Performance and Sensitivity of [99mTc]Tc-sestamibi Compared with Positron Emission Tomography Radiotracers to Measure P-glycoprotein Function in the Kidneys and Liver.

P-glycoprotein (P-gp, encoded in humans by the ABCB1 gene and in rodents by the Abcb1a/b genes) is a membrane transporter that can restrict the intestinal absorption and tissue distribution of many drugs and may also contribute to renal and hepatobiliary drug excretion. The aim of this study was to compare the performance and sensitivity of currently available radiolabeled P-gp substrates for positron emission tomography (PET) with the single-photon emission computed tomography (SPECT) radiotracer [99mTc]Tc-sestamibi for measuring the P-gp function in the kidneys and liver. Wild-type, heterozygous (Abcb1a/b(+/-)), and homozygous (Abcb1a/b(-/-)) Abcb1a/b knockout mice were used as models of different P-gp abundance in excretory organs. Animals underwent either dynamic PET scans after intravenous injection of [11C]N-desmethyl-loperamide, (R)-[11C]verapamil, or [11C]metoclopramide or consecutive static SPECT scans after intravenous injection of [99mTc]Tc-sestamibi. P-gp in the kidneys and liver of the mouse models was analyzed with immunofluorescence labeling and Western blotting. In the kidneys, Abcb1a/b() mice had intermediate P-gp abundance compared with wild-type and Abcb1a/b(-/-) mice. Among the four tested radiotracers, renal clearance of radioactivity (CLurine,kidney) was significantly reduced (-83%) in Abcb1a/b(-/-) mice only for [99mTc]Tc-sestamibi. Biliary clearance of radioactivity (CLbile,liver) was significantly reduced in Abcb1a/b(-/-) mice for [11C]N-desmethyl-loperamide (-47%), [11C]metoclopramide (-25%), and [99mTc]Tc-sestamibi (-79%). However, in Abcb1a/b(+/-) mice, CLbile,liver was significantly reduced (-47%) only for [99mTc]Tc-sestamibi. Among the tested radiotracers, [99mTc]Tc-sestamibi performed best in measuring the P-gp function in the kidneys and liver. Owing to its widespread clinical availability, [99mTc]Tc-sestamibi represents a promising probe substrate to assess systemic P-gp-mediated drug-drug interactions and to measure renal and hepatic P-gp function under different (patho-)physiological conditions.

[18F]2-fluoro-2-deoxy-sorbitol ([18F]FDS) PET imaging repurposed for quantitative estimation of blood-brain barrier permeability in a rat model of Alzheimer's disease.

Numerous studies suggest that blood-brain barrier (BBB) dysfunction may contribute to the progression of Alzheimer's disease (AD). Clinically available neuroimaging methods are needed for quantitative "scoring" of BBB permeability in AD patients. [18F]2-fluoro-2-deoxy-sorbitol ([18F]FDS), which can be easily obtained from simple chemical reduction of commercial [18F]2-fluoro-2-deoxy-glucose ([18F]FDG), was investigated as a small-molecule marker of BBB permeability, in a pre-clinical model of AD using in vivo PET imaging. Chemical reduction of [18F]FDG to [18F]FDS was obtained with a 100% conversion yield. Dynamic PET acquisitions were performed in the APP/PS1 rat model of AD (TgF344-AD, n=3) compared with age-matched littermates (WT, n=4). The brain uptake of [18F]FDS was determined in selected brain regions, delineated from a coregistered rat brain template. The brain uptake of [18F]FDS in the brain regions of AD rats versus WT rats was compared using a 2-way ANOVA. The uptake of [18F]FDS was significantly higher in the whole brain of AD rats, as compared with WT rats (P<0.001), suggesting increased BBB permeability. Enhanced brain uptake of [18F]FDS in AD rats was significantly different across brain regions (P<0.001). Minimum difference was observed in the amygdala (+89.0±7.6%, P<0.001) and maximum difference was observed in the midbrain (+177.8±29.2%, P<0.001). [18F]FDS, initially proposed as radio-pharmaceutical to estimate renal filtration using PET imaging, can be repurposed for non-invasive and quantitative determination of BBB permeability in vivo. Making the best with the quantitative properties of PET imaging, it was possible to estimate the extent of enhanced BBB permeability in a rat model of AD.

