CDK1 and ACTH-producing pituitary gland adenoma: Consistent with these findings, the second-generation CDK1 and CDK2 inhibitor R-roscovitine (seliciclib), inhibiting the association of CDK2/cyclin E complexes (28), caused a reduction of POMC promoter expression in ~40% in a double transgenic POMC : PTTG zebrafish model, and in murine AtT20 corticotroph adenoma models (29–31) Other studies also found murine p27 knock-out was associated with enlarging corticotroph tumors within 12 months (32–34), and molecular research of recurrent human corticotroph adenomas or carcinomas showed lower or absent p27 staining (35).