Abstract 3861: Development of testicular cancer patient derived xenograft models to test combination therapies targeting PI3K/Akt and MDM2
Authors: Vries Gerda de , Rosas-Plaza Ximena , Vugt Marcel A. van , Suurmeijer Albert J.H. , Gietema Jourik A. , Jong Steven de 
Published: July 2017

Abstract
Metastatic testicular cancer (TC) is highly sensitive to cisplatin-based chemotherapy. However, patients with advanced disease in the poor prognosis group only have a 50% 5-year survival resulting from chemoresistance. Previous data showed that both the PI3K/Akt pathway and the MDM2/p53 axis are involved in cisplatin resistance of TC cells. In this study we aim to establish and characterize TC patient-derived xenografts (PDX) in order to investigate PI3K/Akt and/or MDM2 inhibition as possible treatment options for TC.
Excised and minced (8mm3) primary TC tissue was implanted subcutaneously into male NSG mice to obtain a first generation PDX model (F1). Animals were sacrificed when tumor volume exceeded 1500 mm3. The tumor was harvested and minced. Small pieces (8mm3) were implanted in a second generation (F2), as well as stored in FCS-5% DMSO to establish a biobank. In a panel of TC cell lines, combination treatment of Akt inhibition with or without cisplatin or Nutlin-3a was performed. Cleaved caspase-3 staining was assessed to measure apoptosis, and western blot was used to determine the effect of different treatments on sub-cellular localization and phosphorylation status of MDM2.
We have established 3 TC PDX models. Histology of the primary tumors included the following subtypes: mixed germ cell tumors with embryonal- and yolk sac carcinoma and teratoma components. Engraftment efficacy was 100% and tumor growth initiated within 4-5 weeks after implantation. Interestingly, we successfully implanted a biopsy taken from a metastatic lesion of a patient presenting with progressive refractory disease after receiving standard chemotherapy. Histology of the different PDX generations was comparable to the patient material, although a loss of the teratoma component was observed. In our cell line panel, Akt inhibition using MK2206 sensitized the acquired cisplatin resistant cell line TeraCP towards cisplatin treatment, whereas an additive effect was observed in other cell lines. Combination of Akt and MDM2 inhibition was highly synergistic in apoptosis induction in all cell lines. No relation was observed between the synergistic effect of Akt combined with MDM2 inhibition and sub-cellular localization or phosphorylation levels of MDM2.
Taken together, we have successfully established 3 TC PDX models, including a chemo-resistant model. The biobank is currently being expanded. Combined Akt and MDM2 inhibition resulted in synergistic induction of apoptosis, and these combinations or other novel therapies will be tested in established TC PDX models.
Supported by Dutch Cancer Society grant RUG 2014-6691 and CONACYT grant 381543
Citation Format: Gerda de Vries, Ximena Rosas-Plaza, Marcel A. van Vugt, Albert J.H. Suurmeijer, Jourik A. Gietema, Steven de Jong. Development of testicular cancer patient derived xenograft models to test combination therapies targeting PI3K/Akt and MDM2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3861. doi:10.1158/1538-7445.AM2017-3861