2-3-dihydro-1h-imidazo(1-2-b)pyrazole and Alzheimer-Disease

Successful development of iodinated ligands for various neurotransmitter receptors prompted us to explore the feasability of having iodinated ligands to target amyloid plaques of Alzheimer's disease. Several potential iodinated tracers based on various chemical backbone structures have been successfully prepared and evaluated toward this purpose. High binding affinities for Abeta aggregates were consistently observed for those ligands. However, the desirable in vivo properties were generally missing in the majority of those iodinated ligands. Only ligands with the promising in vitro and in vivo characteristics such as IMPY will likely warrant their success to be potential imaging agents mapping amyloid plaques in living human brain.

Topics: Alzheimer Disease; Animals; Binding, Competitive; Brain; Humans; Iodine Radioisotopes; Ligands; Mice; Molecular Probes; Plaque, Amyloid; Pyrazoles; Tomography, Emission-Computed, Single-Photon

Non-invasive determination of amyloid-β peptide (Aβ) deposition has important significance for early diagnosis and medical intervention in Alzheimer's disease (AD). In this study, we investigated the availability of a radioiodinated imidazo[1,2-a]pyridine derivative, termed (125)I-DRK092, as single photon emission computed tomography (SPECT) ligand for in vivo detection of Aβ deposition. DRK092 showed high binding affinity for either synthetic human Aβ fibrils or brain homogenates from amyloid precursor protein transgenic (Tg) mouse (PS1-ki/JU-Tg2576) and AD patient with a dissociation constant (Kd) of one-digit nM, and excellent brain permeability (peak value of uptake: approximately 0.9% of injection dose/g rat brain). Ex vivo autoradiographic analysis showed that measurement with (125)I-DRK092 has higher sensibility for detecting Aβ accumulation than with (125)I-IMPY, a well-known amyloid SPECT ligand, in Tg mice. In vitro autoradiography with (125)I-DRK092 also confirmed higher accumulation of radioactivity in the cortical area, enriched with Aβ plaques, of Tg mouse and AD patient brains, as compared with the corresponding areas in non-Tg mouse and healthy control brains. All the data presented above lead us to draw the conclusion that radioiodinated DRK092 is a potential SPECT ligand for amyloid imaging in AD.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Autoradiography; Brain; Disease Models, Animal; Humans; Imidazoles; Iodine Radioisotopes; Mice; Plaque, Amyloid; Pyrazoles; Pyridines; Rats; Tomography, Emission-Computed, Single-Photon

Metal ions associated with amyloid-β (Aβ) species have been suggested to be involved in neurodegeneration leading to the progression of Alzheimer's disease (AD). The role of metal-involved Aβ species in AD neuropathogenesis, however, is not fully elucidated. In order to advance this understanding and contribute to the therapeutic development for AD, the rational structure-based design of small molecules that specifically target metal ions surrounded by Aβ species has recently received increased attention. To date, only a few compounds have been fashioned for this purpose. Herein, we report the design strategy, synthesis, characterization, and reactivity of new bifunctional IMPY derivatives K1 and K2. Using UV-vis and high-resolution two-dimensional (2D) NMR spectroscopy, the bifunctionality of K1 and K2 (metal chelation and Aβ interaction) was confirmed. These bifunctional IMPY derivatives showed preferential reactivity toward metal-induced Aβ aggregation over metal-free conditions in both in vitro inhibition and disaggregation experiments. Taken together, this study provides another example of a bifunctional small molecule framework that can target metal ions associated with Aβ species.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Chelating Agents; Drug Design; Humans; Metals; Pyrazoles; Pyridines

A series of chaclone derivatives containing an indole moiety were evaluated in competitive binding assays with Aβ(1-42) aggregates versus [(125)I]IMPY. The affinity of these compounds ranged from 4.46 to >1008 nM, depending on the substitution on the phenyl ring. Fluorescent staining in vitro showed that one compound with a N,N-dimethylamino group intensely stained Aβ plaques within brain sections of AD transgenic mice. The radioiodinated probe [(125)I]-(E)-3-(1H-indol-5-yl)-1-(4-iodophenyl)prop-2-en-1-one, [(125)I]4, was prepared and autoradiography in sections of brain tissue from an animal model of AD showed that it labeled Aβ plaques specifically. However, experiments with normal mice indicated that [(125)I]4 exhibited a low uptake into the brain in vivo (0.41% ID/g at 2 min). Additional chemical modifications of this indole-chalcone structure may lead to more useful imaging agents for detecting β-amyloid plaques in the brains of AD patients.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Autoradiography; Chalcone; Fluorescent Dyes; Indoles; Iodine Radioisotopes; Mice; Mice, Transgenic; Microscopy, Fluorescence; Peptide Fragments; Pyrazoles; Radionuclide Imaging; Tissue Distribution

