Methods for developing non-peptidic inhibitors that target the polo-box domain of PLK1 proteins are described. Methods include developing structure activity relationships for peptidic inhibitors followed by development of non-peptide fragment alternatives for portions of the peptide inhibitors. The non-peptide fragment can provide similar structure activity relationship as the replaced peptide. Fragment alternatives to key binding determinants are identified in an iterative computational and synthetic process facilitated through understanding of the peptide structure-activity relationships. The approach is informed by peptide structure-activity data obtained through synthesis and testing of truncated and mutated analogs of known PBD binding motifs.