HDAC9 and cancer: CUDC-907 is a dual PI3K and HDAC inhibitor, and previous studies have demonstrated that HDAC inhibitors act synergistically with PI3K inhibitors to inhibit tumor growth in an MYC-dependent manner in different types of cancer (Fu et al., 2019; Simmons et al., 2017; Mondello et al., 2017; Pei et al., 2016) (Figure 5A).