Techniques for in utero,longitudinal MRI of fetal brain development in baboons at 3 T

Magnetic Resonance Imaging (MRI) is a promising tool for the noninvasive, longitudinal study of developing primate brains. We developed a protocol to scan pregnant baboons serially at 3 T for up to 3 h per session. This protocol includes procedures for animal preparation, anesthesia, MRI scanning, and post-scan animal care. We applied this protocol to scan 5 baboons multiple times across the latter 70% of gestation—from as early as 56 days post-conceptional age to as late as 185 days (term ～180 days). We successfully acquired high-resolution anatomical images and maps of relaxation times (T₁ and T₂) of the fetal brains at multiple time points across gestation. These images and maps demonstrated the convergence of gray and white matter contrast near term, and furthermore demonstrated that the convergence of contrast is a consequence of the continuous change in relaxation times during fetal brain development. We estimated the rates of decrease of T₁ and T₂ in white matter and gray matter, respectively. In addition, we measured the volumes of fetal brain at different gestational ages and calculated the growth rates of whole brain (0.91 ± 0.08 cm³/day) and cortical gray matter (0.40 ± 0.04 cm³/day). We also measured the mean diffusivity in white matter and deep gray matter using diffusion tensor imaging. In conclusion, in utero MRI of fetal baboon brains greatly enhances the use of nonhuman primate models to study fetal brain development longitudinally.     

Synthesis and evaluation of ethyleneoxylated and allyloxylated chalcone derivatives for imaging of amyloid β plaques by SPECT

We report radioiodinated chalcone derivatives as new SPECT imaging probes for amyloid β (Aβ) plaques. The monoethyleneoxy derivative 2 and allyloxy derivative 8 showed a high affinity for Aβ(1–42) aggregates with K_i values of 24 and 4.5 nM, respectively. Fluorescent imaging demonstrated that 2 and 8 clearly stained thioflavin-S positive Aβ plaques in the brain sections of Tg2576 transgenic mice. In vitro autoradiography revealed that [¹²⁵I]2 displayed no clear accumulation toward Aβ plaques in the brain sections of Tg2576 mice, whereas the accumulation pattern of [¹²⁵I]8 matched with the presence of Aβ plaques both in the brain sections of Tg2576 mice and an AD patient. In biodistribution studies using normal mice, [¹²⁵I]2 showed preferable in vivo pharmacokinetics (4.82%ID/g at 2 min and 0.45%ID/g at 60 min), while [¹²⁵I]8 showed only a modest brain uptake (1.62%ID/g at 2 min) with slow clearance (0.56%ID/g at 60 min). [¹²⁵I]8 showed prospective binding properties for Aβ plaques, although further structural modifications are needed to improve the blood brain barrier permeability and washout from brain.     

A 68Ga complex based on benzofuran scaffold for the detection of β-amyloid plaques

Since the imaging of β-amyloid (Aβ) plaques in the brain is believed to be a useful tool for the early diagnosis of Alzheimer’s disease (AD), a number of imaging probes to detect Aβ plaques have been developed. Because the radionuclide ⁶⁸Ga (t_1/2 = 68 min) for PET imaging could become an attractive alternative to ¹¹C and ¹⁸F, we designed and synthesized a benzofuran derivative conjugated with a ⁶⁸Ga complex (⁶⁸Ga-DOTA-C3-BF) as a novel Aβ imaging probe. In an in vitro binding assay, Ga-DOTA-C3-BF showed high affinity for Aβ(1-42) aggregates (K_i = 10.8 nM). The Ga-DOTA-C3-BF clearly stained Aβ plaques in a section of Tg2576 mouse, reflecting the affinity for Aβ(1-42) aggregates in vitro. In a biodistribution study in normal mice, ⁶⁸Ga-DOTA-C3-BF displayed low initial uptake (0.45% ID/g) in the brain at 2 min post-injection. While improvement of the brain uptake of ⁶⁸Ga complexes appears to be essential, these results suggest that novel PET imaging probes that include ⁶⁸Ga as the radionuclide for PET may be feasible.     