Carbon Dioxide Radical Anion by Photoinduced Equilibration between Formate Salts and [11C, 13C, 14C]CO2: Application to Carbon Isotope Radiolabeling.

The need for carbon-labeled radiotracers is increasingly higher in drug discovery and development (carbon-14, ß-, t1/2 = 5730 years) as well as in positron emission tomography (PET) for in vivo molecular imaging applications (carbon-11, ß+, t1/2 = 20.4 min). However, the structural diversity of radiotracers is still systematically driven by the narrow available labeled sources and methodologies. In this context, the emergence of carbon dioxide radical anion chemistry might set forth potential unexplored opportunities. Based on a dynamic isotopic equilibration between formate salts and [13C, 14C, 11C]CO2, C-labeled radical anion CO2•- could be accessed under extremely mild conditions within seconds. This methodology was successfully applied to hydrocarboxylation and dicarboxylation reactions in late-stage carbon isotope labeling of pharmaceutically relevant compounds. The relevance of the method in applied radiochemistry was showcased by the whole-body PET biodistribution profile of [11C]oxaprozin in mice.

Dissimilar Effect of P-Glycoprotein and Breast Cancer Resistance Protein Inhibition on the Distribution of Erlotinib to the Retina and Brain in Humans and Mice.

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are two ATP-binding cassette efflux transporters that are coexpressed at the human blood-brain barrier (BBB) and blood-retina barrier (BRB). While pharmacological inhibition of P-gp and/or BCRP results in increased brain distribution of dual P-gp/BCRP substrate drugs, such as the tyrosine kinase inhibitor erlotinib, the effect of P-gp and/or BCRP inhibition on the retinal distribution of such drugs has hardly been investigated. In this study, we used positron emission tomography (PET) imaging to assess the effect of transporter inhibition on the distribution of [11C]erlotinib to the human retina and brain. Twenty two healthy volunteers underwent two PET scans after intravenous (i.v.) injection of a microdose (<5 µg) of [11C]erlotinib, a baseline scan, and a second scan either with concurrent i.v. infusion of tariquidar to inhibit P-gp (n = 5) or after oral intake of single ascending doses of erlotinib (300 mg, 650 mg, or 1000 mg, n = 17) to saturate erlotinib transport. In addition, transport of [3H]erlotinib to the retina and brain was assessed in mice by in situ carotid perfusion under various drug transporter inhibition settings. In comparison to the baseline PET scan, coadministration of tariquidar or erlotinib led to a significant decrease of [11C]erlotinib total volume of distribution (VT) in the human retina by -25 ± 8% (p ≤ 0.05) and -41 ± 16% (p ≤ 0.001), respectively. In contrast, erlotinib intake led to a significant increase in [11C]erlotinib VT in the human brain (+20 ± 16%, p ≤ 0.001), while administration of tariquidar did not result in any significant changes. In situ carotid perfusion experiments showed that both P-gp and BCRP significantly limit the distribution of erlotinib to the mouse retina and brain but revealed a similar discordant effect at the mouse BRB and BBB following co-perfusion with tariquidar and erlotinib as in humans. Co-perfusion with prototypical inhibitors of solute carrier transporters did not reveal a significant contribution of organic cation transporters (e.g., OCTs and OCTNs) and organic anion-transporting polypeptides (e.g., OATP2B1) to the retinal and cerebral distribution of erlotinib. In conclusion, we observed a dissimilar effect after P-gp and/or BCRP inhibition on the retinal and cerebral distribution of [11C]erlotinib. The exact mechanism for this discrepancy remains unclear but may be related to the function of an unidentified erlotinib uptake carrier sensitive to tariquidar inhibition at the BRB. Our study highlights the great potential of PET to study drug distribution to the human retina and to assess the functional impact of membrane transporters on ocular drug distribution.

Mechanisms of respiratory depression induced by the combination of buprenorphine and diazepam in rats.

