Non-steady-state measurement of in vivo receptor binding with positron emission tomography: "dose-response" analysis

Abstract

We previously developed a non-steady-state technique using positron emission tomography (PET) and the radioligand 18F-spiperone (18F-SP) for the measurement of in vivo radioligand-receptor binding in brain. The purpose of this investigation is to determine the sensitivity of this method to alterations in the apparent number of available specific binding sites. Nine studies were performed on the same baboon. The animal was pretreated with varying doses of unlabeled SP (15-600 micrograms) to compete for specific binding sites. The experimental procedure included measurement of regional cerebral blood flow, cerebral blood volume, and the protein binding of 18F-SP in arterial blood. At least 3.5 hr after pretreatment, no-carrier-added 18F-SP (containing less than 3 micrograms SP) was administered intravenously. Sequential PET scans and measurements of arterial-blood radioactivity due to radioligand and its labeled metabolites continued for 3 hr. A 3-compartment model representing the in vivo behavior of radioligand was used to analyze the data. As expected, we found that an index of binding called the combined forward rate constant (which equals the product of the apparent maximum number of available specific binding sites and the association rate constant of radioligand for receptor) declined with increasing dose of unlabeled SP. Other estimated variables including the dissociation rate constant did not change. This demonstrates that our non-steady-state method for estimating radioligand-receptor binding kinetics can detect a decrease in the apparent number of available specific binding sites. This is an important step in the validation of this in vivo receptor binding assay and its subsequent application.

Non-steady-state measurement of in vivo radioligand binding with positron emission tomography: specificity analysis and comparison with in vitro binding

“…An alternate approach is to determine the ability of the in vivo PET assay to detect predictable alterations in radioligand binding. In this regard, we previously have demonstrated the sensitivity of our non-steady-state method to a decrease in the apparent maximum number of available specific binding sites (Perlmutter et al, 1989). That study, however, did not demonstrate the specificity of the in vivo PET assay.…”

“…Radioligand. No-carrier-added l*F-SP was prepared as described previously (Perlmutter et al, 1989). Specific activities determined by HPLC ranged from 1000 to 5000 Ci/mmol at the time of injection.…”

“…The chemical purity of l*F-SP determined by HPLC showed, in the worst case, a total mass of less than 2 pg SP and less than 2 Mg nitro-SP. The nitro-SP has at least 1 OO-fold lower affinitv for SP bindina sites than SP (Poaun ," using a microfiltration technique (Perlmutter et al, 1989). These determinations were performed in duplicate or triplicate.…”

PET Measurement of Dopamine D2Receptor-Mediated Changes in Striatopallidal Function

“…Third, pharmacological activation of rCBF provides complementary information to other PET methods for studying dopaminergic pathways. This provides less specific information about receptor binding than radioligand studies (Perlmutter et al, , 1989(Perlmutter et al, , 1991bFarde et al, 1989;Sadzot et al, 1991), but may be more sensitive to changes in postsynaptic neurons that affect D 2 signal transduction (Breece et al, 1987). Another complementary technique is to study the pharmacological effects of dopaminergic agents on other neurotransmitter receptors (Dewey et al, 1990(Dewey et al, , 1993, a method that may provide more detail on dopaminergic output to neurons with cholinergic receptors, for example, but may miss effects on other circuits.…”

Failure of the three compartment model to describe the pharmacokinetics in brain of a high affinity substituted benzamide

“…Many investigators have performed multiple experiments to individually determine model parameters. Perlmutter et al (1989) used the standard model to estimate the free receptor concentration after a varying fraction of the receptors had been occupied by unlabelled ligand. He concludes that this approach is sensitive to the available number of receptors.…”