Online solid phase extraction with liquid chromatography–tandem mass spectrometry to analyze remoxipride in small plasma-, brain homogenate-, and brain microdialysate samples

Remoxipride is a selective dopamine D₂ receptor antagonist, and useful as a model compound in mechanism-based pharmacological investigations. To that end, studies in small animals with serial sampling over time are needed. For these small volume samples currently no suitable analytical methods are available. We propose analytical methods for the detection of low concentrations remoxipride in small sample volumes of plasma, brain homogenate, and brain microdialysate, using online solid phase extraction with liquid chromatography–tandem mass spectrometry. Method development, optimization and validation are described in terms of calibration curves, extraction yield, lower limit of quantification (LLOQ), precision, accuracy, inter-day- and intra-day variability. The 20 μl plasma samples showed an extraction yield of 76%, with a LLOQ of 0.5 ng/ml. For 0.6 ml brain homogenate samples the extraction yield was 45%, with a LLOQ of 1.8 ng/ml. The 20 μl brain microdialysate samples, without pre-treatment, had a LLOQ of 0.25 ng/ml. The precision and accuracy were well within the acceptable 15% range. Considering the small sample volumes, the high sensitivity and good reproducibility, the analytical methods are suitable for analyzing small sample volumes with low remoxipride concentrations.     

Faisabilité et intérêt d’un nouvel algorithme de reconstruction des images TEP-18FDG (AW OSEM DR) pour la délimitation des volumes cibles en radiothérapie. À propos d’un cas de néoplasie ORL

ObjectiveWe compared two reconstruction methods for 18fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) images with “attenuation weighted ordered subset expectation maximization” using either the manufacturer-provided (AW-OSEM) or a “Detector response” (AW-OSEM DR) tomographic operator. We looked at the feasibility of using the latter reconstruction for radiotherapy target volumes definition in cancers of the superior aero-digestive tract (VADS). In this preliminary study, we first assessed the spatial resolution of images obtained with AW-OSEM and AW-OSEM DR on a Biograph™ 6, and secondly target volumes of radiotherapy “Gross Tumor Volume” (GTV), “Clinical Target Volume” (CTV) and “Planning Target Volume” (PTV) obtained with each of these reconstruction methods.Material and methodsThe spatial resolution was measured on a test object containing 4 radioactive point sources. Furthermore, radiotherapy target volumes have been defined with the software Eclipse™ on injected scanner (CT IV) and PET/CT (PET AW-OSEM and PET AW-OSEM DR) images.ResultsSpatial resolution was improved with AW-OSEM DR algorithm reconstruction compared to images obtained with AW-OSEM reconstruction (from 7.5 mm down to 5.4 mm for the highest reduction). GTV from AW-OSEM DR reconstruction with 42 and 50% of the “Standard uptake value maximum” (SUVmax) semi-automatic threshold (1.2 and 0.7 cm³ respectively) were lower than those obtained with AW-OSEM (3.6 and 2.2 cm³ respectively). They were also lower than GTV defined with CT IV (5.5 cm³). It was the same for CTV and PTV.ConclusionThis study showed that AW-OSEM DR reconstruction method allows less impaired spatial resolution than AW-OSEM. In the case of radiotherapy target volumes delineation, AW-OSEM DR may decrease the GTV, CTV and PTV and therefore the risk of side effects associated with organs at risk.     

