Currently available PET tracers used in Alzheimer's disease (AD) have limited utility in prognosis and in revealing reliable clinicopathologic correlations of disease. Therefore, identification and validation of novel biomarkers for AD progression and preclinical disease onset through noninvasive neuroimaging is a top priority in biomedical research. We proposed to target microtubules (MTs) as an imaging target for AD in preclinical, postmortem and clinical studies that support the implication of altered regulation of MTs in AD and positively correlated with neurodegeneration process. Furthermore, MT loss in AD is contributed to a large number of mutated proteins, enzymes, and post-translational modifications compared to other imaging targets. Therefore, targeting brain MTs may be advantageous, as cumulative loss of MTs is the final common pathway for a variety of biochemical pathologies leading to neurodegeneration in AD. [ 11 C]MPC-6827 is the pioneer BBB-penetrating PET tracer available for in vivo imaging of MTs in brain. 1,2 Herein, we report the comparative binding of [ 11 C]MPC-6827, and [ 11 C]PiB in Aβ over expressing APP mutated transgenic J20 mice and controls. [ 11 C]MPC-6827 and [ 11 C]PiB were synthesized using GE Tracerlab FX2 MEI and FX2N modules. Dynamic PET scans were performed for 30 min after tail vein injection of [ 11 C]MPC-6827 and [ 11 C]PiB in 6-month-old J20 mice and littermates (n=4) using a Siemens Focus 220 microPET scanner. Image analyses were performed with Mango software on reconstructed data. PET image analyses show ∼30% of reduced whole brain uptake of [ 11 C]MPC-6827 in J20 mice whereas, [ 11 C]PiB exhibited modest higher binding (∼10%) in J20 than control mice. Standardized uptake values (SUVs) show similar trend of binding of tracers in prefrontal cortex (PFC) and hippocampus in J20 and control mice. Our preliminary studies show that in J20 mice, binding of the [ 11 C]MPC-6827 is reduced in whole brain, hippocampus and PFC compared control mice and is inversely correlated with [ 11 C]PiB binding. The effect size of [ 11 C]MPC-6827 seems higher than [ 11 C]PiB. Therefore, [ 11 C]MPC-6827 could be used as a PET tracer for human brain imaging of AD and other NDs. Acknowledgement: This work was funded by Center for Biomedical Neuroscience (CBN) 2020-2021, UT Health San Antonio, Texas, USA.

Microtubules are abundant in brain and their malfunctioning occurs in the early-to-advanced stages of neurodegenerative disorders. At present, there is no in vivo test available for a definitive diagnosis of most of the neurodegenerative disorders. Herein, we present the microPET imaging of microtubules using our recently reported Positron Emission Tomography (PET) tracer, [11C]MPC-6827, in transgenic mice models of tau pathology (rTg4510) and amyotrophic lateral sclerosis pathology (SOD1*G93A) and compared to corresponding age-matched controls. Automated synthesis of [11C]MPC-6827 was achieved in a GE-FX2MeI/FX2M radiochemistry module. In vivo PET imaging studies of [11C]MPC-6827 (3.7 ± 0.8 MBq) were performed in rTg4510 and SOD1*G93A mice groups and their corresponding littermates (n = 5 per group). Dynamic PET images were acquired using a microPET Inveon system (Siemens, Germany) at 55 min for rTg4510 and 30 min for SOD1*G93A and corresponding controls. PET images were reconstructed using the 3D-OSEM algorithm and analyzed using VivoQuant version 4 (Invicro, MA). Tracer uptake in ROIs that included whole brain was measured as %ID/g over time to generate standardized uptake values (SUV) and time–activity curves (TACs). [11C]MPC-6827 exhibit a trend of lower tracer binding in mouse models of Alzheimer’s disease (tau pathology, line rTg4510) and Amyotrophic Lateral Sclerosis (line SOD1*G93A) compared to wild-type littermates. Our finding indicates a trend of loss of microtubule binding of [11C]MPC-6827 in the whole brain of AD and ALS transgenic mice models compared to control mice. The pilot studies described herein show that [11C]MPC-6827 could be used as a PET ligand for preclinical and human brain imaging of Alzheimer’s disease, ALS, and other neurodegenerative diseases. Preclinical Evaluation of a Microtubule PET Ligand [11C]MPC-6827 in Tau and Amyotrophic Lateral Sclerosis Animal Models. J. S. Dileep Kumar, Andrei Molotkov, Jongho Kim, Patrick Carberry, Sidney Idumonyi, John Castrillon, Karen Duff, Neil A. Shneider, Akiva Mintz

