The plasma concentration-time profile, distribution and excretion after a single intravenous administration of ¹⁴C-ONO-5046·Na were investigated in rats.
1. After intravenous bolus administration of ¹⁴C-ONO-5046·Na (0.1 ?? 100 mg/kg) to male rats, the elimination half life of radioactivity ranged from 163.61 to 192.72 min. AUC_0-∞ increased in dose-dependent manner up to 1 mg/kg. Sex-related difference in pharmacokinetic parameter was not clearly observed at dose range of 0.1 ?? 100 mg/kg.
2. During 3 hr intravenous infusion of ¹⁴C-ONO-5046·Na at the doses of 0.1, land 10 mg/kg/hr to male rats, the plasma levels of radioactivity reached the steady-state levels within 1.5 hr. Plasma levels of radioactivity in the steady-state increased in dose-dependent manner, and the elimination half life ranged from 232.29 to 631.63 min.
3. At 30 min after intravenous bolus administration at the dose of 1 mg/kg to male and female rats, the radioactivity was distributed in whole body. Kidney, intestine and its contents, were the tissues highly concentrating radioactivity. Then radioactivity decreased to the level below detection limit in most tissues at 24 hr, and no marked residue in any tissue was found.
4. Within 24 hr after intravenous bolus ad ministration of ¹⁴C-ONO-5046·Na at the dose of 1 mg/kg to male rats, 24.0% and 73.1% of administered radioactivity were excreted into urine and feces, respectively. Total excretion rates into urine and feces within 72 hr was 99.4%. Within 24 hr after intravenous administration of ¹⁴C-ONO-5046·Na in female rats, the excretion rates into urine and feces were 90.2% and 8.2%, respectively. Sex-related difference was observed.
5. Within 2 hr after intravenous bolu s administration of ¹⁴C-ONO-5046·Na at the dose of 1 mg/kg, 33.0% and 14.0% of administered radioactivity were excreted into bile in male and female, respectively. Sex-related difference was observed. Cumulative excretion rates until 48 hr after administration were 35.9% and 15.4%, respectively. Almost all of radioactivity in bile was excreted until 2 hr after administration.
6. Re-absorption rate obtained from urinary and biliary excretion rate of recipient rats after administration to duodenum of the bile, which excreted after intravenous bolus administration of ¹⁴C-ONO-5046·Na at the dose of 1 mg/kg, were 38.9% in male rats, and 42.5% in female rats.

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The plasma concentration-time profile, distribution and excretion after repeated bolus intravenous administrations of ¹⁴C-ONO-5046·Na were investigated in rats. In addition, the effects of repeated administration of ONO-5046·Na on the hepatic drug metabolizing enzyme activities were also examined.
1. Pharmacokinetic parameters after repeated intravenous administration of ¹⁴C-ONO-5046·Na at the dose of 1 mg/kg/day for 7 days to male and female rats were not different from those after a single administration.
2. After repeated intravenous administrations of ¹⁴C-ONO-5046·Na at the dose of 1 mg/kg/day for 7 days to male rats, the radioactivity in almost all organs decreased rapidly with similar to patterns observed after the single administration.
3. During 7 days repeated intravenous administration, the radioactivity was excreted into urine and feces constantly. Cumulative excretion rates in urine until 72 hr after final dosing of repeated administration to male and female rats were 71.9% and 93.9%, and the cumulative excretion rates in feces were 33.4% and 14.3%, respectively.
4. No change was observed in microsomal protein content and hepatic drug metabolizing enzyme activities under repeated intravenous administration of ONO-5046·Na at the dose of 1, 10 and 30 mg/kg/day to male rats for 7 days.

