Mikio Kakumoto

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.

Intravenous Infusion of an Antisense Oligonucleotide Results in Exon Skipping in Muscle Dystrophin mRNA of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease that is characterized by muscle dystrophin deficiency. We report that intravenous (IV) infusion of an antisense oligonucleotide created an in-frame dystrophin mRNA from an out-of-frame DMD mutation (via exon skipping) which led to muscle dystrophin expression. A 10-year-old DMD patient possessing an out-of-frame, exon 20 deletion of the dystrophin gene received a 0.5 mg/kg IV infusion of an antisense 31-mer phosphorothioate oligonucleotide against the splicing enhancer sequence of exon 19. This antisense construct was administered at one-week intervals for 4 wk. No side effects attributable to infusion were observed. Exon 19 skipping appeared in a portion of the dystrophin mRNA in peripheral lymphocytes after the infusion. In a muscle biopsy one week after the final infusion, the novel in-frame mRNA lacking both exons 19 and 20 was identified and found to represent approximately 6% of the total reverse transcription PCR product. Dystrophin was identified histochemically in the sarcolemma of muscle cells after oligonucleotide treatment. These findings demonstrate that phosphorothioate oligonucleotides may be administered safely to children with DMD, and that a simple IV infusion is an effective delivery mechanism for oligonucleotides that lead to exon skipping in DMD skeletal muscles.

Effect of micafungin on cytochrome P450 3A4 and multidrug resistance protein 1 activities, and its comparison with azole antifungal drugs.

The effects of micafungin on cytochrome P450 3A4 (CYP3A4) metabolic and multidrug resistance protein 1 (MDR1) transport activities were investigated and compared with those of amphotericin B and four azole antifungal drugs (ketoconazole, itraconazole, fluconazole and miconazole). The effects on the metabolic activity of CYP3A4 were examined by measuring nifedipine oxidase activity in human liver microsomes and the effects on MDR1 transport activity were evaluated using [3H]digoxin in MDR1‐overexpressing LLC‐GA5‐COL150 cells. An inhibitory effect on CYP3A4 activity was found for ketoconazole, itraconazole and miconazole, with 50% inhibitory concentrations of 11.7, 32.6 and 74.2 nM, respectively. Fluconazole and micafungin had only slight inhibitory effects and amphotericin B had no effect. The MDR1‐mediated transport of [3H]digoxin was inhibited by ketoconazole and itraconazole, and slightly by miconazole. It is suggested that micafungin and amphotericin B would be unlikely to cause drug‐drug interactions by inhibition of CYP3A4 and MDR1. A positive correlation between the inhibitory effects on CYP3A4 and MDR1 activities was observed, and the physicochemical mechanisms involved and impact on clinical treatment should be studied further.

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.

Interaction of digoxin with antihypertensive drugs via MDR1

The multidrug transporter MDR1 (P-glycoprotein)-mediated interaction between digoxin and 29 antihypertensive drugs of various types was examined by using the MDR1 overexpressing LLC-GA5-COL150 cells, which were established by transfecting MDR1 cDNA into porcine kidney epithelial LLC-PK1 cells. These cells construct monolayers with tight junctions, and enable the evaluation of transcellular transport. The MDR1 was highly expressed on the apical membrane (urine side). The basal-to-apical and apical-to-basal transcellular transport of [3H]digoxin in LLC-GA5-COL150 cells was time- and temperature-dependent. The basal-to-apical transport of [3H]digoxin was markedly increased, whereas the apical-to-basal transport was decreased in LLC-GA5-COL150 cells, compared with the host LLC-PK1 cells, suggesting that [3H]digoxin was a substrate for MDR1. Most of the Ca2+ channel blockers used here markedly inhibited basal-to-apical transport and increased apical-to-basal transport. Exceptions were diltiazem, nifedipine and nitrendipine, which hardly showed inhibitory effects on transcellular transport of [3H]digoxin. Alpha-blocker doxazosin and beta-blocker carvedilol also inhibited transcellular transport of [3H]digoxin, but none of the angiotensin converting enzyme inhibitors and AT1 angiotensin II receptor antagonists used here were active. These observations will promote understanding of the digoxin-drug interactions resulting from their actions on MDR1, and which may aid in avoiding these unexpected effects of digoxin.

Effects of carvedilol on MDR1 ‐mediated multidrug resistance: comparison with verapamil

The reversing effects of carvedilol and other β‐adrenoceptor antagonists on multidrug resistance (MDR) were assessed in HeLa cells and the MDR1‐overexpressing derivative Hvr100–6 cells, established by stepwise increases of vinblastine concentration in the culture medium. The inhibitory effects on the transcellular transport and intracellular accumulation of [3H]vinblastine and [3H]daunorubicin were also assessed using LLC‐GA5‐COL150 cell monolayers, established by transfection of human MDR1 cDNA into porcine kidney epithelial LLC‐PK, cells. The cytotoxic effects of vinblastine, paclitaxel, doxorubicin and daunorubicin in Hvr100–6 were reversed 1.4‐ to 7.1‐fold by carvedilol at the realistic clinical concentration of 1 μM, whereas other β‐adrenoceptor antagonists had weaker or no such effects. Transport experiments using LLC‐GA5‐COL150 cell monolayers demonstrated that this effect of carvedilol was due to the inhibition of MDR1‐mediated transport of vinblastine, paclitaxel, doxorubicin and daunorubicin. These MDR1‐mediated reversing effects of carvedilol were similar to those of 1 μM verapamil, suggesting that carvedilol could be a candidate modulator of MDR in clinical use. Since other β‐adrenoceptor antagonists had no inhibitory effect on transport, the effects of carvedilol were not related to β‐adrenoceptors and might have been due to antioxidant activity. (Cancer Sci 2003; 94: 81–86)

