Breast cancer cells were incubated with different concentrations (1 nM to 100 μM) of free PI3‐Kδ/HDAC6, SAHA, IDL, and their encapsulated NPs (IDL‐NPs, SAHA‐NPs, and HSB‐510), to evaluate the relative cytotoxicities. Here, HDAC6 is linked to breast cancer.