CDKN1A and head and neck squamous cell carcinoma: Overall, the present study provides insights into the mode of action of the PCT analogs in HNSCC cells, which includes (1) induction of Cdc2 and its phosphorylation via the Cdc25-pCdc2(Tyr15) pathway, (2) concerted upregulation of p53, p21Cip1/WAF1 and p27kip21, thereby contributing to cell cycle arrest at S/G2-phase and induction of cellular senescence (see Fig 8).