Meeting report of the fifth annual workshop on Principles and Techniques for Improving Preclinical to Clinical Translation in Alzheimer's Disease Research.

The fifth annual workshop on Principles and Techniques for Improving Preclinical Translation of Alzheimer's Disease Research was held in May 2023 at The Jackson Laboratory in Bar Harbor, Maine, USA. The workshop was established in 2018 to address training gaps in preclinical translational studies for Alzheimer's disease (AD). In addition to providing fundamental knowledge and hands-on skills essential for executing rigorous in vivo studies that are designed to facilitate translation, each year the workshop aims to provide insight on state-of-the-field technological advances and new resources including novel animal models, publicly available datasets, novel biomarkers, and new medical imaging tracers. This innovative and comprehensive workshop continues to deliver training for the greater AD research community in order to provide investigators and trainees with the knowledge and skillsets essential for enabling improved preclinical to clinical translation and accelerate the process of advancing safe and effective therapeutic interventions for AD. HIGHLIGHTS: Translational research is not typically available as a course of study at academic institutions, yet there are fundamental skillsets and knowledge required to enable successful translation from preclinical experiments to clinical efficacy. It is important that there are resources and opportunities available to researchers planning preclinical translational experiments. Here we present proceedings from the fifth annual NIA-sponsored workshop focused on enabling improved preclinical to clinical translation for Alzheimer's disease research that includes didactic lectures on state-of-the-field approaches and hands-on practicums for acquiring essential translational laboratory techniques.

Brain metabolic network covariance and aging in a mouse model of Alzheimer's disease.

INTRODUCTION: Alzheimer's disease (AD), the leading cause of dementia worldwide, represents a human and financial impact for which few effective drugs exist to treat the disease. Advances in molecular imaging have enabled assessment of cerebral glycolytic metabolism, and network modeling of brain region have linked to alterations in metabolic activity to AD stage. METHODS: We performed 18 F-FDG positron emission tomography (PET) imaging in 4-, 6-, and 12-month-old 5XFAD and littermate controls (WT) of both sexes and analyzed region data via brain metabolic covariance analysis. RESULTS: The 5XFAD model mice showed age-related changes in glucose uptake relative to WT mice. Analysis of community structure of covariance networks was different across age and sex, with a disruption of metabolic coupling in the 5XFAD model. DISCUSSION: The current study replicates clinical AD findings and indicates that metabolic network covariance modeling provides a translational tool to assess disease progression in AD models.

Assessment of neurovascular uncoupling: APOE status is a key driver of early metabolic and vascular dysfunction.

BACKGROUND: Alzheimer's disease (AD) is the most common cause of dementia worldwide, with apolipoprotein Eε4 (APOEε4) being the strongest genetic risk factor. Current clinical diagnostic imaging focuses on amyloid and tau; however, new methods are needed for earlier detection. METHODS: PET imaging was used to assess metabolism-perfusion in both sexes of aging C57BL/6J, and hAPOE mice, and were verified by transcriptomics, and immunopathology. RESULTS: All hAPOE strains showed AD phenotype progression by 8 months, with females exhibiting the regional changes, which correlated with GO-term enrichments for glucose metabolism, perfusion, and immunity. Uncoupling analysis revealed APOEε4/ε4 exhibited significant Type-1 uncoupling (↓ glucose uptake, ↑ perfusion) at 8 and 12 months, while APOEε3/ε4 demonstrated Type-2 uncoupling (↑ glucose uptake, ↓ perfusion), while immunopathology confirmed cell specific contributions. DISCUSSION: This work highlights APOEε4 status in AD progression manifests as neurovascular uncoupling driven by immunological activation, and may serve as an early diagnostic biomarker. HIGHLIGHTS: We developed a novel analytical method to analyze PET imaging of 18F-FDG and 64Cu-PTSM data in both sexes of aging C57BL/6J, and hAPOEε3/ε3, hAPOEε4/ε4, and hAPOEε3/ε4 mice to assess metabolism-perfusion profiles termed neurovascular uncoupling. This analysis revealed APOEε4/ε4 exhibited significant Type-1 uncoupling (decreased glucose uptake, increased perfusion) at 8 and 12 months, while APOEε3/ε4 demonstrated significant Type-2 uncoupling (increased glucose uptake, decreased perfusion) by 8 months which aligns with immunopathology and transcriptomic signatures. This work highlights that there may be different mechanisms underlying age related changes in APOEε4/ε4 compared with APOEε3/ε4. We predict that these changes may be driven by immunological activation and response, and may serve as an early diagnostic biomarker.

