Resistance of HNSCC cell models to pan-FGFR inhibition depends on the EMT phenotype associating with clinical outcome

Background
Focal adhesion signaling networks involving receptor tyrosine kinases (RTK) and integrins control central aspects of cancer cell survival and therapy resistance. However, co-dependencies between these transmembrane receptors and therapeutically exploitable vulnerabilities remain largely elusive in HPV-negative head and neck squamous cell carcinoma (HNSCC).
Methods
The cytotoxic and radiochemosensitizing potential of targeting 10 RTK and β1 integrin were determined in up to 20 different 3D matrix-grown HNSCC cell models. RNA sequencing and protein‑based biochemical assays were performed for molecular and pathway characterization. Bioinformatically identified transcriptomic signatures were applied to patient cohorts to show clinical relevance.
Results
Our findings indicate that fibroblast growth factor receptors (FGFR 1-4) present with the strongest cytotoxic and radiosensitizing potential, both as a monotherapy and when combined with β1 integrin inhibition, surpassing the efficacy of the other assessed RTKs. Pharmacological pan-FGFR inhibition induced a variable response spectrum ranging from cytotoxicity/radiochemosensitization to resistance/radioprotection. The latter prompted us to perform RNA sequencing analysis revealing an association of these contrasting responses to pan-FGFR inhibition with a mesenchymal-to-epithelial (MET) transition for sensitive cell models, whereas resistant cell models exhibited a partial epithelial-to-mesenchymal transition (EMT). In line, inhibition of EMT-associated kinases such as EGFR, PKC and PAK proved effective in reducing the adaptive FGFR-driven resistance. Finally, the translation of the transcriptomic profiles associated with EMT to HNSCC patient cohorts not only demonstrated its prognostic value but also provided conclusive validation of the presence of EMT-related vulnerabilities that can be strategically harnessed for therapeutic intervention.
Conclusions
This study demonstrates that pan-FGFR inhibition elicits both a highly beneficial radiochemosensitizing and a detrimental radioprotective potential in HNSCC cell models. Adaptive EMT-associated resistance appears to be of clinical importance, and we provide effective molecular approaches to exploit this therapeutically.