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-fluorouracil (5-FU)], 0.4 M 5-chloro-2,4-dihydroxypyridine (a reversible inhibitor of dihydropyrimidine dehydrogenase) and 1 M potassium oxonate (an inhibitor of orotate phosphoribosyltransferase). S-1 has been shown to exert a potent antitumor 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 sarcoma-bearing 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 toxicities 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-FU-treated 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.     

Invention of a tumor-selective 5-fluorouracil derivative named S-1 by biochemical modulation of 5-fluorouracil

A new oral type of 5-fluorouracil (5-FU) derivative possessed of both potent antitumor activity and less gastrointestinal (GI) toxicity was investigated and developed in the form of a combination of tegafur (FT), a masked form of 5-FU, and its two peculiar biochemical modulators. One is 5-chloro-2,4-dihydroxypyridine (CDHP), a new potent inhibitor of 5-FU degradation in vivo, and another is potassium oxonate (Oxo), a characteristic inhibitor of 5-FU phosphorylation, which distributes much higher in GI tract after p.o. administration. 5-FU levels in blood of rats following administration of FT, were markedly elevated and persisted for a long-time by co-oral CDHP corresponding to over 0.4 molar ratio to FT, like the case in continuous infusion of 5-FU, which resulted in an augmentation of antitumor efficacy in Yoshida sarcoma-bearing rats, although severe GI toxicity simultaneously occurred. To reduce 5-FU-induced toxicities such as diarrhea and body weight loss and to maintain the augmented antitumor activity, 0.5 to 2 molar Oxo was orally given to rats with one molar FT plus 0.4 molar CDHP. As a result, both severe GI injury and body weight loss were markedly inhibited by coadministration of 0.5 to 1.0 molar Oxo while high antitumor efficacy (about 90% inhibition of tumor growth) was maintained. However, such almost complete antitumor effect was reduced to about 50% inhibition of tumor growth by over 2 molar Oxo combined with one molar FT plus 0.4 molar CDHP. Based on these results, a novel 5-FU derivative, named S-1, was composed of one molar FT, 0.4 molar CDHP and one molar Oxo. S-1 showed an antitumor activity over 3-fold stronger than UFT (one molar FT plus 4 molar uracil) against Yoshida sarcoma and Sato lung carcinoma in rats and human colon carcinoma (KM12C) xenografted in nude rats when its minimum toxic dose was administered. Co-oral Oxo also significantly reduced the incidence of diarrhea and stomatitis induced by administration of FT-CDHP in beagle dogs. These results suggest that high antitumor activity and less GI toxicity of S-1 was brought about by the elevation in blood and tumor tissues and by selective decrease of 5-fluoronucleotides, an active metabolite of 5-FU, in GI tract.     

Ectopic expression of carbohydrate antigens that determine the metastatic potential of human colorectal carcinoma

Highly malignant and metastatic tumor cells are thought to arise within primary tumors and become predominant during cancer progression. We demonstrated, by the analysis of > 500 surgical specimens, that colorectal carcinomas with increased metastatic potential were characterized by an increased expression of sialyl-Le(x) antigens expressed on mucins. The biological role of sialyl-Le(x) antigens expressed on mucins produced by colon carcinoma cells has been investigated using variant cell lines selected for their expression of this antigen. KM12-HX and KM12-LX, high and low expresser variant cells, differed in their metastatic potential in nude mice after intrasplenic injection. KM12-HX cells contain higher levels of polyA+mRNA for alpha(1-3/4) fucosyltransferase than KM12-LX cells. Sialyl-Le(x) antigenic carbohydrate chains were attached to mucins as well as glycoproteins with various M(r). KM12-HX cells adhered more strongly than KM12-LX cells to human umbilical vein endothelial cells treated with tumor necrosis factor-alpha and to mouse hepatic sinusoidal endothelial cells. We have retrospectively evaluated post-operative survival of colon carcinoma patients for their sialyl-Le(x) antigen levels in the primary tumors according to the percentage of stained cells by specific antibodies. The adjusted survival rate of the patients with high levels of sialyl-Le(x) antigen in their primary tumors was much lower due to recurrence and metastasis than that of the patients with tumors containing low levels of sialyl-Le(x) antigen. The results suggested that sialyl-Le(x) antigen has a potential to be used as a predictive marker for colorectal cancer metastasis.     

