Assessment of tumor necrotic fraction by dynamic contrast-enhanced MRI: a preclinical study of human tumor xenografts with histopathologic correlation.

Contrary to the common notion that tumor necrotic regions are non-enhancing after contrast administration, recent evidence has shown that necrotic regions exhibit delayed and slow uptake of gadolinium tracer on dynamic contrast-enhanced MRI (DCE MRI). The purpose of this study is to explore whether the mapping of tumor voxels with delayed and slow enhancement on DCE MRI can be used to derive estimates of tumor necrotic fraction. Patient-derived tumor xenograft lines of seven human cancers were implanted in 26 mice which were subjected to DCE MRI performed using a spoiled gradient recalled sequence. Gadolinium tracer concentration was estimated using the variable flip angle technique. To identify tumor voxels exhibiting delayed and slow uptake of contrast medium, clustering analysis was performed using a k-means clustering algorithm that classified tumor voxels according to their contrast enhancement patterns. Comparison of the percentage of tumor voxels exhibiting delayed and slow enhancement with the tumor necrotic fraction estimated on histology showed a strong correlation (r = 0.962, p < 0.001). The mapping of tumor regions with delayed and slow contrast uptake on DCE MRI correlated strongly with tumor necrotic fraction, and can potentially serve as a non-invasive imaging surrogate for the in vivo assessment of necrotic fraction.

Preparation of [18F]-N-(2-fluoro-ethyl)-N-methylamine as a building block for PET radiopharmaceuticals.

We have investigated the use of cyclic sulfamidates as precursors to yield secondary amines as building blocks for subsequent reaction with carboxylic acids and acyl chlorides. The preparation of the protonated form of [(18)F]-N-(2-fluoro-ethyl)-N-methylamine from the corresponding cyclic sulfamidate proceeded within a one pot two-step procedure (81 ± 12%, n = 10). The secondary amine reacted readily with acyl chlorides and/or carboxylic acids giving amides with yields ranging from 4 to 17% at the end of synthesis (182 ± 12 min). The new methodology provides a practical approach for the labelling of molecules where intramolecular cyclisation of precursors is favoured under typical radiofluorination conditions.

Cinpanemab in Early Parkinson Disease: Evaluation of Biomarker Results From the Phase 2 SPARK Clinical Trial.

BACKGROUND AND OBJECTIVES: Sensitive, reliable, and scalable biomarkers are needed to accelerate the development of therapies for Parkinson disease (PD). In this study, we evaluate the biomarkers of early PD diagnosis, disease progression, and treatment effect collected in the SPARK. METHODS: Cinpanemab is a human-derived monoclonal antibody binding preferentially to aggregated forms of extracellular α-synuclein. SPARK was a randomized, double-blind, placebo-controlled, phase 2 multicenter trial evaluating 3 cinpanemab doses administered intravenously every 4 weeks for 52 weeks with an active treatment dose-blind extension period for up to 112 weeks. SPARK enrolled 357 participants diagnosed with PD within 3 years, aged 40-80 years, ≤2.5 on the modified Hoehn and Yahr scale, and with evidence of striatal dopaminergic deficit. The primary outcome was change from baseline in the Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale total score. Secondary and exploratory biomarker outcomes evaluated change from baseline at week 52 relative to placebo. Dopamine transporter SPECT and MRI were used to quantify changes in the nigrostriatal dopamine pathway and regional atrophy. CSF and plasma samples were used to assess change in total α-synuclein levels, α-synuclein seeding, and neurofilament light chain levels. SPARK was conducted from January 2018 to April 2021 and terminated due to lack of efficacy. RESULTS: Approximately 3.8% (15/398) of SPECT-imaged participants did not have evidence of dopaminergic deficit and were screen-failed. Binary classification of α-synuclein seeding designated 93% (110/118) of the enrolled CSF subgroup as positive for α-synuclein seeds at baseline. Clinical disease progression was observed, with no statistically significant difference in cinpanemab groups compared with that in placebo. Ninety-nine percent of participants with positive α-synuclein seeding remained positive through week 52. No statistically significant changes from baseline were observed between treatment groups and placebo across biomarker measures. Broadly, there was minimal annual change with high interindividual variability across biomarkers-with striatal binding ratios of the ipsilateral putamen showing the greatest mean change/SD over time. DISCUSSION: Biomarker results indicated enrollment of the intended population with early PD, but there was no significant correlation with disease progression or clear evidence of a cinpanemab treatment effect on biomarker measures. Suitable biomarkers for evaluating disease severity and progression in early PD trials are still needed. TRIAL REGISTRATION INFORMATION: NCT03318523 (clinicaltrials.gov/ct2/show/NCT03318523); Submitted October 24, 2017; First patient enrolled January 2018.