Characterizing molecular and synaptic signatures in mouse models of late-onset Alzheimer's disease independent of amyloid and tau pathology.

INTRODUCTION: MODEL-AD (Model Organism Development and Evaluation for Late-Onset Alzheimer's Disease) is creating and distributing novel mouse models with humanized, clinically relevant genetic risk factors to capture the trajectory and progression of late-onset Alzheimer's disease (LOAD) more accurately. METHODS: We created the LOAD2 model by combining apolipoprotein E4 (APOE4), Trem2*R47H, and humanized amyloid-beta (Aß). Mice were subjected to a control diet or a high-fat/high-sugar diet (LOAD2+HFD). We assessed disease-relevant outcome measures in plasma and brain including neuroinflammation, Aß, neurodegeneration, neuroimaging, and multi-omics. RESULTS: By 18 months, LOAD2+HFD mice exhibited sex-specific neuron loss, elevated insoluble brain Aß42, increased plasma neurofilament light chain (NfL), and altered gene/protein expression related to lipid metabolism and synaptic function. Imaging showed reductions in brain volume and neurovascular uncoupling. Deficits in acquiring touchscreen-based cognitive tasks were observed. DISCUSSION: The comprehensive characterization of LOAD2+HFD mice reveals that this model is important for preclinical studies seeking to understand disease trajectory and progression of LOAD prior to or independent of amyloid plaques and tau tangles. HIGHLIGHTS: By 18 months, unlike control mice (e.g., LOAD2 mice fed a control diet, CD), LOAD2+HFD mice presented subtle but significant loss of neurons in the cortex, elevated levels of insoluble Ab42 in the brain, and increased plasma neurofilament light chain (NfL). Transcriptomics and proteomics showed changes in gene/proteins relating to a variety of disease-relevant processes including lipid metabolism and synaptic function. In vivo imaging revealed an age-dependent reduction in brain region volume (MRI) and neurovascular uncoupling (PET/CT). LOAD2+HFD mice also demonstrated deficits in acquisition of touchscreen-based cognitive tasks.

Quantitative assessment of cerebrospinal fluid flow and volume in enlargement of the subarachnoid spaces of infancy using MRI.

BACKGROUND: The etiology of enlarged subarachnoid spaces of infancy is unknown; however, there is radiologic similarity with normal pressure hydrocephalus. Adults with normal pressure hydrocephalus have been shown to have altered cerebrospinal (CSF) flow through the cerebral aqueduct. OBJECTIVE: To explore potential similarity between enlarged subarachnoid spaces of infancy and normal pressure hydrocephalus, we compared MRI-measured CSF flow through the cerebral aqueduct in infants with enlarged subarachnoid spaces of infancy to infants with normal brain MRIs. MATERIALS AND METHODS: This was an IRB approved retrospective study. Clinical brain MRI examinations including axial T2 imaging and phase contrast through the aqueduct were reviewed for infants with enlarged subarachnoid spaces of infancy and for infants with a qualitatively normal brain MRI. The brain and CSF volumes were segmented using a semi-automatic technique (Analyze 12.0) and CSF flow parameters were measured (cvi42, 5.14). All data was assessed for significant differences while controlling for age and sex using analysis of covariance (ANCOVA). RESULTS: Twenty-two patients with enlarged subarachnoid spaces (mean age 9.0 months, 19 males) and 15 patients with normal brain MRI (mean age 18.9 months, 8 females) were included. Volumes of the subarachnoid space (P < 0.001), lateral (P < 0.001), and third ventricles (P < 0.001) were significantly larger in infants with enlarged subarachnoid spaces of infancy. Aqueductal stroke volume significantly increased with age (P = 0.005), regardless of group. CONCLUSION: CSF volumes were significantly larger in infants with enlarged subarachnoid spaces of infancy versus infants with a normal MRI; however, there was no significant difference in CSF flow parameters between the two groups.

Meeting report of the annual workshop on Principles and Techniques for Improving Preclinical to Clinical Translation in Alzheimer's Disease research.

