Association of enzyme and transporter genotypes with the pharmacokinetics of imatinib.
OBJECTIVE
Our objective was to explore the relationships between imatinib pharmacokinetics and 9 allelic variants in 7 genes coding for adenosine triphosphate-binding cassette transporters (ABCB1 and ABCG2) and enzymes (cytochrome P450 [CYP] 2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A5) of putative relevance for imatinib.


METHODS
Imatinib transport in vitro was studied by use of human embryonic kidney 293 cells transfected with wild-type ABCG2 and an ABCG2 Q141K clone. Steady-state pharmacokinetics of imatinib was obtained in 82 patients with gastrointestinal stromal tumors treated with oral imatinib at doses ranging from 100 to 1000 mg/d. Genotyping was carried out via direct sequencing or restriction fragment length polymorphism-based techniques.


RESULTS
Human embryonic kidney 293 cells transfected with ABCG2 Q141K exhibited greater drug accumulation in vitro in comparison with cells expressing wild-type ABCG2 (P = .028). However, pharmacokinetic parameters of imatinib in vivo were not statistically significantly different in 16 patients who were heterozygous for ABCG2 421C>A compared with 66 patients carrying the wild-type sequence (P = .479). The apparent oral clearance of imatinib was potentially reduced in individuals with at least 1 CYP2D6*4 allele (median, 7.78 versus 10.6 L/h; P = .0695). Pharmacokinetic parameters were not related to any of the other multiple-variant genotypes (P >or= .230), possibly because of the low allele frequencies.


CONCLUSIONS
This study indicates that common genetic variants in the evaluated genes have only a limited impact on the pharmacokinetics of imatinib. Further investigation is required to quantitatively assess the clinical significance of homozygous variant ABCG2 and CYP2D6 genotypes in patients treated with imatinib.
Gardner
Erin R
ER
Clinical Pharmacology Research Core, SAIC-Frederick, Frederick, USA.
Burger
Herman
H
van Schaik
Ron H
RH
van Oosterom
Allan T
AT
de Bruijn
Ernst A
EA
Guetens
Gunther
G
Prenen
Hans
H
de Jong
Floris A
FA
Baker
Sharyn D
SD
Bates
Susan E
SE
Figg
William D
WD
Verweij
Jaap
J
Sparreboom
Alex
A
Nooter
Kees
K
D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D001549:Benzamides; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D045744:Cell Line, Tumor; D015331:Cohort Studies; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D005260:Female; D005770:Gastrointestinal Neoplasms / Q000235:genetics / Q000378:metabolism; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D000068877:Imatinib Mesylate; D007527:Isoenzymes / Q000235:genetics; D008297:Male; D008875:Middle Aged; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D010641:Phenotype; D010879:Piperazines / Q000493:pharmacokinetics*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics; D011743:Pyrimidines / Q000493:pharmacokinetics*; D017154:Stromal Cells / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D001549:Benzamides; D002352:Carrier Proteins; D007527:Isoenzymes; D004364:Pharmaceutical Preparations; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D003577:Cytochrome P-450 Enzyme System; D011505:Protein-Tyrosine Kinases; D019009:Proto-Oncogene Proteins c-kit