Automated segmentation of MR imaging to determine normative central nervous system cerebrospinal fluid volumes in healthy volunteers.

An accurate non-invasive method to determine total body cerebrospinal fluid volume has a number of potential diagnostic and therapeutic applications. Herein we describe a technique for automated segmentation of total body MRI data to determine cranial and spinal CSF volume in 15 healthy adults. These in vivo estimates of CSF volume exceed the standard reported volume of 150mL in human adults and provide normative data for diagnosis of disease states such as hydrocephalus and therapy including pharmacologic dosimetry. No correlation was observed between patient height or weight and total body CSF volume.

Cortical laminar binding of PET amyloid and tau tracers in Alzheimer disease.

UNLABELLED: Neurofibrillary tau pathology and amyloid ß (Aß) plaques, characteristic lesions of Alzheimer disease (AD), show different neocortical laminar distributions. Neurofibrillary-tangle tau pathology tends to be closer to the gray matter-white matter boundary, whereas Aß is dispersed throughout the width of the cortical ribbon. METHODS: Using PET radiotracers for tau and Aß lesions, we developed an image analysis tool to measure the distance of tracer-positive voxels from the gray matter-white matter boundary. We studied 5 AD and 5 healthy subjects with both (18)F-THK5117 (tau) and (11)C-Pittsburgh compound B (Aß) PET. RESULTS: On average, tau-positive voxels were closer to the white matter than were Aß-positive voxels. This effect was found for all AD subjects and for all regions, both before and after regionally adjusting for the nonspecific white matter binding of both tracers. The differential laminar pattern was validated through postmortem examination. CONCLUSION: Within cortical lamina, distance measures may be of value in testing PET tracers for their anatomic selectivity.

Variability in assessing treatment response: metastatic colorectal cancer as a paradigm.

PURPOSE: The cutoff values currently used to categorize tumor response to therapy are neither biologically based nor tailored for measurement reproducibility with contemporary imaging modalities. Sources and magnitudes of discordance in response assessment in metastatic colorectal cancer (mCRC) are unknown. EXPERIMENTAL DESIGN: A subset of patients' CT images of chest, abdomen, and pelvis were randomly chosen from a multicenter clinical trial evaluating insulin-like growth factor receptor type 1-targeted therapy in mCRC. Using Response Evaluation Criteria in Solid Tumors (RECIST), three radiologists selected target lesions and measured "uni" (maximal diameter), "bi" (product of maximal diameter and maximal perpendicular diameter), and "vol" (volume) on baseline and 6-week posttherapy scans in the following ways: (i) each radiologist independently selected and measured target lesions and (ii) one radiologist's target lesions were blindly remeasured by the others. Variability in relative change of tumor measurements was analyzed using linear mixed effects models. RESULTS: Three radiologists independently selected 138, 101, and 146 metastatic target lesions in the liver, lungs, lymph nodes, and other organs (e.g., peritoneal cavity) in 29 patients. Of 198 target lesions total, 33% were selected by all three, 28% by two, and 39% by one radiologist. With independent selection, the variability in relative change of tumor measurements was 11% (uni), 19% (bi), and 22% (vol), respectively. When measuring the same lesions, the corresponding numbers were 8%, 14%, and 12%. CONCLUSIONS: The relatively low variability in change of mCRC measurements suggests that response criteria could be modified to allow more accurate and sensitive CT assessment of anticancer therapy efficacy.

(11)C-MK-8278 PET as a tool for pharmacodynamic brain occupancy of histamine 3 receptor inverse agonists.

UNLABELLED: The histamine 3 (H3) receptor is a presynaptic autoreceptor in the central nervous system that regulates the synthesis and release of histamine and modulates the release of other major neurotransmitters. H3 receptor inverse agonists (IAs) may be efficacious in the treatment of various central nervous system disorders, including excessive daytime sleepiness, attention deficit hyperactivity disorder, Alzheimer disease, ethanol addiction, and obesity. METHODS: Using PET and a novel high-affinity and selective radioligand (11)C-MK-8278, we studied the tracer biodistribution, quantification, and brain H3 receptor occupancy (RO) of MK-0249 and MK-3134, 2 potential IA drugs targeting cerebral H3 receptors, in 6 healthy male subjects (age, 19-40 y). The relationship among H3 IA dose, time on target, and peripheral pharmacokinetics was further investigated in 15 healthy male volunteers (age, 18-40 y) with up to 3 PET scans and 3 subjects per dose level. RESULTS: The mean effective dose for (11)C-MK-8278 was 5.4 ± 1.1 µSv/MBq. Human brain kinetics showed rapid high uptake and fast washout. Binding potential values can be assessed using the pons as a reference region, with a test-retest repeatability of 7%. Drug RO data showed low interindividual variability per dose (mean RO SD, 2.1%), and a targeted 90% RO can be reached for both IAs at clinically feasible doses. CONCLUSION: (11)C-MK-8278 is a useful novel PET radioligand for determination of human cerebral H3 receptor binding and allows highly reproducible in vivo brain occupancy of H3-targeting drugs, hereby enabling the evaluation of novel compounds in early development to select doses and schedules.

Alteration of PHYA expression change circadian rhythms and timing of bud set in Populus.

