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.
Shirasaka
T
T
Institute for Pathogenic Biochemistry in Medicine, Taiho Pharmaceutical Co., Ltd., Saitama, Japan.
Shimamato
Y
Y
Ohshimo
H
H
Yamaguchi
M
M
Kato
T
T
Yonekura
K
K
Fukushima
M
M
D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000009:adverse effects / Q000627:therapeutic use*; D042943:Dihydrouracil Dehydrogenase (NADP); D004357:Drug Synergism; D005472:Fluorouracil / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D005767:Gastrointestinal Diseases / Q000139:chemically induced / Q000517:prevention & control; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008297:Male; D010088:Oxidoreductases / Q000037:antagonists & inhibitors; D010094:Oxonic Acid / Q000008:administration & dosage / Q000627:therapeutic use*; D011355:Prodrugs / Q000008:administration & dosage / Q000627:therapeutic use*; D011725:Pyridines / Q000008:administration & dosage / Q000627:therapeutic use*; D051381:Rats; D011923:Rats, Nude; D012513:Sarcoma, Experimental / Q000188:drug therapy* / Q000473:pathology; D014407:Tumor Cells, Cultured
D011355:Prodrugs; D011725:Pyridines; D010094:Oxonic Acid; D010088:Oxidoreductases; D042943:Dihydrouracil Dehydrogenase (NADP); D005472:Fluorouracil; C104201:gimeracil