Formation pathways of gamma-butyrolactone from the furan ring of tegafur during its conversion to 5-fluorouracil.
Tegafur (FT) is a 5-fluorouracil (5-FU) prodrug that has been clinically used for various cancer chemotherapies. The following metabolites of FT were identified in patients: 5-FU, fluoro-beta-alanine, and gamma-butyrolactone (GBL) and its acidic form, gamma-hydroxybutyrate (GHB). GBL/GHB, which is probably generated from the furan ring of FT, inhibits tumor cell angiogenesis, contributing to the antitumor effect of FT-based therapies. In the present study, we identified the metabolites formed from the furan ring of FT by CYP2A6 and thymidine phosphorylase (TPase) using 2,4-dinitrophenylhydrazine derivatization procedures and clarified the metabolic pathway of FT to GBL/GHB. Succinaldehyde (SA) and 4-hydroxybutanal (4-OH-BTL) were produced as the metabolites because of the cleavage of the furan ring of FT during its conversion to 5-FU in cDNA-expressed CYP2A6 and purified TPase, respectively; however, GBL/GHB was hardly detected in cDNA-expressed CYP2A6 and purified TPase. GBL/GHB was formed after human hepatic microsomes or cDNA-expressed CYP2A6 mixed with cytosol were incubated with FT. Furthermore, 4-OH-BTL was converted to GBL/GHB in the microsomes and cytosol. These results suggest that GBL/GHB is generated from FT through the formation of SA and 4-OH-BTL but not directly from FT. Furthermore, the amount of 5-FU and GBL/GHB formed in the hepatic S9 was markedly decreased in the presence of a CYP2A6 inhibitor, suggesting that GBL/GHB may be mainly generated through the CYP2A6-mediated formation of SA.
Yamamiya
Ikuo
I
Tokushima Research Center, Taiho Pharmaceutical Co., Ltd., Kawauchi-cho, Tokushima, Japan. i-yamamiya@taiho.co.jp
Yoshisue
Kunihiro
K
Matsushima
Eiji
E
Nagayama
Sekio
S
D015107:4-Butyrolactone / Q000378:metabolism*; D000447:Aldehydes / Q000378:metabolism; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000378:metabolism; D000440:Butanols / Q000378:metabolism; D065637:Cytochrome P-450 CYP2A6; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D005472:Fluorouracil / Q000378:metabolism*; D005663:Furans / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000201:enzymology; D008862:Microsomes, Liver / Q000201:enzymology; D010659:Phenylhydrazines / Q000378:metabolism; D012978:Sodium Oxybate / Q000378:metabolism; D005641:Tegafur / Q000378:metabolism*; D013939:Thymidine Phosphorylase / Q000235:genetics / Q000378:metabolism
C553731:4-hydroxybutanal; D000447:Aldehydes; D000440:Butanols; D018076:DNA, Complementary; D005663:Furans; D010659:Phenylhydrazines; D005641:Tegafur; C004787:2,4-dinitrophenylhydrazine; C015515:succindialdehyde; D012978:Sodium Oxybate; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6; D013939:Thymidine Phosphorylase; D015107:4-Butyrolactone; D005472:Fluorouracil; C039281:furan