Zidovudine-β-Lactam Pronucleoside Strategy for Selective Delivery into Gram-Negative Bacteria Triggered by β-Lactamases

Synthesis of β-lactam-zidovudine pronucleosides as potential selective narrow-spectrum antibacterial agents

Since the discovery of penicillin, the forerunner of the most widely used class of antibiotics (i.e. β-lactams), natural compounds and their derivatives represented a major source of antibacterial therapeutic products whose availability enabled modern medical practices (invasive surgery, organ transplant, etc.). However, the relentless emergence of resistant bacteria is challenging the long-term efficacy of antibiotics, also decreasing their economic attractiveness for big pharma, leading to a significant decay in antibacterial development in the 21st century and an increased use of last-resort drugs such as carbapenems or colistin. Indeed, bacteria evolved an arsenal of resistance mechanisms, leading to the emergence of totally-drug resistant isolates, already sporadically isolated among Gram-negative bacterial species. To face this deadly peril, it is fundamental to explore new ground-breaking approaches. In view of the significance of both β-lactam antibiotics and the production of one or more β-lactamases as the major resistance mechanism (especially in Gram-negative bacteria), we implemented an original approach to selectively deliver antibacterial zidovudine (AZT) exploiting the β-lactamase-mediated hydrolysis of a β-lactam-conjugate prodrug. The synthesis of the targeted pronucleosides was performed in 5-7 steps and based on an original Pd-catalyzed cross-coupling reaction. Enzymatic and microbiological evaluations were performed to evaluate the synthesized pronucleosides, yielding new insights into molecular recognition of β-lactamase enzymes. This approach would potentially allow a targeted and selective eradication of antibiotic-resistant β-lactamase-producing (opportunistic) pathogens, as the inactive prodrug is unable to harm the commensal microbial flora.

An engineered prodrug selectively suppresses β-lactam resistant bacteria in a mixed microbial setting

The rise of β-lactam resistance necessitates new strategies to combat bacterial infections. We purposefully engineered the β-lactam prodrug AcephPT to exploit β-lactamase activity to selectively suppress resistant bacteria producing extended-spectrum-β-lactamases (ESBLs). Selective targeting of resistant bacteria requires avoiding interaction with penicillin-binding proteins, the conventional targets of β-lactam antibiotics, while maintaining recognition by ESBLs to activate AcephPT only in resistant cells. Computational approaches provide a rationale for structural modifications to the prodrug to achieve this biased activity. We show AcephPT selectively suppresses gram-negative ESBL-producing bacteria in clonal populations and in mixed microbial cultures, with effective selectivity for both lab strains and clinical isolates expressing ESBLs. Time-course NMR experiments confirm hydrolytic activation of AcephPT exclusively by ESBL-producing bacteria. In mixed microbial cultures, AcephPT suppresses proliferation of ESBL-producing strains while sustaining growth of β-lactamase-non-producing bacteria, highlighting its potential to combat β-lactam resistance while promoting antimicrobial stewardship.

Antibacterial Prodrugs to Overcome Bacterial Antimicrobial Resistance

Antimicrobial resistance (AMR) is an increasingly concerning phenomenon that requires urgent attention because it poses a threat to human and animal health. Bacteria undergo continuous evolution, acquiring novel resistance mechanisms in addition to their intrinsic ones. Multidrug-resistant and extensively drug-resistant bacterial strains are rapidly emerging, and it is expected that bacterial AMR will claim the lives of 10 million people annually by 2050. Consequently, the urgent need for the development of new therapeutic agents with new modes of action is evident. The antibacterial prodrug approach, a strategy that includes drug repurposing and derivatization, integration of nanotechnology, and exploration of natural products, is highlighted in this review. Thus, this publication aims at compiling the most pertinent research in the field, spanning from 2021 to 2023, offering the reader a comprehensive insight into the AMR phenomenon and new strategies to overcome it.

Recent antibacterial carbohydrate-based prodrugs, drugs and delivery systems to overcome antimicrobial resistance

Antimicrobial resistance is an increasing phenomenon that is threatening global health. Tuberculosis causative bacteria and several resistant and multidrug-resistant bacteria are widely spread and listed by the World Health Organization as global priorities for research and development. Hence, new antibacterial agents with new modes of action are urgently required. In this context, carbohydrate-based drugs have been extensively studied and used, presenting several benefits for therapeutical purposes. In this review, the latest efforts done in the carbohydrate-based antibacterial agents research field, reported from 2021 to 2023, are summarized. Carbohydrate-based prodrugs, drugs, and delivery systems are covered, highlighting derivatization of existing antibiotics, use of nanotechnology, and repurposing of available therapeutical agents as the most popular strategies used in antibacterial agents' development.