Ta-Kai Chou

PET imaging of serotonin transporters with 4-[18F]-ADAM in a Parkinsonian rat model.

This study was undertaken to address the effects of fetal mesencephalic tissue transplantation on the serotonin system in a rat model of Parkinsons disease (PD) while also investigating the usefulness of 4-[18F]-ADAM (a serotonin transporter imaging agent) coupled with micro-PET for imaging serotonin transporters (SERTs). A PD model was induced by unilateral injection of 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle of the nigrostriatal pathway, while cell transplantation was performed via intrastriatal injection of mesencephalic brain tissue dissected from embryonic (E14) rats. The 4-[18F]-ADAM/micro-PET scanning was performed following both 6-OHDA lesioning and transplantation. Immunohistochemistry (IHC) studies were also performed following the final PET scan, and the results were compared to show a 17–43% decrease in the specific uptake ratio (SUR) and a 23–52% decrease in serotonin transporter immunoreactivity (SERT-ir) within various brain regions on the lesioned side. The number of methamphetamine-induced rotations also decreased significantly at the 4th week postgraft. In addition, striatal SUR and the SERT-ir levels were restored to 77% and 83% 5 weeks postgraft. These results suggest that Parkinsons disease also affects the serotonergic system, while both the dopaminergic and serotonergic systems can be partially restored in a rat model of PD after E14 mesencephalic tissue transplantation. In addition, we have also determined that 4-[18F]-ADAM/micro-PET can be used to detect serotonergic neuron loss, monitor the progress of Parkinsons disease, and oversee the effectiveness of therapy.

PET Imaging of Serotonin Transporters with 4-[18F]-ADAM in a Parkinsonian Rat Model with Porcine Neural Xenografts:

Parkinsons disease (PD) is a neurodegenerative disease characterized by a loss of dopaminergic neurons in the nigrostriatal pathway. Apart from effective strategies to halt the underlying neuronal degeneration, cell replacement now offers novel prospects for PD therapy. Porcine embryonic neural tissue has been considered an alternative source to human fetal grafts in neurodegenerative disorders because its use avoids major practical and ethical issues. This study was undertaken to evaluate the effects of embryonic day 27 (E27) porcine mesencephalic tissue transplantation in a PD rat model using animal positron emission tomography (PET) coupled with 4-[18F]-ADAM, a serotonin transporter (SERT) imaging agent. The parkinsonian rat was induced by injecting 6-hydroxydopamine into the medial forebrain bundle (MFB) of the right nigrostriatal pathway. The apomorphine-induced rotation behavioral test and 4-[18F]-ADAM/animal PET scanning were carried out following 6-OHDA lesioning. At the second week following 6-OHDA lesioning, the parkinsonian rat rotates substantially on apomorphine-induced contralateral turning. In addition, the mean striatal-specific uptake ratio (SUR) of 4-[18F]-ADAM decreased by 44%. After transplantation, the number of drug-induced rotations decreased markedly, and the mean SUR of 4-[18F]-ADAM and the level of SERT immunoreactivity (SERT-ir) in striatum were partially restored. The mean SUR level was restored to 71% compared to that for the contralateral intact side, which together with the abundant survival of tyrosine hydroxylase (TH) neurons accounted for functional recovery at the fourth week postgraft. In regard to the extent of donor-derived cells, we found the neurons of the xenografts from E27 transgenic pigs harboring red fluorescent protein (RFP) localized with TH-ir cells and SERT-ir in the grafted area. Thus, transplanted E27 porcine mesencephalic tissue may restore dopaminergic and serotonergic systems in the parkinsonian rat. The 4-[18F]-ADAM/animal PET can be used to detect serotonergic neuron loss in PD and monitor the efficacy of therapy.

Synthesis and comparison of 4-[18F]F-ADAM, 2-[18F]F-ADAM, N-Desmethyl-4-[18F]F-ADAM and [18F]F-AFM as serotonin transporter imaging agents

4-[(18)F]F-ADAM (1a), 2-[(18)F]F-ADAM (2a), N-Desmethyl-4-[(18)F]F-ADAM (3a) and [(18)F]F-AFM (4a ) were synthesized in 1.7, 3.9, 2.9 and 0.6% yield (EOS), respectively, in a synthesis time of ~120 min from EOB. PET studies in rats showed that the maximum specific uptake ratios of 1a, 2a, 3a and 4a in midbrain were 3.86, 0.73, 0.35 and 2.23, respectively. Thus, in terms of radiochemical yield, specific binding and in vivo stability, 4-[(18)F]F-ADAM may be the most appropriate SERT imaging agent for human studies.

