Phase I clinical and pharmacokinetic study of oral S-1 in patients with advanced solid tumors.

PURPOSE: To investigate the side effects, determine the maximum-tolerated dose (MTD), and study the pharmacokinetics of S-1, an oral fluoropyrimidine-based antineoplastic agent consisting of the fluorouracil (5-FU) prodrug tegafur combined with two modulators, 5-chloro-2,4-dihydroxypyridine and potassium oxonate. PATIENTS AND METHODS: Patients with advanced solid tumors received S-1 bid for 28 days, followed by 1 week of rest. 5-FU pharmacokinetics were investigated after a single initial dose of S-1 during the first 24 hours and weekly thereafter. RESULTS: Twenty-eight patients received S-1 at the four consecutive dose levels of 25, 45, 35, and 40 mg/m(2). The MTD was initially found at 45 mg/m(2), with diarrhea as the dose-limiting toxicity (DLT). Diarrhea was also the DLT at the dose of 40 mg/m(2), which was the MTD for patients exposed to extensive prior chemotherapy. Other toxicities were generally mild. Two patients had a reduction of more than 50% in tumor dimension. Plasma pharmacokinetics of 5-FU were linear; at the highest S-1 dose level, 5-FU plasma peak concentrations reached 1 to 2 micromol/L, and the half-life of 5-FU was 3 to 4 hours. A statistically significant relationship was observed between the severity of diarrhea and pharmacokinetic parameters of 5-FU. CONCLUSION: The recommended dose of S-1 in chemotherapy-naive or minimally chemotherapy-exposed patients is 40 mg/m(2) bid on 28 consecutive days, every 5 weeks. In heavily pretreated patients, the recommended dose is 35 mg/m(2) bid. Phase II trials are warranted in tumors known to be responsive to 5-FU treatment.     

S-1 review from preclinical pharmacology

S-1, developed by the scientific theory of both potentiating the antitumor efficacy of 5-fluorouracil (5-FU) and reducing the gastrointestinal (GI) toxicity induced by 5-FU, is a new oral formulation consisting of 1 M tegafur, 0.4 M gimeracil, and 1 M potassium oteracil. By combining gimeracil, a potent inhibitor of 5-FU degradation, and potassium oteracil, which protects against 5-FU-induced GI toxicity to tegafur, S-1, as a dihydropyrimidine dehydrogenase (DPD)-inhibitory fluoropyrimidine (DIF), showed higher antitumor activity, with low intestinal toxicity, compared to continuous infusion of 5-FU (the most effective dosing schedule for 5-FU) and compared to clinically useful oral fluoropyrimidines in various murine and human tumors. In regard to combinations of S-1 with other anticancer drugs, S-1 plus CDDP markedly prolonged survival time in mice suffering gastrointestinal (GI) tumors compared to S-1 in combination with mitomycin-C and/or adriamycin. Furthermore, in combination with irinotecan and taxanes (docetaxel), S-1 exercised synergistic antitumor efficacy not only against 5-FU-sensitive GI cancers with low expression levels of thymidylate synthase (TS) but also against 5-FU-resistant GI tumors with originally elevated levels of TS expression. As one of the reasonable mechanisms of anticancer synergism exerted by an S-1 combination, irinotecan and docetaxel were found to downregulate the expression of TS in gastric cancers. Throughout our pharmacological studies of S-1, alone and in combination with other anticancer drugs, we found that S-1 could be expected to contribute greatly to the treatment of patients with gastric cancer.     

