De novo identification of tumor-specific internalizing human antibody-receptor pairs by phage-display methods.

Three tumor-specific, internalizing human single-chain Fvs (scFvs) were obtained by direct selection against tumor cells from a large, nonimmune scFv-phage library pre-subtracted with various normal human cells. After scFv selection and characterization for cell binding and internalization, the scFvs were also employed in immunoprecipitations to identify putative receptors. In the case of a prostate tumor-cell specific scFv PR5, the receptor that mediated endocytosis was shown to be the transferrin receptor. For two pancreatic adenocarcinoma specific scFvs SW1 and PAN10, the alpha(3)beta(1) integrin was identified. The scFv SW1 was studied in further detail and found to induce functional effects as a ligand-mimetic by mediating cell adhesion and migration. The results demonstrated the feasibility of utilizing enhanced phage-display methods as a rapid and general approach for not only direct isolation of human internalizing scFvs, but also for identifying tumor cell-surface receptors from various classes. The use of scFv constructs that target tumor cells and undergo internalization could have significant impact on the future of cancer and gene therapy.