KA-bridged transplantation of mesencephalic tissue and olfactory ensheathing cells in a Parkinsonian rat model

The pathology of Parkinsons disease (PD) results mainly from nigrostriatal pathway damage. Unfortunately, commonly used PD therapies do not repair the disconnected circuitry. It has been reported that using kainic acid (KA, an excitatory amino acid) in bridging transplantation may be useful to generate an artificial tract and reconstruct the nigrostriatal pathway in 6‐hydroxydopamine (6‐OHDA) lesioned rats. In this study, we used KA bridging and a co‐graft of rat olfactory ensheathing cells (OECs) and rat E14 embryonic ventral mesencephalic (VM) tissue to restore the nigrostriatal pathway of the PD model rats. The methamphetamine‐induced rotational behaviour, 4‐[18F]–ADAM (a selectively serotonin transporter radioligand)/micro‐PET imaging, and immunohistochemistry were used to assess the effects of the transplantation. At 9 weeks post‐grafting in PD model rats, the results showed that the PD rats undergoing VM tissue and OECs co‐grafts (VM–OECs) exhibited better motor recovery compared to the rats receiving VM tissue transplantation only. The striatal uptake of 4‐[18F]–ADAM and tyrosine hydroxylase immunoreactivity (TH‐ir) of the grafted area in the VM–OECs group were also more improved than those of the VM alone group. These results suggested that OECs may enhance the survival of the grafted VM tissue and facilitate the recovery of motor function after VM transplantation. Moreover, OECs possibly promote the elongation of dopaminergic and serotonergic axon in the bridging graft. Copyright

Fully automated one-pot two-step synthesis of 4-[18F]-ADAM, a potent serotonin transporter imaging agent

INTRODUCTION N,N-dimethyl-2-(2-amino-4-[(18)F]fluorophenylthio)benzylamine (4-[(18)F]-ADAM, 2) is a potent serotonin transporter (SERT) imaging agent. In order to fulfill the demand of clinical studies, we have developed a fully automated one-pot two-step synthesis of this potent SERT imaging agent. METHODS The 4-[(18)F]-ADAM (2) was synthesized using a commercially available GE TRACERlab FN module. Briefly, the precursor, N,N-dimethyl-2-(2,4-dinitrophenylthio) benzylamine (1) in DMSO was reacted with K[(18)F]/K2.2.2 in a glassy carbon reaction vessel at 120°C for 7.5min followed by reduction of the intermediate with NaBH4/Cu(OAc)2 in EtOH in the same vessel at 80°C for 20min. The reaction mixture was then purified with high-performance liquid chromatography (HPLC) and solid phase extraction (SPE) to give (2). The quality of (2) synthesized by this method was verified by HPLC and TLC as compared to its authentic sample synthesized by two-pot two-step method. RESULTS Using this automated one-pot two-step method, the radiochemical yield (RCY) of (2) was 2.5±0.8% (n=12, EOS) in a synthesis time of 100±6min from EOB with a specific activity of 4.4±1.9Ci/μmol (n=12, EOS). Radioligand (2) was stable over 4h at room temperature. CONCLUSIONS This fully automated one-pot two-step synthetic method using a commercially available GE TRACERlab FN module could simplify the synthesis of 4-[(18)F]-ADAM (2) and fulfill its demand for both animal and human studies, especially for study sites without a cyclotron.

A practical and pyrogen-free preparation of 11C-L-methionine in a good manufacturing practice-compliant approach

Aims: 11C-L-methionine, an amino acid tracer used to delineate certain tumor tissues, has proven to be a prevailing nonfluorodeoxyglucose positron emission tomography (PET) radiopharmaceutical. We intended to prepare 11C-L-methionine by following modified synthetic strategies at a rebuilt working area to meet the PET drug current good manufacturing practice (cGMP) and Pharmaceutical Inspection Co-operation Scheme (PIC/S) regulations. Furthermore, we overcame the problem of pyrogen cross-contamination using a cleaner and more efficient program. Material and Methods: The task of upgrading air filtration equipment was integrated with the set of Web-Based Building Automation system (WebCTRL®). 11C-L-methionine synthesis was carried out in accordance with redesigned methods to meet the requirements of PET drug cGMP. The product quality was tested by a series of quality control tests and was found to be satisfactory. Depyrogenation was carried out by three different methods with different flow rates and flushing durations. The results were examined through limulus amebocyte lysate clotting test. Results: The level of air cleanliness in each section meets the PIC/S GMP standards after the reconstructions. Moreover, after delicate modifications, the radiochemical yield of 11C-L-methionine was 36.20% ± 3.59% (based on 11C-CH3I, n = 7), which is about 10% higher than the average former yield. Besides, the used depyrogenation methods could wipe the bioburden off within 8 h. Conclusions: The modifications done not only offer a good production environment but also protect the products from contamination. The modified approaches in both 11C-L-methionine production and depyrogenation resulted in prominent progress in stability and efficiency as well.

Erratum to: Toxicity and radiation dosimetry studies of the serotonin transporter radioligand [18F]AFM in rats and monkeys

Erratum Unfortunately, the original version of this article was published with incorrect details for one authors name and address. Cheng-Yi Cheng’s name, which had been incorrectly spelled as Chen-Yi Cheng, has been corrected. The author’s correct address is as follows: PET Center, Department of Nuclear Medicine, TriService General Hospital, National Defense Medical Center, 325 Sec. 2, Cheng-Kung Road, Taipei 114, Taiwan.