INTRODUCTION: The second annual 5-day workshop on Principles and Techniques for Improving Preclinical to Clinical Translation in Alzheimer's Disease Research was held October 7-11, 2019, at The Jackson Laboratory in Bar Harbor, Maine, USA, and included didactic lectures and hands-on training. Participants represented a broad range of research across the Alzheimer's disease (AD) field, and varied in career stages from trainees and early stage investigators to established faculty, with attendance from the United States, Europe, and Asia. METHODS: In line with the National Institutes of Health (NIH) initiative on rigor and reproducibility, the workshop aimed to address training gaps in preclinical drug screening by providing participants with the skills and knowledge required to perform pharmacokinetic, pharmacodynamics, and preclinical efficacy experiments. RESULTS: This innovative and comprehensive workshop provided training in fundamental skill sets for executing in vivo preclinical translational studies. DISCUSSION: The success of this workship is expected to translate into practical skills that will enable the goals of improving preclinical to clinical translational studies for AD. HIGHLIGHTS: Nearly all preclinical studies in animal models have failed to translate to successful efficacious medicines for Alzheimer's disease (AD) patients. While a wide variety of potential causes of these failures have been proposed,deficiencies in knowledge and best practices for translational research are not being sufficiently addressed by common training practices. Here we present proceedings from an annual NIA-sponsored workshop focused specifically on preclinical testing paradigms for AD translational research in animal models aimed at enabling improved preclinical to clinical translation for AD.

STOP-AD portal: Selecting the optimal pharmaceutical for preclinical drug testing in Alzheimer's disease.

We propose an unbiased methodology to rank compounds for advancement into comprehensive preclinical testing for Alzheimer's disease (AD). Translation of compounds to the clinic in AD has been hampered by poor predictive validity of models, compounds with limited pharmaceutical properties, and studies that lack rigor. To overcome this, MODEL-AD's Preclinical Testing Core developed a standardized pipeline for assessing efficacy in AD mouse models. We hypothesize that rank-ordering compounds based upon pharmacokinetic, efficacy, and toxicity properties in preclinical models will enhance successful translation to the clinic. Previously compound selection was based solely on physiochemical properties, with arbitrary cutoff limits, making ranking challenging. Since no gold standard exists for systematic prioritization, validating a selection criteria has remained elusive. The STOP-AD framework evaluates the drug-like properties to rank compounds for in vivo studies, and uses an unbiased approach that overcomes the validation limitation by performing Monte-Carlo simulations. HIGHLIGHTS: Promising preclinical studies for AD drugs have not translated to clinical success. Systematic assessment of AD drug candidates may increase clinical translatability. We describe a well-defined framework for compound selection with clear selection metrics.

Purinergic Receptors of the Central Nervous System: Biology, PET Ligands, and Their Applications.

Purinergic receptors play important roles in central nervous system (CNS). These receptors are involved in cellular neuroinflammatory responses that regulate functions of neurons, microglial and astrocytes. Based on their endogenous ligands, purinergic receptors are classified into P1 or adenosine, P2X and P2Y receptors. During brain injury or under pathological conditions, rapid diffusion of extracellular adenosine triphosphate (ATP) or uridine triphosphate (UTP) from the damaged cells, promote microglial activation that result in the changes in expression of several of these receptors in the brain. Imaging of the purinergic receptors with selective Positron Emission Tomography (PET) radioligands has advanced our understanding of the functional roles of some of these receptors in healthy and diseased brains. In this review, we have accumulated a list of currently available PET radioligands of the purinergic receptors that are used to elucidate the receptor functions and participations in CNS disorders. We have also reviewed receptors lacking radiotracer, laying the foundation for future discoveries of novel PET radioligands to reveal these receptors roles in CNS disorders.

Macrophage-derived LTB4 promotes abscess formation and clearance of Staphylococcus aureus skin infection in mice.

The early events that shape the innate immune response to restrain pathogens during skin infections remain elusive. Methicillin-resistant Staphylococcus aureus (MRSA) infection engages phagocyte chemotaxis, abscess formation, and microbial clearance. Upon infection, neutrophils and monocytes find a gradient of chemoattractants that influence both phagocyte direction and microbial clearance. The bioactive lipid leukotriene B4 (LTB4) is quickly (seconds to minutes) produced by 5-lipoxygenase (5-LO) and signals through the G protein-coupled receptors LTB4R1 (BLT1) or BLT2 in phagocytes and structural cells. Although it is known that LTB4 enhances antimicrobial effector functions in vitro, whether prompt LTB4 production is required for bacterial clearance and development of an inflammatory milieu necessary for abscess formation to restrain pathogen dissemination is unknown. We found that LTB4 is produced in areas near the abscess and BLT1 deficient mice are unable to form an abscess, elicit neutrophil chemotaxis, generation of neutrophil and monocyte chemokines, as well as reactive oxygen species-dependent bacterial clearance. We also found that an ointment containing LTB4 synergizes with antibiotics to eliminate MRSA potently. Here, we uncovered a heretofore unknown role of macrophage-derived LTB4 in orchestrating the chemoattractant gradient required for abscess formation, while amplifying antimicrobial effector functions.

