Nobuko Ohmoto

MDR1 genotype-related pharmacokinetics of digoxin after single oral administration in healthy Japanese subjects.

AbstractPurpose. To evaluate the MDR1 genotype frequency in the Japanese population and to study the relationship between the MDR1 genotype and the pharmacokinetics of digoxin after single oral administration in healthy subjects. Methods. The MDR1 genotype at exon 26 was determined in 114 healthy volunteers by polymerase chain reaction-restriction fragment length polymorphism. The serum concentration-time profile of digoxin was examined after single oral administration at a dose of 0.25 mg. Results. It was found that 35.1 % (40/114) of subjects were homozygous for the wild-type allele (C/C), 52.6 % (60/114) were compound heterozygotes with a mutant T-allele (C3435T) (C/T), and 12.3 % (14/114) were homozygous for the mutant allele (T/T). There was no effect of gender or age on the distribution. The serum concentration of digoxin after a single oral administration increased rapidly, attaining a steady state in all subjects; however, it was lower in the subjects harboring the T-allele. AUC0-4 h values (±SD) were 4.11 ± 0.57, 3.20 ± 0.49, and 3.27± 0.58 ng h/ml, respectively, with a significant difference between C/C and C/T or T/T. Conclusions. The serum concentration of digoxin after single oral administration was lower in the subjects harboring a mutant allele (C3435T) at exon 26 of the MDR1 gene.

Simvastatin and lovastatin, but not pravastatin, interact with MDR1

The 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA) reductase inhibitor, pravastatin, was compared with simvastatin and lovastatin from the viewpoint of susceptibility to interaction with or via the multidrug transporter, MDR1 (P‐glycoprotein). This was carried out using the MDR1‐overexpressing cell line LLC‐GA5‐COL150, established by transfection of MDR1 cDNA into porcine kidney epithelial LLC‐PK1 cells, and [3H]digoxin, which is a well‐documented substrate for MDR1. Pravastatin, at 25–100 μM, had no effect on the transcellular transport of [3H]digoxin whereas simvastatin and lovastatin suppressed the basal‐to‐apical transport of [3H]digoxin and increased the apical‐to‐basal transport. It was suggested that recognition by MDR1 was due to the hydrophobicity. In conclusion, simvastatin and lovastatin are susceptible to interaction with or via MDR1, but pravastatin is not. This is important information when selecting the HMG‐CoA reductase inhibitors for patients taking drugs that are MDR1 substrates.

Effects of 12 Ca2+ antagonists on multidrug resistance, MDR1-mediated transport and MDR1 mRNA expression

The effects of 12 Ca(2+) antagonists on MDR1 were examined by two independent models: the inhibitory effect on MDR1-mediated transport of [(3)H]digoxin using MDR1-overexpressing LLC-GA5-COL150 cell monolayers and the reversal effect on cytotoxicity of vinblastine or paclitaxel using MDR1-overexpressing Hvr100-6 cells. The inhibitory effects on [(3)H]digoxin transport were assessed as the 50% inhibitory concentration during 4 h exposure, and the values were the lowest for nicardipine (4.54 microM), manidipine (4.65 microM) and benidipine (4.96 microM), followed by bepridil (10.6 microM), barnidipine (12.6 microM), efonidipine (13.0 microM), verapamil (13.2 microM) and nilvadipine (18.0 microM). The reversal effect on cytotoxicity was assessed by the 50% growth inhibitory concentration after 3 days exposure, and the resistance to vinblastine or paclitaxel in Hvr100-6 cells was reversed by manidipine, verapamil, benidipine, barnidipine, and nicardipine, in that order. Bepridil, barnidipine, efonidipine, verapamil and nilvadipine showed similar inhibitory effects on [(3)H]digoxin transport, but barnidipine and verapamil showed a stronger effect in reversal of cytotoxicity. Real-time quantitative RT-PCR assay indicated a decrease in MDR1 mRNA expression by barnidipine and verapamil. It is concluded that Ca(2+) antagonists cannot only be direct inhibitors of MDR1 but that some may at the same time act as inhibitors of expression of MDR1 via down-regulation of MDR1 mRNA.

Gene expression profiles of ABC transporters and cytochrome P450 3A in Caco-2 and human colorectal cancer cell lines.

AbstractPurpose. The mRNA levels of MDR1 (P-glycoprotein), multidrug resistance-associated proteins (MRP1, MRP2), cytochrome P450 3A (CYP3A) and villin in human colorectal cell lines (HCT-15, LoVo, DLD-1, HCT-116 and SW620) were quantitatively compared with those in Caco-2 cells. Methods. The mRNA levels were determined by real time quantitative polymerase chain reaction and expressed as the relative concentrations of MDR1 mRNA to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA. Results. MDR1 mRNA was expressed in HCT-15 LoVo and DLD-1 cells at similar or lower level to Caco-2. The expression of MRP1 mRNA in the cell lines tested was comparable with Caco-2. MRP2 mRNA was detected only in HCT-116 and SW620 at significantly lower level than Caco-2. CYP3A mRNA was detected in HCT-15, LoVo, DLD-1 and SW620 at similar level to Caco-2. Conclusions. HCT-15 LoVo and DLD-1 cells express proteins important for regulating the intestinal absorption of drugs, i.e., MDR1, MRP1 and CYP3A, whereas HCT-116 and SW620 cells were not acceptable for evaluation of absorption properties of drug candidates.