Magnus Schou

Synthesis and evaluation of pyridylbenzofuran, pyridylbenzothiazole and pyridylbenzoxazole derivatives as 18F-PET imaging agents for β-amyloid plaques

The synthesis and SAR of new β-amyloid binding agents are reported. Evaluation of important properties for achieving good signal-to-background ratio is described. Compounds 27, 33, and 36 displayed desirable lipophilic and pharmacokinetic properties. Compound 27 was further evaluated with autoradiographic studies in vitro on human brain tissue and in vivo in Tg2576 mice. Compound 27 showed an increased signal-to-background ratio compared to flutemetamol 4, indicating its suitability as PET ligand for β-amyloid deposits in AD patients. The preparation of the corresponding (18)F-labeled PET radioligand of compound 27 is presented.

Large Variation in Brain Exposure of Reference CNS Drugs: a PET Study in Nonhuman Primates

Background: Positron emission tomography microdosing of radiolabeled drugs allows for noninvasive studies of organ exposure in vivo. The aim of the present study was to examine and compare the brain exposure of 12 commercially available CNS drugs and one non-CNS drug. Methods: The drugs were radiolabeled with 11C (t 1/2 = 20.4 minutes) and examined using a high resolution research tomograph. In cynomolgus monkeys, each drug was examined twice. In rhesus monkeys, a first positron emission tomography microdosing measurement was repeated after preadministration with unlabeled drug to examine potential dose-dependent effects on brain exposure. Partition coefficients between brain and plasma (K P) were calculated by dividing the AUC0-90 min for brain with that for plasma or by a compartmental analysis (V T). Unbound K P (K P u,u) was obtained by correction for the free fraction in brain and plasma. Results: After intravenous injection, the maximum radioactivity concentration (C max, %ID) in brain ranged from 0.01% to 6.2%. For 10 of the 12 CNS drugs, C max, %ID was >2%, indicating a preferential distribution to brain. A lower C max, %ID was observed for morphine, sulpiride, and verapamil. K P ranged from 0.002 (sulpiride) to 68 (sertraline) and 7 of 13 drugs had K P u,u close to unity. For morphine, sulpiride, and verapamil, K P u,u was <0.3, indicating impaired diffusion and/or active efflux. Brain exposure at microdosing agreed with pharmacological dosing conditions for the investigated drugs. Conclusions: This study represents the largest positron emission tomography study on brain exposure of commercially available CNS drugs in nonhuman primates and may guide interpretation of positron emission tomography microdosing data for novel drug candidates.

Rapid metabolite analysis of positron emission tomography radioligands by direct plasma injection combining micellar cleanup with high submicellar liquid chromatography with radiometric detection

A column-switching liquid chromatographic (LC) system was developed for the radiometabolite analysis of positron emission tomography (PET) radioligands in plasma employing direct injection. This system involves (1) micellar cleanup using a short capture column with a micellar mobile phase for submitting plasma directly into the system, (2) fast-micellar liquid chromatography utilizing a small particle size (2.5 μm) analysis column under high submicellar condition for improving sensitivity, resolution and speed of analysis and (3) highly sensitive flow-through β(+) detection for online measurement of radioligands and their radiometabolites. This system enabled highly sensitive radiometric analysis at the lowest detection limit of about 1 Becquerel (Bq) for (11)C-labelled compounds with a high temporal resolution of <4.0 min without any pre-treatment of plasma. Finally, this novel method could be successfully applied to study the radiometabolism for various PET radioligands and provided reliable determination in both human and monkey plasma.

Rapid and sensitive measurement of PET radioligands in plasma by fast liquid chromatography/radiometric detection.

A fast and sensitive liquid chromatographic (fast-LC) method with radiometric detection was developed and validated to analyze positron emission tomography (PET) radioligands in plasma during PET studies. The plasma samples were deproteinized with acetonitrile and the extracts were injected into the fast-LC system coupled to an on-line radioactivity detector. Under the optimum conditions, complete separation of target PET radioligands from their radioactive metabolites was achieved within the short run time of only 3.5-min. The limits of detection were 1.0-1.2 Becquerel (Bq) for (11)C and (18)F-labeled compounds. This method can successfully be applied to study the metabolism of a wide variety of PET radioligands in human and monkey plasma with higher numbers of samples to be analyzed compared to the traditional LC method.

Quantification and wavelet-aided parametric imaging of cerebral amyloid using the HRRT PET-system and [18F]AZD4694

Introduction: In recent years in vivo PET-imaging of cerebral amyloid depositions in Alzheimers disease has become an important research tool with clinical implications. For quantification of regional amyloid density a common approach is to utilise simple integral PET images normalised to uptake in a reference region. Such images are only semi-quantitative and prone to imaging artefacts due to noise in particular when short acquisition times are used in clinical settings. To handle noise, parametric imaging approaches have been developed having potential to produce quantitative maps showing the distribution of specific binding in a detailed, anatomically unbiased way. [F]AZD4694 is a novel radioligand with high affinity and selectivity for amyloid deposits in preclinical studies in vitro and ex vivo. The study presented here was performed to characterise the kinetic behaviour and test–retest reliability of [F]AZD4694 in subjects with clinically established Alzheimers disease (AD) and cognitively normal, elderly control subjects (CS). Initially, traditional region of interest (ROI) based quantification methods were performed. Then, advanced voxel-based quantification was applied to gauge the feasibility of obtaining parametric images with [F]AZD4694 for possible future use in multivariate pattern analyses.