In many temperate woody species, dormancy is induced by short photoperiods. Earlier studies have shown that the photoreceptor phytochrome A (phyA) promotes growth. Specifically, Populus plants that over-express the oat PHYA gene (oatPHYAox) show daylength-independent growth and do not become dormant. However, we show that oatPHYAox plants could be induced to set bud and become cold hardy by exposure to a shorter, non-24 h diurnal cycle that significantly alters the relative position between endogenous rhythms and perceived light/dark cycles. Furthermore, we describe studies in which the expression of endogenous Populus tremula x P. tremuloides PHYTOCHROME A (PttPHYA) was reduced in Populus trees by antisense inhibition. The antisense plants showed altered photoperiodic requirements, resulting in earlier growth cessation and bud formation in response to daylength shortening, an effect that was explained by an altered innate period that leads to phase changes of clock-associated genes such as PttCO2. Moreover, gene expression studies following far-red light pulses show a phyA-mediated repression of PttLHY1 and an induction of PttFKF1 and PttFT. We conclude that the level of PttPHYA expression strongly influences seasonally regulated growth in Populus and is central to co-ordination between internal clock-regulated rhythms and external light/dark cycles through its dual effect on the pace of clock rhythms and in light signaling.

Development of the 2nd generation neurokinin-1 receptor antagonist LY686017 for social anxiety disorder.

The neurokinin-1 (NK-1) antagonist LY686017 showed activity in preclinical anxiety models. The clinical development of LY686017 included a PET study and a proof-of-concept in social anxiety disorder (SAD). [(11)C]GR205171 was used healthy volunteers receiving 1-100mg/d LY686017 for 28 days to determine brain receptor occupancy (RO). The mean NK-1 RO increased ranged from 25% with 1mg to 93% with 100mg. Subsequently, a 12-week randomized clinical trial tested LY686017 vs. paroxetine, or placebo in SAD. Pharmacokinetic (PK)/RO modeling based on the PET results predicted that once daily dosing of >30mg LY686017 led to sustained trough RO of over 80%. 189 outpatients(1) suffering from SAD were randomly assigned to 12-weeks treatment with 50mg/d LY686017 (N=77), placebo (N=74), or 20mg/d paroxetine (N=38). There was no significant difference between LY686017 and placebo as measured with the Liebowitz Social Anxiety scale (LSAS). The active comparator paroxetine showed positive trends on primary and secondary measures. The plasma concentrations were above the level expected to produce maximal brain NK-1 RO based on the PK/RO relationship obtained in the human PET investigation. Thus, further evaluation of LY686017 for the treatment of SAD does not seem warranted.

Striatal dopamine transporter imaging correlates with anxiety and depression symptoms in Parkinson's disease.

UNLABELLED: We studied the correlation of striatal dopamine transporter (DAT) imaging with anxiety and depression symptoms in Parkinson's disease (PD). METHODS: Patients with idiopathic PD (n = 76) and age-matched healthy volunteers (n = 46) underwent SPECT brain scans with (99m)Tc-TRODAT-1, a radiolabeled tropane that selectively binds to the DAT. TRODAT-1 distribution volume ratios, a reflection of DAT availability, were calculated from the SPECT scan data for 6 regions of interest (ROIs) in the caudate and putamen. The association between neuropsychiatric symptoms (anxiety, depression, and fatigue) and DAT availability was explored for both subject groups, and the impact of disease severity on this association was examined in the PD group. RESULTS: PD patients showed lower DAT availability than did healthy volunteers in all examined regions (for all ROIs, P < 0.001). In PD patients, higher individual affective measures (for anxiety, r = -0.30 and P = 0.01; and for depression, r = -0.24 and P = 0.05) and total affect scores (r = -0.31; P = 0.01) were associated with diminished left anterior putamen DAT availability. The association between total affect scores and DAT availability was present only in the subset of patients with less severe PD (r = -0.35; P = 0.04), but subjects with the highest DAT availability did not show high total affect scores. No association between neuropsychiatric measures and DAT availability was found in the controls. CONCLUSION: These preliminary findings suggest that decreased DAT availability may be necessary for but not invariably associated with the development of affective symptoms in PD. This suggestion is consistent with previous research showing a link between depression and basal ganglia impairment, particularly involving the left hemisphere, and extends this finding to include anxiety.

Synthesis and in vivo evaluation of novel radiotracers for the in vivo imaging of the norepinephrine transporter.

The (R,R) and (S,S) enantiomers of 2-[(2-methoxyphenoxy)phenylmethyl]morpholine (MeNER) have been radiolabelled with carbon-11 in good yield and at high specific activity. These radiotracers are close analogues of reboxetine, a potent and selective ligand for the norepinephrine transporter (NET). They were examined as potential ligands for imaging NET in vivo by positron emission tomography (PET). The in vivo brain distribution of both [(11)C]-labeled enantiomers were evaluated in rats. Following tail-vein injection of the (R,R)-enantiomer regional brain uptake and washout of radioactivity was homogeneous at all time points examined (5-60 min). In contrast, administration of the (S,S)-enantiomer produced a heterogeneous distribution of radioactivity in brain with highest uptake in the hypothalamus, a NET rich region, and lowest uptake in the striatum, a brain region devoid of NET. Hypothalamus to striatum ratios of 2.5 to one were achieved at 60 min post injection of (S,S)-[(11)C]-MeNER. Pre-injection of the norepinephrine reuptake inhibitors, reboxetine or desipramine, reduced hypothalamus to striatum ratios to near unity while reuptake inhibitors of dopamine and serotonin had no significant effect on binding. In vitro autoradiography studies (rat brain slices) with (S,S)-[(11)C]-MeNER produced a regional distribution pattern that was consistent with the reported distribution of NET. (S,S)-[(11)C]-MeNER has the potential to be the first successful PET ligand to image NET.