Inhibitors that are specific for the PBD domain of the PLK1 protein are described. The inhibitors include fragment ligated inhibitors that include one or more amino acids of a starting peptide upon which the inhibitors are based and also include non-peptidic inhibitors. The inhibitors include a benzoic acid-based derivative that mimics the structure activity relationship of amino acid residues of known peptide inhibitors. The inhibitors exhibit high selectivity for the PLK1 isotype.
