Peter Johnström

Imaging Atherosclerotic Plaque Inflammation With [18F]-Fluorodeoxyglucose Positron Emission Tomography

Background—Atherosclerotic plaque rupture is usually a consequence of inflammatory cell activity within the plaque. Current imaging techniques provide anatomic data but no indication of plaque inflammation. The glucose analogue [18F]-fluorodeoxyglucose (18FDG) can be used to image inflammatory cell activity non-invasively by PET. In this study we tested whether 18FDG-PET imaging can identify inflammation within carotid artery atherosclerotic plaques. Methods and Results—Eight patients with symptomatic carotid atherosclerosis were imaged using 18FDG-PET and co-registered CT. Symptomatic carotid plaques were visible in 18FDG-PET images acquired 3 hours post-18FDG injection. The estimated net 18FDG accumulation rate (plaque/integral plasma) in symptomatic lesions was 27% higher than in contralateral asymptomatic lesions. There was no measurable 18FDG uptake into normal carotid arteries. Autoradiography of excised plaques confirmed accumulation of deoxyglucose in macrophage-rich areas of the plaque. Conclusions—This study demonstrates that atherosclerotic plaque inflammation can be imaged with 18FDG-PET, and that symptomatic, unstable plaques accumulate more 18FDG than asymptomatic lesions.

Clinical Validation of 18F-AZD4694, an Amyloid-β–Specific PET Radioligand

Pioneered with the invention of 11C-Pittsburgh compound B, amyloid-β imaging using PET has facilitated research in Alzheimer disease (AD). This imaging approach has promise for diagnostic purposes and evaluation of disease-modifying therapies. Broad clinical use requires an 18F-labeled amyloid-β radioligand with high specific and low nonspecific binding. The aim of the present PET study was to examine the radioligand 18F-AZD4694 in human subjects. Methods: Six control subjects and 10 clinically diagnosed AD patients underwent PET examination with 18F-AZD4694 and a structural MRI scan. Of these, 4 controls and 4 patients underwent a second PET examination for test–retest analysis. Arterial sampling was done to derive a metabolite-corrected plasma input function for traditional compartment modeling. Besides, several simplified quantitative approaches were applied, including the reference Logan approach and simple ratio methods. Results: After intravenous injection of 18F-AZD4694, radioactivity appeared rapidly in brain. In patients, radioactivity was high in regions expected to contain amyloid-β, whereas in controls, radioactivity was low and homogenously distributed. Binding in cerebellum, a reference region, was low and similar between the groups. Specific binding was reversible and peaked at about 27 min after injection in regions with high radioactivity. The time–activity curves could be described using the 2-tissue-compartment model. Distribution volume ratio estimates obtained using compartment models and simplified methods were highly correlated. Standardized uptake value ratios calculated at late times and distribution volume ratios estimated with the reference Logan approach were, in gray matter, significantly lower in control subjects (1.08 [11%] and 1.01 [6%], respectively) than in AD patients (2.15 [24%] and 1.62 [18%], respectively). Among noninvasive methods, the lowest test–retest variability was found with reference Logan, varying between 4% and 6% across brain regions. Conclusion: Noninvasive quantitative approaches provide valid estimates of amyloid-β binding. Because of the radioisotope (18F) used for labeling, the radioligand has potential for wide clinical application. 18F-AZD4694 satisfies the requirements for a promising amyloid-β radioligand both for diagnostic use and for evaluation of disease-modifying therapies in AD.

Preparation of 11C-labelled raclopride, a new potent dopamine receptor antagonist: Preliminary PET studies of cerebral dopamine receptors in the monkey

A new dopamine receptor antagonist, Raclopride (S-(-)-3,5-dichloro-N-[(1-ethyl-2-pyrrolidinyl)]methyl-2-hydroxy- 6-methoxybenzamide, FLA 870) (1), has been labelled using [11C]ethyl iodide for alkylation of the nitrogen of the pyrrolidine ring in the corresponding secondary amine (5). The synthesis of 5 and an efficient method for the preparation of [11C]ethyl iodide are described. The 11C-labelled FLA 870 (1) was purified by HPLC and then used in positron emission tomography to visualize the dopamine receptor-rich areas of the monkey brain. The images obtained show selective accumulation of FLA 870 in striatum and a 10-fold separation between the binding to caudate vs cerebellum.

