Synthesis and preclinical evaluation of [11C]EAI045 as a PET tracer for imaging tumors expressing mutated epidermal growth factor receptor.

BACKGROUND: Mutations in the epidermal growth factor receptor (EGFR) kinase domain are common in non-small cell lung cancer. Conventional tyrosine kinase inhibitors target the mutation site in the ATP binding pocket, thereby inhibiting the receptor's function. However, subsequent treatment resistance mutations in the ATP binding site are common. The EGFR allosteric inhibitor, EAI045, is proposed to have an alternative mechanism of action, disrupting receptor signaling independent of the ATP-binding site. The antibody cetuximab is hypothesized to increase the number of accessible allosteric pockets for EAI045, thus increasing the potency of the inhibitor. This work aimed to gain further knowledge on pharmacokinetics, the EGFR mutation-targeting potential, and the influence of cetuximab on the uptake by radiolabeling EAI045 with carbon-11 and tritium. RESULTS: 2-(5-fluoro-2-hydroxyphenyl)-2-((2-iodobenzyl)amino)-N-(thiazol-2-yl)acetamide and 2-(5-fluoro-2-hydroxyphenyl)-N-(5-iodothiazol-2-yl)-2-(1-oxoisoindolin-2-yl)acetamide were synthesized as precursors for the carbon-11 and tritium labeling of EAI045, respectively. [11C]EAI045 was synthesized using [11C]CO in a palladium-catalyzed ring closure in a 10 ± 1% radiochemical yield (decay corrected to end of [11C]CO2 production), > 97% radiochemical purity and 26 ± 1 GBq/µmol molar activity (determined at end of synthesis) in 51 min. [3H]EAI045 was synthesized by a tritium-halogen exchange in a 0.2% radiochemical yield, 98% radiochemical purity, and 763 kBq/nmol molar activity. The ability of [11C]EAI045 to differentiate between L858R/T790M mutated EGFR expressing H1975 xenografts and wild-type EGFR expressing A549 xenografts was evaluated in female nu/nu mice. The uptake was statistically significantly higher in H1975 xenografts compared to A549 xenografts (0.45 ± 0.07%ID/g vs. 0.31 ± 0.10%ID/g, P = 0.0166). The synergy in inhibition between EAI045 and cetuximab was evaluated in vivo and in vitro. While there was some indication that cetuximab influenced the uptake of [3H]EAI045 in vitro, this could not be confirmed in vivo when tumor-bearing mice were administered cetuximab (0.5 mg), 24 h prior to injection of [11C]EAI045. CONCLUSIONS: EAI045 was successfully labeled with tritium and carbon-11, and the in vivo results indicated [11C]EAI045 may be able to distinguish between mutated and non-mutated EGFR in non-small cell lung cancer mouse models. Cetuximab was hypothesized to increase EAI045 uptake; however, no significant effect was observed on the uptake of [11C]EAI045 in vivo or [3H]EAI045 in vitro in H1975 xenografts and cells.

Development of 18F-Labeled PET Tracer Candidates for Imaging of the Abelson Non-receptor Tyrosine Kinase in Parkinson's Disease.

Activated Abelson non-receptor tyrosine kinase (c-Abl) plays a harmful role in neurodegenerative conditions such as Parkinson's disease (PD). Inhibition of c-Abl is reported to have a neuroprotective effect and be a promising therapeutic strategy for PD. We have previously identified a series of benzo[d]thiazole derivatives as selective c-Abl inhibitors from which one compound showed high therapeutic potential. Herein, we report the development of a complementary positron emission tomography (PET) tracer. In total, three PET tracer candidates were developed and eventually radiolabeled with fluorine-18 for in vivo evaluation studies in mice. Candidate [18F]3 was identified as the most promising compound, since it showed sufficient brain uptake, good washout kinetics, and satisfactory metabolic stability. In conclusion, we believe this tracer provides a good starting point to further validate and explore c-Abl as a target for therapeutic strategies against PD supported by PET.

Synthesis and Preclinical Evaluation of [Methylpiperazine-11C]brigatinib as a PET Tracer Targeting Both Mutated Epidermal Growth Factor Receptor and Anaplastic Lymphoma Kinase.

