Table 2.

Effect of irinotecan administration on the activities of 5-FU–metabolizing enzymes in 4-1-ST, AZ-521, and SC-2 human gastric cancer xenografts in mice.

Tumor	4-1-ST		AZ-521		SC-2
Enzyme	Control	Irinotecan (75 mg/kg/wk × 2)	Control	Irinotecan (75 mg/kg/wk × 2)	Control	Irinotecan (75 mg/kg/wk × 2)
TS	2.163±0.281	1.375±0.184*	0.622±0.095	0.082±0.019*	0.089±0.043	0.086±0.033
DPD	2.22 ± 0.27	1.84 ± 0.34	78.10±12.59	53.87±15.40†	8.580±3.45	8.120±1.46
OPRT	8.119±0.663	7.599±0.806	6.649±0.772	4.726±0.600†	21.01±2.68	22.10±4.00
TP	1.011±0.018	1.168±0.157	0.115±0.030	0.103±0.025	0.647±0.154	0.676±0.105
RNR	2.030±0.975	3.076±1.183	0.483±0.282	0.660±0.099	4.330±1.840	4.150±0.730
TK	15.28±1.90	15.29± 3.41	31.10± 3.75	35.97± 6.86	32.01± 4.20	68.70±13.61

For each tumor, mice received saline (n=5) or irinotecan 75 mg/kg (n=5) administered IV weekly for 2 weeks. At 24 hours after last treatment, tumors were removed and activities of 5-FU-metabolizing enzymes were measured. TS = thymidylate synthase; DPD = dihydropyrimidine dehydrogenase; OPRT = orotate phosphoribosyltransferase; TP = thymidine phosphorylase; RNR = ribonucleotide reductase; TK = thymidine kinase.

^*P < .01

^†P < .05 compared with control group by Dunnett’s test