Al¹⁸F-Labeling Of Heat-Sensitive Biomolecules for Positron Emission Tomography Imaging

Abstract

Positron emission tomography (PET) using radiolabeled biomolecules is a translational molecular imaging technology that is increasingly used in support of drug development. Current methods for radiolabeling biomolecules with fluorine-18 are laborious and require multistep procedures with moderate labeling yields. The Al18F-labeling strategy involves chelation in aqueous medium of aluminum mono[18F]fluoride ({Al18F}2+) by a suitable chelator conjugated to a biomolecule. However, the need for elevated temperatures (100-120 °C) required for the chelation reaction limits its widespread use. Therefore, we designed a new restrained complexing agent (RESCA) for application of the AlF strategy at room temperature.Methods. The new chelator RESCA was conjugated to three relevant biologicals and the constructs were labeled with {Al18F}2+ to evaluate the generic applicability of the one-step Al18F-RESCA-method.Results. We successfully labeled human serum albumin with excellent radiochemical yields in less than 30 minutes and confirmed in vivo stability of the Al18F-labeled protein in rats. In addition, we efficiently labeled nanobodies targeting the Kupffer cell marker CRIg, and performed µPET studies in healthy and CRIg deficient mice to demonstrate that the proposed radiolabeling method does not affect the functional integrity of the protein. Finally, an affibody targeting HER2 (PEP04314) was labeled site-specifically, and the distribution profile of (±)-[18F]AlF(RESCA)-PEP04314 in a rhesus monkey was compared with that of [18F]AlF(NOTA)-PEP04314 using whole-body PET/CT.Conclusion. This generic radiolabeling method has the potential to be a kit-based fluorine-18 labeling strategy, and could have a large impact on PET radiochemical space, potentially enabling the development of many new fluorine-18 labeled protein-based radiotracers.

Antibody Fragment and Affibody ImmunoPET Imaging Agents: Radiolabelling Strategies and Applications

“…The elevated temperatures required to effect this chelation can affect the integrity of proteins if a direct labelling protocol is used. Recently, Bormans and co‐workers have overcome this issue with their (±)‐H3RESCA chelator (Scheme ) . They were able to synthesise [ 18 F]AlF labelled nanobodies and affibodies at room temperature that had been prefunctionalised with their chelator, achieving RCYs similar to those of previously reported NOTA variations.…”

Improved Detection of Molecular Markers of Atherosclerotic Plaques Using Sub-Millimeter PET Imaging

“…This results in the release of [ 18 F]AlF or [ 18 F]F − that returns into blood circulation and accumulates in the bone structures. As this instability appears to be lower in the case of other proteins [20,27], it would be interesting to further investigate the reasons behind the degradation in the case of Nbs.…”

“…However, this time-consuming process often has low efficiency. Herein, we overcame the previous issues by functionalising the Nb with the novel restrained complexing agent (RESCA) developed by Cleeren et al [18], allowing fast and simple 18 F-labelling via the Al 18 F-method [19,20].…”

Chemie der Positronenemissionstomographie: Aktuelle Fortschritte bei 11C‐, 18F‐, 13N‐ und 15O‐Markierungsreaktionen

“…Die neuen acyclischen mehrzähnigen Liganden wiesen eine weniger starre Struktur auf als das macrocyclische NOTA, wodurch die Aktivierungsenergie für die Al‐F‐Komplexierung erheblich gesenkt wurde. Mit ihnen gelang eine schnelle und effiziente Markierung einer ganzen Reihe von Peptiden und Antikörpern (auch vom Affibody‐ unf Nanobody‐Typ) bei 20–40 °C (Schema 33 C2,C) …”