Recently, the feasibility of detecting amyloid plaques in the living brain by positron emission tomography (PET) imaging has been successfully demonstrated. As such, imaging beta-amyloid (A beta) plaques in the brain may further advance the differential diagnosis of the disease and allow clinicians to measure the effectiveness of therapeutic drugs aimed at lowering plaques in the brain. We report herein the preclinical validation of a potential (18)F-labeled biphenylalkyne, AV-138, as a preliminary step toward developing the imaging agent for patients suspected of having Alzheimer's disease.. In vitro binding was carried out in the homogenates prepared from postmortem AD brains with [(125)I]IMPY as the radioligand. [(18)F]AV-138 was successfully prepared using a tosylate precursor and Sumitomo modules for radiosynthesis. Similarly, specific binding of [(18)F]AV-138 (0.02-0.05 nM) to homogenates, prepared from gray and white matters of pooled AD patients and control subjects, was performed. Specific binding to A beta plaques was measured by autoradiography in AD brain sections (n=11), and the same brain sections were fluorescently stained with thioflavin-S (TF-S). Images of both radiolabeling and fluorescent staining of plaques obtained by a phosphor imager were used for correlation image analysis.. As expected, AV-138 displayed a high binding affinity (K(i)=2.4+/-0.7 nM) in AD gray matter homogenates (due to its high level of A beta plaque accumulation). Specific binding can be clearly measured in the AD gray matter homogenates, but not in the AD white matters. Control brain homogenates, due to a lack of A beta plaques, also showed no specific binding. Furthermore, in vitro autoradiography of postmortem AD brain sections showed that the high binding signal of [(18)F]AV-138 was specifically due to A beta plaques. Fluorescent staining of plaques with TF-S correlated well with the radiolabeling of [(18)F]AV-138 in AD brain sections (r>0.90).. Taken together, these preliminary results strongly suggest that [(18)F]AV-138 is potentially useful for imaging A beta plaques in the living human brain.

Topics: Alkynes; Alzheimer Disease; Aniline Compounds; Autoradiography; Binding, Competitive; Brain; Chromatography, High Pressure Liquid; Ethylene Glycols; Fluorine Radioisotopes; Humans; Kinetics; Ligands; Plaque, Amyloid; Positron-Emission Tomography; Pyrazoles; Staining and Labeling

Alzheimer's disease (AD) is a neurodegenerative disorder that results in memory deficits. The effect of AD is the leading cause of dementia in the United States and constitutes a burgeoning public health problem. AD is characterized by the presence of two aberrant structures, senile plaques, and neurofibrillary tangles, present in the brain of the patients. [(18)F]FDDNP and [(123)I]IMPY were developed for the early diagnosis of AD by Dr. J. Barrios and Dr. H. Kung, respectively. These two radiotracers could bind with the amyloid location site in the AD patient brain. The aim of this study was to analyze the acute single toxic effects dose of two nonradiochemical labeled compounds in rats. Animals were injected from the tail vein with nonlabeled-FDDNP (0- 5 mg/kg) and nonlabeled-IMPY (0-300 microg/kg), respectively, and observed for 2 weeks. These doses provide safety margins of 35,000- to 140-fold and 1,000- to 100-fold over the maximal recommend human dose (0.1 mg/70 kg) and (20 microg/60 kg) (by FDDNP and IMPY), respectively. With IMPY, there were no changes in mortality, clinical situation, and gross necropsy. With FDDNP, the high dose (5 mg/kg) produced mortality in 2 of 5 and 1 of 5 in male and female rats, respectively. The high dose of FDDNP showed liver damage in dying animals. No other adverse toxic effects at dose levels up to 1.0 mg/kg of FDDNP were noted. FDDNP exerted no adverse toxic effects in rats given doses up to 1 mg/kg and IMPY at the dose levels up to 300 microg/kg.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Brain; Dementia; Female; Fluorescent Dyes; Fluorodeoxyglucose F18; Humans; Image Enhancement; Male; Neurodegenerative Diseases; Neurofibrillary Tangles; Pyrazoles; Radiopharmaceuticals; Tissue Distribution

