Browsing by Author "Hosono, Naoya"

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    Differential quantification of CYP2D6 gene copy number by four different quantitative real-time PCR assays
    (Ovid Technologies (Wolters Kluwer) - Lippincott Williams & Wilkins, 2010-07) Ramamoorthy, Anuradha; Flockhart, David A.; Hosono, Naoya; Kubo, Michiaki; Nakamura, Yusuke; Skaar, Todd C.; Department of Medicine, IU School of Medicine
    Copy number variations (CNVs) in the CYP2D6 gene contribute to interindividual variation in drug metabolism. As the most common duplicated allele in Asian populations is the nonfunctional CYP2D6*36 allele, the goal of this study was to identify CNV assays that can differentiate between multiple copies of the CYP2D6*36 allele and multiple copies of other CYP2D6 alleles. We determined CYP2D6 gene copy numbers in 32 individuals with known CYP2D6 CNVs from the Coriell Japanese-Chinese panel using four quantitative real-time PCR assays. These assays target different regions of the CYP2D6 gene: 5'-flanking region, intron 2, intron 6, and exon 9 (Ex9). The specific target site of the Ex9 assay was verified by sequencing the PCR amplicon. Three of the CYP2D6 CNV assays (5'-flanking region, intron 2, and intron 6) estimated CYP2D6 copy numbers that were concordant for all 32 individuals. However, the Ex9 assay was concordant in only 10 of 32 samples. The 10 concordant samples did not contain any CYP2D6*36 alleles and the 22 discordant samples contained at least one CYP2D6*36 allele. In addition, the Ex9 assay accurately quantified all of the non-CYP2D6*36 alleles in all samples. Ex9 amplicon sequencing indicated that it targets a region of CYP2D6 exon 9 that undergoes partial gene-conversion in the CYP2D6*36 allele. In conclusion, CYP2D6 Ex9 CNV assay can be used to determine the copy number of non-CYP2D6*36 alleles. Selective amplification of non-CYP2D6*36 sequence by the Ex9 assay should be useful in determining the number of functional copies of CYP2D6 in Asian populations.
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    Significant effect of polymorphisms in CYP2D6 and ABCC2 on clinical outcomes of adjuvant tamoxifen therapy for breast cancer patients
    (American Society of Clinical Oncology, 2010-03-10) Kiyotani, Kazuma; Mushiroda, Taisei; Imamura, Chiyo K.; Hosono, Naoya; Tsunoda, Tatsuhiko; Kubo, Michiaki; Tanigawara, Yusuke; Flockhart, David A.; Desta, Zeruesenay; Skaar, Todd C.; Aki, Fuminori; Hirata, Koichi; Takatsuka, Yuichi; Okazaki, Minoru; Ohsumi, Shozo; Yamakawa, Takashi; Sasa, Mitsunori; Nakamura, Yusuke; Zembutsu, Hitoshi; Department of Medicine, IU School of Medicine
    Purpose The clinical efficacy of tamoxifen is suspected to be influenced by the activity of drug-metabolizing enzymes and transporters involved in the formation, metabolism, and elimination of its active forms. We investigated relationships of polymorphisms in transporter genes and CYP2D6 to clinical outcome of patients receiving tamoxifen. Patients and Methods We studied 282 patients with hormone receptor–positive, invasive breast cancer receiving tamoxifen monotherapy, including 67 patients who have been previously reported. We investigated the effects of allelic variants of CYP2D6 and haplotype-tagging single nucleotide polymorphisms (tag-SNPs) of ABCB1, ABCC2, and ABCG2 on recurrence-free survival using the Kaplan-Meier method and Cox regression analysis. Plasma concentrations of tamoxifen metabolites were measured in 98 patients receiving tamoxifen 20 mg/d. Results CYP2D6 variants were significantly associated with shorter recurrence-free survival (P = .000036; hazard ratio [HR] = 9.52; 95% CI, 2.79 to 32.45 in patients with two variant alleles v patients without variant alleles). Among 51 tag-SNPs in transporter genes, a significant association was found at rs3740065 in ABCC2 (P = .00017; HR = 10.64; 95% CI, 1.44 to 78.88 in patients with AA v GG genotypes). The number of risk alleles of CYP2D6 and ABCC2 showed cumulative effects on recurrence-free survival (P = .000000055). Patients carrying four risk alleles had 45.25-fold higher risk compared with patients with ≤ one risk allele. CYP2D6 variants were associated with lower plasma levels of endoxifen and 4-hydroxytamoxifen (P = .0000043 and .00052), whereas no significant difference was found among ABCC2 genotype groups. Conclusion Our results suggest that polymorphisms in CYP2D6 and ABCC2 are important predictors for the prognosis of patients with breast cancer treated with tamoxifen.