Brigatinib, a tyrosine kinase inhibitor (TKI) with specificity for gene rearranged anaplastic lymphoma kinase (ALK), such as the EML4-ALK, has shown a potential to inhibit mutated epidermal growth factor receptor (EGFR). In this study, N-desmethyl brigatinib was successfully synthesized as a precursor in five steps. Radiolabeling with [11C]methyl iodide produced [methylpiperazine-11C]brigatinib in a 10 ± 2% radiochemical yield, 91 ± 17 GBq/µmol molar activity, and ≥95% radiochemical purity in 49 ± 4 min. [Methylpiperazine-11C]brigatinib was evaluated in non-small cell lung cancer xenografted female nu/nu mice. An hour post-injection (p.i.), 87% of the total radioactivity in plasma originated from intact [methylpiperazine-11C]brigatinib. Significant differences in tumor uptake were observed between the endogenously EML4-ALK mutated H2228 and the control xenograft A549. The tumor-to-blood ratio in H2228 xenografts could be reduced by pretreatment with ALK inhibitor crizotinib. Tracer uptake in EGFR Del19 mutated HCC827 and EML4-ALK fusion A549 was not significantly different from uptake in A549 xenografts.

Synthesis and preclinical evaluation of two osimertinib isotopologues labeled with carbon-11 as PET tracers targeting the tyrosine kinase domain of the epidermal growth factor receptor.

INTRODUCTION: Osimertinib is a third-generation tyrosine kinase inhibitor (TKI) that is able to inhibit the EGFR treatment resistance mutation T790M and primary EGFR mutations Del19 and L858R. The aim of the study was to evaluate the potential of carbon-11 labeled osimertinib to be used as a tracer for the PET imaging of tumors bearing the T790M mutation. METHODS: Osimertinib was labeled with carbon-11 at two positions, and the effect of the labeling position on the metabolism and biodistribution was studied in female nu/nu mice. The mutation status specificity of osimertinib was confirmed in vitro in a cell growth inhibition experiment, and the tumor-targeting potential of the carbon-11 isotopologues was evaluated using female nu/nu mice xenografted with NSCLC cell lines; the wild-type EGFR expressing A549, the primary Del19 EGFR mutated HCC827 and the resistance T790M/L858R mutated H1975. One of the osimertinib tracers was selected based on the results acquired and evaluated for tracer specificity and selectivity by assessment of tumor uptake in a PET study where HCC827 tumor-bearing mice were pretreated with osimertinib or afatinib. RESULTS: [Methylindole-11C]- and [dimethylamine-11C]osimertinib were synthesized by 11C-methylation of precursors AZ5104 and AZ7550, respectively. Rapid metabolism of both analogs of [11C]osimertinib was observed. Although the tumor uptake and retention of [methylindole-11C]- and [dimethylamine-11C]osimertinib in tumors were similar, the tumor-to-muscle ratios appeared to be higher for [methylindole-11C]osimertinib. The highest uptake, tumor-to-blood, and tumor-to-muscle ratio were observed in the Del19 EGFR mutated HCC827 tumors. However, the specificity and selectivity of [methylindole-11C]osimertinib PET could not be demonstrated in HCC827 tumors. The uptake of [methylindole-11C]osimertinib was not significantly higher in T790M resistance mutated H1975 xenografts compared to the negative control cell line A549. CONCLUSIONS: Osimertinib was successfully labeled at two positions with carbon-11, yielding two EGFR PET tracers, [methylindole-11C]osimertinib and [dimethylamine-11C]osimertinib. The preclinical evaluation demonstrated uptake and retention in three NSCLC xenografts; A549, HCC827, and H1975. The highest uptake was observed in the primary Del19 EGFR mutated HCC827. The ability of [methylindole-11C]osimertinib to distinguish between the T790M resistance mutated H1975 xenografts and the wild-type EGFR expressing A549 could not be confirmed in the ex vivo study.

Imaging the TGFß type I receptor in pulmonary arterial hypertension.

Transforming growth factor ß (TGFß) activity is perturbed in remodelled pulmonary vasculature of patients with pulmonary arterial hypertension (PAH), cancer, vascular diseases and developmental disorders. Inhibition of TGFß, which signals via activin receptor-like kinase 5 (ALK5), prevents progression and development of experimental PAH. The purpose of this study was to assess two ALK5 targeting positron emission tomography (PET) tracers ([11C]LR111 and [18F]EW-7197) for imaging ALK5 in monocrotaline (MCT)- and Sugen/hypoxia (SuHx)-induced PAH. Both tracers were subjected to extensive in vitro and in vivo studies. [11C]LR111 showed the highest metabolic stability, as 46 ± 2% of intact tracer was still present in rat blood plasma after 60 min. In autoradiography experiments, [11C]LR111 showed high ALK5 binding in vitro compared with controls, 3.2 and 1.5 times higher in SuHx and MCT, respectively. In addition, its binding could be blocked by SB431542, an adenosine triphosphate competitive ALK5 kinase inhibitor. However, [18F]EW-7197 showed the best in vivo results. 15 min after injection, uptake was 2.5 and 1.4 times higher in the SuHx and MCT lungs, compared with controls. Therefore, [18F]EW-7197 is a promising PET tracer for ALK5 imaging in PAH.

