BAY-1895344 is an inhibitor of ataxia-telangiectasia and Rad3-related protein (ATR) kinase that inhibits proliferation in a panel of human tumor cell lines (mean IC50 = 78 nM). It halts tumor growth in ovarian and colorectal mouse xenograft models and induces complete tumor remission in mantle cell lymphoma mouse xenograft models. BAY-1895344 also exhibits synergistic anti-tumor activity with radium-223 in a mouse xenograft model of castration-resistant prostate cancer bone metastases.