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. 2004 Nov-Dec;6(6):373-84.
doi: 10.1016/j.mibio.2004.08.001.

Synthesis and characterization of a potent, selective, radiolabeled substance-P antagonist for NK1 receptor quantitation: ([18F]SPA-RQ)

Olof Solin  1 , Olli Eskola, Terence G Hamill, Jörgen Bergman, Pertti Lehikoinen, Tove Grönroos, Sarita Forsback, Merja Haaparanta, Tapio Viljanen, Christine Ryan, Raymond Gibson, Gerard Kieczykowski, Jarmo Hietala, Richard Hargreaves, H Donald Burns
Affiliations

Synthesis and characterization of a potent, selective, radiolabeled substance-P antagonist for NK1 receptor quantitation: ([18F]SPA-RQ)

Olof Solin et al. Mol Imaging Biol. 2004 Nov-Dec.

Abstract

Purpose: To develop and characterize a radiolabelled Substance-P antagonist useful for quantitation of neurokinin-1 receptors in the brain via PET imaging.

Procedure: [18F]SPA-RQ (Substance-P antagonist - receptor quantifier) was synthesized in good yield and high specific activity by alkylation of a BOC protected phenolate anion using [18F]bromofluoromethane. Removal of the BOC protecting group with trifluoroacetic acid gave [18F]SPA-RQ.

Results: SPA-RQ has high affinity for human, rhesus monkey and guinea pig NK1 receptors (h-IC50=67 pM) and has a log P value of 1.8. Biodistribution studies in guinea pig showed that this tracer penetrates the blood-brain barrier and selectively labels NK1 receptors in the striatum and cortex.

Conclusion: [18F]SPA-RQ is a potent, high affinity Substance-P antagonist that can be conveniently labeled with high specific activity using [18F]fluoromethylbromide. This tracer is a useful tool for noninvasive imaging of central NK1 receptors.

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