High-throughput method to analyze tegafur and 5-fluorouracil in human tears and plasma using hydrophilic interaction liquid chromatography/tandem mass spectrometry.

RATIONALE: We developed a new high-throughput method to analyze tegafur (FT) and 5-fluorouracil (5-FU) in tear and plasma samples using hydrophilic interaction liquid chromatography (HILIC)/tandem mass spectrometry (MS/MS). METHODS: The tear samples (10 µL) spiked with FT, 5-FU, and 5-chlorouracil (internal standard) were diluted using 40 µL of 2 M ammonium acetate and 250 µL of acetonitrile with 2% formic acid; 20 µL of plasma spiked with the two drugs and internal standard was diluted with 80 µL of 2 M ammonium acetate and 500 µL of acetonitrile with 2% formic acid. After centrifugation, the clear supernatant extract (15 µL) was directly injected into the HILIC/MS/MS instrument, and each drug was separated on a Unison UK-Amino column (50 mm × 3 mm i.d., 3 µm particle size) with a linear gradient elution system composed of 10 mM ammonium acetate (pH 6.8) and acetonitrile at a flow rate of 0.7 mL/min. We performed quantification by multiple reaction monitoring (MRM) with negative-ion atmospheric-pressure chemical ionization. RESULTS: Distinct peaks were observed for the drugs on each MRM channel within 2 min. The regression equations showed good linearity within the range 0.04-4.0 µg/mL for the tear and plasma samples with detection limits at 0.02-0.04 µg/mL. Recoveries for target analytes (FT and 5-FU) for the tear and plasma samples were in the 94-128% and 94-104% ranges, respectively. The intra- and inter-day coefficients of variation for the two drugs were lower than 10.8%. The accuracies of quantitation were 97-115% for both samples. CONCLUSIONS: We established a high-throughput, reproducible, and practical procedure for analyzing FT and 5-FU in human tear and plasma samples using HILIC/MS/MS analysis with an aminopropyl-bonded mixed-mode separation column. This method can be applied to the high-throughput routines used in clinical analyses.

A high throughput immunoassay for the therapeutic drug monitoring of tegafur.

Cancer is a group of diseases in which abnormal cells grow and divide without control, with the potential to invade other parts of the body. Chemotherapy is a type of treatment that uses chemical agents to treat cancer. These drugs are toxic and produce undesirable adverse drug reactions due to their narrow therapeutic window and highly variable pharmacokinetics, thus, they need to be monitored to establish personalized treatment to achieve maximal efficiency and reduce drug toxicity. Nowadays, therapeutic drug monitoring (TDM) is not routinely used for chemotherapy agents, however, TDM has the potential to improve the clinical benefit of chemotherapy drugs. Tegafur, a prodrug of 5-fluorouracil (5FU), is one of the main anti-cancer drugs used worldwide. Herein, a reproducible and sensitive indirect competitive ELISA has been developed and validated in plasma samples. The assay reports an IC50 of 35.6 nM, reaching a limit of detection of 2.7 nM. It is highly reproducible and does not show cross-reactivity with any related compound. In summary, this assay provides a sensitive, accurate and high throughput analytical method for tegafur quantification in plasma, which fits TDM requirements.

[Pharmacokinetics of S-1 capsule in patients with advanced gastric cancer].

