Evaluation of [18F]fluoroestradiol and ChRERα as a gene expression PET reporter system in rhesus monkey brain.

Positron emission tomography (PET) reporter systems are a valuable means of estimating the level of expression of a transgene in vivo. For example, the safety and efficacy of gene therapy approaches for the treatment of neurological and neuropsychiatric disorders could be enhanced via the monitoring of exogenous gene expression levels in the brain. The present study evaluated the ability of a newly developed PET reporter system [18F]fluoroestradiol ([18F]FES) and the estrogen receptor-based PET reporter ChRERα, to monitor expression levels of a small hairpin RNA (shRNA) designed to suppress choline acetyltransferase (ChAT) expression in rhesus monkey brain. The ChRERα gene and shRNA were expressed from the same transcript via lentivirus injected into monkey striatum. In two monkeys that received injections of viral vector, [18F]FES binding increased by 70% and 86% at the target sites compared with pre-injection, demonstrating that ChRERα expression could be visualized in vivo with PET imaging. Post-mortem immunohistochemistry confirmed that ChAT expression was significantly suppressed in regions in which [18F]FES uptake was increased. The consistency between PET imaging and immunohistochemical results suggests that [18F]FES and ChRERα can serve as a PET reporter system in rhesus monkey brain for in vivo evaluation of the expression of potential therapeutic agents, such as shRNAs.

Investigating the Mechanism of Aluminum Fluoride Chelation.

Aluminum fluoride (AlF) complexes have been used over the past decade to incorporate [18F]fluoride into large biomolecules in a highly selective fashion by using relatively facile conditions. However, despite their widespread usage, there are a large number of variations in the reaction conditions, without a definitive discussion provided on the mechanism to understand how these changes would alter the end result. Herein, we report a detailed mechanistic investigation of the reaction, using a mixture of theoretical studies, fluorine-19 and fluorine-18 chemistry, and the consequences it has on the efficient clinical translation of AlF-containing imaging agents.

Evaluation of Tetrazine Tracers for Pretargeted Imaging within the Central Nervous System.

The pretargeting approach separates the biological half-life of an antibody from the physical half-life of the radioisotope label, providing a strategy for reducing the radiation burden. A widely explored pretargeting approach makes use of the bioorthogonal click reaction between tetrazines (Tzs) and trans-cyclooctenes (TCOs), combining the targeting specificity of monoclonal antibodies (mAbs) with the rapid clearance and precise reaction of Tzs and TCOs. Such a strategy can allow for the targeting and imaging (e.g., by positron emission tomography (PET)) of molecular markers, which cannot be addressed by solely relying on small molecules. Tz derivatives that undergo inverse electron-demand Diels-Alder (IEDDA) reactions with an antibody bearing TCO moieties have been investigated. This study describes the synthesis and characterization of 11 cold Tz imaging agent candidates. These molecules have the potential to be radiolabeled with 18F or 3H, and with the former label, they could be of use as imaging tracers for positron emission tomography studies. Selection was made using a multiparameter optimization score for the central nervous system (CNS) PET tracers. Novel tetrazines were tested for their pH-dependent chemical stability. Those which turned out to be stable in a pH range of 6.5-8 were further characterized in in vitro assays with regard to their passive permeability, microsomal stability, and P-glycoprotein transport. Furthermore, selected Tzs were examined for their systemic clearance and CNS penetration in a single-dose pharmacokinetic study in rats. Two tetrazines were successfully labeled with 18F, one of which showed brain penetration in a biodistribution study in mice. Another Tz was successfully tritium-labeled and used to demonstrate a bioorthogonal click reaction on a TCO-modified antibody. As a result, we identified one Tz as a potential fluorine-18-labeled CNS-PET agent and a second as a 3H-radioligand for an IEDDA-based reaction with a modified brain-penetrating antibody.

[18F]FNDP PET neuroimaging test-retest repeatability and whole-body dosimetry in humans.