BACKGROUND: The safety profile of buprenorphine has encouraged its widespread use. However, fatalities have been attributed to benzodiazepine/buprenorphine combinations, by poorly understood mechanisms of toxicity. Mechanistic hypotheses include (i) benzodiazepine-mediated increase in brain buprenorphine (pharmacokinetic hypothesis); (ii) benzodiazepine-mediated potentiation of buprenorphine interaction with opioid receptors (receptor hypothesis); and (iii) combined effects of buprenorphine and benzodiazepine on respiratory parameters (pharmacodynamic hypothesis). METHODS: We studied the neuro-respiratory effects of buprenorphine (30 mg kg-1, i.p.), diazepam (20 mg kg-1, s.c.), and diazepam/buprenorphine combination in rats using arterial blood gas analysis, plethysmography, and diaphragm electromyography. Pretreatments with various opioid and gamma-aminobutyric acid receptor antagonists were tested. Diazepam impact on brain 11C-buprenorphine kinetics and binding to opioid receptors was studied using positron emission tomography imaging. RESULTS: In contrast to diazepam and buprenorphine alone, diazepam/buprenorphine induced early-onset sedation (P<0.05) and respiratory depression (P<0.001). Diazepam did not alter 11C-buprenorphine brain kinetics or binding to opioid receptors. Diazepam/buprenorphine-induced effects on inspiratory time were additive, driven by buprenorphine (P<0.0001) and were blocked by naloxonazine (P<0.01). Diazepam/buprenorphine-induced effects on expiratory time were non-additive (P<0.001), different from buprenorphine-induced effects (P<0.05) and were blocked by flumazenil (P<0.01). Diazepam/buprenorphine-induced effects on tidal volume were non-additive (P<0.01), different from diazepam- (P<0.05) and buprenorphine-induced effects (P<0.0001) and were blocked by naloxonazine (P<0.05) and flumazenil (P<0.05). Compared with buprenorphine, diazepam/buprenorphine decreased diaphragm contraction amplitude (P<0.01). CONCLUSIONS: Pharmacodynamic parameters and antagonist pretreatments indicate that diazepam/buprenorphine-induced respiratory depression results from a pharmacodynamic interaction between both drugs on ventilatory parameters.

Radiolabeling and brain penetration of [11 C]VU0071063, a ligand of type 1 sulfonylurea receptors for positron emission tomography imaging.

Sulfonylurea receptor 1 (SUR1) overexpression in the central nervous system is a potential biomarker for positron emission tomography (PET) imaging of brain damage and recovery. VU0071063, a selective ligand of SUR1 able to cross the blood-brain barrier, was isotopically radiolabeled with carbon-11 from a desmethyl precursor obtained quantitatively in one step. Ready-to-inject [11C]VU0071063 was obtained in 18 ± 2% radiochemical yield and 103 ± 22 GBq/µmol molar activity. PET imaging in healthy rats demonstrated a significant brain penetration and rapid elimination of the tracer in vivo, encouraging further investigation in animal models of SUR1 overexpression.

Abnormal Expression of Synaptic and Extrasynaptic GABAA Receptor Subunits in the Dystrophin-Deficient mdx Mouse.

Duchenne muscular dystrophy (DMD) is a neurodevelopmental disorder primarily caused by the loss of the full-length Dp427 dystrophin in both muscle and brain. The basis of the central comorbidities in DMD is unclear. Brain dystrophin plays a role in the clustering of central gamma-aminobutyric acid A receptors (GABAARs), and its loss in the mdx mouse alters the clustering of some synaptic subunits in central inhibitory synapses. However, the diversity of GABAergic alterations in this model is still fragmentary. In this study, the analysis of in vivo PET imaging of a benzodiazepine-binding site radioligand revealed that the global density of central GABAARs is unaffected in mdx compared with WT mice. In contrast, semi-quantitative immunoblots and immunofluorescence confocal imaging in tissue sections revealed complex and differential patterns of alterations of the expression levels and/or clustered distribution of a variety of synaptic and extrasynaptic GABAAR subunits in the hippocampus, cerebellum, cortex, and spinal cord. Hence, dystrophin loss not only affects the stabilization of synaptic GABAARs but also influences the subunit composition of GABAARs subtypes at both synaptic and extrasynaptic sites. This study provides new molecular outcome measures and new routes to evaluate the impact of treatments aimed at compensating alterations of the nervous system in DMD.

Regulation of P-glycoprotein and Breast Cancer Resistance Protein Expression Induced by Focused Ultrasound-Mediated Blood-Brain Barrier Disruption: A Pilot Study.