Validation of simplified uptake measures against dynamic Patlak Ki for quantification of lesional 89Zr-Immuno-PET antibody uptake.

PURPOSE: Positron emission tomography imaging of zirconium-89-labelled monoclonal antibodies (89Zr-Immuno-PET) allows for visualisation and quantification of antibody uptake in tumours in vivo. Patlak linearization provides distribution volume (VT) and nett influx rate (Ki) values, representing reversible and irreversible uptake, respectively. Standardised uptake value (SUV) and tumour-to-plasma/tumour-to-blood ratio (TPR/TBR) are often used, but their validity depends on the comparability of plasma kinetics and clearances. This study assesses the validity of SUV, TPR and TBR against Patlak Ki for quantifying irreversible 89Zr-Immuno-PET uptake in tumours. METHODS: Ten patients received 37 MBq 10 mg 89Zr-anti-EGFR with 500 mg/m2 unlabelled mAbs. Five patients received two doses of 37 MBq 89Zr-anti-HER3: 8-24 mg for the first administration and 24 mg-30 mg/kg for the second. Seven tumours from four patients showed 89Zr-anti-EGFR uptake, and 18 tumours from five patients showed 89Zr-anti-HER3 uptake. SUVpeak, TPRpeak and TBRpeak values were obtained from one to six days p.i. Patlak linearization was applied to tumour time activity curves and plasma samples to obtain Ki. RESULTS: For 89Zr-anti-EGFR, there was a small variability along the linear regression line between SUV (- 0.51-0.57), TPR (- 0.06‒0.11) and TBR (- 0.13‒0.16) on day 6 versus Ki. Similar doses of 89Zr-anti-HER3 showed similar variability for SUV (- 1.3‒1.0), TPR (- 1.1‒0.53) and TBR (- 1.5‒0.72) on day 5 versus Ki. However, for the second administration of 89Zr-anti-HER3 with a large variability in administered mass doses, SUV showed a larger variability (- 1.4‒2.3) along the regression line with Ki, which improved when using TPR (- 0.38-0.32) or TBR (- 0.56‒0.46). CONCLUSION: SUV, TPR and TBR at late time points were valid for quantifying irreversible lesional 89Zr-Immuno-PET uptake when constant mass doses were administered. However, for variable mass doses, only TPR and TBR provided reliable values for irreversible uptake, but not SUV, because SUV does not take patient and mass dose-specific plasma clearance into account.

[18F]FDG and [18F]FES PET/CT Imaging as a Biomarker for Therapy Effect in Patients with Metastatic ER+ Breast Cancer Undergoing Treatment with Rintodestrant.

PURPOSE: PET with 16α-[18F]-fluoro-17ß-estradiol ([18F]FES) allows assessment of whole body estrogen receptor (ER) expression. The aim of this study was to investigate [18F]-fluorodeoxyglucose ([18F]FDG) and [18F]FES PET/CT imaging for response prediction and monitoring of drug activity in patients with metastatic ER-positive breast cancer undergoing treatment with the selective estrogen receptor downregulator (SERD) rintodestrant. EXPERIMENTAL DESIGN: In this trial (NCT03455270), PET/CT imaging was performed at baseline ([18F]FDG and [18F]FES), during treatment and at time of progression (only [18F]FES). Visual, quantitative, and mutational analysis was performed to derive a heterogeneity score (HS) and assess tracer uptake in lesions, in relation to the mutation profile. The primary outcome was progression-free survival (PFS). RESULTS: The HS and PFS in the entire group did not correlate (n = 16, Spearman's rho, P = 0.06), but patients with a low HS (< 25.0%, n = 4) had a PFS of > 5 months whereas patients with no [18F]FES uptake (HS 100.0%, n = 3) had a PFS of < 2 months. [18F]FES uptake was not affected by estrogen receptor 1 (ESR1) mutations. On-treatment [18F]FES PET/CT scans showed no [18F]FES uptake in any of the baseline [18F]FES-positive lesions. At progression, [18F]FES uptake remained blocked in patients scanned ≤ 1-2 half-lives of rintodestrant whereas it restored in patients scanned ≥ 5 days after end of treatment. CONCLUSIONS: Absence of ER expression on [18F]FES PET is a predictor for no response to rintodestrant. [18F]FES uptake during treatment and at time of progression is useful to monitor the (reversible) effect of therapy and continued mode of action of SERDs. See related commentary by Linden and Mankoff, p. 2015.

