Tetsuhiko Shirasaka

Development of a novel form of an oral 5-fluorouracil derivative (S-1) directed to the potentiation of the tumor selective cytotoxicity of 5-fluorouracil by two biochemical modulators.

We have focused our attention on the development of a novel form of a tegafur-based [FT; a prodrug of 5-fluorouracil (5-FU)] antitumor agent. We have used two biochemical and pharmacological modulators of 5-FU to improve its overall activity. To potentiate the antitumor activity of FT, 5-chloro-2,4-dihydroxypyridine (CDHP) was used as a potent reversible inhibitor of 5-FU degradation. The reduction of gastrointestinal (GI) toxicity, induced in the host by 5-FU, was modulated by potassium oxonate (Oxo), an inhibitor of orotate phosphoribosyltransferase that catalyzes the phosphorylation of 5-FU, a process believed to be responsible for the toxic effects of 5-FU. When CDHP and FT were simultaneously given orally to Yoshida sarcoma-bearing rats in various molar ratios, the antitumor effect of FT was significantly potentiated by the combination consisting of at least a 0.2 versus 1 molar ratio of CDHP to FT, respectively. This augmentation of an antitumor activity was supported by potent and prolonged inhibition of dihydrouracil dehydrogenase activity (5-FU degrading activities) in the liver of tumor-bearing rats after oral CDHP (0.2:0.8 molar ratio) and furthermore by elevation and over 12 h retention of 5-FU levels in the tumors following combined administration of FT and CDHP at a molar ratio of 1:0.4, respectively. Moreover, to reduce the severe GI injury and subsequent loss of body weight, observed in parallel with an increased antitumor efficacy, Oxo was given orally to Yoshida sarcoma-bearing rats and nude rats xenografted with H-81 human gastric carcinoma, during consecutive administration of the FT-CDHP mixture. Combined treatment with Oxo and FT (1:2 molar ratio) supplemented with 0.4 molar CDHP resulted in protection of body weight loss without affecting the high antitumor efficacy of the FT-CDHP mixture. When [2-14C]FT plus CDHP was administered with Oxo, the 14C-labeled fluoronucleotide content was objectively decreased in the GI tract of the tumor-bearing rats but not in the tumor and bone marrow, which supports our initial hypothesis. Based on these promising data, we propose a suitable formulation of a FT-based anticancer drug, called S-1, and consisting of FT, CDHP and Oxo at a 1:0.4:1 molar ratio and showing tumor-selective cytotoxicity of 5-FU.

Antitumor activity and low intestinal toxicity of S-1, a new formulation of oral tegafur, in experimental tumor models in rats

Abstract S-1, a new oral antitumor agent, is composed of 1-(2-tetrahydrofuryl)-5-fluorouracil (Tegafur, FT), 5-chloro-2,4-dihydroxypyridine (CDHP) and potassium oxonate (Oxo) in a molar ratio of 1 : 0.4 : 1. FT which is a masked compound of 5-fluorouracil (5-FU) acts as an effector, while both CDHP and Oxo which do not have antitumor activity themselves act as modulators. In this study, the antitumor activity and intestinal toxicity of S-1 were investigated using experimental tumor models in rats, and compared with those of other oral fluoropyrimidines, namely 5-FU, FT, FCD (1 M FT/0.4 M CDHP) and UFT (combination of FT and uracil). In rats bearing subcutaneous Yoshida sarcoma, S-1 inhibited tumor growth at the lowest dose (ED50 value: S-1 5, UFT 22, FT 82, FCD 5, and 5-FU 19 mg/kg per day), and induced the least host body weight suppression, leading to the highest therapeutic index (TI) (S-1 4.5, UFT 1.4, FT 1.8, FCD 2.0, and 5-FU 1.4). S-1 also showed a higher therapeutic effect than UFT against AH-130 and Sato lung carcinoma. After administration of S-1 and UFT at equitoxic doses, S-1 showed a higher and more prolonged concentration of 5-FU than UFT both in plasma (AUC0-∞: S-1 28 nmol h/ml, UFT 15 nmol⋅h/ml) and in tumor tissue (AUC0-∞: S-1 95 nmol h/g tissue, UFT 52 nmol h/g tissue), leading to a higher 5-FU level incorporated into the RNA fraction (F-RNA level) in tumor tissue (AUC0-24: S-1 7.0 nmol h/mg RNA, UFT 4.3 nmol h/mg RNA) and 5–8% higher thymidylate synthase (TS) inhibition in tumor tissue at every time-point through 24 h. Compared with other oral fluoropyrimidines after administration of the maximal tolerable dose (MTD), S-1 caused the lowest rates of intestinal toxicities, such as diarrhea and occult blood in feces. S-1 also showed a higher antitumor effect on Yoshida sarcoma implanted intracolonically than UFT at an equitoxic dose (tumor weight: S-1 64±30 mg, UFT 133±52 mg; P<0.05). These results suggest that CDHP, which is a potent inhibitor of 5-FU degradation, increases the antitumor activity of FT, and that Oxo, which is an inhibitor of 5-FU phosphorylation, locally protects the gastrointestinal tract from 5-FU-induced toxicity without decreasing the antitumor activity.

