Showing papers by "Richard B. Kim published in 2000"

Pharmacological Inhibition of P-glycoprotein Transport Enhances the Distribution of HIV-1 Protease Inhibitors into Brain and Testes

Abstract: HIV protease inhibitors have proven remarkably effective in treating HIV-1 infection. However, some tissues such as the brain and testes (sanctuary sites) are possibly protected from exposure to HIV protease inhibitors due to drug entry being limited by the membrane efflux transporter P-glycoprotein, located in the capillary endothelium. Intravenous administration of the novel and potent P-glycoprotein inhibitor LY-335979 to mice (1-50 mg/kg) increased brain and testes concentration of [(14)C]nelfinavir, up to 37- and 4-fold, respectively, in a dose-dependent fashion. Similar effects in brain levels were also observed with (14)C-labeled amprenavir, indinavir, and saquinavir. Because [(14)C]nelfinavir plasma drug levels were only modestly increased by LY-335979, the increase in brain/plasma and testes/plasma ratios of 14- to 17- and 2- to 5-fold, respectively, was due to increased tissue penetration. Less potent P-glycoprotein inhibitors like valspodar (PSC-833), cyclosporin A, and ketoconazole, as well as quinidine and verapamil, had modest or little effect on brain/plasma ratios but increased plasma nelfinavir concentrations due to inhibition of CYP3A-mediated metabolism. Collectively, these findings provide "proof-of-concept" for increasing HIV protease inhibitor distribution into pharmacologic sanctuary sites by targeted inhibition of P-glycoprotein using selective and potent agents and suggest a new therapeutic strategy to reduce HIV-1 viral replication.

Cloning and expression of murine sister of P-glycoprotein reveals a more discriminating transporter than MDR1/P-glycoprotein.

Abstract: Sister of P-glycoprotein (SPGP), a novel murine cDNA and member of the ATP-binding cassette superfamily highly homologous to P-glycoprotein (Pgp), was cloned. Moreover, its genomic clone was isolated and localized to chromosome 2 by fluorescence in situ hybridization. SPGP was functionally evaluated relative to MDR1 after subcloning SPGP cDNA into a retroviral bicistronic vector capable of expressing both SPGP and the green fluorescent protein. LLC-PK1 and MDCKII cells were transduced with this retrovirus and SPGP-positive clones were isolated. Drug uptake and efflux was compared in cells ectopically expressing either SPGP or human MDR1. SPGP cells had decreased uptake of taurocholate and vinblastine compared with LLC-PK1 cells. Additional studies revealed that vinblastine efflux was accelerated by SPGP compared with LLC-PK1. Further comparison revealed that although MDR1 easily impaired uptake of vincristine, daunomycin, paclitaxel, and digoxin, SPGP had no effect on uptake of these drugs. However, further studies demonstrated that, like MDR1, SPGP effluxed calcein-acetoxymethyl ester (AM). Unlike MDR1, SPGP was incapable of effluxing rhodamine 123. Although cyclosporine A and reserpine blocked calcein-AM transport by MDR1, these drugs had either minimal or no effect, respectively, on blocking SPGP efflux of calcein-AM. In contrast, ditekiren, a linear hexapeptide, readily and preferentially inhibited SPGP efflux of calcein-AM. Further studies with three structural analogs of ditekiren revealed that one analog inhibited SPGP efflux of calcein-AM, although not as potently as ditekiren. These are the first studies to reveal that SPGP has distinct transport properties compared with MDR1.

Human β2-adrenergic receptor polymorphisms: No association with essential hypertension in black or white Americans

Abstract: Background and Objectives The most common polymorphisms of the human β2-adrenergic receptor-Arg16Gly and Gln27Glu-are associated with alterations in β2-adrenergic receptor responses, both in vitro and in vivo. β2-Adrenergic receptor–mediated vascular responses are affected by ethnicity, blood pressure, and genotype. We tested the hypothesis that these two common β2-adrenergic receptor genetic variants are associated with essential hypertension in black or white Americans. Subjects and Methods In a population-based case-control association study, the relationship between β2-adrenergic receptor genotypes and hypertension was examined in 307 normotensive subjects (128 black and 179 white) and 356 hypertensive subjects (155 black and 201 white). A polymerase chain reaction–based single-stranded conformational polymorphism method with direct sequencing of the bands of interest was used to detect the two frequently occurring β2-adrenergic receptor variants (Arg16Gly, Gln27Glu). Results No significant differences in the distributions of alleles and genotypes of the tested β2-adrenergic receptor variants were found between normotensive and hypertensive groups from either black or white Americans (all P > .05). There was a marked interethnic difference in the frequency of the Gln27Glu β2-adrenergic receptor polymorphism in both normotensive and hypertensive subjects. In normotensive white subjects, the variant Glu27 allele (35.2% versus 18.0%; P < .0001) and Glu27 homozygous genotype (14.0% versus 4.7%; P < .01) were more common than in black subjects. Similarly, in hypertensive white subjects, the variant Glu27 allele (35.8% versus 18.4%; P < .0001) and the Glu27 homozygous genotype (15.9% versus 2.6%; P < .0001) were more common than in black subjects. Conclusions These data suggest that although there are marked ethnic differences in their distribution, the common genetic polymorphisms of the human β2-adrenergic receptor gene do not cosegregate with the presence of hypertension in either black or white Americans. Clinical Pharmacology & Therapeutics (2000) 67, 670–675; doi: 10.1067/mcp.2000.106293

Mibefradil is a P-glycoprotein substrate and a potent inhibitor of both P-glycoprotein and CYP3A in vitro.