Preclinical Comparison of Osimertinib with Other EGFR-TKIs in EGFR-Mutant NSCLC Brain Metastases Models, and Early Evidence of Clinical Brain Metastases Activity

Purpose: Approximately one-third of patients with non–small cell lung cancer (NSCLC) harboring tumors with EGFR-tyrosine kinase inhibitor (TKI)-sensitizing mutations (EGFRm) experience disease progression during treatment due to brain metastases. Despite anecdotal reports of EGFR-TKIs providing benefit in some patients with EGFRm NSCLC brain metastases, there is a clinical need for novel EGFR-TKIs with improved efficacy against brain lesions. Experimental Design: We performed preclinical assessments of brain penetration and activity of osimertinib (AZD9291), an oral, potent, irreversible EGFR-TKI selective for EGFRm and T790M resistance mutations, and other EGFR-TKIs in various animal models of EGFR-mutant NSCLC brain metastases. We also present case reports of previously treated patients with EGFRm-advanced NSCLC and brain metastases who received osimertinib in the phase I/II AURA study (NCT01802632). Results: Osimertinib demonstrated greater penetration of the mouse blood–brain barrier than gefitinib, rociletinib (CO-1686), or afatinib, and at clinically relevant doses induced sustained tumor regression in an EGFRm PC9 mouse brain metastases model; rociletinib did not achieve tumor regression. Under positron emission tomography micro-dosing conditions, [11C]osimertinib showed markedly greater exposure in the cynomolgus monkey brain than [11C]rociletinib and [11C]gefitinib. Early clinical evidence of osimertinib activity in previously treated patients with EGFRm-advanced NSCLC and brain metastases is also reported. Conclusions: Osimertinib may represent a clinically significant treatment option for patients with EGFRm NSCLC and brain metastases. Further investigation of osimertinib in this patient population is ongoing. Clin Cancer Res; 22(20); 5130–40. ©2016 AACR.

Characterization of AZD4694, a novel fluorinated Abeta plaque neuroimaging PET radioligand

J. Neurochem. (2010) 114, 784–794.

Pet Study of Methionine Accumulation in Glioma and Normal Brain Tissue: Competition with Branched Chain Amino Acids

Five patients with glioma were examined with positron emission tomography using ([11C]methyl)-L-methionine. The study was repeated while the patient was being infused with branched chain amino acids (BCAA), 250 μmol/min. The accumulation rates of methionine in tumor tissue and in normal brain tissue were compared without and with the infusion of amino acids. Both tumor tissue and normal brain tissue showed a reduction in the methionine accumulation by 35% while the patient received the infusion. In one patient with a severe blood-tissue barrier disruption the tumor accumulation rate was unaffected. It is concluded that in gliomas without severe blood-tissue barrier disruption, the accumulation of methionine is governed by processes exhibiting similar properties regarding competition with BCAA as in normal brain tissue.

D-Methionine and cisplatin ototoxicity in the guinea pig: D-methionine influences cisplatin pharmacokinetics

D-Methionine has recently been advocated as a protectant against cisplatin toxicity. The use of systemic D-methionine as a protector was studied in 58 guinea pigs. Kinetics and distribution of [11CH(3)]D-methionine was analysed by positron emission tomography. Cisplatin and the monohydrated complex of cisplatin was quantified in blood ultrafiltrate using reversed-phase liquid chromatography with post-column derivatisation. Administration of 300 mg/kg of D-methionine caused a 30% decrease in the area under the concentration-time curve (AUC) of cisplatin. The toxic effect of cisplatin was studied after dose adjustment of cisplatin, i.e. with similar cisplatin AUC in the group receiving D-methionine and the saline control group. A significant ototoxic effect, measured as difference in pre- and 96 h post-treatment electrophysiological hearing threshold (auditory brainstem response), was observed at stimulus frequencies of 30 and 20 kHz. There was no difference between the groups in the extent of threshold shift. Quantitative outer hair cell counts showed a similar loss of cells in the two groups. All animals had a significant increase in plasma-creatinine but there was no difference between the groups. The results indicate that protection from cisplatin ototoxicity by systemic D-methionine can be explained by a lowered systemic exposure to the drug.