Development History and Concept of an Oral Anticancer Agent S-1 (TS-1®): Its Clinical Usefulness and Future Vistas

Dushinsky et al. left a great gift to human beings with the discovery of 5-fluorouracil (5-FU). Approximately 50 years have elapsed from that discovery to the development of S-1 (TS-1®). The concept of developing an anticancer agent that simultaneously possesses both efficacy-enhancing and adverse reaction-reducing effects could be achieved only with a three-component combination drug. S-1 is an oral anticancer agent containing two biochemical modulators for 5-FU and tegafur (FT), a metabolically activated prodrug of 5-FU. The first modulator, 5-chloro-2,4-dihydroxypyridine (CDHP), enhances the pharmacological actions of 5-FU by potently inhibiting its degradation. The second modulator, potassium oxonate (Oxo), localizing in mucosal cells of the gastrointestinal (GI) tract after oral administration, reduces the incidence of GI toxicities by suppressing the activation of 5-FU in the GI tract. Thus, S-1 combines FT, CDHP and Oxo at a molar ratio of 1:0.4:1. In 1999–2007, S-1 was approved for the treatment of the following seven cancers: gastric, head and neck, colorectal, non-small cell lung, breast, pancreatic and biliary tract cancers. ‘S-1 and low-dose cisplatin therapy’ without provoking Grade 3 non-hematologic toxicities was proposed to enhance its clinical usefulness. Furthermore, ‘alternate-day S-1 regimen’ may improve the dosing schedule for 5-FU by utilizing its strongly time-dependent mode of action; the former is characterized by the low incidences of myelotoxicity and non-hematologic toxicities (e.g. ≤Grade 1 anorexia, fatigue, stomatitis, nausea, vomiting and taste alteration). These two approaches are considered to allow long-lasting therapy with S-1.

Anticancer activity and toxicity of S-1, an oral combination of tegafur and two biochemical modulators, compared with continuous i.v. infusion of 5-fluorouracil

S-1 is an oral combined form of 1 M tegafur [a prodrug of 5- fluorouracll (5-FU)], 0.4 M 5-chloro-2,4-dlhydroxypyrldlne (a reversible Inhibitor of dlhydropyrlmldine dehydrogenase) and 1 M potassium oxonate (an inhibitor of orotate phosphoribosyltransferase). S-1 has been shown to exert a potent antltumor effect with low gastrointestinal toxicity in experimental tumor models. We have therefore compared the antitumor effect of oral S-1 with that of continuous Infusion of 5-FU in rats bearing transplants of human and murine tumors. Almost complete inhibition of the tumor growth was obtained on 7 day schedules in Yoshida sarcomabearing rats by consecutive administration of 30 mg/kg/day of oral S-1 and 40 mg/kg/day infusion of 5-FU. However, a significant difference between the incidence of toxiclties of S-1 and 5-FU, including body weight loss and diarrhea, was noted. The rats given the 5-FU infusion had marked weight loss and severe diarrhea, while those given oral S-1 had neither. Although about 50% inhibition of the tumor growth was attained with 15 mg/kg/day of oral S-1 and 30 mg/kg/day infusion of 5-FU in nude rats with xenografted human colon cancer (KM12C), the rate of body weight loss in the 5-FUtreated group was distinctly higher than in the S-1-treated group. The ratio of the 5-fluoronucleotide concentrations in gastrointestinal tissue to that in the tumor was lower In the S- 1-treated rats than In the 5-FU-treated rats. In conclusion, the results suggest that oral S-1 might be more effective in the treatment of cancer patients than continuous infusion of 5- FU, from the standpoint of antitumor potency and toxicity. [© 1998 Lippincott Williams & Wilkins.]

