Evaluation of Two Potent and Selective PET Radioligands to Image COX-1 and COX-2 in Rhesus Monkeys

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Abstract
This study assessed whether the newly developed PET radioligands 11C-PS13 and 11C-MC1 could image constitutive levels of cyclooxygenase-1 (COX-1) and COX-2, respectively, in rhesus monkeys. Methods: After intravenous injection of either radioligand, 24 whole-body PET scans were performed. To measure enzyme-specific uptake, scans of the two radioligands were also performed after administration of a non-radioactive drug preferential for either COX-1 or COX-2. Concurrent venous samples were obtained to measure parent radioligand concentrations. Standardized uptake values were calculated from 10-90 minutes. Results: 11C-PS13 showed specific uptake in most organs including spleen, gastrointestinal tract, kidneys, and brain, which was blocked by COX-1, but not COX-2, preferential inhibitors. Specific uptake of 11C-MC1 was not observed in any organ except the ovaries and possibly kidneys. Conclusion: The findings suggest that 11C-PS13 has adequate signal in monkeys to justify its extension to human subjects. In contrast, 11C-MC1 is unlikely to show significant signal in healthy humans, though it may be able to do so in inflammatory conditions.

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