Autoregulation of 5-fluorouracil metabolism

Conflicting alterations in hepatic expression of CYP3A and enzyme kinetics in rats exposed to 5-fluorouracil: relevance to pharmacokinetics of midazolam

1. 5-Fluorouracil (5-FU) is a pyrimidine derivative widely used for the treatment of cancer. In this study, we investigated the effects of 5-FU on the protein expression of hepatic CYP3A and their enzyme activity for metabolizing midazolam (MDZ), a typical substrate of CYP3A, in rat liver microsomes. We also examined the pharmacokinetic behavior of intravenously administered MDZ in rats treated with 5-FU (120 mg/kg, ip). 2. 5-FU was shown to induce hepatic CYP3A2 protein 2 days after administration without changing the expression of CYP3A1/3A23. However, affinity of 5-FU-inducible CYP3A protein to MDZ for its 4- and 1'-hydroxylation was decreased. Furthermore, the susceptibility of MDZ hydroxylation activity to a CYP3A inhibitor differed between the control and 5-FU groups. 3. Pharmacokinetic analysis of the MDZ disposition demonstrated no significant differences in the total clearance (CL_tot) and elimination rate constant (k_e) between the control and 5-FU-treated rats. Lack of alteration in the metabolic clearance of MDZ may be attributable to the induction of CYP3A protein with reduced affinity for the substrate of CYP3A enzymes. 4. Our findings provide novel information regarding the manifestation of inductive and interfering actions of 5-FU toward hepatic CYP3A to help in assessing the pharmacokinetics of CYP3A substrate drugs.

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.

Combinatorial measurement of CDKN1A/p21 and KIF20A expression for discrimination of DNA damage-induced clastogenicity

In vitro mammalian cytogenetic tests detect chromosomal aberrations and are used for testing the genotoxicity of compounds. This study aimed to identify a supportive genomic biomarker could minimize the risk of misjudgments and aid appropriate decision making in genotoxicity testing. Human lymphoblastoid TK6 cells were treated with each of six DNA damage-inducing genotoxins (clastogens) or two genotoxins that do not cause DNA damage. Cells were exposed to each compound for 4 h, and gene expression was comprehensively examined using Affymetrix U133A microarrays. Toxicogenomic analysis revealed characteristic alterations in the expression of genes included in cyclin-dependent kinase inhibitor 1A (CDKN1A/p21)-centered network. The majority of genes included in this network were upregulated on treatment with DNA damage-inducing clastogens. The network, however, also included kinesin family member 20A (KIF20A) downregulated by treatment with all the DNA damage-inducing clastogens. Downregulation of KIF20A expression was successfully confirmed using additional DNA damage-inducing clastogens. Our analysis also demonstrated that nucleic acid constituents falsely downregulated the expression of KIF20A, possibly via p16 activation, independently of the CDKN1A signaling pathway. Our results indicate the potential of KIF20A as a supportive biomarker for clastogenicity judgment and possible mechanisms involved in KIF20A downregulation in DNA damage and non-DNA damage signaling networks.

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.

Personalized dosing via pharmacokinetic monitoring of 5-fluorouracil might reduce toxicity in early- or late-stage colorectal cancer patients treated with infusional 5-fluorouracil-based chemotherapy regimens

INTRODUCTION

Therapeutic plasma 5-fluorouracil (5-FU) levels are achieved in only 20% to 30% of patients with the current practice of administering 5-FU doses based on body surface area (BSA). Alternatively, 5-FU doses can be adjusted based on 5-FU pharmacokinetic (PK) monitoring. Although benefits of PK monitoring of 5-FU in metastatic colorectal cancer (CRC) have been reported, its utility among patients with early stage disease has not been reported.

PATIENTS AND METHODS

We retrospectively examined the effect of 5-FU PK monitoring in 84 CRC patients (49 stage IV and 35 stage II/III) receiving mFOLFOX6 (modifiedFOLFOX6; modified 5-fluorouracil, leucovorin, oxaliplatin protocol) or mFOLFIRI (modified 5-fluorouracil, leucovorin, irinotecan protocol). Forty-six of the 84 patients received 5-FU doses based on BSA and 38 received doses that were adjusted with PK monitoring. 5-FU plasma levels were measured using a nanoparticle immunoassay method.

RESULTS

5-fluorouracil PK monitoring significantly improved disease-free survival in stage II/III patients (P = .0429). There was also a trend towards improved progression-free survival among stage IV patients who had their 5-FU levels PK-monitored (P = .16). Moreover, 5-FU PK monitoring significantly reduced (P = .0437) and delayed (P = .0144) adverse effects in stage II/III patients. Toxicity occurred after the second 5-FU dose in the BSA group and after the sixth to seventh dose in the PK monitoring group. In stage IV patients, the onset of toxicities was also delayed with PK monitoring (P = .0605).

CONCLUSION

We provide evidence that PK monitoring of 5-FU is potentially beneficial for late stage and early stage CRC. These results contribute to the growing body of evidence regarding patient benefit when treatment decisions are based on the individual patient characteristics, in this case, a patients' 5-FU levels.