A Novel Vector-Based Computer Tomography Alignment Measurement Protocol for Total Knee Arthroplasty.

INTRODUCTION: Component position and overall limb alignment following total knee arthroplasty (TKA) have been shown to influence implant survivorships and clinical outcomes. While most surgeons utilize standard x-ray imaging for preoperative joint assessments, computer tomography scans (CT), coupled with automated digital analyses have been shown to provide additional surgical and clinical benefits. However, to date, a postoperative CT measurement protocol has not been reported for robotic-arm assisted TKA (RATKA). Therefore, the purpose of this paper was to assess the validity of a novel, vector-based CT alignment measurement protocol. Specifically, we compared: 1) final versus planned component alignment and placement; 2) inter-observer reliability; and 3) intra-observer reliability. MATERIALS AND METHODS: The CT-based technique utilized mathematical models to calculate prosthetic alignments from anatomical landmarks. To assess the models, 30 CT scans from multiple centers were collected on RATKA patients at six weeks postoperatively and analyzed using the proposed technique. Results were compared to the surgeons' preoperative plans for accuracy. Analyses were performed on the same protocol to determine inter-observer reliability. These analyses were repeated 30 days later to assess for intra-observer variability. RESULTS: The mean measurement errors compared between final versus planned component positions and alignments were: 0.79±1.48o varus in overall limb alignment (p=0.004); 0.34±1.20o varus (p=0.121); and 0.35±1.15o varus (p=0.17) for femoral and tibial varus/valgus alignment; 0.71±1.77o flexion (p=0.18) and 0.38±1.88o posterior (p=0.41) for femoral flexion and tibial slope. There was strong reproducibility between observers. Correlation analyses showed low variabilities, with slopes between 0.8 to 1.0 and all R>0.8. CONCLUSION: As robotic technologies become widely available in orthopaedic surgery, it is critical to have tools, such as CT protocols, which can quantitatively verify operative decisions concerning limb alignment and component placement. This study described a novel, vector-based, CT alignment measurement protocol for RATKA which has not previously been defined. The method demonstrated excellent accuracy to plan and low intra- and inter-observer variability. This is a valuable analysis tool for RATKA studies where component accuracy is assessed using postoperative CT images.

Beta Cell Imaging-From Pre-Clinical Validation to First in Man Testing.

There are presently no reliable ways to quantify human pancreatic beta cell mass (BCM) in vivo, which prevents an accurate understanding of the progressive beta cell loss in diabetes or following islet transplantation. Furthermore, the lack of beta cell imaging hampers the evaluation of the impact of new drugs aiming to prevent beta cell loss or to restore BCM in diabetes. We presently discuss the potential value of BCM determination as a cornerstone for individualized therapies in diabetes, describe the presently available probes for human BCM evaluation, and discuss our approach for the discovery of novel beta cell biomarkers, based on the determination of specific splice variants present in human beta cells. This has already led to the identification of DPP6 and FXYD2ga as two promising targets for human BCM imaging, and is followed by a discussion of potential safety issues, the role for radiochemistry in the improvement of BCM imaging, and concludes with an overview of the different steps from pre-clinical validation to a first-in-man trial for novel tracers.

Synthesis and in vitro biological evaluation of new P2X7R radioligands [11C]halo-GSK1482160 analogs.