The study is to investigate the pharmacokinetics of S-1 capsule (tegafur, gimeracil and potassium oxonate capsule) in patients with advanced gastric cancer after single and multiple oral administration. Twelve patients with advanced gastric cancer were recruited to the study. The dose of S-1 for each patient was determined according to his/her body surface area (BSA). The dose for single administration was 60 mg every subject. The dose for multiple administration for one subject was as follows: 100 mg x d(-1) or 120 mg x d(-1), 28-days consecutive oral administration. The pharmacokinetic parameters of tegafur, 5-fluorouracil, gimeracil, potassium oxonate and uracil after single oral administration were as follows: (2,207 +/- 545), (220.0 +/- 68.2), (374.9 +/- 103.0), (110.5 +/- 100.8) and (831.1 +/- 199.9) ng x mL(-1) for Cmax; (11.8 +/- 3.8), (4.4 +/- 3.3), (7.8 +/- 5.1), (3.1 +/- 0.9) and (8.8 +/- 4.1) h for t1/2, respectively. After six days oral administration, the average steady state plasma concentrations (Cav) of tegafur, 5-fluorouracil, gimeracil, potassium oxonate and uracil were (2,425 +/- 1,172), (73.88 +/- 18.88), (162.6 +/- 70.8), (36.89 +/- 29.35) and (435.3 +/- 141.0) ng x mL(-1), respectively, and the degree of fluctuation (DF) were (1.0 +/- 0.2), (2.5 +/- 0.4), (3.1 +/- 0.8), (2.4 +/- 0.8) and (1.5 +/- 0.3), respectively. The cumulative urine excretion percentage of tegafur, 5-fluorouracil, gimeracil and potassium oxonate in urine within 48 h were (4.2 +/- 2.8) %, (4.7 +/- 1.6) %, (18.5 +/- 6.0) % and (1.7 +/- 1.2) %, repectively, after single oral administration of S-1. The results exhibited that tegafur had some drug accumulation observed, and gimeracil, potassium oxonate, 5-fluorouracil and uracil had no drug accumulation observed.

Simultaneous quantification method for 5-FU, uracil, and tegafur using UPLC-MS/MS and clinical application in monitoring UFT/LV combination therapy after hepatectomy.

Combination therapy of tegafur/uracil (UFT) and leucovorin (LV) is widely used to treat colorectal cancers. Although this therapy has a significant therapeutic effect, severe adverse effects occur frequently. Therapeutic drug monitoring (TDM) may help to prevent adverse effects. A useful assay that can quantitate plasma levels of 5-FU, uracil, and tegafur simultaneously for TDM has been desired, but such a method is not currently available. In this study, we aimed to develop a sensitive method for simultaneous quantification of 5-FU, uracil, and tegafur in human plasma using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS). After preparing plasma samples by protein precipitation and liquid extraction, 5-FU, uracil, and tegafur were analyzed by UPLC-MS/MS in negative electrospray ionization mode. Validation was performed according to US Food and Drugs Administration guidance. The calibration curves were linear over concentration ranges of 2-500 ng/mL for 5-FU, 20-5000 ng/mL for uracil, and 200-50,000 ng/mL for tegafur. The corresponding average recovery rates were 79.9, 80.9, and 87.8%. The method provides accuracy within 11.6% and precision below 13.3% for all three analytes. Matrix effects of 5-FU, uracil, and tegafur were higher than 43.5, 84.9, and 100.2%, respectively. This assay was successfully applied to assess the time courses of plasma 5-FU, uracil, and tegafur concentrations in two patients with colorectal liver metastasis who received UFT/LV therapy after hepatectomy. In conclusion, we succeeded to develop a sensitive and robust UPLC-MS/MS method for simultaneous quantification of 5-FU, uracil, and tegafur in human plasma. This method is potentially useful for TDM in patients receiving UFT/LV combination therapy.

Two dosages of oral fluoropyrimidine S-1 of 35 and 40 mg/m2 bid: comparison of the pharmacokinetic profiles in Korean patients with advanced gastric cancer.