Utilization of CDKN1A/p21 gene for class discrimination of DNA damage-induced clastogenicity

The in vitro mammalian cytogenetic tests monitor chromosomal aberrations in cultured mammalian cells to test the mutagenicity of compounds. Although these tests are especially useful for evaluating the potential clastogenic effects of chemicals, false positives associated with excessive toxicity occur frequently. There is a growing demand for mechanism-based assays to confirm positive results from cytogenetic tests. We hypothesized that a toxicogenomic approach that is based on gene expression profiles could be used to investigate mechanisms of genotoxicity. Human lymphoblastoid TK6 cells were treated with each of eight different genotoxins that included six DNA damaging compounds-mitomycin C, methyl methanesulfonate, ethyl methanesulfonate, cisplatin, etoposide, hydroxyurea-and two compounds that do not damage DNA-colchicine and adenine. Cells were exposed to each compound for 4h, and Affymetrix U133A microarrays were then used to comprehensively examine gene expression. A statistical analysis was used to select biomarker candidates, and 103 probes met our statistical criteria. Expression of cyclin-dependent kinase inhibitor 1A (CDKN1A)/p21 was ranked highest for discriminating DNA-damaging compounds. To further characterize the biological significance of alterations in gene expression, functional network analysis was performed with the 103 selected probes. Interestingly, a CDKN1A-centered interactome was identified as the most significant network. Together, these findings indicated that DNA-damaging compounds often induced changes in the expression of a large number of these 103 probes and that upregulation of CDKN1A was a common key feature of DNA damage stimuli. The utility of CDKN1A as a biomarker for assessing the genotoxicity of drug candidates was further evaluated; specifically, quantitative RT-PCR was used to assess the effects of 14 additional compounds-including DNA damaging genotoxins and genotoxins that do not damage DNA and five newly-synthesized drug candidates-on CDKN1A expression. In these assays, DNA damage-positive clastogens were clearly separated from DNA damage-negative compounds based on CDKN1A expression. In conclusion, CDKN1A may be a valuable biomarker for identifying DNA damage-inducing clastogens and as a follow-up assay for mammalian cytogenetic tests.

Personalizing colon cancer therapeutics: targeting old and new mechanisms of action

The use of pharmaceuticals for colon cancer treatment has been increasingly personalized, in part due to the development of new molecular tools. In this review, we discuss the old and new colon cancer chemotherapeutics, and the parameters that have been shown to be predictive of efficacy and safety of these chemotherapeutics. In addition, we discuss how alternate pharmaceuticals have been developed in light of a potential lack of response or resistance to a particular chemotherapeutic.

A rapid HPLC-ESI-MS/MS method for determination of dihydrouracil/uracil ratio in plasma: evaluation of toxicity to 5-flurouracil in patients with gastrointestinal cancer

BACKGROUND

A liquid chromatography-tandem mass spectrometry method for the simultaneous quantitation of endogenous uracil (U) and dihydrouracil (UH2) was developed and tested in a Brazilian population of patients with gastrointestinal cancer previously exposed to 5-fluorouracil (5FU).

METHODS

The analytes were extracted by a liquid-liquid method using 5-clorouracil as internal standard. The separation was performed on a reversed-phase XTerra C18 column with a mobile phase composed of methanol and aqueous 0.1% ammonium hydroxide (15:85). Mass spectrometry detection was carried out using negative electrospray ionization and selected reaction monitoring. Bovine serum albumin was employed as an alternative matrix to prepare the calibration standards, aiming to avoid the measurement of physiologic U and UH2. Calibration curves were constructed over the range of 5-200 ng/mL for U and 10-500 ng/mL for UH2.

RESULTS

The mean RSD values in the intrarun precision were 6.5% and 10.0% and in the interrun precision were 7.8% and 9.0% for U and UH2, respectively. The mean accuracy values were within the range of 90%-110% for both analytes. The analytes were stable in plasma under different conditions of temperature and time. The validated method was successfully applied to determine the plasma concentrations of U and UH2 in patients with gastrointestinal cancer (n = 32) previously treated with 5FU and for whom clinical toxicity was well documented. U concentrations varied from 21.8 to 56.6 ng/mL, whereas UH2 concentrations varied from 57.7 to 271.5 ng/mL. UH2/U ratio ranged from 1.56 to 6.18.

CONCLUSIONS

The method has proved to provide a quick, reliable, and reproducible quantitation of the plasma concentrations of U and its metabolite UH2. The UH2/U ratios did not discriminate patients previously exposed to 5FU with and without severe toxicities, possibly due to the small sample. Further studies in a larger population are desirable.

