Siderophore-Pt(IV) Conjugates as Tools to Probe Cytoplasmic Cargo Delivery to Gram-Negative Bacteria

Area of Science:

• Microbiology
• Biochemistry
• Drug Delivery

Background:

• Bacterial siderophores are crucial for iron uptake and homeostasis.
• Understanding siderophore transport is key for developing siderophore-antibiotic conjugates for targeted drug delivery.
• Nonnative and xeno-siderophore uptake mechanisms in Gram-negative bacteria are not fully understood.

Purpose of the Study:

• To elucidate the cellular uptake pathways and localization of native and synthetic siderophores in Gram-negative bacteria.
• To investigate the potential of siderophore-drug conjugates as probes for studying bacterial transport systems.
• To assess the feasibility of using siderophore-drug conjugates for delivering antibiotics into bacterial cytoplasm.

Main Methods:

• Conjugation of triscatecholate siderophores (enterobactin and TRENCAM) to a cisplatin-based Pt(IV) prodrug.
• Utilizing siderophore-Pt(IV) conjugates as probes to study cellular localization in various Gram-negative bacteria, including *Escherichia coli*, *Salmonella enterica*, *Pseudomonas aeruginosa*, and *Acinetobacter baumannii*.
• Employing the Pt(IV) warhead's DNA-targeting and filamentous morphology readout for assessing cytoplasmic delivery.

Main Results:

• The siderophore-Pt(IV) probes successfully tracked siderophore localization within bacterial cells.
• Uropathogenic *E. coli* and *S. enterica* serovar Typhimurium were shown to transport TRENCAM via the FepCDG inner membrane transporter.
• *Acinetobacter baumannii* demonstrated the ability to transport enterobactin and TRENCAM to the cytoplasm, with a putative inner membrane transport system identified.
• The study confirmed the potential of siderophore-Pt(IV) conjugates for probing bacterial cytoplasmic delivery.

Conclusions:

• Siderophore-Pt(IV) prodrug conjugates are effective tools for investigating siderophore transport machinery in Gram-negative bacteria.
• Findings provide insights into the specificity of siderophore uptake, including nonnative and xeno-siderophores.
• This approach highlights the potential of siderophore-antibiotic conjugates for delivering cytoplasmic-targeting antibiotics across diverse Gram-negative pathogens.