Development of a Novel [11C]CO-Labeled Positron Emission Tomography Radioligand [11C]BIO-1819578 for the Detection of O-GlcNAcase Enzyme Activity.

Imaging O-GlcNAcase OGA by positron emission tomography (PET) could provide information on the pathophysiological pathway of neurodegenerative diseases and important information on drug-target engagement and be helpful in dose selection of therapeutic drugs. Our aim was to develop an efficient synthetic method for labeling BIO-1819578 with carbon-11 using 11CO for evaluation of its potential to measure levels of OGA enzyme in non-human primate (NHP) brain using PET. Radiolabeling was achieved in one-pot via a carbon-11 carbonylation reaction using [11C]CO. The detailed regional brain distribution of [11C]BIO-1819578 binding was evaluated using PET measurements in NHPs. Brain radioactivity was measured for 93 min using a high-resolution PET system, and radiometabolites were measured in monkey plasma using gradient radio HPLC. Radiolabeling of [11C]BIO-1819578 was successfully accomplished, and the product was found to be stable at 1 h after formulation. [11C]BIO-1819578 was characterized in the cynomolgus monkey brain where a high brain uptake was found (7 SUV at 4 min). A pronounced pretreatment effect was found, indicating specific binding to OGA enzyme. Radiolabeling of [11C]BIO-1819578 with [11C]CO was successfully accomplished. [11C]BIO-1819578 binds specifically to OGA enzyme. The results suggest that [11C]BIO-1819578 is a potential radioligand for imaging and for measuring target engagement of OGA in the human brain.

A Visual Interpretation Algorithm for Assessing Brain Tauopathy with 18F-MK-6240 PET.

In vivo characterization of pathologic deposition of tau protein in the human brain by PET imaging is a promising tool in drug development trials of Alzheimer disease (AD). 6-(fluoro-18F)-3-(1H-pyrrolo[2,3-c]pyridin-1-yl)isoquinolin-5-amine (18F-MK-6240) is a radiotracer with high selectivity and subnanomolar affinity for neurofibrillary tangles that shows favorable nonspecific brain penetration and excellent kinetic properties. The purpose of the present investigation was to develop a visual assessment method that provides both an overall assessment of brain tauopathy and regional characterization of abnormal tau deposition. Methods: 18F-MK-6240 scans from 102 participants (including cognitively normal volunteers and patients with AD or other neurodegenerative disorders) were reviewed by an expert nuclear medicine physician masked to each participant's diagnosis to identify common patterns of brain uptake. This initial visual read method was field-tested in a separate, nonoverlapping cohort of 102 participants, with 2 additional naïve readers trained on the method. Visual read outcomes were compared with semiquantitative assessments using volume-of-interest SUV ratio. Results: For the visual read, the readers assessed 8 gray-matter regions per hemisphere as negative (no abnormal uptake) or positive (1%-25% of the region involved, 25%-75% involvement, or >75% involvement) and then characterized the tau binding pattern as positive or negative for evidence of tau and, if positive, whether brain uptake was in an AD pattern. The readers demonstrated agreement 94% of the time for overall positivity or negativity. Concordance on the determination of regional binary outcomes (negative or positive) showed agreement of 74.3% and a Fleiss κ of 0.912. Using clinical diagnosis as the ground truth, the readers demonstrated a sensitivity of 73%-79% and specificity of 91%-93%, with a combined reader-concordance sensitivity of 80% and specificity of 93%. The average SUV ratio in cortical regions showed a robust correlation with visually derived ratings of regional involvement (r = 0.73, P < 0.0001). Conclusion: We developed a visual read algorithm for 18F-MK-6240 PET offering determination of both scan positivity and the regional degree of cortical involvement. These cross-sectional results show strong interreader concordance on both binary and regional assessments of tau deposition, as well as good sensitivity and excellent specificity supporting use as a tool for clinical trials.

Development of a PET Tracer for OGA with Improved Kinetics in the Living Brain.

