Dual EGFR and Bcl-2 inhibition overcomes resistance in sinonasal squamous cell carcinoma

Background: Sinonasal cancers are rare head and neck malignancies. Although outcomes for other head and neck cancers have improved, those for sinonasal cancers remain stable, with 5-year overall survival at 55%. This study focuses on sinonasal squamous cell carcinoma (SNSCC), which develops in the mucosal epithelium and accounts for nearly 61% of sinonasal malignancies. A strong association exists between inverted sinonasal papilloma (ISP) and the development of SNSCC, with approximately 50% of cases progressing to malignancy that harbors epidermal growth factor receptor (EGFR) exon 20 mutations. These EGFR-mutated SNSCCs have a significantly poorer prognosis than other sinonasal tumors, underscoring the need for more effective therapies. Methods: We sought to identify therapeutic partners for EGFR inhibitors that could enhance the effectiveness of EGFR blockade. We focused on pairing pathways orthogonal to EGFR activation, such as apoptosis inhibition. To identify synergistic drug pairings with optimal activity, we screened a library of >1,000 signaling inhibitors. Drug sensitivity scores (DSS3) were calculated, identifying Bcl-2 inhibitors as potential synergistic partners with EGFR inhibition. Dose-response curves for EGFR and Bcl-2 inhibitors were generated, and synergy was assessed using the Chou-Talalay method across four cell lines (UM-SCC-112, UM-SCC-33, SCCNC4, MOP-IPST-1) in 3D culture. Western blotting examined expression of EGFR, pro-apoptotic markers (Bax), and pro-survival proteins (Bcl-2). Results: Drug screening revealed that ISP-associated sinonasal carcinoma (SNC) cell lines were highly resistant to both standard and targeted single-agent therapies. In 3D ex vivo cultures, sinonasal papilloma and carcinoma PDOs showed partial responses to EGFR inhibitors, and EGFR inhibition alone failed to suppress growth or induce apoptosis. In contrast, dual or triple combinations of EGFR inhibitors with Bcl-2 and/or PI3K/AKT/mTOR pathway inhibitors produced synergistic cytotoxic effects, suggesting that co-targeting EGFR and anti-apoptotic pathways may overcome intrinsic resistance. Western blot analysis showed that resistant lines had reduced Bcl-2 expression, while lines with higher Bcl-2 levels demonstrated greater synergy with EGFR/Bcl-2 co-inhibition, including those with EGFR mutations, indicating reliance on alternative survival mechanisms. Conclusions: Dual EGFR and Bcl-2 inhibition demonstrate synergistic anticancer potential in ISP-associated SNC, overcoming de novo resistance to EGFR-targeted therapy. These findings underscore the importance of targeting anti-apoptotic pathways in EGFR-mutant sinonasal cancers. Ongoing studies aim to define EGFR-Bcl-2 crosstalk and identify optimal drug combinations for in vivo testing. AI disclosure: AI was used for language editing only; content was verified by the authors.