The blood-brain barrier (BBB) controls brain homeostasis; it is formed by vascular endothelial cells that are physically connected by tight junctions (TJs). The BBB expresses efflux transporters such as P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), which limit the passage of substrate molecules from blood circulation to the brain. Focused ultrasound (FUS) with microbubbles can create a local and reversible detachment of the TJs. However, very little is known about the effect of FUS on the expression of efflux transporters. We investigated the in vivo effects of moderate acoustic pressures on both P-gp and BCRP expression for up to two weeks after sonication. Magnetic resonance-guided FUS was applied in the striatum of 12 rats. P-gp and BCRP expression were determined by immunohistochemistry at 1, 3, 7, and 14 days postFUS. Our results indicate that FUS-induced BBB opening is capable of (i) decreasing P-gp expression up to 3 days after sonication in both the treated and in the contralateral brain regions and is capable of (ii) overexpressing BCRP up to 7 days after FUS in the sonicated regions only. Our findings may help improve FUS-aided drug delivery strategies by considering both the mechanical effect on the TJs and the regulation of P-gp and BCRP.

TSPO PET Imaging as a Potent Non-Invasive Biomarker for Diffuse Intrinsic Pontine Glioma in a Patient-Derived Orthotopic Rat Model.

Diffuse intrinsic pontine gliomas (DIPG), the first cause of cerebral pediatric cancer death, will greatly benefit from specific and non-invasive biomarkers for patient follow-up and monitoring of drug efficacy. Since biopsies are challenging for brain tumors, molecular imaging may be a technique of choice to target and follow tumor evolution. So far, MR remains the imaging technique of reference for DIPG, although it often fails to define the extent of tumors, an essential parameter for therapeutic efficacy assessment. Thanks to its high sensitivity, positron emission tomography (PET) offers a unique way to target specific biomarkers in vivo. We demonstrated in a patient-derived orthotopic xenograft (PDOX) model in the rat that the translocator protein of 18 kDa (TSPO) may be a promising biomarker for monitoring DIPG tumors. We studied the distribution of 18F-DPA-714, a TSPO radioligand, in rats inoculated with HSJD-DIPG-007 cells. The primary DIPG human cell line HSJD-DIPG-007 highly represents this pediatric tumor, displaying the most prevalent DIPG mutations, H3F3A (K27M) and ACVR1 (R206H). Kinetic modeling and parametric imaging using the brain 18F-DPA-714 PET data enabled specific delineation of the DIPG tumor area, which is crucial for radiotherapy dose management.

Influence of Cation Transporters (OCTs and MATEs) on the Renal and Hepatobiliary Disposition of [11C]Metoclopramide in Mice.

PURPOSE: To investigate the role of cation transporters (OCTs, MATEs) in the renal and hepatic disposition of the radiolabeled antiemetic drug [11C]metoclopramide in mice with PET. METHODS: PET was performed in wild-type mice after administration of an intravenous microdose (<1 µg) of [11C]metoclopramide without and with co-administration of either unlabeled metoclopramide (5 or 10 mg/kg) or the prototypical cation transporter inhibitors cimetidine (150 mg/kg) or sulpiride (25 mg/kg). [11C]Metoclopramide PET was also performed in wild-type and Slc22a1/2(-/-) mice. Radiolabeled metabolites were measured at 15 min after radiotracer injection and PET data were corrected for radiolabeled metabolites. RESULTS: [11C]Metoclopramide was highly metabolized and [11C]metoclopramide-derived radioactivity was excreted into the urine. The different investigated treatments decreased (~2.5-fold) the uptake of [11C]metoclopramide from plasma into the kidney and liver, inhibited metabolism and decreased (up to 3.8-fold) urinary excretion, which resulted in increased plasma concentrations of [11C]metoclopramide. Kidney and liver uptake were moderately (~1.3-fold) reduced in Slc22a1/2(-/-) mice. CONCLUSIONS: Our results suggest a contribution of OCT1/2 to the kidney and liver uptake and of MATEs to the urinary excretion of [11C]metoclopramide in mice. Cation transporters may contribute, next to variability in the activity of metabolizing enzymes, to variability in metoclopramide pharmacokinetics and side effects.

Nalmefene alleviates the neuroimmune response to repeated binge-like ethanol exposure: A TSPO PET imaging study in adolescent rats.

