The ATR inhibitor elimusertib exhibits anti‐lymphoma activity and synergizes with the PI3K inhibitor copanlisib

Summary The DNA damage response (DDR) is the cellular process of preserving an intact genome and is often deregulated in lymphoma cells. The ataxia telangiectasia and Rad3‐related (ATR) kinase is a crucial factor of DDR in the response to DNA single‐strand breaks. ATR inhibitors are agents that have shown considerable clinical potential in this context. We characterized the activity of the ATR inhibitor elimusertib (BAY 1895344) in a large panel of lymphoma cell lines. Furthermore, we evaluated its activity combined with the clinically approved PI3K inhibitor copanlisib in vitro and in vivo. Elimusertib exhibits potent anti‐tumour activity across various lymphoma subtypes, which is associated with the expression of genes related to replication stress, cell cycle regulation and, as also sustained by CRISPR Cas9 experiments, CDKN2A loss. In several tumour models, elimusertib demonstrated widespread anti‐tumour activity stronger than ceralasertib, another ATR inhibitor. This activity is present in both DDR‐proficient and DDR‐deficient lymphoma models. Furthermore, a combination of ATR and PI3K inhibition by treatment with elimusertib and copanlisib has in vitro and in vivo anti‐tumour activity, providing a potential new treatment option for lymphoma patients.