5-Fluorouracil prodrug: role of anabolic and catabolic pathway modulation in therapy of colorectal cancer

Following p.o. administration to rats bearing advanced colorectal carcinoma, Ftorafur (FT) is converted to 5-fluorouracil (FUra) by microsomal P450 in the liver. To optimize the therapeutic selectivity of the FUra generated from FT, three approaches were utilized: (a) inhibition of FUra degradation to dihydrofluorouracil by uracil as an alternative substrate for uracil reductase in the molar ratio of 4 uracil:1 FT (UFT); (b) modulation of drug inhibition of thymidylate synthase by leucovorin (LV); and (c) by increasing the level of FUra incorporation into cellular RNA by N-(phosphonacetyl)-L-aspartate (PALA), an inhibitor of aspartate transcarbomylase. The maximum tolerated dose (MTD) of FT and UFT, administered 3 times a day for 28 days, was 150 mg/kg/day and 60 mg/kg/day, respectively. The MTDs were not significantly modified by LV (150 or 600 mg/kg/day), administered by the p.o. route with the drugs, or by PALA (100 mg/kg) administered weekly by the i.v. route. The dose-limiting toxicity of FT alone and in combination with the modulators was stomatitis. The severe alopecia observed with FT alone was reduced significantly by uracil. At the MTD, the antitumor activity of UFT was superior to those of FT and FUra alone and in combination with LV and/or PALA. The 3-month sustained complete tumor regression for UFT, FT, and FUra was 38%, 0%, and 13% (for the weekly schedule), respectively. Although uracil, LV, and PALA individually increased the antitumor activity of FT at its MTD, the combination of the three modulators produced the highest therapeutic efficacy in rats bearing advanced colorectal carcinoma, in which 100% of the treated animals achieved complete and sustained tumor regression. The therapeutic efficacy observed with FT modulation could not be achieved with FUra administered by different schedules, each at its MTD alone or in combination with either LV or PALA. In brief, modulation of FT produced greater therapeutic efficacy and selectivity than FUra. Furthermore, the combined use of modulators capable of inhibiting the degradation pathway of FUra and potentiating the effects of the anabolic metabolites action appears to offer the greatest therapeutic potential.     

Effect of 5-fluorouracil and UFT on experimental liver metastasis model of colorectal cancer using mouse colon 26 cells

Effects of 5-fluorouracil (5-FU) and UFT on an experimental liver metastasis model were compared at equi-effective dosage levels against subcutaneous tumor of mouse colon 26. 5-FU at the dosage level of 40 mg/kg suppressed the subcutaneous tumor growth by 70.0% and 45.0% on day 13 and day 18, respectively, and UFT at 20 mg/kg provided almost equal suppression (63.0% and 48.0%). In the liver metastasis model, 5-FU at 40 mg/kg showed more potent prevention of the formation of metastatic foci (94.9%) than did UFT (60.4%) at 20 mg/kg. 5-FU at 40 mg/kg produced a much higher peak serum level of 5-FU than did UFT at 20 mg/kg and also showed a much higher AUC (area under the curve) level in the portal blood. These results suggest that oral administration of 5-FU might be useful in prevention of liver metastasis of colorectal cancer.     

Late phase II study of novel oral fluoropyrimidine anticancer drug S-1 (1 M tegafur-0.4 M gimestat-1 M otastat potassium) in advanced gastric cancer patients

