Aβ Imaging Research Articles

Synthesis and In Vitro Evaluation of Imidazo[1,2-b]pyridazines as Ligands for β-Amyloid Plaques.

A series of imidazo[1,2-b]pyridazine derivatives were synthesized and evaluated for binding to amyloid plaques in vitro using synthetic aggregates of Aβ1-40. Binding affinities of these compounds were found to range from 11.0 to >1000 nM, depending on the various substitution patterns in the 6-position and 2-position. 2-(4'-Dimethylaminophenyl)-6-(methylthio)imidazo[1,2-b]pyridazine (4) showed high binding affinity (K i = 11.0 nM) and might be useful for the development of novel positron emission tomography radiotracers for imaging Aβ plaques.

Beta-amyloid deposition and the aging brain.

A central issue in cognitive neuroscience of aging research is pinpointing precise neural mechanisms that determine cognitive outcome in late adulthood as well as identifying early markers of less successful cognitive aging. One promising biomarker is beta amyloid (Abeta) deposition. Several new radiotracers have been developed that bind to fibrillar Abeta providing sensitive estimates of amyloid deposition in various brain regions. Abeta imaging has been primarily used to study patients with Alzheimer's Disease (AD) and individuals with Mild Cognitive Impairment (MCI); however, there is now building data on Abeta deposition in healthy controls that suggest at least 20% and perhaps as much as a third of healthy older adults show significant deposition. Considerable evidence suggests amyloid deposition precedes declines in cognition and may be the initiator in a cascade of events that indirectly leads to age-related cognitive decline. We review studies of Abeta deposition imaging in AD, MCI, and normal adults, its cognitive consequences, and the role of genetic risk and cognitive reserve.

In vitro characterisation of BF227 binding to α-synuclein/Lewy bodies

Amyloid-β (Aβ) plaques are a pathological hallmark of Alzheimer's disease and a current target for positron emission tomography (PET) imaging agents. Whilst [ 11C]-PiB is currently the most widely used PET ligand in clinic, a novel family of benzoxazole compounds have shown promise as Aβ imaging agents; particularly BF227. We characterised the in vitro binding of [ 18F]-BF227 toward α-synuclein to address its selectivity for Aβ pathology, to establish whether [ 18F]-BF227 binds to α-synuclein/Lewy bodies, in addition to Aβ plaques. In vitro [ 18F]-BF227 saturation studies were conducted with 200 nM α-synuclein or Aβ 1−42 fibrils or 100 μg of Alzheimer's disease, pure dementia with Lewy bodies or control brain homogenates. Non-specific binding was established with PiB (1 μM). In vitro binding studies indicated that [ 18F]-BF227 binds with high affinity to two binding sites on Aβ 1−42 fibrils (K D1 = 1.31 and K D2 = 80 nM, respectively) and to one class of binding sites on α-synuclein fibrils (K D = 9.63nM). [ 18F]-BF227 bound to Aβ-containing Alzheimer's disease brain (K D = 25 ± 0.5 nM), but failed to bind to Aβ-free dementia with Lewy bodies or age-matched control homogenates. Moreover, BF227 labelled both Aβ plaques and Lewy bodies in immunohistochemical/fluorescence analysis of human Alzheimer's disease and Parkinson's disease brain sections, respectively. This study suggests that [ 18F]-BF227 is not Aβ-selective. Evaluation of BF227 as a potential biomarker for Parkinson's disease is warranted.

