Catabolism of 5-fluoro-2'-deoxyuridine by isolated rat intestinal epithelial cells.
The kinetics of conversion of 5-fluoro-2'-deoxyuridine (FdUrd) to 5-fluorouracil (FUra) by isolated rat intestinal epithelial cells was investigated. Also, the effects of potential inhibitors of this reaction, which is catalyzed by uridine phosphorylase and thymidine phosphorylase, were determined. A 2.5% suspension of isolated cells was incubated with FdUrd or FUra, and at specific times cells were lysed with perchloric acid and fluoropyrimidines were determined by high-performance liquid chromatography. During a 25-min incubation with either FdUrd or FUra, the amount of drug in the incubation system (total volume 0.8 ml) fell by less than 5%. However, in the presence of FdUrd, the amount of FUra increased linearly over 25 min. The apparent Vmax and Km for FUra formation were 17-27 nmole/mg DNA/min and 1.6-2.5 mM, respectively. With each nucleoside phosphorylase inhibitor, the apparent Km increased but Vmax was unaffected. The apparent Ki values were as follows (in mM): 5-nitrouracil (an inhibitor of both uridine phosphorylase and thymidine phosphorylase), 0.12; 4-thiothymine (a uridine phosphorylase-selective inhibitor), 1.52; and 6-benzyl-2-thiouracil (a thymidine phosphorylase-selective inhibitor), 0.73. It was concluded that intestinal epithelial cells are capable of degrading FdUrd to FUra and that the cells possess both uridine phosphorylase and thymidine phosphorylase activity.
Lin
F H
FH
Department of Pharmacology and Toxicology, University of Louisville, Kentucky 40292.
Williams
W M
WM
D000818:Animals; D004848:Epithelium / Q000378:metabolism; D005467:Floxuridine / Q000378:metabolism*; D005472:Fluorouracil / Q000378:metabolism; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D010430:Pentosyltransferases / Q000037:antagonists & inhibitors; D057845:Pyrimidine Phosphorylases; D051381:Rats; D011919:Rats, Inbred Strains; D013936:Thymidine / Q000031:analogs & derivatives / Q000494:pharmacology; D014498:Uracil / Q000031:analogs & derivatives / Q000494:pharmacology
D005467:Floxuridine; D014498:Uracil; C057449:5-nitrouracil; D010430:Pentosyltransferases; D057845:Pyrimidine Phosphorylases; D005472:Fluorouracil; D013936:Thymidine