David Wensbo

AZD2184: a radioligand for sensitive detection of β-amyloid deposits

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.

Recent Advances in Non-Competitive mGlu5 Receptor Antagonists and their Potential Therapeutic Applications

Extensive research into the functions of glutamate and glutamate receptors in the central nervous system (CNS) has shown an essential role of metabotropic glutamate (mGlu) receptors in normal brain functions, but also in neurological and psychiatric disorders. The precise functions of these receptors remain undefined, and progress toward understanding their functions has been hampered by the lack of selective ligands with appropriate pharmacokinetic properties. The Group I mGlu receptor, mGlu5, is well positioned to regulate and fine-tune neuronal excitability and synaptic transmission through its modulation of various signal transduction pathways and interactions with other transmitter systems. Therefore, the mGlu5 receptor may be an important therapeutic target for the treatment of disorders of the central nervous system. The discovery of MPEP 3, a non-competitive mGlu5 receptor antagonist, provided a potent, selective, systemically active tool compound for proof of concept studies in animal models of various disease states. These studies have led to greater understanding of possible therapeutic applications of mGlu5 receptor antagonists in recent years, suggesting their use in a number of disease states, including chronic pain, various psychiatric and neurological disorders, substance abuse and withdrawal, obesity and gastroesophageal reflux disease (GERD). Together, these findings have intensified efforts to find other non-competitive mGlu5 receptor antagonists and have led to the discovery of several second-generation compounds, a few of which are in preclinical evaluations. There have been several recent reviews on mGlu receptor. This article highlights recent efforts on the design, synthesis and development of novel, non-competitive mGlu5 receptor antagonists and studies to understand their in vitro mechanisms of action and in vivo pharmacological profiles. Emphasis is also given to recent advances in the potential therapeutic applications of non-competitive mGlu5 receptor antagonists.

On the relative strength of the 1H-tetrazol-5-yl- and the 2-(triphenylmethyl)-2H-tetrazol-5-yl-group in directed ortho-lithiation

ortho-Lithiation followed by electrophilic trapping of N-unsubstituted and N2-triphenylmethyl substituted 5-aryltetrazoles, further substituted with another ortho-director at the para position of the aryl ring, resulted in the formation of regioisomers of which the ratio depended on the competing para-substituents. By such intramolecular competition experiments, the ortho-directing strength of these tetrazol-5-yl groups in comparison to some commonly employed ortho-directors were found to be: OMe<1H-tetrazol-5-yl<CONEt2<2-(triphenylmethyl)-2H-tetrazol-5-yl<NHCOCMe3, OCONEt2.

Radiosynthesis of the candidate β‐amyloid radioligand [11C]AZD2184: Positron emission tomography examination and metabolite analysis in cynomolgus monkeys

β‐Amyloid accumulation is associated with the pathogenesis of Alzheimers disease (AD). AZD2184, a new radioligand for high‐contrast positron emission tomography (PET) imaging of Aβ‐deposits, has recently been developed and characterized in vitro and in rodents ex vivo. The objective of this study was to label AZD2184 with carbon‐11, to perform in vivo characterization of [11C]AZD2184 ([11C]5) in the cynomolgus monkey brain as well as whole‐body dosimetry, and to examine the metabolism of the labeled radioligand. [11C]5 was prepared by a two‐step radiosynthesis starting with the reaction of 5‐(6‐(tert‐butyldimethylsilyloxy)benzo[d]thiazol‐2‐yl)pyridin‐2‐amine with [11C]methyl iodide followed by deprotection using water. Four brain PET measurements in two cynomolgus monkeys and one whole‐body PET measurement were performed with [11C]5. There was a high and rapid brain uptake (2.2–3.4% of injected dose at 2 min). The distribution of brain radioactivity was fairly uniform, with early to late‐brain concentration ratios (peak vs. 60 min) higher for [11C]5 than ratios previously reported for [11C]PIB (8.2 and 4.6, respectively). Based on the whole‐body data, it was estimated that an effective dose in an adult male would be 6.2 μSv/MBq and thus would be safe from a radiation point of view for multiple scans within the same year. [11C]5 shows binding characteristics, suggesting low levels of white‐matter retention, and may thus provide improved contrast when compared with currently used PET radioligands for visualization of Aβ‐deposits. On the basis of the labeling chemistry and the results of the biological evaluation, we conclude that [11C]5 should be useful for routine clinical studies. Synapse 64:733–741, 2010.