Stature,body mass,and brain size: A two-million-year odyssey

Physical size has been critical in the evolutionary success of the genus Homo over the past 2.4 million-years. An acceleration in the expansion of savannah grasslands in Africa from 1.6 Ma to 1.2 Ma witnessed concomitant increases in physical stature (150–170 cm), weight (50–70 kg), and brain size (750–900 cm³). With the onset of 100,000 year Middle Pleistocene glacial cycles (“ice ages”) some 780,000 years ago, large-bodied Homo groups had reached modern size and had successfully dispersed from equatorial Africa, Central, and Southeast Asia to high-latitude localities in Atlantic Europe and North East Asia. While there is support for incursions of multiple Homo lineages to West Asia and Continental Europe at this time, data does not favour a persistence of Homo erectus beyond ～400,000 years ago in Africa, west and Central Asia, and Europe. Novel Middle Pleistocene Homo forms (780,000–400,000 years) may not have been substantially taller (150–170 cm) than earlier Homo (1.6 Ma–800,000 years), yet brain size exceeded 1000 cm³ and body mass approached 80 kg in some males. Later Pleistocene Homo (400,000–138,000 years) were ‘massive’ in their height (160–190 cm) and mass (70–90 kg) and consistently exceed recent humans. Relative brain size exceeds earlier Homo, yet is substantially lower than in final glacial H. sapiens and Homo neanderthalensis. A final leap in absolute and relative brain size in Homo (300,000–138,000 years) occurred independent of any observed increase in body mass and implies a different selective mediator to that operating on brain size increases observed in earlier Homo.     

Imaging performance of phase-contrast breast computed tomography with synchrotron radiation and a CdTe photon-counting detector

PurposeWithin the SYRMA-CT collaboration based at the ELETTRA synchrotron radiation (SR) facility the authors investigated the imaging performance of the phase-contrast computed tomography (CT) system dedicated to monochromatic in vivo 3D imaging of the female breast, for breast cancer diagnosis.MethodsTest objects were imaged at 38 keV using monochromatic SR and a high-resolution CdTe photon-counting detector. Signal and noise performance were evaluated using modulation transfer function (MTF) and noise power spectrum. The analysis was performed on the images obtained with the application of a phase retrieval algorithm as well as on those obtained without phase retrieval. The contrast to noise ratio (CNR) and the capability of detecting test microcalcification clusters and soft masses were investigated.ResultsFor a voxel size of (60 μm)³, images without phase retrieval showed higher spatial resolution (6.7 mm⁻¹ at 10% MTF) than corresponding images with phase retrieval (2.5 mm⁻¹). Phase retrieval produced a reduction of the noise level and an increase of the CNR by more than one order of magnitude, compared to raw phase-contrast images. Microcalcifications with a diameter down to 130 μm could be detected in both types of images.ConclusionsThe investigation on test objects indicates that breast CT with a monochromatic SR source is technically feasible in terms of spatial resolution, image noise and contrast, for in vivo 3D imaging with a dose comparable to that of two-view mammography. Images obtained with the phase retrieval algorithm showed the best performance in the trade-off between spatial resolution and image noise.     

A new single-photon emission computed tomography (SPECT) imaging agent for serotonin transporters: [125I]Flip-IDAM, (2-((2-((dimethylamino)methyl)-4-iodophenyl)thio)phenyl)methanol

New ligands for in vivo brain imaging of serotonin transporter (SERT) with single photon emission tomography (SPECT) were prepared and evaluated. An efficient synthesis and radiolabeling of a biphenylthiol, FLIP-IDAM, 4, was accomplished. The affinity of FLIP-IDAM was evaluated by an in vitro inhibitory binding assay using [¹²⁵I]-IDAM as radioligand in rat brain tissue homogenates (K_i = 0.03 nM). New [¹²⁵I]Flip-IDAM exhibited excellent binding affinity to SERT binding sites with a high hypothalamus to cerebellum ratio of 4 at 30 min post iv injection. The faster in vivo kinetics for brain uptake and a rapid washout from non-specific regions provide excellent signal to noise ratio. This new agent, when labeled with ¹²³I, may be a useful imaging agent for mapping SERT binding sites in the human brain.     

