Influence of Multidrug Resistance-Associated Proteins on the Excretion of the ABCC1 Imaging Probe 6-Bromo-7-[11C]Methylpurine in Mice

Abstract

Purpose: Multidrug resistance-associated proteins (MRPs) mediate the hepatobiliary and renal excretion of many drugs and drug conjugates. The positron emission tomography (PET) tracer 6-bromo-7-[11 C]methylpurine is rapidly converted in tissues by glutathione-S-transferases into its glutathione conjugate, and has been used to measure the activity of Abcc1 in the brain and the lungs of mice. Aim of this work was to investigate if the activity of MRPs in excretory organs can be measured with 6-bromo-7-[ 11 C]methylpurine.Procedures: We performed PET scans with 6-bromo-7-[ 11 C]methylpurine in groups of wild-type, Abcc4(−/−) and Abcc1 (−/−) mice, with and without pre-treatment with the prototypical MRP inhibitor MK571.Results: 6-Bromo-7-[ 11 C]methylpurine-derived radioactivity predominantly underwent renal excretion. In blood, MK571 treatment led to a significant increase in the AUC and a decrease in the elimination rate constant of radioactivity (k elimination,blood ). In the kidneys, there were significant decreases in the rate constant for radioactivity uptake from the blood (k uptake,kidney ), k elimination,kidney , and the rate constant for tubular secretion of radioactivity (k urine ). Experiments in Abcc4 (−/−) mice indicated that Abcc4 contributed to renal excretion of 6-bromo-7-[ 11 C]methylpurine-derived radioactivity.Conclusions: Our data suggest that 6-bromo-7-[ 11 C]methylpurine may be useful to assess the activity of MRPs in the kidneys as well as in other organs (brain, lungs), although further work is needed to identify the MRP subtypes involved in the disposition of 6-bromo-7-[ 11 C]methylpurinederived radioactivity.Electronic supplementary material The online version of this article (https://

Generation and Characterization of anAbcc1Humanized Mouse Model (hABCC1flx/flx) with Knockout Capability

“…Mice were injected intraperitoneally under anesthesia 30 minutes before the start of the PET scan either with vehicle solution (PBS; wild-type: n 5 6, hABCC1 flx/flx : n 5 5, hABCC1 2/2 : n 5 4, Abcc1 2/2 : n 5 6), or with MK571 (5-(3-(2-(7-Chloroquinolin-2-yl)ethenyl)phenyl)-8dimethylcarbamyl-4,6-dithiaoctanoic acid) (Chemical Abstracts Service Number: 115103-85-0, 300 mg/kg; hABCC1 flx/flx : n 5 3, wildtype: n 5 7). Subsequently, 6-bromo-7-[ 11 C]methylpurine (32.85 6 7.34 MBq; 0.1 ml; 1.26 6 14.80 nmol), which had been synthesized as described previously (Zoufal et al, 2019), was administered as an intravenous bolus via the lateral tail vein and a 90-minute dynamic PET scan was initiated at the start of radiotracer injection (timing window 6 nanoseconds; energy window of 250-750 keV).…”

“…Using AMIDE software (Loening and Gambhir, 2003), whole brain and right lung were manually outlined on the PET images to derive concentration-time curves expressed in units of standardized uptake value [standardized uptake value 5 (radioactivity per gram/injected radioactivity) Â body weight]. From the logtransformed concentration-time curves, the elimination slope of radioactivity washout from tissue [k elimination, brain or k elimination, lung , (hour 21 )] was determined by linear regression analysis of data from 17.5 to 80 minutes after radiotracer injection (Zoufal et al, 2019).…”

“…radioactivity from the mouse brain (Okamura et al, 2009;Zoufal et al, 2019). In addition, in vitro transport experiments have demonstrated that the glutathione conjugate of 6-bromo-7-methylpurine is also a substrate of hABCC1 (Okamura et al, 2007).…”

“…In the lungs, ABCC1 is expressed in the basolateral membrane of pulmonary epithelial cell types (airway epithelial cells and alveolar type 2 and 1 cells) (Nickel et al, 2016). 6-Bromo-7-[ 11 C]methylpurine PET revealed pronounced reductions in the k elimination, lung value in Abcc1 2/2 mice versus wild-type mice (Okamura et al, 2013;Zoufal et al, 2019). These great reductions in k elimination, brain and k elimination, lung values in Abcc1 2/2 versus wild-type mice indicated absence of transporter redundancy for radiolabeled glutathione conjugate efflux in the cell membranes of brain parenchymal and pulmonary epithelial cells.…”

Assessing the Activity of Multidrug Resistance–Associated Protein 1 at the Lung Epithelial Barrier

“…C-BMP was synthesized as described before(15) in a decay-corrected radiochemical yield of 4.7±1.1% (based on 11 C-methane) with a radiochemical purity >98% and a molar activity at the end of synthesis of 129±74 GBq/μmol (n=24). For i.v.…”