A large body of preclinical research has shown that neuroimmunity plays a key role in the deleterious effects of alcohol (ethanol) to the brain. Translational imaging techniques are needed to monitor the efficacy of strategies to prevent or mitigate neuroinflammation and alleviate ethanol-induced neurotoxicity. Opioid receptor antagonists such as nalmefene are antagonists of the toll-like receptor 4, which may block the proinflammatory signaling cascade induced by ethanol at this specific target. Male adolescent rats received a validated protocol of ethanol injection (i.p, 3 g/kg daily for two consecutive days followed by two resting days) during 14 days. Positron emission tomography (PET) imaging with the translocator protein 18 kDa (TSPO) radioligand [18 F]DPA-714 was performed at day-15. Toxicity induced by repeated binge-like ethanol exposure (71% mortality) was drastically reduced by nalmefene pretreatment (0.4 mg/kg, 14% mortality). No mortality was observed in animals that received vehicle (control) or nalmefene alone. Compared with control animals (n = 10), a significant 2.8-fold to 4.6-fold increase in the volume of distribution (VT ) of [18 F]DPA-714 was observed among brain regions in animals exposed to ethanol only (n = 9). Pretreatment with nalmefene significantly alleviated the neuroimmune response to ethanol exposure in all brain regions (1.2-fold to 2.5-fold increase in VT ; n = 5). Nalmefene alone (n = 6) did not impact [18 F]DPA-714 VT compared with the control group. Nalmefene may protect against the neuroinflammatory response and overall toxicity associated with binge drinking. [18 F]DPA-714 PET imaging can be used to noninvasively address the neuroimmune impact of ethanol exposure and its modulation by pharmacological strategies in vivo, with translational perspectives.

Repurposing radiotracers for myelin imaging: a study comparing 18F-florbetaben, 18F-florbetapir, 18F-flutemetamol,11C-MeDAS, and 11C-PiB.

PURPOSE: Drugs promoting myelin repair represent a promising therapeutic approach in multiple sclerosis and several candidate molecules are currently being evaluated, fostering the need of a quantitative method to specifically measure myelin content in vivo. PET using the benzothiazole derivative 11C-PiB has been successfully used to quantify myelin content changes in humans. Stilbene derivatives, such as 11C-MeDAS, have also been shown to bind to myelin in animals and are considered a promising radiopharmaceutical class for myelin imaging. Fluorinated compounds from both classes are now commercially available and thus should constitute clinically useful myelin radiotracers. The aim of this study is to provide a head-to-head comparison of 18F-florbetaben, 18F-florbetapir, 18F-flutemetamol, 11C-MeDAS, and 11C-PiB with regard to brain kinetics and binding in white matter (WM). METHODS: Four baboons underwent a 90-min dynamic PET scan for each radioligand. Arterial blood samples were collected during the exam for each radiotracer, except for 18F-florbetapir, to obtain a radiometabolite-corrected input function. Standardized uptake value ratio between 75 at 90 min (SUVR75-90), binding potential (BP) estimated with Logan method with input function, and distribution volume ratio (DVR) estimated with Logan reference method (using cerebellar gray matter as reference region) were calculated in WM and compared between tracers using mixed effect models. RESULTS: In WM, 18F-florbetapir had the highest SUVR75-90 (1.38 ± 0.03), followed by 18F-flutemetamol (1.34 ± 0.02), 18F-florbetaben (1.32 ± 0.07), 11C-MeDAS (1.27 ± 0.04), and 11C-PiB (1.25 ± 0.07). With regard to BP, 18F-florbetaben had the highest value (0.32 ± 0.06) compared with 18F-flutemetamol (0.20 ± 0.03), 11C-MeDAS (0.17 ± 0.03), and 11C-PiB (0.16 ± 0.03). No difference in DVR was detected between 18F-florbetaben (1.26 ± 0.06) and 18F-florbetapir (1.27 ± 0.03), but both were significantly higher in DVR than 18F-flutemetamol (1.17 ± 0.02), 11C-MeDAS (1.16 ± 0.03), and 11C-PiB (1.14 ± 0.02). CONCLUSIONS: Given their higher binding and longer half-life, our study indicates that 18F-florbetapir and 18F-florbetaben are promising tracers for myelin imaging which are readily available for clinical application in demyelinating diseases.

