Irradiation‑induced cellular senescence is linked to pro‑survival signaling and checkpoint regulation in a 2D and 3D model for head and neck cancer

Fractionated irradiation causes premature senescence of tumor cells. Interactions between senescence, the immune system and survival signaling are poorly understood to date. As MAP kinases are implicated in immune resistance, the present study addressed the detection of senescence‑associated modulation of postradiogenic programmed death‑ligand 1 (PD‑L1) and MAP kinase ERK1/2 expression in an <i>in vitro</i> and <i>ex vivo</i> model for head and neck squamous cell carcinoma (HNSCC). Established HNSCC cell lines (UM-SCC-11B, UM-SCC-14C and UM-SCC-22B) were employed to study the expression levels of p21, histone H2AX (γH2AX), PD-L1 and phosphorylated (p)ERK1/2 via immunohistochemistry following application of 4x2 Gy. Using senescence‑associated β‑galactosidase (SA‑ß‑Gal) staining, postradiogenic induction of senescence was additionally assessed. Results were validated in a 3D <i>ex vivo</i> HNSCC model with vital explants. Upon ionizing radiation (IR), senescence‑like subpopulations were observed in all cell lines, showing upregulation of PD‑L1 and pERK1/2 as well as of established senescence markers p21 and γH2AX. SA‑β‑Gal‑positive cells were found in all lines. These results were supported in a 3D tumor model. Fractionated IR can generate a subpopulation of HNSCC cells characterized by senescence‑typical cellular changes and marked expression of PD‑L1 and pERK1/2. Postradiogenic senescence in both 2D and 3D cancer models was possibly related to survival signaling and immune checkpoint regulation, crucial elements in tumor development and progress.