O-GlcNAcylation is thought to play a role in the development of tau pathology in Alzheimer's disease because of its ability to modulate tau's aggregation propensity. O-GlcNAcylation is regulated by 2 enzymes: O-GlcNAc transferase and O-GlcNAcase (OGA). Development of a PET tracer would therefore be an essential tool for developing therapeutic small-molecule inhibitors of OGA, enabling clinical testing of target engagement and dose selection. Methods: A collection of small-molecule compounds was screened for inhibitory activity and high-affinity binding to OGA, as well as favorable PET tracer attributes (multidrug resistance protein 1 efflux, central nervous system PET multiparameter optimization, etc.). Two lead compounds with high affinity and selectivity for OGA were selected for further profiling, including OGA binding to tissue homogenate using a radioligand competition binding assay. In vivo pharmacokinetics were established using a microdosing approach with unlabeled compounds in rats. In vivo imaging studies were performed in rodents and nonhuman primates (NHPs) with 11C-labeled compounds. Results: Two selected candidates, BIO-735 and BIO-578, displayed promising attributes in vitro. After radiolabeling with tritium, [3H]BIO-735 and [3H]BIO-578 binding in rodent brain homogenates demonstrated dissociation constants of 0.6 and 2.3 nM, respectively. Binding was inhibited, concentration-dependently, by homologous compounds and thiamet G, a well-characterized and structurally diverse OGA inhibitor. Imaging studies in rats and NHPs showed both tracers had high uptake in the brain and inhibition of binding to OGA in the presence of a nonradioactive compound. However, only BIO-578 demonstrated reversible binding kinetics within the time frame of a PET study with a 11C-labeled molecule to enable quantification using kinetic modeling. Specificity of tracer uptake was confirmed with a 10 mg/kg blocking dose of thiamet G. Conclusion: We describe the development and testing of 2 11C PET tracers targeting the protein OGA. The lead compound BIO-578 demonstrated high affinity and selectivity for OGA in rodent and human postmortem brain tissue, leading to its further testing in NHPs. NHP PET imaging studies showed that the tracer had excellent brain kinetics, with full inhibition of specific binding by thiamet G. These results suggest that the tracer [11C]BIO-578 is well suited for further characterization in humans.

Exploratory Tau Biomarker Results From a Multiple Ascending-Dose Study of BIIB080 in Alzheimer Disease: A Randomized Clinical Trial.

Importance: Accumulation of hyperphosphorylated, tangled microtubule-associated protein tau (MAPT) is a pathological hallmark of Alzheimer disease (AD) associated with disease progression and cognitive decline. Objective: To evaluate the effect of tau synthesis reduction on tau biomarkers in patients with mild AD. Design, Setting, and Participants: This randomized clinical trial was a double-blind, placebo-controlled 36-week multiple-ascending dose (MAD) phase 1b trial (October 2017 to September 2020), followed by a 64- or 71-week open-label long-term extension (LTE) (October 2019 to May 2022). After being assessed for eligibility at 12 sites in Canada and Europe, participants with mild AD and confirmed amyloid pathology were randomized 3:1 (BIIB080:placebo) in 4 dose cohorts. Intervention: Intrathecal administration of BIIB080, a MAPT-targeting antisense oligonucleotide, or placebo. Active dose arms included 10 mg every 4 weeks, 30 mg every 4 weeks, 60 mg every 4 weeks, and 115 mg every 12 weeks during the MAD period and 60 mg every 12 weeks or 115 mg every 12 weeks during the LTE. Main Outcome and Measures: The original primary end point was safety. Additionally, BIIB080, total tau (t-tau), and phosphorylated tau 181 (p-tau181) cerebrospinal fluid (CSF) concentrations were evaluated. Tau positron emission tomography (PET) was collected in a substudy, and standard uptake value ratios (SUVRs) were calculated in a priori-defined composite regions of interest. Results: Of 102 participants assessed for eligibility, 46 participants with mild AD were enrolled; 23 (50%) were female, and mean (SD) age was 65.8 (5.70) years. BIIB080 was generally well tolerated and was associated with a dose-dependent reduction in CSF t-tau and p-tau181 in the MAD period (56% reduction; 95% CI, 50% to 62%; and 51% reduction; 95% CI, 38% to 63%, of CSF t-tau in the 2 higher-dose cohorts) that continued and/or was maintained through quarterly dosing in the LTE. Tau PET demonstrated reduced accumulation vs placebo at week 25 (n = 13). At week 100, tau PET showed a reduction from baseline across all regions assessed (n = 12), with the largest reductions from baseline observed in the temporal composite (-0.71 SUVR; 95% CI, -1.40 to -0.02). A moderate correlation was observed between model-predicted cumulative CSF drug exposure and tau PET change. Conclusions and Relevance: In this randomized clinical trial, BIIB080 reduced tau biomarkers, including CSF t-tau, CSF p-tau181, and tau PET, which is associated with cognitive decline, in participants with mild AD. Effects of BIIB080 on biomarkers and clinical outcomes are being further evaluated in a phase 2 trial. Trial Registration: ClinicalTrials.gov Identifier: NCT03186989.

