Therapeutic peptidomimetic strategies for costimulation blockade in multiple sclerosis and transplantation / conformational peptide vaccines of the HER-2/neu dimerization loop are effective in inhibiting mammary tumor growth in vivo

by Allen, Stephanie D.

Cognate interactions between immune effector cells and antigen presenting cells (APCs) govern immune responses. Specific signals occur between the T cell receptor, peptide and APCs as well as nonspecific signals between pairs of costimulatory molecules. Costimulation signals are required for full T cell activation and are thought to regulate T cell responses as well as other aspects of the immune system. Costimulation requirements for T cell regulation have been extensively studied as a way to control many autoimmune diseases and downregulate inflammatory reactions. The CD28:B7 and the CD40:CD40L families of molecules are considered to be critical costimulatory molecules and have been studied extensively. Blocking the interaction between these molecules results in a state of immune unresponsiveness termed anergy. Several different strategies for blockade of these interactions have been explored including monoclonal antibodies (mAbs), Fab fragments, chimeric, and/or fusion proteins. We developed novel, immune-specific approaches that interfere with these interactions. Using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis mediated by CNS-specific T cells and transplantation models, we developed an approach that utilizes peptides for blockade of costimulatory molecules. Our laboratory has designed blocking peptide mimics that retain the functional binding area of the parent protein while reducing the overall size and are able ii to block signal transduction. We present data showing the ability of costimulatory molecule peptide mimics to suppress autoimmune disease and propose a mechanism for disease suppression. The epidermal growth factor (ErbB or HER) family of receptors is made up of four members, HER-1 (EGFR), HER-2, HER-3, and HER-4 that form homo- and heterodimers resulting in receptor activation and downstream signaling pathways. Unlike other members of the ErbB family, HER-2/neu does not have a known high affinity ligand but is the preferred dimerization partner for the ErbB receptor family. Pertuzumab (Omnitarg) is a humanized monoclonal antibody against the HER-2/neu dimerization region that inhibits HER-2/neu mediated signaling. The recent crystal structure of HER- 2/neu in complex with pertuzumab shows that the dimerization region encompasses residues 266-333. Peptide vaccines that elicit conformation-dependent, high affinity antibodies have the added benefit of immunological memory and therefore do not require frequent dosing as monoclonal antibody treatment does, in addition to decreasing the chance of the patient developing resistance to treatment. Based on the 3-D structure of the complex of pertuzumab with HER-2/neu, we have designed a conformational peptide construct to mimic the dimerization loop of the HER-2/neu receptor. This construct was shown to elicit high affinity peptide antibodies that disrupt a number of signaling pathways including HER-2/neu specific inhibition of cellular proliferation, cytoplasmic phosphorylation (dimerization blockade), and ADCC activity. The chimeric peptide constructs were also able to abrogate transplantable tumor growth in FVB/n and Balb/c mice as well as spontaneous tumor growth in VEGF iii +/-Neu2-5+/- mice, suggesting a novel vaccine candidate for immunity of breast cancer.