Novel engineered trastuzumab conformational epitopes demonstrate in vitro and in vivo antitumor properties against HER-2/neu.

Abstract

Trastuzumab is a growth-inhibitory humanized Ab targeting the oncogenic protein HER-2/neu. Although trastuzumab is approved for treatment of advanced breast cancer, a number of concerns exist with passive immunotherapy. Treatment is expensive and has a limited duration of action, necessitating repeated administrations of the mAb. Active immunotherapy with conformational B cell epitopes affords the possibility of generating an enduring immune response, eliciting protein-reactive high-affinity anti-peptide Abs. The three-dimensional structure of human HER-2 in complex with trastuzumab reveals that the Ag-binding region of HER-2 spans residues 563-626 that comprises an extensive disulfide-bonding pattern. To delineate the binding region of HER-2, we have designed four synthetic peptides with different levels of conformational flexibility. Chimeric peptides incorporating the measles virus fusion "promiscuous" T cell epitope via a four-residue linker sequence were synthesized, purified, and characterized. All conformational peptides were recognized by trastuzumab and prevented the function of trastuzumab inhibiting tumor cell proliferation, with 563-598 and 597-626 showing greater reactivity. All epitopes were immunogenic in FVB/N mice with Abs against 597-626 and 613-626 recognizing HER-2. The 597-626 epitope was immunogenic in outbred rabbits eliciting Abs which recognized HER-2, competed with trastuzumab for the same epitope, inhibited proliferation of HER-2-expressing breast cancer cells in vitro and caused their Ab-dependent cell-mediated cytotoxicity. Moreover, immunization with the 597-626 epitope significantly reduced tumor burden in transgenic BALB-neuT mice. These results suggest the peptide B cell immunogen is appropriate as a vaccine for HER-2-overexpressing cancers because the resulting Abs show analogous biological properties to trastuzumab.

• Authors: Joan T Garrett, Sharad Rawale, Stephanie D Allen, Gary Phillips, Guido Forni, John C Morris, Pravin T P Kaumaya
• Journal: Journal of immunology (Baltimore, Md. : 1950) (J Immunol) Vol. 178 Issue 11 Pg. 7120-31 (Jun 01 2007) ISSN: 0022-1767 [Print] United States
• PMID: 17513761 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Antibodies, Monoclonal
• Antibodies, Monoclonal, Humanized
• Antineoplastic Agents
• Cancer Vaccines
• Epitopes
• Peptide Fragments
• Receptor, ErbB-2
• Trastuzumab

Topics

• Amino Acid Sequence
• Animals
• Antibodies, Monoclonal (chemistry, therapeutic use)
• Antibodies, Monoclonal, Humanized
• Antineoplastic Agents (chemical synthesis, therapeutic use)
• Cancer Vaccines (chemical synthesis, therapeutic use)
• Cell Line, Tumor
• Epitopes (chemistry, therapeutic use)
• Female
• Humans
• Mammary Neoplasms, Experimental (immunology, metabolism, prevention & control)
• Mice
• Mice, Inbred BALB C
• Mice, Transgenic
• Molecular Sequence Data
• Peptide Fragments (chemical synthesis, therapeutic use)
• Protein Conformation
• Protein Engineering
• Rabbits
• Rats
• Receptor, ErbB-2 (antagonists & inhibitors, immunology)
• Trastuzumab