S-1 review from preclinical pharmacology

S-1, developed by the scientific theory of both potentiating the antitumor efficacy of 5-fluorouracil (5-FU) and reducing the gastrointestinal (GI) toxicity induced by 5-FU, is a new oral formulation consisting of 1 M tegafur, 0.4 M gimeracil, and 1 M potassium oteracil. By combining gimeracil, a potent inhibitor of 5-FU degradation, and potassium oteracil, which protects against 5-FU-induced GI toxicity to tegafur, S-1, as a dihydropyrimidine dehydrogenase (DPD)-inhibitory fluoropyrimidine (DIF), showed higher antitumor activity, with low intestinal toxicity, compared to continuous infusion of 5-FU (the most effective dosing schedule for 5-FU) and compared to clinically useful oral fluoropyrimidines in various murine and human tumors. In regard to combinations of S-1 with other anticancer drugs, S-1 plus CDDP markedly prolonged survival time in mice suffering gastrointestinal (GI) tumors compared to S-1 in combination with mitomycin-C and/or adriamycin. Furthermore, in combination with irinotecan and taxanes (docetaxel), S-1 exercised synergistic antitumor efficacy not only against 5-FU-sensitive GI cancers with low expression levels of thymidylate synthase (TS) but also against 5-FU-resistant GI tumors with originally elevated levels of TS expression. As one of the reasonable mechanisms of anticancer synergism exerted by an S-1 combination, irinotecan and docetaxel were found to downregulate the expression of TS in gastric cancers. Throughout our pharmacological studies of S-1, alone and in combination with other anticancer drugs, we found that S-1 could be expected to contribute greatly to the treatment of patients with gastric cancer.     

Combination chemotherapy with S-1 and carboplatin for head and neck cancers

Chemotherapy plays an important role in the treatment of head and neck cancer (HNC) patients with recurrent and/or metastatic unresectable disease. The standard regimen for HNC has been a combination of cisplatin (CDDP) and 5-fluorouracil (5-FU). We planned to develop a new outpatient regimen that could be carried out safely and had an antitumor activity equivalent to the regimen of CDDP plus 5-FU. For this purpose, we selected a combination of S-1 and carboplatin. The overall response rate of 40.9% in this study was almost equivalent to the study previously reported on 5-FU plus CDDP. This regimen of S-1 plus carboplatin has the possibility of yielding tumor responses equivalent to a conventional regimen of 5-FU combined with CDDP in patients with recurrent and/or metastatic head and neck carcinoma as a second-line palliative chemotherapy.     

A phase I study of sorafenib in combination with S-1 plus cisplatin in patients with advanced gastric cancer

Background

Sorafenib inhibits several receptor tyrosine kinases involved in tumor progression and angiogenesis. S-1, an oral fluorouracil antitumor drug, plus cisplatin (CDDP) is the standard regimen for advanced gastric adenocarcinoma (AGC) in Japan. The purpose of this phase I study was to evaluate the safety, pharmacokinetics, and preliminary efficacy of sorafenib in combination with S-1 plus CDDP.

Methods

Patients with histologically confirmed previously untreated AGC were evaluated for eligibility and treated with sorafenib (400 mg bid, days 1–35), S-1 (40 mg/m² bid, days 1–21), and CDDP (60 mg/m², day 8). Treatment was continued until disease progression or unacceptable toxicity. Pharmacokinetics for sorafenib, 5-FU, and CDDP were investigated in cycle 1.

Results

Thirteen patients were enrolled and received at least one dose of the study treatment. No specific or serious adverse event was newly reported in this study. Five patients had partial response and 8 had stable disease as the best response. Pharmacokinetic analysis showed no significant differences in the exposures of sorafenib when administered alone or in combination with S-1 and CDDP.

Conclusions

The present phase I study demonstrates the acceptable toxicity and preliminary efficacy of combined treatment with S-1, CDDP, and sorafenib.     

Phase I and pharmacokinetic study of once daily oral administration of S-1 in patients with advanced cancer.