Fibrillar amyloid-β burden in cognitively normal people at 3 levels of genetic risk for Alzheimer's disease

Fibrillar amyloid-beta (Abeta) is found in the brains of many cognitively normal older people. Whether or not this reflects a predisposition to Alzheimer's disease (AD) is unknown. We used Pittsburgh Compound B (PiB) PET to characterize the relationship between fibrillar Abeta burden and this predisposition in cognitively normal older people at 3 mean levels of genetic risk for AD. Dynamic PiB PET scans, the Logan method, statistical parametric mapping, and automatically labeled regions of interest (ROIs) were used to characterize and compare cerebral-to-cerebellar PIB distribution volume ratios, reflecting fibrillar Abeta burden, in 28 cognitively normal persons (mean age, 64 years) with a reported family history of AD and 2 copies, 1 copy, and no copies of the apolipoprotein E (APOE) epsilon4 allele. The 8 epsilon4 homozygotes, 8 heterozygotes, and 12 noncarriers did not differ significantly in terms of age, sex, or cognitive scores. Fibrillar Abeta was significantly associated with APOE epsilon4 carrier status and epsilon4 gene dose in AD-affected mean cortical, frontal, temporal, posterior cingulate-precuneus, parietal, and basal ganglia ROIs, and was highest in an additional homozygote who had recently developed mild cognitive impairment. These findings suggest that fibrillar Abeta burden in cognitively normal older people is associated with APOE epsilon4 gene dose, the major genetic risk factor for AD. Additional studies are needed to track fibrillar Abeta accumulation in persons with different kinds and levels of AD risk; to determine the extent to which fibrillar Abeta, alone or in combination with other biomarkers and risk factors, predicts rates of cognitive decline and conversion to clinical AD; and to establish the role of fibrillar Abeta imaging in primary prevention trials.

Synthesis and β-amyloid binding properties of rhenium 2-phenylbenzothiazoles

As a first step toward the development of 99mTc PiB analogs, we have synthesized six neutral Re 2-phenylbenzothiazoles via pendant or integrated approach. These Re compounds bind to Aβ 1–40 fibrils with fairly good affinities ( K i = 10.0–88.6 nM) and have moderate lipophilicities (log P C18 = 1.21–3.26). The Re compounds prepared via the integrated approach are smaller in size, and therefore their corresponding 99mTc analogs would have a greater chance of crossing the blood-brain barrier well. For potential clinical applications, further optimization on the structure–activity relationship to obtain Re 2-phenylbenzothiazoles with higher binding affinities (<10 nM) might be needed. The integrated approach reported here to obtain neutral, compact and lipophilic Re 2-phenylbenzothiazoles could to be applied to other high affinity pharmacophores as well as to generate 99mTc analogs that could hold promise for extending the use of Aβ imaging in living human brain to many more clinical settings because they could be used with SPECT.

18F-Labeled benzylideneaniline derivatives as new ligands for β-amyloid plaque imaging in Alzheimer's disease

Noninvasive early detection of beta-amyloid (Abeta) plaques might be useful for the treatment of patients with Alzheimer's disease (AD). We herein describe the synthesis of (18)F-labeled benzylideneaniline derivatives using a novel labeling approach for imaging Abeta plaques in AD patients. Benzylidenaniline derivatives were synthesized by reacting fluorobenzaldehyde and corresponding aniline derivatives. Fluorobenzaldehyde was labeled with (18)F by incubating [(18)F]fluoride with N,N,N-trimethylbenzaldehyde in the presence of tetrabutylammonium bicarbonate. In vitro binding assay, stability test and biodistribution study were performed. These compounds were stable at alkaline pH (pH >9); however, they were hydrolyzed rapidly at physiological pH (pH approximately 7.4). The K(i) values of amine-containing benzylideneaniline derivatives for Abeta(1-40) and Abeta(1-42) aggregates were 26-78 nM. These (18)F-labeled benzylideneaniline derivatives showed high brain uptake and rapid clearance after intravenous administration in normal mice (1.8-3.1%ID/g at 2 min and 0.1-1.2%ID/g at 30 min). The low level of bone activity at 30 min indicated that these (18)F-labeled benzylideneanilines are not prone to defluorination. Furthermore, the compounds have suitable lipophilicity - a property required to penetrate the blood-brain barrier. These results showed that the instability of these compounds could cause a higher early phase/late phase ratio due to rapid clearance in the normal brain. The findings from this study suggest that these (18)F-labeled benzylideneaniline derivatives are feasible for the imaging of Abeta plaques.