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The metabolism and binding to serum protein of ONO-5046·Na in various animal species were investigated.
1. The structure of main metabolite (M-1) in the rat was confirmed by comparison with authentic sample (ONO-EI-601) using LC/MS/MS. Also the sulfate and glucuronide of M-1 were found.
2. The plasma composition of ONO-5046·Na and its metabolites was investigated after intravenous administration of ¹⁴C-ONO-5046·Na (dose: 1 mg/kg) to male and female rats. At 15 min after administration, 25.5 ?? 26.5% of plasma radioactivity consisted of ONO-5046·Na and 56.6 ?? 67.5% consisted of M-1. The plasma concentration of M-1 sulfate in male rats was about 10 times higher than that in female rats. At 2 hr after administration to male and female rats, the main metabolite in plasma was M-1.
3. The urine composition of metabolites was investigated after intravenous administration of ¹⁴C-ONO-5046·Na (dose: 1 mg/kg) to male and female rats. ONO-5046·Na was hardly detected in urine, and most of the radioactivity was presented by M-1. The excretion rate of M-1 sulfate in male rats was about 3.5 times higher than that in female rats.
4. The bile composition of metabolites was investigated after intravenous administration of ¹⁴C-ONO-5046·Na (dose: 1 mg/kg) to male and female rats. The rate of excretion of ONO-5046·Na in bile was below 0.1% of the dose. No sex-related difference was observed in the excretion rate of M-1 glucuronide and M-1, and the rate of M-1 sulfate in male rats was about 3.5 times higher than that in female rats.
5. ONO-5046·Na was stable in rat, dog and human plasma and hydrolyzed in a short time by liver 9000×g supernatant of rat and dog.
6. The serum protein binding of ¹⁴C-ONO-5046·Na (10 μg/ml) in rat, dog, hamster and human were 99.6, 96.7, 99.6 and 99.6%, respectively. In all species, serum protein binding decreased when the concentration of ONO-5046·Na was more than 60 μg/ml.
7. At 5 and 30 min after intravenou s bolus administration of ¹⁴C-ONO-5046·Na (dose: 1 mg/kg) to male rats, serum protein binding were 99.79 and 99.07%, respectively.

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Feto-placental transfer and excretion into milk were investigated in pregnant and lactating female rats after a single intravenous bolus administration of ¹⁴C-ONO-5046·Na.
1. At 30 min after intravenous administration of ¹⁴C-ONO-5046·Na at the dose of 1 mg/kg to pregnant rats on 17 days, the radioactivity in the fetus was 0.004 times of that in plasma, then declined to the level below detection limit at 4 hr after administration.
2. The radioactivity was dete cted in the milk after intravenous administration of ¹⁴C-ONO-5046·Na at the dose of 1 mg/kg to lactating rats. Maximal level of radioactivity in the milk was 349.95 ng eq./ml, lower than plasma level of radioactivity.

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The absorption, distribution, metabolism and excretion of ebselen were investigated by single oral administration of radio-labelled ¹⁴C-ebselen to fasted male rats at a dose of 50 mg/kg.
1. The radioactivity in plasma reached the C_max of 14.78 μg equiv. to ebselen/ml at 1 hr after administration, eliminated with an apparent half-life (t_1/2) of 2.1 hr (1-3 hr), reached the second peak at 4 hr, eliminated with t_1/2 of 6.6 hr (4-8 hr), reached the third peak at 12 hr, and then eliminated.
2. The radioactivity was distributed to tissues, reaching maximum leve ls by 2 hr after administration in most part of tissues. Relatively higher levels of radioactivity were observed in fat, brown fat, adrenal gland, skin, liver, Harderian gland and kidney. The levels of radioactivity in most part of tissues were comparable with or higher than that in plasma. At 96 hr after administration, the levels of radioactivity in all the tissues were reduced to 0.1% or less of their maximum levels, showing little retention of radioactivity in tissues. The binding ratio of radioactivity to blood cells was 4.5-28.4% from 0.5 to 12 hr after administration, and then increased with time and almost all radioactivity in blood was found in blood cells at 72 hr after administration. The binding ratio of radioactivity to plasma proteins was high, being 92-97% from 1 to 24 hr after administration. After charcoal treatment, 14% of the initial radioactivity remained in the plasma sample at 1 hr after administration. The binding ratio of radioactivity to plasma proteins was 99% or more when 0.2-20 μg/ml of ¹⁴C-ebselen was added to blank plasma samples. After charcoal treatment, 71% of the initial radioactivity remained in the plasma sample after addition of 18 μg/ml of ¹⁴C-ebselen.
3. Unchanged ebselen is not found in urine, plasma or bile. A selenosulfid e (Se-S) complex formed from ebselen with plasma thiol proteins, S-[2-(phenylcarbamoyl)phenylseleno] protein (Se-S complex, “protein” represents mainly albumin in plasma) was found in plasma. The Se-S complex concentration was determined as the radioactivity which was released from plasma proteins by dithiothreitol reduction after single oral administration of ¹⁴C-ebselen to male rats. The Se-S complex concentration in plasma reached the C_max of 3.39 μg eq. to ebselen/ml at 1 hr after administration and eliminated with an apparent half-life of 7 hr. The complex could be reduced, forming a selenol intermediate. The Se atom in the selenol is proposed to be methylated or glucuronidated, forming M-7 and M-1, respectively, and M-7 is proposed to be further oxidized, forming M-4. M-7, M-4 and polar metabolites including M-1 were found in plasma after single oral administration of ¹⁴C-ebselen to male rats.
4. The radioactivity was excreted almost completely within 48 hr after administration. Within 96 hr after administration, 58.9% of radioactivity was excreted in urine and 40.1% of that in feces.