PURPOSE: Soluble epoxide hydrolase (sEH) is an enzyme that shapes immune signaling through its role in maintaining the homeostasis of polyunsaturated fatty acids and their related byproducts. [18F]FNDP is a radiotracer developed for use with positron emission tomography (PET) to image sEH, which has been applied to imaging sEH in the brains of healthy individuals. Here, we report the test-retest repeatability of [18F]FNDP brain PET binding and [18F]FNDP whole-body dosimetry in healthy individuals. METHODS: Seven healthy adults (4 men, 3 women, ages 40.1 ± 4.6 years) completed [18F]FNDP brain PET on two occasions within a period of 14 days in a test-retest study design. [18F]FNDP regional total distribution volume (VT) values were derived from modeling time-activity data with a metabolite-corrected arterial input function. Test-retest variability, mean absolute deviation, and intraclass correlation coefficient (ICC) were investigated. Six other healthy adults (3 men, 3 women, ages 46.0 ± 7.0 years) underwent [18F]FNDP PET/CT for whole-body dosimetry, which was acquired over 4.5 h, starting immediately after radiotracer administration. Organ-absorbed doses and the effective dose were then estimated. RESULTS: The mean test-retest difference in regional VT (ΔVT) was 0.82 ± 5.17%. The mean absolute difference in regional VT was 4.01 ± 3.33%. The ICC across different brain regions ranged from 0.92 to 0.99. The organs with the greatest radiation-absorbed doses included the gallbladder (0.081 ± 0.024 mSv/MBq), followed by liver (0.077 ± 0.018 mSv/MBq) and kidneys (0.063 ± 0.006 mSv/MBq). The effective dose was 0.020 ± 0.003 mSv/MBq. CONCLUSION: These data support a favorable test-retest repeatability of [18F]FNDP brain PET regional VT. The radiation dose to humans from each [18F]FNDP PET scan is similar to that of other 18F-based PET radiotracers.

An optimized radiosynthesis of [18 F]DK222, a PET radiotracer for imaging PD-L1.

A radiochemical synthesis of [18 F]DK222, a peptide binder of programmed death ligand 1 protein, suitable for human PET studies is described, and results from validation productions are presented. The high specific activity radiotracer product is prepared as a sterile, apyrogenic solution that conforms to current Good Manufacturing Practice (cGMP) requirements. In addition, the production is extended to use a commercial synthesizer platform (General Electric FASTlab 2).

Fluid Resuscitation and Progression to Renal Replacement Therapy in Patients With COVID-19.

BACKGROUND: Coronavirus disease 2019 (COVID-19) is associated with respiratory symptoms and renal effects. Data regarding fluid resuscitation and kidney injury in COVID-19 are lacking, and understanding this relationship is critical. OBJECTIVES: To determine if there is an association between fluid volume administered in 24 h and development of renal failure in COVID-19 patients. METHODS: Retrospective chart review; 14 hospitals in Indiana. Included patients were adults admitted between March 11, 2020 and April 13, 2020 with a positive test for severe acute respiratory syndrome coronavirus 2 within 3 days of admission. Patients requiring renal replacement therapy prior to admission were excluded. Volumes and types of resuscitative intravenous fluids in the first 24 h were obtained with demographics, medical history, and other objective data. The primary outcome was initiation of renal replacement therapy. Logistic regression modeling was utilized in creating multivariate models for determining factors associated with the primary outcome. RESULTS: The fluid volume received in the first 24 h after hospital admission was associated with initiation of renal replacement therapy in two different multivariate logistic regression models. An odds ratio of 1.42 (95% confidence interval 1.01-1.99) was observed when adjusting for age, heart failure, obesity, creatinine, bicarbonate, and total fluid volume. An odds ratio of 1.45 (95% confidence interval 1.02-2.05) was observed when variables significant in univariate analysis were adjusted for. CONCLUSIONS: Each liter of intravenous fluid administered to patients with COVID-19 in the first 24 h of presentation was independently associated with an increased risk for initiation of renal replacement therapy, supporting judicious fluid administration in patients with this disease.

