TRIM24 (tripartite motif-containing protein 24) and BRPF1 (bromodomain and PHD finger containing protein 1) are epigenetics "readers" and potential therapeutic targets for cancer and other diseases. Here we describe the structure-guided design of 1-(indolin-1-yl)ethan-1-ones as novel TRIM24/BRPF1 bromodomain inhibitors. The representative compound 20l (Y08624) is a new TRIM24/BRPF1 dual inhibitor, with IC<sub>50</sub> values of 0.98 and 1.16 μM, respectively. Cellular activity of 20l was validated by viability assay in prostate cancer (PC) cell lines. In PC xenograft models, 20l suppressed tumor growth (50 mg/kg/day, TGI = 53%) without exhibiting noticeable toxicity. Compound 20l represents a versatile starting point for the development of more potent TRIM24/BRPF1 inhibitors.