Infection Imaging: Focus on New Tracers?

18F-labelled gentiobiose as potential PET-radiotracer for specific bacterial imaging: precursor synthesis, radiolabelling and in vitro evaluation

AIM

Bacterial infections are a clinical challenge, requiring fast and specific diagnosis to ensure effective treatment. Therefore, this project is dedicated to development of positron emission tomography (PET) radiotracers specifically targeting bacteria. Unlike previously developed bacteria-specific radiotracers, which are successful in detecting Gram-negative bacteria, tracers capable of imaging Gram-positive infections are still lacking.

METHODS

The disaccharide gentiobiose as abundant part of the cell wall of Gram-positive bacteria could fill this gap. Herein, the synthesis and evaluation of 2'-deoxy-2'-[18F]fluorogentiobiose ([18F]FLA280) is reported. The precursor for radiolabelling was obtained from a convergent synthesis under application of a benzylidene/benzyl group protecting strategy.

RESULTS

The first catalytic hydrogenation in 18F-radiochemistry is reported as proof of concept. The deprotection was carried out without any side product formation, giving the final radiotracer [18F]FLA280 in good radiochemical yield and excellent radiochemical purity. [18F]FLA280 was proven to be stable in murine and human blood serum for 120 minutes and was subjected to in vitro bacterial uptake studies towards S. aureus and E. coli resulting in a low bacterial uptake.

CONCLUSION

The observed bacterial uptake indicates that [18F]FLA280 may be not a promising tracer candidate for in vivo translation and alternative candidates particularly for Gram-positive bacteria are required. However, further development on the concept of labelled carbohydrates and cell wall building blocks might be promising.

Microbial communities, antibiotic resistance genes, and virulence factors in urinary infectious stone-associated urinary tract infections

Urinary infectious stones are challenging due to bacterial involvement, necessitating a comprehensive understanding of these conditions. Antibiotic-resistant urease-producing bacteria further complicate clinical management. In this study, analysis of urine and stone samples from urinary tract infection (UTI) patients revealed microbial shifts, gene enrichment in stones, and metabolic pathway disparities; antibiotic resistance gene trends were phylum-specific, urease-producing bacteria are at risk of acquiring AMR carried by Enterobacteriaceae under antibiotic, emphasizing potential AMR dissemination between them; Correlations of key pathogenic species in kidney stone and urine microbial communities highlight the need for targeted therapeutic strategies to manage complexities in UTIs; Stones and urine contain a variety of deleterious genes even before antibiotic use, and piperacillin/tazobactam better reduced the abundance of antibiotic resistance genes in stones and urine. The presence of diverse antibiotic resistance and virulence genes underscores challenges in clinical management and emphasizes the need for effective treatment strategies to mitigate risks associated with UTIs and urinary infectious stone formation. Ongoing research is vital for advancing knowledge and developing innovative approaches to address these urological conditions.

A novel radiolabelled salmochelin derivative for bacteria-specific PET imaging: synthesis, radiolabelling and evaluation

For specific imaging of bacterial infections we aimed at targeting the exclusive bacterial iron transport system via siderophore-based radiotracers. De novo synthesis and radiolabeling yielded the salmochelin-based PET radiotracer [68Ga]Ga-RMA693, which showed a favourable biodistribution and a bacteria-specific uptake in an animal model of Escherichia coli infection.