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Assessment of drug transporter function using fluorescent cell imaging.

ABSTRACT: ATP-binding cassette (ABC) proteins, including the breast cancer resistance protein (BCRP) and multidrug resistance proteins (MDRs), actively transport structurally diverse chemicals from a number of tissues and are being increasingly cited as mediators of clinically relevant drug-drug interactions. The potential outcomes of concomitantly administering two drugs that interact at the same transporter include altered disposition and toxicity and/or efficacy of one or both of the drugs. Research demonstrating the role of transporters in clinical pharmacokinetics has shed light on the need for in vitro screening methods that detect drug-transporter interactions during preclinical development. This unit describes cell-based procedures for detecting functional inhibitors of BCRP and MDR1 by measuring fluorescent substrate accumulation in suspended cells using an automated cell counter, which offers convenience, sensitivity, and speed in measuring intracellular fluorescence and identifying new inhibitors. An alternative method is provided for making similar measurements using a spectrophotometer with fluorescence detection capabilities.

SUBMITTER: Bircsak KM

PROVIDER: S-EPMC3920305 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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Assessment of drug transporter function using fluorescent cell imaging.

Bircsak Kristin M KM Gibson Christopher J CJ Robey Robert W RW Aleksunes Lauren M LM

Current protocols in toxicology 20130923

ATP-binding cassette (ABC) proteins, including the breast cancer resistance protein (BCRP) and multidrug resistance proteins (MDRs), actively transport structurally diverse chemicals from a number of tissues and are being increasingly cited as mediators of clinically relevant drug-drug interactions. The potential outcomes of concomitantly administering two drugs that interact at the same transporter include altered disposition and toxicity and/or efficacy of one or both of the drugs. Research de ...[more]

PMID: 24510579

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Project description:ObjectiveThe objective of this study was to use noninvasive dynamic contrast-enhanced magnetic resonance imaging (MRI) techniques to study, in vivo, the distribution and elimination of the hepatobiliary contrast agent gadoxetate in the human body and characterize the transport mechanisms involved in its uptake into hepatocytes and subsequent efflux into the bile using a novel tracer kinetic model in a group of healthy volunteers.Materials and methodsTen healthy volunteers (age range, 18-29 years), with no history of renal or hepatic impairment, were recruited via advertisement. Participants attended 2 MRI visits (at least a week apart) with gadoxetate as the contrast agent. Dynamic contrast-enhanced MRI data were acquired for approximately 50 minutes with a 3-dimensional gradient-echo sequence in the axial plane, at a temporal resolution of 6.2 seconds. Data from regions of interest drawn in the liver were analyzed using the proposed 2-compartment uptake and efflux model to provide estimates for the uptake rate of gadoxetate in hepatocytes and its efflux rate into the bile. Reproducibility statistics for the 2 visits were obtained to examine the robustness of the technique and its dependence in acquisition time.ResultsEight participants attended the study twice and were included into the analysis. The resulting images provided the ability to simultaneously monitor the distribution of gadoxetate in multiple organs including the liver, spleen, and kidneys as well as its elimination through the common bile duct, accumulation in the gallbladder, and excretion in the duodenum. The mean uptake (ki) and efflux (kef) rates in hepatocytes, for the 2 visits using the 50-minute acquisition, were 0.22 ± 0.05 and 0.017 ± 0.006/min, respectively. The hepatic extraction fraction was estimated to be 0.19 ± 0.04/min. The variability between the 2 visits within the group level (95% confidence interval; ki: ±0.02/min, kef: ±0.004/min) was lower compared with the individual variability (repeatability; ki: ±0.06/min, kef: ±0.012/min). Data truncation demonstrated that the uptake rate estimates retained their precision as well as their group and individual reproducibility down to approximately 10 minutes of acquisition. Efflux rate estimates were underestimated (compared with the 50-minute acquisition) as the duration of the acquisition decreased, although these effects were more pronounced for acquisition times shorter than approximately 30 minutes.ConclusionsThis is the first study that reports estimates for the hepatic uptake and efflux transport process of gadoxetate in healthy volunteers in vivo. The results highlight that dynamic contrast-enhanced MRI with gadoxetate can provide novel quantitative insights into liver function and may therefore prove useful in studies that aim to monitor liver pathology, as well as being an alternative approach for studying hepatic drug-drug interactions.

Project description:Elucidating the precise properties of cancer stem cells (CSCs) is indispensable for the development of effective therapies against tumors, because CSCs are key drivers of tumor development, metastasis and relapse. We previously reported that the Hoechst 33342 dye-low staining side population (SP) method can enrich for CSCs in the C6 glioma cell line, and that the positively stained main population (MP) cells are non-CSCs. Presence of cancer stem-like SP cells is reported in various types of cancer. Although altered cellular energy metabolism is a hallmark of cancer, very little has been studied on the applicability of fluorescent probes for the understanding of CSC energy metabolism.The metabolic status of C6 SP and MP cells are evaluated by CellROX, MitoTracker Green (MTG) and JC-1 for cellular oxidative stress, mitochondrial amount, and mitochondrial membrane potential, respectively.SP cells were found to exhibit significantly lower fluorescent intensities of CellROX and MTG than MP cells. However, inhibition of ATP binding cassette (ABC) transporters by verapamil enhanced the intensities of these probes in SP cells to the levels similar to those in MP cells, indicating that SP cells expel the probes outside of the cells through ABC transporters. Next, SP cells were stained with JC-1 dye which exhibits membrane potential dependent accumulation in mitochondrial matrix, followed by formation of aggregates. The mitochondrial membrane potential indicated by the aggregates of JC-1 was 5.0-fold lower in SP cells than MP cells. Inhibition of ABC transporters enhanced the fluorescent intensities of the JC-1 aggregates in both SP and MP cells, the former of which was still 2.2-fold lower than the latter. This higher JC-1 signal in MP cells was further found to be due to the Hoechst 33342 dye existing in MP cells. When SP and MP cells were recultured to deprive the intracellular Hoechst 33342 dye and then stained with JC-1 in the presence of verapamil, the intensities of JC-1 aggregates in such SP and MP cells became comparable.Inhibiting ABC transporters and depriving Hoechst 33342 dye are required for the accurate assessment of side population-defined C6 glioma stem cell metabolism using fluorescent probes.

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Assessment of drug transporter function using fluorescent cell imaging.

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Assessment of drug transporter function using fluorescent cell imaging.

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