Non-invasive Imaging of Antisense Oligonucleotides in the Brain via In Vivo Click Chemistry.

PURPOSE: The treatment of complex neurological diseases often requires the administration of large therapeutic drugs, such as antisense oligonucleotide (ASO), by lumbar puncture into the intrathecal space in order to bypass the blood-brain barrier. Despite the growing number of ASOs in clinical development, there are still uncertainties regarding their dosing, primarily around their distribution and kinetics in the brain following intrathecal injection. The challenge of taking measurements within the delicate structures of the central nervous system (CNS) necessitates the use of non-invasive nuclear imaging, such as positron emission tomography (PET). Herein, an emergent strategy known as "pretargeted imaging" is applied to image the distribution of an ASO in the brain by developing a novel PET tracer, [18F]F-537-Tz. This tracer is able to undergo an in vivo "click" reaction, covalently binding to a trans-cyclooctene conjugated ASO. PROCEDURES: A novel small molecule tracer for pretargeted PET imaging of ASOs in the CNS is developed and tested in a series of in vitro and in vivo experiments, including biodistribution in rats and non-human primates. RESULTS: In vitro data and extensive in vivo rat data demonstrated delivery of the tracer to the CNS, and its successful ligation to its ASO target in the brain. In an NHP study, the slow tracer kinetics did not allow for specific binding to be determined by PET. CONCLUSION: A CNS-penetrant radioligand for pretargeted imaging was successfully demonstrated in a proof-of-concept study in rats, laying the groundwork for further optimization.

Widespread cell stress and mitochondrial dysfunction occur in patients with early Alzheimer's disease.

Cell stress and impaired oxidative phosphorylation are central to mechanisms of synaptic loss and neurodegeneration in the cellular pathology of Alzheimer's disease (AD). In this study, we quantified the in vivo expression of the endoplasmic reticulum stress marker, sigma 1 receptor (S1R), using [11C]SA4503 positron emission tomography (PET), the mitochondrial complex I (MC1) with [18F]BCPP-EF, and the presynaptic vesicular protein SV2A with [11C]UCB-J in 12 patients with early AD and in 16 cognitively normal controls. We integrated these molecular measures with assessments of regional brain volumes and cerebral blood flow (CBF) measured with magnetic resonance imaging arterial spin labeling. Eight patients with AD were followed longitudinally to estimate the rate of change of the physiological and structural pathology markers with disease progression. The patients showed widespread increases in S1R (≤ 27%) and regional reduction in MC1 (≥ -28%) and SV2A (≥ -25%) radioligand binding, brain volume (≥ -23%), and CBF (≥ -26%). [18F]BCPP-EF PET MC1 binding (≥ -12%) and brain volumes (≥ -5%) showed progressive reductions over 12 to 18 months, suggesting that they both could be used as pharmacodynamic indicators in early-stage therapeutics trials. Associations of reduced MC1 and SV2A and increased S1R radioligand binding with reduced cognitive performance in AD, although exploratory, suggested a loss of metabolic functional reserve with disease. Our study thus provides in vivo evidence for widespread, clinically relevant cellular stress and bioenergetic abnormalities in early AD.

Microfluidic reactions using [11C]carbon monoxide solutions for the synthesis of a positron emission tomography radiotracer.