Conceptual changes in cancer chemotherapy : from an oral fluoropyrimidine prodrug, UFT, to a novel oral fluoropyrimidine prodrug, S-1, and low-dose FP therapy in Japan

The conventional concept in cancer chemotherapyconsiders that no efficacy can be attained withoutprovoking adverse reactions. We presented concretedescriptions based on a novel concept allowing us toemerge from the old one. Relief of adverse reactions,e.g., diarrhea, stomatitis, anorexia, and H&Fsyndrome, not only improves QOL of the patient butalso allows prolongation of the treatment periodwithout lowering patient compliance.We describe in this paper a therapeutic modality which is basedon SRC (self-rescuing concept)featuring dual activity, i.e., effect-enhancingactivity and adverse reaction-reducing activity.We present the theory and practice of S-1, anovel oral fluoropyrimidine anticancer agent designedto enhance anticancer activity and reducegastrointestinal toxicity through the deliberatecombination of the following components: an oralfluoropyrimidine agent tegafur; a DPD inhibitor (CDHP)which is more potent than uracil used in UFT; and anORTC inhibitor (Oxo) which localizes in thegastrointestinal tract. Furthermore, we refer tocombination therapy with 5-FU (CIV) and low-doseconsecutive CDDP in which CDDP was used as a modulatorof 5-FU and to the theory and practice of combinationtherapy with 5-FU (CVI) intermittent (Monday,Wednesday, and Friday) administration and low-doseCDDP consecutive administration in which a differencein cell cycle between gastrointestinal mucosal celland tumor cell or between bone marrow cell and tumorcell was utilized. We intend in future to combinethe abovementioned therapeutic modalities provokingless adverse reactions and being gentle to patientswith cancer in an effort to further increase theirlife expectancy.

Combination phase I trial of a novel oral fluorouracil derivative S-1 with low-dose cisplatin for unresectable and recurrent gastric cancer (JFMC27-9902).

Purpose: The Japanese Foundation for Multidisciplinary Treatment of Cancer conducted a Phase I study of a novel oral fluorouracil derivative, S-1, combined with a low dose of cisplatin in unresectable and recurrent gastric cancer. Experimental Design: S-1 was administered orally at 80–120 mg/body/day, depending on body surface area. One course consisted of consecutive administration for 28 days followed by a rest of 14 days. Low-dose cisplatin was given i.v. on days 1–5, 8–12, 15–19, and 22–26 of each course. The dose escalation of cisplatin began with an initial dose of 1 mg/m2/day as level 1 and was stepped up to 2, 3, 4, and 6 mg/m2/day as level 2, 3, 4, and 5, respectively. The regimen was repeated for at least two courses. Results: A total of 24 patients was entered in the study. There was no treatment-related death. At level 5, consisting of 5 evaluable patients, dose-limiting toxicity was experienced as grade 3 appetite loss in 2 patients and grade 4 neutropenia in 1 patient. The maximum-tolerated dose of cisplatin was estimated to be 6 mg/m2/day. We decided on a recommended dose of cisplatin of 4 mg/m2/day because the dosage was one level under the maximum-tolerated dose. All 3 patients at level 4 showed partial response, suggesting promising clinical efficacy with this dosage. The serum concentration of cisplatin at level 4 was 918 ± 92 ng/ml on day 26 of the first course. Conclusions: S-1 with low-dose cisplatin may become an effective regimen with acceptable toxicity for gastric cancer.

