Peptide Vaccines Against the HER-2/neu Dimerization Loop

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The Ohio State University

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Studies indicate that many tumors overexpress normal self-proteins. Multiple regulatory mechanisms of the body minimize the immune response to antigens perceived as self allowing the unregulated growth of cancerous cells expressing self-proteins. Different from active immunization for infectious diseases, which triggers an immune response to foreign antigens, vaccination for cancer treatment and prevention often targets antigens that are perceived by the immune system as native, and therefore must be capable of circumventing the body’s defenses. HER-2 (Human epidermal growth factor receptor-2) is a self-protein overexpressed in 20-30% of breast, as well as, ovarian, lung, stomach, bladder, and salivary cancers. HER-2 is a member of the ErbB family of receptors, which convey signals by homo- or heterodimerization of the extracellular domain. Dimerization causes transphosphorylation of the receptors, which triggers downstream signaling and results in increased development, proliferation and differentiation of cells. The overexpression and the preference of HER-2 as a dimerization partner make it an ideal target in cancers for active and passive immunotherapy. Active immunization with tumor vaccines can be used to employ the patient’s own immune system to destroy mammary tumor cells, leading to sustained anti-tumor resistance due to immunological memory, which would eliminate the requirement for continual, repetitive cycles of therapy. In this study, the specific HER-2 B-cell epitope evaluated was the extracellular dimerization loop region. The specific HER-2 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. A portion of the B-cell epitope synthesized was altered to form a disulfide bond between two cysteines to mimic the structure of the native HER-2 receptor dimerization region, giving a cyclized (Cyc) construct (containing the disulfide bond) and a linear (NC) construct. These rationally designed peptide vaccines were analyzed for their ability to induce antibodies with anti-proliferative capabilities. Both epitopes induced high-titered antibodies in outbred rabbits. Analysis by flow cytometry revealed antibody recognition and binding of the native HER-2 protein in human HER-2 overexpressing BT-474 cells, as well as the rat neu homolog of human HER-2 in mouse NT2.5 cells. These antibodies caused antibody-dependent cell mediated cytoxicity of HER-2 positive breast cancer cells in vitro. Passive and active immunotherapeutic experiments were carried out in transgenic mice. Inbred Neu2-5+/- mice vaccinated with the target peptide showed delayed onset of tumor development and a decrease in tumor volume. Double transgenic (VEGF+/- Neu2-5+/-) mice were tested by passive immunotherapy due to rapid tumor onset in these mice. VEGF+/- Neu2-5+/- mice injected with peptide antibodies had smaller average sized tumors demonstrating the ability of the induced antibodies to inhibit HER-2-dependent proliferation and dimerization. These synthetic peptide vaccines have therapeutic potential to elicit antibodies that will successfully prevent or limit the growth of HER-2 overexpressing cancers.


Winner of Biological Sciences Colloquium 2006


cancer, HER-2, breast cancer, cancer research