title: Engineering and biological characterization of VB6-845, an anti-EpCAM immunotoxin containing a T-cell epitope-depleted variant of the plant toxin bouganin.
abstract: The clinical development of immunotoxins in the treatment of solid tumors has been impeded in part, by the induction of an immune response directed primarily against the toxin moiety. Bouganin, a type I ribosome inactivating protein isolated from the leaf of Bougainvillea spectabilis Willd, was mutated to remove the T-cell epitopes while preserving the biological activity of the wild-type molecule. The T-cell epitope-depleted variant of bouganin (de-bouganin) was genetically linked to an anti-epithelial cell adhesion molecule (EpCAM) Fab moiety via a peptidic linker containing a furin proteolytic site to create the fusion construct VB6-845. To determine the optimal construct design for VB6-845, several dicistronic units where de-bouganin was genetically linked to either the N-terminal or C-terminal of either the heavy or light chain were engineered. Only the C-terminal variants expressed the full-length molecule. An in vitro assessment of the biological activity of VB6-845 showed that it bound and selectively killed EpCAM-positive cell lines with a greater potency than many commonly used chemotherapeutic agents. In vivo efficacy was demonstrated using an EpCAM-positive human tumor xenograft model in SCID mice with the majority of the mice treated being tumor free at the end of the study.
authors.affiliation: Viventia Biotechnologies Inc, Manitoba, Canada.
authors.forename: Jeannick
authors.initials: J
authors.lastname: Cizeau
authors.forename: Danielle M
authors.initials: DM
authors.lastname: Grenkow
authors.forename: Jennifer G
authors.initials: JG
authors.lastname: Brown
authors.forename: Joycelyn
authors.initials: J
authors.lastname: Entwistle
authors.forename: Glen C
authors.initials: GC
authors.lastname: MacDonald
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000276:immunology / Q000627:therapeutic use*; D015815:Cell Adhesion Molecules / Q000276:immunology* / Q000378:metabolism; D045744:Cell Line, Tumor; D018984:Epitopes, T-Lymphocyte / Q000235:genetics / Q000276:immunology; D005260:Female; D006801:Humans; D000922:Immunotoxins / Q000235:genetics / Q000276:immunology / Q000627:therapeutic use*; D051379:Mice; D016513:Mice, SCID; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000188:drug therapy*; D039281:Nyctaginaceae / Q000235:genetics / Q000276:immunology; D010940:Plant Proteins / Q000235:genetics / Q000276:immunology / Q000627:therapeutic use; D015202:Protein Engineering; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology / Q000627:therapeutic use*; D016415:Sequence Alignment; D023041:Xenograft Model Antitumor Assays
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D015815:Cell Adhesion Molecules; D018984:Epitopes, T-Lymphocyte; D000922:Immunotoxins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; C544011:VB6-845 fusion protein