Imaging quantitative changes in blood-brain barrier permeability using [18F]2-fluoro-2-deoxy-sorbitol ([18F]FDS) PET in relation to glial cell recruitment in a mouse model of endotoxemia

The quantitative relationship between the disruption of the blood-brain barrier (BBB) and the recruitment of glial cells was explored in a mouse model of endotoxemia. [18F]2-Fluoro-2-deoxy-sorbitol ([18F]FDS) PET imaging was used as a paracellular marker for quantitative monitoring of BBB permeability after i.v injection of increasing doses of lipopolysaccharide (LPS) or vehicle (saline, n = 5). The brain distribution of [18F]FDS (VT, mL.cm-3) was estimated using kinetic modeling. LPS dose-dependently increased the brain VT of [18F]FDS after injection of LPS 4 mg/kg (5.2 ± 2.4-fold, n = 4, p < 0.01) or 5 mg/kg (9.0 ± 9.1-fold, n = 4, p < 0.01) but not 3 mg/kg (p > 0.05, n = 7). In 12 individuals belonging to the different groups, changes in BBB permeability were compared with expression of markers of astrocyte (GFAP) and microglial cell (CD11b) using ex vivo immunohistochemistry. Increased expression of CD11b and GFAP expression was observed in mice injected with 3 mg/kg of LPS, which did not increase with higher LPS doses. Quantitative [18F]FDS PET imaging can capture different levels of BBB permeability in vivo. A biphasic effect was observed with the lowest dose of LPS that triggered neuroinflammation without disruptive changes in BBB permeability, and higher LPS doses that increased BBB permeability without additional recruitment of glial cells.

Impact of Radiolabeling Strategies on the Pharmacokinetics and Distribution of an Anti-PD-L1 PET Ligand

Molecular imaging with PET offers an alternative method to quantify programmed-death-ligand 1 (PD-L1) to accurately select patients for immunotherapies. More and more clinical and preclinical trials involve radiolabeling of antibody fragments for their desirably fast clearance and high tumor penetration. As the radiolabeling strategy can significantly impact pharmacokinetics and biodistribution, we explored in this work a site-specific radiofluorination strategy on an anti-PD-L1 fragment antigen-binding (Fab) and compared the pharmacokinetic and biodistribution properties with the same Fab labeled using stochastic radiolabeling chemistry. We applied an enzymatic bioconjugation mediated by a variant of the lipoic acid ligase (LplA) that promotes the formation of an amide bond between a short peptide cloned onto the C terminus of the Fab. A synthetic analogue of the enzyme natural substrate, lipoic acid, was radiolabeled with fluorine-18 for site-specific conjugation by LplA. We compared the biodistribution of the site-specifically labeled Fab with a stochastically labeled Fab on lysine side chains in tumor-bearing mice. The two methods of fluorination demonstrate a comparable whole-body biodistribution. The ⁸⁹Zr-labeled Fab had different biodistribution compared to either ¹⁸F-labeled Fab. We attribute the difference to [⁸⁹Zr] metabolism. Fab-LAP-[¹⁸F]FPyOctA therefore reflects better the true pharmacokinetic profile of the Fab.

PET/Fluorescence Imaging: An Overview of the Chemical Strategies to Build Dual Imaging Tools

Molecular imaging is a biomedical research discipline that has quickly emerged to afford the observation, characterization, monitoring, and quantification of biomarkers and biological processes in living organism. It covers a large array of imaging techniques, each of which provides anatomical, functional, or metabolic information. Multimodality, as the combination of two or more of these techniques, has proven to be one of the best options to boost their individual properties, hence offering unprecedented tools for human health. In this review, we will focus on the combination of positron emission tomography and fluorescence imaging from the specific perspective of the chemical synthesis of dual imaging agents. Based on a detailed analysis of the literature, this review aims at giving a comprehensive overview of the chemical strategies implemented to build adequate imaging tools considering radiohalogens and radiometals as positron emitters, fluorescent dyes mostly emitting in the NIR window and all types of targeting vectors.

Original synthesis of radiolabeling precursors for batch and on resin one-step/late-stage radiofluorination of peptides

Radiolabeling of peptides with fluorine-18 is hurdled by their chemical sensitivity and complicated processes. Original triflyl-pyridine intermediates afforded ammonium precursors that were radiolabeled at low temperature. From that study, a generic tag has been designed to allow a simple one-step/late-stage radiolabelling of peptides. The strategy has been transposed to an automated "on-resin" radiolabelling.

[18 F]FPyZIDE: A versatile prosthetic reagent for the fluorine-18 radiolabeling of biologics via copper-catalyzed or strain-promoted alkyne-azide cycloadditions

Methods for the radiolabeling of biologics with fluorine-18 have been of interest for several decades. A common approach consists in the preparation of a prosthetic reagent, a small molecule bearing a fluorine-18 that is conjugated with the macromolecule to an appropriate function. Click chemistry, and more particularly cycloadditions, is an interesting approach to radiolabel molecules thanks to mild reaction conditions, high yields, low by-products formation, and strong orthogonality. Moreover, the chemical functions involved in the cycloaddition reaction are stable in the drastic radiofluorination conditions, thus allowing a simple radiosynthetic route to prepare the prosthetic reagent. We report herein the radiosynthesis of ¹⁸ F-FPyZIDE, a pyridine-based azide-bearing prosthetic reagent. We exemplified its conjugation via copper-catalyzed cycloaddition (CuAAC) and strain-promoted cycloaddition (SPAAC) with several terminal alkyne or strained alkyne model compounds.

New fluorine-18 pretargeting PET imaging by bioorthogonal chlorosydnone–cycloalkyne click reaction

A PET pretargeting approach using strain-promoted sydnone–alkyne cycloaddition.

Copper(I)-catalyzed cycloaddition of 4-bromosydnones and alkynes for the regioselective synthesis of 1,4,5-trisubstituted pyrazoles

Copper-catalyzed cycloaddition of alkynes with 4-bromosydnones provides a convenient, mild, and regioselective method for the synthesis of a wide range of bromopyrazoles. The broad functional group tolerance of the cycloaddition reaction and further palladium-catalyzed cross-coupling reactions allowed the preparation of polyfunctionalized 1,4,5-pyrazoles that are otherwise difficult to obtain by conventional methods.

One-pot synthesis of 1,4-disubstituted pyrazoles from arylglycines via copper-catalyzed sydnone-alkyne cycloaddition reaction

A robust method for constructing 1,4-pyrazoles from arylglycines was developed using the copper-catalyzed sydnone-alkyne cycloaddition reaction. The procedure offers a straightforward and general route to the pyrazole heterocycle through a three-step one-pot procedure.

4-Halogeno-sydnones for fast strain promoted cycloaddition with bicyclo-[6.1.0]-nonyne

4-Halogeno-sydnones were found to be efficient dipole partners for the strain promoted click reaction with bicyclo-[6.1.0]-nonyne. This bioorthogonal reaction has been applied to protein labeling.