Dual Inhibition of SYK and EGFR Overcomes Chemoresistance by Inhibiting CDC6 and Blocking DNA Replication.

Targeting multiple signaling pathways has been proposed as a strategy to overcome resistance to single-pathway inhibition in cancer therapy. A previous study in epithelial ovarian cancers identified hyperactivity of spleen tyrosine kinase (SYK) and epidermal growth factor receptor (EGFR), which mutually phosphorylate and activate each other. Given the potential for pharmacologic inhibition of both kinases with clinically available agents, this study aimed to assess the antitumor efficacy of both pharmacologic and genetic SYK and EGFR co-inhibition using a multifaceted approach to analyze the global phosphoproteome and chemoresistant ovarian cancer cell lines, patient-derived organoids, and xenograft models. Dual inhibition of SYK and EGFR in chemoresistant ovarian cancer cells elicited a highly synergistic antitumor effect. Notably, the combined inhibition strategy activated the DNA damage response, induced G1 cell cycle arrest, and promoted apoptosis. The phosphoproteomic analysis revealed that perturbation of SYK and EGFR signaling induced a significant reduction in both phosphorylated and total protein levels of cell division cycle 6 (CDC6), a crucial initiator of DNA replication. Together, this study offers preclinical evidence supporting dual inhibition of SYK and EGFR as a promising treatment for chemoresistant ovarian cancer that disrupts DNA synthesis by impairing formation of the prereplication complex. These findings warrant further clinical investigation to explore the potential of this combination therapy in overcoming drug resistance and improving patient outcomes.