Testicular cancer (TC) patients with metastatic disease and poor prognosis have a 50% 5-year survival. It has been reported that resistant TC cell lines show hyperactivation of the PI3K/Akt/mTOR pathway. In this study we investigated the potential benefit from PI3K, Akt and mTOR inhibition in combination with cisplatin in TC.

Our panel of embryonal carcinoma cell lines include the cisplatin-sensitive cells: Tera and 833KE and the cisplatin-resistant cells: Scha, TeraCP and NCCIT. Western blotting showed that the resistant TC cell line TeraCP expresses higher levels of p-Akt compared to the sensitive cell line Tera. To evaluate sensitization towards cisplatin, TC cell lines were treated with cisplatin and/or PI3K inhibitor GDC0941, Akt inhibitor MK2206, mTORC1 inhibitor everolimus and mTORC1/2 inhibitors AZD8055 and AZD2014 for 24 hours and DilC5/PI staining was performed to estimate apoptosis with flow cytometry. All TC cell lines were strongly sensitized by mTORC1/2 inhibition by increasing cisplatin induced apoptosis to 60-80% when cisplatin alone induced only 15-30%. TC cells were also sensitized by mTORC1 and PI3K inhibition but to a lesser extent. Akt inhibition did not sensitize Scha or Tera cells to cisplatin, while TeraCP was marginally sensitized. We then evaluated clonogenic capacity in cells pretreated with AZD8055 for 24 hours and seeded in the presence of different concentrations of cisplatin for 6 days. Clonogenic capacity was reduced in Tera and TeraCP after mTORC1/2 inhibition with AZD8055 compared with control cells treated with cisplatin only. Western blot done with Scha, Tera and TeraCP lysates treated for 24 hours with AZD8055, everolimus, GDC0941 and MK2206 showed that only mTOR inhibition was able to block S6 phosphorylation. In addition, we performed immunohistochemistry of p-S6 and Ki-67 in paraffin embedded tissue from TC patients. IHC showed that patient derived xenografts showed high expression of these markers compared to non-cancerous tissue, meaning that the mTOR pathway is very active in this tumor type.

These data indicate that TC relies on the PI3K/Akt/mTOR pathway for survival and mTORC1/2 inhibition showed the stronger sensitizing effect towards cisplatin treatment. We consider adding mTORC1C/2 inhibition to cisplatin based treatment a potential therapeutic option for chemoresistant TC patients that warrants further in vivo investigations.

Supported by CONACYT grant 381543 and Dutch Cancer Society grant RUG 2014-6691

Citation Format: Fernanda Ximena Rosas Plaza, Gerda de Vries, Albert J. Suurmeijer, Jourik A. Gietema, Marcel A.T.M. van Vugt, Steven de Jong. Dual mTORC1/2 inhibition sensitizes testicular cancer cell lines toward cisplatin treatment [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 152. doi:10.1158/1538-7445.AM2017-152