Molecular imaging of therapeutic response to epidermal growth factor receptor blockade in colorectal cancer.
OBJECTIVE
To evaluate noninvasive molecular imaging methods as correlative biomarkers of therapeutic efficacy of cetuximab in human colorectal cancer cell line xenografts grown in athymic nude mice. The correlation between molecular imaging and immunohistochemical analysis to quantify epidermal growth factor (EGF) binding, apoptosis, and proliferation was evaluated in treated and untreated tumor-bearing cohorts.


METHODS
Optical imaging probes targeting EGF receptor (EGFR) expression (NIR800-EGF) and apoptosis (NIR700-Annexin V) were synthesized and evaluated in vitro and in vivo. Proliferation was assessed by 3'-[18F]fluoro-3'-deoxythymidine ([18F]FLT) positron emission tomography. Assessment of inhibition of EGFR signaling by cetuximab was accomplished by concomitant imaging of NIR800-EGF, NIR700-Annexin V, and [18F]FLT in cetuximab-sensitive (DiFi) and insensitive (HCT-116) human colorectal cancer cell line xenografts. Imaging results were validated by measurement of tumor size and immunohistochemical analysis of total and phosphorylated EGFR, caspase-3, and Ki-67 immediately following in vivo imaging.


RESULTS
NIR800-EGF accumulation in tumors reflected relative EGFR expression and EGFR occupancy by cetuximab. NIR700-Annexin V accumulation correlated with cetuximab-induced apoptosis as assessed by immunohistochemical staining of caspase-3. No significant difference in tumor proliferation was noted between treated and untreated animals by [18F]FLT positron emission tomography or Ki-67 immunohistochemistry.


CONCLUSIONS
Molecular imaging can accurately assess EGF binding, proliferation, and apoptosis in human colorectal cancer xenografts. These imaging approaches may prove useful for serial, noninvasive monitoring of the biological effects of EGFR inhibition in preclinical studies. It is anticipated that these assays can be adapted for clinical use.
Manning
H Charles
HC
Vanderbilt Institute of Imaging Science, Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.
Merchant
Nipun B
NB
Foutch
A Coe
AC
Virostko
John M
JM
Wyatt
Shelby K
SK
Shah
Chirayu
C
McKinley
Eliot T
ET
Xie
Jingping
J
Mutic
Nathan J
NJ
Washington
M Kay
MK
LaFleur
Bonnie
B
Tantawy
Mohammed Noor
MN
Peterson
Todd E
TE
Ansari
M Sib
MS
Baldwin
Ronald M
RM
Rothenberg
Mace L
ML
Bornhop
Darryl J
DJ
Gore
John C
JC
Coffey
Robert J
RJ
D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D000068818:Cetuximab; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy*; D003952:Diagnostic Imaging / Q000379:methods*; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism*; D005462:Fluorine Radioisotopes; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007150:Immunohistochemistry; D051379:Mice; D008819:Mice, Nude; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D019265:Spectroscopy, Near-Infrared; D013936:Thymidine; D023041:Xenograft Model Antitumor Assays
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D005462:Fluorine Radioisotopes; D019275:Radiopharmaceuticals; D066246:ErbB Receptors; D000068818:Cetuximab; D013936:Thymidine