Measuring α4β2∗ Nicotinic Acetylcholine Receptor Density in Vivo with [18F]nifene PET in the Nonhuman Primate

Abstract

[18F]Nifene is an agonist PET radioligand developed to image α4β2∗ nicotinic acetylcholine receptors (nAChRs). This work aims to quantify the receptor density ( Bmax) of α4β2∗ nAChRs and the in vivo (apparent) dissociation constant ( KDapp) of [18F]nifene. Multiple-injection [18F]nifene experiments with varying cold nifene masses were conducted on four rhesus monkeys with a microPET P4 scanner. Compartment modeling techniques were used to estimate regional Bmax values and a global value of KDapp. The fast kinetic properties of [18F]nifene also permitted alternative estimates of Bmax and KDapp at transient equilibrium with the same experimental data using Scatchard-like methodologies. Averaged across subjects, the compartment modeling analysis yielded Bmax values of 4.8 ± 1.4, 4.3 ±1.0, 1.2 ± 0.4, and 1.2 ± 0.3 pmol/mL in the regions of antereoventral thalamus, lateral geniculate, frontal cortex, and subiculum, respectively. The KDapp of nifene was 2.4 ± 0.3 pmol/mL. The Scatchard analysis based on graphical evaluation of the data after transient equilibrium yielded Bmax estimations comparable to the modeling results with a positive bias of 28%. These findings show the utility of [18F]nifene for measuring α4β2∗ nAChR Bmax in vivo in the rhesus monkey with a single PET experiment.