Advances in nanoscale engineering of cyclotides: Overcoming biological barriers toward precision therapeutics

Cyclotides are macrocyclic peptides derived from plants, distinguished by a cyclic cystine-knot (CCK) motif that provides remarkable rigidity and resistance to thermal, chemical, and enzymatic degradation. This distinctive architecture facilitates the molecular grafting of therapeutic epitopes, rendering cyclotides important scaffolds for drug discovery and precision nanomedicine. Despite their significant biological activities, the clinical application is still impeded by inadequate membrane permeability and restricted systemic transport. Recent advancements in nanotechnology have introduced innovative strategies to address these challenges. Documented methodologies encompass the self-assembly of cyclotides into nanofibers, their incorporation into polymeric matrices, conjugation with cell-penetrating peptides to augment intracellular uptake, lipid modification to extend circulation time, and integration with two-dimensional nanomaterials to enhance delivery efficiency. While these methods show encouraging proof-of-concept results, there remains a lack of extensive in vivo studies regarding pharmacokinetics, biodistribution, immunogenicity, and long-term safety. The present review emphasizes the importance of mechanistic and rational design principles that combine cyclotide engineering with sophisticated nanoplatforms. Improving current limitations in scaffold optimization and pharmacological evaluation may enable the advancement of cyclotides from being structurally stable yet transport-limited peptides to clinically applicable precision therapeutics with extensive biomedical potential.