Affinity enhancement of polo-like kinase 1 polo-box domain-binding peptides by <i>N</i> -methylation and lipidation

Cell membrane permeability is one of the biggest issues for bioactive peptides targeting intracellular proteins because of their high polarity and flexibility. To overcome this issue, cell-penetrating peptides (CPPs) are often attached to peptides. Additional approaches include backbone modifications, such as <i>N</i>-methylation and lipidation, which increase structural rigidity and hydrophobicity. Herein, we synthesized and evaluated <i>N</i>-methylated or lipidated Plk1 PBD-binding peptides. <i>N</i>-Methylated and lipidated analogs showed up to 4-fold and 260-fold enhanced PBD affinities, respectively, as compared with the parent PBD-binding peptide. However, none of these analogs showed significant cytotoxicity against HeLa cells. These results suggest that further optimization is required to develop practical Plk1 PBD-binding inhibitors that exhibit cellular activities.