PURPOSE: To determine the maximum tolerated dose, dose-limiting toxicities(DLTs), and pharmacokinetics of S-1, a combination of tegafur, 5-chloro-2,4-dihydroxypyridine (CDHP), and oxonic acid, administered once daily in patients with advanced cancer. EXPERIMENTAL DESIGN: Eighteen patients with refractory malignancies were treated with S-1 administered once daily for 21 consecutive days, followed by a 1-week break. Of 16 evaluable patients, 6 were treated at a dose of 50 mg/m(2)/day, and 10 were treated at 60 mg/m(2)/day. RESULTS: DLTs were observed in 1 of 6 evaluable patients treated with 50 mg/m(2)/day and in 4 of 10 evaluable patients treated with 60 mg/m(2)/day. DLTs included diarrhea, nausea/vomiting, fatigue, and hyperbilirubinemia. The maximum tolerated dose was 50 mg/m(2)/day. Pharmacokinetic data are consistent with potent modulation of 5-fluorouracil (5-FU) by CDHP, with prolonged half-life and 5-FU AUC at least 10-fold higher than reported in previous studies of equitoxic doses of tegafur modulated by uracil. Pharmacodynamic analysis demonstrated a correlation between diarrhea grade and both 5-FU C(max) (r = 0.57, P < 0.05) and 5-FU area under the curve (r = 0.74, P < 0.01). CONCLUSIONS: The recommended Phase II dose of S-1 administered once daily for 21 consecutive days of 28 is 50 mg/m(2). The pharmacokinetic data presented provide evidence of 5-FU modulation by CDHP. Pharmacodynamic analyses suggest that the utility of pharmacology-based dosing of S-1 should be explored in future trials. Evaluation of once-daily dosing of S-1 in malignancies for which fluoropyrimidines have known antitumor activity is warranted.     

Evaluation of pre-operative chemotherapy with S-1 plus CDDP against advanced gastric cancer with paraaortic lymph node metastasis

We evaluated the effectiveness of pre-operative chemotherapy with S-1 plus CDDP against advanced gastric cancer with paraaortic lymph node metastasis. 8 patients received pre-operative chemotherapy with S-1 plus CDDP, according to the following regimen: S-1, 80 mg/m(2), was administered for 21 consecutive days followed by a 14-day rest period, and CDDP, 60 mg/m(2), was administered on day 8. The adverse event rate was 50%. However, a grade greater than 3 was not revealed. There were 5 partial responses (PR) and 3 stable diseases (SD). We performed 7 total gastrectomies and one distal gastrectomy, and the surgical curability (cur) resulted in 6 cases of cur B and two cases of cur C. The histological antitumor effect was grade 2 in three cases. The median overall survival rate was 623 days and the one-year survival rate was 75%. Analyzing for overall survival with antitumor effect and operative curability, both groups of PR and cur B prolonged survival. Pre-operative chemotherapy with S-1 plus CDDP, when used against advanced gastric cancer with paraaortic lymph node metastasis, might be an effective treatment.     

S-1+Low-Dose CDDP

A review of the published literature was undertaken to ascertain the trends in treatment schedules of combination of an oral fluorouracil derivative S-1 with low-dose CDDP (25 mg/m2 or less) for un-resectable and recurrent gastric cancer. The case reports demonstrated as follows: S-1 was given as standard doses of 80-120 mg/body. With regard to CDDP administration, 4 mg/m2 or less was given for 4-consecutive weeks following 2-weeks rest and 6-10 mg/m2 was given for 3-consecutive weeks following 2-weeks rest in the case of 5-day/week CDDP administration. There have been reports of 6-8 mg/m2 CDDP given once or twice a week and weekly CDDP of 10-25 mg/m2 without grade 3 or more adverse events. A phase I study demonstrated the recommend dose of CDDP in the case of 5-day/week was 4 mg/m2 in the regimen of 4-consecutive weeks and 2-weeks rest with a standard dose of S-1. Three phase I studies on weekly low-dose CDDP with S-1 showed the recommend doses were 20-25 mg/m2. S-1+low-dose and a high-dose (30-90 mg/m2) CDDP have come into wide use in Japan. There have been no differences between the case reports and the clinical studies in quantity and quality for both regimens. The unified regimen of S-1+low-dose CDDP as an outpatient based chemotherapy should be developed.     

