A concisely automated synthesis of TSPO radiotracer [18 F]FDPA based on spirocyclic iodonium ylide method and validation for human use.

Fluorine-18 labeled N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide ([18 F]FDPA) is a potent and selective radiotracer for positron-emission tomography (PET) imaging of the translocator protein 18 kDa (TSPO). Our previous in vitro and in vivo evaluations have proven that this tracer is promising for further human translation. Our study addresses the need to streamline the automatic synthesis of this radiotracer to make it more accessible for widespread clinical evaluation and application. Here, we successfully demonstrate a one-step radiolabeling of [18 F]FDPA based on a novel spirocyclic iodonium ylide (SCIDY) precursor using tetra-n-butyl ammonium methanesulfonate (TBAOMs), which has demonstrated the highest radiochemical yields and molar activity from readily available [18 F]fluoride ion. The nucleophilic radiofluorination was completed on a GE TRACERlab FX2 N synthesis module, and the formulated [18 F]FDPA was obtained in nondecay corrected (n.d.c) radiochemical yields of 15.6 ± 4.2%, with molar activities of 529.2 ± 22.5 GBq/µmol (14.3 ± 0.6 Ci/µmol) at the end of synthesis (60 minutes, n = 3) and validated for human use. This methodology facilitates efficient synthesis of [18 F]FDPA in a commercially available synthesis module, which would be broadly applicable for routine production and widespread clinical PET imaging studies.

Novel (E)-5-styryl-2,2'-bithiophene derivatives as ligands for ß-amyloid plaques.

In continuation of our investigation on the bithiophene structure as potential ß-amyloid probes, a series of (E)-5-styryl-2,2'-bithiophene (SBTP) derivatives was designed and synthesized. In vitro binding showed that all of them displayed high binding affinities to Aß(1-42) aggregates (K(i)=0.10-41.05nM). Moreover, two radio-iodinated probes, [(125)I]-(E)-5-(4-iodostyryl)-2,2'-bithiophene ([(125)I]8) and [(125)I]-(E)-5-iodo-5'-(4-methoxystyryl)-2,2'-bithiophene ([(125)I]31) were prepared. Both of them displayed specific labeling of Aß plaques in the brain sections of AD model mice with low background. In vivo biodistribution in normal mice indicated that [(125)I]8 exhibited high initial brain uptake (2.11% ID/g at 2 min) and rapid clearance (0.41% ID/g at 30 min). These preliminary results suggest that SBTP derivatives may be served as novel ß-amyloid imaging probes.

Synthesis and biological evaluation of novel 4-benzylpiperazine ligands for sigma-1 receptor imaging.

We report the synthesis and evaluation of 4-benzylpiperazine ligands (BP-CH(3), BP-F, BP-Br, BP-I, and BP-NO(2)) as potential σ(1) receptor ligands. The X-ray crystal structure of BP-Br, which crystallized with monoclinic space group P2(1)/c, has been determined. In vitro competition binding assays showed that all the five ligands exhibit low nanomolar affinity for σ(1) receptors (K(i)=0.43-0.91nM) and high subtype selectivity (σ(2) receptor: K(i)=40-61nM; K(i)σ(2)/K(i)σ(1)=52-94). [(125)I]BP-I (1-(1,3-benzodioxol-5-ylmethyl)-4-(4-iodobenzyl)piperazine) was prepared in 53±10% isolated radiochemical yield, with radiochemical purity of >99% by HPLC analysis after purification, via iododestannylation of the corresponding tributyltin precursor. The logD value of [(125)I]BP-I was found to be 2.98±0.17, which is within the range expected to give high brain uptake. Biodistribution studies in mice demonstrated relatively high concentration of radiolabeled substances in organs known to contain σ(1) receptors, including the brain, lung, kidney, heart, and spleen. Administration of haloperidol 5min prior to injection of [(125)I]BP-I significantly reduced the concentration of radioactivity in the above-mentioned organs. The accumulation of radiolabeled substance in the thyroid was quite low suggesting that [(125)I]BP-I is relatively stable to in vivo deiodination. These findings suggest that the binding of [(125)I]BP-I to σ(1) receptors in vivo is specific.

99mTc- and Re-labeled 6-dialkylamino-2-naphthylethylidene derivatives as imaging probes for ß-amyloid plaques.

Based on the conjugate strategy, two neutral (99m)Tc labeled 2-(1-(6-(dialkylamino)naphthalen-2-yl)ethylidene)malononitrile (DDNP) and 1-(6-(dialkylamino)naphthalen-2-yl)ethanone (ENE) derivatives, and their corresponding rhenium complexes were synthesized. In vitro fluorescent staining indicated that the corresponding rhenium derivatives selectively stained the ß-amyloid (Aß) plaques in the brain sections of AD model mice with low background. Compared with FDDNP and FENE, the affinities of the corresponding rhenium derivatives to Aß aggregates decreased about 10-14-fold. In vivo biodistribution experiments in normal mice showed that (99m)Tc-MAMA-ENE displayed medium initial brain uptake (0.65%ID/g at 2min) with a reasonable washout from the brain (0.19%ID/g at 2h) while (99m)Tc-MAMA-DDNP showed a low brain uptake (0.28%ID/g at 2 min). Further optimize these (99m)Tc-labeled tracers in order to improve their binding affinities to Aß plaques and diffusion through the blood brain barrier may generate useful imaging agents for SPECT.

Preparation of classical Re/99mTc(CO)3(+) and novel 99mTc(CO)2(NO)2+ cores complexed with flavonol derivatives and their binding characteristics for Abeta(1-40) aggregates.

Classical (99m)Tc(CO)(3)(+) and novel (99m)Tc(CO)(2)(NO)(2+) cores complexed with flavonol derivatives were prepared. Autoradiography of postmortem AD transgenic mice (Tg C57, APP, PS1 12-month-old) brain section confirmed the binding property of [(99m)Tc(CO)(3)(+)-3-OH-flavone](0) to Abeta((1-40)) aggregates, while the novel (99m)Tc(CO)(2)(NO)(2+) labeled compounds showed no binding sites in AD transgenic mice sections. Intravenous administration of [(99m)Tc(CO)(3)(+)-3-OH-flavone](0) resulted in moderate brain uptake (0.48+/-0.05%ID/g) at 5 min post-injection and slow clearance from the brain issues in 2h post-injection (120 min: 0.39+/-0.08%ID/g). Then an Abeta((1-40))-receptor-targeted Re(CO)(3)(+)-3-OH-flavone, was prepared to identify the structure of the technetium complex. UV-vis absorption and fluorescence emission properties have been studied at room temperature in order to determine the natures of the lowest electronically excited states of Re(CO)(3)(+)-3-OH-flavone and the ligand. The fluorescent rhenium complex Re(CO)(3)(+)-3-OH-flavone showed high affinity for Abeta((1-40)) aggregates in vitro by fluorescence spectra (dissociation constant (K(d))=11.16 nM). In conclusion, the results suggested that (99m)Tc(CO)(3)(+)-3-OH-flavone should be a suitable candidate as Abeta plaque SPECT imaging agent for AD.

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

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