Inhibition of thymidylate synthase after administration of doxifluridine in a transplantable colon carcinoma in the rat.
Parameters for inhibition of thymidylate synthase (TS) in a DMH-induced transplantable rat colon carcinoma were studied after intraperitoneal administration of bolus doxifluridine (5'-dFUR) 200 mg/kg. Levels of 5'-dFUR, 5-fluorouracil (5-FU), fluorouridinediphosphate (FUDP), and fluorouridinetriphosphate (FUTP) were determined by use of high-performance liquid chromatography. Micromethods for analysis of 5-fluoro-2'-deoxyuridylate (FdUMP) and TS were used to study the in vivo intracellular pharmacokinetics of TS inhibition. Peak values of 5'-dFUR and 5-FU were found at 30 min and showed exponential declines with values close to zero at 5 hr. Substantial levels of FUDP and FUTP were found throughout the 24 h observation time. Peak FdUMP levels were modest compared to those observed after equimolar administration of 5-FU, but FdUMP persisted in amounts well above available binding sites on TS for the 24 h observation time. Reduction of free TS enzyme to undetectable levels (less than 0.05 pmol/g) lasted for 4 h, and at 24 h, there was still almost 70% enzyme inhibition. The total amount of TS (TStot) defined as free [3H]FdUMP-titrable enzyme (TSf) plus TS bound to FdUMP in a ternary complex (TSb) increased as a result of 5'-dFUR bolus injection from 15 to 50 pmol/g during the 24 hr observation time. We conclude from these data that 5'-dFUR is converted to 5-FU and subsequently to FdUMP, and the results suggest that 5'-dFUR exerts its cytotoxic effects through inhibition of TS and incorporation into RNA.
Berne
M
M
Department of Surgery, Ostra Sjukhuset University of Gothenburg, Sweden.
Gustavsson
B
B
Almersjö
O
O
Spears
P
P
Sundström
E
E
D000818:Animals; D002277:Carcinoma / Q000201:enzymology*; D003110:Colonic Neoplasms / Q000201:enzymology*; D005260:Female; D005467:Floxuridine / Q000493:pharmacokinetics* / Q000494:pharmacology; D005468:Fluorodeoxyuridylate / Q000493:pharmacokinetics; D005472:Fluorouracil / Q000493:pharmacokinetics; D008297:Male; D009368:Neoplasm Transplantation; D051381:Rats; D011919:Rats, Inbred Strains; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors* / Q000235:genetics
D005467:Floxuridine; D005468:Fluorodeoxyuridylate; D013940:Thymidylate Synthase; D005472:Fluorouracil; C025034:doxifluridine