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The absorption, distribution and excretion of ebselen were investigated after repeated oral administration of ¹⁴C-ebselen to male rats at a daily dose of 50 mg/kg for a maximum of 21 days.
1. The blood levels of radioactivity at 24 hr after dosing reached a steady state by 17th do sing, indicating 4 times higher level than that at the first dosing. After 21st dosing, the blood level of radioactivity reached the C_max of 8.04 μg equiv. to ebselen/ml at 2 hr after dosing, eliminated with a half life (t_1/2) of 2.37 hr (2-4 hr), reached the second peak at 8 hr and then eliminated with t_1/2 of 8.64 day (24-168 hr). The Cmax after 21st dosing was 1.6 times higher, and the elimination rate from 24 hr after dosing was slower, than those parameters in single dosing.
2. After 21st dosing, the level of radioactivity in the limb joint was 7 times higher than that in single dosing, the levels in the liver, testis and lung were 3-4 times higher, and those in the other tissues were 2 times or less. After final dosing, the levels of radioactivity in thyroid gland and blood cells at 576 hr after dosing were still 41% and 24% of their respective maximum levels, showing relatively slower elimination rates than those observed in the other tissues.
3. The cumulative excreti on of radioactivity in urine and feces did not change with the number of dosing after 4th dosing, ranging from 50.2 to 54.7% and from 45.4 to 48.3%, respectively, up to 24 hr after every daily dosing.

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In order to clarify whether ebselen, 2-phenyl-1, 2-benzisoselenazol-3(2H)-one is metabolized to liberate its selenium atom as an inorganic compound(s) or not in vivo, blood level of radioactivity and excretion of radioactivity in urine and feces were determined, and whole body autoradiograms were prepared after oral administration of ⁷⁵Se-ebselen (50 mg/kg) or intravenous injection of Na₂⁷⁵SeO₃, an inorganic selenium compound, as a control (1 mg/kg) to male rats. Following results were obtained:
1. For ⁷⁵Se-ebselen dosing group, the mean blood levels of radioactivity reached the C_max of 29.17 nmol eq. to ebselen/ml (8.00 μg eq./ml) at 1 hr and declined with a half-life, t_1/2 of 7.6 hr from 2 to 24 hr after dosing. For Na₂⁷⁵SeO₃ dosing group, the blood level of radioactivity was 57.75 nmol eq. to Na₂⁷⁵SeO₃/ml (9.99 μgeq./ml) at the first sampling time and thereafter declined slowly with a half-life, t_1/2 of 190 hr from 24 to 168 hr after dosing.
2. For ⁷⁵Se-ebselen dosing group, the highest levels of radioactivity were observed in the gastric and intestinal contents, followed by fat, brown fat and liver, showing higher radioactivity than that in blood. The overall distribution of radioactivity decreased with time and the radioactivity was not detected at 168 hr after dosing. For Na₂⁷⁵SeO₃ dosing group, high levels of radioactivity remained in liver, kidney and blood even at 168 hr after dosing.
3. For ⁷⁵Se-ebselen dosing group, within 168 hr after dosing, 53.8% of the dosed radioactivity was excreted in urine, and 45.8% of that in feces. The residual radioactivity in the carcass was not detected. For Na₂⁷⁵SeO₃ dosing group, within 168 hr after dosing, 44.8% of the dosed radioactivity was excreted in urine, and 8.0% of that in feces. The radioactivity remained in the carcass, being 41.1% of the dose. From the results above, the extent of inorganic selenium release from ebselen was estimated to be 0.0% of the dose.

