Synthesis and evaluation of [11C]PyrATP-1, a novel radiotracer for PET imaging of glycogen synthase kinase-3β (GSK-3β)

Abstract

Introduction The dysfunction of glycogen synthase kinase-3β(GSK-3β) has been implicated in a number of diseases, including Alzheimer’s disease. The ability to non-invasively quantify GSK-3βactivity in vivo is therefore of critical importance, and this work is focused upon development of inhibitors of GSK-3βradiolabeled with carbon-11 to examine quantification of the enzyme using positron emission tomography (PET) imaging. Methods [11C]PyrATP-1 was prepared from the corresponding desmethyl-piperazine precursor in an automated synthesis module. In vivo rodent and primate imaging studies were conducted on a Concorde MicroPET P4 scanner to evaluate imaging properties, and in vitro autoradiography studies with rat brain samples were carried out to examine specific binding. Results 2035 ± 518 MBq (55 ± 14 mCi) of [11C]PyrATP-1 were obtained (1–2% noncorrected radiochemical yield at end-of-synthesis based upon [11C]CO2) with high chemical (>95%) and radiochemical (>99%) purities, and good specific activities (143 ± 52 GBq/µmol (3874 ± 1424 Ci/mmol)), n = 5. In vivo microPET imaging studies revealed poor brain uptake in rodents and non-human primates. Pretreatment of rodents with cyclosporin A resulted in moderately increased brain uptake suggesting Pgp transporter involvement. Autoradiography demonstrated high levels of specific binding in areas of the rodent brain known to be rich in GSK-3β. Conclusion [11C]PyrATP-1 is readily synthesized using standard carbon-11 radiochemistry. However, the poor brain uptake in rodents and non-human primates indicates that the radiotracer is not suitable for the purposes of quantifying GSK-3βin neurological and psychiatric disorders.

Radiosynthesis and in Vivo Evaluation of [11C]A1070722, a High Affinity GSK-3 PET Tracer in Primate Brain

“…26 The radiotracer also exhibited poor brain uptake in rodent and primate brain with moderate increase in uptake during pretreatment with cyclosporine. 26,27 [ 11 C]SB-216763 ( K i = 9 nM) penetrates the BBB in mice and baboon, but shows homogeneous distribution. 28–30 In vivo evaluation of a series of [ 11 C]labeled oxindole analogues (IC 50 = 66–35 nM) also was proven unsuccessful in normal and cold water stress (CWS)-induced tau hyperphosphorylation mice model.…”

Discovery of a Highly Selective Glycogen Synthase Kinase‐3 Inhibitor (PF‐04802367) That Modulates Tau Phosphorylation in the Brain: Translation for PET Neuroimaging

“…[ 11 C]SB-216763 showed good brain uptake in rodents and non-human primates (NHPs) but was not selective against other structurally similar kinases. [11] [ 11 C]PyrATP-1 [12] and 11 C-oxadiazole [13] -based radiotracers failed to show appreciable uptake in vivo.N one of the PET radiotracers for GSK-3 has yet proven to be successful for in vivo imaging studies with specificity and/or suitable brain uptake ( Figure 1). Thus an acute need for PET neuroimaging of GSK-3 remains, specifically for clinical research applications in AD and non-AD tauopathies.…”

Synthesis and preliminary characterization of radioiodinated benzofuran‐3‐yl‐(indol‐3‐yl)maleimide derivatives as potential SPECT imaging probes for the detection of glycogen synthase kinase‐3β (GSK‐3β) in the brain

“…As a result, [ 11 C]AR‐A014418 showed markedly low levels of radioactivity in all brain regions, indicating that this PET imaging probe cannot be used for the in vivo detection of GSK‐3β. Thereafter, Cole et al reported on the synthesis and evaluation of [ 11 C]PyrATP‐1, which is a 11 C‐labeled GSK‐3β inhibitor based on the pyrazine scaffold . Similarly to [ 11 C]AR‐A014418, the poor brain uptake of [ 11 C]PyrATP‐1 revealed that it may be inappropriate for the quantification of GSK‐3β.…”