POMC and neoplasm: Moreover, in vitro evaluation on AtT20 mouse corticotroph tumor cell line demonstrated that roscovitine decreased ACTH secretion and cell proliferation, inhibiting cyclin E and inducing cell cycle inhibitors (p27Kip1, p57Kip2, and p21Cip1) expression, as well as inhibiting phosphorylation of retinoblastoma protein (46).