Synthesis and preclinical evaluation of [11C]LR111 and [18F]EW-7197 as PET tracers of the activin-receptor like kinase-5.

The transforming growth factor ß (TGFß) pathway plays a complex role in cancer biology, being involved in both tumour suppression as well as promotion. Overactive TGFß signalling has been linked to multiple diseases, including cancer, pulmonary arterial hypertension, and fibrosis. One of the key meditators within this pathway is the TGFß type I receptor, also termed activin receptor-like kinase 5 (ALK5). ALK5 expression level is a key determinant of TGFß signalling intensity and duration, and perturbation has been linked to diseases. A validated ALK5 positron emission tomography (PET) tracer creates an opportunity, therefore, to study its role in human diseases. To develop ALK5 PET tracers, two small molecule ALK5 kinase inhibitors were selected as lead compounds, which were labelled with carbon-11 and fluorine-18, respectively. [11C]LR111 was synthesized with a yield of 17 ± 6%, a molar activity of 126 ± 79 GBq·µmol-1 and a purity of >95% (n = 44). [18F]EW-7197 was synthesized with a yield of 10 ± 5%, a molar activity of 183 ± 126 GBq·µmol-1 and a purity of >95% (n = 11). Metabolic stability was evaluated in vivo in mice, showing 39 ± 2% of intact [11C]LR111 and 21 ± 2% of intact [18F]EW-7197 in blood plasma at 45 min p.i. In vitro binding experiments were conducted in breast cancer MDA-MB-231 and lung cancer A431 cell lines. In addition, both tracers were used for PET imaging in MDA-MB-231 xenograft models. Selective uptake of [18F]EW-7197 and [11C]LR111 was observed in MDA-MB-231 cells, in the MDA-MB-231 tumour xenografts in vivo and in the autoradiograms. As [11C]LR111 and [18F]EW-7197 showed selectivity of binding to ALK5 in vivo and in vitro. Both tracers are thereby valuable tools for the detection of ALK5 activity.

Relationship between Biodistribution and Tracer Kinetics of 11C-Erlotinib, 18F-Afatinib and 11C-Osimertinib and Image Quality Evaluation Using Pharmacokinetic/Pharmacodynamic Analysis in Advanced Stage Non-Small Cell Lung Cancer Patients.

BACKGROUND: Patients with non-small cell lung cancer (NSCLC) driven by activating epidermal growth factor receptor (EGFR) mutations are best treated with therapies targeting EGFR, i.e., tyrosine kinase inhibitors (TKI). Radiolabeled EGFR-TKI and PET have been investigated to study EGFR-TKI kinetics and its potential role as biomarker of response in NSCLC patients with EGFR mutations (EGFRm). In this study we aimed to compare the biodistribution and kinetics of three different EGFR-TKI, i.e., 11C-erlotinib, 18F-afatinib and 11C-osimertinib. METHODS: Data of three prospective studies and 1 ongoing study were re-analysed; data from thirteen patients (EGFRm) were included for 11C-erlotinib, seven patients for 18F-afatinib (EGFRm and EGFR wild type) and four patients for 11C-osimertinib (EGFRm). From dynamic and static scans, SUV and tumor-to-blood (TBR) values were derived for tumor, lung, spleen, liver, vertebra and, if possible, brain tissue. AUC values were calculated using dynamic time-activity-curves. Parent fraction, plasma-to-blood ratio and SUV values were derived from arterial blood data. Tumor-to-lung contrast was calculated, as well as (background) noise to assess image quality. RESULTS: 11C-osimertinib showed the highest SUV and TBR (AUC) values in nearly all tissues. Spleen uptake was notably high for 11C-osimertinib and to a lesser extent for 18F-afatinib. For EGFRm, 11C-erlotinib and 18F-afatinib demonstrated the highest tumor-to-lung contrast, compared to an inverse contrast observed for 11C-osimertinib. Tumor-to-lung contrast and spleen uptake of the three TKI ranked accordingly to the expected lysosomal sequestration. CONCLUSION: Comparison of biodistribution and tracer kinetics showed that 11C-erlotinib and 18F-afatinib demonstrated the highest tumor-to-background contrast in EGFRm positive tumors. Image quality, based on contrast and noise analysis, was superior for 11C-erlotinib and 18F-afatinib (EGFRm) scans compared to 11C-osimertinib and 18F-afatinib (EGFR wild type) scans.

Validation and test-retest repeatability performance of parametric methods for [11C]UCB-J PET.