OBJECTIVE: In this study, we compared the pharmacokinetic profiles of 5-fluorouracil (5-FU), tegafur, 5-chloro-2,4-dihydroxypyridine (CDHP) and potassium oxonate (Oxo) after administration of S-1 at 35 or 40 mg/m(2) bid for 28 consecutive days, in Cycles 1 and 3, in patients with advanced gastric cancer. METHODS: Three patients were enrolled for each dosage. S-1 dosage was assigned based on body surface area (BSA), which is different from the Japanese dosing system. The median daily dose per BSA was 76 mg/m(2), ranging from 70 to 88 mg/m(2). RESULTS: Plasma levels of 5-FU, tegafur, CDHP and Oxo at 4 h post-dose reached steady-state on day 8. The estimated steady-state level was dependent on S-1 dosage. There were no intercyclic differences of pre-dose and 4 h post-dose levels between Cycles 1 and 3, implying no cumulative effect of S-1 was shown probably due to 2-week drug-resting period. Pharmacokinetic profiles on day 28 were similar to previous Japanese report. C(max) and AUC(0-48 h) values of each S-1 component increased depending on S-1 dosage. Pharmacokinetic parameters were not correlated with tumor response or toxicity. CONCLUSIONS: We suggest that these pharmacokinetic profiles of Asian population could provide a basis for schedule optimization and for additional studies on interaction with other antitumor drugs.

Pharmacokinetic and bioequivalence study between two formulations of S-1 in Korean gastric cancer patients.

PURPOSE: S-1 is an oral fluoropyrimidine anticancer drug consisting of the 5-fluorouracil prodrug tegafur combined with gimeracil and oteracil. The purpose of this study was to evaluate the pharmacokinetic (PK), bioequivalence, and safety of a newly developed generic formulation of S-1 compared with the branded reference formulation, in Korean gastric cancer patients. METHODS: This was a single-center, randomized, open-label, single-dose, two-treatment, two-way crossover study. Eligible subjects were randomly assigned in a 1:1 ratio to receive the test formulation or reference formulation, followed by a one-week washout period and administration of the alternate formulation. Serial blood samples were collected at 0 hrs (predose), 0.25, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 24, 36, and 48 hrs after dosing in each period. The plasma concentrations of tegafur, 5-FU, gimeracil, and oteracil were analyzed using a validated liquid chromatography-tandem mass spectrometry method. The PK parameters were calculated using a non-compartmental method. RESULTS: In total, 29 subjects completed the study. All of the 90% confidence intervals (CIs) of the geometric mean ratios (GMRs) fell within the predetermined acceptance range. No serious adverse events were reported during the study. CONCLUSION: The new S-1 formulation met the Korean regulatory requirement for bioequivalence. Both S-1 formulations were well tolerated in all subjects.Clinical trial registry: https://cris.nih.go.kr CRIS KCT0003855.

Circadian variations in the pharmacokinetics of the oral anticancer agent tegafur-uracil (UFT) and its metabolites in rats.

Uracil-tegafur (UFT) is an oral anticancer drug containing uracil and 5­fluorouracil prodrug tegafur and is widely used for adjuvant chemotherapy of colorectal cancer. Although clinical data show circadian variations in plasma 5­fluorouracil concentrations during its long-term infusion, and feasibility studies of chronomodulated administration have been previously reported, the circadian pattern in plasma 5­fluorouracil concentration after UFT administrations remains unclear. The aim of this study was to identify factors causing circadian variations in UFT pharmacokinetics and estimate circadian patterns of plasma 5­fluorouracil concentration corresponding to UFT dosing time in rats. Rats were orally administered UFT (15 mg/kg as tegafur) at three different times of the day: 07:00 (23 h after light onset, HALO), 13:00 (5 HALO), or 19:00 (11 HALO), and then plasma concentrations of tegafur, 5­fluorouracil, and uracil were measured after UFT administration. We found that the area under the plasma concentration-time curves (AUC0-∞) of 5­fluorouracil depended on the UFT dosing time of day with a 2.4-fold difference between the peak (at 19:00: 13.7 ±â€¯1.4 µmol·h/L) and trough (at 13:00: 5.6 ±â€¯1.3 µmol·h/L). The simulated population mean clearance of 5­fluorouracil followed a 24-h cosine circadian curve, with the highest value in the early light phase being 2.2-fold higher than the lowest value in the early dark phase, which was an inverse circadian pattern compared to the plasma 5­fluorouracil concentration. The plasma tegafur levels suggested that circadian variation in tegafur absorption and conversion to 5­fluorouracil are factors causing variations in plasma 5­fluorouracil levels following UFT administration. In conclusion, the circadian pattern of 5­fluorouracil clearance and circadian variations in tegafur pharmacokinetics are important determinants of plasma 5­fluorouracil concentrations following UFT administration. This knowledge could help in developing a chronomodulated administration strategy of UFT for improving clinical outcomes.