Positron emission tomography using 18F-labelled endothelin-1 reveals prevention of binding to cardiac receptors owing to tissue-specific clearance by ETB receptors in vivo

1 Our aim was to synthesise an 18F analogue of endothelin‐1 (ET‐1), to dynamically image ET receptors in vivo by positron emission tomography (PET) and to elucidate the function of the ETB subtype as a clearing receptor in organs expressing high densities including kidney and lung. 2 [18F]‐ET‐1 was characterised in vitro and bound with a single subnanomolar affinity (KD=0.43±0.05 nM, Bmax=27.8±2.1 fmol mg−1 protein) to human left ventricle (n=4). 3 The in vivo distribution of [18F]‐ET‐1 in anaesthetised rats was measured using a dedicated small animal PET scanner (microPET) and ex vivo analysis. 4 Dynamic PET data demonstrated that high levels of radioligand accumulated rapidly in the lung, kidney and liver, consistent with receptor binding. The in vivo distribution correlated with the anatomical localisation of receptors detected in vitro using [125I]‐ET‐1. However, the receptor density visualised in the heart was unexpectedly low compared with that predicted from the in vitro measurements. 5 [18F]‐ET‐1 binding in lungs could not be displaced by the ETB selective antagonist BQ788, in agreement with the proposed internalisation of ET‐1 by ETB receptors. In contrast, infusion of BQ788 prior to injecting [18F]‐ET‐1 significantly reduce the amount of radioligand visualised in the ETB rich lung and kidney by 85% (P<0.05, n=3) and 55% (P<0.05, n=3), respectively. 6 Under conditions of ETB receptor blockade, the heart could be visualised by microPET imaging. 7 These results suggest that clearance by ETB receptors in the lung and kidney prevents binding of ET‐1 to receptors in the heart.

Effect of the myeloperoxidase inhibitor AZD3241 on microglia: a PET study in Parkinson’s disease

Impaired mitochondrial function, oxidative stress and formation of excessive levels of reactive oxygen species play a key role in neurodegeneration in Parkinsons disease. Myeloperoxidase is a reactive oxygen generating enzyme and is expressed by microglia. The novel compound AZD3241 is a selective and irreversible inhibitor of myeloperoxidase. The hypothesized mechanism of action of AZD3241 involves reduction of oxidative stress leading to reduction of sustained neuroinflammation. The purpose of this phase 2a randomized placebo controlled multicentre positron emission tomography study was to examine the effect of 8 weeks treatment with AZD3241 on microglia in patients with Parkinsons disease. Parkinson patients received either AZD3241 600 mg orally twice a day or placebo (in 3:1 ratio) for 8 weeks. The binding of (11)C-PBR28 to the microglia marker 18 kDa translocator protein, was examined using positron emission tomography at baseline, 4 weeks and 8 weeks. The outcome measure was the total distribution volume, estimated with the invasive Logan graphical analysis. The primary statistical analysis examined changes in total distribution volume after treatment with AZD3241 compared to baseline. Assessments of safety and tolerability of AZD3241 included records of adverse events, vital signs, electrocardiogram, and laboratory tests. The patients had a mean age of 62 (standard deviation = 6) years; 21 were male, three female and mean Unified Parkinsons Disease Rating Scale III score (motor examination) ranged between 6 and 29. In the AD3241 treatment group (n = 18) the total distribution volume of (11)C-PBR28 binding to translocator protein was significantly reduced compared to baseline both at 4 and 8 weeks (P < 0.05). The distribution volume reduction across nigrostriatal regions at 8 weeks ranged from 13-16%, with an effect size equal to 0.5-0.6. There was no overall change in total distribution volume in the placebo group (n = 6). AZD3241 was safe and well tolerated. The reduction of (11)C-PBR28 binding to translocator protein in the brain of patients with Parkinsons disease after treatment with AZD3241 supports the hypothesis that inhibition of myeloperoxidase has an effect on microglia. The results of the present study provide support for proof of mechanism of AZD3241 and warrant extended studies on the efficacy of AZD3241 in neurodegenerative disorders.

IN VIVO EVALUATION OF THE BIODISTRIBUTION OF 11C-LABELED PD153035 IN RATS WITHOUT AND WITH NEUROBLASTOMA IMPLANTS

The biodistribution of 11C-labeled 4-(3-bromoanilino)-6,7-dimethoxyquinazoline, an inhibitor of the epidermal growth factor (EGF) receptor tyrosine kinase, has been evaluated in vivo in rats using positron emission tomography (PET). Time-activity data obtained after i.v. administration in one rat revealed that the radiotracer rapidly cleared from plasma with subsequent uptake in major organs of the body (brain, heart, liver, gastrointestinal tract and bladder). Uptake in proliferating tissue in rats with human neuroblastoma xenografts indicate that [O-11C-methyl]PD153035 shows promise as a new agent for in vivo imaging of tumors with PET.