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). CDHP inhibits dihydropyrimidine dehydrogenase (DPD), an enzyme which degrades 5-FU, and maintains prolonged 5-FU concentrations in the blood and tumours. Oxo is distributed in the gastrointestinal tract at a high concentration after oral administration and alleviates gastrointestinal toxicity due to 5-FU. S-1 improves the tumour-selective toxicity of 5-FU by the actions of two modulators, CDHP and Oxo. We conducted a late phase II clinical trial of S-1 as an open trial in patients with advanced gastric cancer, to confirm its antitumour effect and adverse reactions. 51 patients with advanced gastric cancer were enrolled in the trial. S-1 was administered orally twice daily after meals, at a standard dose of 80 mg/m2/day. One course consisted of consecutive administration for 28 days and 14 days' rest. Administration was repeated over four courses. A complete response was obtained in 1 patient and partial responses in 24 patients, producing a response rate of 49% (25/51) (95% confidence interval (CI) 35.9-62.3%). The incidence of adverse reactions was 78% (40/51) and that of adverse reactions of grades 3 and 4 was 20%. Adverse reactions of grades 3 and 4 included a decrease in the haematocrit, leucopenia, granulocytopenia, diarrhoea, malaise and proteinuria. No serious unexpected adverse reactions were observed. In conclusion, S-1 was effective and well tolerated in patients with advanced gastric cancer.     

Advantage of post-operative oral administration of UFT (tegafur and uracil) for completely resected p-stage I-IIIa non-small cell lung cancer (NSCLC)

OBJECTIVE: Although adjuvant therapy after surgery for non-small cell lung cancer (NSCLC) has been reported to be ineffective, it has been recently reported in prospective randomised studies conducted by two different groups in Japan that oral administration of a 5-fluorouracil (5-FU) derivative drug, UFT (a combination drug of tegafur and uracil) can improve the post-operative survival [The Study Group of Adjuvant Chemotherapy for Lung Cancer (Chubu, Japan). A randomized trial of postoperative adjuvant chemotherapy in non-small cell lung cancer (the second cooperative study). Eu J Surg Oncol 1995;21:69-77; Wada, H., Hitomi, S., Teramatsu, T, West Japan Study Group for Lung Cancer Surgery. Adjuvant chemotherapy after complete resection in non-small-cell lung cancer. J Clin Oncol 1996;14:1048-1054]. To examine the efficacy of UFT as post-operative adjuvant therapy, a retrospective study was performed. METHODS: A total of 655 consecutive patients who underwent complete tumor resection for pathologic stage I-IIIa, NSCLC at the Department of Thoracic Surgery, Chest Disease Research Institute, Kyoto University between 1976 and 1992 were retrospectively reviewed. As post-operative adjuvant therapy, UFT was administrated to 98 patients (UFT group), and was not administered to the other 557 patients (Control group). RESULTS: The 5-year survival rate of the UFT group was 76.5%, which was significantly better than that of the Control group (5-year survival rate: 58.6%, P = 0.005). Stratified with pathologic stage, the efficacy of UFT was seen in the p-stage I disease (5-year survival rate: 88.6% for the UFT group, 72.0% for the Control group, P = 0.013) and in the p-stage IIIa, pN2 disease (5-year survival rate: 54.3% for the UFT group, 37.5% for the Control group, P = 0.037). Multivariate analysis of the prognostic factors also revealed the efficacy of UFT (P = 0.004, 95% confidence interval of relative risk: 0.325-0.840). Post-operative intravenous chemotherapy or radiation therapy did not prove to be significant factors affecting the prognosis. CONCLUSIONS: Efficacy of oral administration of UFT as post-operative adjuvant therapy for completely resected NSCLC was proposed. To confirm the efficacy, a prospective randomized study for a more homogenous patient group is needed.     

Effects of recombinant human tumor necrosis factor on the development of ascitic tumor and expression of c-erbB2 in the nude mouse models of ovarian cancer

OBJECTIVE: To investigate the effects of recombinant human tumor necrosis factor (rhTNF) on the growth of ascitic tumor and expression of c-erbB2 in the nude mouse models of ovarian cancer. METHODS: By intraabdominal injection, rhTNF was delivered to the peritoneal cavity of nude mouse with ovarian cancer as well as control group, after 6 days treatment, tumor cell counting and expression of c-erbB2 were detected by indirect fluorescence flow cytometry. RESULTS: There is a significant difference in tumor cell counting between the study group and control group (P < 0.01). Expression of c-erbB2 in study group was lower than that in control group. CONCLUSION: rhTNF was demonstrated to have effects on both inhibition of ascitis tumor development and down regulation of c-erbB2 expression in nude mouse with ovarian cancer.     

A clinical nude mouse metastatic model for highly malignant human pancreatic cancer

Pancreatic cancer is a highly aggressive and treatment-refractory cancer. A clinically-relevant animal model is necessary to develop therapy for metastatic pancreatic cancer. In this study we evaluated the efficacy of mitomycin C (MMC) and 5-FU against the human pancreatic adenocarcinoma cell line PAN-12 in an orthotopic human metastatic pancreatic cancer nude mice model. The model is constructed by surgical orthotopic implantation (SOI) of histologically intact tumor tissue in the tail portion of the pancreas near the spleen. PAN-12 grew very aggressively in the control group of nude mice with extensive local invasion and distant metastasis to various organs with a propensity for the lung but to other organs as well, including the liver, kidney and regional and distant lymph nodes. In a striking effect none of the mice in the MMC-treated group developed tumor. Although mice in the 5-FU treated group survived statistically significantly longer than those in the untreated control, the overall incidence of metastasis in these mice was equivalent to those in the control. However no liver or kidney metastases were found in the 5-FU treated animals perhaps accounting in part for their longer survival. This "clinical" nude mouse model of highly metastatic pancreatic cancer can now be used to discover new effective agents for this disease.     

New drugs in the treatment of colorectal carcinoma

BACKGROUND: Treatment with 5-fluorouracil (5-FU) plus leucovorin has been the unofficial standard therapy for patients with colorectal carcinoma (CRC) for more than a decade; however, the optimal dose and schedule remain a matter of debate. Recently several new drugs have shown activity in this disease. These include irinotecan (CPT-11); oxaliplatin; the thymidylate synthase inhibitors raltitrexed, uracil/tegafur (UFT), capecitabine, and S-1; the biochemical modulators trimetrexate and 5-ethynyluracil; and the monoclonal antibody 17-1A. METHODS: The results of clinical trials with these and other new agents, as well as their current status and main characteristics, were reviewed. RESULTS: Several of these agents, some with a novel mechanism of action, show promising activity in CRC. In combination with 5-FU and leucovorin, trimetrexate showed encouraging response rates in Phase II studies. Other interesting agents include capecitabine, UFT, and S-1. The biochemical modulator 5-ethynyluracil may allow the oral administration of 5-FU; however, results of Phase II clinical trials are not yet available. CPT-11 is in the most advanced stage of development and, based on consistent data generated in extensive Phase II studies, currently appears to be a reasonable choice for 5-FU-resistant or refractory disease. Another promising agent is oxaliplatin, which showed activity as first-line and second-line treatment. CONCLUSIONS: Several new agents have shown promise in the treatment of CRC, and changes in the standard treatment of advanced or high risk CRC appear likely in the near future.     

Phase I study of UFT plus leucovorin in advanced colorectal cancer: a double modulation proposal

Twenty-six patients with advanced colorectal cancer were treated with UFT and leucovorin (LV). On day 1, patients received LV 500 mg/m2 in IV infusion, followed by 15 mg/12 h for 13 days. On days 1 to 14, patients took oral UFT twice daily. Three cycles were given every 28 days, unless grade III-IV toxicity appeared. The initial dose of UFT (200 mg/day) was increased until 800 mg/day. Dose limiting toxicities were stomatitis, diarrhea and epigastralgia. The maximum tolerated dose of UFT was 390 +/- 10 mg/m2. Three out of 24 evaluable patients achieved a partial response and 1 a complete response with UFT doses of 260 to 390 mg/m2. These results warrant confirmation in phase II studies.     