Radiation Dosimetry of β-Amyloid Tracers 11C-PiB and 18F-BAY94-9172

Beta-amyloid (Abeta) imaging has great potential to aid in the diagnosis of Alzheimer disease and the development of therapeutics. The radiation dosimetry of Abeta radioligands may influence their application; therefore, we calculated and compared the effective doses (EDs) of 11C-PiB and a new 18F-labeled ligand, 18F-BAY94-9172. Attenuation-corrected whole-body scans were performed at 0, 15, 30, 45, and 60 min after injection of 350+/-28 MBq (mean+/-SD) of 11C-PiB in 6 subjects and at 0, 20, 60, 120, and 180 min after injection of 319+/-27 MBq of 18F-BAY94-9172 in 3 subjects. Coregistered CT was used to define volumes of interest (VOIs) on the PET images. The source organs were the brain, lungs, liver, kidneys, spleen, and vertebrae. The VOIs for the contents of the gallbladder, urinary bladder, lower large intestine, upper large intestine, and small intestine were also defined. Total activity in each organ at each time point was calculated by use of reference organ volumes. The resultant time-activity curves were fitted with constrained exponential fits, and cumulated activities were determined. A dynamic bladder voiding model was used. The OLINDA/EXM program was used to calculate the whole-body EDs from the acquired data. For 11C-PiB, the highest absorbed doses were in the gallbladder wall (44.80+/-29.30 microGy/MBq), urinary bladder wall (26.30+/-8.50 microGy/MBq), liver (19.88+/-3.58 microGy/MBq), and kidneys (12.92+/-3.37 microGy/MBq). The ED was 5.29+/-0.66 microSv/MBq. For 18F-BAY94-9172, the highest doses were also in the gallbladder wall (132.40+/-43.40 microGy/MBq), urinary bladder wall (24.77+/-7.36 microGy/MBq), and liver (39.07+/-8.31 microGy/MBq). The ED was 14.67+/-1.39 microSv/MBq. The estimated organ doses for 11C-PiB were comparable to those reported in earlier research. With the doses used in published studies (300-700 MBq), the EDs would range from 1.6 to 3.7 mSv. The ED of 18F-BAY94-9172 was 30% lower than that of 18F-FDG and, at the published dose of 300 MBq, would yield an ED of 4.4 mSv. The dosimetry of both Abeta radioligands is suitable for clinical and research applications.

Aβ-binding molecules: Possible application as imaging probes and as anti-aggregation agents

As amyloid β (Aβ) is at the centre of pathogenesis of Alzheimer’s disease (AD), Aβ aggregate-specific probes for in vivo studies of Aβ are potentially important for the early diagnosis and the assessment of new treatment strategies in the AD brain by noninvasive imaging. Several series of compounds derived from Congo red (CR) and Thioflavin T (ThT) have been evaluated as potential probes for the Aβ imaging. They include a diversity of core structures contributing to their affinities to Aβ. Small-molecule inhibitors were known to inhibit the formation of Aβ oligomers and fibrils. This inhibition has to be performed in such a way that these inhibitors bind to Aβ in the binding channel where Aβ-binding probes should sit. Therefore, several of them were used as novel core structures to develop Aβ probes, with their derivatives exhibiting good Aβ affinities. This approach will facilitate the design of a variety of candidates for Aβ probe molecules and anti-aggregation-therapeutic drugs. Moreover, the finding of Aβ probes with diverse core structures recognized by binding sites on Aβs will likely provide a promising perspective for the design of 99mTc-labeled probe-derived molecules.

