Mdm2 antagonists induce apoptosis and synergize with cisplatin overcoming chemoresistance in TP53 wild‐type ovarian cancer cells

Abstract

Ovarian cancer (OVCa) is the leading cause of death from gynecological malignancies. Although treatment for advanced OVCa has improved with the introduction of taxane-platinum chemotherapy, the majority of patients will develop resistance to the treatment, leading to poor prognosis. One of the causes of chemoresistance is the reduced ability to undergo apoptosis. Cisplatin is a genotoxic drug that leads cells to apoptosis through the activation of the p53 pathway. Defective signaling in this pathway compromises p53 function, and thus cisplatin does not induce apoptosis. A new group of nongenotoxic small molecules called Nutlins have been developed to inhibit p53-Mdm2 binding, inducing apoptosis in chemoresistant tumors through the activation of the p53 pathway. The wild-type p53 cisplatin-resistant ovarian cancer cell-line A2780cis was used to test the effect of Nutlin-3a (Nut3a) on apoptosis response. The results showed that Nut3a synergized with cisplatin, inducing cell-cycle arrest in G2/M and potentiating apoptotic cell death. Increased apoptosis was also induced in wild-type TP53 primary OVCa cultures by double cisplatin-Nut3a treatment. In conclusion, Nut3a appears to sensitize chemoresistant OVCa cells to cisplatin, inducing apoptosis. As increased response was generalized in primary tumors, this cisplatin-Nut3a combination could be useful for the treatment of patients harboring wild-type TP53 who do not respond to standard chemotherapy.Ovarian cancer (OVCa) kills~115,000 women annually worldwide. The majority of patients with OVCa are diagnosed with advanced disease and managed with surgical cytoreduction followed by platinum and taxane-based chemotherapy, 1 but the majority of them will eventually recur and die as a consequence of metastatic spread. Crystalline cis-dichlorodiammine platinum (II) [cisplatin (CDDP)] is the cytotoxic agent used as therapy, but it leads to chemoresistance, the largest obstacle in treating patients with recurrent disease. Multidrug resistance, DNA mismatch repair and alterations in the p53 pathway are examples of tumor-cell features that may lead to CDDP resistance. 2Defects in apoptosis are one of the mechanisms that can lead to chemoresistance. The p53 protein is recognized as an important cell-regulatory element that arrests the growth of cells containing damaged DNA. Cell-cycle control and activation of apoptosis appear to be tightly linked functions of p53. The importance of p53 in human malignances was highlighted by the detection of abnormal p53 in more than 50% of human cancers. 3,4 Mutations in TP53 are associated with a lack of response to high-dose CDDP therapy in OVCa patients. 5The short-lived protein p53 and its cellular levels are controlled by the rate at which it is degraded. Although several U3 ubiquitin ligases have been implicated in p53

Pre-clinical efficacy and synergistic potential of the MDM2-p53 antagonists, Nutlin-3 and RG7388, as single agents and in combined treatment with cisplatin in ovarian cancer

“…A single limited previous study examined the combination of Nutlin-3a with cisplatin in A2780p, A2780cis and the OV90 cell lines. The results showed a synergistic effect in A2780p and A2780cis, consistent with our study [10]. …”

“…This suggests some mutant forms of p53 still show evidence of degradation by MDM2 which is prevented by the MDM2 inhibitors. These results are consistent with limited previous studies [10, 21] demonstrating that wild-type TP53 ovarian cancer cell lines are responsive to Nutlin-3 and extends observations to the second generation MDM2 inhibitor RG7388 currently in early phase clinical trials.…”

“…RG7388 was subsequently developed as a second generation MDM2 inhibitor with superior potency, selectivity and oral bioavailability suitable for clinical development to inhibit the MDM2-p53 interaction and activate the p53 pathway [7, 8]. These compounds target a small hydrophobic pocket on MDM2, to which p53 normally binds, leading to p53 stabilization and upregulation of p53 downstream transcriptional targets involved in cell cycle arrest and/or apoptosis, including genes encoding p21 WAF1 , BAX and BBC3 (PUMA) [9, 10]. Using MDM2-p53 antagonists as single-agent therapy has been suggested to be potentially limited due to acquisition of resistance through continuous exposure to MDM2 inhibitors followed by de novo mutations [11] and (reviewed by [12]).…”

Mechanisms of Targeting the MDM2-p53-FOXM1 Axis in Well-Differentiated Intestinal Neuroendocrine Tumors

“…Enhanced effects of recovering a proapoptotic p53 function and induction of genotoxic stress are probable, and a sensitizing effect of a combined treatment has been demonstrated for several cancer entities [26][27][28]. Furthermore, nutlin-3a has been shown to inhibit FOXM1 activity and expression, which is usually activated after cisplatin treatment and contributes to platin-based che- motherapy resistance [29][30][31].…”

Understanding p53: new insights into tumor suppression

“…Despite these agents needing to overcome intrinsic mechanisms that confer protection against apoptosis to cancer cells, these trials are yielding promising results. Synergistic effects have been noted when Nutlin-3, an MDM2 inhibitor that is known to arrest the cell cycle in a p53-dependent manner, was combined with established anticancer agents such as doxorubicin, vincristine or cisplatin, among others [5][6][7]. The most intriguing results in the development of such therapies have recently been described in an extensive review by Hoe et al [4].…”