Identification of functional single nucleotide polymorphism haplotypes in the cytidine deaminase promoter.

Cytidine deaminase (CDA) hydrolytically deaminates and irreversibly deactivates the chemotherapeutic agent cytosine arabinoside (Ara-C), a deoxycytidine analog used for treatment of acute leukemias and lymphomas. To determine if single nucleotide polymorphisms (SNPs) in the promoter region of CDA affected gene expression, we sequenced approximately 1.6 Kb upstream of the CDA translation initiation site and containing the proximal promoter of CDA. We identified 6 SNPs; -92A>G, -205C>G, -451C>T, -897C>A, -1075A>G and -1181G>A. Based on predicted changes in transcription factor binding sites, three SNPs (-92A>G, -451C>T and -897C>A) were chosen for further investigation. The five haplotypes segregating in the population were cloned into a luciferase expression plasmid, transfected into Cos-1 cells and reporter activity measured at 24 and 48 h. Four haplotypes showed an average expression which was 2.5-fold higher at 24 h (P<0.0001) and 3.3-fold higher at 48 h (P<0.0001) than the lowest expressing haplotype. When reanalyzed as single SNP genotypes, the differences in expression were significant, except for -897 C/A, at 24 h, but the magnitude of difference was reduced, suggesting that no single SNP completely accounts for the expression differences observed at the haplotype level. As predicted from the in vitro analysis, individuals homozygous for common haplotype (ACC/ACC) showed higher levels of CDA enzymatic activity as individuals heterozygous for the wild type and low expressing haplotype (ACC/ATC). As CDA promoter region haplotypes may influence Ara-C chemosensitivity, shown here in in vitro and in vivo studies, the clinical relevance of these findings should be examined.

Effect of St John's wort on imatinib mesylate pharmacokinetics.

OBJECTIVE: Imatinib is a potent inhibitor of the Bcr-Abl and c- kit tyrosine kinases and is approved for the treatment of Philadelphia chromosome-positive chronic myelogenous leukemia and gastrointestinal stromal tumors. Because imatinib is predominantly metabolized by cytochrome P450 (CYP) 3A4, its pharmacokinetics may be altered when it is coadministered with drugs or herbs (eg, St John's wort) that modulate CYP3A4 activity. Thus we examined the effects of St John's wort on imatinib pharmacokinetics. METHODS: This 2-period, open-label, fixed-sequence study was completed by 12 healthy subjects (6 men and 6 women) aged between 20 and 51 years. Each subject received 400 mg imatinib orally on study day 1, St John's wort (300 mg 3 times daily) on days 4 to 17, and 400 mg imatinib again on day 15. Serial blood samples were obtained over a 72-hour period after each imatinib dose. Imatinib and N -desmethyl-imatinib (CGP 74588) were quantified in plasma by liquid chromatography-mass spectrometry. RESULTS: St John's wort administration increased imatinib clearance by 43% ( P < .001), from 12.5 +/- 3.6 L/h to 17.9 +/- 5.6 L/h; imatinib area under the concentration versus time curve (AUC) extrapolated to infinity was decreased by 30%, from 34.5 +/- 9.5 microg . h/mL to 24.2 +/- 7.0 microg . h/mL ( P < .001). Imatinib half-life (12.8 hours versus 9.0 hours) and maximum concentration (C max ) (2.2 microg/mL versus 1.8 microg/mL) were also significantly decreased ( P < .005). N -desmethyl-imatinib C max was increased from 285 +/- 95 ng/mL to 318 +/- 95 ng/mL during St John's wort dosing, but the AUC from 0 to 72 hours was not altered. CONCLUSIONS: These data indicate that St John's wort increases imatinib clearance. Thus patients taking imatinib should avoid taking St John's wort. Concomitant use of enzyme inducers, including St John's wort, may necessitate an increase in the imatinib dose to maintain clinical effectiveness.