Macrocyclic peptides and peptidomimetics as modulators of protein-protein interactions

Macrocyclic peptides and peptidomimetics (MPPs) have emerged as a powerful therapeutic class in peptide-based drug discovery, uniquely positioned to modulate challenging protein-protein interactions (PPIs). While dysregulated PPIs drive diverse human pathologies, including cancer, metabolic disorders, neurodegenerative proteinopathies, inflammatory conditions, and microbial infections, targeting them remains difficult. Traditional small molecules lack the surface area to bind large, flat PPI interfaces, whereas linear peptides suffer from rapid proteolytic degradation and poor cell permeability. MPPs overcome these limitations by bridging the gap between small molecules and biologics. Their cyclic architecture provides conformational rigidity minimizing entropic penalties and maximizing binding affinity and selectivity. This structural pre-organization also enhances metabolic robustness, protease resistance, and cellular permeability. This review comprehensively examines the biological significance of PPIs in human disease and details how MPPs effectively modulate historically undruggable targets. We highlight current synthetic strategies, peptide engineering platforms, and the clinical and preclinical status of leading MPP candidates, while weighing their operational advantages and limitations. Finally, we analyze the contemporary market trajectory and emerging commercial opportunities, positioning MPPs as next-generation, PPI-targeting therapeutics.