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Overexpression of the ErbB2 receptor is associated with the progression of breast cancer, and is a sign of a poor prognosis. Herceptin, a humanized antibody directed to the ErbB2 receptor, has been proven to be effective in the immunotherapy of breast cancer. However, it can result in cardiotoxicity, and a large fraction of breast cancer patients are resistant to Herceptin treat-ment. | ỊFEBS Journal Differential binding of human immunoagents and Herceptin to the ErbB2 receptor Fulvia Troise1 Valeria Cafaro1 Concetta Giancola2 Giuseppe D Alessio1 and Claudia De Lorenzo1 1 Dipartimento di Biologia Strutturale e Funzionale Universita di Napoli Federico II Italy 2 Dipartimento di Chimica Universita di Napoli Federico II Italy Keywords binding affinity ErbB2 herceptin immunoRNase immunotherapy Correspondence C. De Lorenzo Dipartimento di Biologia Strutturale e Funzionale University di Napoli Federico II Via Cinthia 80126 Naples Italy Fax 39081679159 Tel 39081679158 E-mail cladelor@unina.it These authors contributed equally to this work Received 9 June 2008 revised 29 July 2008 accepted 1 August 2008 doi 10.1111 j.1742-4658.2008.06625.x Overexpression of the ErbB2 receptor is associated with the progression of breast cancer and is a sign of a poor prognosis. Herceptin a humanized antibody directed to the ErbB2 receptor has been proven to be effective in the immunotherapy of breast cancer. However it can result in cardiotoxicity and a large fraction of breast cancer patients are resistant to Herceptin treatment. We have engineered three novel fully human anti-ErbB2 immunoagents Erbicin a human single-chain antibody fragment ERB-hRNase a human immunoRNase composed of Erbicin fused to a human RNase ERB-hcAb a human compact antibody in which two Erbicin molecules are fused to the Fc fragment of a human IgG1. Both ERB-hRNase and ERB-hcAb strongly inhibit the growth of ErbB2-positive cells in vivo. The interactions of the Erbicin-derived immunoagents and Herceptin with the extracellular domain of ErbB2 ErbB2-ECD were investigated for the first time by three different methods. Erbicin-derived immunoagents bind soluble extracellular domain with a lower affinity than that measured for the native antigen on tumour cells. Herceptin by contrast shows a higher affinity for soluble ErbB2-ECD. Accordingly ErbB2-ECD abolished the in vitro antitumour activity of .
