HPV-positive head and neck squamous cell carcinoma cells lose viability during triggered myocyte lineage differentiation

Head and neck squamous cell carcinoma (HNSCC) is a highly malignant disease, and death rates have remained at approximately 50% for decades. New tumor-targeting treatment strategies are desperately needed. Using patient-derived tumor cells, we created an HNSCC differentiation model of HPV+ tumor cells from two patients. We observed a loss of malignant characteristics in differentiating cell culture conditions, including irregularly enlarged cell morphology, cell cycle arrest with downregulation of Ki67, and reduced cell viability. RNA-seq showed myocyte-like differentiation with upregulation of markers of myofibril assembly, including TPM1, TAGLN, and ACTA1. Immunofluorescence staining of differentiated and undifferentiated primary HPV+ HNSCC cells confirmed an upregulation of these markers and the formation of parallel actin fibers reminiscent of myoblast-lineage cells. Moreover, immunofluorescence of HPV+ tumor tissue revealed areas of cells co-expressing the identified markers of myofibril assembly, HPV surrogate marker p16, and stress-associated basal keratinocyte marker KRT17, indicating that the observed myocyte-like in vitro differentiation occurs in human tissue. A recent sarcoma study was able to turn rhabdomyosarcoma into muscle-like cells. We are the first to report that carcinoma cells can undergo a triggered myocyte differentiation. Our study suggests that the targeted myo-differentiation of tumor cells might be therapeutically valuable in HPV+ HNSCCs.