Abstract 3971: Genome-wide CRISPR/Cas9 screening reveals ATR as a therapeutic target that overcomes osteosarcoma chemoresistance

Abstract Osteosarcoma (OS) is the most common bone cancer in pediatric patients. Therapeutic target identification in OS has been extremely challenging due to the high degree of heterogeneity in its genetic profile and lack of specific oncogenic driver genes. Despite extensive research efforts, the treatment and survival outcomes for OS patients have stagnated over the past 30 years. OS remains a lethal cancer due to metastasis and development of resistance to current chemotherapies. Study of chemo-resistance mechanisms and identification of novel targets that can be used in combination therapy are therefore critical to improve OS treatment. The combination of gene essentiality concept and clustered, regularly interspaced, short palindromic repeats-associated nuclease Cas9 (CRISPR/Cas9) functional knockout screen is an ideal new strategy to address the genetic complexity and drug-resistance in OS. A gene is considered essential if it is critical for reproductive success in an organism under specified condition. The recent introduction of genome editing using the CRISPR/Cas9 system with pooled library of guided RNAs (gRNAs) makes it feasible to systematically identify the genes required for the proliferation. By comparing the fold change of gRNA abundance in the surviving population of cells relative to the initial population, the essential genes under different settings can be identified.As a novel therapeutic approach for identifying combination therapies for OS, we conducted genome-wide (GW) CRISPR/Cas9 screen in SaOS2 OS cell lines parallel with RNA-sequencing in different conditions (control, Cisplatin, Doxorubicin), followed by gene essentiality score calculation. Cisplatin (CIS) and Doxorubicin (DOX) combination is among those commonly used as first-line therapies for OS treatment. The objective of our studies is to bring forth new perspectives in target identification and chemo-resistance study for OS. The gene targets and pathways that become more essential for OS cell proliferation in the presence of chemo drugs were revealed. Drugs specific for some of these target could then be added to the established CIS or DOX regimen to overcome existing drug resistance. On the other hand, the genes that become less essential after treatment could provide additional chemo-resistant mechanisms. Multiple gene targets were identified in the screen. Among these, we’ve successfully identified and validated Berzosertib, an ataxia telangiectasia and Rad3-related protein kinase inhibitor (ATRi), as a synergistic lethality partner to Cisplatin in vitro for OS treatment. Efficacy and safety measurement of Berzosertib and Cisplatin combination therapy in an OS xenograft mouse model and in several OS patient-derived xenograft models is in progress. Citation Format: Shan Tang, Karen E. Pollok, Pankita H. Pandya, Ryan D. Roberts, Xue Wu, Lang Li. Genome-wide CRISPR/Cas9 screening reveals ATR as a therapeutic target that overcomes osteosarcoma chemoresistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3971.