MicroRNA miR-7 is preferentially expressed in endocrine cells of the developing and adult human pancreas

MicroRNAs (miRNA) are small non-coding RNAs that inhibit gene expression through binding to complementary messenger RNA sequences. miRNAs have been predicted to target genes important for pancreas development, proper endocrine cell function and metabolism. We previously described that miRNA-7 (miR-7) was the most abundant and differentially expressed islet miRNA, with 200-fold higher expression in mature human islets than in acinar tissue. Here we have analyzed the temporal and spatial expression of miR-7 in human fetal pancreas from 8 to 22 weeks of gestational age (wga). Human fetal (8–22 wga) and adult pancreases were processed for immunohistochemistry, in situ hybridization, and quantitative RT-PCR of miRNA and mRNA. miR-7 was expressed in the human developing pancreas from around 9 wga and reached its maximum expression levels between 14 and 18 wga, coinciding with the exponential increase of the pancreatic endocrine hormones. Throughout development miR-7 expression was preferentially localized to endocrine cells and its expression persisted in the adult pancreas. The present study provides a detailed analysis of the spatiotemporal expression of miR-7 in developing human pancreas. The specific localization of miR-7 expression to fetal and adult endocrine cells indicates a potential role for miR-7 in endocrine cell differentiation and/or function. Future functional studies of a potential role for miR-7 function in islet cell differentiation and physiology are likely to identify novel targets for the treatment of diabetes and will lead to the development of improved protocols for generating insulin-producing cells for cell replacement therapy.     

Radiosynthesis of N-(4-chloro-3-[11C]methoxyphenyl)-2-picolinamide ([11C]ML128) as a PET radiotracer for metabotropic glutamate receptor subtype 4 (mGlu4)

N-(Chloro-3-methoxyphenyl)-2-picolinamide (3, ML128, VU0361737) is an mGlu₄ positive allosteric modulator (PAM), which is potent and centrally penetrating. 3 is also the first mGlu₄ PAM to show efficacy in a preclinical Parkinson disease model upon systemic dosing. As a noninvasive medical imaging technique and a powerful tool in neurological research, positron emission tomography (PET) offers a possibility to investigate mGlu₄ expression in vivo under physiologic and pathological conditions. We synthesized a carbon-11 labeled ML128 ([¹¹C]3) as a PET radiotracer for mGlu₄, and characterized its biological properties in Sprague Dawley rats. [¹¹C]3 was synthesized from N-(4-chloro-3-hydroxyphenyl)-2-picolinamide (2) using [¹¹C]CH₃I. Total synthesis time was 38 ± 2.2 min (n = 7) from the end of bombardment to the formulation. The radioligand [¹¹C]3 was obtained in 27.7 ± 5.3% (n = 5) decay corrected radiochemical yield based on the radioactivity of [¹¹C]CO₂. The radiochemical purity of [¹¹C]3 was >99%. Specific activity was 188.7 ± 88.8 GBq/mol (n = 4) at the end of synthesis (EOS).PET images were conducted in 20 normal male Sprague Dawley rats including 11 control studies, 6 studies blocking with an mGlu₄ modulator (4) to investigate specificity and 3 studies blocking with an mGlu₅ modulator (MTEP) to investigate selectivity. These studies showed fast accumulation of [¹¹C]3 (peak activity between 1–3 min) in several brain areas including striatum, thalamus, hippocampus, cerebellum, and olfactory bulb following with fast washout. Blocking studies with the mGlu₄ modulator 4 showed 22–28% decrease of [¹¹C]3 accumulation while studies of selectivity showed only minor decrease supporting good selectivity over mGlu₅. Biodistribution studies and blood analyses support fast metabolism. Altogether this is the first PET imaging ligand for mGlu₄, in which the labeled ML128 was used for imaging its in vivo distribution and pharmacokinetics in brain.     

