Practical Aspects of Transporter Model Systems: A Case Study Involving SQV

Pharmacokinetics and in vivo biodistribution of optimized PLGA nanoparticulate drug delivery system for controlled release of emtricitabine

The objective of this study was to develop systematically optimized (OPT) nanoparticles (NPs) providing a controlled release using PLGA of emtricitabine (FTC) employing Formulation by Design (FbD), and evaluate their in vitro and in vivo performance. FTC generates severe adverse effects with risks of toxicity. Thus, NPs were prepared to reduce these drawbacks in this study. The NPs were prepared by water-in-oil-in-water (w/o/w) emulsion method, followed by high-pressure homogenization. The FTC NPs were systematically OPT using 3(2) central composite design and the OPT formulation located using overlay plot. The pharmacokinetics and in vivo biodistribution of OPT-FTC NPs were investigated in male Wistar rats via the oral administration. Transmission electron microscopy studies on OPT-FTC NPs demonstrated uniform shape and size of particles. In vitro release was sustained up to 15 days in PBS pH 7.4. Augmentation in the values of Cmax (1.63 fold) and AUC0-∞ (5.39 fold) indicated significant enhancement in the rate and extent of bioavailability by the OPT-FTC NPs compared to pure drug. OPT-FTC NPs showed 2.325 fold increase in the values of FTC concentrations in liver. The OPT-FTC NPs was found to be quite stable during 6 months of study period. Hence, the developed OPT-FTC NPs can be used as drug carrier for sustained/prolonged drug release and/or to reduce toxic effects.

Impact of ATP-binding cassette transporters on human immunodeficiency virus therapy

Even though potent antiretrovirals are available against human immunodeficiency virus (HIV)-1 infection, therapy fails in a significant fraction of patients. Among the most relevant reasons for treatment failure are drug toxicity and side effects, but also the development of viral resistance towards the drugs applied. Efflux by ATP-binding cassette (ABC-) transporters represents one major mechanism influencing the pharmacokinetics of antiretroviral drugs and particularly their distribution, thus modifiying the concentration within the infected cells, that is, at the site of action. Moreover, drug-drug interactions may occur at the level of these transporters and modulate their activity or expression thus influencing the efficacy and toxicity of the substrate drugs. This review summarizes current knowledge on the interaction of antiretrovirals used for HIV-1 therapy with ABC-transporters and highlights the impact of ABC-transporters for cellular resistance and therapeutic success. Moreover, the suitability of different cell models for studying the interaction of antiretrovirals with ABC-transporters is discussed.

Interactions of Cyclosporin A with Breast Cancer Resistance Protein

The objective of this study was to investigate whether cyclosporin A (CsA) is a modulator for breast cancer resistance protein (BCRP). The interactions between CsA and BCRP were evaluated by using both membrane- and cell-based assays. CsA inhibited BCRP or BCRP R482T mutant-associated ATPase with an IC(50) of 26.1 and 7.3 microM (31,388 and 8779 ng/ml), respectively, indicating that CsA is a modulator for BCRP and its R482T mutant. The apparent permeability (P(app)) of CsA was not affected by the BCRP-specific inhibitor Ko143 in both apical-to-basolateral (A-to-B) and basolateral-to-apical (B-to-A) directions in hBCRP- or mBcrp-transfected MDCKII cells, whereas CsA at 50 microM significantly increased the A-to-B transport and decreased B-to-A transport of BCRP substrates, [(3)H]estrone-3-sulfate ([(3)H]E3S) and [(3)H]methotrexate ([(3)H]MTX), in hBCRP- and mBcrp1-trasfected MDCKII cells. Similar to cellular transport studies, CsA did not exhibit ATP-dependent uptake in BCRP-expressed membrane vesicles but inhibited the ATP-mediated E3S and MTX uptake in the same vesicles. The inhibitory constant (K(i)) of CsA toward BCRP was 6.7 microM (8507 ng/ml) and 7.8 microM (9380 ng/ml) when using E3S or MTX, respectively, as a BCRP substrate. The inhibitory potency of CsA on BCRP wild type or its R482T mutant was lower than that on P-glycoprotein. The present studies demonstrate that CsA is an inhibitor but not a substrate for BCRP, and has low potential to cause drug-drug interactions with BCRP substrate drugs due to its weak inhibitory effect on BCRP and BCRP R482T mutant at its normal therapeutic blood concentrations (200-400 ng/ml) (Blood 91:362-363, 1998).