MDM4 and neoplasm: Although Mdmx (murine/human double minute X) has no ubiquitination activity, it can either bind to the N-terminus of p53 and inactivate it directly or ubiquitinate p53 by heterodimerizing with Mdm2.375 Nutlin-3 exhibits poor inhibition of Mdmx–p53 interactions, and there is a need for dual inhibitors of both Mdm2 and Mdmx due to the high expression of Mdmx in some cancers.392,393 ATSP-7041, a dual inhibitor, can induce p53-dependent tumor growth suppression.394 NSC207895, targeting Mdmx specifically, can act additively with nutlin-3a to activate p53 and induce apoptosis (Fig. 5).395