Haloperidol is an inhibitor but not substrate for MDR1/P-glycoprotein

The involvement of the multidrug resistant transporter MDR1/P‐glycoprotein in the penetration of haloperidol into the brain and absorption in the intestine was investigated to examine its role in inter/intra‐individual variability, using the porcine kidney epithelial cell line LLC‐PK1 and its MDR1‐overexpressing transfectant, LLC‐GA5‐COL150. The inhibitory effect of haloperidol on other MDR1 substrates was also investigated in terms of the optimization of haloperidol‐based pharmacotherapy. The transepithelial transport of [3H]haloperidol did not differ between the two cell lines, and vinblastine, a typical MDR1 substrate, had no effect on the transport, suggesting that haloperidol is not a substrate for MDR1, and it is unlikely that MDR function affects haloperidol absorption and brain distribution, and thereby the response to haloperidol. However, haloperidol was found to have an inhibitory effect on the MDR1‐mediated transport of [3H]digoxin and [3H]vinblastine with an IC50 value of 7.84 ± 0.76 and 3.60 ± 0.64 μM, respectively, suggesting that the intestinal absorption, not distribution into the brain, of MDR1 substrate drugs could be altered by the co‐administration of haloperidol in the clinical setting, although further clinical studies are needed.

Fractional Absorption of Active Absorbable Algal Calcium (AAACa) and Calcium Carbonate Measured by a Dual Stable-Isotope Method

With the use of stable isotopes, this study aimed to compare the bioavailability of active absorbable algal calcium (AAACa), obtained from oyster shell powder heated to a high temperature, with an additional heated seaweed component (Heated Algal Ingredient, HAI), with that of calcium carbonate. In 10 postmenopausal women volunteers aged 59 to 77 years (mean ± S.D., 67 ± 5.3), the fractional calcium absorption of AAACa and CaCO3 was measured by a dual stable isotope method. 44Ca-enriched CaCO3 and AAACa were administered in all subjects one month apart. After a fixed-menu breakfast and pre-test urine collection (Urine 0), 42Ca-enriched CaCl2 was intravenously injected, followed by oral administration of 44Ca-enriched CaCO3 without carrier 15 minutes later, and complete urine collection for the next 24 hours (Urine 24). The fractional calcium absorption was calculated as the ratio of Augmentation of 44Ca from Urine 0 to Urine 24/ augmentation of 42Ca from Urine 0 to Urine 24. Differences and changes of 44Ca and 42Ca were corrected by comparing each with 43Ca. Fractional absorption of AAACa (mean ± S.D., 23.1 ± 6.4), was distinctly and significantly higher than that of CaCO3 (14.7 ± 6.4; p = 0.0060 by paired t-test). The mean fractional absorption was approximately 1.57-times higher for AAACa than for CaCO3. The serum 25(OH) vitamin D level was low (mean ± S.D., 14.2 ± 4.95 ng/ml), as is common in this age group in Japan. Among the parameters of the bone and mineral metabolism measured, none displayed a significant correlation with the fractional absorption of CaCO3 and AAACa. Higher fractional absorption of AAACa compared with CaCO3 supports previous reports on the more beneficial effect of AAACa than CaCO3 for osteoporosis.

Effects of α-adrenoceptor antagonist doxazosin on MDR1-mediated multidrug resistance and transcellular transport

The purpose of this study is to examine the effects of doxazosin, an alpha-adrenoceptor antagonist, on P-glycoprotein/MDR1-mediated multidrug resistance (MDR) and the transport of anticancer drugs. The effects of doxazosin, prazosin, and terazosin on MDR1-mediated MDR were assessed in human cervical carcinoma HeLa cells and the MDR1-overexpressing derivative Hvrl00-6, established by stepwise increases of the vinblastine concentration in the culture medium. The effects of doxazosin on the transcellular transport and intracellular accumulation of [3H]vinblastine, [3H]daunorubicin, and [3H]digoxin, all MDR1 substrates, were evaluated using LLC-GA5-COL150 cell monolayers, established by transfection of human MDR1 cDNA into porcine kidney epithelial LLC-PK1 cells. The sensitivity to vinblastine and paclitaxel of Hvrl00-6 cells was increased at 3.4- and 17.5-fold, respectively, by the addition of 1 microM doxazosin, whereas prazosin and terazosin had weaker or no such effects. Prazosin at 1 microM had a reversal effect on the sensitivity to vinblastine, whereas terazosin had no effect. In transport experiments, doxazosin concentration dependently increased the apical-to-basal transport of radiolabeled drugs in LLC-GA5-COL150 cells, but did not show remarkable effects on the basal-to-apical transport. In addition, doxazosin restored the intracellular accumulation in a concentration-dependent manner in LLC-GA5-COL150 cells. Doxazosin may partly reverse MDR by inhibiting MDR1-mediated transport, making it a candidate lead compound in the development of a reversing agent for MDR.