Abstract: Mibefradil, a calcium T- and L-channel blocker developed for use in hypertension, was recently removed from the market after reports of severe drug-drug interactions. Mibefradil is known to inhibit various cytochrome P450 enzymes involved in drug metabolism, particularly CYP3A. However, the extent and the severity of the observed drug interactions in humans suggest that inhibition of additional systems important to drug disposition, such as the drug transporter P-glycoprotein (P-gp), may also have contributed to the severity of the mibefradil interactions. A polarized epithelial cell line, LLC-PK1, which does not express P-gp, and the derived L-MDR1 cell line, which overexpresses human P-gp, were used to study the effects of mibefradil on drug transport. A markedly greater basal-to-apical versus apical-to-basal transport of [H3]mibefradil was seen in the L-MDR1, but not in the LLC-PK1 cells, suggesting that the drug is a substrate of P-gp. Using a human intestinal cancer-derived cell line Caco-2, which constitutively expresses P-gp, mibefradil was shown to be a potent inhibitor of P-gp-mediated digoxin transport, with an IC50 of 1.6 microM. Additionally, the effect of mibefradil on CYP3A was assessed using human liver microsomes. Mibefradil inhibited CYP3A-mediated nifedipine oxidase activity with an IC50 of 0.8 microM, and a Ki of 0.6 microM. Thus, mibefradil is not only a P-gp substrate, but also a potent inhibitor of both P-gp and CYP3A. These data suggest that the severity of drug interactions seen with mibefradil use is due to the dual inhibition of both P-gp and CYP3A.

Uptake of enalapril and expression of organic anion transporting polypeptide 1 in zonal, isolated rat hepatocytes.

Abstract: Sinusoidal entry is the first obligatory process preceding intracellular drug removal in liver. Transport of the angiotensin converting enzyme inhibitor enalapril (1–750 μM with [3H]enalapril), a substrate of Oatp1, the sodium-independent organic anion transporting polypeptide 1 cloned from rat liver, was studied in rat hepatocytes isolated from all zones of the liver (homogeneous) and from enriched periportal (PP) and perivenous (PV) hepatocytes prepared by collagenase perfusion and zone-selective destruction with digitonin, respectively. Uptake was linear over 1 min and was concentration-dependent. Transport by the homogeneous hepatocytes (in the presence and absence of Na+) and PP and PV cells was described by single saturable components of similar kinetic constants (Kmvalues of 344–461 μM and Vmax values of 9.5–11.6 nmol/min/106 cells; P > .05, ANOVA). The Km value for enalapril uptake in hepatocytes was of the same order of magnitude compared with that for Oatp1 expressed in HeLa cells transfected with cDNA-Oatp1 and Western blot analysis revealed similar levels of immunoreactive Oatp1 expression in PP and PV hepatocytes. However, enalapril was not taken up by Oatp2 nor by the human OATP expressed in recombinant vaccinia systems.

Antiviral therapy use of p-glycoprotein modulators

Abstract: The present invention relates to a pharmaceutical composition comprising a 10, 11 methanodibenzosuberane and use thereof for the treatment of HIV infection. Co-administration of the 10, 11 methanodibenzosuberane with an HIV protease inhibitor increases the concentration of the protease inhibitor in certain tissues, including the brain and testes, without substantially increasing plasma levels of the protease inhibitor. Accordingly, additional antiviral therapy can be achieved without use of increased drug dosages, thereby reducing the potential for occurrence of undesirable side effects deriving from drug toxicity.

Drug efflux transporters and antiviral drug therapy

Abstract: It is now becoming increasingly clear that for a drug to become truly successful as a therapeutic agent it must be not only specific and potent, but also capable of reaching target sites at relevant concentrations. This is particularly important for anti-infectives since failure to fully eradicate the pathogen may mean persistence or progression of the infection, which may allow for the emergence of drug-resistant variants. A key process governing target tissue drug levels appears to be the presence of carrier-mediated processes or transporters. Moreover, in addition to their role in drug distribution into various tissues, expression of drug transporters in organs such as the intestine, liver and kidney also affects absorption and excretion of many drugs. Clearly, consideration of transport systems earlier in the drug screening/discovery process may lead to candidate compounds with greater likelihood of more favourable disposition and target tissue penetration profiles in vivo. Accordingly, this review wi...