Pharmacologically Increasing Mdm2 Inhibits DNA Repair and Cooperates with Genotoxic Agents to Kill p53-Inactivated Ovarian Cancer Cells

Abstract

The Mdm2 oncogene is a negative regulator of the p53 tumor suppressor and recently identified inhibitor of DNA break repair. Nutlin-3 is a small molecule inhibitor of Mdm2/p53 interaction that can induce apoptosis in cancer cells through activation of p53. While this is promising therapy for those cancers with wild-type p53, half of all human cancers have inactivated p53. Here, we reveal a previously unappreciated effect of Nutlin is inhibition of DNA break repair, stemming from its ability to increase Mdm2 protein levels. The Nutlin-induced increase in Mdm2 inhibited DNA double-strand break (DSB) repair and prolonged DNA damage response signaling independent of p53. Mechanistically, this effect of Nutlin required Mdm2 and acted through Nbs1 of the Mre11/Rad50/Nbs1 DNA repair complex. In ovarian cancer cells where >90% have inactivated p53, Nutlin combined with the genotoxic agents, cisplatin or etoposide, had a cooperative lethal effect resulting in increased DNA damage and apoptosis. Therefore, these data demonstrate an unexpected consequence of pharmacologically increasing Mdm2 levels that when utilized in combination with genotoxic agents induces synthetic lethality in ovarian cancer cells, and likely other malignant cell types, that have inactivated p53. Implications Data reveal a therapeutically beneficial effect of pharmacologically increasing Mdm2 levels combined with chemotherapeutic agents for malignancies that have lost functional p53.

Mdm2 Is Required for Survival and Growth of p53-Deficient Cancer Cells

“…Mdm2 protein levels were increased in p53 -null sarcoma cells treated with Nutlin-3 (Fig. 7C), as we and others previously reported in other cell types (11,33,34). Notably, sarcoma cells treated with 30μM Nutlin-3 showed no change in cell number in G 2 /M over 48 hours relative to control; however, there was a significant increase of cells in G 1 of the cell cycle (Fig.…”

Genome Stability Requires p53

“…However, recently, new approaches to capitalize on the genome instability of cancer cells for treatment are being tested. For example, pharmacologically increasing Mdm2 levels with Nutlin in ovarian carcinoma cells that lack functional p53 causes a delay in DNA break repair that results in increased sensitivity to DNA-damage agents, such as cisplatin and etoposide (Carrillo et al 2015b). Topoisomerase II inhibitors were shown to cooperate with Nutlin in pancreatic cancer cells that lacked functional p53 (Conradt…”

Amyloid Beta Peptide 1-42 Induces SH-SY5Y Cell Apoptosis via the Promotion of Meg3 Long Noncoding RNA Expression

“…It can form an autoregulatory negative feedback loop with p53 in the cell to tightly regulate the levels and activity of p53. Also, it has been shown that MDM2 is an oncogene, and it was identified as an inhibitor of DNA break repair [11,12]. In our study, we identified exogenous Aβ 1-42 -stimulated Meg3 lncRNA as a new regulator that directly repressed MDM2 to activate p53 and enhance p53 function in SH-SY5Y cells (fig.…”

“…In contrast, when the expression of Meg3 lncRNA siRNA was silenced in transfected SH-SY5Y cells treated with exogenous Aβ peptides, the cytotoxic effects of Aβ were significantly reduced and these cells maintained their normal state. In addition, MDM2, one of the E3 ubiquitin ligases, is a direct p53 transcriptional target and also the most critical negative regulator of p53 [11,12]. It can form an autoregulatory negative feedback loop with p53 in the cell to tightly regulate the levels and activity of p53.…”