Combined effect of S-1 and CDDP as a modulator for colon 26 liver metastasis

S-1 is a novel oral anticancer drug, composed of tegafur (FT), gimestat (CDHP) and otastat potassium (Oxo) in a molar ratio of 1:0.4:1, based on the biochemical modulation of 5-fluorouracil (5-FU). In this study the combined effect of S-1 and low-dose CDDP as a modulator for colon 26 liver metastasis in mice was evaluated. In an experiment with S-1 (5 mg/kg/day: po) and CDDP (0.25 mg/kg/day: i.p.) for 14 days, the combined effects for both liver metastasis and tumor of spleen were not superior to those with S-1 or CDDP alone group. Body weight loss was not greater in the S-1 + CDDP group than in the control group. In an experiment with S-1 (5 mg x 2/kg/day: po) and CDDP (0.25 mg/kg/day: i.p.) for 7 days, the inhibitory effects of S-1 + CDDP of liver metastasis and tumor of the spleen were remarkable compared with the S-1 alone group. However a greater loss of body weight was seen in the S-1 + CDDP group than in other groups. This study suggests that low-dose CDDP might be a modulator of S-1 for colon 26 liver metastasis. Further study is needed to determine the optimum dose and duration of treatment.     

Long-term administration of low-dose cisplatin plus 5-fluorouracil prolongs the postoperative survival of patients with esophageal cancer

To evaluate the efficacy of long-term postoperative adjuvant chemotherapy with low-dose cisplatin (CDDP) plus 5-fluorouracil (5-FU) (CDDP/5-FU), we retrospectively examined 167 patients with squamous cell carcinoma of the esophagus who received the treatment after curative surgery (R0 resection). We classified the patients into the following three groups according to their postoperative therapies and analyzed their outcomes: a) low-dose CDDP (10 mg body(-1) day(-1) x 5 days) plus 5-FU (250-500 mg body(-1) day(-1) x 5 days) repeated every 6 months for 3 years, with an oral fluoropyrimidine (5-FU 150-200 mg body(-1) day(-1) or UFT 300-400 mg body(-1) day(-1)) administered between each treatment cycle (low-dose CDDP/5-FU group, 98 patients); b) high-dose CDDP (80 mg body(-1) day(-1) x 1 day) plus 5-FU (750-1,000 mg body(-1) day(-1) x 5 days) administered once only, followed by treatment with an oral fluoropyrimidine (5-FU 150-200 mg body(-1) day(-1) or UFT 300-400 mg body(-1) day(-1)) for 3 years (high-dose CDDP/5-FU group, 17 patients); or c) surgery alone (surgery alone group, 52 patients). The 3-year survival rates were 83.7% in the low-dose CDDP/5-FU group, 61.4% in the high-dose CDDP/5-FU group, and 62.2% in the surgery alone group; the difference between the low-dose CDDP/5-FU group and surgery alone group was significant (log-rank, p<0.05). A significantly better outcome in the low-dose CDDP/5-FU group than in the surgery alone group was associated with pStage III disease (p<0.001), pN1 lymph node metastasis (p<0.001), and lymphatic invasion (p<0.01). We conclude that long-term postoperative treatment with low-dose CDDP/5-FU is therapeutically beneficial and prolongs survival in patients with esophageal cancer who have regional lymph node metastasis or lymphatic invasion.     

Combination therapy with S-1 and CDDP for head and neck cancer

The combination with cisplatin (CDDP) and 5-FU is considered the first choice chemotherapy for squamous cell carcinoma of the head and neck (HNSCC). S-1, a modulation of tegafur developed in Japan, is an active agent for HNSCC. Some clinical phase I/II studies about the combination with CDDP and S-1 have been reported. The combination showed a good response rate of 67.6% for advanced and recurrent HNSCC in our clinical phase I/II study. The regimens of S-1 combined with carboplatin or nedaplatin have also been reported. Regimens containing S-1 appear to have been effective for HNSCC. Multi-institutional phase II studies with a large sample size are needed in the future. The compliance for patients is better than a 5-FU injection because S-1 is orally administrated. The adverse effect, especially for bone mallow toxicity, is equal or upgraded compared with a 5-FU injection. The efficacy and adverse effects of CDDP plus S-1 should be studied in carefully designed phase II/III trials. S-1 will be one of the key drugs for HNSCC in the future.     