The ART of Loss: Aβ Imaging in the Evaluation of Alzheimer’s Disease and other Dementias

Molecular neuroimaging based on annihilation radiation tomographic (ART) techniques such as positron emission tomography (PET), in conjunction with related biomarkers in plasma and cerebrospinal fluid (CSF), are proving valuable in the early and differential diagnosis of Alzheimer's disease (AD). With the advent of new therapeutic strategies aimed at reducing beta-amyloid (Abeta) burden in the brain to potentially prevent or delay functional and irreversible cognitive loss, there is increased interest in developing agents that allow assessment of Abeta burden in vivo. Abeta burden as assessed by molecular imaging matches histopathological reports of Abeta plaque distribution in aging and dementia and appears more accurate than FDG for the diagnosis of AD. Abeta imaging is also a very powerful tool in the differential diagnosis of AD from fronto-temporal dementia (FTD). Although Abeta burden as assessed by PET does not correlate with measures of cognitive decline in AD, it does correlate with memory impairment and rate of memory decline in mild cognitive impairment (MCI) and healthy older subjects. Approximately 30% of asymptomatic controls present cortical (11)C-PiB retention. These observations suggest that Abeta deposition is not part of normal ageing, supporting the hypothesis that Abeta deposition occurs well before the onset of symptoms and is likely to represent preclinical AD. Further longitudinal observations are required to confirm this hypothesis and to better elucidate the role of Abeta deposition in the course of Alzheimer's disease.

IC-PL2: Amyloid imaging: Developments, challenges, future direction

The first in vivo positron emission tomography (PET) imaging studies of amyloid-beta (Aβ) in human subjects were reported by the UCLA group in 2002 using a fluorine-18 labeled membrane dye derivative, [F-18]FDDNP, that bound preferentially to both Aβ plaques and neurofibrillary tangles (NFT) in the brains of Alzheimer's disease (AD) patients relative to elderly control subjects. Groups from Pittsburgh and Toronto followed in 2004 with literature reports of PET imaging studies in AD and control subjects using Aβ-selective carbon-11 labeled thioflavin-T ([C-11]PIB) and stilbene ([C-11]SB-11) derivatives, respectively. Researchers have sought to employ these PET agents in cross-sectional and longitudinal studies of Aβ deposition in a variety of non-invasive imaging studies in amyloid-based diseases. In addition, investigators have sought to expand the choice of Aβ-specific radioligands to include other F-18 and C-11 labeled compounds for PET imaging applications, as well as I-123 labeled agents for single photon emission computed tomography (SPECT) imaging studies. Over the past 4 years, literature reports of Aβ imaging in human subjects using PET have exploded, with more than 70 publications in a variety of subject populations. The vast majority of these studies have utilized [C-11]PIB, but the relatively short half-life of carbon-11 (20 min) has limited its distribution to about 40 specialized PET radiochemistry facilities throughout the world. The development of a more convenient, longer-lived (110 min) F-18 labeled radioligand with in vivo properties comparable to those of [C-11]PIB has been an active area of research over the past several years with some recent encouraging results. In contrast, efforts to develop a SPECT Aβ imaging agent have been largely unsuccessful. PET Aβ imaging studies have provided some important insights into the pathophysiology of amyloid deposition, particularly in mild cognitive impairment (MCI), healthy elderly controls, and familial AD subjects. Aβ PET methodology is proving valuable in helping to assess the amyloid cascade hypothesis, as a diagnostic agent for brain amyloid deposition, and as a potential surrogate marker of therapeutic efficacy in anti-Aβ drug trials.

Imaging of amyloid β in Alzheimer's disease with 18F-BAY94-9172, a novel PET tracer: proof of mechanism

