Abstract A02: High-capacity drug screen identification of novel synergistic drug pairs with venetoclax in acute myeloid leukemia

Advancements in the development of targeted therapies have changed the therapeutic paradigm in acute myeloid leukemia (AML) in recent years. The orally available BCL-2 inhibitor venetoclax is effective and well tolerated in combination with either a hypomethylating agent (HMA) or low-dose cytarabine (LDAC). BCL-2 is a anti-apoptotic protein which binds to and sequesters pro-apoptotic proteins such as BAX, BAK, PUMA and NOXA and prevents pro-apoptotic proteins from initiating mitochondrial apoptosis leading to sustained survival in cancer cells. Venetoclax specifically antagonizes BCL-2 protein and allows unbound pro-apoptotic proteins to initiate apoptosis. Venetoclax antagonizes BCL-2 and allows pro-apoptotic proteins to initiate apoptosis. Venetoclax with HMA or LDAC received FDA approval in 2020 for the frontline treatment of AML patients unfit for standard chemotherapy. However, therapeutic resistance is common and there is an urgent need to improve the efficacy and durability of venetoclax in this setting. Combinatory drug approaches allow for targeting of multiple molecular drivers/pathogenic mutations, lower therapeutic concentrations, increased efficacy, and overcoming resistance. Here, we aimed to develop novel synergistic drug combinations with venetoclax to improve venetoclax safety, efficacy and overcome resistance in cell lines with potential clinical applications in AML. Venetoclax IC50 values in eight AML cell lines range from <0.01 µM to >5 µM highlighting differential response among the panel. THP-1 cells were identified as the most venetoclax resistant cell line with little response observed at any concentration up to 72 hours exposure. Western blot and qPCR analyses demonstrated BCL-2 is ubiquitously expressed across the cell lines. A single agent drug screen of 1,971 FDA approved compounds was performed at two concentrations (100 nM and 1 µM), in THP-1 cells at three timepoints (24, 48, and 72 hours). 364 of 1971 compounds (18.5%) induced >50% cell death and were identified as hits. A secondary screen was performed to investigate the top 180 most effective compounds in combination with venetoclax. Dose response matrices and cell viability data were used to calculate synergy scores. Combinations with synergy scores of >10 were considered synergistic. Many combinations were synergistic at one timepoint (n=117, 65%), others were synergistic at 2 timepoints (n=45, 25%) and few were synergistic at all 3 timepoints (n=5, 2.78%). Validation experiments are currently ongoing to investigate the synergistic relationship of top candidate combinations and identify an optimum dose for further investigations including additional validation experiments, mechanistic studies, and toxicity studies. Citation Format: Ruairidh Harrigan, Evangeline Johnston, Kyle B Matchett, Tony J Bjourson. High-capacity drug screen identification of novel synergistic drug pairs with venetoclax in acute myeloid leukemia [abstract]. In: Proceedings of the AACR Special Conference: Acute Myeloid Leukemia and Myelodysplastic Syndrome; 2023 Jan 23-25; Austin, TX. Philadelphia (PA): AACR; Blood Cancer Discov 2023;4(3_Suppl):Abstract nr A02.