Evaluation of neoadjuvant chemotherapy with paclitaxel, 5-fluorouracil and cisplatin for advanced gastric cancer with pyloric stenosis

S-1 is currently recognized as one of the standard treatments for advanced and recurrent gastric cancer in Japan. However, there are some patients who can not take oral medication due to pyloric stenosis. We performed a critical evaluation of neoadjuvant chemotherapy (NAC) with paclitaxel (PTX), 5-fluorouracil (5-FU) and cisplatin (CDDP); (PTX+FP) for patients with advanced gastric cancer with pyloric stenosis. Since September 2001, 13 patients with far advanced or non-curative respectable gastric cancer with pyloric stenosis received NAC. These patients were treated with paclitaxel 40 mg/m(2) infusions on days 1 and 8, combined with CDDP (6.5 mg/m(2)) and 5-FU (350 mg/m(2)) on days 1 through 8 followed by 2 weeks rest as one course. After at least 2 courses of treatment, the patients underwent gastrectomy with lymphadectomy. The overall response rate was 38.5% (CR: 0, PR: 5), 7 patients had SD and 1 patient had PD. Seven patients had received staging laparoscopy before NAC and 6 patients had free cancer cells in the peritoneal cavity. Of 6 patients with positive cytology at laparoscopy, 4 had no free cancer cells at operation. The MST was 405 days and one-year survival rate was 55.6%. Toxicities were generally mild, and no serious adverse reactions were observed. There were only 2 cases of grade 3 neutropenia. In conclusion, combination of PTX+FP for NAC appears to be an effective treatment for patients with advanced gastric cancer with pyloric stenosis.     

A case of complete response to combination therapy of S-1 and CDDP for Stage IV gastric cancer with Virchow's lymph node and para-aorta lymph node metastasis

The patient was a 53-year-old male with Stage IV gastric cancer with Virchow's lymph node and para-aorta lymph node metastasis. The chemotherapy regimen was given S-1 orally at 80 mg/m(2) day on day 1 to 21 and CDDP intravenously at 60 mg/m(2) day on day 8, repeated for 35 days. After two courses and a reduced regimen with S-1 64 mg/m(2) day plus CDDP 35 mg/m(2) day, the tumor lesion became CR and the serum CEA 575 ng/mL level before therapy decreased to the normal level. The patient received six courses of oral S-1(64 mg/m(2) day)for 28 days followed by a 14- day rest as maintenance therapy. The serum CEA elevated 13 months after the treatment, and the patient received a reduced course and two-course S-1/CDDP therapy. The serum CEA decreased to normal level and the patient has now survived 1 year 5 months without recurrence.     

Sequence-dependence of cisplatin and 5-fluorouracil in advanced and recurrent gastric cancer

This randomized controlled clinical trial was designed to compare the safety and effectiveness of different sequences of treatment with cisplatin (CDDP) and 5-fluorouracil (5-FU) in patients with unresectable advanced and post-operative recurrent gastric cancer. Patients with unresectable advanced or post-operative recurrent gastric cancer were randomly assigned by a registration center to group A or B. Group A received CDDP (80 mg/m(2)) as a continuous 2-h intravenous infusion on day 1 and 5-FU (700 mg/m(2)) as a continuous intravenous infusion on days 2-5. Group B was given 5-FU (700 mg/m(2)) as a continuous intravenous infusion on days 1-4, followed by CDDP (80 mg/m(2)) as a continuous 2-h intravenous infusion on day 5. Each course of chemotherapy was repeated every 28 days. A total of 74 patients were enrolled. One patient died accidentally, and 5 could not be evaluated. Response was assessable in 68 patients. The response rate was 31.3% (10/32) in group A as compared with 13.9% (5/36) in group B. Although the response rate was higher in Group A, the difference was not significant (p=0.085). The response rate in patients with diffuse type tumors was significantly lower in group B. There was no difference between the groups in response among patients with intestinal type tumors. The median overall survival was 239 and 174 days and time to progression was 175 and 140 days in group A and group B, respectively. Although there were trends toward longer survival and time to progression in group A, the differences between the groups were not statistically significant. There was also no difference in the type or incidence of adverse reactions. The results of this controlled study indicate that the overall response rate was slightly but not significantly higher in patients who received CDDP before 5-FU. Among patients with diffuse type tumors, the response rate was significantly lower when 5-FU was administered before CDDP. Our results suggest that CDDP should be given before 5-FU in patients with gastric cancer when treated with a combination of CDDP and 5-FU.     