Microfluidic technology has been used to perform [(11)C]carbonylation reactions using solutions containing [(11)C]CO in the form of the complex, copper(i)tris(3,5-dimethylpyrazolyl)borate-[(11)C]carbonyl (Cu(Tp*)[(11)C]CO). The synthesis of the model compound [(11)C]N-benzylbenzamide and the known tracer molecule [(11)C]trans-N-[5-(2-flurophenyl)-2-pyrimidinyl]-3-oxospiro[5-azaisobenzofurane-1(3H),1'-cyclohexane]-4'-carboxamide ([(11)C]MK-0233), a ligand for the neuropeptide Y Y5 receptor, have been performed using this technique. Following semi-preparative HPLC purification and reformulation, 1262 ± 113 MBq of [(11)C]MK-0233 was produced at the end of the synthesis with a specific activity of 100 ± 30 GBq µmol(-1) and a >99% radiochemical purity. This corresponds to a decay corrected radiochemical yield of 7.2 ± 0.7%. Using a 3 mL vial as the reaction vessel, and following semi-preparative HPLC purification and reformulation, 1255 ± 392 MBq of [(11)C]MK-0233 was produced at the end of the synthesis with a specific activity of 100 ± 15 GBq µmol(-1) and a >99% radiochemical purity. This corresponds to a decay corrected radiochemical yield of 7.1 ± 2.2%.

Test-retest characteristic of [18F]MK-6240 quantitative outcomes in cognitively normal adults and subjects with Alzheimer's disease.

[18F]MK-6240 is a selective, high-affinity PET radiotracer for imaging neurofibrillary tangles (NFT) in Alzheimer's disease (AD). Herein, we report test-retest (T-RT) reproducibility of [18F]MK-6240 in AD and healthy volunteers (HV). Twelve subjects with AD and three cognitively normal HV were enrolled in the study and dynamically scanned for 150 min with [18F]MK-6240 under a T-RT protocol. Two radioactivity doses were investigated: 165 ± 3 MBq (n = 6) and 300 ± 40 MBq (n = 9). Serial arterial blood samples were taken for each scan to obtain metabolite-corrected input functions. Following intravenous administration of [18F]MK-6240, the tracer rapidly partitioned into the brain and its heterogenous distribution pattern was consistent with known NFT pathology in AD. In contrast, uptake in HV was low and uniform across the brain parenchyma. Across all subjects, average T-RT variabilities in NFT-rich regions were ∼21%, ∼14% and ∼6% for various quantitative metrics: total distribution volume (VT), binding potential (BPND), and standardized uptake ratio (SUVR90-120), respectively. No significant differences in SUVR T-RT variability were observed between the high and low injected radioactivity groups (5.6% and 6.1%, respectively). This work suggests [18F]MK-6240 has adequate SUVR T-RT characteristics supporting the use of this outcome in future studies.

Copper(I) scorpionate complexes and their application in palladium-mediated [(11)C]carbonylation reactions.

Solutions of copper(I) tris(pyrazolyl)borate complexes have been used to greatly improve the solubility of [(11)C]carbon monoxide, enabling it to be used in low-pressure, 'one-pot' palladium-mediated carbonylation reactions to form (11)C-radiolabelled amides and ureas for use in positron emission tomography.

Structural Basis for Achieving GSK-3ß Inhibition with High Potency, Selectivity, and Brain Exposure for Positron Emission Tomography Imaging and Drug Discovery.

Using structure-guided design, several cell based assays, and microdosed positron emission tomography (PET) imaging, we identified a series of highly potent, selective, and brain-penetrant oxazole-4-carboxamide-based inhibitors of glycogen synthase kinase-3 (GSK-3). An isotopologue of our first-generation lead, [3H]PF-367, demonstrates selective and specific target engagement in vitro, irrespective of the activation state. We discovered substantial ubiquitous GSK-3-specific radioligand binding in Tg2576 Alzheimer's disease (AD), suggesting application for these compounds in AD diagnosis and identified [11C]OCM-44 as our lead GSK-3 radiotracer, with optimized brain uptake by PET imaging in nonhuman primates. GSK-3ß-isozyme selectivity was assessed to reveal OCM-51, the most potent (IC50 = 0.030 nM) and selective (>10-fold GSK-3ß/GSK-3α) GSK-3ß inhibitor known to date. Inhibition of CRMP2T514 and tau phosphorylation, as well as favorable therapeutic window against WNT/ß-catenin signaling activation, was observed in cells.

Molecular imaging in oncology drug development.

Tremendous breakthroughs are being made in cancer drug discovery and development. However, such breakthroughs come at a high financial cost. At a time when there is increasing pressure on drug pricing, in part because of increased life expectancy, it is more important than ever to drive new therapeutics towards patients as efficiently as possible. In this review we discuss the applications of molecular imaging in oncology drug development, with a focus on its ability to enable better early decision making, to increase efficiency and thereby to lower costs.