Amyloid-beta (Abeta) plaque formation is a hallmark of Alzheimer's disease (AD) and precedes the onset of dementia. Abeta imaging should allow earlier diagnosis, but clinical application is hindered by the short decay half-life of current Abeta-specific ligands. (18)F-BAY94-9172 is an Abeta ligand that, due to the half-life of (18)F, is suitable for clinical use. We thus studied the effectiveness of this ligand in identifying patients with AD. 15 patients with mild AD, 15 healthy elderly controls, and five individuals with frontotemporal lobar degeneration (FTLD) were studied. (18)F-BAY94-9172 binding was quantified by use of the standardised uptake value ratio (SUVR), which was calculated for the neocortex by use of the cerebellum as reference region. SUVR images were visually rated as normal or AD. (18)F-BAY94-9172 binding matched the reported post-mortem distribution of Abeta plaques. All AD patients showed widespread neocortical binding, which was greater in the precuneus/posterior cingulate and frontal cortex than in the lateral temporal and parietal cortex. There was relative sparing of sensorimotor, occipital, and medial temporal cortex. Healthy controls and FTLD patients showed only white-matter binding, although three controls and one FTLD patient had mild uptake in frontal and precuneus cortex. At 90-120 min after injection, higher neocortical SUVR was observed in AD patients (2.0 [SD 0.3]) than in healthy controls (1.3 [SD 0.2]; p<0.0001) or FTLD patients (1.2 [SD 0.2]; p=0.009). Visual interpretation was 100% sensitive and 90% specific for detection of AD. (18)F-BAY94-9172 PET discriminates between AD and FTLD or healthy controls and might facilitate integration of Abeta imaging into clinical practice.

Impaired Spine Stability Underlies Plaque-Related Spine Loss in an Alzheimer's Disease Mouse Model

Dendritic spines, the site of most excitatory synapses in the brain, are lost in Alzheimer's disease and in related mouse models, undoubtedly contributing to cognitive dysfunction. We hypothesized that spine loss results from plaque-associated alterations of spine stability, causing an imbalance in spine formation and elimination. To investigate effects of plaques on spine stability in vivo, we observed cortical neurons using multiphoton microscopy in a mouse model of amyloid pathology before and after extensive plaque deposition. We also observed age-matched nontransgenic mice to study normal effects of aging on spine plasticity. We found that spine density and structural plasticity are maintained during normal aging. Tg2576 mice had normal spine density and plasticity before plaques appeared, but after amyloid pathology is established, severe disruptions were observed. In control animals, spine formation and elimination were equivalent over 1 hour of observation ( approximately 5% of observed spines), resulting in stable spine density. However, in aged Tg2576 mice spine elimination increased, specifically in the immediate vicinity of plaques. Spine formation was unchanged, resulting in spine loss. These data show a small population of rapidly changing spines in adult and even elderly mouse cortex; further, in the vicinity of amyloid plaques, spine stability is markedly impaired leading to loss of synaptic structural integrity.

Requirement of aggregation propensity of Alzheimer amyloid peptides for neuronal cell surface binding

BackgroundAggregation of the amyloid peptides, Aβ40 and Aβ42, is known to be involved in the pathology of Alzheimer's disease (AD). Here we investigate the relationship between peptide aggregation and cell surface binding of three forms of Aβ (Aβ40, Aβ42, and an Aβ mutant).ResultsUsing confocal microscopy and flow cytometry with fluorescently labelled Aβ, we demonstrate a correlation between the aggregation propensity of the Alzheimer amyloid peptides and their neuronal cell surface association. We find that the highly aggregation prone Aβ42 associates with the surface of neuronal cells within one hour, while the less aggregation prone Aβ40 associates over 24 hours. We show that a double mutation in Aβ42 that reduces its aggregation propensity also reduces its association with the cell surface. Furthermore, we find that a cell line that is resistant to Aβ cytotoxicity, the non-neuronal human lymphoma cell line U937, does not bind either Aβ40 or Aβ42.ConclusionTaken together, our findings reveal that amyloid peptide aggregation propensity is an essential determinant of neuronal cell surface association. We anticipate that our approach, involving Aβ imaging in live cells, will be highly useful for evaluating the efficacy of therapeutic drugs that prevent toxic Aβ association with neuronal cells.

