title: Mouse double minute antagonist Nutlin-3a enhances chemotherapy-induced apoptosis in cancer cells with mutant p53 by activating E2F1.
abstract: MDM2 is a critical negative regulator of the p53 tumor suppressor protein. Recently, small-molecule antagonists of MDM2, the Nutlins, have been developed to inhibit the p53-MDM2 interaction and activate p53 signaling. However, half of human cancers have mutated p53 and they are resistant to Nutlin treatment. Here, we report that treatment of the p53-mutant malignant peripheral nerve sheath (MPNST) and p53-null HCT116 cells with cisplatin (Cis) and Nutlin-3a induced a degree of apoptosis that was significantly greater than either drug alone. Nutlin-3a also increased the cytotoxicity of both carboplatin and doxorubicin in a series of p53-mutant human tumor cell lines. In the human dedifferentiated liposarcoma cell line (LS141) and the p53 wild-type HCT116 cells, Nutlin-3a induced downregulation of E2F1 and this effect appeared to be proteasome dependent. In contrast, in MPNST and HCTp53-/- cells, Nutlin-3a inhibited the binding of E2F1 to MDM2 and induced transcriptional activation of free E2F1 in the presence of Cis-induced DNA damage. Downregulation of E2F1 by small interfering RNA significantly decreased the level of apoptosis induced by Cis and Nutlin-3a treatment. Moreover, expression of a dominant-negative form of E2F1 rescued cells from apoptosis, whereas cells overexpressing wild-type E2F1 showed an increase in cell death. This correlated with the induction of the proapoptotic proteins p73alpha and Noxa, which are both regulated by E2F1. These results indicate that antagonism of MDM2 by Nutlin-3a in cells with mutant p53 enhances chemosensitivity in an E2F1-dependent manner. Nutlin-3a therefore may provide a therapeutic benefit in tumors with mutant p53 provided it is combined with chemotherapy.
authors.affiliation: Laboratory of New Drug Development, Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
authors.forename: G
authors.initials: G
authors.lastname: Ambrosini
authors.forename: E B
authors.initials: EB
authors.lastname: Sambol
authors.forename: D
authors.initials: D
authors.lastname: Carvajal
authors.forename: L T
authors.initials: LT
authors.lastname: Vassilev
authors.forename: S
authors.initials: S
authors.lastname: Singer
authors.forename: G K
authors.initials: GK
authors.lastname: Schwartz
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D016190:Carboplatin / Q000494:pharmacology; D002945:Cisplatin / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007093:Imidazoles / Q000378:metabolism / Q000494:pharmacology*; D051379:Mice; D009687:Nuclear Proteins / Q000187:drug effects / Q000378:metabolism; D010879:Piperazines / Q000378:metabolism / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000187:drug effects / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D007093:Imidazoles; D009687:Nuclear Proteins; C498702:PMAIP1 protein, human; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; C000606368:Trp73 protein, mouse; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C482205:nutlin 3; D004317:Doxorubicin; D016190:Carboplatin; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D002945:Cisplatin