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S-1, a new oral anti-cancer drug, is composed of tegafur (FT), gimestat (CDHP) and potassium otastat (Oxo) in a molar ratio of 1 : 0.4 : 1. FT which is masked compound of 5-fluorouracil (5-FU) plays a role as an effector compound. Both CDHP and Oxo which do not have antitumor activity themselves play roles as modulators. In this paper, the metabolism of S-1 (the identification of metabolites, urinary excretion rate of the unchanged S-1 components and their metabolites, and in vitro metabolism) was investigated in rats.
1. Main metabolites: FT was already examined in detail in previous reports. Any other special metabolites of FT were not formed after oral administration of S-1. Main metabolites of CDHP was sulfate, but mainly excreted as unchanged form. Oxo was metabolized mainly to cyanuric acid (CA).
2. Concentrations in plasma and tissues: Proportions of the CDHP, Oxo and their metabolites in the tissues as well as in the tumor after administration of S-1 to tumor-bearing rats were investigated. CDHP was found as the unchanged form both in the tissues and the digestive tract contents, and the conjugated metabolite (sulfate) was not detected. Oxo was assumed to be decomposed in the stomach, however found to be stable in the digestive tract of rats. A possibility of the intestinal bacterial flora to be involved in the metabolism of Oxo in the digestive tract was indicated.
3. Urinary and fecal excretion: After administration of [¹⁴C-FT]-S-1 to rats, in urine (the main route of excretion), DH-FT, 3′-OH-FT, 4′-OH-FT, 5-FU, FUR, FUdR, FUPA, F-β-Alanine and F-Nucleotide were detected and ratio of radioactivity of these metabolites to total radioactivity was almost 100%, showing no other new metabolites except for known metabolites. After administration of [¹⁴C-CDHP]-S-1 to rats, the proportions of CDHP and the sulfate of CDHP in the urine collected for a period up to 24 hr post-dose were 37.52 and 4.56% of the dose, respectively. Those values in the urine and feces collected for a period up to 24 hr post-dose were 50.97 and 34.11%, respectively. After administration of [¹⁴C-Oxo]-S-1 to rats, the proportions of Oxo and CA in the urine collected for a period up to 24 hr post-dose were 3.11 and 9.86% of the dose, respectively. Those values in the urine and feces collected for a period up to 24 hr post-dose were 31.35 and 51.31%, respectively.
4. In vitro metabolism: It was demonstrated in the present study that the liver is mainly involved in for the metabolism of FT, and participation of other tissues is not considerable. CDHP was not metabolized by any organ investigated, nor was formed sulfo-conjugate. CDHP was quite stable in plasma as well. Oxo was metabolized quickly to CA by homogenates of tumor and liver tissues and was stable in plasma and homogenate of small intestine. The homogenate of caecum contents (the intestinal bacterial flora), also metabolized Oxo to CA.