Abstract 2641: AZD4635 A2A receptor occupancy in cynomolgus monkey using PET and its application to an oncology clinical development program

Introduction AZD4635 is an A2A receptor antagonist currently being tested as monotherapy and in combination with durvalumab in patients with advanced solid cancers. High adenosine levels found in tumors are immune suppressive and therefore AZD4635 could potentiate immune checkpoint inhibitors such as durvalumab (anti-PDL1). Predictions of A2A receptor engagement in patients at different doses and at different time points may enable better interpretation of clinical biomarker data measuring effects on immune modulation. A quantitative assessment of the receptor occupancy in the brain of non-human primates was conducted for AZD4635 with PET imaging and the resulting PK/PD model was applied to predict occupancy in humans in tumors. Methods PET measurements of A2AR occupancy in brain was performed using the radioligand [18F]MNI-444 in three anesthetized cynomologus monkeys. PET data acquisition was performed for 120 min following IV-administration of [18F]MNI-444 at baseline and following pretreatment of AZD4635. Sampling for AZD4635 plasma exposure determination was performed. As part of PK/PD analysis of the occupancy data, a novel modification of the non Invasive-LOGAN data analysis of the PET data was performed to obtain a time course of occupancy for each dose. A bio-phase PK/PD mathematical model was then used to describe the relationship of occupancy with circulating concentrations of AZD4635. In parallel, a PK model for AZD4635 in humans was developed using data from cohort 1 (Clinical trial NCT02740985) after 125 mg and used for PK predictions for alternative doses of AZD4635 in the clinic. Results A clear Exposure-Effect relationship was observed for AZD4635-driven A2AR occupancy in cyno brain when dosed 30 min prior to PET measurement. The PK/PD analysis of cyno PET-determined receptor occupancy provided an Occ50 that is in line with the in vitro potency for the compound under physiological concentrations of adenosine in the brain. The resulting PK/PD model has then been applied to predict the level of occupancy in human tumours at other clinically relevant doses. Different simulations were done varying the amount of endogenous adenosine levels. Conclusions AZD4635 was shown to occupy A2AR in cyno brain in an exposure dependent manner. The resulting PK/PD model built using this dataset was used to run simulations of expected tumor receptor occupancy in man and aid clinical dose selection for AZD4635. Sensitivity analysis has shown that prediction of human occupancy in the tumour is highly dependent on adenosine concentrations in the tumour. Simulations with tumor adenosine concentrations of 1 μM indicate that AZD4635 is predicted to provide ~90% receptor occupancy over the whole dosing interval at a clinically relevant dose. Citation Format: Peter Johnstrom, Pablo Morentin Gutierrez, Katarina Varnas, Magnus Schou, Akihiro Takano, Lorraine Jones, Ganesh Mugundu, Patricia McCoon, Paul Lyne, Jeffrey Infante, Gerald Falchook, Manish Patel, Janet Karlix, Melinda Merchant, James Clarke, Alan Cross, Nicholas Seneca, Lars Farde, Miles Congreve, Jon S. Mason, Fiona H. Marshall. AZD4635 A2A receptor occupancy in cynomolgus monkey using PET and its application to an oncology clinical development program [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2641. doi:10.1158/1538-7445.AM2017-2641

[18F]AZD4694—A new PET radioligand for sensitive detection of β-amyloid deposits

PET radioligands that bind selectively to β-amyloid plaques (Ab) are imaging tools having potential to support the clinical diagnosis of Alzheimers disease (AD) and the evaluation of new drugs aiming to modify amyloid plaque load. For extended clinical use there is a particular need for radioligands labeled with fluorine-18, a radionuclide allowing for central synthesis followed by wide distribution. The development of fluorinated radioligands is however challenging due to the lipophilic nature of aromatic fluorine, rendering fluorinated ligands more prone to have high unspecific white matter binding. We have developed the new potential radioligand, AZD4694 with high affinity for β-amyloid fibrils in vitro (Kd 2.3±0.3 nM). Here we present the preclinial characterization in vitro and in vivo. In cortical sections from human AD brain [H]labeled AZD4694 bound selectively to β-amyloid deposits in gray matter with low level of non-specific binding to plaque devoid white matter. Ex vivo autoradiography in aged tg2576 mice showed that [H]AZD4694 selectively labelled β-amyloid plaques with low levels of nonspecific binding. Congo red labelling in adjacent sections from the same brain confirmed that [H]AZD4694 and Congo red labeled apparently identical structures. The suitability of [F]AZD4694 as a potential PET radioligand was examined further in young cynomolgus monkeys not expected to have amyloid deposits. [F]AZD4694 rapidly entered the monkey brain with a peak exposure of about 5% of the total injected radioactivity. Within 2 min after injection. Brain radioactivity cleared rapidly thereafter and was at a homogenous low level throughout the PETmeasurement. Taken together, the preclinical profile of AZD4694 suggests that fluorine-18 labelled AZD4694 have potential for selective PETvisualization of β-amyloid deposits in the living human brain.