An improved radiosynthesis of [18 F]FAraG, a PET radiotracer for imaging T-cell activation.

In this concise practitioner protocol, the radiochemical synthesis of 2'-deoxy-2'-[18 F]fluoro-9-ß-d-arabinofuranosylguanine ([18 F]FAraG) suitable for human positron emission tomography (PET) studies is described and the results from validation productions are presented. The high specific activity (sometimes referred to as molar activity) radiotracer product is prepared as a sterile, apyrogenic solution that conforms to current Good Manufacturing Practice (cGMP) requirements established by the U.S. Food and Drug Administration.

Characteristics of COVID-19 patients with bacterial coinfection admitted to the hospital from the emergency department in a large regional healthcare system.

INTRODUCTION: The rate of bacterial coinfection with SARS-CoV-2 is poorly defined. The decision to administer antibiotics early in the course of SARS-CoV-2 infection depends on the likelihood of bacterial coinfection. METHODS: We performed a retrospective chart review of all patients admitted through the emergency department with confirmed SARS-CoV-2 infection over a 6-week period in a large healthcare system in the United States. Blood and respiratory culture results were abstracted and adjudicated by multiple authors. The primary outcome was the rate of bacteremia. We secondarily looked to define clinical or laboratory features associated with bacteremia. RESULTS: There were 542 patients admitted with confirmed SARS-CoV-2 infection, with an average age of 62.8 years. Of these, 395 had blood cultures performed upon admission, with six true positive results (1.1% of the total population). An additional 14 patients had positive respiratory cultures treated as true pathogens in the first 72 h. Low blood pressure and elevated white blood cell count, neutrophil count, blood urea nitrogen, and lactate were statistically significantly associated with bacteremia. Clinical outcomes were not statistically significantly different between patients with and without bacteremia. CONCLUSIONS: We found a low rate of bacteremia in patients admitted with confirmed SARS-CoV-2 infection. In hemodynamically stable patients, routine antibiotics may not be warranted in this population.

First-in-human neuroimaging of soluble epoxide hydrolase using [18F]FNDP PET.

PURPOSE: Soluble epoxide hydrolase (sEH) is an enzyme with putative effect on neuroinflammation through its influence on the homeostasis of polyunsaturated fatty acids and related byproducts. sEH is an enzyme that metabolizes anti-inflammatory epoxy fatty acids to the corresponding, relatively inert 1,2-diols. A high availability or activity of sEH promotes vasoconstriction and inflammation in local tissues that may be linked to neuropsychiatric diseases. We developed [18F]FNDP to study sEH in vivo with positron emission tomography (PET). METHODS: Brain PET using bolus injection of [18F]FNDP followed by emission imaging lasting 90 or 180 min was completed in healthy adults (5 males, 2 females, ages 40-53 years). The kinetic behavior of [18F]FNDP was evaluated using a radiometabolite-corrected arterial plasma input function with compartmental or graphical modeling approaches. RESULTS: [18F]FNDP PET was without adverse effects. Akaike information criterion favored the two-tissue compartment model (2TCM) in all ten regions of interest. Regional total distribution volume (VT) values from each compartmental model and Logan analysis were generally well identified except for corpus callosum VT using the 2TCM. Logan analysis was assessed as the choice model due to stability of regional VT values from 90-min data and due to high correlation of Logan-derived regional VT values with those from the 2TCM. [18F]FNDP binding was higher in human cerebellar cortex and thalamus relative to supratentorial cortical regions, which aligns with reported expression patterns of the epoxide hydrolase 2 gene in human brain. CONCLUSION: These data support further use of [18F]FNDP PET to study sEH in human brain.

Incidence of Venous Thromboembolism in Critically Ill Coronavirus Disease 2019 Patients Receiving Prophylactic Anticoagulation.