18F-labeled flavones for in vivo imaging of β-amyloid plaques in Alzheimer’s brains

In vivo imaging of β-amyloid (Aβ) aggregates in the brain may lead to early detection of Alzheimer’s disease (AD) and monitoring of the progression and effectiveness of treatment. The purpose of this study was to develop novel ¹⁸F-labeled amyloid-imaging probes based on flavones as a core structure. Fluoropegylated (FPEG) flavone derivatives were designed and synthesized. The affinity of the derivatives for Aβ aggregates varied from 5 to 321 nM. In brain sections of AD model mice, FPEG flavones with the dimethylamino group intensely stained β-amyloid plaques. In biodistrubution experiments using normal mice, they displayed high uptake in the brain ranging from 2.9 to 4.2%ID/g at 2 min postinjection. The radioactivity washed out from the brain rapidly (1.3–2.0%ID/g at 30 min), which is highly desirable for β-amyloid imaging agents. FPEG flavones may be potential PET imaging agents for β-amyloid plaques in Alzheimer’s brains.     

Synthesis and evaluation of copper-64 labeled benzofuran derivatives targeting β-amyloid aggregates

In vivo imaging of β-amyloid (Aβ) aggregates consisting of Aβ(1–40) and Aβ(1–42) peptides by positron emission tomography (PET) contributes to the diagnosis and therapy for Alzheimer’s disease (AD). Because ⁶⁴Cu (t_1/2 = 12.7 h) is a radionuclide for PET with a longer physical half-life than ¹¹C (t_1/2 = 20 min) and ¹⁸F (t_1/2 = 110 min), it is an attractive radionuclide for the development of Aβ imaging probes that are suitable for routine use. In the present study, we designed and synthesized two novel ⁶⁴Cu labeled benzofuran derivatives and evaluated their utility as PET imaging probes for Aβ aggregates. In an in vitro binding assay, 6 and 8 showed binding affinity for Aβ(1–42) aggregates with a K_i value of 33 and 243 nM, respectively. In addition, these probes bound to Aβ plaques deposited in the brain of an AD model mouse in vitro. In a biodistribution experiment using normal mice, these probes showed low brain uptake (0.33% and 0.36% ID/g) at 2 min post-injection. Although refinement to enhance brain uptake is needed, [⁶⁴Cu]6 and [⁶⁴Cu]8 demonstrated the feasibility of developing novel PET probes for imaging Aβ aggregates.     

Synthesis and biological evaluation of 18F-labled 2-phenylindole derivatives as PET imaging probes for β-amyloid plaques

A novel series of fluorinated 2-phenylindole derivatives were synthesized and evaluated as β-amyloid imaging probes for PET. The in vitro inhibition assay demonstrated that their binding affinities for Aβ_1–42 aggregates ranged from 28.4 to 1097.8 nM. One ligand was labeled with ¹⁸F ([¹⁸F]1a) for its high affinity (K_i = 28.4 nM), which was also confirmed by in vitro autoradiography experiments on brain sections of transgenic mouse (C57BL6, APPswe/PSEN1, 11 months old, male). In vivo biodistribution experiments in normal mice showed that this radiotracer displayed high initial uptake (5.82 ± 0.51% ID/g at 2 min) into and moderate washout (2.77 ± 0.31% ID/g at 60 min) from the brain. [¹⁸F]1a could be developed as a promising new PET imaging probe for Aβ plaques although necessary modifications are still needed.     

Syntheses and pharmacological characterization of novel thiazole derivatives as potential mGluR5 PET ligands

Four novel thiazole containing ABP688 derivatives were synthesized and evaluated for their binding affinity towards the metabotropic glutamate receptor subtype 5 (mGluR5). (E)-3-((2-(Fluoromethyl)thiazol-4-yl)ethynyl)cyclohex-2-enone O-methyl oxime (FTECMO), the ligand with the highest binding affinity (K_i = 5.5 ± 1.1 nM), was labeled with fluorine-18. [¹⁸F]-FTECMO displayed optimal lipophilicity (log D_pH7.4 = 1.6 ± 0.2) and high stability in rat and human plasma as well as sufficient stability in rat liver microsomes. In vitro autoradiography with [¹⁸F]-FTECMO revealed a heterogeneous and displaceable binding in mGluR5-rich brain regions. PET imaging with [¹⁸F]-FTECMO in Wistar rats, however, showed low brain uptake. Uptake of radioactivity into the skull was observed suggesting in vivo defluorination. Thus, although [¹⁸F]-FTECMO is an excellent ligand for the detection of mGluR5 in vitro, its in vivo characteristics are not optimal for the imaging of mGluR5 in rats in vivo.     