[11C]UCB-J is a PET radioligand that binds to the presynaptic vesicle glycoprotein 2A. Therefore, [11C]UCB-J PET may serve as an in vivo marker of synaptic integrity. The main objective of this study was to evaluate the quantitative accuracy and the 28-day test-retest repeatability (TRT) of various parametric quantitative methods for dynamic [11C]UCB-J studies in Alzheimer's disease (AD) patients and healthy controls (HC). Eight HCs and seven AD patients underwent two 60-min dynamic [11C]UCB-J PET scans with arterial sampling over a 28-day interval. Several plasma-input based and reference-region based parametric methods were used to generate parametric images using metabolite corrected plasma activity as input function or white matter semi-ovale as reference region. Different parametric outcomes were compared regionally with corresponding non-linear regression (NLR) estimates. Furthermore, the 28-day TRT was assessed for all parametric methods. Spectral analysis (SA) and Logan graphical analysis showed high correlations with NLR estimates. Receptor parametric mapping (RPM) and simplified reference tissue model 2 (SRTM2) BPND, and reference Logan (RLogan) distribution volume ratio (DVR) regional estimates correlated well with plasma-input derived DVR and SRTM BPND. Among the multilinear reference tissue model (MRTM) methods, MRTM1 had the best correspondence with DVR and SRTM BPND. Among the parametric methods evaluated, spectral analysis (SA) and SRTM2 were the best plasma-input and reference tissue methods, respectively, to obtain quantitatively accurate and repeatable parametric images for dynamic [11C]UCB-J PET.

Biodistribution of 18F-FES in Patients with Metastatic ER+ Breast Cancer Undergoing Treatment with Rintodestrant (G1T48), a Novel Selective ER Degrader.

16α-18F-fluoro-17ß-estradiol (18F-FES) is a PET tracer characterizing the expression of the estrogen receptor (ER). Because therapy can interfere with the kinetics and biodistribution of 18F-FES, the aim of this study was to describe the biodistribution of 18F-FES in patients with metastatic ER-positive (ER+) breast cancer undergoing treatment with rintodestrant (G1T48), a novel selective ER degrader. Methods: Eight patients underwent 18F-FES PET/CT imaging at baseline, 4-6 wk during treatment with rintodestrant (interim), and after treatment. After intravenous administration of 200 MBq (±10%) of 18F-FES, a 50-min dynamic PET/CT scan of the thorax was obtained, followed by a whole-body PET/CT scan 60 min after injection. Blood samples were drawn for measuring whole blood and plasma activity concentration and the parent fraction of 18F-FES. Volumes of interest were placed in the aorta ascendens and in healthy tissues on both dynamic and whole-body PET scans. SUVs and target-to-blood ratios (TBRs) were calculated. Areas under the curve (AUCs) of input functions and time-activity curves were calculated as a measure of uptake in different regions. Results:18F-FES concentration in whole blood (and plasma) significantly (P < 0.05) increased at interim with median AUCs of 96.6, 116.6, and 110.3 at baseline, interim, and after treatment, respectively. In ER-expressing tissues, that is, the uterus and the pituitary gland, both SUV and TBR showed high 18F-FES uptake at baseline, followed by a decrease in uptake at interim (uterus: SUV -50.6% and TBR -58.5%; pituitary gland: SUV -39.0% and TBR -48.3%), which tended to return to baseline values after treatment (uterus: SUV -21.5% and TBR -37.9%; pituitary gland: SUV -14.2% and TBR -26.0%, compared with baseline). In other healthy tissues, tracer uptake remained stable over the 3 time points. Conclusion: The biodistribution of 18F-FES is altered in blood and in ER-expressing healthy tissues during therapy with rintodestrant. This indicates that rintodestrant alters the kinetics of the tracer, possibly affecting interpretation and quantification of 18F-FES uptake. Of note, 6 d or more after treatment with rintodestrant ended, the biodistribution returned to baseline values, consistent with recovery of ER availability after washout of the drug.

Synthesis and evaluation of [18F]cinacalcet for the imaging of parathyroid hyperplasia.

