Abstract
(1) Background: Oral squamous cell carcinoma (OSCC) is a significant health burden worldwide. This study aimed to determine the potentials of Refametinib, an orally bioavailable selective MEK1/2 inhibitor, to increase the effectiveness of 5-Fluorouracil (5-FU), a common cytotoxic drug, in the SCC4 cell line. (2) Methods: SCC4 cells were treated with increasing concentrations of 5-FU, either alone or in combination with Refametinib. The chemosensitivity to treatment was assessed via cell viability assay, microscopic observation, colony formation assay, and detection of apoptotic markers using Western blotting. The whole-cell expression and surface expression of programmed death-ligand 1 (PD-L1), an immune checkpoint protein which contributes to chemoresistance and affects treatment response, were also determined using Western blotting and flow cytometry, respectively. (3) Results: The combined treatment suppressed cell proliferation and promoted apoptosis in a more potent way than 5-FU treatment alone did. Additionally, MEK/ERK inhibition mitigated 5-FU-induced PD-L1 upregulation. (4) Conclusions: This is the first report of an enhanced anticancer effect and reduced PD-L1 expression for the combination of 5-FU with Refametinib in OSCC, suggesting a new promising combination strategy.