Effect of 5-fluorouracil treatment on SN-38 absorption from intestine in rats

5-Fluorouracil (5-FU)-based chemotherapies with irinotecan have been applied for the treatment of cancers, and a common dose-limiting toxicity is neutropenia and diarrhea. In this study, we investigated the effect of 5-FU treatment on expression levels of drug transporters for SN-38 transportation and SN-38 absorption from the intestine following 5-FU treatment. Expression levels of several drug transporters and nuclear receptors in rats after 5-FU treatment were evaluated. SN-38 absorption from the intestine was evaluated by SN-38 concentration levels in serum following SN-38 injection into the intestine of 5-FU treated rats. The levels of renal multidrug resistance protein 2 (Mrp2) on day 4 after treatment (400 mg/kg) showed significant upregulation, 359.2 ± 33.2% (mean ± S.E.) of control. Mrp2 levels in the intestine were downregulated to 26.2 ± 8.4% of control. 5-FU treatment (400 mg/kg) also significantly downregurated expression levels of P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) to 41.2 ± 14.7%, 15.7 ± 4.3% of control, respectively. To evaluate SN-38 absorption from the intestine, SN-38 was loaded in to the intestine on day 4 after 5-FU treatment. Pretreatment with 5-FU significantly increased SN-38 concentration in the blood 30, 60 and 90 min after SN-38 administration. The area under the curve for SN-38 in the 5-FU group was significantly higher than in vehicle groups. 5-FU treatment decreased expression levels of P-glycoprotein and Bcrp in intestine. The present study suggests that combination chemotherapy of 5-FU with irinotecan (CPT-11) may elevate SN-38 absorption from intestine.

The Value of Dihydrouracil/Uracil Plasma Ratios in Predicting 5-Fluorouracil-Related Toxicity in Colorectal Cancer Patients

This study investigated the relationship between the dihydrouracil/uracil (UH2/U) plasma ratio, a surrogate marker of dihydropyrimidine dehydrogenase (DPD) activity, and 5-fluorouracil (5-FU)-related early toxicity. Plasma UH2/U ratios were determined in 68 colorectal cancer patients and 100 healthy controls. A cutoff value indicative of DPD deficiency was calculated using receiver operator characteristics. Patients experiencing toxicity were screened for the DPD G-to-A point mutation within the 5′-splicing donor site of intron 14 (IVS14+1G>A). Overall, 24/68 patients (35%) experienced toxicity (all grades) and abnormal UH2/U ratios were demonstrated in 21/24 (87.5%) patients. Drug concentrations up to 130 times the recommended level were found in 13/24 (54%) patients experiencing toxicity. One patient experiencing toxicity was a heterozygous carrier of the IVS14+1G>A mutation. A low UH2/U plasma ratio had a sensitivity of 0.87 and specificity of 0.93 for predicting 5-FU-induced toxicity. Systematic detection of DPD-deficient patients using the UH2/U ratio could optimize 5-FU-based chemotherapy and minimize life-threatening toxicity.

The influence of circadian rhythms on the kinetics of drugs in humans

In clinical practice, it is important to consider circadian rhythms in pharmacokinetics and cell responses to therapy in order to design proper protocols for drug administration. Scientists have arrived at this conclusion after several experiments in animals and in humans have clearly demonstrated that all organisms are highly organised according to circadian rhythms. These temporal cycles influence different physiological functions and, consequently, can influence the pharmacokinetic phases of drugs. A drug's pharmacokinetics can be modified according to the time of drug administration. In fact, the circadian changes of > 100 different compounds have been documented. The results obtained have led several scientific societies to provide guidelines concerning the timing of drug dosing for anticancer, cardiovascular, respiratory, anti-ulcer, anti-inflammatory, immunosuppressive and antiepileptic drugs. Absorption may be influenced by circadian rhythms and most lipophilic drugs seem to be absorbed faster when the drug is taken in the morning compared with the evening; for water-soluble compounds, no circadian variation in the absorption of drugs has been found. Concerning drug distribution, the higher the blood flow fraction an organ receives, the higher the rate constant for transferring drugs out of the capillaries. This drug pharmacokinetic phase may be influenced by circadian variations in the protein binding of acidic and basic drugs. Drug metabolism may be influenced by daily modifications of blood flow. For drugs with a high extraction ratio, metabolism depends on hepatic blood flow, while that of drugs with a low extraction ratio depends on liver enzyme activity. Hepatic blood flow has been shown to be greatest at 8 am and metabolism seems to be reduced during the night. Finally, concerning drug elimination, the clearance of 'flow-limited' drugs that present a high extraction rate is affected by the blood flow delivered to the organ, independent of the cardiac output fraction supplied. Chronopharmacokinetics can explain individual differences in drug levels revealed by therapeutic drug monitoring and can be used to optimise the management of patients receiving drug therapy.

Dihydropyrimidine dehydrogenase activity during long-term adjuvant treatment with oral uracil and tegafur for colorectal cancer

BACKGROUND

Dihydropyrimidine dehydrogenase (DPD) is a rate-limiting enzyme for the degradation of 5-fluorouracil. The effect of long-term treatment with oral fluoropyrimidines on DPD activity has not been investigated. This study was conducted to examine changes in DPD activity in peripheral mononuclear cells (PMNC) during long-term treatment with oral uracil and tegafur (UFT) for colorectal cancer.

METHODS

UFT was administered for 5 consecutive days and not administered the next 2 days for 6 months after surgery. PMNC-DPD activity was measured before and 1, 2, 4 and 6 months after starting UFT administration.

