title: Preclinical Evaluation of 18F-Labeled Anti-HER2 Nanobody Conjugates for Imaging HER2 Receptor Expression by Immuno-PET.
abstract: The human growth factor receptor type 2 (HER2) is overexpressed in breast as well as other types of cancer. Immuno-PET, a noninvasive imaging procedure that could assess HER2 status in both primary and metastatic lesions simultaneously, could be a valuable tool for optimizing application of HER2-targeted therapies in individual patients. Herein, we have evaluated the tumor-targeting potential of the 5F7 anti-HER2 Nanobody (single-domain antibody fragment; ∼13 kDa) after (18)F labeling by 2 methods.
  
  
  
  The 5F7 Nanobody was labeled with (18)F using the novel residualizing label N-succinimidyl 3-((4-(4-(18)F-fluorobutyl)-1H-1,2,3-triazol-1-yl)methyl)-5-(guanidinomethyl)benzoate ((18)F-SFBTMGMB; (18)F-RL-I) and also via the most commonly used (18)F protein-labeling prosthetic agent N-succinimidyl 3-(18)F-fluorobenzoate ((18)F-SFB). For comparison, 5F7 Nanobody was also labeled using the residualizing radioiodination agent N-succinimidyl 4-guanidinomethyl-3-(125)I-iodobenzoate ((125)I-SGMIB). Paired-label ((18)F/(125)I) internalization assays and biodistribution studies were performed on HER2-expressing BT474M1 breast carcinoma cells and in mice with BT474M1 subcutaneous xenografts, respectively. Small-animal PET/CT imaging of 5F7 Nanobody labeled using (18)F-RL-I also was performed.
  
  
  
  Internalization assays indicated that intracellularly retained radioactivity for (18)F-RL-I-5F7 was similar to that for coincubated (125)I-SGMIB-5F7, whereas that for (18)F-SFB-5F7 was lower than coincubated (125)I-SGMIB-5F7 and decreased with time. BT474M1 tumor uptake of (18)F-RL-I-5F7 was 28.97 ± 3.88 percentage injected dose per gram of tissue (%ID/g) at 1 h and 36.28 ± 14.10 %ID/g at 2 h, reduced by more than 90% on blocking with trastuzumab, indicating HER2 specificity of uptake, and was also 26%-28% higher (P < 0.05) than that of (18)F-SFB-5F7. At 2 h, the tumor-to-blood ratio for (18)F-RL-I-5F7 (47.4 ± 13.1) was significantly higher (P < 0.05) than for (18)F-SFB-5F7 (25.4 ± 10.3); however, kidney uptake was 28-36-fold higher for (18)F-RL-I-5F7.
  
  
  
  (18)F-RL-I-5F7 is a promising tracer for evaluating HER2 status by immuno-PET; however, in settings in which renal background is problematic, strategies for reducing its kidney uptake may be needed.
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, North Carolina ganesan.v@duke.edu.
authors.forename: Ganesan
authors.initials: G
authors.lastname: Vaidyanathan
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, North Carolina.
authors.forename: Darryl
authors.initials: D
authors.lastname: McDougald
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, North Carolina.
authors.forename: Jaeyeon
authors.initials: J
authors.lastname: Choi
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, North Carolina.
authors.forename: Eftychia
authors.initials: E
authors.lastname: Koumarianou
authors.affiliation: Department of Radiation Oncology and Cancer Biology, Duke University Medical Center, Durham, North Carolina; and.
authors.forename: Douglas
authors.initials: D
authors.lastname: Weitzel
authors.affiliation: Department of Surgery, Duke University Medical Center, Durham, North Carolina.
authors.forename: Takuya
authors.initials: T
authors.lastname: Osada
authors.affiliation: Department of Surgery, Duke University Medical Center, Durham, North Carolina.
authors.forename: H Kim
authors.initials: HK
authors.lastname: Lyerly
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, North Carolina.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Zalutsky
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D005462:Fluorine Radioisotopes; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D018796:Immunoconjugates / Q000737:chemistry / Q000276:immunology* / Q000493:pharmacokinetics; D007553:Isotope Labeling; D051379:Mice; D000072078:Positron Emission Tomography Computed Tomography / Q000379:methods*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000276:immunology*; D061905:Single-Domain Antibodies / Q000276:immunology*; D014018:Tissue Distribution
chemical_list: D005462:Fluorine Radioisotopes; D018796:Immunoconjugates; D018719:Erb-b2 Receptor Tyrosine Kinases; D061905:Single-Domain Antibodies
keywords: 18F; HER2; Nanobody; immuno-PET; residualizing label