P-glycoprotein and transporter MRP1 reduce HIV protease inhibitor uptake in CD4 cells: potential for accelerated viral drug resistance?

Jones, Kevin F.; Pg, Bray; Sh, Khoo; Davey, RA; Er, Meaden; Ward, Stephen A.; Dj, Back

doi:10.1097/00002030-200107270-00004

Cited by 136 publications

(109 citation statements)

References 26 publications

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“…Saquinavir, nelfinavir, and ritonavir all showed significant nonspecific binding, which was corrected for throughout this study to provide true kinetic parameters. Nelfinavir has previously been shown to exhibit a higher degree of intracellular accumulation compared with other PIs (Jones et al, 2001;Khoo et al, 2002). Significantly higher metabolic rates (corresponding to lower K m values) were observed when the kinetics of saquinavir, nelfinavir, and ritonavir in rat liver microsomes were compared with suspended rat hepatocytes, ranging from 6-fold lower for ritonavir and saquinavir to 30-fold lower for nelfinavir.…”

Section: Hepatocellular Uptake and Drug Metabolic Clearancementioning

confidence: 96%

“…In vivo, hepatocytes express both efflux and uptake transporters, and it is important to consider that the apparent uptake rate may be affected by efflux rate, especially because PIs are well documented to be substrates for efflux transporters (Srinivas et al, 1998). An increase in uptake rate in cell lines expressing both P-gp and uptake transporters has been observed using P-gp inhibitors (Jones et al, 2001;Su et al, 2004). In freshly isolated rat hepatocytes, expression of efflux transporters may be significantly lower than in vivo due to downregulation and internalization of the apical membrane, and although P-gp has been detected on the hepatocyte apical membrane after isolation using immunohistochemical techniques, it is at a lower abundance than in vivo (Bow et al, 2008).…”

Section: Downloaded Frommentioning

confidence: 99%

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Rate-Limiting Steps in Hepatic Drug Clearance: Comparison of Hepatocellular Uptake and Metabolism with Microsomal Metabolism of Saquinavir, Nelfinavir, and Ritonavir

Parker

Houston²

2008

Drug Metab Dispos

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ABSTRACT:The intrinsic metabolic clearance of saquinavir, nelfinavir, and ritonavir was determined over a range of concentrations (0.02-20 M) in both rat liver microsomes and fresh isolated rat hepatocytes in suspension. Clearance values were found to be concentration dependent for both systems, and at low concentrations, microsomal clearance was much greater (7-14-fold) than in hepatocytes. Kinetic parameters showed substantially lower microsomal K m values (5-42 nM) compared with suspended rat hepatocytes (34-270 nM) but similar scaled V max values (2-26 nmol/min/g liver). In the absence of metabolism (achieved by pretreating hepatocytes with a mechanism-based inhibitor of cytochrome P450), saquinavir, nelfinavir, and ritonavir were actively and rapidly taken up into hepatocytes (cell/medium concentration ratios of 306-3352), and intracellular unbound drug concentrations between 5-and 12-fold higher than extracellular unbound concentrations were achieved. Comparison of the rate of uptake into hepatocytes with the rate of metabolism in hepatocytes and microsomes indicates that the former is the rate-limiting step at low concentrations. The rate of metabolism saturates at lower concentrations (100-400-fold) than the rate of uptake; hence, at the high concentrations metabolic rate-limited clearance occurs. In conclusion, the clearance of saquinavir, nelfinavir, and ritonavir is extremely rapid, and it is proposed that in the case of hepatocytes and by inference in vivo, the rate of uptake limits the metabolic clearance of these three drugs.

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Section: Hepatocellular Uptake and Drug Metabolic Clearancementioning

confidence: 96%

Section: Downloaded Frommentioning

confidence: 99%

Rate-Limiting Steps in Hepatic Drug Clearance: Comparison of Hepatocellular Uptake and Metabolism with Microsomal Metabolism of Saquinavir, Nelfinavir, and Ritonavir

Parker

Houston²

2008

Drug Metab Dispos

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“…Because the equilibrium between extra-and intracellular concentrations is often regulated by efflux proteins, changes in efflux protein activity may alter the sensitivity of the cells to these compounds like it has been demonstrated for saquinavir, ritonavir, and lopinavir (12,18,19). Decreased intra-cellular availability of the drug in response to upregulation of efflux transporters will therefore shift IC 50 values for antiproliferative effects towards higher (extracellular) concentrations and thus protect the cells.…”

