Radiosynthesis andin vivo evaluation of11C-Iabeled 1,5-diarylpyrazole derivatives for mapping cyclooxygenases
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We prepared11C-labeled5-(4-chlorophenyl)-l-(4-methoxyphenyl)-3-(trifluoromethyl)-lH-pyrazole ([11C] 1) and 4-[5-(4-methoxyphenyl)-3-trifluoromethyl-lH-pyrazol-1 -yljbenzenesulfonamide ([11C]2) for imaging COX-1 and COX-2 isoforms, respectively, by positron emission tomography. [11C]l and [11C]2 were synthesized in high radiochemical yields byO-[11C]methylation with [11C]methyl triflate in acetone containing an equivalent of NaOH as a base with respect to the phenolic precursors.In vivo evaluation in rats bearing AH109A hepatoma demonstrated minimal specific binding of [11C]1 to COX-1 in peripheral organs, such as the spleen and small intestine. Carrier-saturable uptake of [11C]2 was found in the spleen, but COX-2-specific binding of [101C]2 was not identifiable in the brain, AH109A hepatoma or other peripheral organs, althoughex vivo autoradiography showed regionally different distribution in the brain and AH 109A. The results suggest that neither [11C]1 nor [11C]2 is a suitable radioligand forin vivo biomarkers of COX enzymes, mainly because of marked non-specific binding.