CUDC-907 (dual PI3K and HDAC inhibitor) inhibits growth and proliferation of both Ibrutinib-sensitive and Ibrutinib-resistant MCL primary cells in vitro and induces apoptosis and cell cycle arrest through downregulation of PLK1, polo-like kinase 1, a key regulator of mitosis [71]. Here, HDAC9 is linked to mantle cell lymphoma.