Development of a pharmacokinetic model to optimize the dosage regimen of TS-1, a combination preparation of tegafur, gimeracil and oteracil potassium.

BACKGROUND: TS-1 is a combination preparation of tegafur, a prodrug of 5-fluorouracil (5-FU), with gimeracil, a potent inhibitor of dihydropyrimidine dehydrogenase (DPD), which mediates the inactivation of 5-FU. UFT is a combination preparation of tegafur with uracil, which also inhibits DPD, though less potently; UFT has a higher content of tegafur than that in TS-1. We aimed to develop a pharmacokinetic model to describe the kinetics of tegafur and 5-FU after the administration of TS-1 and UFT. METHODS: We developed a model incorporating the inhibition of DPD by gimeracil and uracil, and fitted the model to the observed kinetics of tegafur and 5-FU after the administration of TS-1 and UFT. Then, we simulated the plasma 5-FU profiles in patients with renal dysfunction and those after replacement of TS-1 with UFT and compared them with the observed profiles. RESULTS: The developed model could appropriately describe the plasma concentration profiles of 5-FU and tegafur after the administration of TS-1 in patients with normal and impaired renal function. CONCLUSION: The developed model may be useful to optimize the dosage regimen of TS-1 under various clinical conditions.

[A phase I study of postoperative combination therapy with TS-1 and low dose cisplatin against stage IV gastric carcinoma].

A dose-escalation study was conducted for postoperative patients with stage IV gastric cancer to determine the recommended dose of daily intravenous cisplatin combined with a fixed dose of TS-1. TS-1 was administered orally twice daily for 2 weeks followed by a 1-week rest. The dose of TS-1 was based on the body surface area (BSA) as follows: 80 mg/day for BSA less than 1.25, 100 mg/day for BSA 1.25 to less than 1.50, and 120 mg/day for BSA 1.5 or more. Three dose levels of cisplatin (2, 4, 6 mg/m(2)) were studied, and two courses were performed. Cisplatin was infused on day 1-5 and 8-12 for 30 minutes. The National Cancer Institute common toxicity criteria (NCI-CTC Version 3) were used to evaluate the grade of toxicity. Three patients enrolled in each level. Dose escalation was performed when dose-limiting toxicities (DLT) were seen in 0/3, and 3 more cases of the same level were added when DLTs were seen 1-2/3. Maximum-tolerated dose (MTD) were determined when DLTs were seen in 3 cases. DLTs were not recorded during the administration of CDDP up to 4 mg/m(2). However, DLTs were seen 3/3 at level 3. From these results, cisplatin of 4 mg/m(2)was determined to be the recommended dose (RD) in this protocol for postoperative stage IV gastric carcinoma.

Pharmacokinetics of S-1 in patients with peritoneal dissemination of gastric cancer.