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1. S-1, a new oral anti-tumor drug, is composed of 5-fluoro-1-(tetrahydro-2-furanyl)-2, 4(1H, 3H)-pyrimidinedione (Tegafur, FT), 5-chloro-2, 4-dihydroxypyridine (Gimestat, CDHP) and potassium 1, 2, 3, 4-tetrahydro-2, 4-dioxo-1, 3, 5-triazine-6-carboxylate(potassium otastat, Oxo) at a molar ratio of 1 : 0.4 : 1. FT which is masked compound of 5-Fluorouracil (5-FU) plays a role as an effector compound. Both CDHP and Oxo which do not have antitumor activity themselves play roles as modulators.
After administration of S-1 or FT to tumor bearing rats, the C_max and AUC of 5-FU were 20.8 pmol/ml and 207.6 pmol·hr/ml, in FT group and 1, 192.0 pmol/ml and 5, 203.0 pmol·hr/ml, in S-1 group. Thus, the S-1 group showed higher plasma 5-FU levels by 57 times in C_max and by 25 times in AUC than those in the FT group. Similar to the plasma concentration, the concentration of 5-FU in tumor in the S-1 group was also higher than that in the FT group by 23 times in C_max and by 16 times in AUC.
2. After administration of S-1 to tumor bearing rats, the plasma concentratio n of CDHP, the reversible competitive inhibitor of dihydropyrimidine dehydrogenase (EC1.3.1.2), showed a C_max value of 2, 054.8 pmol/ml at 30 min post-dose. The concentration of Oxo, the inhibitor of orotate phosphoribosyltransferase (EC2.4.2.10), in small intestine showed a C_max value of 36, 156.5 pmol/g at 30 min post-dose, and showed still high concentration of 2, 813.6 pmol/g even at 3 hr post-dose.
3. AUC of 5-FU in plasma and various tissues after a dministration of S-1 were found to be greater than those AUC after administration of UFT (combination of FT and uracil). AUC of fluoroureidopropionic acid (FUPA) and fluoro-β-alanine (FBAL) in the S-1 group were smaller than those in the UFT group.

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S-1, a new oral anti-cancer drug, is composed of 5-fluoro-1-(tetrahydro-2-furanyl)-2, 4(1H, 3H)-pyrimidinedione (tegafur: FT), 5-chloro-2, 4-dihydroxypyridine (gimestat: CDHP) and potassium 1, 2, 3, 4-tetrahydro-2, 4-dioxo-1, 3, 5-triazine-6-carboxylate (potassium otastat: Oxo) in a molar ratio of 1 : 0.4 : 1. FT which is masked compound of 5-Fluorouracil (5-FU) plays a role as an effector compound. Both CDHP and Oxo which do not have antitumor activity themselves play roles as modulators. In this paper, species differences and dose-proportionality of S-1 components were investigated after a single administration of S-1 to mice, rats and dogs.
1. The pharmacokinetic parameter of FT, 5-FU, CDHP and Oxo in various animal species were obtained from mice, rats and dogs treated with S-1 (5 mg/kg as FT). C_max of FT was not different among any animal species. However, AUC of FT in dogs, rats and mice were 103, 155 ng·hr/ml, 53, 600 ng·hr/ml and 4, 180 ng·hr/ml, respectively. These species differences were also shown in the case of half-lives of FT. The highest C_max of 5-FU among all species was in mice (1, 081 ng·hr/ml), and the lowest was in rats (282 ng·hr/ml). But half-life of 5-FU was smaller in mice than these in rats and dogs. Cmax of CDHP in mice, 1, 815 ng·hr/ml, was the highest in other species, however AUC of CDHP were not qualitatively different among mice, rats and dogs. C_max and AUC of Oxo were the highest in mice, and the lowest in rats.
2. The bioavailabilities of FT both in rats and dogs were approximately 100%. However, that of CDHP in rats and dogs were 36.8% and 27.0%, that of Oxo was 3.0% and 9.9%, respectively.
3. After oral administration (2, 5, 10 mg/kg as FT) of S-1 to dogs, AUC a nd C_max of the unchanged drug increased linearly, depending on dose escalation. But both C_max and AUC of 5-FU were more increased than dose escalation. We considered that this phenomenon was due to the higher inhibition of metabolism of 5-FU by CDHP at dose escalation.

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