-Sulfonatocalix[4]arene turns peptide aggregates into an efficient cell-penetrating peptide.

A novel cell-penetrating peptide (CPP) called -YR, with as a fluorescent probe, was developed. Initially, we aimed to use Y as a supramolecular host for water-insoluble drugs, with R driving the complex into cells. However, an unexpected hurdle was discovered; the peptide self-assembled into amorphous aggregates, rendering it ineffective for our intended purpose. Molecular dynamics simulations revealed that intermolecular cation-π interactions between arginine and tyrosine caused this aggregation. By decorating the R sidechains with -sulfonatocalix[4]arene (CX4), we successfully dissolved most of the aggregates, significantly improved the peptide's solubility and enhanced the cell uptake with MCF7 and A549 cells both direct penetration and endocytosis. The binding strength between CX4 and R, as well as the interaction between curcumin and tyrosines was quantified. Encouragingly, our results showed that -YR, with CX4, effectively delivered curcumin - as a model for poorly water-soluble drugs - into cells which exhibited potent anticancer activity. Using R/CX4 instead of the conventional R oligoarginine-based CPP simplifies peptide synthesis and offers higher yields. CX4 shows promise for addressing aggregation issues in other peptides that undergo a similar aggregation mechanism.