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Abstract Overcoming the efflux mediated by ATP–binding cassette (ABC) transporters at the blood-brain barrier (BBB) remains a challenge for the delivery of small molecule tyrosine kinase inhibitors (TKIs) such as erlotinib to the brain. Inhibition of ABCB1 and ABCG2 at the mouse BBB improved the BBB permeation of erlotinib but could not be achieved in humans. BBB disruption induced by focused ultrasound (FUS) was investigated as a strategy to overcome the efflux transport of erlotinib in vivo. In rats, FUS combined with microbubbles allowed for a large and spatially controlled disruption of the BBB in the left hemisphere. ABCB1/ABCG2 inhibition was performed using elacridar (10 mg/kg i.v). The brain kinetics of erlotinib was studied using 11C-erlotinib Positron Emission Tomography (PET) imaging in 5 groups (n = 4–5 rats per group) including a baseline group, immediately after sonication (FUS), 48 h after FUS (FUS + 48 h), elacridar (ELA) and their combination (FUS + ELA). BBB integrity was assessed using the Evan's Blue (EB) extravasation test. Brain exposure to 11C-erlotinib was measured as the area under the curve (AUC) of the brain kinetics (% injected dose (%ID) versus time (min)) in volumes corresponding to the disrupted (left) and the intact (right) hemispheres, respectively. EB extravasation highlighted BBB disruption in the left hemisphere of animals of the FUS and FUS + ELA groups but not in the control and ELA groups. EB extravasation was not observed 48 h after FUS suggesting recovery of BBB integrity. Compared with the control group (AUC Baseline = 1.4 ± 0.5%ID.min), physical BBB disruption did not impact the brain kinetics of 11C-erlotinib in the left hemisphere (p >.05) either immediately (AUC FUS = 1.2 ± 0.1%ID.min) or 48 h after FUS (AUC FUS+48h = 1.1 ± 0.3%ID.min). Elacridar similarly increased 11C-erlotinib brain exposure to the left hemisphere in the absence (AUC ELA = 2.2 ± 0.5%ID.min, p <.001) and in the presence of BBB disruption (AUC FUS+ELA = 2.1 ± 0.5%ID.min, p <.001). AUC left was never significantly different from AUC right (p >.05), in any of the tested conditions. BBB integrity is not the rate limiting step for erlotinib delivery to the brain which is mainly governed by ABC-mediated efflux. Efflux transport of erlotinib persisted despite BBB disruption. Graphical abstract Unlabelled Image Highlights • ABC-transporters limit the blood-brain barrier (BBB) permeation of erlotinib. • Ultrasound-induced BBB disruption is used to enhance the brain exposure to drugs. • The brain kinetics of 11C-erlotinib was assessed using in vivo PET imaging in rats. • Erlotinib was able to freely cross the BBB when ABC-transporters were inhibited. • ABC-mediated efflux of erlotinib persisted despite ultrasound-based BBB disruption. [ABSTRACT FROM AUTHOR]

In many transcranial ultrasound studies on rats, the transmission factor is assumed to be independent of animal weight and losses resulting from non-normal incidence angles of the beam are not accounted for. In this study, we measured acoustic transmission factors through 13 excised skulls of male Sprague-Dawley rats weighing between 90 and 520g, at different positions on each skull and at 1, 1.25, 1.5, 1.75 and 2MHz. Our results revealed that insertion loss through rat skull increases linearly with both body mass and frequency and strongly depends on the position, decreasing from the front to the back and from the midline to the lateral sides. Skull thickness also scales linearly with body mass. Reflection explains the main part of the insertion loss compared with attenuation and aberration. These data are helpful in predicting the acoustic pressure at the focus in the brain. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles (MNPs) have great potential in biomedical and clinical applications because of their many unique properties. This contribution provides an overview of the MNPs mainly used in the field of amyloid diseases. The first part discusses their use in understanding the amyloid mechanisms of fibrillation, with emphasis on their ability to control aggregation of amyloidogenic proteins. The second part deals with the functionalization by various moieties of numerous MNPs' surfaces (molecules, peptides, antibody fragments, or whole antibodies of MNPs) for the detection and the quantification of amyloid aggregates. The last part of this review focuses on the use of MNPs for magnetic-resonance-based amyloid imaging in biomedical fields, with particular attention to the application of gadolinium-based paramagnetic nanoparticles (AGuIX), which have been recently developed. Biocompatible AGuIX nanoparticles show favorable characteristics for in vivo use, such as nanometric and straightforward functionalization. Their properties have enabled their application in MRI. Here, we report that AGuIX nanoparticles grafted with the Pittsburgh compound B can actively target amyloid aggregates in the brain, beyond the blood-brain barrier, and remain the first step in observing amyloid plaques in a mouse model of Alzheimer's disease. [ABSTRACT FROM AUTHOR]

