G4/HDAC-IN-1 (compound a6) is a G4/HDAC dual-targeting compound. G4/HDAC-IN-1 inhibits intracellular HDAC activity with an IC 50 value of 1.1 μM, and induces G4 formation. G4/HDAC-IN-1 inhibits TNBC proliferation and tumor growth in TNBC xenograft model. G4/HDAC-IN-1 can be used for the research of cancer.