HDAC/HSP90-IN-1 (compound 20) is a potent dual inhibitor targeting HDAC (IC50 = 194 nM) and HSP90 (HSP90α IC50 = 153 nM). It induces the expression of HSP70, downregulates HSP90 substrate proteins, and enhances the acetylation of α-tubulin and histone H3 in cancer cells. Additionally, HDAC/HSP90-IN-1 reduces PD-L1 expression in IFN-γ-treated H1975 cells. This compound is applicable in research on cancers such as lung and colon cancer.