Clustering of spatial gene expression patterns in the mouse brain and comparison with classical neuroanatomy

Spatial gene expression profiles provide a novel means of exploring the structural organization of the brain. Computational analysis of these patterns is made possible by genome-scale mapping of the C57BL/6J mouse brain in the Allen Brain Atlas. Here we describe methodology used to explore the spatial structure of gene expression patterns across a set of 3041 genes chosen on the basis of consistency across experimental observations (N = 2). The analysis was performed on smoothed, co-registered 3D expression volumes for each gene obtained by aggregating cellular resolution image data. Following dimensionality and noise reduction, voxels were clustered according to similarity of expression across the gene set. We illustrate the resulting parcellations of the mouse brain for different numbers of clusters (K) and quantitatively compare these parcellations with a classically-defined anatomical reference atlas at different levels of granularity, revealing a high degree of correspondence. These observations suggest that spatial localization of gene expression offers substantial promise in connecting knowledge at the molecular level with higher-level information about brain organization.     

Synthesis and evaluation of 18F-labeled CJ-042794 for imaging prostanoid EP4 receptor expression in cancer with positron emission tomography

The potent and selective prostanoid EP4 receptor antagonist CJ-042794 was radiolabeled with ¹⁸F, and evaluated for imaging EP4 receptor expression in cancer with positron emission tomography (PET). The fluorination precursor, arylboronic acid pinacol ester 4, was prepared in 4 steps with 42% overall yield. ¹⁸F-CJ-042794 was synthesized via a copper-mediated ¹⁸F-fluorination reaction followed by base hydrolysis, and was obtained in 1.5 ± 1.1% (n = 2) decay-corrected radiochemical yield. PET/CT imaging and biodistribution studies in mice showed that ¹⁸F-CJ-042794 was excreted through both renal and hepatobiliary pathways with significant retention in blood. The EP4-receptor-expressing LNCaP prostate cancer xenografts were clearly visualized in PET images with 1.12 ± 0.08%ID/g (n = 5) uptake value and moderate tumour-to-muscle contrast ratio (2.73 ± 0.22) at 1 h post-injection. However, the tumour uptake was nonspecific as it could not be blocked by co-injection of cold standard, precluding the application of ¹⁸F-CJ-042794 for PET imaging of EP4 receptor expression in cancer.     

68Ga labeled Erlotinib: A novel PET probe for imaging EGFR over-expressing tumors

Molecular imaging using radiolabeled Tyrosine Kinase Inhibitors (TKI) is a promising strategy for detection and staging of EGFR-positive cancers. A novel analogue of one such TKI, Erlotinib has been developed for PET imaging by derivatizing the parent Erlotinib molecule for conjugation with the bifunctional chelator p-SCN-Bn-NOTA towards radiolabeling with ⁶⁸Ga. NOTA-Erlotinib conjugate was synthesized and characterized by NMR and ESI-MS techniques. The conjugate was radiolabeled with ⁶⁸Ga in 95 ± 2% yield, as evidenced by HPLC characterization. The log P value of ⁶⁸Ga-NOTA-Erlotinib was – (0.6 ± 0.1). The ⁶⁸Ga-NOTA-Erlotinib conjugate was characterized using its ^natGa-NOTA-Erlotinib surrogate. Cell viability studies showed that the NOTA-Erlotinib conjugate retained the biological efficacy of the parent Erlotinib molecule. Further, ⁶⁸Ga-NOTA-Erlotinib exhibited an uptake of 9.8 ± 0.4% in A431 cells which was inhibited by 55.1 ± 0.2% on addition of cold Erlotinib (10 µg) confirming the specificity of the radioconjugate for EGFR expressing cells. In the biodistribution studies carried out in tumor bearing SCID mice, ⁶⁸Ga-NOTA-Erlotinib conjugate showed moderate tumor accumulation (1.5 ± 0.1% ID/g at 30 min p.i.; 0.7 ± 0.2% ID/g at 1 h p.i.). Hepatobiliary clearance of the radioconjugate was observed. The ⁶⁸Ga-NOTA-Erlotinib conjugate was found to have high in vivo stability as determined by the metabolite analysis study using urine sample of the Swiss mice injected with the preparation. The overall properties of ⁶⁸Ga-NOTA-Erlotinib are promising and merit further exploration. To the best of our knowledge, this is the first report on the design of a ⁶⁸Ga labeled Erlotinib for PET imaging of EGFR and opens avenues for the successful development of ⁶⁸Ga labeled TKI for imaging of EGFR over-expressing tumors.     