Fluorinase mediated C-(18)F bond formation, an enzymatic tool for PET labelling.

The fluorinase enzyme from S. cattleya is applied as a catalyst for the efficient incorporation of [18F]-fluoride into [18F]-5'-fluoro-5'-deoxyadenosine, [18F]-5'-fluoro-5'-deoxyinosine and [18F]-5-fluoro-5-deoxyribose for positron emission tomography (PET) applications.

Synthesis, radiosynthesis, and biological evaluation of carbon-11 and fluorine-18 (N-fluoroalkyl) labeled 2beta-carbomethoxy-3beta-(4'-(3-furyl)phenyl)tropanes and -nortropanes: candidate radioligands for in vivo imaging of the serotonin transporter with positron emission tomography.

2beta-Carbomethoxy-3beta-(4'-(3-furyl)phenyl)nortropane (1) was synthesized along with the N-methyl (2), N-fluoroethyl (3), N-fluoropropyl (4), and N-fluorobutyl (5) derivatives. The binding affinity for each compound to the human serotonin, dopamine, and norepinephrine transporters was determined using transfected HEK-293 cells. Radiolabeling and microPET brain imaging studies were performed with [(11)C]1, [(11)C]2, and [(18)F]3 to determine their utility as in vivo imaging agents.

Human Kinetic Modeling of the 5HT6 PET Radioligand 11C-GSK215083 and Its Utility for Determining Occupancy at Both 5HT6 and 5HT2A Receptors by SB742457 as a Potential Therapeutic Mechanism of Action in Alzheimer Disease.

UNLABELLED: Antagonism of 5-hydroxytrypamine-6 (5HT6) receptors is associated with procognitive effects in preclinical species, suggesting a therapeutic potential for this mechanism in Alzheimer disease (AD) and other cognitive diseases. In a phase 2 dose study, SB742457, a novel 5HT6 antagonist, showed increasing procognitive effects in patients with AD as the dose increased, with a procognitive signal in AD patients at a dose of 35 mg/d superior to the other doses tested (5 and 15 mg/d). METHODS: In this article, we describe the quantification and pharmacologic selectivity of a new 5HT6 PET ligand ((11)C-GSK215083) in healthy volunteers and its use to measure occupancies achieved at various doses of SB742457. RESULTS: Kinetic analysis of (11)C-GSK215083 uptake in the human brain demonstrated the multilinear model, MA2, to represent the method of choice when a blood input was available and the full tissue reference method when no input was available. Pharmacologic dissection of the in vivo (11)C-GSK215083-specific binding showed the ligand bound mostly the 5HT6 in the striatum (blocked by SB742457 but not by the selective 5-hydroxytryptamine-2A (5HT2A) antagonist ketanserin) and the 5HT2A in the frontal cortex (blocked by both ketanserin and SB742457). Repeated administration of SB742457 (3, 15, and 35 mg/d) saturated the 5HT6 receptors at all doses. In the cortex, 5HT2A receptor occupancy was 24% ± 6% (3 mg/d), 35% ± 4% (15 mg/d), and 58% ± 19% (35 mg/d; mean ± SD), suggesting a progressive engagement of 5HT2A as the dose increased. CONCLUSION: Collectively, these data support the use of (11)C-GSK215083 as a 5HT6 clinical imaging tool and suggest that blocking both the 5HT6 and the 5HT2A receptors may be required for the optimal therapeutic action of SB742457 in AD.

Intravoxel incoherent imaging of renal fibrosis induced in a murine model of unilateral ureteral obstruction.

PURPOSE: To evaluate non-invasive imaging biomarkers for assessing renal fibrosis. DWI is used to assess renal function; intravoxel incoherent motion (IVIM) provides additional measures of perfusion-related diffusion (D*, blood flow; f, perfusion fraction). We aim to determine if reduced ADC seen in renal fibrosis is attributable to perfusion-related diffusion changes or to known reduction in tissue diffusivity (D). MATERIALS AND METHODS: Unilateral ureteral obstruction (UUO) was created in six mice to induce renal fibrosis. DWI was performed the day before and 7 days post-UUO. A range of b-values from 0 to 1200 s/mm(2) were used. IVIM parameters were obtained using region of interests drawn over the renal parenchyma. Histopathological analysis of both kidneys was performed in all mice. Results were analyzed using the paired t-test with P<0.05 considered statistically significant. RESULTS: D and f were significantly lower in the ligated kidneys at Day 7 compared to before ligation and no significant difference was found for D*. Comparing non-ligated and ligated kidneys within the same mouse at Day 7, significantly lower D values were observed in the ligated kidneys, while no significant difference was found for f and D*, although the values of f were generally lower. Histopathological analysis confirmed development of fibrosis and reduction in glomeruli in all the ligated kidneys at Day 7. CONCLUSION: Our study shows that the reduction in ADC seen in renal fibrosis is attributable not only to reduced D as previously encountered but also a decrease in vascularity as assessed by f. Reduction in f is possibly related to a reduction in glomeruli.

