2005 Ohio Student Research Forum

Abstract

Peptide Vaccine Against the HER-2/neu Dimerization Loop
Audra Jones
Ohio State University, Department of Biochemistry
Mentor: Dr. Pravin Kaumaya

Rationally designed peptide vaccines based on a hairpin loop in extracellular subdomain II of the human epidermal growth factor receptor 2 (HER-2) were analyzed for their ability induce antibodies with anti-proliferative capabilities. There are different proteins that are overexpressed in certain types of cancer, which leads to the investigation of peptides as an active mode of immunotherapy. In this study, the specific HER-2 B-cell epitope evaluated was residues 266-296. This sequence was chosen based on the 3.2 Å X-ray crystal complex structure of HER-2 and the antigen binding fragment of pertuzumab, an anti-HER-2 monoclonal antibody. The HER-2 (266-296) B-cell epitope was co-linearly synthesized with the promiscuous T-helper epitope MVF (288-302), which originated from the measles virus fusion protein (MVF). The B-cell and promiscuous T- cell epitopes were connected by a flexible four-residue turn (GPSL) allowing the B-cell and T-cell epitopes to fold independently. B-cell epitopes are specific antibody recognition sites. Results from previous studies have shown that the MVF addition enhances the antigenic property of B-cell epitopes. One B-cell epitope was altered to form a disulfide bond between cys 268 and cys 295 to mimic the structure of the native HER-2 receptor dimerization region. The two peptide constructs synthesized were MVF-HER-2 (266-296) cyclized (Cyc), which contained the cysteine bridge and MVF-HER-2 (266-296) non-cyclized (NC), the linear construct. Both epitopes induced high-titered antibodies in outbred rabbits. These antibodies also caused antibody-dependent cell mediated cytoxicity of HER-2 positive breast cancer cells in vitro. Analysis by flow cytometry revealed antibody recognition and binding of the native HER-2 protein. This supports the notion that these antibodies may be capable of inhibiting HER-2 proliferation and/or dimerization. These synthetic peptide vaccines may have therapuetic potential to successfully prevent or limit the growth of HER-2 overexpressing cancers.