RESULTS

In 70 eligible patients, there were no significant variations of PMNC-DPD activity during postoperative administration of UFT for 6 months. Grade 2 or higher adverse events were observed in significantly more patients with low DPD than with high DPD activity (p = 0.018).

CONCLUSION

There were no significant variations of PMNC-DPD activity during the postoperative administration of UFT for 6 months. Low PMNC-DPD activity before UFT treatment was considered to be a predicting factor for toxicity.

Thymidylate synthase and dihydropyrimidine dehydrogenase mRNA expression after administration of 5-fluorouracil to patients with colorectal cancer

This study explores the effect of 5-fluorouracil (5FU) exposure on mRNA levels of its target enzyme thymidylate synthase (TS) and the rate-limiting catabolic enzyme dihydropyrimidine dehydrogenase (DPD) in tumors of colorectal cancer patients. TS and DPD mRNA levels were determined in primary tumor and liver metastasis samples from patients who were either not pretreated (n = 29) or given one presurgery bolus of 5FU (n = 67). In both groups a wide variation in TS mRNA levels was observed. Median TS mRNA expression in 17 primary tumors of exposed patients was 3.0-fold higher than in 19 primary tumors of unexposed patients (p = 0.015). TS mRNA expression in liver metastasis samples of exposed patients (n = 16) was also higher (5.2-fold) than that of unexposed patients (n = 48; p < 0.001). Also DPD mRNA expression displayed a large degree of interpatient variation. No difference in DPD expression in liver metastasis samples was observed between exposed and unexposed patients. However, median DPD mRNA expression in 15 primary tumors of exposed patients was 3.2-fold lower than in 18 primary tumors of unexposed patients (p = 0.027). In conclusion, administration of 5FU in vivo influences the gene expression of TS and DPD.

Characterization of DNA reactive and non-DNA reactive anticancer drugs by gene expression profiling

Gene expression profiling technology is expected to advance our understanding of genotoxic mechanisms involving direct or indirect interaction with DNA. We exposed human lymphoblastoid TK6 cells to 14 anticancer drugs (vincristine, paclitaxel, etoposide, daunorubicin, camptothecin, amsacrine, cytosine arabinoside, hydroxyurea, methotrexate, 5-fluorouracil, cisplatin, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU), and bleomycin) for 4-h and examined them immediately or after a 20-h recovery period. Cytotoxicity and genotoxicity, respectively, were evaluated by cell counting and by in vitro micronucleus assay at 24h. Effects on the cell cycle were determined by flow cytometry at 4 and 24h. Gene expression was profiled at both sampling times by using human Affymetrix U133A GeneChips (22K). Bioanalysis was done with Resolver/Rosetta software and an in-house annotation program. Cell cycle analysis and gene expression profiling allowed us to classify the drugs according to their mechanisms of action. The molecular signature is composed of 28 marker genes mainly involved in signal transduction and cell cycle pathways. Our results suggest that these marker genes could be used as a predictive model to classify genotoxins according to their direct or indirect interaction with DNA.

Regulation of human dihydropyrimidine dehydrogenase: implications in the pharmacogenetics of 5-FU-based chemotherapy

Dihydropyrimidine dehydrogenase is the enzyme that is critical for the efficacy and toxicity of the anticancer reagent 5-fluorouracil. It has been demonstrated that the regulation of the dihydropyrimidine dehydrogenase gene has an important role in the determination of the enzyme activity of dihydropyrimidine dehydrogenase. The regulation of the gene expression is thus discussed from two aspects: normal regulation by specificity proteins, and the epigenetic regulation by promoter methylation. The influence of the polymorphism on dihydropyrimidine dehydrogenase enzyme activity and other factors that have been suggested to be involved in dihydropyrimidine dehydrogenase regulation are also discussed.

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

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

Inhibitory Effect of 5-Fluorouracil on Cytochrome P450 2C9 Activity in Cancer Patients

Drug interactions have been reported between 5-fluorouracil and cytochrome P450 2C9 (CYP2C9) substrates, S-warfarin and phenytoin. This study was performed to determine the influence of 5-fluorouracil on cytochrome P450 2C9 (CYP2C9) activity in colorectal cancer patients (n=17) receiving 5-fluorouracil. Losartan was used as a marker to assess CYP2C9 activity. Losartan and its CYP2C9 dependent metabolite, E-3174, were determined in urine. The ratios of urinary losartan/E-3174 before and after the 5-fluorouracil treatment were compared for each patient. Genotyping was performed to detect the CYP2C9*2 and CYP2C9*3. At the end of the first cycle of 5-fluorouracil, losartan/E-3174 ratio was increased by 28.0% compared to the pre-treatment values (P=0.15). In five patients recruited for phenotyping after three 5-fluorouracil cycles, the metabolic ratio was increased significantly by 5.3 times (P=0.03). The results suggest that in most patients 5-fluorouracil inhibited CYP2C9 activity. This inhibition was more pronounced when the total administered dose increased. This finding may help explain the mechanism of interaction between 5-fluorouracil and CYP2C9 substrates.

