Radiolabelling of lipid-based nanocarriers with fluorine-18 for in vivo tracking by PET.

Organic nanoparticles made out of biodegradable and biocompatible materials have attracted increased attention in the therapeutic and diagnostic fields. In this study, we attempted to explore a new radiolabelling chelating free strategy for biodegradable sphingomyelin nanometric emulsions with fluorine-18 (18F), a radioisotope regularly used in clinic. [18F]fluoride was produced by the cyclotron and was incorporated into 4-[18F]fluorobenzamido-N-ethylmaleimide ([18F]FBEM), which was coupled next to the emulsions previously functionalized with a thiol group, via inclusion of either a thiol-PEG-lipid (SH-PEG12-C18), or a peptide-PEG-lipid (Cys-Pro-Ile-Glu-Asp-Arg-Pro-Met-Cys-PEG8-C18) derivative. Radiolabelled emulsions were obtained in a rapid and efficient fashion through facile-conjugated chemistry without the use of organic solvents, and characterized in terms of size, polydispersity, surface charge, pH, and osmolarity. PET imaging and biodistribution studies in BALB/c mice allowed obtaining the pharmacokinetics of the radiolabelled emulsions and determining the clearance pathways. Altogether, we confirmed the potential of this new technique for the radiolabelling of lipid-based drug nanosystems for application in PET imaging diagnosis.

Automated radiosynthesis of [18F]FBEM, a sulfhydryl site specific labeling agent for peptides and proteins.

In the process of developing [18F]FBEM coupled target peptide, we have instituted a robust automated synthesis of [18F]FBEM, a sulfhydryl (-SH) site specific agent for radiolabeling of peptides and proteins. The radiosynthesis generated 1.67-3.89 GBq (45.1-105.1 mCi, 7.5-18.8% non-decay corrected yield) of [18F]FBEM from 22.2 GBq (600 mCi) of starting [18F]fluoride with molar activity of 31.8 ±â€¯5.3 GBq/µmol (0.86 ±â€¯0.14 mCi/nmol) (n = 3) at the end of synthesis. Radiochemical purity was greater than 98%, and total synthesis time was ~90 min.

Regiospecific radiolabelling of Nanofitin on Ni magnetic beads with [18F]FBEM and in vivo PET studies.

INTRODUCTION: Nanofitins are low molecular weight, single chain and cysteine-free protein scaffolds able to selectively bind a defined biological target. They derive from Sac7d bacterial protein family and are highly stable over a wide range of pH (0-13) and temperature (Tm ~80°C). Their extreme stability, low cost of production and high tolerability for chemical coupling make Nanofitins a very interesting alternative to antibodies and their fragments. Here, a hexahistidine tagged model Nanofitin (H4) directed against hen egg white lysozyme was radiolabelled and injected in mice to provide a baseline biodistribution and pharmacokinetic profiles to support future Nanofitin development programs. METHOD: A single cysteine residue has been genetically inserted in a model Nanofitin and its regioselective radiolabelling has been performed with 4-[18F]fluorobenzamido-N-ethylamino-maleimide ([18F]FBEM). The synthesis of [18F]FBEM has been completely implemented on a radiosynthesis unit (FastLab) including HPLC purification and formulation. Coupling with the [18F]FBEM has been achieved on a solid support (Ni magnetic beads) allowing rapid purification at room temperature without organic solvent. PET-MRI studies on C57BL/6 mice were conducted after injection of [18F]FBEM-Cys-H4 in order to access the biodistribution of this Nanofitin model. RESULTS: Radiochemical yield (decay corrected) of 54±7% (n=4) was obtained after optimization for coupling the [18F]FBEM to Nanofitin. Pharmacokinetics results of [18F]FBEM-Cys-H4 revealed a fast clearance through the liver and the kidneys. CONCLUSION: An efficient new method on Ni magnetic beads was developed to radiolabelled his-tagged biomolecules with [18F]FBEM. This procedure was applied on a Nanofitin model Cys-H4 and biodistribution kinetic studies were achieved to evaluate the potential use of Nanofitin for diagnostic imaging. Fast clearance indicates that Nanofitins represent very interesting tools for diagnostic imaging.

18F-Labeled wild-type annexin V: comparison of random and site-selective radiolabeling methods.

Early stage apoptosis is characterized by the externalization of phosphatidylserine (PS) from the inner leaflet of the plasma membrane to the outer periphery. Consequently, PS represents an excellent target for non-invasive imaging of apoptosis by positron emission tomography. Annexin V is a 36 kDa protein which binds with high affinity to PS. Radiolabeling of wild-type annexin V with fluorine-18 ((18)F) can be accomplished via random acylation of 23 amine groups (22 lysine residues and one N-terminal amine) with [(18)F]SFB or site-specific alkylation reaction on cysteine residue at position 315 with maleimide-containing prosthetic groups like [(18)F]FBEM. The effect upon random and site-directed (18)F labeling of annexin V was studied with EL4 mouse lymphoma cells. Both, randomly and site-selectively radiolabeled annexin V demonstrated comparable binding to apoptotic EL4 cells. This finding suggests that the (18)F radiolabeling method has no significant effect on the ability of (18)F-labeled wild-type annexin V to bind PS in apoptotic cells.