Siderophore-Based Drug Repurposing of Platinum Anticancer Agents as Targeted Antibiotics and Investigation of Pt-Induced DNA Damage in Gram-Negative Bacteria

Abstract

Bacterial infections are a growing threat to human health. This crisis has been exacerbated by the overuse of broad-spectrum antibiotics, resulting in adverse consequences such as the rapid emergence and spread of antibiotic resistance. Additionally, the use of broad-spectrum antibiotics disrupts the human microbiota, potentially leading to the onset of diseases associated with microbial dysbiosis. Consequently, there is an urgent need for innovative strategies to develop narrow-spectrum antibiotics. One promising approach involves the development of siderophore–antibiotic conjugates (SACs), which aim to achieve targeted antibacterial activity by leveraging siderophores, secondary metabolites utilized by bacteria to acquire the essential transition metal nutrient iron (Fe). This SAC approach exploits the molecular recognition between siderophores and their cognate transport machinery, hijacking siderophore-based Fe acquisition pathways for selective and efficient drug delivery as a “Trojan-horse” strategy. This thesis explores the application of a SAC strategy based on enterobactin (Ent), a native triscatecholate siderophore, to repurpose platinum (Pt) anticancer agents as targeted antibiotics against Gram-negative bacteria, involving four Ent-based conjugates incorporating Pt(V) prodrugs (Ent–Pt(IV)).

Chapter 1 introduces the fundamental concepts and background relevant to this thesis. It includes a comprehensive discussion of siderophores and antibiotic development using synthetic SACs. This chapter also highlights previous studies conducted by the Nolan laboratory, specifically focusing on the utilization of Ent for SAC development and its broader applications. Furthermore, it explores the role of Pt anticancer agents within the context of this research.

Chapter 2 focuses on repurposing cisplatin, the first FDA-approved Pt anticancer drug, as a targeted antibiotic with enhanced potency. This study demonstrates that through the conjugation of Ent onto the axial ligand of a cisplatin-based Pt(IV) prodrug, the resulting conjugates selectively inhibit growth and induce filamentous morphology in E. coli via the Ent uptake machinery. Ent conjugation facilitates Pt accumulation in E. coli cells while reducing Pt uptake in the human cell line HEK293T. This proof-of-concept study represents the first example of using the SAC approach to repurpose Pt compounds as antibiotics.

Chapter 3 expands the scope of Ent–Pt(IV) conjugates by repurposing oxaliplatin, the third-generation Pt anticancer drug, as a targeted antibiotic against Gram-negative bacteria that express the Ent uptake machinery. This study further investigates the DNA damage induced by Ent–Pt(IV) conjugates based on cisplatin and oxaliplatin. These findings establish a correlation between the antibacterial activities and the levels of DNA damage caused by Pt complexes. Collectively, this study generalizes the Ent-based drug repurposing strategy and provides insights into the cellular consequences of Ent–Pt(IV) conjugates in bacterial cells.