Abstract 1072: Combination screening of DNA damaging agents temozolomide and trabectedin with inhibitors of DNA repair using a complex spheroid model with a panel of patient-derived and established tumor cell lines
Authors: Coussens Nathan P. , Parchment Ralph E. , Moscow Jeffrey A. , Doyle L. Austin , Delosh René , Laudeman Julie , Reinhart Russell , Ogle Chad , Silvers Thomas , Dexheimer Thomas S. , Morris Joel , Teicher Beverly A. , Doroshow James H. 
Published: July 2021

Abstract
DNA-damaging agents are important anticancer therapeutics but are rarely curative. The current study combines the DNA-damaging agents trabectedin and temozolomide with varied DNA repair inhibitors to identify combinations that increase malignant cell kill and therefore might improve therapeutic benefit. Twenty-seven tumor cell lines focused on sarcoma and small cell lung cancer (https://pdmr.cancer.gov/models/database.htm) were grown as complex spheroids containing 60% tumor cells, 25% endothelial cells and 15% mesenchymal stem cells as an in vitro model for human solid tumors. After 3 days of growth, the complex spheroids were screened using a 3-log concentration range with the highest concentration at the clinical Cmax for each agent. The spheroids were treated with temozolomide or trabectedin as single agents or in combination with a PARP inhibitor (olaparib or talazoparib), an ATM inhibitor (AZD-1390), an ATR inhibitor (berzosertib (M6620) or BAY-1895344), a DNA-PK inhibitor (nedisertib (M3814) or VX984) or a BET bromodomain inhibitor (birabresib). Seven days after drug exposure, ATP was measured with CellTiter-Glo 3D. Olaparib or talazoparib produced additive to greater than additive cell killing in combination with either trabectedin or temozolomide. Whereas cell killing with temozolomide alone was modest, greater than 1 log of cell killing was achieved in combination with either olaparib or talazoparib. The ATM inhibitor AZD-1390 in combination with trabectedin showed greater than additive responses in most models and approximately 3 logs of cell killing in sarcoma and small cell lung cancer models at higher trabectedin concentrations. The ATR inhibitors BAY-1895344 and berzosertib had additive and greater than additive responses in combination with temozolomide or trabectedin among the small cell lung cancer models tested and produced greater than 2 logs of cell kill in many models when combined with temozolomide. When combined with trabectedin, the DNA-PK inhibitor VX-984 had additive responses, whereas nedisertib had greater than additive responses in most models. The BET inhibitor birabresib had greater than additive responses in many models when combined with trabectedin and additive responses with temozolomide. Overall, greater than additive responses were observed more frequently with trabectedin combinations containing the ATM inhibitor AZD-1390 or the DNA-PK inhibitor nedisertib, as well as temozolomide combinations with the PARP inhibitors olaparib or talazoparib or the ATR inhibitor BAY-1895344, particularly among sarcoma and small cell lung cancer models. These results might inform the prioritization of drug combinations for further investigation. This project was funded in part with federal funds from the NCI, NIH, under contract no. HHSN261200800001E.
Citation Format: Nathan P. Coussens, Ralph E. Parchment, Jeffrey A. Moscow, L. Austin Doyle, René Delosh, Julie Laudeman, Russell Reinhart, Chad Ogle, Thomas Silvers, Thomas S. Dexheimer, Joel Morris, Beverly A. Teicher, James H. Doroshow. Combination screening of DNA damaging agents temozolomide and trabectedin with inhibitors of DNA repair using a complex spheroid model with a panel of patient-derived and established tumor cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1072.