Inhibition of EIF2α Dephosphorylation Decreases Cell Viability and Synergizes with Standard-of-Care Chemotherapeutics in Head and Neck Squamous Cell Carcinoma

SIMPLE SUMMARY: Head and neck squamous cell carcinoma (HNSCC) arises in the mucosal membranes in the head and neck and constitutes 3.9% of new cancer cases annually. Its pathogenesis is stepwise; the formation of invasive and metastatic cancer is preceded by premalignant mucosal changes. With little improvement in overall survival over the last decade, HNSCC remains an important cause of patient morbidity. Therapy options include surgery, radiochemotherapy, and immunotherapy, but resistance is common. A way to overcome drug resistance is to target cellular processes present in all cells, such as protein biosynthesis, i.e., translation. This study found that eukaryotic translation initiation factor 2α (EIF2α) is highly expressed in HNSCC in comparison to normal tissue, and its expression mirrors the progression to malignancy. Pharmacological targeting of EIF2α by inhibition of its dephosphorylation with salubrinal decreases cell viability, the ability to form colonies, and disrupts the cell cycle. Salubrinal also works synergistically with standard chemotherapeutics. ABSTRACT: Drug resistance is a common cause of therapy failure in head and neck squamous cell carcinoma (HNSCC). One approach to tackling it is by targeting fundamental cellular processes, such as translation. The eukaryotic translation initiation factor 2α (EIF2α) is a key player in canonical translation initiation and integrates diverse stress signals; when phosphorylated, it curbs global protein synthesis. This study evaluates EIF2α expression and phosphorylation in HNSCC. A small-molecule inhibitor of EIF2α dephosphorylation, salubrinal, was tested in vitro, followed by viability assays, flow cytometry, and immunoblot analyses. Patient-derived 3D tumor spheres (PD3DS) were cultured with salubrinal and their viability assessed. Lastly, salubrinal was evaluated with standard-of-care chemotherapeutics. Our analysis of RNA and proteomics data shows elevated EIF2α expression in HNSCC. Immunohistochemical staining reveals increasing EIF2α abundance from premalignant lesions to invasive and metastatic carcinoma. In immunoblots from intraoperative samples, EIF2α expression and steady-state phosphorylation are higher in HNSCC than in neighboring normal tissue. Inhibition of EIF2α dephosphorylation decreases HNSCC cell viability and clonogenic survival and impairs the G(1)/S transition. Salubrinal also decreases the viability of PD3DS and acts synergistically with cisplatin, 5-fluorouracil, bleomycin, and proteasome inhibitors. Our results indicate that pharmacological inhibition of EIF2α dephosphorylation is a potential therapeutic strategy for HNSCC.