Combination chemotherapy of S-1 and docetaxel on advanced and recurrent gastric cancer

In the present article, we have summarized the phase I/II clinical trials on combination therapy of S-1 and docetaxel. With result of the phase I study, patients were treated with intravenous infusion of 40 mg/m2 docetaxel on day 1 and oral S-1 80 mg/m2/day on days 1 to 14 every 3 weeks. Forty eight patients received a total of 272 treatment cycles. No complete responses (CRs) and 27 partial responses (PRs) were observed for an overall response rate (CR+PR) of 56.2% (95% CI, 38-66%). Eighteen patients (37.5%) had stable disease (SD), and 3 patients (6.2%) had progressive disease (PD) as best response. The tumor control rate (CR+PR+SD) was 93.8% (95% CI, 83-98%). The median overall survival was 14.3 months (95% CI: 10.7-20.3 months) and the median time to tumor progression was 7.3 months (95% CI: 4.2-10.7 months). The most common grade 3-4 hematologic toxicities were neutropenia 58.3%, leukopenia 41.7%, febrile neutropenia 8.3%, and anemia 8.3%. The most common grade 3 nonhematologic toxicities were anorexia 14.6%, stomatitis 8.3%, nausea 6.3%, diarrhea 4.2%, constipation 4.2%, and vomiting 2.1%. No grade 4 nonhematologic toxicities were reported, and all treatment-related toxicities were resolved. The mechanisms underlying these synergistic effects of S-1 and docetaxel were examined by expression and activity analyses of 5-FU metabolic enzymes. The expressions of thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) were decreased and that of orotate phosphorybosyl transferase (OPRT) was increased in mRNA, protein level and activity assay after the treatment with docetaxel and 5-FU in the TMK-1 gastric cancer cell. These findings strongly indicate that the combination chemotherapy of docetaxel and S-1 is effective against gastric carcinomas and therefore is a good candidate as a standard chemotherapeutic strategy in treating these tumors.     

S-1 in gastric cancer: a comprehensive review

The current basic and clinical studies of S-1 (TS-1^®) were reviewed. S-1 is a novel oral dihydropyrimidine dehydrogenase (DPD) inhibitory fluoropyrimidine (DIF) based on a biochemical modulation of 5-fluorouracil (5-FU); S-1 contains tegafur (FT) and two types of enzyme inhibitor; 5-chloro-2,4-dihydroxypyridine (CDHP) and potassium oxonate (Oxo) in a molar ratio of 1?:?0.4?:?1. In pharmacokinetic studies, S-1 showed high 5-FU concentration in blood for long periods of time. In a combined analysis of two pivotal late phase II studies in gastric cancer, the overall response rate was 44.6% (45/101), and median survival time and 1-year survival rate were 244 days and 37%, respectively. A postmarketing survey was conducted, and in the interim analysis, tolerability and safety profiles were shown in 3294 patients with gastric cancer. The oral dose form and low incidence of adverse reactions permit treatment on an outpatient basis. To evaluate the survival benefit of S-1 in advanced gastric cancer, a phase III study of S-1 vs 5-FU vs cisplatin (CDDP) plus irinotecan (CPT-11) has been conducted. The effect of S-1 in adjuvant chemotherapy is also promising. Currently, a phase III study of surgery alone vs S-1 in patients with curative resection of gastric cancer is in progress. Further therapeutic benefits are expected to be gained by combining S-1 with other chemotherapeutic agents. Several preliminary results of combination phase I/II studies of S-1 with CDDP or CPT-11 have recently been obtained, and phase II studies are in progress. Thus, S-1 is currently the first candidate as the standard anticancer drug for gastric cancer. Further evaluations by well-controlled clinical trials are still needed.     

