Effects of gemcitabine on cis-platinum-DNA adduct formation and repair in a panel of gemcitabine and cisplatin-sensitive or -resistant human ovarian cancer cell lines.

Gemcitabine (dFdC) can increase the sensitivity of both cisplatin (CDDP)-sensitive and -resistant cell lines. It has been postulated that both formation and repair of platinum-(Pt)-DNA adducts are related to these effects. Therefore, we investigated the effects of dFdC on the formation and repair of Pt-DNA adducts in the human ovarian cancer cell line, A2780, and its CDDP- or dFdC-resistant variants, ADDP and AG6000, which have a different expression of various repair enzymes. Cells were exposed for 1 h to CDDP alone or combined with dFdC in IC50 concentrations, followed by a 1-h exposure to thiourea and, subsequently, by a drug-free period of 1, 3 or 23 h (i.e. 2, 4 or 24 h after CDPP +/- dFdC removal). Pt-DNA adducts were quantified with 32P-post-labeling. The gene expression of the repair enzymes, XPA and XRCC1, was the same in all 3 cell lines but ERCC1, ERCC3 and XPC were 2-6 times higher in AG6000 compared to A2780 cells. In contrast, both ERCC1 and ERCC3 were 10- and 1.5-fold lower in ADDP cells compared to A2780. The mismatch enzyme, MLH1, was lower in ADDP cells. At equally toxic CDDP concentrations, all cell lines formed comparable peak levels of total Pt-DNA adducts (36-48 fmol/microg DNA). However, the time at which peak levels were reached showed large variation. The repair of the adducts was very efficient in the resistant cell lines whereas, in A2780 cells, plateau levels were retained until 24 h after CDDP exposure. In A2780 cells, dFdC shifted the adduct peaks from 4 h to directly after CDDP exposure and increased peak levels by >3.9-fold. dFdC also enhanced the repair of adducts by >1.7-fold and increased the Pt-GG:Pt-AG ratio compared to CDDP alone by >1.4-fold. Overall, dFdC decreased the area under the Pt-DNA adduct-time curve (AUA0-25 h) in A2780 cells by 2.7-fold. In ADDP cells, dFdC shifted the adduct peaks from 2 to 4 h and increased them by >2.2-fold. dFdC also increased the Pt-GG:Pt-AG ratio during the repair process by 1.4-fold. Overall, dFdC increased the AUA0-25 h in ADDP cells by 1.7-fold. In AG6000 cells, dFdC increased the Pt-GG:Pt-AG ratio by 1.6-fold directly after exposure but did not clearly affect the AUA0-25 h. In conclusion, dFdC can affect both Pt-DNA adduct formation and repair, depending on the initial sensitivity of the cells.

The effect of food on the pharmacokinetics of S-1 after single oral administration to patients with solid tumors.

PURPOSE: The purpose is to determine the effect of food on the bioavailability of S-1, an oral formulation of the 5-fluorouracil (5FU) prodrug Ftorafur (FT), 5-chloro-2,4-dihydroxypyridine (CDHP), a dihydropyrimidine dehydrogenase inhibitor, and oxonic acid (an inhibitor of 5FU phosphoribosylation in normal gut mucosa) in a molar ratio of 1:0.4:1. EXPERIMENTAL DESIGN: Eighteen patients received a single dose of S-1 of 35 mg/m(2) with (535-885 kcal) or without food in a crossover study design: in arm A without breakfast on day -7 and with breakfast on day 0 and in arm B the reversed sequence. Blood samples were taken before and after S-1 administration. This food effect was evaluated according to the Food and Drug Administration guidelines using log-transformed data. RESULTS: Pharmacokinetic parameters for 5FU without breakfast were as follows: Tmax, 107 min; Cmax, 1.60 microm; area under the plasma concentration-time curve (AUC) 441 microm x min; and T(1/2), 104 min. Fasting decreased Tmax of FT, 5FU, CDHP, and oxonic acid significantly (P < 0.006) and increased the Cmax (P < 0.013). The food/fast ratio for the AUC of FT was not different, which for 5FU was 0.84 (P = 0.041), for CDHP was 0.89 (P = 0.191), for oxonic acid was 0.48 (P < 0.0005), and for cyanuric acid, the breakdown product of oxonic acid, was 5.1 (P = 0.019). Accumulation of uracil, indicative for dihydropyrimidine dehydrogenase inhibition, was not affected, as well as the T(1/2) of FT, 5FU, CDHP, and oxonic acid. Evaluation of the log-transformed data demonstrated that the 90% confidence interval for the food/fast ratio for the Cmax and AUC of FT, 5FU, CDHP, and uracil were within 70-143% and 80-125%, respectively, indicating no food effect. Only for oxonic acid and cyanuric acid were these values outside this interval. CONCLUSIONS: Food intake affected only the pharmacokinetics of the S-1 constituent oxonic acid but not of FT, CDHP, and 5FU. Because oxonic acid is included to protect against gastrointestinal toxicity, this observation might affect the gastrointestinal toxicity and thus the efficacy of S-1.

High-dose 5-Fluorouracil with uridine-diphosphoglucose rescue increases thymidylate synthase inhibition but not 5-Fluorouracil incorporation into RNA in murine tumors.

5-Fluorouracil (5FU) shows a steep dose response curve in several experimental systems, but the clinical use of high doses is hampered by the toxic side effects of this drug. Uridine diphosphoglucose (UDPG) rescue allows an increase in the maximum tolerated dose of 5FU in mice from 100 (FU(100)) to 150 mg/kg (5FU(150)+UDPG) and the higher dose is more effective than the standard treatment against several tumors. In the present paper we report on the effect of high-dose 5FU on thymidylate synthase (TS) levels and on 5FU incorporation into RNA. In the resistant murine tumor (Colon 26A) high-dose 5FU inhibited TS catalytic activity 8 h after treatment (4-fold; p = 0.00041) and the inhibition persisted until day 3 (p < 10(-4)). Standard-dose 5FU did not significantly inhibit TS activity. In a relatively sensitive tumor (Colon 26-10), there was no difference in the initial extent of TS inhibition by the two 5FU doses, but TS was still inhibited (2-fold) on day 3 after (5FU(150)+UDPG) while it was within the normal range after 5FU(100). In both tumor types TS activity showed an impressive rebound (3-fold) on days 3-7, and this occurred after both 5FU doses. In Colon 26A, however, a new 5FU injection on day 7 was still able to inhibit TS but not as effectively as the first dose. 5FU incorporation into RNA reached similar peak values (8 pmol/microg RNA) after the two 5FU doses, but the clearance was faster in mice receiving UDPG rescue. We conclude that UDPG does not interfere with the extent of TS inhibition by 5FU, but UDPG allows the use of a higher dose of 5FU resulting in enhanced TS inhibition. UDPG, however, increases 5FU clearance from RNA. In this experimental system the inhibition of TS seems essential in order to obtain a good antitumor activity, while 5FU incorporation into RNA does not seem to play a role in the antitumor activity of 5FU. Since preliminary results indicate that UDPG is well tolerated by patients, the use of higher 5FU doses may improve the response rate of human tumors.