Palbociclib inhibits the progression of head and neck cancer and improves the Cetuximab response under specific condition in vitro and in vivo

In head and neck squamous cell carcinoma (HNSCC) with human papillomavirus (HPV)-negative, deregulation of cell cycle is partly due to inactivation of p16INK4 and overexpression of cyclin D1. Here we investigated the in vitro and in vivo effects of the CDK4/6 inhibitor Palbociclib alone or combined with EGFR inhibitor Cetuximab in HNSCC. CCK-8, soft agar assay, colony formation assay, wound healing assay and transwell assay, β-galactosidase assay, western blotting, and cell-derived xenografts were used to investigated the in vitro and in vivo activity of drugs. Cell viability and colony formation decreased in a dose-dependent manner in Tu686, AMC-HN8, and Fadu cells under Palbociclib treatment. Palbociclib remarkably inhibited migration, invasion and the expression MMP-9 in HNSCC cells. Palbociclib also induced senescence. Palbociclib caused the dephosphorylation of RB but increased the cyclin D1 level in a dose-dependent manner. Moreover, combination with Cetuximab could significantly prevent the induction of cyclin D1 and activation of EGFR signals from Palbociclib treatment. Nevertheless, only within the range of certain concentrations, a synergistic inhibitory effect on cell growth was observed when combined with Palbociclib and Cetuximab. Although the synergistic effect in Palbociclib/Cetuximab combined therapy was comparable to that in traditional chemotherapeutic regimens (cisplatin/Cetuximab) in Fadu tumor xenograft, the combination therapy was less active than Cetuximab monotherapy in Tu686 tumor xenograft. In HPV-negative HNSCC, CDK4/6 inhibitor shows promising anti-tumor effects, which exhibits a synergistic effect when combined with EGFR inhibitor only in specific drug concentration and mouse model.