A peptide with G2 checkpoint-abrogating activity. G2 checkpoint inhibitor CBP501 inhibits multiple serine/threonine kinases, including MAPKAP-K2, C-Tak1, and CHK1, that phosphorylate serine 216 of the dual-specific phosphatase Cdc25C (cell division checkpoint 25 C); disruption of Cdc25C activity results in the inhibition of Cdc25C dephosphorylation of the mitotic cyclin-dependent kinase complex Cdc2/cyclin B, preventing entry into the mitotic phase of the cell cycle.