Considering that TMP195 interacts with the substrate-binding pockets of ABCB1 and ABCG2, and that the overexpression of these transporters is associated with reduced efficacy of several HDAC inhibitors in cancer cells [30,39,40], we thus compared the cytotoxicity of TMP195 in ABCB1- or ABCG2-overexpressing multidrug-resistant cell lines to their respective drug-sensitive parental cell lines (Figure 6). The gene discussed is HDAC9; the disease is cancer.