Hands On Review,Zosurabalpin, a macrocyclic peptide

The relentless rise of antimicrobial resistance (AMR) poses a significant global health threat, necessitating the urgent discovery and development of novel therapeutic agents. In this critical endeavor, macrocyclic peptide antibiotics are emerging as a promising and powerful class of compounds with the potential to revolutionize our fight against drug-resistant bacteria. Their unique structural characteristics and diverse mechanisms of action make them important sources for discovering new antibiotics, offering a much-needed alternative to conventional treatments.

Macrocyclic peptides (MCPs) are characterized by their macrocyclic ring structure formed via amide or other covalent bonds. This cyclic arrangement confers remarkable structural stability and a distinct three-dimensional conformation, which are crucial for their potent antibacterial activity. Unlike linear peptides, this constrained architecture often leads to improved resistance against degradation by proteases, enhancing their pharmacokinetic properties and therapeutic potential. Macrocyclic antibiotics are a class of antimicrobial agents defined by these large, ring-shaped molecular structures.

The versatility of macrocyclic peptides is evident in their ability to target a wide range of bacterial processes. Research has identified macrocyclic peptides that kill bacteria by blocking essential cellular functions. For instance, Zosurabalpin, a macrocyclic peptide, has demonstrated efficacy against highly resistant bacteria like Carbapenem-resistant *Acinetobacter baumannii* by effectively blocking cross-membrane transport. This specific mechanism of action, targeting lipid transport, is a testament to the novel ways macrocyclic peptide antibiotics can disrupt bacterial viability. Furthermore, some peptides arrest the growth of specific bacterial strains by inhibiting outer membrane protein (OMP) assembly, a critical process for Gram-negative bacteria.

The discovery of new macrocyclic peptide antibiotics is being accelerated by innovative research methodologies. Display technologies are proving instrumental in identifying optimized and non-toxic macrocyclic peptide antibiotic candidates that retain in vivo function. This approach has led to the identification of tethered macrocyclic peptides (MCP) that exhibit effectiveness against challenging pathogens. Moreover, advances in rule-based omics mining are revealing novel aminovinyl-(methyl)cysteine (Avi(Me)Cys)-containing peptide antibiotics, expanding the known repertoire of these potent molecules. These discoveries highlight the potential of Avi(Me)Cys-containing peptides in broadening the arsenal of antibiotics against multi-drug-resistant organisms.

The structural diversity within the macrocyclic peptide family is vast. Some macrocyclic peptide-based scaffolds have yielded preclinical and clinical-stage antibiotics, while others serve as valuable starting points for medicinal chemists. For example, certain macrocyclic peptides bear close structural resemblance to historically significant compounds, such as the enigmatic biphenomycins, suggesting a continuum of discovery building upon past knowledge. Natural macrocyclic peptide-based products have already provided novel antibiotics and antibiotic scaffolds that target essential bacterial cell envelope components.

The potential applications of macrocyclic peptides extend beyond direct antibacterial action. Macrocyclic antimicrobial peptides are conjugated to other molecules, such as antibodies, to create targeted delivery systems or synergistic therapeutic agents. This approach combines the strengths of biologics with the potency of macrocyclic peptides, offering enhanced efficacy and reduced off-target effects. Researchers at MSD are actively exploring macrocyclic peptides as a novel way to combine the properties of biologics with the convenience of oral administration.

The field of macrocyclic peptide drug development is experiencing significant advancements. Among the six peptide drugs approved in 2023, three were macrocyclic peptides, underscoring their growing importance in modern medicine. This trend is expected to continue as scientists delve deeper into the therapeutic potential of these molecules. Macrocyclic \u03b2-hairpin peptides represent a promising group for future antibiotic development due to their inherent stability, potency, and ability to employ diverse mechanisms of action. For instance, Thanatin is a \u03b2-hairpin antimicrobial peptide that has demonstrated potent broad-spectrum activity against bacterial and fungal pathogens.

The development of macrocyclic peptide antibiotics is not limited to naturally occurring compounds. Synthetic approaches are yielding innovative antibiotics inspired by natural product scaffolds. These chimeric agents often incorporate \u03b2-hairpin structures, leveraging their inherent properties for potent antibacterial effects. The ongoing research into macrocyclic peptide antibiotics is crucial for addressing antimicrobial resistance, ensuring that we have effective tools to combat infectious diseases in the future. The exploration of macrocyclic peptides promises to yield powerful new antibiotic drugs and drug candidates, solidifying their role as a critical frontier in antibacterial research. Ultimately, AMPs are known for their multifunctional role in disrupting bacterial processes, offering a promising alternative to conventional antibiotics.