Abstract
Stapled peptides with covalently cross-linked side chains have been put to ever-increasing use for the development of peptide-based drugs, especially derived from α-helical peptide sequences. Nowadays, a variety of stapling technologies have been developed and allows for the stabilization of helical conformation responsible for the activity of biological helical peptides. Our group found that brefeldin A-inhibited guanine nucleotide-exchange protein 3 (BIG3), over-expressed in breast cancer cell, inhibits the tumor-suppressive effect of prohibitin 2 (PHB2) through the BIG3-PHB2 proteins interaction. Requiring a short α-helical segment of BIG3, the protein-protein interaction was selected as a target of great versatility for growth inhibition of the cancer cells. Therefore, the α-helical segment of BIG3 was subjected to the stapling strategy to develop anti-breast cancer peptides. Glutamine (Gln 165), aspartic acid (Asp 169), and Gln 173 residues in the α-helical region, indispensable for the PPI with PHB2, lie on the same face of the α-helix with i and i + 4 spacing. Several thirteen-residue stapled peptides derived from BIG3 were synthesized and examined their biological activity using culture cell lines and mouse xenograft model. Among the synthetic stapled peptides, the peptides, with the pivotal residues in the same helical face fixed by incorporating the staple on the opposite face with i and i + 4 spacing, showed anti-tumor effects superior to original 28-residue estrogen receptor-α (ERα) activity-regulator synthetic peptide (ERAP) with a oligoArg cell-penetrating peptide (CPP). Stapled version of ERAP (stERAP) more efficiently inhibited the estrogen-induced cancer cell growth than the original ERAP. Furthermore, the long-lasting in vivo anti-tumor effect of the stERAPs in breast cancer xenografts in mice was observed.
