title: Advantage of a residualizing iodine radiolabel in the therapy of a colon cancer xenograft targeted with an anticarcinoembryonic antigen monoclonal antibody.
abstract: OBJECTIVE
  A disadvantage of conventionally radioiodinated monoclonal antibodies (mAb) for cancer therapy is the short retention time of the radionuclide within target cells. To address this issue, we recently developed a method in which radioiodine is introduced onto antibodies using an adduct consisting of a nonmetabolizable peptide attached to the aminopolycarboxylate diethylenetriaminepentaacetic acid, designated IMP-R4. This adduct causes the radioiodine to become trapped in lysosomes following antibody catabolism. Clinical-scale production of 131I-IMP-R4-labeled antibodies is possible using a recently developed facile method.
  
  
  METHODS
  The properties of 131I-IMP-R4-labeled anticarcinoembryonic antigen (CEA) humanized mAb hMN-14 were compared with the directly radioiodinated hMN-14 (131I-hMN-14) in CEA-expressing human colon cancer cell lines, LoVo and LS174T, and in nude mice bearing established LoVo tumor xenografts.
  
  
  RESULTS
  125I-IMP-R4-hMN-14 retention in the cell lines was significantly increased (61.5% after 3 days) compared with 125I-hMN-14. In vivo, a significant improvement in tumor accretion of radiolabel was obtained using 131I-IMP-R4-hMN-14, which led to a marked improvement in therapeutic efficacy. Eight weeks post-treatment, mean tumor volumes were 0.16 +/- 0.19 and 1.99 +/- 1.35 cm3 in mice treated with 131I-IMP-R4-hMN-14 and 131I-hMN-14, respectively, with complete remissions observed in 27% of mice treated with 131I-IMP-R4-hMN-14 and none using 131I-hMN-14.
  
  
  CONCLUSIONS
  131I-IMP-R4-hMN-14 provides a significant therapeutic advantage in comparison to the conventionally 131I-labeled antibody. The ability of this labeling method to lend itself to clinical-scale labeling, the broad applicability of a humanized anti-CEA mAb for CEA-expressing cancers, and the clinical benefits of radioimmunotherapy with anti-CEA mAb shown recently for small-volume and minimal residual disease combine to make 131I-IMP-R4-hMN-14 a promising new agent for radioimmunotherapy.
authors.affiliation: Garden State Cancer Center, Center for Molecular Medicine and Immunology, Belleville, New Jersey and Immunomedics Inc., Morris Plains, New Jersey, USA. rstein@gscancer.org
authors.forename: Rhona
authors.initials: R
authors.lastname: Stein
authors.forename: Serengulam V
authors.initials: SV
authors.lastname: Govindan
authors.forename: Marianne
authors.initials: M
authors.lastname: Hayes
authors.forename: Gary L
authors.initials: GL
authors.lastname: Griffiths
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Hansen
authors.forename: Ivan D
authors.initials: ID
authors.lastname: Horak
authors.forename: David M
authors.initials: DM
authors.lastname: Goldenberg
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology / Q000627:therapeutic use*; D002272:Carcinoembryonic Antigen / Q000276:immunology*; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007457:Iodine Radioisotopes; D051379:Mice; D008819:Mice, Nude; D016499:Radioimmunotherapy / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics / Q000494:pharmacology / Q000627:therapeutic use; D015203:Reproducibility of Results; D013997:Time Factors; D014018:Tissue Distribution; D016896:Treatment Outcome; D023041:Xenograft Model Antitumor Assays
chemical_list: D000911:Antibodies, Monoclonal; D002272:Carcinoembryonic Antigen; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals