title: An interaction between S*tag and S*protein derived from human ribonuclease 1 allows site-specific conjugation of an enzyme to an antibody for targeted drug delivery.
abstract: We have previously demonstrated that an antibody-avidin fusion protein could be used to deliver biotinylated enzymes to tumor cells for antibody-directed enzyme prodrug therapy. However, the presence of the chicken protein avidin suggests that immunogenicity may be a problem. To address this concern, we developed a new delivery system consisting of human proteins. The amino-terminal 15-amino-acid peptide derived from human ribonuclease 1 (human S*tag) can bind with high affinity to human S*protein (residues 21-124 of the same ribonuclease). We constructed an antibody-S*protein fusion protein in which S*protein was genetically linked to an anti-rat transferrin receptor IgG3 at the carboxyl terminus of the heavy chain. We also constructed an enzyme-S*tag fusion protein in which S*tag was genetically linked to the carboxyl terminus of Escherichia coli purine nucleoside phosphorylase (PNP). When these two fusion proteins were mixed, S*tag and S*protein interacted specifically and produced homogeneous antibody/PNP complexes that retained the ability to bind antigen. Furthermore, in the presence of the prodrug 2-fluoro-2'-deoxyadenosine in vitro, the complex efficiently killed rat myeloma cells overexpressing the transferrin receptor. These results suggest that human ribonuclease-based site-specific conjugation can be used in vivo for targeted chemotherapy of cancer.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of California Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095, USA.
authors.forename: Tsuneaki
authors.initials: T
authors.lastname: Asai
authors.forename: Letitia A
authors.initials: LA
authors.lastname: Wims
authors.forename: Sherie L
authors.initials: SL
authors.lastname: Morrison
mesh_terms: D000818:Animals; D000912:Antibodies, Neoplasm / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D000951:Antigens, Neoplasm / Q000276:immunology / Q000378:metabolism; D000970:Antineoplastic Agents / Q000633:toxicity*; D016503:Drug Delivery Systems / Q000379:methods*; D004926:Escherichia coli / Q000201:enzymology; D006801:Humans; D007074:Immunoglobulin G / Q000737:chemistry / Q000276:immunology; D011683:Purine-Nucleoside Phosphorylase / Q000737:chemistry; D051381:Rats; D011990:Receptors, Transferrin / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D012259:Ribonuclease, Pancreatic / Q000737:chemistry / Q000235:genetics*
chemical_list: D000912:Antibodies, Neoplasm; D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D007074:Immunoglobulin G; D011990:Receptors, Transferrin; D011993:Recombinant Fusion Proteins; D011683:Purine-Nucleoside Phosphorylase; D012259:Ribonuclease, Pancreatic