Identification of internalizing ScFvs for EGFR inhibition and apoptosis induction in cholangiocarcinoma cells.

Cholangiocarcinoma (CCA) is an aggressive malignancy with limited treatment options. EGFR overexpression is associated with tumor recurrence and poor prognosis, yet current EGFR-targeted therapies show limited efficacy. To identify alternative therapeutic candidates, we performed subtractive bio-panning of a naïve human single-chain variable fragment (scFv) phage display library against CCA cell lysates. Three novel scFv antibodies-E1, G8, and H2-were selected based on preferential binding to CCA cells with minimal cross-reactivity to unrelated cancers and normal fibroblasts. Surface plasmon resonance and kinase inhibition assays demonstrated that G8 and H2 bound the EGFR tyrosine kinase (EGFR-TK) domain with nanomolar affinities and suppressed kinase activity, whereas E1 showed weak binding and no kinase inhibition. All three scFvs exhibited efficient internalization into EGFR-overexpressing HuCCA-1 cells. Functional analyses revealed distinct effects on cell growth: G8 and H2 reduced EGFR phosphorylation, decreased cell viability, and induced apoptosis accompanied by S/G₂-M phase accumulation, whereas E1 primarily inhibited proliferation through G₁-phase arrest without significantly affecting EGFR phosphorylation. Molecular docking predicted that G8 interacts near the ATP-binding pocket and H2 at the dimerization interface of EGFR-TK. These interactions may contribute to EGFR inhibition in HuCCA-1 cells. These findings suggest that G8 and H2 function as intracellular inhibitors of EGFR-TK activity and are promising candidates for antibody-based therapy in EGFR-driven CCA.