OBJECTIVES: One of the defining features of the novel coronavirus disease 2019 infection has been high rates of venous thromboses. The present study aimed to describe the prevalence of venous thromboembolism in critically ill patients receiving different regimens of prophylactic anticoagulation. DESIGN: Single-center retrospective review using data from patients with confirmed severe acute respiratory syndrome coronavirus 2 requiring intubation. SETTING: Tertiary-care center in Indianapolis, IN, United States. PATIENTS: Patients hospitalized at international units Health Methodist Hospital with severe acute respiratory syndrome coronavirus 2 requiring intubation between March 23, 2020, and April 8, 2020, who underwent ultrasound evaluation for venous thrombosis. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A total of 45 patients were included. Nineteen of 45 patients (42.2%) were found to have deep venous thrombosis. Patients found to have deep venous thrombosis had no difference in time to intubation (p = 0.97) but underwent ultrasound earlier in their hospital course (p = 0.02). Sequential Organ Failure Assessment scores were similar between the groups on day of intubation and day of ultrasound (p = 0.44 and p = 0.07, respectively). D-dimers were markedly higher in patients with deep venous thrombosis, both for maximum value and value on day of ultrasound (p < 0.01 for both). Choice of prophylactic regimen was not related to presence of deep venous thrombosis (p = 0.35). Ultrasound evaluation is recommended if D-dimer is greater than 2,000 ng/mL (sensitivity 95%, specificity 46%) and empiric anticoagulation considered if D-dimer is greater than 5,500 ng/mL (sensitivity 53%, specificity 88%). CONCLUSIONS: Deep venous thrombosis is very common in critically ill patients with coronavirus disease 2019. There was no difference in incidence of deep venous thrombosis among different pharmacologic prophylaxis regimens, although our analysis is limited by small sample size. D-dimer values are elevated in the majority of these patients, but there may be thresholds at which screening ultrasound or even empiric systemic anticoagulation is indicated.

Vasodilator Therapies in the Treatment of Acute Heart Failure.

PURPOSE OF REVIEW: Vasodilators are commonly recommended to treat acute heart failure (AHF), yet they are infrequently used. This review aims to evaluate the clinical utility of traditional, historical, and novel vasodilators in the treatment of AHF. RECENT FINDINGS: No traditional vasodilator (i.e., nitroglycerin) therapy definitely improves short- or long-term outcomes. Despite repeated efforts to develop new pharmacologic treatments, no novel therapy outperforms traditional management. At the present time, we continue to recommend traditional vasodilators, such as nitroglycerin. The use of select vasodilators in the treatment of AHF improves hemodynamics and provides short-term relief; however, data regarding long-term benefits is lacking.

Radiosynthesis and validation of [Carboxy-11 C]4-Aminobenzoic acid ([11 C]PABA), a PET radiotracer for imaging bacterial infections.

In this practitioner protocol, the radiochemical synthesis of [11 C] PABA is described in detail, and a quality control summary of three validation productions is presented. The results indicate that the radiotracer product can be produced in good radiochemical yield (14% at end-of-synthesis (EOS)) at high specific activity (molar activity 11 Ci/µmole EOS; 407 GBq/µmole) and high chemical and radiochemical purity as a sterile, pyrogen-free solution suitable for injection conforming to current Good Manufacturing Practice (cGMP) requirements.

Radiosynthesis and validation of [5-cyano-N-(4-(4-[11 C]methylpiperazin-1-yl)-2-(piperidin-1-yl)phenyl) furan-2-carboxamide] ([11 C]CPPC), a PET radiotracer for imaging CSF1R, a microglia-specific marker.

In this practitioner protocol, the radiochemical synthesis of [11 C]CPPC is described in detail, and a quality control summary of three validation productions is presented. The results indicate that the radiotracer product can be produced in good radiochemical yield (> 60 mCi (2.22 GBq) at end-of-synthesis (EOS)), at high specific activity (molar activity > 11,435 mCi/µmole (423 GBq/µmole) at EOS) and high chemical and radiochemical purity. The entire production conforms to current Good Manufacturing Practice (cGMP) requirements. The final product is formulated as a sterile, pyrogen-free solution suitable for human injection.