A potential single-photon emission computed tomography imaging agent for labeling of A beta plaques of Alzheimer's disease, IMPY (2-(4'-dimethylaminophenyl)-6-iodo-imidazo[1,2-a]pyridine), would be effective in detection of prion amyloid deposits in transmissible spongiform encephalopathies (TSEs).. In vitro autoradiographic studies were carried out with [125 I]IMPY on brain sections from scrapie-infected mice and age-matched controls. Competition study was performed to evaluate the prion deposit binding specificity with nonradioactive IMPY.. Binding of [125 I]IMPY was observed in infected brain sections, while on age-matched control brain sections, there was no or very low labeling. Prion deposit binding was confirmed by histoblots with prion protein-specific monoclonal antibody 2D6. In the presence of nonradioactive IMPY, the binding of [125 I]IMPY was significantly inhibited in all regions studied.. These findings indicate that IMPY can detect the prion deposits in vitro in scrapie-infected mice. Labeled with 123 I, this ligand may be useful to quantitate prion deposit burdens in TSEs by in vivo imaging.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Antibodies, Monoclonal; Autoradiography; Binding, Competitive; Brain; Disease Models, Animal; Humans; Iodine Radioisotopes; Isotope Labeling; Mice; Plaque, Amyloid; Prions; Pyrazoles; Radionuclide Imaging; Radiopharmaceuticals; Scrapie

(123)I-IMPY (6-iodo-2-(4'-dimethylamino-)phenyl-imidazo[1,2-a]pyridine) is a novel radiopharmaceutical that selectively binds to Alzheimer's disease (AD) amyloid plaques. As a first step toward validating this radiopharmaceutical as an imaging biomarker for AD, we measured the whole-body biokinetics and radiation dosimetry of (123)I-IMPY in AD patients and cognitively normal control subjects. The pharmacologic safety profile of the compound was simultaneously assessed.. The sample included 9 subjects ranging in age from 44 to 80 y. Whole-body images were obtained for each subject (mean +/- SD, 9.0 +/- 3.2 scans per subject) for up to 48 h after the intravenous administration of 185 MBq (5 mCi) of (123)I-IMPY. The fraction of administered activity in 12 regions of interest was quantified from the attenuation-corrected geometric mean counts in conjugate views. Multiexponential functions were iteratively fit to each time-activity curve using a nonlinear, least-squares regression algorithm. These curves were numerically integrated to yield cumulated activity values for source organs. Radiation doses were then estimated with the MIRD technique.. The radiotracer had no pharmacologic effects (produced no changes in heart rate, blood pressure, or laboratory results) on any of the subjects. Radiation dosimetry estimates indicated that the dose-limiting organ was the gallbladder, which received an average of 0.135 mGy/MBq (range, 0.075-0.198 mGy/MBq). The effective dose equivalent and effective dose for (123)I-IMPY were 0.042 +/- 0.003 mSv/MBq and 0.035 +/- 0.001 mSv/MBq, respectively. The mean effective dose for (123)I-IMPY was similar to that for (111)In-diethylenetriaminepentaacetic acid (0.035 mGy/MBq), less than half that for (111)In-pentetreotide (0.81 mGy/MBq), and approximately twice that for (123)I-IMP (0.018 mGy/MBq). No significant differences were found between men and women or between AD patients and control subjects.. (123)I-IMPY may be a safe radiotracer with appropriate biokinetics for imaging amyloid plaques in AD patients.

Topics: Adult; Aged; Aged, 80 and over; Alzheimer Disease; Amyloid; Female; Humans; Iodine Radioisotopes; Male; Middle Aged; Models, Chemical; Pyrazoles; Radiometry; Radionuclide Imaging; Tissue Distribution; Whole Body Imaging