title: Ganglioside GD2-specific trifunctional surrogate antibody Surek demonstrates therapeutic activity in a mouse melanoma model.
abstract: BACKGROUND
  Trifunctional bispecific antibodies (trAb) are a special class of bispecific molecules recruiting and activating T cells and accessory immune cells simultaneously at the targeted tumor. The new trAb Ektomab that targets the melanoma-associated ganglioside antigen GD2 and the signaling molecule human CD3 (hCD3) on T cells demonstrated potent T-cell activation and tumor cell destruction in vitro. However, the relatively low affinity for the GD2 antigen raised the question of its therapeutic capability. To further evaluate its efficacy in vivo it was necessary to establish a mouse model.
  
  
  METHODS
  We generated the surrogate trAb Surek, which possesses the identical anti-GD2 binding arm as Ektomab, but targets mouse CD3 (mCD3) instead of hCD3, and evaluated its chemical and functional quality as a therapeutic antibody homologue. The therapeutic and immunizing potential of Surek was investigated using B78-D14, a B16 melanoma transfected with GD2 and GD3 synthases and showing strong GD2 surface expression. The induction of tumor-associated and autoreactive antibodies was evaluated.
  
  
  RESULTS
  Despite its low affinity of approximately 10(7) M(-1) for GD2, Surek exerted efficient tumor cell destruction in vitro at an EC(50) of 70 ng/ml [0.47 nM]. Furthermore, Surek showed strong therapeutic efficacy in a dose-dependent manner and is superior to the parental GD2 mono-specific antibody, while the use of a control trAb with irrelevant target specificity had no effect. The therapeutic activity of Surek was strictly dependent on CD4(+) and CD8(+) T cells, and cured mice developed a long-term memory response against a second challenge even with GD2-negative B16 melanoma cells. Moreover, tumor protection was associated with humoral immune responses dominated by IgG2a and IgG3 tumor-reactive antibodies indicating a Th1-biased immune response. Autoreactive antibodies against the GD2 target antigen were not induced.
  
  
  CONCLUSIONS
  Our data suggest that Surek revealed strong tumor elimination and anti-tumor immunization capabilities. The results warrant further clinical development of the human therapeutic equivalent antibody Ektomab.
authors.affiliation: TRION Research GmbH, Martinsried, Germany. peter.ruf@trionresearch.de
authors.forename: Peter
authors.initials: P
authors.lastname: Ruf
authors.forename: Beatrix
authors.initials: B
authors.lastname: Schäfer
authors.forename: Nina
authors.initials: N
authors.lastname: Eissler
authors.forename: Ralph
authors.initials: R
authors.lastname: Mocikat
authors.forename: Juergen
authors.initials: J
authors.lastname: Hess
authors.forename: Matthias
authors.initials: M
authors.lastname: Plöscher
authors.forename: Susanne
authors.initials: S
authors.lastname: Wosch
authors.forename: Ivonne
authors.initials: I
authors.lastname: Suckstorff
authors.forename: Christine
authors.initials: C
authors.lastname: Zehetmeier
authors.forename: Horst
authors.initials: H
authors.lastname: Lindhofer
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D018033:Antibodies, Bispecific / Q000276:immunology / Q000494:pharmacology / Q000627:therapeutic use*; D000912:Antibodies, Neoplasm / Q000276:immunology / Q000494:pharmacology / Q000627:therapeutic use; D000918:Antibody Specificity / Q000276:immunology*; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D004306:Dose-Response Relationship, Immunologic; D005732:Gangliosides / Q000276:immunology*; D006801:Humans; D007106:Immune Sera; D056724:Immunity, Humoral / Q000187:drug effects / Q000276:immunology; D007114:Immunization; D007074:Immunoglobulin G / Q000276:immunology; D008545:Melanoma / Q000097:blood / Q000188:drug therapy* / Q000276:immunology*; D051379:Mice; D012878:Skin Neoplasms / Q000097:blood / Q000188:drug therapy* / Q000276:immunology*; D016019:Survival Analysis; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D018033:Antibodies, Bispecific; D000912:Antibodies, Neoplasm; D005732:Gangliosides; D007106:Immune Sera; D007074:Immunoglobulin G; C019403:ganglioside, GD2