Brain PET Imaging of α7-nAChR with [18F]ASEM: Reproducibility, Occupancy, Receptor Density, and Changes in Schizophrenia.

Background: The α7 nicotinic acetylcholine receptor increasingly has been implicated in normal brain physiology, as well as in neuropsychiatric disorders. The highly cortical distribution of α7 nicotinic acetylcholine receptor suggests a role in cognition. Methods: We expanded the first-in-human PET imaging of α7 nicotinic acetylcholine receptor with [18F]ASEM from 5 to 21 healthy nonsmoking volunteers and added a feasibility study in 6 male patients with schizophrenia. Study aims included: (1) confirmation of test-retest reproducibility of [18F]ASEM binding, (2) demonstration of specificity by competition with DMXB-A, an α7 nicotinic acetylcholine receptor partial agonist, (3) estimation of [18F]ASEM binding potentials and α7 nicotinic acetylcholine receptor density in vivo in humans, and (4) demonstrating the feasibility of studying α7 nicotinic acetylcholine receptor as a target for schizophrenia. Results: Test-retest PET confirmed reproducibility (>90%) (variability ≤7%) of [18F]ASEM volume of distribution (VT) estimates in healthy volunteers. Repeated sessions of PET in 5 healthy subjects included baseline and effect of inhibition after oral administration of 150 mg DMXB-A. From reduction of binding potentials, we estimated the dose-dependent occupancy of α7 nicotinic acetylcholine receptor by DMXB-A at 17% to 49% for plasma concentrations at 60 to 200 nM DMXB-A. In agreement with evidence postmortem, α7 nicotinic acetylcholine receptor density averaged 0.67 to 0.82 nM and inhibitor affinity constant averaged 170 to 385 nM. Median VT in a feasibility study of 6 patients with schizophrenia was lower than in healthy volunteers in cingulate cortex, frontal cortex, and hippocampus (P = 0.02, corrected for multiple comparions, Mann-Whitney test). Conclusions: The current results confirm the reproducibility of [18F]ASEM VT estimates and the specificity of the tracer for α7 nicotinic acetylcholine receptor. Preliminary findings from our feasibility study of [18F]ASEM binding in patients with schizophrenia are suggestive and provide guidance for future studies with more subjects.

An optimized radiosynthesis of [18 F]FNDP, a positron emission tomography radiotracer for imaging soluble epoxide hydrolase (sEH).

In this concise practitioner protocol, the radiochemical synthesis of [18 F]FNDP suitable for human positron emission tomography studies is described and the results from validation productions are presented. The high specific activity radiotracer product is prepared as a sterile, apyrogenic solution that conforms to current Good Manufacturing Practice requirements.

When high working memory capacity is and is not beneficial for predicting nonlinear processes.

Predicting the development of dynamic processes is vital in many areas of life. Previous findings are inconclusive as to whether higher working memory capacity (WMC) is always associated with using more accurate prediction strategies, or whether higher WMC can also be associated with using overly complex strategies that do not improve accuracy. In this study, participants predicted a range of systematically varied nonlinear processes based on exponential functions where prediction accuracy could or could not be enhanced using well-calibrated rules. Results indicate that higher WMC participants seem to rely more on well-calibrated strategies, leading to more accurate predictions for processes with highly nonlinear trajectories in the prediction region. Predictions of lower WMC participants, in contrast, point toward an increased use of simple exemplar-based prediction strategies, which perform just as well as more complex strategies when the prediction region is approximately linear. These results imply that with respect to predicting dynamic processes, working memory capacity limits are not generally a strength or a weakness, but that this depends on the process to be predicted.

Convergent Aspects of Acoustic Communication in Darters, Sculpins, and Gobies.