Superior antitumour activity of S-1 in tumours with a high dihydropyrimidine dehydrogenase activity

To elucidate the mechanism of the enhanced antitumour activity of S-1 (1 M tegafur, 0.4 M 5-chloro-2, 4-dihydroxypyridine, and 1 M potassium oxonate) in terms of the phosphorylation and degradation pathways of 5-fluorouracil (5-FU) metabolism, we investigated tumoral thymidylate synthase (TS) content, dihydropyrimidine dehydrogenase (DPD) activity, the TS inhibition rate (TS-IR), and 5-FU incorporated into RNA (F-RNA) in four human gastric cancer xenografts (MKN-28, MKN-74, GCIY and GT3TKB) and compared the results obtained with S-1 with those obtained with 5-FU and UFT (1 M tegafur, 4 M uracil). 5-FU was administered intraperitoneally (i.p.) to mice at a dose of 50 mg/kg, three times, on days 0, 4 and 8. S-1 and UFT were administered orally at doses of 10 and 24 mg/kg, respectively, once a day, for 9 consecutive days. Antitumour activity was evaluated as the maximum inhibition of tumour growth in each animal. S-1 showed a better antitumour activity than 5-FU and UFT in tumours with a high DPD activity (GCIY and GT3TKB). There were inverse correlations between the antitumour activity and both TS content and DPD activity in the 5-FU and UFT groups. However, no such correlations were observed in the S-1 group. In GCIY and GT3TKB xenografts, TS-IR was significantly higher in the S-1 group than in the 5-FU or UFT groups. In GT3TKB xenografts, the F-RNA level was significantly higher in the S-1 group than in the 5-FU or UFT groups. The superior cytotoxicity of S-1 appears to be attributable to both an increased inhibition of DNA synthesis and an enhanced blockade of RNA function against tumours with a high DPD activity.

Alternate-day oral therapy with TS-1 for advanced gastric cancer.

BackgroundTS-1 (1 M tegafur-0.4 M 5-chloro-2,4-dihydroxypyrimidine-1 M potassium oxonate) has a high single-agent response rate, of more than 40%, for gastric cancer; however, the recommended regimen of 4 weeks of administration interrupted by 2 weeks of drug withdrawal frequently causes adverse effects. The alternate-day dosage of pyrimidine fluoride anticancer drugs could reduce their adverse effects without compromising their effects. We attempted an alternate-day therapy with TS-1 aiming at the avoidance of adverse effects and significantly longer duration of administration.MethodsWe observed patients for clinical effects and adverse effects under alternate-day dosage of TS-1, and determined blood 5-fluorouracil (FU) levels. The judgment of clinical effects was based on the New Guidelines to Evaluate the Response to Treatment in Solid Tumors (RECIST), whereas the evaluation of adverse effects was based on the National Cancer Institute NCI-common toxicity criteria (CTC).ResultsIn 72 (78%) of 92 patients, the TS-1 regimen was converted to the alternate-day dosage because of adverse effects. Twenty patients were treated with the alternate-day dosage regimen from the start because of the fear of adverse effects. The alternate-day dosage was clinically effective, as 28 of 34 patients after relatively curative resection remained alive and free from recurrence. The median survival time of 58 patients after noncurative resection or with unresectable or recurrent cancer was 332 days. Fifty-three percent of these 58 patients achieved partial response and stable disease of more than 12 weeks’ duration. We followed time-dependent changes in blood 5-FU levels in 36 of the patients on alternate-day therapy, in whom TS-1 had been administered daily before being administered every other day. The trough level was significantly lower when TS-1 was administered on alternate days, and blood 5-FU reached a peak at sufficiently effective levels at 2 h even after administration on the alternate-day basis.ConclusionThis study demonstrated that, compared with daily administration, alternate-day administration of TS-1 reduces adverse effects, and simultaneously ensures effective blood levels and provides sufficient clinical effects.