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.     

Synthesis and evaluation of novel benzothiazole derivatives based on the bithiophene structure as potential radiotracers for β-amyloid plaques in Alzheimer’s disease

In this study, six novel benzothiazole derivatives based on the bithiophene structure were developed as potential β-amyloid probes. In vitro binding studies using Aβ aggregates showed that all of them demonstrated high binding affinities with K_i values ranged from 0.11 to 4.64 nM. In vitro fluorescent staining results showed that these compounds can intensely stained Aβ plaques within brain sections of APP/PS1 transgenic mice, animal model for AD. Two radioiodinated compounds [¹²⁵I]-2-(5′-iodo-2,2′-bithiophen-5-yl)-6-methoxybenzo[d]thiazole [¹²⁵I]10 and [¹²⁵I]-2-(2,2′-bithiophen-5-yl)-6-iodobenzo[d]thiazole [¹²⁵I]13 were successfully prepared through an iododestannylation reaction. Furthermore, in vitro autoradiography of the AD model mice brain sections showed that both [¹²⁵I]10 and [¹²⁵I]13 labeled the Aβ plaques specifically with low background. In vivo biodistribution studies in normal mice indicated that [¹²⁵I]13 exhibited high brain uptake (3.42% ID/g at 2 min) and rapid clearance from the brain (0.53% ID/g at 60 min), while [¹²⁵I]10 showed lower brain uptake (0.87% ID/g at 2 min). In conclusion, these preliminary results of this study suggest that the novel radioiodinated benzothiazole derivative [¹²⁵I]13 may be a candidate as an in vivo imaging agent for detecting β-amyloid plaques in the brain of AD patients.     

Synthesis of 18F-labelled 2-(4′-fluorophenyl)-1,3-benzothiazole and evaluation as amyloid imaging agent in comparison with [11C]PIB

2-(4′-[¹⁸F]fluorophenyl)-1,3-benzothiazole was synthesized as a fluorine-18 labelled derivative of the Pittsburg Compound-B (PIB), which has known affinity for amyloid β and promising characteristics as tracer for in vivo visualisation of amyloid deposits in patients suffering from Alzheimer’s disease (AD). Both the nitro-precursor 2-(4′-nitrophenyl)-1,3-benzothiazole and the non-radioactive reference compound were synthesized using a 1-step synthesis pathway. Labelling was achieved by direct aromatic nucleophilic substitution of the nitro-precursor using [¹⁸F]fluoride by heating for 20 min at 150 °C and with a radiochemical yield of 38%. The reference compound showed high affinity for amyloid in an in vitro competition binding study using human AD brain homogenates (K_i = 9.0 nM) and fluorescence imaging of incubated transgenic APP mouse brain slices confirmed binding to amyloid plaques. A biodistribution study in normal mice showed a high brain uptake at 2 min pi (3.20% ID/g) followed by a fast washout (60 min pi: 0.21% ID/g). A dynamic μPET study was performed in a transgenic APP and normal WT mouse, but, similar to [¹¹C]PIB, no difference was seen in tracer retention between both kind of mice. The new ¹⁸F-labelled 2-phenylbenzothiazole showed excellent preclinical characteristics comparable with those of the ¹¹C-labelled PIB.