title: Imaging epidermal growth factor receptor expression in vivo: pharmacokinetic and biodistribution characterization of a bioconjugated quantum dot nanoprobe.
abstract: OBJECTIVE
  To develop and validate an optical imaging nanoprobe for the discrimination of epidermal growth factor (EGF) receptor (EGFR)-overexpressing tumors from surrounding normal tissues that also expresses EGFR.
  
  
  METHODS
  Near-infrared (NIR) quantum dots (QD) were coupled to EGF using thiol-maleimide conjugation to create EGF-QD nanoprobes. In vitro binding affinity of these nanoprobes and unconjugated QDs was evaluated in a panel of cell lines, with and without anti-EGFR antibody pretreatment. Serial optical imaging of HCT116 xenograft tumors was done after systemic injection of QD and EGF-QD.
  
  
  RESULTS
  EGF-QD showed EGFR-specific binding in vitro. In vivo imaging showed three distinct phases, tumor influx ( approximately 3 min), clearance ( approximately 60 min), and accumulation (1-6 h), of EGF-QD nanoprobes. Both QD and EGF-QD showed comparable nonspecific rapid tumor influx and clearance followed by attainment of an apparent dynamic equilibrium at approximately 60 min. Subsequently (1-6 h), whereas QD concentration gradually decreased in tumors, EGF-QDs progressively accumulated in tumors. On delayed imaging at 24 h, tumor fluorescence decreased to near-baseline levels for both QD and EGF-QD. Ex vivo whole-organ fluorescence, tissue homogenate fluorescence, and confocal microscopic analyses confirmed tumor-specific accumulation of EGF-QD at 4 h. Immunofluorescence images showed diffuse colocalization of EGF-QD fluorescence within EGFR-expressing tumor parenchyma compared with patchy perivascular sequestration of QD.
  
  
  CONCLUSIONS
  These results represent the first pharmacokinetic characterization of a robust EGFR imaging nanoprobe. The measurable contrast enhancement of tumors 4 h after systemic administration of EGF-QD and its subsequent normalization at 24 h imply that this nanoprobe may permit quantifiable and repetitive imaging of EGFR expression.
authors.affiliation: Department of Experimental Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Parmeswaran
authors.initials: P
authors.lastname: Diagaradjane
authors.forename: Jacobo M
authors.initials: JM
authors.lastname: Orenstein-Cardona
authors.forename: Norman E
authors.initials: NE
authors.lastname: Colón-Casasnovas
authors.forename: Amit
authors.initials: A
authors.lastname: Deorukhkar
authors.forename: Shujun
authors.initials: S
authors.lastname: Shentu
authors.forename: Norihito
authors.initials: N
authors.lastname: Kuno
authors.forename: David L
authors.initials: DL
authors.lastname: Schwartz
authors.forename: Juri G
authors.initials: JG
authors.lastname: Gelovani
authors.forename: Sunil
authors.initials: S
authors.lastname: Krishnan
mesh_terms: D000818:Animals; D016466:CHO Cells; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D004797:Enzyme-Linked Immunosorbent Assay; D066246:ErbB Receptors / Q000032:analysis* / Q000378:metabolism; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D036103:Nanotechnology; D011789:Quantum Theory; D014018:Tissue Distribution; D014183:Transplantation, Heterologous
chemical_list: D066246:ErbB Receptors