Evaluation of [Ga]Ga-DOTA-AeK As a Potential Imaging Tool for PET Imaging of Cell Wall Synthesis in Bacterial Infections

Overview

Journal Pharmaceuticals (Basel)

Publisher MDPI

Specialty Chemistry

Date 2024 Sep 28

PMID 39338315

Authors

Palesa C Koatale

Mick M Welling

Sipho Mdanda

Amanda Mdlophane

John Takyi-Williams

Chrisna Durandt

Iman van den Bout

Frederik Cleeren

Mike M Sathekge

Thomas Ebenhan

Affiliations

Soon will be listed here.

Abstract

The ability of bacteria to recycle exogenous amino acid-based peptides and amino sugars for peptidoglycan biosynthesis was extensively investigated using optical imaging. In particular, fluorescent AeK-NBD was effectively utilized to study the peptidoglycan recycling pathway in Gram-negative bacteria. Based on these promising results, we were inspired to develop the radioactive AeK conjugate [Ga]Ga-DOTA-AeK for the in vivo localization of bacterial infection using PET/CT. An easy-to-implement radiolabeling procedure for DOTA-AeK with [Ga]GaCI followed by solid-phase purification was successfully established to obtain [Ga]Ga-DOTA-AeK with a radiochemical purity of ≥95%. [Ga]Ga-DOTA-AeK showed good stability over time with less protein binding under physiological conditions. The bacterial incorporation of [Ga]Ga-DOTA-AeK and its fluorescent Aek-NBD analog were investigated in live and heat-killed () and (). Unfortunately, no conclusive in vitro intracellular uptake of [Ga]Ga-DOTA-AeK was observed for or live and heat-killed bacterial strains ( > 0.05). In contrast, AeK-NBD showed significantly higher intracellular incorporation in live bacteria compared to the heat-killed control ( < 0.05). Preliminary biodistribution studies of [Ga]Ga-DOTA-AeK in a dual-model of chronic infection and inflammation revealed limited localization at the infection site with non-specific accumulation in response to inflammatory markers. Finally, our study demonstrates proof that the intracellular incorporation of AeK is necessary for successful bacteria-specific imaging using PET/CT. Therefore, Ga-68 was not a suitable radioisotope for tracing the bacterial uptake of AeK tripeptide, as it required chelation with a bulky metal chelator such as DOTA, which may have limited its active membrane transportation. An alternative for optimization is to explore diverse chemical structures of AeK that would allow for radiolabeling with F or C.

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