Uracil-ftorafur: an oral fluoropyrimidine active in colorectal cancer

PURPOSE AND DESIGN:This review describes the early clinical development of uracil-ftorafur (UFT), an oral fluoropyrimidine, designed in 1978 by adding uracil to ftorafur. The review focuses on the treatment of colorectal cancer and summarizes the Japanese experience and the phase I and II trials performed in the United States and Europe. RESULTS: Clinical trials of UFT published in the Western world have included 581 patients with colorectal cancer. UFT has been administered in these trials as a single agent or biomodulated by leucovorin (LV). UFT was administered daily in split doses for periods that ranged from 14 to 28 days. The activity of oral UFT in large-bowel cancer when administered with oral LV (approximately 50 mg/dose) has resulted in objective response rates of approximately 40%. Response rates of approximately 25% (range, 17% to 39%) were reported when UFT was administered as a single agent or with lower doses of LV. The highest dose-intensities of UFT are achieved with 28-day schedules of administration. The maximum-tolerated dose (MTD) of UFT with this schedule, when administered concomitantly with oral LV 150 mg daily, is 300 mg/m2 daily. The dose-limiting toxicity (DLT) of UFT has generally been diarrhea. Other commonly described toxicities include nausea and vomiting, fatigue, and stomatitis. Myelosuppression occurs infrequently. Typically, hand-foot syndrome and neurologic toxicity are lacking. CONCLUSION: UFT is a fluoropyrimidine active in colorectal cancer. The oral route of administration and improved safety profile represent important advantages over both conventional and infusional fluorouracil (5-FU) regimens.     

5-FU concentrations in the blood and tumor tissue after 5'-DFUR or UFT administration in the patients with uterine cervical cancer

In order to verify the antitumor activity of fluorinated pyrimidine drugs, we conducted an investigation of the clinical pharmacology with two drugs, 5'-DFUR and UFT. Total 21 cases of cervical cancer were alloted randomly into 5'-DFUR group (daily dose 800 mg for 3 days) consisting of 11 patients and UFT group (daily dose 600 mg for 3 days) consisting of 10 patients, the unchanged substances (5'-DFUR in the 5'-DFUR group and tegafur concentrations in the UFT group) and 5-FU concentrations in serum and tissues were measured 6 hours after administration of the drugs. The 5'-DFUR concentration in the 5'-DFUR group was not detected in serum and less than a detectable limit for all of cancerous tissues, normal cervical tissues, and lymph nodes. The tegafur concentrations in the UFT treated group was 13.8 +/- 7.0 micrograms/ml for serum, 10.4 +/- 6.4 micrograms/g for cancerous tissues, 14.1 +/- 7.3 micrograms/g for normal cervical tissues, and 4.5 +/- 4.2 micrograms/g for lymph nodes. The 5-FU concentrations in the 5'-DFUR treated group were 0.018 +/- 0.046 micrograms/g for cancerous tissues, but less than a detectable limit for serum and normal cervical tissues. On the other hand, in the UFT group, 0.271 +/- 0.247 micrograms/g for a cancerous tissue, 0.035 +/- 0.018 micrograms/ml for serum, 0.125 +/- 0.073 micrograms/g for normal cervical tissues, showing significantly high values (p < 0.01, p < 0.001, and p < 0.01, respectively) compared to those in the 5'-DFUR treated group. These results suggest that UFT is a promising drug for the treatment of cancer of the uterine cervix.     

Angiotensin II mediates cell hypertrophy in vascular smooth muscle cultures from hypertensive Ren-2 transgenic rats by an amiloride- and furosemide-sensitive mechanism

Matrix metalloproteinases (MMP) are enzymes responsible for extracellular matrix degradation, a critical component influencing the growth and metastatic potential of cancer. The purpose of this study was to determine the in vitro effects of MMP inhibition on human pancreatic cancer cells and to document its effect on cancer growth in vivo. The effect of MMP inhibition was determined using the MMP inhibitor BB-94 and a moderately differentiated pancreatic cancer cell line (HPAC). In vitro, a dose response curve was generated over 5 days utilizing the MTT [3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. In vivo, using an established orthotopic model for pancreatic cancer (LD100 = 80 days), 22 nude mice with orthotopic tumors (30 were implanted) received either BB-94 or vehicle beginning 4 days prior to implantation and continuing to death or sacrifice on Day 70. Mice were weighted weekly. At death/sacrifice, tumors were weighted, volume determined, and metastases/ distant spread documented. In vitro, BB-94 had little effect on HPAC proliferation at 40 ng/ml but achieved progressively greater to near complete inhibition at doses up to 4000 ng/ml while maintaining cell viability. In vivo, BB-94 significantly increased length of survival (69 +/- 0.1 days vs. 56 +/- 3.1 days) and necropsy weight (25.7 +/- 1.67 g vs. 19.8 +/- 1.14 g) while decreasing metastatic rate (1 vs. 20) and tumor size (0.14 +/- 0.02 g vs. 0.65 +/- 0.1 g). MMP inhibition limits HPAC proliferation in a dose-dependent fashion without direct cytotoxic effects in vitro. Mice harboring orthotopic tumors treated with BB-94 demonstrated significant reductions in tumor weight, volume, and metastases which corresponded to increased animal weight and prolonged survival.     

