Imaging Leucine-Rich Repeat Kinase 2 In Vivo with ¹⁸F-Labeled Positron Emission Tomography Ligand

Abstract

Leucine-rich repeat kinase 2 (LRRK2) has been demonstrated to be closely involved in the pathogenesis of Parkinson's disease (PD), and pharmacological blockade of LRRK2 represents a new opportunity for therapeutical treatment of PD and other related neurodegenerative conditions. The development of an LRRK2-specific positron emission tomography (PET) ligand would enable a target occupancy study in vivo and greatly facilitate LRRK2 drug discovery and clinical translation as well as provide a molecular imaging tool for studying physiopathological changes in neurodegenerative diseases. In this work, we present the design and development of compound 8 (PF-06455943) as a promising PET radioligand through a PET-specific structure−activity relationship optimization, followed by comprehensive pharmacology and ADME/neuroPK characterization. Following an efficient 18 F-labeling method, we have confirmed high brain penetration of [ 18 F]8 in nonhuman primates (NHPs) and validated its specific binding in vitro by autoradiography in postmortem NHP brain tissues and in vivo by PET imaging studies.

Evaluation of [18F]PF-06455943 as a Potential LRRK2 PET Imaging Agent in the Brain of Nonhuman Primates

“…23 An in vitro autoradiography study of [ 18 F]PF-06455943 in a baboon brain tissue showed high binding in the caudate, hippocampus, thalamus, and cortex, while lower binding was observed in the hypothalamus. 19 Our in vivo imaging results agree with those findings in vitro.…”

“…Favorable in vivo specific binding was also demonstrated by a LC-MS/MS study in mice. 19 In this study, dynamic PET scans were performed in macaques (n = 2) using [ 18 F]PF-06455943 with arterial blood sampling to compare kinetic modeling approaches to determine the optimal kinetic models describing the performance of the radiotracer. 22 As demonstrated in Figure 1a, the [ 18 F]PF-06455943 metabolism rate was moderate.…”

“…19 Additionally, [ 18 F]PF-06455943 exhibited a good selectivity in 39 different kinases with only 1 hit from kinase MST2, revealing 58% inhibition at 1 μM in the presence of 1 mM ATP. 19 Arterial Plasma and Metabolite Analysis. Blood samples were drawn from the arterial line after the bolus injection of the tracer with ∼5 s intervals for the initial 3 min (∼1 mL each).…”

“…14 Building upon previous effort by our group and others, 18 we have successfully developed [ 18 F]PF-06455943 as a novel potential PET ligand for LRRK2 imaging. 19 Biochemistry assays and autoradiography studies show that [ 18 F]PF-06455943 has good binding affinity (IC 50 = 3.6 nM) and selectivity toward LRRK2, good brain permeability, and a predicted low risk of nonspecific binding with favorable unbound fraction in the brain and plasma. 19 In the current study, we performed in vivo PET imaging using [ 18 F]PF-06455943 in nonhuman primates with arterial blood sampling to characterize the pharmacokinetics of this novel tracer.…”

“…19 Biochemistry assays and autoradiography studies show that [ 18 F]PF-06455943 has good binding affinity (IC 50 = 3.6 nM) and selectivity toward LRRK2, good brain permeability, and a predicted low risk of nonspecific binding with favorable unbound fraction in the brain and plasma. 19 In the current study, we performed in vivo PET imaging using [ 18 F]PF-06455943 in nonhuman primates with arterial blood sampling to characterize the pharmacokinetics of this novel tracer. In addition, we conducted an in vivo occupancy study using unlabeled PF-06455943 to confirm specific binding.…”