Radiolabeled amino acids for tumor imaging with PET: radiosynthesis and biological evaluation of 2-amino-3-[18F]fluoro-2-methylpropanoic acid and 3-[18F]fluoro-2-methyl-2-(methylamino)propanoic acid.

Novel radiopharmaceuticals, including amino acids, that target neoplasms through their altered metabolic states have shown promising results in preclinical and clinical studies. Two fluorinated analogues of alpha-aminoisobutyric acid, 2-amino-3-fluoro-2-methylpropanoic acid (FAMP) and 3-fluoro-2-methyl-2-(methylamino)propanoic acid (N-MeFAMP), have been radiolabeled with fluorine-18, characterized in amino acid uptake assays, and evaluated in vivo in normal rats and a rodent tumor model. The key steps in the syntheses of both radiotracers involved the preparation of cyclic sulfamidate precursors. Radiosyntheses of both [18F]FAMP and [18F]N-MeFAMP via no-carrier-added nucleophilic substitution provided high yields (>78% decay-corrected) in high radiochemical purity (>99%). Amino acid transport assays using 9L gliosarcoma cells demonstrated that both compounds are substrates for the A type amino acid transport system, with [18F]N-MeFAMP showing higher specificity than [18F]FAMP for A type transport. Tissue distribution studies in normal Fischer rats and Fischer rats implanted intracranially with 9L gliosarcoma tumor cells were also performed. At 60 min postinjection, the tumor vs normal brain ratio of radioactivity was 36:1 in animals receiving [18F]FAMP and 104:1 in animals receiving [18F]N-MeFAMP. On the basis of these studies, both [18F]FAMP and [18F]N-MeFAMP are promising imaging agents for the detection of intracranial neoplasms via positron emission tomography.

Synthesis of syn- and anti-1-amino-3-[18F]fluoromethyl-cyclobutane-1-carboxylic acid (FMACBC), potential PET ligands for tumor detection.

syn- and anti-1-amino-3-[18F]fluoromethyl-cyclobutane-1-carboxylic acid (FMACBC, 16 and 17), analogues of anti-1-amino-3-[18F]fluorocyclobutyl-1-carboxylic acid (FACBC), were prepared to evaluate the contributions of C-3 substitution and configuration on the uptake of these radiolabeled amino acids in a rodent model of brain tumors. Radiofluorinated targets [18F]16 and [18F]17 were prepared by no-carrier-added radiofluorination from their corresponding methanesulfonyl esters 12 and 13, respectively, with decay-corrected radiochemical yields of 30% for [18F]16 and 20% for [18F]17. In amino acid transport assays performed in vitro using 9L gliosarcoma cells, both [18F]16 and [18F]17 were substrates for L type amino acid transport, while [18F]17 but not [18F]16 was a substrate for A type transport. Biodistribution studies in normal Fischer rats with [18F]16 and [18F]17 showed high uptake of radioactivity (>2.0% dose/g) in the pancreas while other tissues studied, including liver, heart, lung, kidney, blood, muscle, and testis, showed relatively low uptake of radioactivity (<1.0% dose/g). In rats implanted intracranially with 9L gliosarcoma cells, the retention of radioactivity in tumor tissue was high at 5, 60, and 120 min after intravenous injection of [18F]16 and [18F]17 while the uptake of radioactivity in brain tissue contralateral to the tumor remained low (<0.3% dose/g). Ratios of tumor uptake to normal brain uptake for [18F]16 were 7.5:1, 7:1, and 5:1 at 5, 60, and 120 min, respectively, while for [18F]17 the ratios were 7.5:1, 9:1, and 9:1 at the same time points. This work demonstrates that like anti-[18F]FACBC, [18F]16 and [18F]17 are excellent candidates for imaging brain tumors.