Suppression of human bladder cancer growth by increased expression of C-CAM1 gene in an orthotopic model

Recently, we demonstrated that an immunoglobulin-like cell adhesion molecule, C-CAM, acts as a tumor suppressor in prostate cancer. It is known that C-CAM is expressed in many epithelial cell types. In this study, we tested the possibility that C-CAM may also suppress bladder cancer progression. We used an orthotopic tumor model, which provides a relevant organ condition for examining the interaction between primary tumor cells and their microenvironment; this interaction has a critical impact on the behavior of carcinoma. We constructed a recombinant adenovirus expressing C-CAM1 (an isoform of C-CAM) and infected the 253J B-V cell line, a tumorigenic human bladder carcinoma subline. In vitro, C-CAM1 protein was detected in C-CAM1 adenovirus-infected cells but not in antisense control virus-infected cells, and the levels of expression showed dose dependency. When these cells were injected orthotopically in nude mice, we found that the increased expression of C-CAM1 in the 253J B-V cells repressed the growth of 253J B-V-induced tumors. Taken together, these data indicate that C-CAM1 is a potent tumor suppressor in human bladder cancer.     

Effect of gastrectomy on the pharmacokinetics of tegafur, uracil, and 5-fluorouracil after oral administration of a 1:4 tegafur and uracil combination

The effects of gastrectomy on the pharmacokinetics of UFT, a combined oral preparation of 1-(2-tetrahydrofuryl)-5-fluorouracil (tegafur) and uracil at a molar ratio of 1:4, were examined in 26 patients with macroscopic Stage I gastric cancer. In all, 200 mg UFT (in terms of tegafur) was given to 17 patients who underwent partial gastrectomy (9 cases of Billroth I reconstruction, 8 cases of Billroth II reconstruction) and to 9 patients who underwent total gastrectomy with modified Roux-en-Y reconstruction. Before the operation, the area under the curve (AUC) for tegafur, uracil, and 5-fluorouracil (5-FU) was 79.28 +/- 26.88, 4.41 +/- 1.78, and 0.51 +/- 0.20 micrograms h ml-1, respectively. Partial (Billroth I and II) and total gastrectomy did not alter the AUC of tegafur, and partial gastrectomy using the Billroth I and II methods decreased the AUCs of uracil and 5-FU during the first 2 weeks postoperation. However, plasma levels of uracil and 5-FU reverted to preoperative values at 3 months postsurgery. Our findings show that when UFT is prescribed for patients treated in the early postoperative period following partial gastrectomy for cancer, dose increases and the timing of administration should be given close attention.     

Oral fluoropyrimidines in the treatment of colorectal cancer

5-Fluorouracil (5-FU) has been the mainstay of systemic therapy for colorectal cancer since its initial development 40 years ago. Efforts to improve the therapeutic index of 5-FU have included alteration of schedule and addition of biochemical modulators. An understanding of 5-FU mechanisms of action has resulted in major therapeutic advances in the past 10 years; however, a plateau has been reached in the efficacy of 5-FU, mandating a paradigm shift for those involved in colorectal cancer drug development. One direction vigorously pursued is the development of orally administered fluoropyrimidines that maintain or improve upon the effectiveness of intravenous 5-FU. In this paper the preclinical and clinical development of oral fluoropyrimidines and their modulators is reviewed, including UFT, capecitabine, ethynyluracil and S-1.     