Radioiodinated aza-diphenylacetylenes as potential SPECT imaging agents for β-amyloid plaque detection

Two new iodinated fluoro- and hydroxy-pegylated aza-diphenylacetylene derivatives, 1 and 2, targeting β-amyloid (Aβ) plaques have been successfully prepared. In vitro binding carried out in tissue homogenates prepared from postmortem AD brains with [ 125I]IMPY (6-iodo-2-(4′-dimethylamino)phenyl-imidazo[1,2-a]pyridine) as the radioligand indicated good binding affinities ( K i = 9.2 and 16.8 nM for 1 and 2, respectively). Brain penetrations of the corresponding radioiodinated ligands, evaluated in the normal mice, showed good initial brain penetrations (3.55% and 5.67% ID/g for [ 125I] 1 and [ 125I] 2 at 2 min post-injection). The washout from normal mice brain was relatively fast (0.33% and 0.91% ID/g at 2 h post-injection). The specific binding of these radioiodinated ligands to β-amyloid plaques was clearly demonstrated using film autoradiography of AD brain sections. Taken together, these preliminary results strongly suggest that these novel iodinated aza-diphenylacetylenes may be potentially useful for imaging Aβ plaques in the living human brain.

Biphenyls labeled with technetium 99m for imaging β-amyloid plaques in the brain

Formation and accumulation of excess aggregates of β-amyloid (Aβ) plaques in the brain are critical factors contributing to the development and progression of Alzheimer's disease (AD). There is an urgent need for in vivo imaging agents that can specifically demonstrate the location and density of Aβ plaques in the brain. The aim of this study was to develop potential technetium 99m ( 99mTc)-labeled diagnostic imaging agents specific for the detection of Aβ plaques. Based on previously obtained Aβ plaque-specific biphenyls containing a p- N, N-dimethylaminophenyl group, a series of 99mTc and Re–N 2S 2–biphenyl derivatives was prepared. The stable neutral and lipophilic 99mTc complexes, [ 99mTc] 19 and [ 99mTc] 23, A+B, were successfully obtained. As surrogates for the 99mTc complexes, the corresponding surrogates, Re complexes of 23, were also prepared. Surprisingly, it was found that the Re complexes showed distinctively different retention profiles as compared with the corresponding 99mTc complexes. Biodistribution studies indicated that [ 99mTc] 23A readily passed through the blood–brain barrier (1.18% dose/brain at 2 min) in contrast to the low brain penetration of [ 99mTc] 19 (0.29% dose/brain at 2 min). Initial results suggested that [ 99mTc] 23A showed selective binding to the Aβ plaque-like structures in the brain sections from transgenic mice but not in the postmortem human brain tissue of patients with confirmed AD. The results provide encouraging evidence that development of a 99mTc-labeled agent for imaging Aβ plaques in the brain may be feasible. Caution should be taken when comparing these 99mTc complexes with the corresponding surrogates — the Re complexes.

Imaging beta-amyloid plaques and neurofibrillary tangles in the aging human brain.

The development of radioligands to image beta-amyloid (A beta) plaques and neurofibrillary tangles (NFTs) in vivo in the aging human brain is an important and active area of radiopharmaceutical design. When used in combination with positron emission tomography (Pet) or single photon emission computed tomography (spect), amyloid-imaging tracers could facilitate the evaluation of the efficacy of anti-amyloid therapies currently under intense development by many major pharmaceutical companies throughout the world. Amyloid-imaging agents could also serve as surrogate markers in early diagnosis and neuropathogenesis studies of Alzheimer's disease and other aging-related neurodegenerative disorders. In this review article, the design and biological evaluation of amyloid-imaging agents are discussed. The structures of these agents vary from large proteins and peptides such as radiolabeled A beta peptides and monoclonal antibodies to small molecules derived from Congo red, Chrysamine-G, thioflavin-T, and Acridine Orange. In vitro studies indicate that amyloid plaques contain multiple binding sites that can accommodate structurally diverse compounds, providing flexibility for radiopharmaceutical design of amyloid imaging agents. Compared to large biomolecules, small molecule radiotracers are often readily accessible through chemical synthesis and can display superior brain permeability. Several small molecule amyloid-imaging radioligands display high binding affinities to A beta and sufficient brain penetration for imaging studies. Recent studies demonstrate the feasibility of imaging amyloid plaques in vivo in human subjects with PET. Imaging NFTs, separately or in concert with A beta plaques, is not as far advanced as imaging A beta plaques and remains to be fully characterized and demonstrated.