S-1 for gastric cancer-S-1 monotherapy and its progress

Two pivotal phase II studies of S-1 in advanced gastric cancer showed response rates of 44% and 49%, and the overall survival time was 207 and 250 days, respectively. The response rate of S-1 exceeded the response rates of other approved drugs, and was comparable to that of combination chemotherapies such as 5-fluorouracil (5-FU) plus cisplatin (CDDP). These data suggested that S-1 could be used as a first-line drug for gastric cancer with a great advantage in quality of life (QOL), because it is an oral drug and can be used at an outpatient clinic. The overall incidences of adverse reactions in the phase II studies were 74.3%, and that of grade 3 or worse were 14.9%. The main adverse reactions were myelosuppression and GI toxicities. As hematological toxicity was more common than other oral fluoropyrimidine derivatives such as UFT, a careful hematological monitoring is necessary. To confirm the survival benefit of S-1 in advanced gastric cancer, a phase III trial of S-1 vs 5-FU vs CDDP plus irinotecan (CPT-11) has been conducted by the Japan Clinical Oncology Group (JCOG), and these results have been awaited. Furthermore, the combination of S-1 with CDDP, CPT-11 or taxane for the treatment of gastric cancer is feasible and active, and phase III studies of S-1 vs several combination therapies including S-1 are also in progress. The effect of S-1 in adjuvant setting is also promising. Currently, a phase III study of surgery alone vs S-1 in patients with a curative resection of gastric cancer has been developed. Further therapeutic benefits are also expected by combining S-1 with other chemotherapeutic agents such as molecular targeted agents.     

The current evidence of S-1 and irinotecan hydrochloride combination chemotherapy with tri-weekly schedule

A combination therapy of irinotecan hydrochloride (CPT-11) with continuous intravenous infusions of (infusional) 5-fluorouracil (5-FU) and Leucovorin (LV) is often used to treat advanced colorectal cancer. However, recent concerns on safety and convenience have prompted the development of new oral fluoropyrimidine derivatives which improved regimens. Yamada et al conducted a phase I study to assess the maximum tolerated dose and recommended dose of S-1 combined with CPT-11. The study recommended that 150 mg/m2 of CPT-11 be given on day 1 and 80 mg/m2 of S-1 daily on days 1 to 14 every 3 weeks. Recently, several phase I/II studies assessed the efficacy and safety of the combined therapy with S-1 and CPT-11 in patients with advanced colorectal cancer. Some of the studies which were ongoing assessed a tri-weekly schedule regimen. Our results showed that S-1 plus CPT-11 was very effective, with a response rate of 63% and PFS of 8 months. Toxicity was generally mild and manageable on an outpatient basis. The current evidence showed that a combination of S-1 and CPT-11 was more convenient and easier to administer than a combination of CPT-11 plus infusional 5-FU and LV. It will be essential to prove that the combination of S-1 plus CPT-11 can replace the combination of infusional 5-FU and LV plus CPT-11 without negatively affecting efficacy and toxicity.     