INTRODUCTION: Parathyroid hyperplasia is a disease characterized by overactive parathyroid glands secreting increased levels of parathyroid hormone. Surgical removal of the parathyroid glands is the standard treatment but requires precise pre-operative localization of the glands. However, currently available imaging modalities show limited sensitivity. Since positron emission tomography (PET) is a molecular imaging technique with high accuracy and sensitivity, our aim was to develop a new PET tracer for overactive parathyroid glands imaging by radiolabelling cinacalcet, a drug binding to the calcium-sensing receptor of the parathyroid glands. METHODS: [18F]Cinacalcet was synthesized by copper-catalysed [18F]trifluoromethylation of a boronic acid precursor using high molar activity [18F]fluoroform. Ex vivo biodistribution and metabolism were evaluated in 12 healthy male Wistar rats at 5, 15, 45 and 90 min. PET scans were performed at baseline and after blocking with NPS R-568. RESULTS: [18F]Cinacalcet was obtained in an overall radiosynthesis time of 1 h with a radiochemical purity of 98 ± 1%, a radiochemical yield of 8 ± 4% (overall, n = 7, corrected for decay) and a molar activity of 40 ± 11 GBq/µmol (n = 7, at EOS). The ex vivo biodistribution showed uptake in the thyroid and parathyroid glands as well as in other glands such as adrenals, salivary glands and pancreas. The tracer was rapidly cleared from the blood via liver and kidneys and showed fast metabolism. PET images confirmed uptake in the target organ. However, in a blocking study with NPS R-568 specific binding of [18F]cinacalcet to the CaSR could not be confirmed. CONCLUSIONS: [18F]Cinacalcet was successfully synthesized. First in vivo experiments in healthy rats showed uptake of the tracer in the target organ and fast metabolism, encouraging further in vivo evaluation of this tracer.

Novel Thienopyrimidine-Based PET Tracers for P2Y12 Receptor Imaging in the Brain.

The P2Y12 receptor (P2Y12R) is uniquely expressed on microglia in the brain, and its expression level directly depends on the microglial activation state. Therefore, P2Y12R provides a promising imaging marker for distinguishing the pro- and anti-inflammatory microglial phenotypes, both of which play crucial roles in neuroinflammatory diseases. In this study, three P2Y12R antagonists were selected from the literature, radiolabeled with carbon-11 or fluorine-18, and evaluated in healthy Wistar rats. Brain imaging was performed with and without blocking of efflux transporters P-glycoprotein and breast cancer resistance protein using tariquidar. Low brain uptake in healthy rats was observed for all tracers at baseline conditions, whereas blocking of efflux transporters resulted in a strong (6-7 fold) increase in brain uptake for both of them. Binding of the most promising tracer, [18F]3, was further evaluated by in vitro autoradiography on rat brain sections, ex vivo metabolite studies, and in vivo P2Y12R blocking studies. In vitro binding of [18F]3 on rat brain sections indicated high P2Y12R targeting with approximately 70% selective and specific binding. At 60 min post-injection, over 95% of radioactivity in the brain accounted for an intact tracer. In blood plasma, still 40% intact tracer was found, and formed metabolites did not enter the brain. A moderate P2Y12R blocking effect was observed in vivo by positron emission tomography (PET) imaging with [18F]3 (p = 0.04). To conclude, three potential P2Y12R PET tracers were obtained and analyzed for P2Y12R targeting in the brain. Unfortunately, the brain uptake appeared low. Future work will focus on the design of P2Y12R inhibitors with improved physicochemical characteristics to reduce efflux transport and increase brain penetration.

Kinetics and 28-day test-retest repeatability and reproducibility of [11C]UCB-J PET brain imaging.

[11C]UCB-J is a novel radioligand that binds to synaptic vesicle glycoprotein 2A (SV2A). The main objective of this study was to determine the 28-day test-retest repeatability (TRT) of quantitative [11C]UCB-J brain positron emission tomography (PET) imaging in Alzheimer's disease (AD) patients and healthy controls (HCs). Nine HCs and eight AD patients underwent two 60 min dynamic [11C]UCB-J PET scans with arterial sampling with an interval of 28 days. The optimal tracer kinetic model was assessed using the Akaike criteria (AIC). Micro-/macro-parameters such as tracer delivery (K1) and volume of distribution (VT) were estimated using the optimal model. Data were also analysed for simplified reference tissue model (SRTM) with centrum semi-ovale (white matter) as reference region. Based on AIC, both 1T2k_VB and 2T4k_VB described the [11C]UCB-J kinetics equally well. Analysis showed that whole-brain grey matter TRT for VT, DVR and SRTM BPND were -2.2% ± 8.5, 0.4% ± 12.0 and -8.0% ± 10.2, averaged over all subjects. [11C]UCB-J kinetics can be well described by a 1T2k_VB model, and a 60 min scan duration was sufficient to obtain reliable estimates for both plasma input and reference tissue models. TRT for VT, DVR and BPND was <15% (1SD) averaged over all subjects and indicates adequate quantitative repeatability of [11C]UCB-J PET.

Identifying advanced stage NSCLC patients who benefit from afatinib therapy using 18F-afatinib PET/CT imaging.

