Abstract A45: Targeted drug therapies for osteosarcoma
Authors: Sayles Leanne C. , Breese Marcus R. , Martell Henry , Lee Alex G. , Leung Stanley , Shah Avanthi T. , Sweet-Cordero E. Alejandro 
Published: August 2020

Abstract
Osteosarcoma (OS) is a highly aggressive cancer that has had no new treatments options in over 30 years. OS is a heterogeneous disease that is characterized by widespread and recurrent somatic copy-number alterations (SCNAs) with relatively few recurrent point mutations. Our laboratory has recently published that SCNAs contain key oncogenic drivers that can be used to identify patient-specific candidates for targeted therapies (Sayles, Breese, et al., Cancer Discovery Jan. 2019). Using patient-derived tumor xenografts (PDX), we demonstrated that targeting of patient-specific oncogenes within SCNAs leads to significant decrease in tumor burden. However, no single-agent therapy was able to regress tumors completely, suggesting that combination therapies would be required for disease management. In order to assess the applicability of our PDX models to the patient tumor and the stability of the oncogenes within SCNAs, we performed whole-genome sequencing (WGS). We observed that SCNAs are highly stable across samples from the same patient in addition to multiple PDX passages and PDX-derived cell lines, highlighting the equivalence between the PDX models and their derived cell lines to the human disease. This allows us to use the PDX cell lines as a surrogate for the identification of combination drug therapies that may be of benefit in OS. Currently, we have generated 6 PDX cell lines that encompass the most common SCNAs observed in patients, including MYC, CCNE1, and CDK4 gain and alterations in the PI3K/PTEN pathway. We have performed a single-agent drug screen with 38 agents and have identified several efficacious compounds, including HDAC inhibitors and cell cycle and Wee1 inhibitors. We also observed a differential response between PDX cell lines to various chemotherapeutics, including gemcitabine, paclitaxel, and SN-38. We are currently testing combination drug therapies in vitro and will validate using our PDX xenografts in vivo. While these experiments are still ongoing, we can report that MYC-driven OS PDX xenografts show a striking resensitization to cisplatin after AURKB inhibitor (barasertib) pretreatment. We have 2 aggressive PDX models with high MYC amplification generated from metastatic lesions. These PDX models are resistant to cisplatin, which is part of the standard of care. We treated these PDX with barasertib and then with cisplatin for two cycles. This resulted in a decrease in tumor volume for the combination therapy compared to vehicle or either single agent alone. Additionally, we observed retention of the platinum adduct 24 hrs after cisplatin dosing only when tumors were pretreated with barasertib. Further work is needed to assess the mechanism of this synergy and whether it can be of use in other SCNA-driven OS and to identify other possible combination therapies that could be of importance in this disease.
Citation Format: Leanne C. Sayles, Marcus R. Breese, Henry Martell, Alex G. Lee, Stanley Leung, Avanthi T. Shah, E. Alejandro Sweet-Cordero. Targeted drug therapies for osteosarcoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A45.