Targeting epithelial-to-mesenchymal transition (EMT) in feline oral squamous cell carcinoma (FOSCC)

Squamous cell carcinoma of the head and neck (HNSCC) is an extremely common and devastating disease with a bleak prognosis. Despite intensive research, survival rates have not improved over the past 30 years principally due to untreatable recurrent/metastasising disease. Feline oral squamous cell carcinoma (FOSCC) is an equally common disease in cats with an even less favourable prognosis than humans. Human and feline squamous cell carcinomas share similar etiopathogenesis, molecular markers, tumour biology and treatment thus making FOSCC an excellent model for HNSCC. Epithelial to mesenchymal transition (EMT), under the direction microRNAs (miRNAs/mirs) could be a key driver in oncogenic transformation and chemoresistance. The aim of this study was to induce resistance to characterise the EMT/resistance phenotype and to investigate whether common miRNA-mediated pathways are present in HNSCC and FOSCC that drive this phenomenon. We used epidermal growth factor (EGFR)-inhibitor gefitinib to induce resistance in HNSCC and FOSCC and investigated the associated EMT-related molecular changes. In vitro and in vivo invasive and migratory properties of both species were explored to determine whether resistance and/or EMT status conferred a functional advantage. We determined the miRNA expression pattern during acquisition of resistance to gefitinib in both species by next generation sequencing and screened candidate miRNAs as potential therapeutics. We found that gefitinib-resistance produced a previously unrecognised biphasic response that consisted of two distinct phenotypes, a highly invasive mesenchymal phenotype during early resistance, and a more epithelial phenotype associated with established resistance. The biphasic nature of this transition may prove critical in establishing effective therapeutic targets and the timing of treatment to overcome resistance or in preventing local invasion or metastatic spread of squamous cell carcinoma. We found that the major anti-apoptotic PI3K/AKT pathway was activated in transitioning and resistant cells of both species as demonstrated upregulation of AKT, pAKT and c-FLIP together with inactivation of PTEN by phosphorylation. This indicates that avoidance of apoptosis may be a major pathway in resistance that could be targeted therapeutically. We showed that three miRNAs were differentially expressed in both gefitinib-resistant human and feline cell lines: miR-107 was downregulated, and miR-551b and miR-574 were upregulated. These microRNAs provide potential therapeutic targets in the fight against drug resistance in head and neck cancer although much further research needs to be conducted to elucidate the complex network of interactions that may be affected by targeting these powerful regulatory molecules.