OBJECTIVES: Non-small cell lung cancer (NSCLC) tumors harboring common (exon19del, L858R) and uncommon (e.g. G719X, L861Q) activating epidermal growth factor receptor (EGFR) mutations are best treated with EGFR tyrosine kinase inhibitors (TKI) such as the first-generation EGFR TKI erlotinib, second-generation afatinib or third-generation osimertinib. However, identifying these patients through biopsy is not always possible. Therefore, our aim was to evaluate whether 18F-afatinib PET/CT could identify patients with common and uncommon EGFR mutations. Furthermore, we evaluated the relation between tumor 18F-afatinib uptake and response to afatinib therapy. MATERIALS AND METHODS: 18F-afatinib PET/CT was performed in 12 patients: 6 EGFR wild type (WT), 3 EGFR common and 3 EGFR uncommon mutations. Tumor uptake of 18F-afatinib was quantified using TBR_WB60-90 (tumor-to-whole blood activity ratio 60-90 min post-injection) for each tumor. Response was quantified per lesion using percentage of change (PC): [(response measurement (RM)-baseline measurement (BM))/BM]×100. Statistical analyses were performed using t-tests, correlation plots and sensitivity/specificity analysis. RESULTS: Twenty-one tumors were identified. Injected dose was 348 ± 31 MBq. Group differences were significant between WT versus EGFR (common and uncommon) activating mutations (p = 0.03). There was no significant difference between EGFR common versus uncommon mutations (p = 0.94). A TBR_WB60-90 cut-off value of 6 showed the best relationship with response with a sensitivity of 70 %, a specificity of 100 % and a positive predictive value of 100 %. CONCLUSION: 18F-afatinib uptake was higher in tumors with EGFR mutations (common and uncommon) compared to WT. Furthermore, a TBR_WB60-90 cut-off of 6 was found to best predict response to therapy. 18F-afatinib PET/CT could provide a means to identify EGFR mutation positive patients who benefit from afatinib therapy.

Open-label study with the monoamine stabilizer (-)-OSU6162 in myalgic encephalomyelitis/chronic fatigue syndrome.

OBJECTIVES: The purpose of the present study was to investigate the safety and tolerability of the monoaminergic stabilizer (-)-OSU6162 in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). In addition, a potential therapeutic effect of (-)-OSU6162 in ME/CFS was evaluated by means of observer-rated scales and self-assessment rating scales. MATERIALS AND METHODS: In the current study using an open-label single-arm design ME/CFS patient received treatment with (-)-OSU6162 during 12 weeks. The patients received the following doses of (-)-OSU6162: 15 mg b.i.d. during the first 4-week period, up to 30 mg b.i.d. during the second 4-week period and up to 45 mg b.i.d. during the third 4-week period, with follow-up visits after 16 and 20 weeks. RESULTS: Out of 33 included patients, 28 completed the 12 weeks treatment period. (-)-OSU6162 was well tolerated; only one patient discontinued due to an adverse event. Vital signs and physical examinations showed no abnormal changes. Blood analyses showed an increase in serum prolactin. Therapeutically, improvements were seen on the Clinical Global Impression of Change scale, the FibroFatigue scale, the Mental Fatigue Scale, the Fatigue Severity Scale, Beck Depression Inventory, and the Short Form 36 Health Survey Questionnaire. CONCLUSIONS: (-)-OSU6162 is well tolerated in ME/CFS patients and shows promise as a novel treatment to mitigate fatigue and improve mood and health-related quality of life in ME/CFS. Obviously, the present results need to be confirmed in future placebo-controlled double-blind trials.

In vivo tau pathology is associated with synaptic loss and altered synaptic function.

BACKGROUND: The mechanism of synaptic loss in Alzheimer's disease is poorly understood and may be associated with tau pathology. In this combined positron emission tomography (PET) and magnetoencephalography (MEG) study, we aimed to investigate spatial associations between regional tau pathology ([18F]flortaucipir PET), synaptic density (synaptic vesicle 2A [11C]UCB-J PET) and synaptic function (MEG) in Alzheimer's disease. METHODS: Seven amyloid-positive Alzheimer's disease subjects from the Amsterdam Dementia Cohort underwent dynamic 130-min [18F]flortaucipir PET, dynamic 60-min [11C]UCB-J PET with arterial sampling and 2 × 5-min resting-state MEG measurement. [18F]flortaucipir- and [11C]UCB-J-specific binding (binding potential, BPND) and MEG spectral measures (relative delta, theta and alpha power; broadband power; and peak frequency) were assessed in cortical brain regions of interest. Associations between regional [18F]flortaucipir BPND, [11C]UCB-J BPND and MEG spectral measures were assessed using Spearman correlations and generalized estimating equation models. RESULTS: Across subjects, higher regional [18F]flortaucipir uptake was associated with lower [11C]UCB-J uptake. Within subjects, the association between [11C]UCB-J and [18F]flortaucipir depended on within-subject neocortical tau load; negative associations were observed when neocortical tau load was high, gradually changing into opposite patterns with decreasing neocortical tau burden. Both higher [18F]flortaucipir and lower [11C]UCB-J uptake were associated with altered synaptic function, indicative of slowing of oscillatory activity, most pronounced in the occipital lobe. CONCLUSIONS: These results indicate that in Alzheimer's disease, tau pathology is closely associated with reduced synaptic density and synaptic dysfunction.