Inhibition of ABCB1 and ABCG2 at the Mouse Blood-Brain Barrier with Marketed Drugs To Improve Brain Delivery of the Model ABCB1/ABCG2 Substrate [11C]erlotinib.

P-Glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) are two efflux transporters at the blood-brain barrier (BBB), which effectively restrict brain distribution of diverse drugs, such as tyrosine kinase inhibitors. There is a crucial need for pharmacological ABCB1 and ABCG2 inhibition protocols for a more effective treatment of brain diseases. In the present study, seven marketed drugs (osimertinib, erlotinib, nilotinib, imatinib, lapatinib, pazopanib, and cyclosporine A) and one nonmarketed drug (tariquidar), with known in vitro ABCB1/ABCG2 inhibitory properties, were screened for their inhibitory potency at the BBB in vivo. Positron emission tomography (PET) using the model ABCB1/ABCG2 substrate [11C]erlotinib was performed in mice. Tested inhibitors were administered as i.v. bolus injections at 30 min before the start of the PET scan, followed by a continuous i.v. infusion for the duration of the PET scan. Five of the tested drugs increased total distribution volume of [11C]erlotinib in the brain ( VT,brain) compared to vehicle-treated animals (tariquidar, + 69%; erlotinib, + 19% and +23% for the 21.5 mg/kg and the 43 mg/kg dose, respectively; imatinib, + 22%; lapatinib, + 25%; and cyclosporine A, + 49%). For all drugs, increases in [11C]erlotinib brain distribution were lower than in Abcb1a/b(-/-)Abcg2(-/-) mice (+149%), which suggested that only partial ABCB1/ABCG2 inhibition was reached at the mouse BBB. The plasma concentrations of the tested drugs at the time of the PET scan were higher than clinically achievable plasma concentrations. Some of the tested drugs led to significant increases in blood radioactivity concentrations measured at the end of the PET scan (erlotinib, + 103% and +113% for the 21.5 mg/kg and the 43 mg/kg dose, respectively; imatinib, + 125%; and cyclosporine A, + 101%), which was most likely caused by decreased hepatobiliary excretion of radioactivity. Taken together, our data suggest that some marketed tyrosine kinase inhibitors may be repurposed to inhibit ABCB1 and ABCG2 at the BBB. From a clinical perspective, moderate increases in brain delivery despite the administration of high i.v. doses as well as peripheral drug-drug interactions due to transporter inhibition in clearance organs question the translatability of this concept.

Cortico-Amygdala-Striatal Activation by Modafinil/Flecainide Combination.

Background: Modafinil, a nonamphetaminic wake-promoting compound, is prescribed as first line therapy in narcolepsy, an invalidating disorder characterized by excessive daytime sleepiness and cataplexy. Although its mode of action remains incompletely known, recent studies indicated that modafinil modulates astroglial connexin-based gap junctional communication as administration of a low dose of flecainide, an astroglial connexin inhibitor, enhanced the wake-promoting and procognitive activity of modafinil in rodents and healthy volunteers. The aim of this study is to investigate changes in glucose cerebral metabolism in rodents, induced by the combination of modafinil+flecainide low dose (called THN102). Methods: The impact of THN102 on brain glucose metabolism was noninvasively investigated using 18F-2-fluoro-2-deoxy-D-glucose Positron Emission Tomography imaging in Sprague-Dawley male rats. Animals were injected with vehicle, flecainide, modafinil, or THN102 and further injected with 18F-2-fluoro-2-deoxy-D-glucose followed by 60-minute Positron Emission Tomography acquisition. 18F-2-fluoro-2-deoxy-D-glucose Positron Emission Tomography images were coregistered to a rat brain template and normalized from the total brain Positron Emission Tomography signal. Voxel-to-voxel analysis was performed using SPM8 software. Comparison of brain glucose metabolism between groups was then performed. Results: THN102 significantly increased regional brain glucose metabolism as it resulted in large clusters of 18F-2-fluoro-2-deoxy-D-glucose uptake localized in the cortex, striatum, and amygdala compared with control or drugs administered alone. These regions, highly involved in the regulation of sleep-wake cycle, emotions, and cognitive functions were hence quantitatively modulated by THN102. Conclusion: Data presented here provide the first evidence of a regional brain activation induced by THN102, currently being tested in a phase II clinical trial in narcoleptic patients.