Combinations of antiangiogenic and cytotoxic agents show promising results in the treatment of cancer. However, there is a lack of single agent with both antiangiogenic and cytotoxic activities for clinical application. AG-488 aka FLAG-003 is a novel ligand with established antiangiogenetic properties via activation of receptor thymidine kinase (RTK) and anti-tubulin properties in tumor cells. AG-488 is also reported to reduce tumor volume and prolong survival in preclinical animal models of glioblastoma multiforme, breast cancer and is in clinical stage. Higher expression of RTKs and tubulins is reported in various cancers. This study reveals the development of [11C]AG-488, a high affinity dual target inhibitor binding to RTK and anti-tubulin activities. We rationale that antiangiogenic RTK and anti-tubulin activity of [11C]AG-488 may enhance the tumor to tissue ratio, assisting in cancer drug development. [11C]AG-488 was synthesized in 35 ± 5 % radiochemical yield by radiomethylating the corresponding phenolate using [11C]CH3I. MicroPET studies in mice indicated blood-brain barrier penetration of [11C]AG-488 and retention in the brain. However, blocking studies with antitubulin and RTK agent HD-800 and microtubule depolymerizing agent MPC-6827 show increased binding of [11C]AG-488 in brain. The pattern of tracer binding in blocking conditions is similar to the baseline conditions. The higher binding may be due to the increased plasma uptake of radiotracer or the formation of more free tubulins due to microtubule dynamic instability during the blocking conditions.

Altered expression of VEGFR2 is reported in the pathology of neurological, neuropsychiatric, brain malignancies and developmental disorders. PET imaging that allows for in vivo visualization of specific targets on the molecular level allows early detection, diagnosis and treatment monitoring non-invasively and accelerates therapeutic development. Our ongoing effort to derive a PET tracer that can be used to quantify the changes in VEGFR2 and resulted in the identification of N-(benzo furan-5-yl)-N-2,6-trimethylfuro[2,3–d]pyrimidin-4-amine (BTFP) (IC50 = 5.8 nM). In this report, the automated radiochemical synthesis and in vivo evaluation of a high affinity VEGFR2 ligand, [11C]BTFP by using PET is described. [11C]BTFP is synthesized in 35 ± 5% radiochemical yield by radiomethylating the N-desmethyl-BTFP precursor using [11C]CH3I. MicroPET studies in mice indicated a blood–brain barrier penetration of [11C]BTFP, with modest uptake and specific binding. Although, the low brain uptake of [11C]BTFP diminished its utility for in vivo imaging application, it can be used as a lead molecule for developing new PET tracers for central nervous system imaging.

