Combinatorial Treatment with Gefitinib and Bay11-7085 Sensitizes Primary Gefitinib-resistant OSCC Cells by Influencing the EGFR- NFκB Signaling Axis

EGFR-targeted therapies are reported to yield modest effect in OSCC. Activation of NFκB signaling is considered as molecular driver of EGFR inhibitor resistance in various cancers. In this scenario, present study focused on the molecular crosstalk between EGFR and NFκB signaling pathways and its therapeutic importance in OSCC. The EGFR- NFκB p65 co-expressed human OSCC cell lines UPCI:SCC066, UPCI:SCC040 and UM-SCC083B were used for in vitro studies. Recombinant human EGF, siRNAs, Western blot and qRT-PCR were used to dissect the molecular crosstalk between EGFR-NFκB signaling pathways in OSCCs. The effect of NFκB p65 knockdown on cancer hallmarks was studied by respective functional assays and RNA-Seq analysis was performed to identify the differentially expressed genes upon NFκB p65 knockdown. Gefitinib and Bay 11-7085 combination treatment was done to study the chemotherapeutic potential of EGFR- NFκB axis. Significant positive correlation between EGFR and NFκB p65 expression was observed in Head and Neck TCGA data set. EGFR induction or knockdown respectively stimulate or impair the NFκB signaling in EGFR- NFκB p65 co-expressed OSCC cell lines. NFκB p65 knockdown causes apoptosis and suppresses the viability, colony formation, migration, invasion, and spheroid formation. Using RNA-seq analysis, we identified PIK3CD as the NFκB target gene, which is commonly involved in these functions. Gefitinib and Bay 11-7085 combination treatment was found to be useful in chemosensitizing the Gefitinib-resistant OSCC cells by capitulating the EGFR- NFκB signaling axis. Combination treatment using Gefitinib and Bay 11-7085 enhanced the apoptosis and reduced cell viability and colony formation in a synergistic way. Our data demonstrated that EGFR-NFκB signaling axis plays a key role in the pathogenesis of OSCCs. Therefore, simultaneous therapeutic intervention of these pathways may be a good alternative approach for the management of OSCCs.