Effect of consecutive lower-dose cisplatin in enhancement of 5-fluorouracil cytotoxicity in experimental tumor cells in vivo

It is known that cisplatin (CDDP) potentiates the cytotoxicity of 5-fluorouracil (5-FU), and that the biochemical mechanism is an increase in the intracellular reduced folate levels in the tumor cells. We investigated the effect of consecutive administration with lower-dose CDDP on intracellular accumulation of reduced folate and the activity of methionine synthase, a key enzyme in intracellular methionine synthesis. When CDDP (1 mg/kg) was administered i.p. to ascitic Yoshida sarcoma-bearing rats for 4 consecutive days, both the reduced folate levels and methionine synthase activity in the cells significantly increased, as the same as a single 5 mg/kg dose of CDDP. Furthermore, when Yoshida sarcoma-bearing rats were pre-treated with 1 mg/kg CDDP for 5 consecutive days, [14C]L-methionine incorporation into the isolated ascitic cells was significantly inhibited as compared to that in non-treated cells, suggesting that consecutive administration of lower-dose CDDP is capable of inducing the intracellular modulation of reduced folate levels and methionine synthase activity via inhibition of cellular uptake of methionine. In addition, 5-day administration of lower-dose (1 mg/kg) CDDP potentiated the antitumor effect of 5 mg/kg S-1, a new oral preparation of tegafur, given for 7 consecutive days, and this combined effect was almost similar to the antitumor effect of a combination of S-1 and a single conventional dose (5 mg/kg) of CDDP. Consecutive lower-dose CDDP also may be concluded to act as an important modulator of the enhancement of 5-FU cytotoxicity in experimental tumors.

Comparison of alternate-day versus consecutive-day treatment with S-1: assessment of tumor growth inhibition and toxicity reduction in gastric cancer cell lines in vitro and in vivo

BackgroundThe toxic effects of S-1 can lead to discontinuation of treatment. Strategies for reducing toxicity without compromising therapeutic effectiveness are required.MethodsWe used the human gastric cancer cell lines MKN28 and MKN45 to examine such strategies in vitro. The cell lines were treated with three different regimens, given on alternate days (alternate-day) or on consecutive days (consecutive-day). On consecutive days, treatment A provided the same total dose as the alternate-day treatment, and treatment B was given for the same number of days as the alternate-day treatment. A fourth group served as control. In vitro, the relative inhibition (RI) of tumor growth by 5-fluorouracil was calculated using the 2-(2-methyl-4-nitrophenyl)-3-(4-nitrophyl)-5-2, 4-disulfophenyl)-2H-tetrazolium (WST-8) method. We also carried out an in vivo experiment in which tumor-bearing nude mice (BALBc/nu-nu) were used to examine the antitumor activity of S-1. Leukocyte counts and gastrointestinal mucosal injury were compared in mice that received alternate-day and consecutive-day treatments.ResultsIn vitro, for MKN28, the RI was 22.9% for alternate-day, 34.1% for consecutive-day A, and 37.7% for consecutive-day B treatments. For MKN45, the RI was 51.1% for alternate-day, 52.2% for consecutive-day A, and 50.5% for consecutive-day B treatments. In vivo, for MKN28, the treated groups showed higher inhibition than the control, and inhibition of tumor growth was higher with alternate-day than with consecutive-day treatment. The RI was significantly higher with alternate-day (49.3%) than with consecutive-day treatment (16.2%; P < 0.05). For MKN45, the RI was greater than 50% in both treated groups. With consecutive-day treatment, 5 of the 14 mice used died during treatment. Leukocyte counts were lower in the mice with consecutive-day than with alternate-day treatment, or control. Atrophic changes and inflammatory cell infiltration of the small intestinal mucosa were severe after consecutive-day, but minimal after alternate-day treatment.ConclusionExperimentally, alternate-day treatment with S-1 is equivalent to consecutive-day treatment in terms of RI of tumor growth, with lower toxicity.