Background The upregulation of cyclooxygenase-2 (COX-2) is involved in neuroinflammation associated with many neurological diseases as well as cancers of the brain. Outside the brain, inflammation and COX-2 induction contribute to the pathogenesis of pain, arthritis, acute allograft rejection, and in response to infections, tumors, autoimmune disorders, and injuries. Herein, we report the radiochemical synthesis and evaluation of [ 18 F]6-fluoro-2-(4-(methylsulfonyl)phenyl)- N -(thiophen-2-ylmethyl)pyrimidin-4-amine ([ 18 F]FMTP), a high-affinity COX-2 inhibitor, by cell uptake and PET imaging studies. Methods The radiochemical synthesis of [ 18 F]FMTP was optimized using chlorine to fluorine displacement method, by reacting [ 18 F]fluoride/K222/K 2 CO 3 with the precursor molecule. Cellular uptake studies of [ 18 F]FMTP was performed in COX-2 positive BxPC3 and COX-2 negative PANC-1 cell lines with unlabeled FMTP as well as celecoxib to define specific binding agents. Dynamic microPET image acquisitionwas performed in anesthetized nude mice ( n = 3), lipopolysaccharide (LPS) induced neuroinflammation mice ( n = 4), and phosphate-buffered saline (PBS) administered control mice ( n = 4) using a Trifoil microPET/CT for a scan period of 60 min. Results A twofold higher binding of [ 18 F]FMTP was found in COX-2 positive BxPC3 cells compared with COX-2 negative PANC-1 cells. The radioligand did not show specific binding to COX-2 negative PANC-1 cells. MicroPET imaging in wild-type mice indicated blood–brain barrier (BBB) penetration and fast washout of [ 18 F]FMTP in the brain, likely due to the low constitutive COX-2 expression in the normal brain. In contrast, a ~ twofold higher uptake of the radioligand was found in LPS-induced mice brain than PBS treated control mice. Conclusions Specific binding to COX-2 in BxPC3 cell lines, BBB permeability, and increased brain uptake in neuroinflammation mice qualifies [ 18 F]FMTP as a potential PET tracer for studying inflammation.

Abstract Background Serotonin 1A (5-HT1A) receptors are implicated in the pathogenesis of several psychiatric and neurodegenerative disorders motivating the development of suitable radiotracers for in vivo positron emission tomography (PET) neuroimaging. The gold standard PET imaging agent for this target is [carbonyl-11C]WAY-100635, labeled via a technically challenging multi-step reaction that has limited its widespread use. While several antagonist and agonist-based PET radiotracers for 5-HT 1A receptors have been developed, their clinical translation has been hindered by methodological challenges and/or and non-specific binding. As a result, there is continued interest in the development of new and more selective 5-HT1A PET tracers having a relatively easier and reliable radiosynthesis process for routine production and with favorable metabolism to facilitate tracer-kinetic modeling. The purpose of the current study was to develop and characterize a radioligand with suitable characteristics for imaging 5-HT1A receptors in the brain. The current study reports the in vitro characterization and radiosyntheses of three candidate 5-HT1A receptor antagonists, DF-100 (1), DF-300 (2) and DF-400 (3), to explore their suitability as potential PET radiotracers. Results Syntheses of 1–3 and corresponding precursors for radiolabeling were achieved from isonicotinic, picolinic acid or picolino nitrile. In vitro binding studies demonstrated nanomolar affinity of the compounds for 5-HT1A receptors. Binding of 1–3 for other biogenic amines, neurotransmitter receptors, and transporters was negligible with the exception of moderate affinities for α1-adrenergic receptors (4–6-fold less potent than that for 5-HT1A receptor). Radioligands [11C]1–3 were efficiently prepared by 11C-O-methylation of the corresponding phenolic precursor in non-decay corrected radiochemical yields of 7–11% with > 99% chemical and radiochemical purities. Dynamic PET studies in rats demonstrated negligible brain uptake of [11C]1 and [11C]2. In contrast, significant brain uptake of [11C]3 was observed with an early peak SUV of 4–5. However, [11C]3 displayed significant off-target binding attributed to α1-adrenergic receptors based on regional distribution (thalamus>hippocampus) and blocking studies. Conclusion Despite efficient radiolabeling, results from PET imaging experiments limit the application of [11C]3 for in vivo quantification of 5-HT1A receptors. Nevertheless, derivatives of compound 3 may provide a scaffold for alternative PET radiotracers with improved selectivity for 5-HT 1A receptors or α1-adrenergic receptors.