Pharmacokinetic and pharmacodynamic comparison of fluoropyrimidine derivatives, capecitabine and 5'-deoxy-5-fluorouridine (5'-DFUR)

PURPOSE

Capecitabine is a three-step prodrug that was rationally designed to be a more effective and safer alternative to its intermediate metabolite, 5'-deoxy-5-fluorouridine (5'-DFUR). We compared the pharmacokinetics/pharmacodynamics of these drugs in metastatic breast cancer patients.

METHODS

Six patients received oral capecitabine at 1657 mg/m2 twice daily and 17 received 5'-DFUR at 400 mg three times daily. Both drugs were administered for 21 days followed by a 7-day rest.

RESULTS

Median daily 5'-DFUR AUC was significantly higher for capecitabine than for 5'-DFUR (81.1 vs 32.6 mmol h/l; P = 0.01). Following treatment with 5'-DFUR, the median AUC and Cmax of 5'-DFUR tended to be higher in patients with a partial response (3.83 microg h/ml and 4.88 microg/ml) and stable disease (6.46 microg h/ml and 4.96 microg/ml) than in those with disease progression (2.53 microg h/ml and 1.36 microg/ml). The AUC and Cmax of 5'-DFUR was significantly related to overall survival.

CONCLUSIONS

These results support the superiority of capecitabine over 5'-DFUR.

Single Ascending Dose Tolerability, Pharmacokinetic–Pharmacodynamic Study of Dihydropyrimidine Dehydrogenase Inhibitor Ro 09-4889

PURPOSE

Ro 09-4889 was designed to enhance the anticancer efficacy of capecitabine (Xeloda) by generating a dihydropyrimidine dehydrogenase inhibitor (DPDi) 5-vinyluracil (5-VU) preferentially in tumor tissues. This study assessed the tolerance to Ro 09-4889 treatment, and related pharmacokinetic and pharmacodynamic data such as inhibition of DPD activity in peripheral blood mononuclear cells (PBMCs) and plasma uracil levels.

EXPERIMENTAL DESIGN

This was a single-center, double-blind, placebo-controlled, single-dose escalation study in 64 healthy male volunteers at 1-, 5-, 20-, 50-, 75-, 100-, and 200-mg oral dose of Ro 09-4889. Also, food effect was assessed separately in a group dosed with 20 mg of the compound.

RESULTS

No serious adverse effects or significant laboratory and electrocardiogram abnormalities were observed during the study. Ro 09-4889 has a short elimination half-life (t(1/2)) of 0.5 h, followed by metabolites 5'-deoxy-5-vinyluridine (5'-DVUR), 5'-deoxy-5-vinylcytidine (5'-DVCR), and 5-VU with t(1/2) of 1.3, 1.2, and 2 h, respectively. The major metabolite excreted in urine was 5-DVCR (45% of dose). The inhibition of PBMC DPD activity and the increase in plasma uracil were related to Ro 09-4889 dose. DPD inhibition versus dose and uracil AUC (area under the curve) versus dose were modeled using the E(max) model with a baseline effect. The model-predicted ED(50) value was 100 mg.

CONCLUSION

Single oral doses of Ro 09-4889 ranging from 1 to 200 mg were well tolerated. On the basis of these findings, a 10-to-30-mg dose range of Ro 09-4889 combined with capecitabine could be appropriate for further evaluation in cancer patients.

Effect of 5-fluorouracil and epidermal growth factor on cell growth and dihydropyrimidine dehydrogenase regulation in human uterine cervical carcinoma SKG-IIIb cells

We previously demonstrated that epidermal growth factor (EGF) induces a decrease in dihydropyrimidine dehydrogenase (DPD), which is the first and rate-limiting enzyme in the catabolism of 5-fluorouracil (5-FU), in EGF receptor (EGFR)-positive human SKG-IIIb uterine cervical carcinoma cells, and thereby increased the sensitivity of the cells to 5-FU. In the present study, we examined the individual and combined effects of 5-FU and EGF on growth and DPD activity in SKG-IIIb cells, and also investigated the mode of regulation of DPD activity. The cells showed sensitivity to 5-FU, and growth was stimulated by EGF. When the agents were used in combination, the sensitivity of SKG-IIIb cells to 5-FU was increased roughly sixfold at maximum, as judged in terms of the 50% growth-inhibitory concentration. We then examined the effects of 5-FU and EGF on DPD. Either agent inhibited DPD activity and protein expression in a concentration-dependent manner. Expression of DPD mRNA was concentration-dependently inhibited by treatment with 5-FU and by EGF at a concentration that strongly stimulated cell growth. Further, combination treatment inhibited DPD activity, as well as DPD protein and mRNA expression, more strongly than did treatment with 5-FU or EGF alone. These results suggest that inhibition of DPD activity by EGF or 5-FU is regulated at least at the level of protein expression and that regulation via mRNA is also involved. The above findings indicate that 5-FU and EGF act synergistically in suppressing DPD activity and that the use of 5-FU against tumors in which EGF plays an important role would maximize the potential of 5-FU as an anticancer drug.

