Enhancing the Cell Permeability and Metabolic Stability of Peptidyl Drugs by Reversible Bicyclization.

Therapeutic applications of peptides are currently limited by their proteolytic instability and impermeability to the cell membrane. A general, reversible bicyclization strategy is now reported to increase both the proteolytic stability and cell permeability of peptidyl drugs. A peptide drug is fused with a short cell-penetrating motif and converted into a conformationally constrained bicyclic structure through the formation of a pair of disulfide bonds. The resulting bicyclic peptide has greatly enhanced proteolytic stability as well as cell-permeability. Once inside the cell, the disulfide bonds are reduced to produce a linear, biologically active peptide. This strategy was applied to generate a cell-permeable bicyclic peptidyl inhibitor against the NEMO-IKK interaction.