The reference standards halo-GSK1482160 (F-, Br-, and I-) and their corresponding precursors desmethyl-halo-GSK1482160 (F-, Br-, and I-) were synthesized from (S)-1-methyl-5-oxopyrrolidine-2-carboxylic acid or (S)-5-oxopyrrolidine-2-carboxylic acid and 2-halo-3-(trifluoromethyl)benzylamine (F-, Br-, and I-) in one step with 45-93% yields. The target tracers [11C]halo-GSK1482160 (F-, Br-, and I-) were prepared from desmethyl-halo-GSK1482160 (F-, Br-, and I-) with [11C]CH3OTf under basic conditions (NaOH-Na2CO3, solid, w/w 1:2) through N-[11C]methylation and isolated by HPLC combined with SPE in 40-50% decay corrected radiochemical yield. The radiochemical purity was >99%, and the molar activity (AM) at end of bombardment (EOB) was 370-740 GBq/µmol. The potency of halo-GSK1482160 (F-, Br-, and I-) in comparison with GSK1482160 (Cl-) was determined by a radioligand competitive binding assay using [11C]GSK1482160, and the binding affinity Ki values for halo-GSK1482160 (F-, Br-, and I-) and GSK1482160 (Cl-) are 54.2, 2.5, 1.9 and 3.1 nM, respectively.

Frontal Occipital and Frontal Temporal Horn Ratios: Comparison and Validation of Head Ultrasound-Derived Indexes With MRI and Ventricular Volumes in Infantile Ventriculomegaly.

OBJECTIVE. The purpose of our study was to assess whether linear ventricular dimensions-specifically, the frontal occipital horn ratio (FOHR) and frontal temporal horn ratio (FTHR) obtained from ultrasound (US)-are reliable measures of ventriculomegaly in infants. Our hypothesis was that these US measures would show good correlation with linear ventricular indexes and ventricular volumes obtained from MRI. MATERIALS AND METHODS. We retrospectively identified 90 infants (age ≤ 6 months corrected gestational age) with ventriculomegaly from 2014 to 2017 who had a total of 100 sets of US and MRI studies performed in a 3-day period. FOHR and FTHR were independently measured on US and MRI by two pediatric radiologists and two pediatric neuroradiologists, respectively. Ventricular and brain volumes were segmented from the MR images, and the ventricle-to-intracranial volume ratio was calculated. MRI served as the reference standard. Intraclass correlation coefficients and Bland-Altman analyses were generated to evaluate interobserver and US-MRI concordance. We assessed correlation of the FOHR and FTHR with the ventricle-to-intracranial volume ratio. RESULTS. Bland-Altman plots of the FOHR and FTHR between US and MRI showed excellent concordance with a bias of 0.05 (95% CI, -0.04 to 0.14) and 0.03 (95% CI, -0.06 to 0.13), respectively. There was good-to-excellent interobserver concordance for FOHR and FTHR on head US or MRI (r = 0.86-0.96). There was good correlation between ventricle-to-intracranial volume ratios and US- and MRI-derived FOHRs and FTHRs (r = 0.79-0.87). CONCLUSION. FOHR and FTHR obtained from US in infants with ventriculomegaly have excellent interobserver concordance, are concordant with MRI-derived linear ratios, and correlate with MRI-derived ventricular volumes. Therefore, US-derived FOHR and FTHR are reliable indexes for clinical follow-up of infantile ventriculomegaly.

Chronic Embolic Pulmonary Hypertension Caused by Pulmonary Embolism and Vascular Endothelial Growth Factor Inhibition.

Our understanding of the pathophysiological basis of chronic thromboembolic pulmonary hypertension (CTEPH) will be accelerated by an animal model that replicates the phenotype of human CTEPH. Sprague-Dawley rats were administered a combination of a single dose each of plastic microspheres and vascular endothelial growth factor receptor antagonist in polystyrene microspheres (PE) + tyrosine kinase inhibitor SU5416 (SU) group. Shams received volume-matched saline; PE and SU groups received only microspheres or SU5416, respectively. PE + SU rats exhibited sustained pulmonary hypertension (62 ± 13 and 53 ± 14 mmHg at 3 and 6 weeks, respectively) with reduction of the ventriculoarterial coupling in vivo coincident with a large decrement in peak rate of oxygen consumption during aerobic exercise, respectively. PE + SU produced right ventricular hypokinesis, dilation, and hypertrophy observed on echocardiography, and 40% reduction in right ventricular contractile function in isolated perfused hearts. High-resolution computed tomographic pulmonary angiography and Ki-67 immunohistochemistry revealed abundant lung neovascularization and cellular proliferation in PE that was distinctly absent in the PE + SU group. We present a novel rodent model to reproduce much of the known phenotype of CTEPH, including the pivotal pathophysiological role of impaired vascular endothelial growth factor-dependent vascular remodeling. This model may reveal a better pathophysiological understanding of how PE transitions to CTEPH in human treatments.

