Imaging epidermal growth factor receptor expression in vivo: pharmacokinetic and biodistribution characterization of a bioconjugated quantum dot nanoprobe.
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.
Diagaradjane
Parmeswaran
P
Department of Experimental Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
Orenstein-Cardona
Jacobo M
JM
Colón-Casasnovas
Norman E
NE
Deorukhkar
Amit
A
Shentu
Shujun
S
Kuno
Norihito
N
Schwartz
David L
DL
Gelovani
Juri G
JG
Krishnan
Sunil
S
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
D066246:ErbB Receptors