The response of gastric cancer with peritoneal dissemination to systemic chemotherapy may be negatively affected by poor drug delivery due to the blood-peritoneal barrier. However, S-1 has been reported to be effective. We examined the pharmacokinetics of S-1 in 14 patients who had gastric cancer with peritoneal dissemination. S-1 was given from the morning of the day before surgery to the morning of surgery. Concentrations of 5-fluorouracil (5-FU) and gimeracil (CDHP) were measured in the serum, ascites, disseminated peritoneal nodes, and normal peritoneum. There was a strong correlation between 5-FU and CDHP concentrations in peritoneal tissues. The concentrations of 5-FU and CDHP in the serum were similar to those in ascites. The concentration of 5-FU was significantly higher in disseminated nodes than in the normal peritoneum. After administration of S-1 to gastric cancer patients with peritoneal dissemination, 5-FU and CDHP in the serum linearly pass through the peritoneum and enter the ascites. High concentrations of 5-FU selectively penetrate disseminated peritoneal cells.

Hydroxylated metabolies of R,S-1-(tetrahydro-2-furanyl)-5-fluorouracil (Ftorafur) in rats and rabbits.

Two hydroxylated metabolies (M1 and M2) have been isolated from rabbit urine after administration of Ftorafur (FT). The structures of 3'-OH-FT and 4'-OH-FT were assigned to M1 and M2, respectively. A reverse-phase high performance liquid chromatography assay was developed for jeasuring FT, M1, M2, and 5-fluorouracil (FU) plasma levels. M1, M2, and FU were present in rabbit and rat plasma in greatly varying concentrations after FT administration. Pharmacokinetic studies suggest that FU formation proceeds via metabolic intermediate(s) and that the extent of FT activation is variable. A horse liver thymidine phosphorylase ,reparation capable of catalyzing the conversion of beta-ribo-2'-deoxy-5-fluorouracil to FU was inactive against FT and M1. However, 20% of M2 was converted to FU by this enzume, which suggests that the urinary metabolite M2 consisted of a mixture of enantiomers with 20% present in the natural beta-D configuration. The stereochemistry of M1 remains unknown. Hydroxylation of FT to beta-D-4'-OH-FT and subsequent cleavage to FU by thymidine phosphorylase represents one possible activation mechanism of FT to FU. ,owever, lack of correlation between plasma levels of M2 and FU indicates that this mode of metabolic activation may account for only part of the overall activation of FT in vivo.

Disposition and metabolism of 1-(tetrahydro-2-furanyl)-5-fluorouracil (ftorafur) in humans.

The pharmacology of high-dose 1-(tetrahydro-2-furanyl)-5-fluorouracil (FT) has been studied by radiochemical and chromatographic techniques in eight patients. Plasma disappearance of FT was exponential, with a half-life of 8.8 hr. Plasma concentrations of 5-fluorouracil (FUra) were sustained at 12.8 nmol/ml (1.7 microgram/ml) for at least 48 hr after FT administration. The concentrations of FUra derived from the administration of FT were considerably greater than were those achieved by constant infusion of FUra at the maximal tolerated dose of 1.1 g/sq m without causing unacceptable mucositis. The cumulative urinary excretion was 20% of the administered dose in 24 hr. FT underwent in vivo biotransformation to 2 hydroxytetrahydrofuranyl-5-fluorouracil derivatives in addition to anabolites and catabolites of FUra. High concentrations of FT and FUra were present in the cerebrospinal fluid, which could account for the severe central nervous system toxicity of FT at high doses. We conclude that the antitumor activity of FT is partially attributable to its slow release of FUra.

Sensitive MS/MS-liquid chromatography assay for simultaneous determination of tegafur, 5-fluorouracil and 5-fluorodihydrouracil in plasma.

Ftorafur (FT), an oral prodrug of 5-FU, is part of UFT and S1, two oral prodrugs widely used in digestive tract cancer. We set up a liquid chromatography tandem mass spectrometry (LC/MS-MS) method, chosen for its specificity of detection, for simultaneously measuring in human plasma FT, 5-FU and 5-FUH2. Separation was performed on a Hypercarb column. Linearity, precision and accuracy were validated in the concentration range studied for each compound. This simple and reliable LC/MS-MS method allows specific, sensitive and reproducible quantification of FT, 5-FU and FUH2 in human plasma and can be applied to further pharmacokinetic studies in patients treated with FT-based prodrugs.

