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Head and neck squamous cell carcinoma (HNSCC) is frequently characterized by high resistance to radiotherapy, which critically depends on both altered signaling pathways within tumor cells and their dynamic interaction with the tumor microenvironment. This study evaluated the prognostic value of the phosphorylation status of AKT on Ser473 and Thr308 for the clinical outcome of patients with advanced HNSCC on radiotherapy. Furthermore, we investigated the impact of AKT(Ser473) phosphorylation [p-AKT(Ser473)] in the context of radioresistance using ex vivo tissue cultures that resemble the complex tissue architecture and paracrine interaction with the tumor microenvironment. In a cohort of 120 patients with advanced HNSCC, who were treated with primary or adjuvant radiotherapy, a significant association was found between relative p-AKT(Ser473) levels and overall survival (p = 0.006) as well as progression-free survival (p = 0.021), while no significant correlation was revealed for relative p-AKT(Thr308) levels. In ex vivo tissue cultures p-AKT(Ser473) levels were increased upon irradiation and treatment with the PI3K inhibitor LY294002 inhibited both basal and irradiation induced AKT(Ser473) phosphorylation. Strikingly, pretreatment with LY294002 sensitized tissue cultures derived from primary and recurrent tumors to radiotherapy as determined by impaired tumor cell proliferation and enhanced DNA damage. In conclusion, phosphorylation status of AKT(Ser473) in tumor specimens serves as a novel biomarker to identify patients with advanced HNSCC at high risk for treatment failure following radiotherapy, and our data from ex vivo tissue cultures support the assumption that pharmacological inhibition of AKT(Ser473) phosphorylation might circumvent radioresistance to improve efficiency and reduce toxicity of current treatment modalities.

Head and neck squamous cell carcinoma (HNSCC) is frequently characterized by high resistance to radiotherapy, which critically depends on both altered signaling pathways within tumor cells and their dynamic interaction with the tumor microenvironment. This study evaluated the prognostic value of the phosphorylation status of AKT on Ser473 and Thr308 for the clinical outcome of patients with advanced HNSCC on radiotherapy. Furthermore, we investigated the impact of AKT(Ser473) phosphorylation [p-AKT(Ser473)] in the context of radioresistance using ex vivo tissue cultures that resemble the complex tissue architecture and paracrine interaction with the tumor microenvironment. In a cohort of 120 patients with advanced HNSCC, who were treated with primary or adjuvant radiotherapy, a significant association was found between relative p-AKT(Ser473) levels and overall survival (p = 0.006) as well as progression-free survival (p = 0.021), while no significant correlation was revealed for relative p-AKT(Thr308) levels. In ex vivo tissue cultures p-AKT(Ser473) levels were increased upon irradiation and treatment with the PI3K inhibitor LY294002 inhibited both basal and irradiation induced AKT(Ser473) phosphorylation. Strikingly, pretreatment with LY294002 sensitized tissue cultures derived from primary and recurrent tumors to radiotherapy as determined by impaired tumor cell proliferation and enhanced DNA damage. In conclusion, phosphorylation status of AKT(Ser473) in tumor specimens serves as a novel biomarker to identify patients with advanced HNSCC at high risk for treatment failure following radiotherapy, and our data from ex vivo tissue cultures support the assumption that pharmacological inhibition of AKT(Ser473) phosphorylation might circumvent radioresistance to improve efficiency and reduce toxicity of current treatment modalities.

p16(INK4a) immunohistochemical overexpression is an overall reliable surrogate marker of human papillomavirus (HPV)-associated head and neck squamous cell carcinomas (HNSCC). However, cases of ambiguous p16(INK4a) overexpression are regularly detected in the head and neck: p16(INK4a) expression can be observed in non-malignant tissue, such as tonsillar crypt epithelium and a proportion of branchial cleft cysts. Additionally, diverse patterns of p16(INK4) expression can complicate interpretation of "p16(INK4a) -positivity". These aspects impede the unrestricted application of p16(INK4a) as a diagnostic marker in the head and neck. We hypothesized that combined detection of p16(INK4a) and the proliferation marker Ki-67 could support clarification of ambiguous p16(INK4a) expression in the head and neck by specifically indicating p16(INK4a) -expressing cells with proliferative activity. p16(INK4a) /Ki-67 co-expression in a combined staining procedure was correlated to distinct p16(INK4a) expression patterns and HPV status (HPV DNA followed by E6*I oncogene mRNA detection) in 147 HNSCC and 50 non-malignant head and neck samples. p16(INK4a) /Ki-67 co-expression only occurred in transformed cells of the head and neck. Co-expression was never detected in non-transformed cells. Combined p16(INK4a) /Ki-67 expression was stringently associated with a diffuse p16(INK4a) expression pattern. All HPV oncogene-expressing HNSCC showed p16(INK4a) /Ki-67 co-expression. We demonstrate that p16(INK4a) /Ki-67 co-expression occurs exclusively in transformed cells of the head and neck. Our findings indicate a substantial impact of combined p16(INK4a) /Ki-67 expression in the assessment of ambiguous p16(INK4a) expression in the head and neck by specifically identifying p16(INK4a) -expressing cells with proliferative activity. This property will be of considerable significance for head and neck histo- and cytopathology.

Proteoglycans are often overexpressed in tumors and can be found on several normal and neoplastic stem cells. In this study, we analyzed in-depth the role of CSPG4 in head and neck squamous cell carcinomas (HNSCC). Analysis of CSPG4 in a homogeneous study sample of HPV-negative stage IVa HNSCCs revealed overexpression of protein and mRNA levels in a subgroup of HNSCC tumors and a significant association of high CSPG4 protein levels with poor survival. This could be validated in three publicly available microarray datasets. As a potential cause for upregulated CSPG4 expression, we identified DNA hypomethylation in a CpG-island of the promoter region. Accordingly, we found an inverse correlation of methylation and patient outcome. Finally, CSPG4 re-expression was achieved by demethylating treatment of highly methylated HNSCC cell lines establishing a direct link between methylation and CSPG4 expression. In conclusion, we identified CSPG4 as a novel biomarker in HNSCC on several biological levels and established a causative link between DNA methylation and CSPG4 protein and mRNA expression.