The P-glycoprotein (P-gp/ABCB1) is a major efflux transporter which impedes the brain delivery of many drugs across the blood-brain barrier (BBB). Focused ultrasound with microbubbles (FUS) enables BBB disruption, which immediate and delayed impact on P-gp function remains unclear. Positron emission tomography (PET) imaging using the radiolabeled substrate [11C]metoclopramide provides a sensitive and translational method to study P-gp function at the living BBB. A FUS protocol was devised in rats to induce a substantial and targeted disruption of the BBB in the left hemisphere. BBB disruption was confirmed by the Evan ' s Blue extravasation test or the minimally-invasive contrast-enhanced MRI. The expression of P-gp was measured 24 h or 48 h after FUS using immunostaining and fluorescence microscopy. The brain kinetics of [11C]metoclopramide was studied by PET at baseline, and both immediately or 24 h after FUS, with or without half-maximum P-gp inhibition (tariquidar 1 mg/kg). In each condition (n = 4–5 rats per group), brain exposure of [11C]metoclopramide was estimated as the area-under-the-curve (AUC) in regions corresponding to the sonicated volume in the left hemisphere, and the contralateral volume. Kinetic modeling was performed to estimate the uptake clearance ratio (R 1) of [11C]metoclopramide in the sonicated volume relative to the contralateral volume. In the absence of FUS, half-maximum P-gp inhibition increased brain exposure (+135.0 ± 12.9%, p < 0.05) but did not impact R 1 (p > 0.05). Immediately after FUS, BBB integrity was selectively disrupted in the left hemisphere without any detectable impact on the brain kinetics of [11C]metoclopramide compared with the baseline group (p > 0.05) or the contralateral volume (p > 0.05). 24 h after FUS, BBB integrity was fully restored while P-gp expression was maximally down-regulated (−45.0 ± 4.5%, p < 0.001) in the sonicated volume. This neither impacted AUC nor R 1 in the FUS + 24 h group (p > 0.05). Only when P-gp was inhibited with tariquidar were the brain exposure (+130 ± 70%) and R 1 (+ 29.1 ± 15.4%) significantly increased in the FUS + 24 h/tariquidar group, relative to the baseline group (p < 0.001). We conclude that the brain kinetics of [11C]metoclopramide specifically depends on P-gp function rather than BBB integrity. Delayed FUS-induced down-regulation of P-gp function can be detected. Our results suggest that almost complete down-regulation is required to substantially enhance the brain delivery of P-gp substrates. [Display omitted] • P-glycoprotein (P-gp) hinders the blood-brain barrier (BBB) passage of many drugs. • BBB disruption induced by focused ultrasound (FUS) enables targeted brain delivery. • P-gp function at the BBB can be studied in vivo using [11C]metoclopramide PET imaging. • Immediately after FUS, BBB disruption did not impact the P-gp-mediated efflux in rats. • P-gp expression was decreased 24 h to 48 h after FUS, with limited impact on function. [ABSTRACT FROM AUTHOR]

Epidermal growth factor receptor (EGFR), involved in cell proliferation and migration, is overexpressed in ~50% of glioblastomas. Anti-EGFR based strategies using monoclonal antibodies (mAb) such as cetuximab (CTX) have been proposed for central nervous system (CNS) cancer therapy. However, the blood-brain barrier (BBB) drastically restricts their brain penetration which limits their efficacy for the treatment of glioblastomas. Herein, a longitudinal PET imaging study was performed to assess the relevance and the impact of focused ultrasound (FUS)-mediated BBB permeabilization on the brain exposure to the anti-EGFR mAb CTX over time. For this purpose, FUS permeabilization process with microbubbles was applied on intact BBB mouse brain before the injection of 89Zr-labeled CTX for longitudinal imaging monitoring. FUS induced a dramatic increase in mAb penetration to the brain, 2 times higher compared to the intact BBB. The transfer of 89Zr-CTX from blood to the brain was rendered significant by FUS (k uptake = 1.3 ± 0.23 min−1 with FUS versus k uptake = 0 ± 0.006 min−1 without FUS). FUS allowed significant and prolonged exposure to mAb in the brain parenchyma. This study confirms the potential of FUS as a target delivery method for mAb in CNS. Unlabelled Image • FUS and MB significantly increase the delivery of CTX across the BBB. • PET is a powerful method to assess the PK of the passage of mAb through the BBB. • 89Zr-DFO-CTX was used to follow quantitatively enhanced brain exposure to CTX. • ImmunoPET-combined FUS is a clinically relevant strategy for GBM innovative therapy. [ABSTRACT FROM AUTHOR]