Polyclonal Antibody against Different Extracellular Subdomains of HER2 Induces Tumor Growth Inhibition in vitro

Background: Human epidermal growth factor receptor 2 (HER2) has a crucial role in several malignancies. The extracellular domain of HER2 (HER2-ECD) has been extensively employed as an important target in passive and active immunotherapy. Isolated recombinant prokaryotic HER2-ECD subdomains were previously found to be ineffective in inducing anti-tumor antibody response. Objective: To employ recombinant eukaryotic HER2-ECD subdomains to raise anti-HER2 antibodies and determine their anti-tumor activity in vitro. Methods: Two paired subdomains of HER2-ECD (DI+II and DIII+IV), representing Pertuzumab and Trastuzumab binding domains, respectively, along with the full extracellular domain of HER2 were generated in CHO-K1 cells. Polyclonal antibodies were raised against these subdomains and characterized using ELISA, flow cytometry, and immunoblot and their anti-tumor activity was assessed by XTT assay. The cross-reactivity of these antibodies was specified along with other members of the human HER family. Results: Similar to Trastuzumab and anti-HER2-ECD antibody, anti-DI+II and DIII+IV polyclonal antibodies reacted with recombinant HER2-ECD and native HER2 expressed on tumor cells. These two polyclonal antibodies were able to inhibit the binding of Pertuzumab and Trastuzumab to HER2, respectively, and did not cross-react with other members of HER family. These antibodies were able to inhibit tumor cell growth in vitro, similar to Trastuzumab. Conclusion: The high immunogenicity of human HER2 DI+II and DIII+IV subdomains in rabbits and the tumor inhibitory activity of the purified specific antibodies imply that they might be suitable for active immunotherapy in formulation with appropriate adjuvants and in combination with other HER2 specific therapeutics.