A novel mutant allele of the CYP2A6 gene (CYP2A6*11 ) found in a cancer patient who showed poor metabolic phenotype towards tegafur.
In a clinical study, a newly developed anticancer drug, TS-1 capsule, which contained tegafur (FT) and 5-chloro-2,4-dihydroxypyridine, an inhibitor of dihydropyrimidine dehydrogenase, was orally administered to five gastric cancer patients (patients 1-5). The total area under the plasma FT concentration-time curve in patient 1 was four-fold higher than in other patients. Since cytochrome P450 2A6 (CYP2A6) has been reported to metabolize FT to yield 5-fluorouracil (5-FU), it was postulated that the poor metabolic phenotype of patient 1 was caused by mutations of the CYP2A6 gene. Thus, alleles for the CYP2A6 genes derived from patient 1 were completely sequenced. It was found that one allele was CYP2A6*4C, which was a whole deleted allele for the human CYP2A6 gene. The other allele was a novel mutant allele (CYP2A6*11) in which thymine at nucleotide 670 was changed to cytosine. The nucleotide change caused an amino acid change from serine at residue 224 to proline. To examine whether or not the amino acid change affected CYP2A6 activity, we expressed an intact or mutant CYP2A6 together with NADPH-P450 oxidoreductase in Escherichia coli, and compared the capacity of the wild and mutant enzymes to metabolize FT to 5-FU. The Vmax value for FT metabolism by the mutant CYP2A6 was approximately one-half of the value of the intact CYP2A6, although the Km values were nearly the same. From these results, we conclude that the poor metabolic phenotype of patient 1 was caused by the existence of the two mutant alleles, CYP2A6*4C and the new variant CYP2A6*11.
Daigo
Satoshi
S
Laboratory of Drug Metabolism, Division of Pharmacobiodynamics, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Hokkaido, Japan.
Takahashi
Yoshiki
Y
Fujieda
Masaki
M
Ariyoshi
Noritaka
N
Yamazaki
Hiroshi
H
Koizumi
Wasaburo
W
Tanabe
Satoshi
S
Saigenji
Katsunori
K
Nagayama
Sekio
S
Ikeda
Kazumasa
K
Nishioka
Yasuhiko
Y
Kamataki
Tetsuya
T
D000284:Administration, Oral; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D019540:Area Under Curve; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics* / Q000378:metabolism; D003374:Coumarins / Q000378:metabolism; D065637:Cytochrome P-450 CYP2A6; D017931:DNA Primers / Q000737:chemistry; D004273:DNA, Neoplasm / Q000097:blood / Q000378:metabolism; D004338:Drug Combinations; D004926:Escherichia coli; D005838:Genotype; D006801:Humans; D007700:Kinetics; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010094:Oxonic Acid / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D011725:Pyridines / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D013274:Stomach Neoplasms / Q000201:enzymology / Q000235:genetics*; D005641:Tegafur / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D014162:Transfection
D000964:Antimetabolites, Antineoplastic; D003374:Coumarins; D017931:DNA Primers; D004273:DNA, Neoplasm; D004338:Drug Combinations; D011725:Pyridines; D011994:Recombinant Proteins; C079198:S 1 (combination); D005641:Tegafur; D010094:Oxonic Acid; C030123:coumarin; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6; C104201:gimeracil