Effect of acetylcholinesterase inhibitors on the binding of nicotinic α4β2 receptor PET radiotracer, ¹⁸F‐nifene: A measure of acetylcholine competition

Abstract

Acetylcholinesterase inhibitors (AChEI's) are used to treat Alzheimer's disease (AD), and the putative mode of action is to increase acetylcholine (ACh) levels. Our goal is to evaluate competition of ACh with nicotinic alpha4beta2 receptor PET agonist radiotracer, 2-[(18)F]fluoro-3-[2-((S)-3-pyrrolinyl)methoxy]pyridine ((18)F-nifene). This ability to measure ACh-(18)F-nifene competition may have potential to assess efficacy of AChEI's in vivo. In vitro studies in rat brain slices used two AChEI's, physostigmine (PHY) and galanthamine (GAL). Brain slices were incubated with (18)F-nifene and various concentrations of PHY (0.2-20 microM) or GAL (0.4-4 microM) prior to (18)F-nifene treatment. For ACh competition, slices were also incubated with PHY + 100 nM ACh or GAL + 100 nM ACh or 100 nM ACh alone. Nonspecific binding of (18)F-nifene was determined using 300 microM nicotine. In the in vitro rat brain homogenate binding assay, ACh inhibited (3)H-cytisine binding to alpha4beta2 receptors with K(i) values of 19.2 nM (with PHY) and 34.7 microM (no PHY) indicating approximately 1.8 x 10(3) weaker binding of ACh in the absence of AChEI. Binding of (18)F-nifene was not affected by PHY (0.2-20 microM) or ACh 100 nM alone but decreased substantially by PHY + ACh 100 nM in all brain regions (down by >40% of control in thalamus). Similarly, for GAL (4 microM) no effect on (18)F-nifene binding occurred but GAL (0.4-4 microM) + ACh 100 nM showed a reduction of (18)F-nifene binding in all brain regions (down by approximately 15%). The reduction in both cases is a result of ACh competition with (18)F-nifene in the presence of AChEI. These preliminary in vitro results suggest that ACh is able to compete with (18)F-nifene at the alpha4beta2 receptors in the presence of PHY or GAL. The effect is AChEI-concentration dependent and is greater for PHY than GAL. Thus (18)F-nifene has promise for assessing ACh levels and AChEI effects in vivo.

Development of novel approach to diagnostic imaging of lung cancer with 18F-Nifene PET/CT using A/J Mice treated with NNK

“…Normal lung distribution and kinetics of 18 F-Nifene in mice was characterized by us in a previous work [33]. Binding of 18 F-Nifene in rat brain correlates very well with the known distribution of α 4 β 2 receptors, as defined by 125 I-iodoepibatidine [30, 34, 35] and confirmed in the studies with β 2-knockout mice (36). The goal of this study was to evaluate utility of 18 F-Nifene as an imaging probe in the early diagnosis of lung cancer.…”

“…Previous works have established that 18 F-Nifene is a highly specific radioligand of α 4 β 2 nAChR [30–32, 34–36]. Herein, we tested the hypothesis that 18 F-Nifene can visualize α 4-made nAChRs in the lung tumors of NNK-treated A/J mice, thus enabling early diagnosis of lung cancer.…”

Altered Neural Cholinergic Receptor Systems in Cocaine-Addicted Subjects

“…Third, our small sample of cocaine-addicted non-smokers and controls smokers did not suggest a nicotine-relevant effect (Figure 3). Finally, a recent study by Easwaramoorthy et al (2007) reveals that physostigmine infusion, in the absence of an additional infusion of ACh, does not alter a 4 b 2 nAChR binding. On the other hand, Carson et al (1998) found that the administration of physostigmine to nonhuman primates produced a 35% decrease in mAChR cortical binding.…”

Imaging of cerebral α4β2* nicotinic acetylcholine receptors with (−)-[18F]Flubatine PET: Implementation of bolus plus constant infusion and sensitivity to acetylcholine in human brain

“…This conclusion is based on a large body of literature reporting small changes in radioligand binding following physostig-mine administration with 5-[ 123 I]IA-85380 in rhesus monkeys (Fujita et al, 2003) and humans (Esterlis et al, 2013), 2-[ 18 F]FA-85380 in baboons (Valette et al, 2005), [ 18 F]nifene in rats (Hillmer et al, 2013), and importantly a dose-dependent effect with (−)-[ 18 F]flubatine in rhesus monkeys (Gallezot et al, 2014). Physostigmine does not directly compete with 5-[ 123 I]IA-85380 (Mukhin et al, 2000) or [ 18 F]nifene (Easwaramoorthy et al, 2007) in vitro, making it unlikely that physostigmine directly displaced (−)-[ 18 F]flubatine at the ${\alpha }_4{\beta }_2^{\ast }$ nAChR site. However, changes in receptor-radioligand affinity due to physostigmine or increased acetylcholine may confound interpretation of this measure.…”