Pan-fibroblast growth factor receptor inhibition induces epithelial-to-mesenchymal transition-based resistance and associates with clinical outcome in head and neck squamous cell carcinoma

Integrins and receptor tyrosine kinases (RTKs) interact at focal adhesions. These sites on the cell membrane serve as giant signaling hubs that contribute crucially to key aspects of cancer cell survival and resistance to therapy. Despite the fact that these receptors mutually interact, the dependencies between these receptors and the associated therapeutically exploitable vulnerabilities in HPV-negative head and neck squamous cell carcinoma (HNSCC) are still largely unclear. Here, we investigated the cytotoxic and radio chemo sensitizing potential of β1 integrin and 10 RTK in up to 20 different HNSCC cell models grown in a 3D matrix. RNA sequencing and protein-based biochemical assays were conducted for molecular and pathological characterization. Bioinformatically identified transcriptomic signatures were applied to patient cohorts to demonstrate clinical relevance. Our observations show that fibroblast growth factor receptors (FGFR 1-4) have the strongest cytotoxic and radio sensitizing potential, both as monotherapy and in combination with β1-integrin inhibition, and outperform the efficacy of the other RTKs studied. Pharmacological pan-FGFR inhibition resulted in a variable spectrum of responses, ranging from cytotoxicity/radio chemo sensitization to resistance/radioprotection. Transcriptomic characterization revealed an association of these different responses to FGFR inhibition with mesenchymal-to-epithelial transition (MET) in sensitive cell models and partial epithelial-to-mesenchymal transition (EMT) for resistant cell models. Accordingly, deactivation of EMT associated kinases like EGFR, PKC and PAK proved effective in diminishing the adaptive FGFR-driven resistance. Importantly, the translation of the adaptive resistance profiles to HNSCC patient cohorts showed its prognostic value and provided conclusive validation of the presence of EMT-related vulnerabilities that can be strategically used for therapeutic intervention. In conclusion, our study demonstrates that pan-FGFR inhibition induces both a highly beneficial radio chemo sensitizing and a detrimental radio protective effect in HNSCC cell models. Adaptive EMT-associated resistance appears to be of clinical importance, and we provide effective molecular approaches to exploit this therapeutically. (author)