Effects of 5-fluorouracil and a combination of tegafur and uracil (UFT) on nucleotide metabolism in L1210 ascites tumor

Effect of Phyllanthus amarus Extract on 5-Fluorouracil-Induced Perturbations in Ribonucleotide and Deoxyribonucleotide Pools in HepG2 Cell Line

The aim of this study was to investigate the antitumor activities of Phyllanthus amarus (PHA) and its potential of herb–drug interactions with 5-Fluorouracil (5-FU). Cell viability, ribonucleotides (RNs) and deoxyribonucleotides (dRNs) levels, cell cycle distribution, and expression of thymidylate synthase (TS) and ribonucleotide reductase (RR) proteins were measured with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, high performance liquid chromatography tandem mass spectrometry (HPLC/MS/MS) method, flow cytometry and Western blot analysis, respectively. Our standardized PHA extract showed toxicity to HepG2 cells at high concentrations after 72 h exposure and induced G2/M cell cycle arrest. Combined use of 5-FU with PHA resulted in significant decreases in ATP, CTP, GTP, UTP and dTTP levels, while AMP, CMP, GMP and dUMP levels increased significantly compared with use of 5-FU alone. Further, PHA could increase the role of cell cycle arrest at S phase induced by 5-FU. Although PHA alone had no direct impact on TS and RR, PHA could change the levels of RNs and dRNs when combined with 5-FU. This may be due to cell cycle arrest or regulation of key enzyme steps in intracellular RNs and dRNs metabolism.

Plasma, intestine and tumor levels of 5-fluorouracil in mice bearing L1210 ascites tumor following oral administration of 5-fluorouracil, UFT (mixed compound of tegafur and uracil), carmofur and 5'-deoxy-5-fluorouridine

Several 5-fluorouracil (5-FU) derivatives, 1-hexylcarbamoyl-5-fluorouracil (HCFU), 5'-deoxy-5-fluorouridine (5'-DFUR) and UFT (mixed compound of tegafur and uracil), have been developed and clinically widely used. However, comparative pharmacokinetic studies of the parent compound and other fluorinated drivatives have not been precisely reported. The dosage of the oral clinical use for human cancer of 5-FU, HCFU, 5'-DFUR and UFT as tegafur (FT) is 200-300mg/d, 600mg/d, 800-1,200mg/d and 300-600mg/d respectively. These amounts of the drugs are almost equimolar. Previously, we reported the effect of oral equimolar administration of each four drugs on thymidilate synthase activity, deoxyribonucleotide metabolism and cell cycle progression in L1210 ascites tumor. (1,2) In this study, we examined the antitumor effect and 5-FU concentration in the plasma, intestine and tumor after oral equimolar administrations of each drug using BDF1 mice bearing L1210 ascites tumor. In our study, UFT showed the best life prolongation among these four drugs. The intestine 5-FU level was highest by treatment with 5-FU during the initial 4 h. The plasma 5-FU level was highest by treatment with HCFU for 4 h. But the tumor 5-FU level was highest by treatment with UFT over the 24 h. In spite of the high plasma 5-FU concentration after the treatment with HCFU, the 5-FU concentration in the tumor was below the detectable level until 24 h. These findings suggested that the highest specific accumulation of 5-FU in tumor cells may explain the best therapeutic results of UFT.

Enhanced cytotoxic interaction between 5-fluorouracil and 4-hydroperoxycyclophosphamide against L1210 murine leukemic cells: applicability to ex vivo purging

Eradication of contaminated tumor cells in bone marrow is a matter of utmost concern in the setting of autologous bone marrow transplantation. 4-Hydroperoxycyclophosphamide (4-HC) is often used for ex vivo chemical purging of contaminated tumor cells in bone marrow. The marrow from patients pretreated with 5-fluorouracil (5-FU) is enriched with multifactor-responsive high proliferative potential colony-forming cells. To develop an efficient ex vivo chemical purging system, we evaluated interaction between 4-HC and 5-FU. We investigated the antitumor effect of cyclophosphamide, a mother compound of 4-HC, and 5-FU against L1210 ascites tumor in B6D2F1 mice. The median lifespan of the mice treated with 4-HC or 5-FU alone was 8 and 12 days, respectively. The combination of both drugs significantly extended the median lifespan to 18.5 days. The median effect plot analysis indicated a synergistic cytotoxic interaction between 5-FU and 4-HC in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl terazolium bromide (MTT) assay. Clonogenic assay also showed that combination of 4-HC and 5-FU significantly reduced L1210 leukemic colonies to 20% of untreated control. Bone marrow cells from the mice treated with 5-FU at 150 mg/kg body weight was resistant to 4-HC at concentrations as high as 0.2 microgram/ml, which was more than 70% inhibitory concentration for colony formation in L1210 leukemic cells. Findings suggest that sequential treatment with in vivo 5-FU followed by ex vivo 4-HC could selectively enhance antitumor effects of 4-HC in tumor cells remaining in bone marrow.

Effects of UFT (mixed compound of tegafur and uracil) on cell kinetics and inhibition of thymidylate synthase in L1210 ascites tumor

Previous work in our laboratory showed that UFT (mixed compound of tegafur and uracil, molar ratio 1:4, respectively) caused the prolonged reduction of dTTP in L1210 leukemia cells in comparison with 5-fluorouracil (5-FU). The purpose of this study was to assess the effect of UFT on cell cycle distribution and thymidylate synthase activity of a leukemia cell line as compared with 5-FU. UFT and 5-FU were orally given to BDF1 mice bearing L1210 ascites tumor on day 3 after the tumor inoculation. Cell cycle distribution patterns at 24 hr after the drug administration showed a higher percentage of S phase in tumor cells treated with UFT than in those treated with 5-FU. Until 6 hr after the oral administration of the drugs, UFT inhibited the incorporation of [3H] deoxyuridine into DNA more long than 5-FU did. These results indicated that UFT has longer and stronger inhibitory effects on DNA replication than 5-FU in vivo under the employed experimental conditions (i.e., low and single doses of these fluorinated pyrimidines).