Chimeric anti-ganglioside GM2 antibody with antitumor activity

Ganglioside GM2, which is one of the major gangliosides expressed on the cell surface of human tumors of neuroectodermal origin, has been focused on as a target molecule for passive immunotherapy. GM2 is thought to be one of the T-cell-independent antigens and to elicit only IgM antibody responses in rodents and humans. We have previously established two murine anti-GM2 monoclonal antibodies with high specificity and strong binding activity, KM696 and KM697, both of which are of the IgM class. Variable heavy and light chain complementary DNAs of these two murine monoclonal antibodies were cloned and used in the construction of mouse/human IgG1 chimeric antibodies, KM966 and KM967, respectively, in this study. One of the chimeric antibodies, KM966, retained strong and specific reactivity with GM2 and showed the similarity of the binding activity with tumor cell lines to that of the original murine monoclonal antibody. Indirect immunofluorescence staining of tumor cell lines with the chimeric KM966 revealed that the antigen was expressed in substantial amounts on pulmonary tumor cells and leukemia cells as well as neuroectodermal origin tumor cells. When human serum and human peripheral blood mononuclear cells were used as effectors in complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity, respectively, chimeric KM966 was fully effective in killing GM2-expressing tumor cells. In addition, i.v. injection of chimeric KM966 markedly suppressed the establishment of human tumor xenografts in nude mice. Taken together, chimeric KM966 is the first antibody of the human IgG class to ganglioside GM2 and has strong antitumor activity both in vitro and in vivo. It is likely that chimeric KM966 will be a useful agent for passive immunotherapy of human cancer.     

5-Fluorouracil-resistant colonic tumors are highly responsive to sodium butyrate/interleukin-2 bitherapy in rats

Advanced colorectal cancer is generally refractory to 5-fluorouracil (5-FU) chemotherapy. This is linked to the emergence of resistant cell populations, probably due to a selection process. The identification of molecular markers and the improvement of alternative therapies thus remain important. We have used as an experimental model a rat colon cancer cell line (PROb), which exhibits features similar to those of the human situation. 5-FU treatment of rats bearing PROb tumors enhanced their survival but did not lead to cure. A PROb 5-FU-resistant subline (PRObR1) was obtained by continuous in vitro exposure to 5-FU. Resistance to 5-FU was accompanied by a 2-fold increase in thymidylate synthase activity and a substantially higher incorporation of thymidine in the presence of 5-FU, compared with parental PROb cells. Unexpectedly, in syngeneic rats, PRObR1 tumors exhibited delayed growth when compared with parental PROb tumors. This was ascribed to an increased sensitivity of PRObR1 cells to host immune response since no growth delay was observed in immunocompromised nude mice and since there was no detectable difference in proliferation rates between PROb and PRObR1 cells. 5-FU treatment was inefficient in prolonging the survival of rats bearing PRObR1 tumors. In contrast, an immunotherapeutic protocol combining sodium butyrate and recombinant interleukin-2 (NaBut/rIL-2) cured 80% of the rats bearing established PRObR1 tumors. Our results suggest that NaBut/rIL-2 treatment is efficient against 5-FU-chemoresistant rat colon cancer.     

Postsurgical oral administration of uracil and tegafur inhibits progression of micrometastasis of human breast cancer cells in nude mice

We recently established a metastasis model in nude mice using the MKL-4 cell line, a contransfectant of the MCF-7 human breast cancer cell line with fgf-4 and lacZ in which micrometastases in several organs can be quantitatively observed. First, to develop a new postsurgical metastasis model, we investigated the timing of occurrence of micrometastasis and the influence of tumor removal on the progression of micrometastasis in this model. Micrometastases into lymph nodes and lungs were detected 3 weeks after the cell injections. Tumor removal 3 weeks after the injections significantly enhanced the progression of micrometastasis into lymph nodes and bone. Second, to study the effect of a mixed compound, UFT (a molar ratio of uracil:tegafur of 4:1), which has been widely used in the postsurgical adjuvant setting in Japan, 15 or 20 mg/kg UFT were administered p.o. for 4 weeks to tumor-bearing mice or to mice in which transplanted tumors were resected 3 weeks after the injections. Either dose of UFT significantly inhibited the tumor growth as well as the progression of micrometastasis into lymph nodes, lungs, liver, and brain. In addition, enhanced progression of micrometastasis in all explored organs by the tumor removal was significantly inhibited by the administration of either dose of UFT. In conclusion, this new postsurgical metastasis model may be useful for evaluating the efficacy of agents used in the postoperative adjuvant setting. UFT may be an effective drug for inhibiting the progression of micrometastasis after surgery.