Head and neck cancer cells can differentiate and resemble their tissue of origin

Head and neck squamous cell carcinoma (HNSCC) is a highly malignant disease with a mortality rate of about 50%. It represents the sixth most common type of malignant tumor in the world. Risk factors include tobacco and alcohol usage and infection with the human papilloma virus (HPV). HPV-negative HNSCCs frequently display areas of cornification evident by keratin pearls in the tumor tissue. Cornification represents a natural differentiation path of keratinocytes in the normal epidermis and oral mucosa. To investigate the mechanisms of HNSCC cell differentiation we have established spheroid cell cultures from patient-derived HNSCC and parotid gland adenoid cystic carcinoma (ACC) tissue that grow in suspension under serum-free conditions. The use of a specific differentiation medium induced striking adhesion, loss of proliferation, and differentiation in tumor cells. Spheroid cells grew as single cell clones under serum-free conditions with a cloning efficiency of 40-60%, which was fully diminished under differentiating conditions. HNSCC cells cornified as indicated by the formation of lamellar bodies in the cytoplasm of adherent cells and an upregulation of cornification markers SPRR3 and involucrin. ACC cells upregulated parotid gland differentiation markers including α-amylase. RNA-seq analysis in HNSCC cells confirmed an upregulation of signaling pathways associated with cornification and epithelial cell differentiation. Conversely, pathways regulating the three-dimensional organization of the genome were downregulated upon differentiation. This was accompanied by the formation of ATRX-positive heterochromatin foci in the nucleus of differentiated ACC and HNSCC cells resembling those previously described to arise during therapy-induced senescence. Moreover, gas chromatography mass spectrometry analysis revealed a lack of essential amino acids including leucine to be implicated in the differentiation process. Altogether, our spheroid model of HNSCC and ACC cells is suitable to analyze the mechanisms underlying tumor cell differentiation and might lead to new therapeutic approaches that can drive long-term repopulating HNSCC and ACC cells into differentiation. Citation Format: Felix Oppel, Senyao Shao, Sarah Gendreizig, Philipp Kühnel, Vivien Przybycin, Carsten Hain, Pascal Schmidt, Matthias Schürmann, Peter Goon, Karsten Niehaus, Jörn Kalinowski, Holger Sudhoff. Head and neck cancer cells can differentiate and resemble their tissue of origin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 111.