Structure-activity relationship of imidazo[1,2-a]pyridines as ligands for detecting beta-amyloid plaques in the brain.

A series of novel beta-amyloid (A beta) aggregate-specific ligands, 2-(4'-dimethylaminophenyl)-6-iodoimidazo[1,2-a]pyridine, 16(IMPY), and its related derivatives were prepared. An in vitro binding study with preformed A beta aggregates showed that 16(IMPY) and its bromo derivative competed with binding of 2-(4'-dimethylaminophenyl)-6-iodobenzothiazole, [125I]7(TZDM), a known ligand for A beta aggregates, with high binding affinities (K(i) = 15 and 10 nM, respectively). In vitro autoradiography of brain sections of a transgenic mouse (Tg2576) with [125I]16(IMPY) displayed high selective binding to amyloid-like structures, comparable to that observed by staining with thioflavin-S visualized under fluorescence. In vivo biodistribution after an intravenous injection of [125I]16(IMPY) in normal mice showed a high initial brain uptake and fast washout, indicating a low background activity associated with this iodinated ligand. Taken together, the data suggests that [123I]16(IMPY) may be useful for imaging A beta aggregates in patients with Alzheimer's disease.

Filamentous phage as vector-mediated antibody delivery to the brain.

Early diagnosis of Alzheimer's disease is prevented by lack of means to visualize and target beta amyloid plaques in the brains of affected people. There are many methods of detecting amyloid plaques by staining postmortem brain tissue, but none are available for monitoring in living patients. We propose anti-beta amyloid antibodies as a highly specific probe to monitor amyloid plaque formation in living patients. Intranasal administration of filamentous phage as delivery vector of anti-beta amyloid antibody fragment into Alzheimer's APP transgenic mice enables in vivo targeting of beta amyloid plaques. The plaques were co-visualized both by thioflavin-S and fluorescent-labeled anti-phage antibodies in the olfactory bulb and the hippocampus region. The genetically engineered filamentous bacteriophage proved to be an efficient and nontoxic viral delivery vector to the brain, offering an obvious advantage over other mammalian vectors. The ability to image A beta deposits in vivo would arguably provide the most useful diagnostic and monitoring test for early diagnosis of Alzheimer's disease.

Drug Targeting to the Brain Using Avidin-Biotin Technology in the Mouse (Blood-Brain Barrier, Monoclonal Antibody, Transferrin Receptor, Alzheimer's Disease)

Aβ1-40 peptide radiopharmaceuticals could be used to image Aβ brain amyloid in transgenic mouse models of Alzheimer's disease should the Aβ peptide radiopharmaceutical be made transportable through the blood-brain barrier (BBB) in vivo. The present studies used the RI7-217 rat monoclonal antibody to the mouse transferrin receptor as a BBB drug targeting vector for the delivery to brain of Aβ1-40 radiolabeled with either 125-Iodine or 111-Indium. The Aβ peptide radiopharmaceutical is conjugated to the RI7 MAb using avidin biotin technology, wherein the Aβ1-40 peptide radiopharmaceutical is monobiotinylated (bio) and bound to a conjugate of the RI7 MAb and streptavidin (SA). The [125I]-bio-Aβ1-40 or the [111In]-bio-Aβ1-40 either free or bound to the RI7/SA conjugate was injected intravenously into anesthetized adult mice and plasma pharmacokinetics and organ uptake were measured over the next 60 minutes. The Aβ1-40 peptide radiopharmaceutical radiolabeled with 111-Indium was the preferred formulation, compared to peptide labeled with 125-Iodine, because there was a greater metabolic stability and reduced artifactual organ uptake of metabolites associated with the use of the 111-Indium nuclide. However, biotinylated Aβ1-40 peptide radiopharmaceuticals conjugated to the RI7/SA brain drug targeting system were metabolically unstable in mice in vivo owing to active biotinidase activity. Future work involving brain drug targeting in mice that utilizes avidin biotin technology will need to incorporate biotin analogues that are resistant to biotinidase.