Synthesis and in vivo evaluation of F-18-desbromo-DuP-697 as a PET tracer for cyclooxygenase-2 expression

Cyclooxygenase-2 (COX-2) overexpression has been observed in various pathologies, such as inflammation, cancer, ischemia, and Alzheimer's disease. As an initial step toward a noninvasive PET technique to assay COX-2 expression, this study describes the synthesis and preliminary evaluation of the radiolabeled COX-2 inhibitor F-18-desbromo-DuP-697. Methods: Desbromo-DuP-697 was radiolabeled by a nucleophilic aromatic substitution reaction of the nitro precursor with F-18-fluoride. Biodistribution studies of the tracer were performed in a carrageenan-induced hyperalgesia rat model. Brain uptake was investigated with autoradiography. To confirm the results of the biodistribution, COX activity was determined by a peroxidase assay. Results: Biodistribution studies showed specific binding of the tracer to COX-2 in heart, kidney, brain, and blood cells, but not in the inflamed paw, which was probably due to low COX-2 expression. In the brain, regional differences in tracer uptake were observed, with high uptake in cortical regions. F-18-Desbromo-DuP-697 did not show any binding to COX-1. Nonspecific uptake was high in fat and intestines. Conclusion: Because of its ability to cross the blood-brain barrier, F-18-desbromo-DuP-697 appears to be suitable for COX-2 imaging in the brain. Its high nonspecific uptake in the intestines may limit its use for imaging in the abdominal region.