CDK2 (Cyclin-dependent kinase 2) is a member of the eukaryotic S/T protein kinase family and its function is to catalyze the phosphoryl transfer of ATP γ-phosphate to serine or threonine hydroxyl (denoted as S ₀ /T ₀ ) in a protein substrate. The fully active CDK2 is in complex with HHASPRK (an optimal peptide substrate), namely interactions of CDK2 with peptide substrate and the dynamics of the G-loop. CDK2 participates in eukaryotic cell cycle regulation at the G1/S boundary. CDK2 deregulation has been proved to occur in tumor cells, evoking a strong interest in artificial and native inhibitors. CDK2 activity is tightly regulated by a complex mechanism, including a positive regulatory subunit binding, and phosphorylations at positive and/or negative regulatory sites.