The presence of β‐amyloid plaques in brain is a hallmark of Alzheimer’s disease (AD) and serves as a biomarker for confirmation of diagnosis postmortem. Positron emission tomography (PET) radioligands such as Pittsburgh compound B ([11C]‐2‐(3‐fluoro‐4‐methylamino‐phenyl)‐benzothiazol‐6‐ol) (PIB) binds selectively to β‐amyloid and are promising new tools supporting the clinical diagnoses of AD. In addition, such methodology may be useful for evaluation of new drugs aiming at reduction of amyloid plaque load. The objective of this study is to develop a new amyloid selective PET radioligand with higher signal‐to‐background ratio when compared with existing amyloid PET ligands. The lead compound, AZD2184, (2‐[6‐(methylamino)pyridin‐3‐yl]‐1,3‐benzothiazol‐6‐ol) was found to have high affinity for amyloid fibrils in vitro (Kd: 8.4 ± 1.0 nM). Two minutes after i.v. administration in rats, about 1% of the dose was in brain. In vitro autoradiography on cortical brain sections from amyloid‐beta precursor protein/presenilin 1 (APP/PS1) mice and AD patients showed that while [3H]AZD2184 and [3H]PIB are mutually displaceable, [3H]AZD2184 displays a higher signal‐to‐background ratio primarily by virtue of lower background binding levels. The ratio of binding ability in prefrontal cortex (high plaque load) to subcortical white matter (background) was 4.5 for [3H]AZD2184 and 0.8 for [3H]PIB at 1 nM. In adjacent cortical sections from APP/PS1 mouse as well as from AD cortical tissue, [3H]AZD2184 and antibodies to human β‐amyloid labeled identical structures. In vivo administration of [3H]AZD2184 to APP/PS1 mice further showed that [3H]AZD2184 labels amyloid deposits with low non‐specific background binding. Taken together, the pre‐clinical profile of AZD2184 in relation to the reference ligand PIB, suggests that 11C‐labeled AZD2184 is a potential radioligand for PET‐visualization of β‐amyloid deposits in the living human brain.

J. Neurochem. (2010) 114, 784–794. Abstract Positron emission tomography (PET) radioligands that bind selectively to β‐amyloid plaques (Aβ) are promising imaging tools aimed at supporting the diagnosis of Alzheimer’s disease and the evaluation of new drugs aiming to modify amyloid plaque load. For extended clinical use, there is a particular need for PET tracers labeled with fluorine‐18, a radionuclide with 110 min half‐life allowing for central synthesis followed by wide distribution. The development of fluorinated radioligands is, however, challenging because of the lipophilic nature of aromatic fluorine, rendering fluorinated ligands more prone to have high non‐specific white matter binding. We have here developed the new benzofuran‐derived radioligand containing fluorine, AZD4694 that shows high affinity for β‐amyloid fibrils in vitro (Kd = 2.3 ± 0.3 nM). In cortical sections from human Alzheimer’s disease brain [3H]AZD4694 selectively labeled β‐amyloid deposits in gray matter, whereas there was a lower level of non‐displaceable binding in plaque devoid white matter. Administration of unlabeled AZD4694 to rat showed that it has a pharmacokinetic profile consistent with good PET radioligands, i.e., it quickly entered and rapidly cleared from normal rat brain tissue. Ex vivo binding data in aged Tg2576 mice after intravenous administration of [3H]AZD4694 showed selective binding to β‐amyloid deposits in a reversible manner. In Tg2576 mice, plaque bound [3H]AZD4694 could still be detected 80 min after i.v. administration. Taken together, the preclinical profile of AZD4694 suggests that fluorine‐18 labeled AZD4694 may have potential for PET‐visualization of cerebral β‐amyloid deposits in the living human brain.

We compare three different approaches to scale clearance (CL) from human hepatocyte and microsome CL(int) (intrinsic CL) for 52 drug compounds. By using the well-stirred model with protein binding included only 11% and 30% of the compounds were predicted within 2-fold and the average absolute fold errors (AAFE) for the predictions were 5.9 and 4.1 for hepatocytes and microsomes, respectively. When predictions were performed without protein binding, 59% of the compounds were predicted within 2-fold using either hepatocytes or microsomes and the AAFE was 2.2 and 2.3, respectively. For hepatocytes and microsomes there were significant correlations (P = 8.7 x 10(-13), R(2) = 0.72; P = 2.8 x 10(-9), R(2) = 0.61) between predicted CL(int in vivo) (obtained from in vitro CL(int)) and measured CL(int in vivo) (obtained using the well-stirred model). When CL was calculated from the regression, 76% and 70% of the compounds were predicted within 2-fold and the AAFE was 1.6 and 1.8 for hepatocytes and microsomes, respectively. We demonstrate that microsomes and hepatocytes are in many cases comparable when scaling of CL is performed from regression. By using the hepatocyte regression, CL for 82% of the compounds in an independent test set (n = 11) were predicted within 2-fold (AAFE 1.4). We suggest that a regression line that adjusts for systematic under-predictions should be the first-hand choice for scaling of CL.

Glycogen synthase kinase-3β, also called tau phosphorylating kinase, is a proline-directed serine/threonine kinase which was originally identified due to its role in glycogen metabolism. Active forms of GSK3β localize to pretangle pathology including dystrophic neuritis and neurofibrillary tangles in Alzheimer's disease (AD) brain. By using a high throughput screening (HTS) approach to search for new chemical series and cocrystallization of key analogues to guide the optimization and synthesis of our pyrazine series, we have developed highly potent and selective inhibitors showing cellular efficacy and blood-brain barrier penetrance. The inhibitors are suitable for in vivo efficacy testing and may serve as a new treatment strategy for Alzheimer's disease.

Abnormal tau phosphorylation resulting in detachment of tau from microtubules and aggregation are critical events in neuronal dysfunction, degeneration, and neurofibrillary pathology seen in Alzheimer's disease. Glycogen synthase kinase3b (GSK3b) is a key target for drug discovery in the treatment of Alzheimer's disease and related tauopathies because of its potential to abnormally phosphorylate proteins and contribute to synaptic degeneration. We report the discovery of AZD1080, a potent and selective GSK3 inhibitor that demonstrates peripheral target engagement in Phase 1 clinical studies. AZD1080 inhibits tau phosphorylation in cells expressing human tau and in intact rat brain. Interestingly, subchronic but not acute administration with AZD1080 reverses MK-801-induced deficits, measured by long-term potentiation in hippocampal slices and in a cognitive test in mice, suggesting that reversal of synaptic plasticity deficits in dysfunctional systems requires longer term modifications of proteins downstream of GSK3b signaling. The inhibitory pattern on tau phosphorylation reveals a prolonged pharmacodynamic effect predicting less frequent dosing in humans. Consistent with the preclinical data, in multiple ascending dose studies in healthy volunteers, a prolonged suppression of glycogen synthase activity was observed in blood mononuclear cells providing evidence of peripheral target engagement with a selective GSK3 inhibitor in humans.