Effect of 5-fluorouracil on the anticoagulant activity and the pharmacokinetics of warfarin enantiomers in rats

The interaction between the antineoplastic agent 5-fluorouracil (5-FU) and the oral anticoagulant warfarin enantiomers was investigated in rats. An increase in hypoprothrombinaemic response, assessed by means of percent changes of prothrombin complex activity and clotting factor VII activity, to warfarin, was observed following oral administration of 1.5 mg/kg racemic warfarin to rats during a 8-day intraperitoneal dose regimen of 5-FU (13.3 mg/kg daily). 5-FU had no apparent effect on the baseline blood coagulation, the in vitro rat serum protein binding as well as the absorption and distribution of the S- and R-enantiomers of warfarin in rats. Yet treatment with 5-FU produced a significant decrease in the total serum clearance value of S-warfarin in rats. The decreased total clearance was attributed mainly to a significant decrease in the formation rate of the overall oxidative metabolites of the more potent S-enantiomer of warfarin.

Increased risk of grade IV neutropenia after administration of 5-fluorouracil due to a dihydropyrimidine dehydrogenase deficiency: high prevalence of the IVS14+1g>a mutation

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5-FU), and it is suggested that patients with a partial deficiency of this enzyme are at risk of developing severe 5-FU-associated toxicity. We evaluated the importance of DPD deficiency, gender and the presence of the IVS14+1G>A mutation in the etiology of 5-FU toxicity. In 61% of cases, decreased DPD activity could be detected in peripheral blood mononuclear cells. Furthermore, the number of females (65%) in the total group of patients appeared to be higher than the number of males (35%) (p = 0.03). Patients with partial DPD deficiency appeared to have a 3.4-fold higher risk of developing grade IV neutropenia than patients with normal DPD activity. Analysis of the DPYD gene of patients suffering from grade IV neutropenia for the presence of the IVS14+1G>A mutation showed that 50% of the patients investigated were heterozygous or homozygous for the IVS14+1G>A mutation. Adopting a threshold level for DPD activity of 70% of that observed in the normal population, 14% of the population is prone to the development of severe 5-FU-associated toxicity. Below this threshold level, 90% of individuals heterozygous for a mutation in the DPYD gene can be identified. Considering the common use of 5-FU in the treatment of cancer, the severe 5-FU-related toxicities in patients with low DPD activity and the apparently high prevalence of the IVS14+1G>A mutation, screening of patients at risk before administration of 5-FU is warranted.

Implications of dihydropyrimidine dehydrogenase on 5-fluorouracil pharmacogenetics and pharmacogenomics

A prominent example of the potential application of pharmacogenomics and pharmacogenetics to oncology is the study of dihydropyrimidine dehydrogenase (DPD) in 5-fluorouracil (5-FU) metabolism. 5-FU is currently one of the most widely administered chemotherapeutic agents used for the treatment of epithelial cancers. DPD is the rate-limiting enzyme in the catabolism and clearance of 5-FU. The observation of a familial linkage of DPD deficiency from a patient exhibiting 5-FU toxicity suggested a possible molecular basis for variations in 5-FU metabolism. Molecular studies have suggested there is a relationship between allelic variants in the DPYD gene (the gene that encodes DPD) and a deficiency in DPD activity, providing a potential pharmacogenetic basis for 5-FU toxicity. In the last decade, studies have correlated tumoral DPD activity with 5-FU response, suggesting it may be a useful pharmacogenomic marker of patient response to 5-FU-based chemotherapy. This article reviews the basis and discusses the challenges of pharmacogenetic and pharmacogenomic testing of DPD for the determination of 5-FU efficacy and toxicity.

Reduced 5-FU clearance in a patient with low DPD activity due to heterozygosity for a mutant allele of the DPYD gene

5-fluorouracil pharmacokinetics, dihydropyrimidine dehydrogenase-activity and DNA sequence analysis were compared between a patient with extreme 5-fluorouracil induced toxicity and six control patients with normal 5-fluorouracil related symptoms. Patients were treated for colorectal cancer and received chemotherapy consisting of leucovorin 20 mg m(-2) plus 5-fluorouracil 425 mg m(-2). Blood sampling was carried out on day 1 of the first cycle. The 5-fluorouracil area under the curve(0-->3h) in the index patient was 24.1 mg h l(-1) compared to 9.8+/-3.6 (range 5.4-15.3) mg h l(-1) in control patients. The 5-fluorouracil clearance was 520 ml min(-1) vs 1293+/-302 (range 980-1780) ml min(-1) in controls. The activity of dihydropyrimidine dehydrogenase in mononuclear cells was lower in the index patient (5.5 nmol mg h(-1)) compared to the six controls (10.3+/-1.6, range 8.0-11.7 nmol mg h(-1)). Sequence analysis of the dihydropyrimidine dehydrogenase gene revealed that the index patient was heterozygous for a IVS14+1G>A point mutation. Our results indicate that the inactivation of one dihydropyrimidine dehydrogenase allele can result in a strong reduction in 5-fluorouracil clearance, causing severe 5-fluorouracil induced toxicity.

