG4^−/− Nalm-6 clones and wild-type cells were also comparable. These data indicate that the replication-blocking agents can cause chromosomal breaks unassociated with DSBs. In contrast with DSB-repair-deficient cells, chicken DT40 cells deficient in PIF1 or ATRIP, which molecules contribute to the completion of DNA replication, displayed higher numbers of mitotic chromosomal breaks induced by aphidicolin than did wild-type cells, suggesting that single-strand gaps left unreplicated may result in mitotic chromosomal breaks.

Pharmacogenetic markers of toxicity for chemotherapy in colorectal cancer patients

Chemotherapeutic agents used in colorectal cancer are frequently associated with severe adverse reactions that compromise the efficacy of treatment. Predicting toxicity could enable therapy to be tailored. Genetic variations have been associated with toxicity in patients treated with fluoropyrimidines (5-fluorouracil, capecitabine and tegafur), oxaliplatin, irinotecan and cetuximab. Complexity of treatment and variability in toxicity classifications make it difficult to compare studies. This article analyzes the association between toxicity and polymorphisms in DPYD, TYMS, MTHFR, ABCB1, UGT1A1, ERCC1, ERCC2, XRCC1, GSTT1 and GSTM1. In addition, the state-of-the-art and future perspectives are discussed.

Pharmacogenomics of breast cancer therapy: an update

Clinical and histopathologic characteristics of breast cancer have long played an important role in treatment decision-making. Well-recognized prognostic factors include tumor size, node status, presence or absence of metastases, tumor grade, and hormone receptor expression. High tumor grade, presence of hormone receptors, and HER2-positivity are a few predictive markers of response to chemotherapy, endocrine manipulations, and anti-HER2 agents, respectively. However, there is much heterogeneity of outcomes in patients with similar clinical and pathologic features despite equivalent treatment regimens. Some of the differences in response to specific therapies can be attributed to somatic tumor characteristics, such as degree of estrogen receptor expression and HER2 status. In recent years, there has been great interest in evaluating the role that pharmacogenetics/pharmacogenomics, or variations in germline DNA, play in alteration of drug metabolism and activity, thus leading to disparate outcomes among patients with similar tumor characteristics. The utility of these variations in treatment decision-making remains debated. Here we review the data available to date on genomic variants that may influence response to drugs commonly used to treat breast cancer. While none of the variants reported to date have demonstrated clinical utility, ongoing prospective studies and increasing understanding of pharmacogenetics will allow us to better predict risk of toxicity or likelihood of response to specific treatments and to provide a more personalized therapy.

High-resolution melting analysis of the common c.1905+1G>A mutation causing dihydropyrimidine dehydrogenase deficiency and lethal 5-fluorouracil toxicity

Dihydropyrimidine dehydrogenase (DPD) deficiency is a pharmacogenetic syndrome associated with life-threatening toxicity following exposure to the fluoropyrimidine drugs 5-fluorouracil (5-FU) and capecitabine (CAP), widely used for the treatment of colorectal cancer and other solid tumors. The most prominent loss-of-function allele of the DPYD gene is the splice-site mutation c.1905+1G>A. In this study we report the case of a 73-year old woman with metastatic colorectal cancer who died from drug-induced toxicity after the first cycle of 5-FU-containing chemotherapy. Her symptoms included severe neutropenia, thrombocytopenia, mucositis and diarrhea; she died 16 days later despite intensive care measures. Post-mortem genetic analysis revealed that the patient was homozygous for the c.1905+1G>A deleterious allele and several family members consented to being screened for this mutation. This is the first report in Spain of a case of 5-FU-induced lethal toxicity associated with a genetic defect that results in the complete loss of the DPD enzyme. Although the frequency of c.1905+1G>A carriers in the white population ranges between 1 and 2%, the few data available for the Spanish population and the severity of this case prompted us to design a genotyping procedure to prevent future toxic effects of 5-FU/CAP. Since our group had previously developed a high-resolution melting (HRM) assay for the simultaneous detection of KRAS, BRAF, and/or EGFR somatic mutations in colorectal and lung cancer patients considered for EGFR-targeted therapies, we included the DPYD c.1905+1G>A mutation in the screening test that we describe herein. HRM provides a rapid, sensitive, and inexpensive method that can be easily implemented in diagnostic settings for the routine pre-therapeutic testing of a gene mutation panel with implications in the pharmacologic treatment.

Gender-specific elimination of continuous-infusional 5-fluorouracil in patients with gastrointestinal malignancies: results from a prospective population pharmacokinetic study

BACKGROUND

This study was initiated to assess the quantitative impact of patient anthropometrics and dihydropyrimidine dehydrogenase (DPYD) mutations on the pharmacokinetics (PK) of 5-fluorouracil (5FU) and to explore limited sampling strategies of 5FU.

PATIENTS AND METHODS

We included 32 patients with gastrointestinal malignancies, receiving 46-h continuous-infusional 5FU and performed PK-sampling at baseline, 15, 30, 45 min, 1 and 2 h after the start of infusion and at the end of infusion, for 2 subsequent cycles. Plasma concentrations of 5FU, 5-fluorodihydrouracil (5FUH2), uracil (U) and 5,6-dihydrouracil (UH2) were determined using LC-MS/MS and submitted to population PK analysis using nonlinear mixed-effects modeling. Broad genotyping of DPYD was performed, and the potential impact of the DPYD genotype on the elimination of 5FU was assessed. Limited sampling strategies were evaluated for their accuracy to predict steady-state concentrations of 5FU (CSS(5FU)), using data simulations based on the final PK-model.

RESULTS

The area-under-the concentration-time curve of 5FU (AUC(5FU)) was found to be <20 mg h/L in 33 occasions (58 %), between 20 and 30 mg h/L in 17 occasions (30 %) and >30 mg h/L in 7 occasions (12 %). Men had a 26 % higher elimination of 5FU and a 18 % higher apparent elimination of 5FUH2. Accordingly, women had a higher AUC(5FU) compared to men (22 vs. 18 mg h/L, p = 0.04). No DPYD risk variants were found, and the DPYD variants detected (c.496A>G, c.1601G>A, c.1627A>G) were not significantly associated with the elimination of 5FU. Individual baseline UH(2)/U ratio was significantly associated with AUC(5FU) (R = -0.49, p < 0.001). Limited sampling strategies with time-points <3 h after the start of infusion were not adequate to predict CSS(5FU). Female gender was the only predictor of nausea/emesis in the multivariate model.

CONCLUSIONS

Gender-specific elimination of 5FU is supported by the present data and may partly explain the gender-specific association between DPYD risk variants and 5FU-specific toxicity.

Let's get personal: predicting thiopurine and fluoropyrimidine toxicity

The US FDA now recognizes the need to individualize treatment paradigms using biomarkers that predict response to therapy. In clinical practice the best example of this is TPMT testing, which is used to rationalize the starting dose of azathioprine and mercaptopurine. The more recent addition of drug metabolite monitoring means that thiopurine therapy can now be personalized to unprecedented levels. Of interest, parallels exist between TPMT deficiency as an explanation for thiopurine toxicity and DPD deficiency in fluoropyrimidine toxicity. For these drugs, variations in a single locus predict severe toxicity. However, while TPMT testing has translated into routine clinical practice, DPD testing has not. This article summarizes the recent research investigating interindividual differences in the metabolism of thiopurine and fluoropyrimidine drugs, and explores the attitudes which influence the uptake of pharmacogenetic testing.