Effect of food on the oral bioavailability of UFT and leucovorin in cancer patients.

UFT is composed of tegafur (FT), a prodrug of 5-fluorouracil (5-FU), and uracil in a fixed combination (1:4). In conjunction with leucovorin, UFT is being developed for the first-line oral treatment of metastatic colorectal cancer. The effect of food on the oral bioavailability of UFT (2 x 100 mg capsules; dose in terms of FT) and leucovorin (2 x 15 mg tablets) was evaluated in a single-dose, randomized, two-way crossover study. Patients (n = 25) were assigned to receive both drugs after an overnight fast or 5 min after completion of a high-fat meal (721 calories) with a 3-day washout period between treatments; then they were permitted to continue on oral UFT/leucovorin therapy for safety assessment. UFT (300 mg/m2/day as three divided doses) and leucovorin (90 mg/day as three divided doses) were given for 28 days. After a 7-day rest, the 28-day cycle was repeated. Pharmacokinetics (n = 22 patients) were determined for FT, 5-FU, uracil, leucovorin, and 5-methyltetrahydrofolate (an active metabolite of leucovorin). The absence of food-effect on peak plasma concentration (CMAX) and the area under the curve (AUC) was concluded if the 90% confidence interval for the ratio of the treatment means was entirely contained in 0.75-1.33. Administration of UFT with food resulted in a 34% decrease in CMAX of FT, whereas the AUC of FT remained unchanged. Food decreased the CMAX and AUC values of uracil and 5-FU by 37-76%. On the contrary, the CMAX and AUC values of leucovorin and 5-methyltetrahydrofolate were increased by 14-60% with food. Time to reach CMAX for all analytes was significantly (P < or = 0.001) delayed by food. Except for the AUCs of FT, the statistical criterion for concluding a lack of food-effect was not met. These data suggest that UFT/leucovorin should not be dosed simultaneously with food. It is recommended that food should not be consumed for 1 h before and after an oral dose of UFT and leucovorin in a manner similar to pivotal Phase III trials. The 28-day oral regimen of UFT and leucovorin was generally well tolerated in the population studied.

Pharmacokinetic study of S-1, a novel oral fluorouracil antitumor drug.

S-1 is a novel oral fluorouracil antitumor drug that combines three pharmacological agents: tegafur (FT), which is a prodrug of 5-fluorouracil (5-FU); 5-chloro-2,4-dihydroxypyridine (CDHP), which inhibits dihydropyrimidine dehydrogenase (DPD) activity; and potassium oxonate (Oxo), which reduces gastrointestinal toxicity. Phase I and early Phase II clinical trials have already been completed. On the basis of the results of these trials, 80 mg/m2/day, given daily in two divided doses after breakfast and supper, a 28-day consecutive oral regimen is recommended. In this study, we investigated the pharmacokinetics of 5-FU, intact FT, CDHP, and Oxo, after administration of S-1, at a standard dose of 80 mg/m2/day, in advanced cancer patients. Twelve patients were recruited to the study; 5 patients with gastric cancer, 4 with colorectal cancer, and 3 with breast cancer. Among them, analysis was conducted on 12 patients for single administration and on 10 patients for consecutive administration. The initial dose of S-1 for each patient was determined according to his/her body surface area (BSA) as follows: for BSA < 1.25 m2, 80 mg/body/day; for 1.25 m2 < or = BSA < 1.5 m2, 100 mg/day; and for 1.5 m2 < or = BSA, 120 mg/day. For single administration, half of the standard dose was used. For 28-day consecutive administration, the standard dose was given daily in two divided doses. The average single dose per BSA was 35.9 mg/m2 (31.7-39.7 mg/m2). Pharmacokinetic parameters of plasma 5-FU were as follows: Cmax, 128.5 +/- 41.5 ng/ml; Tmax, 3.5 +/- 1.7 h; AUC(0-14), 723.9 +/- 272.7 ng x h/ml; and T(1/2), 1.9 +/- 0.4 h. In the 28-day consecutive regimen, there were no fluctuations in pharmacokinetics nor any drug accumulation. Because the pharmacokinetics of orally administered S-1 is almost similar to that of continuous i.v. infusion of 5-FU, we concluded that S-1 may improve patients' quality of life.