Altered dynamics of microtubules (MT) are implicated in the pathophysiology of a number of brain diseases. Therefore, radiolabeled MT targeted ligands that can penetrate the blood brain barrier (BBB) may offer a direct and sensitive approach for diagnosis, and assessing the clinical potential of MT targeted therapeutics using PET imaging. We recently reported two BBB penetrating radioligands, [11C]MPC-6827 and [11C]HD-800 as specific PET ligands for imaging MTs in brain. The major metabolic pathway of the above molecules is anticipated to be via the initial labeling site, O-methyl, compared to the N-methyl group. Herein, we report the radiosynthesis of N-11CH3-MPC-6827 and N-11CH3-HD-800 and a comparison of their in vivo binding with the corresponding O-11CH3 analogues using microPET imaging and biodistribution methods. Both O-11CH3 and N-11CH3 labeled MT tracers exhibit high specific binding and brain. The N-11CH3 labeled PET ligands demonstrated similar in vivo binding characteristics compared with the corresponding O-11CH3 labeled tracers, [11C]MPC-6827 and [11C]HD-800 respectively.

In healthy neurons, tau binds to microtubules to regulate its stability; in AD brains, however, tau is detached from microtubules and phosphorylated at multiple sites. There is a critical need for early AD biomarkers that capture changes in neuronal integrity and stability, especially in the context of Aβ and tau pathology. Microtubule PET imaging agent could be an ideal bridge between classical biomarkers and molecular imaging tools, providing a solid platform to image brain functions (early on) in AD. We have recently reported the radiochemical synthesis of the first brain-penetrating MT PET ligand, [11C]MPC-6827 and it's in vivo PET imaging in normal mice. In this presentation, we report the in vivo evaluations of [11C]MPC-6827 in Aβ-over expressing (APP-PS1, 5xFAD) and tau-over expressing (P301S) transgenic and wild-type Alzheimer mice. Dynamic PET imaging was performed in both transgenic and wild-type (n=3/group) APP-PS1 (at 22 months), 5xFAD (at 15 months) and P301S mice (at 8 months) by injecting 120 ± 20 μCi of [11C]MPC-6827. Ex vivo post-PET biodistribution studies were performed in both transgenic and wild-type APP/PS1 mice (n=3/group). Post-PET blocking biodistribution studies were performed in transgenic 5xFAD mice (n=6) by injecting the non-radioactive MPC-6827 (5 mg/kg), 45 min before the radiotracer injection. Through Regions of interest (ROI) PET analyses in whole brain, [11C]MPC-6827 showed significant lower radioactive uptake in the transgenic APP-PS1 (∼3.2 fold), 5xFAD (∼3.4 fold) and P301S mice (∼1.5 fold) over their corresponding wild-type control mice. Through biodistribution studies, APP/PS1 transgenic mice displayed ∼3.3-fold lower brain uptake compared to wild-type mice: %ID (injected dose)/g of 1.9213 ± 0.536 (wild-type) and 0.5167 ± 0.391 (transgenic). More importantly, these data showed that post-PET biodistribution results in brain corroborated well with the microPET/CT analysis. We observed a significant blocking (∼75%) in the brain uptake of blockade transgenic 5xFAD mice compared to the baseline, demonstrating specificity of the tracer towards microtubules in AD mice. [11C]MPC-6827 demonstrated differential (lower) binding in transgenic mice models of AD, through both in vivo microPET and ex vivo biodistribution studies. [11C]MPC-6827 could be used as a potential PET tracer for preclinical and human imaging of AD.

Objective: The objective of this study was to evaluate the uptake and specificity of [11 Methods: [ C]MPC-6827, a MT targeted PET ligand in prostate, glioblastoma and breast cancer cells. 11C]MPC-6827 was synthesized by reacting corresponding desmethyl precursors with [11C]CH3I in a GE-FX2MeI/FX2M radiochemistry module. In vitro binding of [11 Results: [ C]MPC-6827 was performed in breast cancer MDA-MB-231, glioblastoma (GBM) patient-derived tumor (GBM-PDX), GBM U251 and prostate cancer 3 (PC3) cell lines at 37 °C in quadruplicate at 5, 15, 30, 60, and 90 minute incubation time. The nonspecific bindings were determined by incubation with unlabeled microtubule targeting agents MPC-6827, HD-800, colchicine, paclitaxel and docetaxel (5.0 μM). 11C]MPC-6827 provided the highest binding in the breast cancer cell, MDA-MB-231, among all the cells studied, with 90% specific binding. [11C]MPC-6827 binds to glioblastoma PDX and U251 cells with ~50% and 40% specific binding, whereas, prostate cancer cell line, PC3 cells showed 40% specific binding. [11 Conclusion: These data indicate that [ C]MPC-6827 also exhibits binding to the taxane and colchicine binding sites of MTs, in MDA-MB-231 cells.

