Performance benchmarking of microbubble-localization algorithms for ultrasound localization microscopy.

Ultrafast ultrasound localization microscopy can be used to detect the subwavelength acoustic scattering of intravenously injected microbubbles to obtain haemodynamic maps of the vasculature of animals and humans. The quality of the haemodynamic maps depends on signal-to-noise ratios and on the algorithms used for the localization of the microbubbles and the rendering of their trajectories. Here we report the results of benchmarking of the performance of seven microbubble-localization algorithms. We used metrics for localization errors, localization success rates, processing times and a measure of the reprojection of the localization of the microbubbles on the original beamformed grid. We combined eleven metrics into an overall score and tested the algorithms in three simulated microcirculation datasets, and in angiography datasets of the brain of a live rat after craniotomy, an excised rat kidney and a mammary tumour in a live mouse. The algorithms, metrics and datasets, which we have made openly available at https://github.com/AChavignon/PALA and https://doi.org/10.5281/zenodo.4343435 , will facilitate the identification or generation of optimal microbubble-localization algorithms for specific applications.

In vitro Three-Dimensional Sprouting Assay of Angiogenesis using Mouse Embryonic Stem Cells for Vascular Disease Modeling and Drug Testing.

Recent advances in induced pluripotent stem cells (iPSC) and gene editing technologies enable the development of novel human cell-based disease models for phenotypic drug discovery (PDD) programs. Although these novel devices could predict the safety and efficacy of investigational drugs in humans more accurately, their development to the clinic still strongly rely on mammalian data, notably the use of mouse disease models. In parallel to human organoid or organ-on-chip disease models, the development of relevant in vitro mouse models is therefore an unmet need for evaluating direct drug efficacy and safety comparisons between species and in vivo and in vitro conditions. Here, a vascular sprouting assay that utilizes mouse embryonic stem cells differentiated into embryoid bodies (EBs) is described. Vascularized EBs cultured onto 3D-collagen gel develop new blood vessels that expand, a process called sprouting angiogenesis. This model recapitulates key features of in vivo sprouting angiogenesis-formation of blood vessels from a pre-existing vascular network-including endothelial tip cell selection, endothelial cell migration and proliferation, cell guidance, tube formation, and mural cell recruitment. It is amenable to screening for drugs and genes modulating angiogenesis and shows similarities with recently described three-dimensional (3D) vascular assays based on human iPSC technologies.

Nanohybrids with Magnetic and Persistent Luminescence Properties for Cell Labeling, Tracking, In Vivo Real-Time Imaging, and Magnetic Vectorization.

Once injected into a living organism, cells diffuse or migrate around the initial injection point and become impossible to be visualized and tracked in vivo. The present work concerns the development of a new technique for therapeutic cell labeling and subsequent in vivo visualization and magnetic retention. It is hypothesized and subsequently demonstrated that nanohybrids made of persistent luminescence nanoparticles and ultrasmall superparamagnetic iron oxide nanoparticles incorporated into a silica matrix can be used as an effective nanoplatform to label therapeutic cells in a nontoxic way in order to dynamically track them in real-time in vitro and in living mice. As a proof-of-concept, it is shown that once injected, these labeled cells can be visualized and attracted in vivo using a magnet. This first step suggests that these nanohybrids represent efficient multifunctional nanoprobes for further imaging guided cell therapies development.

Chemically engineered persistent luminescence nanoprobes for bioimaging.

Imaging nanoprobes are a group of nanosized agents developed for providing improved contrast for bioimaging. Among various imaging probes, optical sensors capable of following biological events or progresses at the cellular and molecular levels are actually actively developed for early detection, accurate diagnosis, and monitoring of the treatment of diseases. The optical activities of nanoprobes can be tuned on demand by chemists by engineering their composition, size and surface nature. This review will focus on researches devoted to the conception of nanoprobes with particular optical properties, called persistent luminescence, and their use as new powerful bioimaging agents in preclinical assays.

Non-aqueous sol-gel synthesis of ultra small persistent luminescence nanoparticles for near-infrared in vivo imaging.

Ultra-small ZnGa2 O4 :Cr(3+) nanoparticles (6 nm) that exhibit near-infrared (NIR) persistent luminescence properties are synthesized by using a non-aqueous sol-gel method assisted by microwave irradiation. The nanoparticles are pegylated, leading to highly stable dispersions under physiological conditions. Preliminary in vivo studies show the high potential for these ultra-small ZnGa2 O4 :Cr(3+) nanoparticles to be used as in vivo optical nanotools as they emit without the need for in situ excitation and, thus, avoid the autofluorescence of tissues.

Design, Properties, and In Vivo Behavior of Super-paramagnetic Persistent Luminescence Nanohybrids.

With the fast development of noninvasive diagnosis, the design of multimodal imaging probes has become a promising challenge. If many monofunctional nanocarriers have already proven their efficiency, only few multifunctional nanoprobes have been able to combine the advantages of diverse imaging modalities. An innovative nanoprobe called mesoporous persistent luminescence magnetic nanohybrids (MPNHs) is described that shows both optical and magnetic resonance imaging (MRI) properties intended for in vivo multimodal imaging in small animals. MPNHs are based on the assembly of chromium-doped zinc gallate oxide and ultrasmall superparamagnetic iron oxide nanoparticles embedded in a mesoporous silica shell. MPNHs combine the optical advantages of persistent luminescence, such as real time imaging with highly sensitive and photostable detection, and MRI negative contrast properties that ensure in vivo imaging with rather high spatial resolution. In addition to their imaging capabilities, these MPNHs can be motioned in vitro with a magnet, which opens multiple perspectives in magnetic vectorization and cell therapy research.

The in vivo activation of persistent nanophosphors for optical imaging of vascularization, tumours and grafted cells.

Optical imaging for biological applications requires more sensitive tools. Near-infrared persistent luminescence nanoparticles enable highly sensitive in vivo optical detection and complete avoidance of tissue autofluorescence. However, the actual generation of persistent luminescence nanoparticles necessitates ex vivo activation before systemic administration, which prevents long-term imaging in living animals. Here, we introduce a new generation of optical nanoprobes, based on chromium-doped zinc gallate, whose persistent luminescence can be activated in vivo through living tissues using highly penetrating low-energy red photons. Surface functionalization of this photonic probe can be adjusted to favour multiple biomedical applications such as tumour targeting. Notably, we show that cells can endocytose these nanoparticles in vitro and that, after intravenous injection, we can track labelled cells in vivo and follow their biodistribution by a simple whole animal optical detection, opening new perspectives for cell therapy research and for a variety of diagnosis applications.

3-(Oxazolo[4,5-b]pyridin-2-yl)anilides as a novel class of potent inhibitors for the kinetoplastid Trypanosoma brucei, the causative agent for human African trypanosomiasis.

A whole organism high-throughput screen of approximately 87,000 compounds against Trypanosoma brucei brucei led to the recent discovery of several novel compound classes with low micromolar activity against this organism and without appreciable cytotoxicity to mammalian cells. Herein we report a structure-activity relationship (SAR) investigation around one of these hit classes, the 3-(oxazolo[4,5-b]pyridin-2-yl)anilides. Sharp SAR is revealed, with our most active compound (5) exhibiting an IC50 of 91 nM against the human pathogenic strain T.b. rhodesiense and being more than 700 times less toxic towards the L6 mammalian cell line. Physicochemical properties are attractive for many compounds in this series. For the most potent representatives, we show that solubility and metabolic stability are key parameters to target during future optimisation.