Clinical pharmacokinetics of 5-fluorouracil with consideration of chronopharmacokinetics

Even though 5-fluorouracil (FU) is one of the oldest anticancer drugs, its use in cancer chemotherapy continues to increase. Fluorouracil is a pro-drug that requires intracellular activation to exert its effects. This makes it difficult to associate blood drug concentration with cell toxicity directly, although data from the literature show the existence of such a relationship. The relationship between FU pharmacokinetics and patient response has been explored extensively and reports attest a link between systemic drug exposure and response and survival. This has led to the concept of maximal tolerated exposure, and strategies to achieve this rely on pharmacokinetic follow-up and individual dose adjustment. More than 80% of the administered FU dose is eliminated by catabolism through dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme. Dihydropyrimidine dehydrogenase activity is found in most tissues but is highest in the liver. Peripheral blood mononuclear cells (PBMC) are used to monitor clinically DPD activity. A significant, but weak correlation between PBMC and liver DPD activity has been observed. The relationship between PBMC-DPD activity and FU systemic clearance is weak (r2 = 0.10); thus, simply determining PBMC-DPD is not sufficient to predict accurately FU clearance. Population pharmacokinetic analysis identified patient co-variables that influence FU clearance; drug kinetics is significantly reduced by increased age, high serum alkaline phosphatase, length of drug infusion, and low PBMC-DPD. Autoregulation of FU metabolism also is suggested; inhibition of DPD activity was observed after FU administration in both colorectal cancer patients and an animal model. Circadian rhythmicity in DPD activity is suggested from both human and animal investigations. In patients receiving protracted low dose 5-FU infusion, the circadian rhythm in FU plasma concentration peaks at 11:00h and is lowest at 23:00h, on average. The inverse relationship observed between the circadian profile of FU plasma concentration and PBMC-DP activity in these same patients suggests a link between DPD activity and FU pharmacokinetics. The impact of the biological time of drug administration was also studied with short venous infusions; clearance was 70% greater at 13:00h than at 01:00h. Similarly, peak drug concentration occurred in the first half of the night in patients receiving constant rate 5-FU infusion for 2-5d. Several studies describe wide interindividual variation in the timing of the peak and trough of the 24h rhythm in DPD activity. The rational for FU chronomodulated therapy has been the circadian rhythm in host drug tolerance, which is greatest during the night time when the proliferation of normal target tissue is least. A randomized study of chronomodulated FU therapy with maximal delivery rate at 04:00h was shown clearly to be significantly more effective and less toxic than control flat FU therapy. Future research must focus on easy-to-obtain markers of specific rhythms to individualize the chronomodulated FU delivery.

Thymidine phosphorylase and dihydropyrimidine dehydrogenase protein expression in colorectal cancer

It is essential for actively proliferating cells to increase their rate of DNA synthesis to progress through the cell cycle. This is reflected in the increased uracil usage that is a common feature in solid tumours. Thymidine phosphorylase (TP) anabolises formation of pyrimidine nucleosides available for DNA synthesis, whereas dihydropyrimidine dehydrogenase (DPD) catabolises the degradation of pyrimidine bases, thereby reducing levels of uracil and thymine available for DNA synthesis. In addition, tissue levels of TP or DPD have been associated with the clinical efficacy of pyrimidine anti-metabolites commonly used in the treatment of colorectal cancer. There is little information, however, on the relative expression or degree of co-ordinated regulation of either protein in primary or metastatic colorectal cancer. DPD and TP protein levels were measured in 15 primary colorectal carcinomas, 10 colorectal liver metastases and 25 adjacent uninvolved tissues. DPD was reduced in 67% (10/15) of colorectal tumours (mean tumour/normal = 0.52) and in all liver metastases (mean tumour/normal = 0.41) compared with the corresponding normal tissue. In contrast, TP was increased in 80% (12/15) of colorectal tumours (mean tumour/normal = 18.91) and in all metastases (mean tumour/normal = 3.70). TP and DPD protein expression were highly variable in uninvolved and tumour tissues. The ratio of TP:DPD was higher in 87% of colorectal tumours and in all liver metastases compared with the adjacent uninvolved tissues. This suggests the presence of co-ordinated regulation of these pyrimidine metabolic enzymes and offers a strategy for optimising the use of pyrimidine-based chemotherapy.

Raltitrexed/5-fluorouracil-based combination chemotherapy regimens in anticancer therapy

Preclinical evidence of a schedule-dependent synergism between raltitrexed and 5-fluorouracil (5-FU) has prompted clinical studies of this combination. We review the main preclinical and clinical results of raltitrexed/5-FU-based combination chemotherapy regimens in anticancer therapy. Promising results include: response rates of 25 and 23% with combinations of raltitrexed/5-FU/levofolinic acid (LFA) as first-line treatment and oxaliplatin/raltitrexed/5-FU/LFA as second-line treatment of metastatic colorectal cancer, respectively; and a 67% response rate in a phase I study of cisplatin/raltitrexed/5-FU/LFA as first-line treatment of advanced head and neck cancer, including a 100% response rate at the recommended dose. These combinations were well tolerated, with neutropenia as the main dose-limiting toxicity, allowing the drugs to be combined at the doses used in monotherapy. These results suggest a role for raltitrexed within combination regimens in colorectal cancer therapy, as well as other tumors such as head and neck cancer. A further potential application of raltitrexed in combination therapies is within multidisciplinary chemo-radiotherapy strategies, mainly in rectal cancer. Phase II studies are planned/ongoing to investigate these interesting possibilities.