PURPOSE:5-HT2AR exists in high and low affinity states. Agonist PET tracers measure binding to the active high affinity site and thus provide a functionally relevant measure of the receptor. Limited in vivo data have been reported so far for a comparison of agonist versus antagonist tracers for 5-HT2AR used as a proof of principle for measurement of high and low affinity states of this receptor. We compared the in vivo binding of [11C]CIMBI-5, a 5-HT2AR agonist, and of the antagonist [11C]M100907, in monkeys and baboons.METHODS:[11C]CIMBI-5 and [11C]M100907 baseline PET scans were performed in anesthetized male baboons (n=2) and male vervet monkeys (n=2) with an ECAT EXACT HR+ and GE 64-slice PET/CT Discovery VCT scanners. Blocking studies were performed in vervet monkeys by pretreatment with MDL100907 (0.5 mg/kg, i.v.) 60 minutes prior to the scan. Regional distribution volumes and binding potentials were calculated for each ROI using the likelihood estimation in graphical analysis and Logan plot, with either plasma input function or reference region as input, and simplified reference tissue model approaches.RESULTS:PET imaging of [11C]CIMBI-5 in baboons and monkeys showed the highest binding in 5-HT2AR-rich cortical regions, while the lowest binding was observed in cerebellum, consistent with the expected distribution of 5-HT2AR. Very low free fractions and rapid metabolism were observed for [11C]CIMBI-5 in baboon plasma. Binding potential values for [11C]CIMBI-5 were 25-33% lower than those for [11C]MDL100907 in the considered brain regions.CONCLUSION:The lower binding potential of [11C]CIMBI-5 in comparison to [11C]MDL100907 is likely due to the preferential binding of the former to the high affinity site in vivo in contrast to the antagonist,  [11C]MDL100907, which binds to both high and low affinity sites.

Objective: The objective of this study was to evaluate the uptake and specificity of [11C]MPC-6827, a MT targeted PET ligand in prostate, glioblastoma and breast cancer cells. Methods: [11C]MPC-6827 was synthesized by reacting corresponding desmethyl precursors with [11C]CH3I in a GE-FX2MeI/FX2M radiochemistry module. In vitro binding of [11C]MPC-6827 was performed in breast cancer MDA-MB-231, glioblastoma (GBM) patient-derived tumor (GBM-PDX), GBM U251 and prostate cancer 3 (PC3) cell lines at 37 °C in quadruplicate at 5, 15, 30, 60, and 90 minute incubation time. The nonspecific bindings were determined by incubation with unlabeled microtubule targeting agents MPC-6827, HD-800, colchicine, paclitaxel and docetaxel (5.0 mM). Results: [11C]MPC-6827 provided the highest binding in the breast cancer cell, MDA-MB-231, among all the cells studied, with 90% specific binding. [11C]MPC-6827 binds to glioblastoma PDX and U251 cells with ~50% and 40% specific binding, whereas, prostate cancer cell line, PC3 cells showed 40% specific binding. [11C]MPC-6827 also exhibits binding to the taxane and colchicine binding sites of MTs, in MDA-MB-231 cells. Conclusion: These data indicate that [11C]MPC-6827 can be a promising PET radiotracer for preclinical imaging of the brain and peripheral cancers.

