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Identification and Characterization of a Peptide with Affinity to Head and Neck Cancer

¹ Department of Nuclear Medicine, University of Heidelberg, Heidelberg, Germany; ² Clinical Cooperation Unit Nuclear Medicine, German Cancer Research Centre (DKFZ), Heidelberg, Germany; ³ Bayer Schering Pharma AG, Berlin, Germany; ⁴ Department of Neurosurgery, Division of Neurosurgical Research, University of Heidelberg, Heidelberg, Germany; and ⁵ Department of Radiopharmaceutical Chemistry, German Cancer Research Centre (DKFZ), Heidelberg, Germany

Correspondence: For correspondence or reprints contact: Eva-Maria Nothelfer, Department of Nuclear Medicine, University of Heidelberg, Im Neuenheimer Feld 400, D-69120, Heidelberg, Germany. E-mail: E.Nothelfer{at}dkfz.de

Combination therapy has improved the quality of life for patients with squamous cell carcinomas of the head and neck (HNSCCs) but has not decisively changed prognosis. Targeted therapies, which enhance accumulation of the drug in the tumor, may be realized using tumor-specific binding peptides. This paper identifies and characterizes an HNSCC affine peptide. Methods: From a phage library comprising 10⁹ different displayed peptides, 1 peptide was enriched after 5 in vitro selection rounds on HNO223 tumor cells. Subsequently, the gained peptide sequence H₂N-SPRGDLAVLGHKY-CONH₂ (HBP-1) was synthesized as an amide and labeled with ¹²⁵I. In vitro studies for binding kinetics and competition were performed with 5 different HNSCC cell lines. Furthermore, the stability of the peptide was evaluated in human serum. The in vivo biodistribution of ¹³¹I-labeled peptide was determined in HNSCC tumor–bearing nude mice. The results were further validated in human HNSCC tumor tissue sections using fluorescence-labeled HBP-1. Competition experiments were performed to determine the binding sequence and validate the target. Results: The HBP-1 motif was enriched in 62% of all phages sequenced. Labeled ¹²⁵I-HBP-1 showed binding to 5 different HNSCC cell lines and a maximum binding to HNO97 cells, with 11% of the applied dose per 10⁶ cells and an inhibitory concentration of 50% of 38.9 nM. Stability experiments in human serum showed a half-life of 55 min. In 2 different HNSCC tumor xenografts, ¹³¹I-HBP-1 accumulated rapidly, with stable uptake until 45 min after intravenous application. Peptide immunohistochemistry of HNSCC tissue sections exhibited tumor staining by HBP-1, whereas normal tissue remained negative. Sequence mutation and competition experiments revealed that the intrinsic RGD motif in combination with the intrinsic LXXL motif is responsible for the binding ability of HBP1. The RGDLXXL sequence within this peptide is known and indicates that binding occurs via the _vβ₆ rather than the _vβ₃ integrin. Conclusion: Within the sequence of HBP-1 is a RGDLXXL motif, and most likely it is targeting the _vβ₆ receptor of the integrin family of cell adhesion receptors. HBP-1 represents a promising lead structure for the development of targeted therapies or diagnostic procedures in patients with HNSCC.

Key Words: tumor targeting • peptides • RGD • phage display • integrin _vβ₆ • head and neck cancer

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