Changes in thymidylate synthase mRNA in blood leukocytes from patients with colorectal cancer after bolus administration of 5-fluorouracil

5-fluorouracil (5-FU) is considered the standard antineoplastic drug of choice for metastatic colorectal cancer. It has been suggested that 5-FU administered as bolus infusion is cytotoxic mainly through an RNA damaging effect. We investigated the effect of i.v. bolus 5-FU 500-600 mg/m2 on the 5-FU target enzyme, thymidylate synthase (TS) mRNA, in blood leukocytes before and after courses 1 and 3 in 21 patients with colorectal cancer. TS mRNA expression was quantified using an RT-PCR assay with an internal RNA standard. Median TS mRNA expression decreased significantly 30 min after course no. 1 (p = 0.004), and both 15 min and 30 min after course 3 (p = 0.01). After course 1, the median TS mRNA expression decreased by 31% and after course 3 by 24%. Pharmacokinetic parameters were similar for individual patients during the two courses but did not correlate with the degree of TS mRNA inhibition. The present results indicate that TS mRNA in blood leukocytes may be an early indicator of an RNA damaging effect after i.v. bolus infusion of 5-FU.

Cloning and initial characterization of the human DPYD gene promoter

Dihydropyrimidine dehydrogenase (DPD) is the rate-limiting enzyme in the degradation of pyrimidine bases and pyrimidine-based antimetabolites. Reduced DPD activity is associated with toxicity to 5-fluorouracil (5FU) therapy in cancer patients and with neurological abnormalities in paediatric patients. Although variant DPYD alleles have been identified in DPD-deficient patients, they do not adequately explain polymorphic DPD activity or associated clinical phenotypes in vivo. DPD may be transcriptionally regulated as mRNA levels correlate with activity and are differentially regulated in human tissues. A 1.85 kb 5' flanking region of the human DPYD gene was cloned and has transcriptional activity in cultured cells. Analysis of this 5' flanking region in rhesus and cynomolgus monkeys demonstrated conservation (>96%) between humans and primates. Putative binding sites for ubiquitous and cell-specific factors were identified. A polymorphism that disrupts a putative gamma-interferon response element was identified in a cancer patient with reduced DPD activity and severe 5FU toxicity. Further insight into regulation of DPD expression may identify new avenues for the treatment of clinical problems associated with DPD deficiency.

Known variant DPYD alleles do not explain DPD deficiency in cancer patients

Dihydropyrimidine dehydrogenase (DPD) degrades over 80% of administered 5-fluorouracil (5FU), thereby regulating the efficacy of this commonly used anticancer agent. DPD activity is highly variable (8-21-fold) and individuals with reduced activity have a high risk of 5FU toxicity. DPYD encodes DPD protein and 13 different mutations have been reported in DPD-deficient subjects. However, the contribution of these variant genotypes to polymorphic DPD activity in vivo is not clear. The previously described DPYD mutations are contained in 10 exons. These 10 exons were sequenced in a cohort of cancer patients with reduced (n = 23) or normal (n = 14) DPD activity to determine the contribution of each variant allele to low DPD activity in vivo. Eight of the 13 previously defined DPYD mutations (G62A, delta TCAT295-298, C703T, G1003T, G1156T, delta C1897, G2657A, and G2983T) were not detected. A previously defined exon 13 mutation (G1601A) was detected in three individuals with reduced DPD activity. An exon 14 splice donor site mutation (intron14 G1A) was detected in a normal DPD activity individual. It was demonstrated that T85C, A1627G and G2194A are common polymorphisms. A novel exonic mutation (T1679G) was detected in a patient with reduced DPD activity and 5FU toxicity. In addition, three novel common polymorphisms were detected in introns 10 and 13. Only three patients did not have any mutations and 30 had multiple DPYD mutations in the regions examined. However, only 17% (4/23) of the patients with a low DPD phenotype have a molecular basis for reduced activity. Although novel DPYD variants have been identified in this study, the 17 DPYD mutations now described do not entirely explain polymorphic DPD activity and toxic response to 5FU. These data emphasize the complex nature of the molecular mechanisms controlling polymorphic DPD activity in vivo.

Can dihydropyrimidine dehydrogenase impact 5-fluorouracil-based treatment?

More than 80% of an administered 5-fluorouracil (5-FU) dose is degraded by dihydropyrimidine dehydrogenase (DPD), making it an important regulator of this commonly used anticancer agent. The high variation in population DPD activity, association with 5-FU activity, and development of DPD inhibitors have all contributed to the current focus on this enzyme. This review details the impact of DPD on 5-FU pharmacology, catalogues recent information on DPD mutations, evaluates the case for tumour DPD as a source of 5-FU resistance and introduces the clinical case for DPD inhibitors as a mechanism for the use of oral fluoropyrimidine therapies.