18F-NaF and 18F-FDG as molecular probes in the evaluation of atherosclerosis.

The early detection of atherosclerotic disease is vital to the effective prevention and management of life-threatening cardiovascular events such as myocardial infarctions and cerebrovascular accidents. Given the potential for positron emission tomography (PET) to visualize atherosclerosis earlier in the disease process than anatomic imaging modalities such as computed tomography (CT), this application of PET imaging has been the focus of intense scientific inquiry. Although 18F-FDG has historically been the most widely studied PET radiotracer in this domain, there is a growing body of evidence that 18F-NaF holds significant diagnostic and prognostic value as well. In this article, we review the existing literature on the application of 18F-FDG and 18F-NaF as PET probes in atherosclerosis and present the findings of original animal and human studies that have examined how well 18F-NaF uptake correlates with vascular calcification and cardiovascular risk.

Synthesis and preliminary biological evaluation of a novel P2X7R radioligand [18F]IUR-1601.

The reference standard IUR-1601 ((S)-N-(2-chloro-3-(trifluoromethyl)benzyl)-1-(2-fluoroethyl)-5-oxopyrrolidine-2-carboxamide) was synthesized from tert-butyl (S)-5-oxopyrrolidine-2-carboxylate, fluoroethylbromide, and 2-chloro-3-(trifluoromethyl)benzylamine with overall chemical yield 12% in three steps. The target tracer [18F]IUR-1601 ((S)-N-(2-chloro-3-(trifluoromethyl)benzyl)-1-(2-[18F]fluoroethyl)-5-oxopyrrolidine-2-carboxamide) was synthesized from desmethyl-GSK1482160 with 2-[18F]fluoroethyl tosylate, prepared from 1,2-ethylene glycol-bis-tosylate and K[18F]F/Kryptofix2.2.2, in two steps and isolated by HPLC combined with SPE in 1-3% decay corrected radiochemical yield. The radiochemical purity was >99%, and the molar activity at end of bombardment (EOB) was 74-370 GBq/µmol. The potency of IUR-1601 in comparison with GSK1482160 was determined by a radioligand competitive binding assay using [11C]GSK1482160, and the binding affinity Ki values for IUR-1601 and GSK1482160 are 4.31 and 5.14 nM, respectively.

Quantitative MR Evaluation of Chronic Pancreatitis: Extracellular Volume Fraction and MR Relaxometry.

OBJECTIVE: The purpose of this study was to determine if extracellular volume fraction and T1 mapping can be used to diagnose chronic pancreatitis (CP). MATERIALS AND METHODS: This HIPAA-compliant study analyzed 143 consecutive patients with and without CP who underwent MR imaging between May 2016 and February 2017. Patients were selected for the study according to inclusion and exclusion criteria that considered history and clinical and laboratory findings. Eligible patients (n = 119) were grouped as normal (n = 60) or with mild (n = 22), moderate (n = 27), or severe (n = 10) CP on the basis of MRCP findings using the Cambridge classification as the reference standard. T1 maps were acquired in unenhanced and late contrast-enhanced phases using a 3D dual flip-angle gradient-echo sequence. All patients were imaged on the same 3-T scanner using the same imaging parameters, contrast agent, and dosage. RESULTS: Mean extracellular volume fractions and T1 relaxation times were significantly different within the study groups (one-way ANOVA, p < 0.001). Using the AUC curve analysis, extracellular volume fraction of > 0.27 showed 92% sensitivity (54/59) and 77% specificity (46/60) for the diagnosis of CP (AUC = 0.90). A T1 relaxation time of > 950 ms revealed 64% sensitivity (38/59) and 88% specificity (53/60) (AUC = 0.80). Combining extracellular volume fraction and T1 mapping yielded sensitivity of 85% (50/59) and specificity of 92% (55/60) (AUC = 0.94). CONCLUSION: Extracellular volume fraction and T1 mapping may provide quantitative metrics for determining the presence and severity of acinar cell loss and aid in the diagnosis of CP.

Synthesis and preliminary biological evaluation of [11C]methyl (2-amino-5-(benzylthio)thiazolo[4,5-d]pyrimidin-7-yl)-d-leucinate for the fractalkine receptor (CX3CR1).