Effect of Rifampicin on the Distribution of [11C]Erlotinib to the Liver, a Translational PET Study in Humans and in Mice.

Organic anion-transporting polypeptides (OATPs) mediate the uptake of various drugs from blood into the liver in the basolateral membrane of hepatocytes. Positron emission tomography (PET) is a potentially powerful tool to assess the activity of hepatic OATPs in vivo, but its utility critically depends on the availability of transporter-selective probe substrates. We have shown before that among the three OATPs expressed in hepatocytes (OATP1B1, OATP1B3, and OATP2B1), [11C]erlotinib is selectively transported by OATP2B1. In contrast to OATP1B1 and OATP1B3, OATP2B1 has not been thoroughly explored yet, and no specific probe substrates are currently available. To assess if the prototypical OATP inhibitor rifampicin can inhibit liver uptake of [11C]erlotinib in vivo, we performed [11C]erlotinib PET scans in six healthy volunteers without and with intravenous pretreatment with rifampicin (600 mg). In addition, FVB mice underwent [11C]erlotinib PET scans without and with concurrent intravenous infusion of high-dose rifampicin (100 mg/kg). Rifampicin caused a moderate reduction in the liver distribution of [11C]erlotinib in humans, while a more pronounced effect of rifampicin was observed in mice, in which rifampicin plasma concentrations were higher than in humans. In vitro uptake experiments in an OATP2B1-overexpressing cell line indicated that rifampicin inhibited OATP2B1 transport of [11C]erlotinib in a concentration-dependent manner with a half-maximum inhibitory concentration of 72.0 ± 1.4 µM. Our results suggest that rifampicin-inhibitable uptake transporter(s) contributed to the liver distribution of [11C]erlotinib in humans and mice and that [11C]erlotinib PET in combination with rifampicin may be used to measure the activity of this/these uptake transporter(s) in vivo. Furthermore, our data suggest that a standard clinical dose of rifampicin may exert in vivo a moderate inhibitory effect on hepatic OATP2B1.

Imaging the neuroimmune response to alcohol exposure in adolescent baboons: a TSPO PET study using 18 F-DPA-714.

The effects of acute alcohol exposure to the central nervous system are hypothesized to involve the innate immune system. The neuroimmune response to an initial and acute alcohol exposure was investigated using translocator protein 18 kDa (TSPO) PET imaging, a non-invasive marker of glial activation, in adolescent baboons. Three different alcohol-naive adolescent baboons (3-4 years old, 9 to 14 kg) underwent 18 F-DPA-714 PET experiments before, during and 7-12 months after this initial alcohol exposure (0.7-1.0 g/l). The brain distribution of 18 F-DPA-714 (VT ; in ml/cm3 ) was estimated in several brain regions using the Logan plot analysis and the metabolite-corrected arterial input function. Compared with alcohol-naive animals (VTbrain  = 3.7 ± 0.7 ml/cm3 ), the regional VT s of 18 F-DPA-714 were significantly increased during alcohol exposure (VTbrain  = 7.2 ± 0.4 ml/cm3 ; p < 0.001). Regional VT s estimated several months after alcohol exposure (VTbrain  = 5.7 ± 1.4 ml/cm3 ) were lower (p < 0.001) than those measured during alcohol exposure, but remained significantly higher (p < 0.001) than in alcohol-naive animals. The acute and long-term effects of ethanol exposure were observed globally across all brain regions. Acute alcohol exposure increased the binding of 18 F-DPA-714 to the brain in a non-human primate model of alcohol exposure that reflects the 'binge drinking' situation in adolescent individuals. The effect persisted for several months, suggesting a 'priming' of glial cell function after initial alcohol exposure.

Acute Morphine Exposure Increases the Brain Distribution of [18F]DPA-714, a PET Biomarker of Glial Activation in Nonhuman Primates.

