RT Journal Article SR Electronic T1 18F-MCL-524, an 18F-Labeled Dopamine D2 and D3 Receptor Agonist Sensitive to Dopamine: A Preliminary PET Study JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1164 OP 1170 DO 10.2967/jnumed.113.133876 VO 55 IS 7 A1 Sjoerd J. Finnema A1 Vladimir Stepanov A1 Ryuji Nakao A1 Anna W. Sromek A1 Tangzhi Zhang A1 John L. Neumeyer A1 Susan R. George A1 Philip Seeman A1 Michael G. Stabin A1 Cathrine Jonsson A1 Lars Farde A1 Christer Halldin YR 2014 UL http://jnm.snmjournals.org/content/55/7/1164.abstract AB PET has been used to examine changes in neurotransmitter concentrations in the living brain. Pioneering PET studies on the dopamine system have used D2 and D3 receptor (D2/D3) antagonists such as 11C-raclopride. However, more recently developed agonist radioligands have shown enhanced sensitivity to endogenous dopamine. A limitation of available agonist radioligands is that they incorporate the short-lived radioisotope 11C. In the current study, we developed the 18F-labeled D2/D3 receptor agonist (R)-(−)-2-18F-fluoroethoxy-N-n-propylnorapomorphine (18F-MCL-524). Methods: In total, 10 PET measurements were conducted on 5 cynomolgus monkeys. Initially, the binding of 18F-MCL-524 was compared with that of 11C-MNPA in 3 monkeys. Second, the specificity of 18F-MCL-524 binding was examined in pretreatment studies using raclopride (1.0 mg/kg) and d-amphetamine (1.0 mg/kg). Third, a preliminary kinetic analysis was performed using the radiometabolite-corrected arterial input function of the baseline studies. Finally, 2 whole-body PET measurements were conducted to evaluate biodistribution and radiation dosimetry after intravenous injection of 18F-MCL-524. Results: 18F-MCL-524 entered the brain and provided striatum-to-cerebellum ratios suitable for reliable quantification of receptor binding using the multilinear reference tissue model. Mean striatal nondisplaceable binding potential (BPND) values were 2.0 after injection of 18F-MCL-524 and 1.4 after 11C-MNPA. The ratio of the BPND values of 18F-MCL-524 and 11C-MNPA was 1.5 across striatal subregions. After administration of raclopride and d-amphetamine, the 18F-MCL-524 BPND values were reduced by 89% and 56%, respectively. Preliminary kinetic analysis demonstrated that BPND values obtained with the 1-tissue- and 2-tissue-compartment models were similar to values obtained with the multilinear reference tissue model. Estimated radiation doses were highest for gallbladder (0.27 mSv/MBq), upper large intestine (0.19 mSv/MBq), and small intestine (0.17 mSv/MBq). The estimated effective dose was 0.035 mSv/MBq. Conclusion: The 18F-labeled agonist 18F-MCL-524 appears suitable for quantification of D2/D3 receptor binding in vivo, and the results encourage extension to human studies. The longer half-life of 18F makes 18F-MCL-524 attractive for studies on modulation of the dopamine concentration—for example, in combination with simultaneous measurement of changes in blood-oxygen-level–dependent signal using bimodal PET/functional MRI.