Discovery and characterization of AZD9272 and AZD6538—Two novel mGluR5 negative allosteric modulators selected for clinical development

AZD9272 and AZD6538 are two novel mGluR5 negative allosteric modulators selected for further clinical development. An initial high-throughput screening revealed leads with promising profiles, which were further optimized by minor, yet indispensable, structural modifications to bring forth these drug candidates. Advantageously, both compounds may be synthesized in as little as one step. Both are highly potent and selective for the human as well as the rat mGluR5 where they interact at the same binding site than MPEP. They are orally available, allow for long interval administration due to a high metabolic stability and long half-lives in rats and permeate the blood brain barrier to a high extent. AZD9272 has progressed into phase I clinical studies.

Synthesis and evaluation of 2-pyridylbenzothiazole, 2-pyridylbenzoxazole and 2-pyridylbenzofuran derivatives as 11C-PET imaging agents for β-amyloid plaques

The syntheses and SAR of new series of beta-amyloid binding agents are reported. The effort to optimize signal-to-background ratios for these ligands are described. Compounds 8, 21 and 30 displayed desirable lipophilicity and pharmacokinetic properties. Compounds 8 and 21 were evaluated with in vitro autoradiographic studies and in vivo in APP/PS1 transgenic mice. It is shown that it was possible to increase the signal-to-background ratios compared to PIB 1, as demonstrated by compounds 8 and 21.

Palladium mediated 11C-cyanation and characterization in the non-human primate brain of the novel mGluR5 radioligand [11C]AZD9272

INTRODUCTION The aims of the present positron emission tomography (PET) study were to set up a system for (11)C-cyanation labeling of the selective mGluR5-antagonist [(11)C]AZD9272 and to perform the first in vivo characterization of [(11)C]AZD9272 binding in cynomolgus monkeys. METHODS [(11)C]AZD9272 was labeled using palladium mediated (11)C-cyanation. Altogether seven PET measurements were performed in three cynomolgus monkeys including baseline and co-injection experiments with unlabelled AZD9272 (0.04 and 0.4 mg/kg). Radiometabolites in plasma were measured using HPLC. RESULTS [(11)C]AZD9272 was prepared in over 50% incorporation yield from hydrogen [(11)C]cyanide in a total synthesis time of 45-50 min. The radiochemical purity of the radioligand in its final formulation was high (>99%) and the mean specific radioactivity was 47 GBq/ μmol (1278 Ci/mmol, n=7) calculated at end of bombardment (EOB). In the baseline measurements 10% of the total injected radioactivity was present in monkey brain at five minutes after i.v. injection. The radioactivity concentration was high in the caudate, cingulate gyrus and thalamus whereas it was moderate in the temporal cortex and lower for the cerebellum. After co-injection with cold AZD9272 the binding of [(11)C]AZD9272 was reduced in a dose-dependent fashion. Analysis of radiometabolites showed relatively slow metabolism and resulted only in hydrophilic radiometabolites. CONCLUSION A fast and efficient method was developed to label AZD9272 with (11)C. PET-examination in Cynomolgus monkeys showed that [(11)C]AZD9272 entered the brain to a high extent, that binding was saturable and that the regional radioactivity pattern was in accordance with the known distribution of mGluR5. The results support further examination of [(11)C]AZD9272 binding in human subjects.

Synthesis of novel tetrahydroisoquinoline bronchodilators

The synthesis and bronchorelaxing effects of a series of novel tetrahydroisoquinoline amides are described. The compounds were evaluated for their ability to relax LTD4 contracted isolated human small airways ex-vivo. Several compounds demonstrated highly efficacious bronchorelaxing properties. Cinnamide 71 was selected for further studies and constitutes a promising candidate as a novel bronchorelaxing agent for the treatment of pulmonary disorders.

The novel mGluR5 radioligand [11C]AZ11696415: Palladium mediated 11C-cyanation and initial in vivo characterization in the cynomolgus monkey brain using positron emission tomography (PET)

Introduction: The mGluR5 is believed to be an important therapeutic target for a number of CNS disorders including anxiety, schizophrenia, Parkinsons disease, addiction, epilepsy as well as various pain states. The therapeutic potential of a drug targeting mGluR5 has led to recent advances in the development of negative allosteric modulators. Most ligands that are being developed are diaryl alkynes, based on the structure of the prototypical mGluR5 antagonists MPEP and MTEP. The proposed mGluR5 ligand AZ11696415 belongs to a novel class of mGluR5 ligands which does not depend on the presence of an alkyne moiety. In vitro binding studies have shown that AZ11696415 binds with high affinity and selectivity to the same allosteric site as MPEP in the transmembrane region of mGluR5. Here we report the palladium mediated C-cyanation of [C]AZ11696415 (3-fluoro-5-(3-(5-fluoropyridin-2-yl)-1,2,4-oxadiazol-5-yl)benzo-[C]-nitrile) and a first in vivo characterization in cynomolgus monkeys using positron emission tomography.