COX-2 selective inhibitors (COXIBs) are non-steroidal anti-inflammatory drugs (NSAIDs), with fewer side effects compared with non-selective NSAIDs, and are used for the treatment of arthritis, headaches, and other inflammatory diseases of the brain and peripheral tissues. Radiolabeled COXIBs may permit positron emission tomography (PET) imaging of COX-2 localization and activity in diseases, enable monitoring of inflammatory processes, and determine target occupancy of COX-2 activity by NSAIDs, thus, accelerating the development of novel CIXIBs. We synthesized [11C]celecoxib, one of the COXIBs and a prescription drug, and here report its in vivo uptake in the brain, whole body biodistribution, and radiation dosimetry in baboons using PET. Brain imaging experiments were performed in one baboon and whole body PET scans were performed in triplicates in two male baboons using an ECAT ACCEL (Siemens Medical Solutions, Inc. Knoxville) under anesthetic conditions. PET studies in baboons show that [11C]celecoxib penetrates the blood brain barrier (BBB) and accumulates in the brain, followed by a washout of radioactivity. The liver has the highest residence time and the gallbladder is the critical organ for [11C]celecoxib. Organ Level Internal Dose Assessment (OLINDA) estimates indicate that the maximum permissible single study dosage of [11C]celecoxib in humans is 1110 MBq (30 mCi) for both males and females under the 21 CFR 361.1 dose limit for research subjects.

Serotonin receptor, 5-HT1AR, agonists and partial agonists have established drug candidates for psychiatric and neurologic disorders. Recently, we reported the synthesis and evaluation of arylpiperazine derivatives of 3,5-dioxo-(2H,4H)-1,2,4-triazine as 5-HT1AR ligands. Herein, we generated a homology model of the receptor and docked the ligands against it, predicted the stability of the receptor model and complexes by molecular dynamics and generated a 3D-QSAR model for the arylpiperazine derivatives of 3,5-dioxo-(2H,4H)-1,2,4-triazine. The model suggests the hydrophobic part that arises from the aromatic region and the electron withdrawing parts play a vital role in the agonist activity of the lead molecules.

Overexpression of Cyclooxygenase-2 (COX-2) enzyme is associated with the pathogenesis of inflammation, cancers, stroke, arthritis, and neurological disorders. Because of the involvement of COX-2 in these diseases, quantification of COX-2 expression using Positron Emission Tomography (PET) may be a biological marker for early diagnosis, monitoring of disease progression, and an indicator of effective treatment. At present there is no target-specific or validated PET tracer available for in vivo quantification of COX-2. The objective of this study is to evaluate [C-11]TMI, a selective COX-2 inhibitor (Ki <= 1 nM) in nonhuman primates using PET imaging. PET imaging in baboons showed that [C-11]TMI penetrates the blood brain barrier (BBB) and accumulates in brain in a somewhat heterogeneous pattern. Metabolite analyses indicated that [C-11]TMI undergoes no significant metabolism of parent tracer in the plasma for baseline scans, however a relative faster metabolism was found for blocking scan. All the tested quantification approaches provide comparable tracer total distribution volume (V-T) estimates in the range of 3.2-7 (mL/cm(3)). We observed about 25% lower V-T values in blocking studies with meloxicam, a nonselective COX-2 inhibitor, compared to baseline [C-11]TMI binding. Our findings indicate that [C-11]TMI may be a suitable PET tracer for the quantification of COX-2 in vivo. Further experiments are needed to confirm the potential of this tracer in COX-2 overexpressing models for brain diseases.

Radiosynthesis and in vivo evaluation of [C-11]4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl] benzenesulfonamide (methoxy analogue of valdecoxib, [C-11]MOV), a COX-2 inhibitor, was conducted in rat and baboon. Synthesis of the reference standard MOV (3), and its desmethyl precursor 2 for radiolabeling were performed using 1,2-diphenylethan-1-one as the starting material in five steps with 15% overall yield. Radiosynthesis of [C-11]MOV was accomplished in 40 +/- 10% yield and > 99% radiochemical purity by reacting the precursor 2 in dimethyl formamide (DMF) with [C-11] CH3I followed by removal of the dimethoxytrityl (DMT) protective group using trifluroacetic acid. PET studies in anesthetized baboon showed very low uptake and homogeneous distribution of [C-11]MOV in brain. The radioligand underwent rapid metabolism in baboon plasma. MicroPET studies in male Sprague Dawley rats revealed [C-11]MOV binding in lower thorax. The tracer binding in rats was partially blocked in heart and duodenum by the administration of 1 mg/kg oral dose of COX-2 inhibitor valdecoxib.

