Abstract 6229: MDM2 inhibitors sensitize testicular cancer models to mTORC1/2 inhibitors and cisplatin

Abstract

Abstract Testicular cancer (TC) is one of the most common solid tumors in young men that can effectively be treated with cisplatin-based chemotherapy. However, 10% of those wild type p53 expressing TC patients will not survive their disease. The aim of this study was to identify effective combinations with MDM2 inhibitors in TC models. A panel of cisplatin sensitive and -resistant human TC cell lines and TC patient-derived xenograft (PDX) models have been treated with MDM2 inhibitors (Nutlin-3a, RG7388), cisplatin and AKT/mTORC1/2 inhibitors (MK2206, AZD8055 and INK128). Survival, apoptosis, and clonogenic assays were performed. Transcriptional activity of p53 was determined using chromatin immunoprecipitation (CHIP) followed by quantitative PCR of target promoters. Mechanisms of apoptosis induction were studied by measuring mitochondrial priming, siRNA approaches and BH3 mimetics. We found that MDM2 inhibitors sensitized TC cell lines to cisplatin and mTORC1/2 inhibition. Nutlin-3a in combination with cisplatin or AZD8055 treatment induced caspase 3 and PARP cleavage and reduced clonogenic outgrowth. Enriched p53 binding to the promoter regions of known activators of extrinsic and intrinsic apoptosis, FAS, PUMA and NOXA, was observed in response to Nutlin-3a or cisplatin. BH3 profiling of mitochondria and siRNA mediated silencing identified PUMA and NOXA as key pro-apoptotic proteins in TC cell lines. Interestingly, addition of the BH3 mimetics ABT-737 and A-1210477, mimicking PUMA and NOXA respectively, to combination treatments shifted the balance towards apoptosis as well. In vivo experiments showed reduced tumor growth especially in the wild type p53 PDX model TC1 treated with RG7388/cisplatin, which was reflected in p53 activation and increased caspase-3 activity. No potentiating effect of this combination was observed in the p53 wild type PDX model TC4. In conclusion, we have demonstrated that targeting of MDM2 in combination with chemotherapy can be very effective in TC models. Our results warrant further investigation of this drug combination in the treatment of TC. Supported by a grant from the Dutch Cancer Society (RUG 2014-6691) Citation Format: Steven de Jong, Gerda de Vries, Gert Jan Meersma, Albert J.H. Suurmeijer, Marcel A.T.M. van Vugt, Jourik A Gietema. MDM2 inhibitors sensitize testicular cancer models to mTORC1/2 inhibitors and cisplatin [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6229.