Section: Growth Inhibition Assaysmentioning

confidence: 99%

Induction of Multiple Drug Transporters by Efavirenz

et al. 2009

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Abstract. Efavirenz, an important component of human immunodeficiency virus 1 (HIV-1) therapy, causes substantial drug interactions as an inducer of cytochromes and the transporter ABCB1. So far its effect on the expression of other transporters is unknown. We therefore investigated the effect of long-term exposure of cells to efavirenz on expression of a large number of important drug transporters and on cell proliferation as a surrogate of intracellular availability. LS180 cells were used as a surrogate for the major site of drug interactions and Jurkat cells were used as a surrogate for the main target cells of HIV therapy. Cells were treated with efavirenz over 4 weeks and mRNA expression of drug transporters was repeatedly quantified. After 4 weeks, efavirenz significantly up-regulated the mRNA of ABCB1, ABCG2, ABCC2, ABCC3, ABCC5, and SLCO3A1 in LS180 cells and ABCG2, ABCC1, ABCC4, ABCC5, and SLCO2B1 in Jurkat cells. However these changes in transporter expression did not influence cell proliferation indicating that intracellular efavirenz concentrations were likely not altered. Efavirenz induces mRNA expression of several drug transporters critically modulating the kinetics of other drugs. While these expressional changes will most likely not influence the efficiency of efavirenz itself, they might change the effect of other co-administered drugs.

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“…Due to the short half-lives of the PI's in rodents, 33) if auto-inhibition was not present and if steady-state concentrations had been reached prior to day 7, we would have expected plasma levels to remain more or less constant. 33) Recent studies found that P-gp inhibition could possibly have a superior influence over CYP3A4 modification in altering pharmacokinetics. 34) Over time, an equilibrium is reached and an increase in levels are observed.…”

Section: Discussionmentioning

confidence: 99%

Evidence for Time-Dependent Interactions between Ritonavir and Lopinavir/Ritonavir Plasma Levels Following P-Glycoprotein Inhibition in Sprague-Dawley Rats

Plooy

Viljoen

Rheeders

2011

Biological & Pharmaceutical Bulletin

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Protease inhibitors (PI's), such as ritonavir and lopinavir, form an integral part of combination antiretroviral therapy. The metabolism of the PI's is complex and is influenced by both the cytochrome P450 (CYP P450) enzymes in the liver as well as the efflux transporter, P-glycoprotein (P-gp). 1)However, there is conflicting reports in the literature on the influence of these two systems on the plasma levels of lopinavir and ritonavir after acute and chronic treatment. 1,2)The PI's are substrates for CYP P450 oxidative metabolism, predominantly CYP3A4.3) However, most of the PI's inhibit CYP3A4 specifically, 3) with ritonavir being one of the most potent. Earlier studies have found that ritonavir markedly increases the plasma concentration and prolongs the elimination of many concomitant drugs. 4) Indeed, the combination of ritonavir and lopinavir (LPV/r) has been designed specifically on the ability of ritonavir to enhance the bioavailability of lopinavir. 4) Studies in rats have noted that the bioavailability of lopinavir can be lower by as much as 25% when administered alone as compared to its levels following the administration of LPV/r. Moreover, the combination is associated with a significant increase in maximum plasma concentration (C max ) and area under the curve (AUC) for both ritonavir and lopinavir. 5) However, contradictory reports have found that plasma concentrations of ritonavir, or other co-administered drugs, are 'reduced' after chronic ritonavir treatment. 2,6,7)The multidrug efflux transporter, P-gp, is responsible for extracting substrate drugs from the site of absorption, and as such limits their intracellular drug accumulation and can thus contribute to treatment failure. 8) P-gp is an ATP-dependant membrane transporter with broad substrate specificity, capable of mediating efflux of a variety of structurally diverse drugs.9) There is a strong suggestion that different binding sites exist on the P-gp transporter, 10,11) while there is also evidence of competitive and non-competitive inhibition of these sites. 11) P-gp is expressed in a multitude of organs such as the liver, intestinal epithelial cells, kidney and blood-brain barrier in both humans and rodents. [12][13][14] The expression of this glycoprotein and its action to limit drug absorption and penetration into a desired target organ has important therapeutic implications, including the potential for sub-therapeutic drug levels, viral resistance and contributing to treatment failure.15) Controversy relating to the effect of PI's on the P-gp transport system is widely recognised, including whether these drugs are responsible for P-gp induction, 16) whether ritonavir and lopinavir are P-gp inhibitors 17) or whether or not PI's affect P-gp expression. 18)The calcium channel blocker, verapamil, is often used as an inhibitor of P-gp to investigate interactions between antiretroviral (ARV) drugs.19) Despite the aforementioned controversy, the effect of P-gp on ARV therapy is nevertheless significant. A number of studies in the literatur...

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P-glycoprotein and transporter MRP1 reduce HIV protease inhibitor uptake in CD4 cells: potential for accelerated viral drug resistance?

Cited by 136 publications

References 26 publications

Rate-Limiting Steps in Hepatic Drug Clearance: Comparison of Hepatocellular Uptake and Metabolism with Microsomal Metabolism of Saquinavir, Nelfinavir, and Ritonavir

Rate-Limiting Steps in Hepatic Drug Clearance: Comparison of Hepatocellular Uptake and Metabolism with Microsomal Metabolism of Saquinavir, Nelfinavir, and Ritonavir

Induction of Multiple Drug Transporters by Efavirenz

Evidence for Time-Dependent Interactions between Ritonavir and Lopinavir/Ritonavir Plasma Levels Following P-Glycoprotein Inhibition in Sprague-Dawley Rats

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