The reference standard methyl (2-amino-5-(benzylthio)thiazolo[4,5-d]pyrimidin-7-yl)-d-leucinate (5) and its precursor 2-amino-5-(benzylthio)thiazolo[4,5-d]pyrimidin-7-yl)-d-leucine (6) were synthesized from 6-amino-2-mercaptopyrimidin-4-ol and BnBr with overall chemical yield 7% in five steps and 4% in six steps, respectively. The target tracer [11C]methyl (2-amino-5-(benzylthio)thiazolo[4,5-d]pyrimidin-7-yl)-d-leucinate ([11C]5) was prepared from the acid precursor with [11C]CH3OTf through O-[11C]methylation and isolated by HPLC combined with SPE in 40-50% radiochemical yield, based on [11C]CO2 and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the specific activity (SA) at EOB was 370-1110GBq/µmol with a total synthesis time of ∼40-min from EOB. The radioligand depletion experiment of [11C]5 did not display specific binding to CX3CR1, and the competitive binding assay of ligand 5 found much lower CX3CR1 binding affinity.

Synthesis and preliminary biological evaluation of radiolabeled 5-BDBD analogs as new candidate PET radioligands for P2X4 receptor.

P2X4 receptor has become an interesting molecular target for treatment and PET imaging of neuroinflammation and associated brain diseases such as Alzheimer's disease. This study reports the first design, synthesis, radiolabeling and biological evaluation of new candidate PET P2X4 receptor radioligands using 5-BDBD, a specific P2X4 receptor antagonist, as a scaffold. 5-(3-Hydroxyphenyl)-1-[11C]methyl-1,3-dihydro-2H-benzofuro[3,2-e][1,4]diazepin-2-one (N-[11C]Me-5-BDBD analog, [11C]9) and 5-(3-Bromophenyl)-1-[11C]methyl-1,3-dihydro-2H-benzofuro[3,2-e][1,4]diazepin-2-one (N-[11C]Me-5-BDBD, [11C]8c) were prepared from their corresponding desmethylated precursors with [11C]CH3OTf through N-[11C]methylation and isolated by HPLC combined with SPE in 30-50% decay corrected radiochemical yields with 370-1110GBq/µmol specific activity at EOB. 5-(3-[18F]Fluorophenyl)-1,3-dihydro-2H-benzofuro[3,2-e][1,4]diazepin-2-one ([18F]F-5-BDBD, [18F]5a) and 5-(3-(2-[18F]fluoroethoxy)phenyl)-1,3-dihydro-2H-benzofuro[3,2-e][1,4]diazepin-2-one ([18F]FE-5-BDBD, [18F]11) were prepared from their corresponding nitro- and tosylated precursors by nucleophilic substitution with K[18F]F/Kryptofix 2.2.2 and isolated by HPLC-SPE in 5-25% decay corrected radiochemical yields with 111-740GBq/µmol specific activity at EOB. The preliminary biological evaluation of radiolabeled 5-BDBD analogs indicated these new radioligands have similar biological activity with their parent compound 5-BDBD.

Novel application of complementary imaging techniques to examine in vivo glucose metabolism in the kidney.

The metabolic status of the kidney is a determinant of injury susceptibility and a measure of progression for many disease processes; however, noninvasive modalities to assess kidney metabolism are lacking. In this study, we employed positron emission tomography (PET) and intravital multiphoton microscopy (MPM) to assess cortical and proximal tubule glucose tracer uptake, respectively, following experimental perturbations of kidney metabolism. Applying dynamic image acquisition PET with 2-18fluoro-2-deoxyglucose (18F-FDG) and tracer kinetic modeling, we found that an intracellular compartment in the cortex of the kidney could be distinguished from the blood and urine compartments in animals. Given emerging literature that the tumor suppressor protein p53 is an important regulator of cellular metabolism, we demonstrated that PET imaging was able to discern a threefold increase in cortical 18F-FDG uptake following the pharmacological inhibition of p53 in animals. Intravital MPM with the fluorescent glucose analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) provided increased resolution and corroborated these findings at the level of the proximal tubule. Extending our observation of p53 inhibition on proximal tubule glucose tracer uptake, we demonstrated by intravital MPM that pharmacological inhibition of p53 diminishes mitochondrial potential difference. We provide additional evidence that inhibition of p53 alters key metabolic enzymes regulating glycolysis and increases intermediates of glycolysis. In summary, we provide evidence that PET is a valuable tool for examining kidney metabolism in preclinical and clinical studies, intravital MPM is a powerful adjunct to PET in preclinical studies of metabolism, and p53 inhibition alters basal kidney metabolism.