PET imaging of cyclooxygenase-2 (COX-2) in a pre-clinical colorectal cancer model.
BACKGROUND
Cyclooxygenase-2 (COX-2) is the inducible isoform of the cyclooxygenase enzyme family. COX-2 is involved in tumor development and progression, and frequent overexpression of COX-2 in a variety of human cancers has made COX-2 an important drug target for cancer treatment. Non-invasive imaging of COX-2 expression in cancer would be useful for assessing COX-2-mediated effects on chemoprevention and radiosensitization using COX-2 inhibitors as an emerging class of anti-cancer drugs, especially for colorectal cancer. Herein, we describe the radiopharmacological analysis of [(18)F]Pyricoxib, a novel radiolabeled COX-2 inhibitor, for specific PET imaging of COX-2 in colorectal cancer.


METHODS
Uptake of [(18)F]Pyricoxib was assessed in human colorectal cancer cell lines HCA-7 (COX-2 positive) and HCT-116 (COX-2 negative). Standard COX-2 inhibitors were used to test for specificity of [(18)F]Pyricoxib for COX-2 binding in vitro and in vivo. PET imaging, biodistribution, and radiometabolite analyses were included into radiopharmacological evaluation of [(18)F]Pyricoxib.


RESULTS
Radiotracer uptake in COX-2 positive HCA-7 cells was significantly higher than in COX-2 negative HCT-116 cells (P < 0.05). COX-2 inhibitors, celecoxib, rofecoxib, and SC58125, blocked uptake of [(18)F]Pyricoxib in HCA-7 cells in a concentration-dependent manner. The radiotracer was slowly metabolized in mice, with approximately 60 % of intact compound after 2 h post-injection. Selective COX-2-mediated tumor uptake of [(18)F]Pyricoxib in HCA-7 xenografts was confirmed in vivo. Celecoxib (100 mg/kg) selectively blocked tumor uptake by 16 % (PET image analysis; P < 0.05) and by 51 % (biodistribution studies; P < 0.01).


CONCLUSIONS
The novel PET radiotracer [(18)F]Pyricoxib displays a promising radiopharmacological profile to study COX-2 expression in cancer in vivo.
Department of Oncology, University of Alberta, 11560- University Avenue, Edmonton, AB, T6G 1Z2, Canada.
Ole
O
Tietz
Department of Oncology, University of Alberta, 11560- University Avenue, Edmonton, AB, T6G 1Z2, Canada.
Melinda
M
Wuest
Department of Oncology, University of Alberta, 11560- University Avenue, Edmonton, AB, T6G 1Z2, Canada.
Alison
A
Marshall
Department of Oncology, University of Alberta, 11560- University Avenue, Edmonton, AB, T6G 1Z2, Canada.
Darryl
D
Glubrecht
Department of Oncology, University of Alberta, 11560- University Avenue, Edmonton, AB, T6G 1Z2, Canada.
Ingrit
I
Hamann
Department of Oncology, University of Alberta, 11560- University Avenue, Edmonton, AB, T6G 1Z2, Canada.
Monica
M
Wang
Department of Oncology, University of Alberta, 11560- University Avenue, Edmonton, AB, T6G 1Z2, Canada.
Cody
C
Bergman
Department of Oncology, University of Alberta, 11560- University Avenue, Edmonton, AB, T6G 1Z2, Canada.
Jenilee D
JD
Way
Department of Oncology, University of Alberta, 11560- University Avenue, Edmonton, AB, T6G 1Z2, Canada. wuest@ualberta.ca.|Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada. wuest@ualberta.ca.
Frank
F
Wuest
COX-2 inhibitor; Colorectal cancer; Cyclooxygenase-2 (COX-2); Positron emission tomography (PET)