Linear epitopes that generate anti-HER-2 antibody responses with trastuzuab- (herceptin) like biological activity

The therapeutic monoclonal antibody trastuzumab, which recognizes a conformation-dependent epitope on the extracellular domain of HER-2, has revolutionized the treatment of HER-2pos breast cancers. However, high costs and short half-life of the antibody spurs the search for other ways to induce therapeutic anti-HER-2 antibodies. Linear T cell epitopes have already been discovered for HER-2, and these have shown promise in vaccine studies where strong cell-mediated responses have been generated. Identifying conformation-independent B cell epitopes would allow the construction of linear T-B vaccine constructs that would generate both cellular and humoral anti-HER-2 responses with potential anti-cancer activity. We therefore produced a synthetic peptide library consisting of 62 overlapping 20-mers spanning the HER-2 extracellular domain. These were used to vaccinate Balb/c (H-2d) mice. Resulting antisera were characterized and screened for reactivity against peptide and recombinant extracellular domain protein via ELISA, and whole native protein by immuno-fluorescent microscopy and FACS analysis. Sera reactive by all these criteria were tested against trastuzumab for their ability to disrupt HER-2 and HER-2/HER-3 dimer signaling in the presence and absence of heregulin. We identified a linear peptide capable of downregulating the phosphorylation of upstream HER-2 and HER-3, and downstream Akt and ERK 1/2 in a manner similar to trastuzumab. This suggests that a linear epitope/vaccination approach may be feasible for generating effective anti-HER-2 antibody responses.