Anti-HER2 immunotoxin scFv-PE35KDEL internalizes via receptor-mediated endocytosis and induces apoptosis in ovarian cancer cells

Ovarian cancer remains a major cause of cancer-related mortality among women worldwide, highlighting the need for more effective targeted therapies. Immunotoxins have emerged as promising therapeutic agents for recurrent and metastatic ovarian cancer. In this study, we evaluated the binding, cellular uptake, cytotoxicity, and pro-apoptotic activity of an anti-HER2 immunotoxin, anti-HER2-scFv-PE35KDEL, composed of an anti-HER2 single-chain variable fragment (scFv) derived from pertuzumab fused to a modified 35-kDa fragment of Pseudomonas exotoxin A containing a KDEL sequence. The binding activity and cellular uptake of anti-HER2-scFv-PE35KDEL were evaluated in two ovarian cancer cell lines, SK-OV-3 and OVCAR-3, using flow cytometry, fluorometric analysis, and fluorescence microscopy. Cytotoxicity was assessed using MTT assay, while apoptosis induction was analyzed by Annexin V/PI staining and Western blot analysis of apoptosis-related proteins. The immunotoxin demonstrated significantly greater binding and cellular uptake in HER2-overexpressing SK-OV-3 cells compared with HER2-low OVCAR-3 cells, suggesting receptor-mediated internalization. Chlorpromazine treatment reduced cellular uptake, indicating the possible involvement of clathrin-mediated endocytosis. MTT analysis revealed concentration-dependent cytotoxicity against SK-OV-3 cells with an IC50 value of 10.90 nM, whereas OVCAR-3 cells exhibited substantially lower sensitivity with an IC50 value of 76.79 nM. Furthermore, treatment with anti-HER2-scFv-PE35KDEL induced apoptosis in SK-OV-3 cells in a concentration-dependent manner and increased the Bax/Bcl-2 ratio. These findings suggest that anti-HER2-scFv-PE35KDEL may exert preferential cytotoxic and pro-apoptotic effects against HER2-overexpressing ovarian cancer cells and support further preclinical investigation of this immunotoxin as a potential targeted therapeutic agent.