Non-invasive Standardised Uptake Value for Verification of the Use of Previously Validated Reference Region for [18F]Flortaucipir and [18F]Florbetapir Brain PET Studies.

PURPOSE: The simplified reference tissue model (SRTM) is commonly applied for the quantification of brain positron emission tomography (PET) studies, particularly because it avoids arterial cannulation. SRTM requires a validated reference region which is obtained by baseline-blocking or displacement studies. Once a reference region is validated, the use should be verified for each new subject. This verification normally requires volume of distribution (VT) of a reference region. However, performing dynamic scanning and arterial sampling is not always possible, specifically in elderly subjects and in advanced disease stages. The aim of this study was to investigate the use of non-invasive standardised uptake value (SUV) approaches, in comparison to VT, as a verification of the previously validated grey matter cerebellum reference region for [18F]flortaucipir and [18F]florbetapir PET imaging in Alzheimer's disease (AD) patients and controls. PROCEDURES: Dynamic 130-min [18F]flortaucipir PET scans obtained from nineteen subjects (10 AD patients) and 90-min [18F]florbetapir dynamic scans obtained from fourteen subjects (8 AD patients) were included. Regional VT's were estimated for both tracers and were considered the standard verification of the previously validated reference region. Non-invasive SUVs corrected for body weight (SUVBW), lean body mass (SUL), and body surface area (SUVBSA) were obtained by using later time intervals of the dynamic scans. Simulations were also performed to assess the effect of flow and specific binding (BPND) on the SUVs. RESULTS: A low SUV corresponded well with a low VT for both [18F]flortaucipir and [18F]florbetapir. Simulation confirmed that SUVs were only slightly affected by flow changes and that increases in SUV were predominantly determined by the presence of specific binding. CONCLUSIONS: In situations where dynamic scanning and arterial sampling is not possible, a low SUV(80-100 min) for [18F]flortaucipir and a low SUV(50-70 min) for [18F]florbetapir may be used as indication for absence of specific binding in the grey matter cerebellum reference region.

11C-Sorafenib and 15O-H2O PET for Early Evaluation of Sorafenib Therapy.

Sorafenib leads to clinical benefit in a subgroup of patients, whereas all are exposed to potential toxicity. Currently, no predictive biomarkers are available. The purpose of this study was to evaluate whether 11C-sorafenib and 15O-H2O PET have potential to predict treatment efficacy. Methods: In this prospective exploratory study, 8 patients with advanced solid malignancies and an indication for sorafenib treatment were included. Microdose 11C-sorafenib and perfusion 15O-H2O dynamic PET scans were performed before and after 2 wk of sorafenib therapy. The main objective was to assess whether tumor 11C-sorafenib uptake predicts sorafenib concentrations during therapy in corresponding tumor biopsy samples measured with liquid chromatography tandem mass spectrometry. Secondary objectives included determining the association of 11C-sorafenib PET findings, perfusion 15O-H2O PET findings, and sorafenib concentrations after therapeutic dosing with response. Results:11C-sorafenib PET findings did not predict sorafenib concentrations in tumor biopsy samples during therapy. In addition, sorafenib plasma and tumor concentrations were not associated with clinical outcome in this exploratory study. Higher 11C-sorafenib accumulation in tumors at baseline and day 14 of treatment showed an association with poorer prognosis and correlated with tumor perfusion (Spearman correlation coefficient = 0.671, P = 0.020). Interestingly, a decrease in tumor perfusion measured with 15O-H2O PET after only 14 d of therapy showed an association with response, with a decrease in tumor perfusion of 56% ± 23% (mean ± SD) versus 18% ± 32% in patients with stable and progressive disease, respectively. Conclusion: Microdose 11C-sorafenib PET did not predict intratumoral sorafenib concentrations after therapeutic dosing, but the association between a decrease in tumor perfusion and clinical benefit warrants further investigation.