Published in Cancer Detection and Prevention 2000; 24(Supplement 1).

Growth inhibition of tumor cells by monoclonal antibodies and small peptide mimetic targeting a specific epitope on p185her2/neu

H Zhang PhD, B Park MD, A Berezov PhD, R Murali PhD, MI Greene MD PhD

University of Pennsylvania, Devon PA USA,

AIM: Two monoclonal anti-p185 antibodies have been shown to have anti-Her2/neu tumor activity: 7.16.4 and 4D5 (Herceptin) which were raised against the ectodomain of rat and human homologs of p185her2/neu respectively. Studies on the three dimensional structure of these two antibodies indicate that they share structural similarity in the variable region, especially the CDR3 region, which is relevant to antibody-antigen interactions. We used these features to aid in the design of a small peptide to mimic the function of 4D5. METHODS: Flow cytometry and Biacore binding studies were used to test antibody-antigen binding. Growth inhibition activity was assessed by MTT, focus formation, and in vivo tumor growth. RESULTS: 7.16.4 and 4D5 share an epitope on the p185 receptor demonstrated by the competitive binding assay. 7.16.4 can also inhibit proliferation and transformation caused by the overexpressed human p185her2/neu. AHNP, a small exocyclicmimetic peptide mimetic designed from the CDR3 region of 4D5, specifically binds to p185her2/neu with high affinity (KD=300 nM). AHNP inhibits proliferation of p185her2/neu-overexpressing tumor cells; and reduces focus formation in vitro as well as growth of p185her2/neu-expressing tumors in athymic mice. The AHNP mimetics are water-soluble, relatively protease-resistant and may exhibit improved tissue penetration. CONCLUSIONS: Binding to the specific epitope on p185her2/neu is critical for the antibody to affect the aggressive growth potential of the cell. The structure-based design of the AHNP represents a novel strategy for the design of receptor-specific tumor therapies.

KEY WORDS: p185^her2/neu, antibody, peptide mimetic, tumor growth inhibition.

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Paper presented at the International Symposium on Impact of Biotechnology on Cancer Diagnostic & Prognostic Indicators; Geneva, Switzerland; October 28 - 31, 2000; in the section on novel therapies.