Additionally, combined treatment with 4SC-202, a novel selective class I histone deacetylase (HDAC) inhibitor, and INK128, a selective mTORC1/C2 inhibitor, synergistically inhibits SOX2 expression and cell growth, and reduces ALDH1+ CSCs and sphere-forming ability of HNSCC cells [189], suggesting that combined HDAC and mTORC1/C2 inhibition selectively targets the self-renewing capacity of CSCs and is more effective and promising than conventional chemotherapy. Here, HDAC9 is linked to head and neck squamous cell carcinoma.