Peptide Vaccines of the HER-2/ neu Dimerization Loop Are Effective in Inhibiting Mammary Tumor Growth In Vivo

Abstract

Human epidermal growth factor receptor-2 (HER-2)/neu (ErbB2), a member of the epidermal growth factor family of receptors, is overexpressed in 20–30% of breast cancers. It is an attractive target for receptor-directed antitumor therapy using mAbs. Unlike other epidermal growth factor receptor family members, HER-2/neu does not bind a high-affinity ligand, but rather functions as the preferred dimerization partner. Pertuzumab (Omnitarg) is a humanized mAb directed against the HER-2/neu dimerization domain that inhibits receptor signaling. The recent definition of the crystal structure of the HER-2/neu-pertuzumab complex demonstrated that the receptor dimerization region encompassed residues 266–333. Based on the three-dimensional structure of the complex, we have designed three conformational peptide constructs (sequences 266–296, 298–333, and 315–333) to mimic regions of the dimerization loop of the receptor and to characterize their in vitro and in vivo antitumor efficacy. All the constructs elicited high-affinity peptide Abs that inhibited multiple signaling pathways including HER-2/neu-specific inhibition of cellular proliferation and cytoplasmic receptor domain phosphorylation. All the peptide Abs showed Ab-dependent cellular cytotoxicity to varying degrees with the 266–296 constructs being equally effective as compared with Herceptin. The 266–296 peptide vaccine had statistically reduced tumor onset in both transplantable tumor models (FVB/n and BALB/c) and significant reduction in tumor development in two transgenic mouse tumor models (BALB-neuT and VEGF+/−Neu2–5+/−). The 266–296 construct represents the most promising candidate for antitumor vaccination and could also be used to treat a variety of cancers with either normal or elevated expression of HER-2 including breast, lung, ovarian, and prostate.