The two closely related proteins MDM2 and MDMX function as negative regulators of p53, a tumor suppressor protein. MDMX shares ~57% sequence identity with MDM2 in p53 binding domain but so far known MDM2 inhibitors show reduced activity on MDMX. The MDMX protein is overexpressed in most retinoblastomas, as well as in head and neck, breast, colon, lung, hepatocellular, and bladder carcinomas (J Biol Chem 2010, 285, 10786-10796).