Darters (Perciformes, Percidae), sculpins (Perciformes, Cottidae), and gobioids (Gobiiformes, Gobioidei) exhibit convergent life history traits, including a benthic lifestyle and a cavity nesting spawning mode. Soniferous species within these taxa produce pulsed and/or tonal sounds with peak frequencies below 200 Hz (with some exceptions), primarily in agonistic and/or reproductive contexts. The reduced or absent swim bladders found in these taxa limit or prevent both hearing enhancement via pressure sensitivity and acoustic amplification of the contracting sonic muscles, which are associated with the skull and pectoral girdle. While such anatomies constrain communication to low frequency channels, optimization of the S/N (signal-to-noise) ratio in low frequency channels is evident for some gobies, as measured by habitat soundscape frequency windows, nest cavity sound amplification, and audiograms. Similar S/N considerations are applicable to many darter and sculpin systems. This chapter reviews the currently documented diversity of sound production in darters, sculpins, and gobioids within a phylogenetic context, examines the efficacy of signal transmission from senders to receivers (sound production mechanisms, audiograms, and masking challenges), and evaluates the potential functional significance of sound attributes in relation to territorial and reproductive behaviours.

Synthesis and quality control of [(18) F]T807 for tau PET imaging.

The detailed synthesis and quality control of [(18) F]T807, radiotracer for tau protein aggregate imaging, are described. The radiotracer synthesis was accomplished in an average of 48 min with an average specific activity at end-of-synthesis of over 4.4 TBq/µmole (120 Ci/µmole) and an average radiochemical yield of 32%. Compliance with all standard US Pharmacopeia Chapter <823> acceptance tests was observed.

An improved synthesis of the radiolabeled prostate-specific membrane antigen inhibitor, [(18) F]DCFPyL.

The radiosynthesis of [(18) F]DCFPyL on 2 distinct automated platforms with full regulatory compliant quality control specifications is described. The radiotracer synthesis was performed on a custom-made radiofluorination module and the Sofie Biosciences ELIXYS. The radiofluorination module synthesis was accomplished in an average of 66 minutes from end of bombardment with an average specific activity at end of synthesis (EOS) of 4.4 TBq/µmol (120 Ci/µmol) and an average radiochemical yield of 30.9% at EOS. The ELIXYS synthesis was completed in an average of 87 minutes with an average specific activity of 2.2 TBq/µmol (59.3 Ci/µmol) and an average radiochemical yield of 19% at EOS. Both synthesis modules produced large millicurie quantities of [(18) F]DCFPyL while conforming to all standard US Pharmacopeia Chapter <823> acceptance testing criteria.

Determination of [11C]rifampin pharmacokinetics within Mycobacterium tuberculosis-infected mice by using dynamic positron emission tomography bioimaging.

Information about intralesional pharmacokinetics (PK) and spatial distribution of tuberculosis (TB) drugs is limited and has not been used to optimize dosing recommendations for new or existing drugs. While new techniques can detect drugs and their metabolites within TB granulomas, they are invasive, rely on accurate resection of tissues, and do not capture dynamic drug distribution in the tissues of interest. In this study, we assessed the in situ distribution of (11)C-labeled rifampin in live, Mycobacterium tuberculosis-infected mice that develop necrotic lesions akin to human disease. Dynamic positron emission tomography (PET) imaging was performed over 60 min after injection of [(11)C]rifampin as a microdose, standardized uptake values (SUV) were calculated, and noncompartmental analysis was used to estimate PK parameters in compartments of interest. [(11)C]rifampin was rapidly distributed to all parts of the body and quickly localized to the liver. Areas under the concentration-time curve for the first 60 min (AUC0-60) in infected and uninfected mice were similar for liver, blood, and brain compartments (P > 0.53) and were uniformly low in brain (10 to 20% of blood values). However, lower concentrations were noted in necrotic lung tissues of infected mice than in healthy lungs (P = 0.03). Ex vivo two-dimensional matrix-assisted laser desorption ionization (MALDI) imaging confirmed restricted penetration of rifampin into necrotic lung lesions. Noninvasive bioimaging can be used to assess the distribution of drugs into compartments of interest, with potential applications for TB drug regimen development.