title: Antiepidermal growth factor variant III scFv fragment: effect of radioiodination method on tumor targeting and normal tissue clearance.
abstract: BACKGROUND
  MR1-1 is a single-chain Fv (scFv) fragment that binds with high affinity to epidermal growth factor receptor variant III, which is overexpressed on gliomas and other tumors but is not present on normal tissues. The objective of this study was to evaluate four different methods for labeling MR1-1 scFv that had been previously investigated for the radioiodinating of an intact anti-epidermal growth factor receptor variant III (anti-EGFRvIII) monoclonal antibody (mAb) L8A4.
  
  
  METHODS
  The MR1-1 scFv was labeled with (125)I/(131)I using the Iodogen method, and was also radiohalogenated with acylation agents bearing substituents that were positively charged--N-succinimidyl-3-[*I]iodo-5-pyridine carboxylate and N-succinimidyl-4-guanidinomethyl-3-[*I]iodobenzoate ([*I]SGMIB)--and negatively charged--N-succinimidyl-3-[*I]iodo-4-phosphonomethylbenzoate ([*I]SIPMB). In vitro internalization assays were performed with the U87MGDeltaEGFR cell line, and the tissue distribution of the radioiodinated scFv fragments was evaluated in athymic mice bearing subcutaneous U87MGDeltaEGFR xenografts.
  
  
  CONCLUSIONS
  As seen previously with the anti-EGFRvIII IgG mAb, retention of radioiodine activity in U87MGDeltaEGFR cells in the internalization assay was labeling method dependent, with SGMIB and SIPMB yielding the most prolonged retention. However, unlike the case with the intact mAb, the results of the internalization assays were not predictive of in vivo tumor localization capacity of the labeled scFv. Renal activity was dependent on the nature of the labeling method. With MR1-1 labeled using SIPMB, kidney uptake was highest and most prolonged; catabolism studies indicated that this uptake primarily was in the form of epsilon-N-3-[*I]iodo-4-phosphonomethylbenzoyl lysine.
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Sriram
authors.initials: S
authors.lastname: Shankar
authors.forename: Ganesan
authors.initials: G
authors.lastname: Vaidyanathan
authors.forename: Chien-Tsun
authors.initials: CT
authors.lastname: Kuan
authors.forename: Darell D
authors.initials: DD
authors.lastname: Bigner
authors.forename: Michael R
authors.initials: MR
authors.lastname: Zalutsky
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000493:pharmacokinetics* / Q000627:therapeutic use; D045744:Cell Line, Tumor; D016503:Drug Delivery Systems / Q000379:methods; D066246:ErbB Receptors / Q000378:metabolism*; D005910:Glioma / Q000378:metabolism* / Q000532:radiotherapy; D006801:Humans; D007128:Immunoglobulin Fragments / Q000378:metabolism; D007457:Iodine Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics* / Q000627:therapeutic use; D007553:Isotope Labeling / Q000379:methods; D008657:Metabolic Clearance Rate; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009928:Organ Specificity; D016499:Radioimmunotherapy / Q000379:methods*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics / Q000627:therapeutic use; D014018:Tissue Distribution
chemical_list: D000911:Antibodies, Monoclonal; D007128:Immunoglobulin Fragments; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; C410723:epidermal growth factor receptor VIII; D066246:ErbB Receptors