[TS-1 treatment for progressive gastric cancer in a patient on chronic dialysis--assessment of dosage regimen by monitoring blood concentrations of therapeutic drugs (TDM)].

The optimum dose of TS-1 for the treatment of peritoneally disseminated gastric cancer in a patient with chronic renal failure undergoing chronic dialysis was estimated by monitoring the blood concentrations of 5-FU and gimeracil (CDHP) [therapeutic drug monitoring (TDM)] during administration of TS-1. Immediately after dialysis, 50 mg or 40 mg of TS-1, corresponding to 50% and 40% of the standard dose (100mg for this patient), respectively, was administered orally once a day every other day, and TDM was conducted. Compared with the pharmacokinetic parameters of 5-FU at the time of the initial administration of 50 mg or 40 mg of TS-1 and that of cancer patients with normal renal function, the AUC shown in the administration of 40 mg was equivalent to that observed with a single safe dose of 100 mg in patients with normal renal function. Based on this observation, the daily TS-1 dose was set at 40 mg in this patient, and TS-1 treatment was started after confirming the absence of the accumulation of 5-FU or CDHP during repeated administrations. In this treatment protocol, TS-1 was administered 11 times at a daily dose of 40 mg every other day immediately after dialysis, followed by a rest. This .administration schedule was defined as one course. Under these conditions, the patient was treated on an outpatient basis, and the treatment could be safely continued without the development of any severe adverse events, such as myelosuppression.

Postgastrectomy pharmacokinetic changes of S-1 in patients with localized advanced gastric cancer.

S-1 is an oral 5-fluorouracil agent containing tegafur, 5-chloro-2, 4-dihydroxypyridine (CDHP), and potassium oxonate. This study explored the pharmacokinetics of S-1 and pharmacokinetic changes after gastric surgery in patients with resectable gastric cancer who received pre- and postoperative S-1 plus docetaxel. Serial blood was drawn before and after gastrectomy from 37 patients for pharmacokinetic analysis. The pharmacokinetics of tegafur, 5-fluorouracil, and CDHP were analyzed by noncompartmental analysis (NCA) methods and by modeling. In modeling analysis, CHDP concentrations were incorporated in the model as a time-varying covariate that inhibits the clearance of 5-fluorouracil following an inhibitory Emax model. In NCA, the pharmacokinetics of tegafur and 5-FU before and after gastric surgery were similar, although average maximum concentrations of 5-FU were decreased with statistical significance after gastrectomy. Median Tmax of tegafur was shorter after surgery without statistical significance. In modeling analysis, tegafur was best fitted by mixed zero and first-order absorption. The only difference in the final pharmacokinetic model around gastrectomy was the presence of an absorption lag of 0.23 hours before surgery. Incorporation of CDHP concentrations significantly improved the model. Although some pharmacokinetic results showed statistically significant changes after gastrectomy, these differences seem to be too small to have any clinical implication.

A novel mutant allele of the CYP2A6 gene (CYP2A6*11 ) found in a cancer patient who showed poor metabolic phenotype towards tegafur.

In a clinical study, a newly developed anticancer drug, TS-1 capsule, which contained tegafur (FT) and 5-chloro-2,4-dihydroxypyridine, an inhibitor of dihydropyrimidine dehydrogenase, was orally administered to five gastric cancer patients (patients 1-5). The total area under the plasma FT concentration-time curve in patient 1 was four-fold higher than in other patients. Since cytochrome P450 2A6 (CYP2A6) has been reported to metabolize FT to yield 5-fluorouracil (5-FU), it was postulated that the poor metabolic phenotype of patient 1 was caused by mutations of the CYP2A6 gene. Thus, alleles for the CYP2A6 genes derived from patient 1 were completely sequenced. It was found that one allele was CYP2A6*4C, which was a whole deleted allele for the human CYP2A6 gene. The other allele was a novel mutant allele (CYP2A6*11) in which thymine at nucleotide 670 was changed to cytosine. The nucleotide change caused an amino acid change from serine at residue 224 to proline. To examine whether or not the amino acid change affected CYP2A6 activity, we expressed an intact or mutant CYP2A6 together with NADPH-P450 oxidoreductase in Escherichia coli, and compared the capacity of the wild and mutant enzymes to metabolize FT to 5-FU. The Vmax value for FT metabolism by the mutant CYP2A6 was approximately one-half of the value of the intact CYP2A6, although the Km values were nearly the same. From these results, we conclude that the poor metabolic phenotype of patient 1 was caused by the existence of the two mutant alleles, CYP2A6*4C and the new variant CYP2A6*11.

Phase I and pharmacologic study of oral ftorafur and X ray therapy in advanced gastrointestinal cancer.

We have treated 15 patients with advanced gastrointestinal carcinoma with a cyclical regimen of combined Ftorafur (N1-((2-furanidyl-))-5-Fluorouracil, a 5-FU pro-drug) and external beam radiation. The Ftorafur (FT) was administered orally in daily doses of between 1.0 and 2.5 g/m2/day in 3 divided doses in a Phase I format. The drug was given daily for 5 days along with conventional X ray treatment portals and daily radiation doses of 250 rad on each of the first 4 days of each treatment cycle. The patients were then rested for a minimum of 10 days or until all significant side effects had passed. The total number of 1,000 rad cycles and radiation dose were dictated by tolerance and by normal organ dose limitations. The most common toxicity in general, and the most common limiting toxicity was nausea and vomiting, in contrast to oral FT alone where diarrhea is more prominent. Stomatitis was seen only once and no other form of serious toxicity was encountered. Two-thirds of the patients responded in subjective terms (pain relief). There was 1 partial response to FT alone (pulmonary metastases outside the treatment field). The sole patient whose treatment field was outside the abdomen (chest portals for esophageal carcinoma) developed pneumonitis which contributed to his death. No other delayed effects were noted. Serum FT levels were related to the ingested dose and in the microgram range while serum 5-FU levels were in the nanogram range indicating slow decomposition of FT into 5-FU. The therapy was reasonably well tolerated at doses of 2.0 g/m2/day or lower with abdominal radiation. FT offers the potential for replacing intra-venous infused 5-FU as a clinical radiosensitizer.

Potentiation of the chemotherapeutic action of tegafur against solid adenocarcinoma 755 by combination with L-cystine.

The chemotherapeutic action of tegafur (FT) against adenocarcinoma 755 in mice was markedly potentiated by oral administration of L-cysteine and L-cystine without increasing its toxicity. In particular, the combination of FT at 200 mg/kg per day (maximum dose) and 1000 mg/kg per day of L-cystine markedly inhibited tumor growth. The dose ratio of L-cysteine or L-cystine to FT needs 5 by weight to potentiate the antitumor activity of FT. The antitumor activity of 5-fluorouracil (FU) was slightly, but not significantly, increased by L-cysteine. The total concentration of FT in the plasma and the tumor when it was given in combination with L-cystine was significantly increased when compared with FT alone 1 h after oral administration. The FU level in the plasma after administration of the combination of FT and L-cystine was three times higher than that after FT alone, and the FU level in the tumor after treatment with the combination of FT and L-cystine was also higher (about 20%) than that after FT alone. This significant increase in FT and FU levels in the plasma and the tumor may be related to the potentiation of the antitumor activity of FT by L-cystine.