Combination therapy of continuous venous infusion (CVI) of 5-FU and low dose consecutive cisplatin (CDDP), and the new oral anti-cancer drug S-1 for advanced gastro-intestinal cancer

Highly effective treatment is required for patients with advanced GI cancer. Returning to the starting point for reconsideration of cancer chemotherapy, with the aim of attaining a therapy (self rescuing concept: SRC) with more potential efficacy and less toxicity than current therapy, we report two kinds of chemotherapy in the present paper. They were set up preclinically using the theory of 5-FU biochemical modulation, and demonstrated their usefulness in clinical practice. S-1 is a newly developed oral anti-cancer drug which is a combination of Tegafur (FT), a prodrug of 5-FU and two modulators (CDHP, an inhibitor of 5-FU degradation and Oxo, a selective inhibitor GI toxicity by 5-FU) at a molar ratio of 1:0.4:1. In combination with CDHP, 5-FU gradually released from FT remained longer in plasma, and consequently had high anti-tumor activity, while the combined Oxo significantly suppressed GI toxicity due to 5-FU. The response rate to S-1 of stomach cancer in a phase II study was 46.5% (60/129). Toxicity at more than G3 was less than 10%. In the combination therapy employing 5-FU by CVI (5-FU: 250-350 mg/body for 24 h, 4-6 wks) and low dose consecutive CDDP, CDDP acts mainly as a modulator of 5-FU (to increase 5-FU sensitivity for tumor by inhibition of intracellular Met incorporation). For this purpose, it was found that daily consecutive administration is required, even at low dose of CDDP (3-5 mg/body/day for 5 days). A high response rate (40-60%) was obtained for advanced GI cancer. Toxicity at more than G3 was less than 10%. On the other hand, the possibility has been suggested that so far as 5-FU is concerned, CVI every other day (500-750 mg/body/day for 3 days) is more favorable than long term CVI, with regard to decreasing GI and myelotoxicities based upon the difference in generation time between normal cell (GI mucous membrane and stem cell) and tumor cell cycles. The possibility is suggested that the above-mentioned chemotherapy can become a standard therapy for GI cancer.     

Plasma concentrations of 5-fluorouracil and F-beta-alanine following oral administration of S-1, a dihydropyrimidine dehydrogenase inhibitory fluoropyrimidine,as compared with protracted venous infusion of 5-fluorouracil

The pharmacokinetics and pharmacodynamics of oral S-1, a dihydropyrimidine dehydrogenase (DPD) inhibitory fluoropyrimidine, were compared with those of protracted venous infusion (PVI) of 5-fluorouracil (5-FU). In all, 10 patients with gastric cancer received PVI of 5-FU at a dose of 250 mg m(-2) day(-1) for 5 days. After a washout period of 9 days, the patients received two divided doses daily for 28 days. S-1 was administered orally at about 0900 and 1900 hours. The daily dose of S-1 in terms of tegafur was 80 mg day(-1) in patients with a body surface area (BSA) of <1.25 m(2), 100 mg day(-1) in those with a BSA of >or=1.25 m(2) to <1.5 m(2), and 120 mg day(-1) in those with a BSA of >or=1.5 m(2). Plasma concentrations of 5-FU and F-beta-alanine (FBAL) were measured for pharmacokinetic analysis, and the plasma uracil concentration was monitored as a surrogate marker of DPD inhibition (pharmacodynamic analysis) in the same patients on days 1-5 of PVI of 5-FU and on days 1-5 of oral S-1. The area under the curve (AUC(0-10 h)) of 5-FU on day 5 was 728+/-113 ng h ml(-1) for PVI of 5-FU and 1364+/-374 ng h ml(-1) for S-1. The median 5-FU PVI : S-1 ratio of the AUC(0-10 h) of 5-FU was 1.9. The AUC(0-10 h) of FBAL on day 5 of PVI of 5-FU was 9465+/-3225 ng h ml(-1), AUC(0-10 h), as compared with 1725+/-605 ng h ml(-1) on day 5 of S-1 treatment. The AUC(0-10 h) of uracil on day 5 was 252+/-60 ng h ml(-1) with PVI of 5-FU and 12 582+/-3060 ng h ml(-1) with S-1. The AUC(0-10 h) of FBAL was markedly lower and plasma uracil concentrations were significantly higher for S-1 than for PVI of 5-FU, clearly demonstrating the effect of DPD inhibition.