Enhanced Intracellular Delivery by Twisted CC-Loop Conformation in Cyclic Cell-Penetrating Peptides.

Biological drugs hold great promise for treating various diseases, but their efficacy is often limited by poor cellular uptake. Herein, we introduce cyclic cell-penetrating peptides (CPPs) to enhance the delivery efficiency. Three cyclic peptides with varying ring sizes were designed from a classic amphiphilic CPP disulfide bond formation. Among them, adopted a twisted CC-loop conformation distinct from the typical β-hairpin on negatively charged cell surfaces. This unique structure enhanced membrane penetration, enabling superior delivery compared with linear and other cyclic variants. efficiently delivered functional siRNA targeting METTL3, achieving knockdown comparable to that of Lipofectamine 2000. It also transported GFP and plasmids, demonstrating versatility. Computational analysis revealed molecular-level insights into the enhanced interaction between the CC-loop structure and membranes. These findings establish a new CPP conformation that advances therapeutic delivery and opens new avenues for drug transport strategies.