Abstract B004: ATR-CHK1-WEE1 pathway is a critical dependency in the context of DNA damage and replicative stress in osteosarcoma

Abstract

Osteosarcoma (OS) is characterized by widespread somatic copy number alterations (SCNAs) and structural variations (SVs) with few recurrent point mutations. We previously demonstrated proof-of-principle for a genome-informed strategy for treatment of OS based on rank-ordering SCNAs within specific oncogenes identified by WGS and RNAseq. Although we identified several potentially effective therapeutic strategies using this approach, it is likely that effective therapy for OS will require use of combination therapies. To identify new combination therapy approaches for OS, we used a panel of PDX-derived cell lines (PDXC) and performed a combination drug screen. We assessed 5 drug backbones against 15 targeted agents in 8 PDXC and 2 established OS cell lines. When we combined Gemcitabine with agents that target the ATR-CHK1-WEE1 pathway, we observed strong synergy across all PDXC tested. These results were validated in a secondary screen using a combination matrix across 10 PDXC. Use of targeted agents inhibiting ATR, CHK1 or WEE1 in combination with Gemcitabine led to decreased proliferation and a marked increase in apoptosis in vitro. In subcutaneous tumor models, we observed that decreased tumor growth with either ATRi or Gemcitabine alone, whereas tumors shrank when treated with the combination. However, when we treated OS774 in vivo, there was no effect on tumor growth for either single agent alone or when in combination. This effect was dependent on the presence of ATR as a PDXC with no ATR detectable by western blotting showed not effect in vivo. In an orthotopic model in which PDXC are implanted along the tibia, this combination therapy effectively decreased tumor growth. In a lung metastasis model, ATRi and Gemcitabine resulted a durable reduction in metastatic lesions over time. In summary, we have identified a susceptibility to the ATR-CHK1-WEE1 pathway when combined with gemcitabine. These studies suggest that further investigation ATR-CHK1-WEE1 and gemcitabine are warranted to address the unmet need for new therapeutic approaches for relapsed and recurrent OS patients. Citation Format: Leanne C. Sayles, Henry Martell, Amanda Koehne, Kean-Hooi Ang, Chris Wilson, Michelle Arkin, E. Alejandro Sweet-Cordero. ATR-CHK1-WEE1 pathway is a critical dependency in the context of DNA damage and replicative stress in osteosarcoma [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B004.