Background: The neuroinflammatory response to morphine exposure modulates its antinociceptive effects, tolerance, and dependence. Positron emission tomography radioligands for translocator protein-18kDa such as [18F]DPA-714 are noninvasive biomarkers of glial activation, a hallmark of neuroinflammation. Methods: [18F]DPA-714 positron emission tomography imaging was performed in 5 baboons at baseline and 2 hours after i.m. morphine injection (1 mg/kg). Brain kinetics and metabolite-corrected input function were measured to estimate [18F]DPA-714 brain distribution. Results: Morphine significantly increased [18F]DPA-714 brain distribution by a 1.3 factor (P<.05; paired t test). The effect was not restricted to opioid receptor-rich regions. Differences in baseline [18F]DPA-714 binding were observed among baboons. The response to morphine predominated in animals with the highest baseline uptake. Conclusions: [18F]DPA-714 positron emission tomography imaging may be useful to noninvasively investigate the brain immune component of morphine pharmacology. Correlation between baseline brain distribution and subsequent response to morphine exposure suggest a role for priming parameters in controlling the neuroinflammatory properties of opioids.

Simultaneous Determination of Eight ß-Lactam Antibiotics, Amoxicillin, Cefazolin, Cefepime, Cefotaxime, Ceftazidime, Cloxacillin, Oxacillin, and Piperacillin, in Human Plasma by Using Ultra-High-Performance Liquid Chromatography with Ultraviolet Detection.

A simple and rapid ultra-high-performance liquid chromatography (UHPLC) method using UV detection was developed for the simultaneous determination of eight ß-lactam antibiotics in human plasma, including four penicillins, amoxicillin (AMX), cloxacillin (CLX), oxacillin (OXA), and piperacillin (PIP), and four cephalosporins, cefazolin (CFZ), cefepime (FEP), cefotaxime (CTX), and ceftazidime (CAZ). One hundred-microliter samples were spiked with thiopental as an internal standard, and proteins were precipitated by acetonitrile containing 0.1% formic acid. Separation was achieved on a pentafluorophenyl (PFP) column with a mobile phase composed of phosphoric acid (10 mM) and acetonitrile in gradient elution mode at a flow rate of 500 µl/min. Detection was performed at 230 nm for AMX, CLX, OXA, and PIP and 260 nm for CFZ, FEP, CTX, and CAZ. The total analysis time did not exceed 13 min. The method was found to be linear at concentrations ranging from 2 to 100 mg/liter for each compound, and all validation parameters fulfilled international requirements. Between- and within-run accuracy errors ranged from -5.2% to 11.4%, and precision was lower than 14.2%. This simple method requires small-volume samples and can easily be implemented in most clinical laboratories to promote the therapeutic drug monitoring of ß-lactam antibiotics. The simultaneous determination of several antibiotics considerably reduces the time to results for clinicians, which may improve treatment efficiency, especially in critically ill patients.

Differential influence of propofol and isoflurane anesthesia in a non-human primate on the brain kinetics and binding of [(18)F]DPA-714, a positron emission tomography imaging marker of glial activation.

Translocator protein 18 kDa (TSPO) expression at the mitochondrial membrane of glial cells is related to glial activation. TSPO radioligands such as [(18)F]DPA-714 are useful for the non-invasive study of neuroimmune processes using positron emission tomography (PET). Anesthetic agents were shown to impact mitochondrial function and may influence [(18)F]DPA-714 binding parameters and PET kinetics. [(18) F]DPA-714 PET imaging was performed in Papio anubis baboons anesthetized using either intravenous propofol (n = 3) or inhaled isoflurane (n = 3). Brain kinetics and metabolite-corrected input function were measured to estimate [(18) F]DPA-714 brain distribution (VT). Displacement experiments were performed using PK11195 (1.5 mg/kg). In vitro [(18)F]DPA-714 binding experiments were performed using baboon brain tissue in the absence and presence of tested anesthetics. Brain radioactivity peaked higher in isoflurane-anesthetized animals compared with propofol (SUVmax = 2.7 ± 0.5 vs. 1.3 ± 0.2, respectively) but was not different after 30 min. Brain VT was not different under propofol and isoflurane. Displacement resulted in a 35.8 ± 8.4% decrease of brain radioactivity under propofol but not under isoflurane (0.1 ± 7.0%). In vitro, the presence of propofol increased TSPO density and dramatically reduced its affinity for [(18)F]DPA-714 compared with control. This in vitro effect was not significant with isoflurane. Exposure to propofol and isoflurane differentially influences TSPO interaction with its specific radioligand [(18)F]DPA-714 with subsequent impact on its tissue kinetics and specific binding estimated in vivo using PET. Therefore, the choice of anesthetics and their potential influence on PET data should be considered for the design of imaging studies using TSPO radioligands, especially in a translational research context.