Microtubules (MTs) are highly abundant throughout the cytoskeleton, and their dysfunction is implicated in the pathogenesis of malignancies, various neurodegenerative disorders, and brain injuries. Validated radiotracers reported so far for MTs are [11C]paclitaxel, [18F]fluoropaclitaxel, and [11C]docetaxel; however, they are well-characterized substrates of efflux transporters and consequently have poor uptake into the brain due to minimal blood brain barrier (BBB) penetration. PET imaging of MT expression requires radiolabeled BBB penetrating MT ligands, and it may offer a direct and more sensitive approach for early diagnosis, monitoring disease progression, and treatment effects in brain diseases and assessing the clinical potential of targeted therapeutics and treatments. We have identified N-(4-methoxyphenyl)-N-5-dimethylfuro[2,3-d]pyrimidin-4-amine (HD-800) as a high affinity and selective colchicine site tubuline inhibitor amenable to radiolabel with C-11, a positron emitting isotope. HD-800 and desmethyl-HD-800 were synthesized in one step with 75% and 80% yields respectively from commercial synthons. The radiosynthesis of [11C]HD-800 was achieved in 45 ± 5% yield at EOS. Ex vivo biodistribution binding data of [11C]HD-800 indicate that the radioligand penetrated the BBB and it was retained in brain with 75% specific binding. Apart from the brain, specific binding was observed in muscle (55%), heart (50%), lungs (43%), blood (37%), and pancreas (30%). MicroPET imaging in mice showed excellent binding in brain that was blocked by preadministration of unlabeled HD-800 and a colchicine site binding MT ligand MPC-6827. The above results indicate that [11C]HD-800 may be a suitable PET ligand for the in vivo quantification of MT inside and outside the brain.

Abnormalities of microtubules (MTs) are implicated in the pathogenesis of many CNS diseases. Despite the potential of an MT imaging agents, no PET ligand is currently available for in vivo imaging of MTs in the brain. We radiolabeled [11C]MPC-6827, a high affinity MTA, and demonstrated its specific binding in rat and mice brain using PET imaging. Our experiments show that [11C]MPC-6827 has specific binding to MT in brain, and it is the first MT-binding PET ligand.

Dysfunction of glycogen synthase kinase 3 (GSK-3) is implicated in the etiology of Alzheimer's disease, Parkinson's disease, diabetes, pain, and cancer. A radiotracer for functional positron emission tomography (PET) imaging could be used to study the kinase in brain disorders and to facilitate the development of small molecule inhibitors of GSK-3 for treatment. At present, there is no target-specific or validated PET tracer available for the in vivo monitoring of GSK-3. We radiolabeled the small molecule inhibitor [11C]1-(7-methoxy- quinolin-4-yl)-3-(6-(trifluoromethyl)pyridin-2-yl)urea ([11C]A1070722) with high affinity to GSK-3 (Ki = 0.6 nM) in excellent radiochemical yield. PET imaging experiments in anesthetized vervet/African green monkey exhibited that [11C]A1070722 penetrated the blood-brain barrier (BBB) and accumulated in brain regions, with highest radioactivity binding in frontal cortex followed by parietal cortex and anterior cingulate, and with the lowest bindings found in caudate, putamen, and thalamus, similarly to the known distribution of GSK-3 in human brain. Our studies suggest that [11C]A1070722 can be a potential PET radiotracer for the in vivo quantification of GSK-3 in brain.

Continuous-flow microfluidics has shown increased applications in radiochemistry over the last decade, particularly for both pre-clinical and clinical production of fluorine-18 labeled radiotracers. The main advantages of microfluidics are the reduction in reaction times and consumption of reagents that often result in increased radiochemical yields and rapid optimization of reaction parameters for 18F-labeling. In this paper, we report on the two-step microfluidic radiosynthesis of the high affinity partial agonist of the serotonin 1A receptor, [18F]FEMPT (pKi = 9. 79; Ki = 0.16 nM) by microfluidic radiochemistry. [18F]FEMPT was obtained in ≈7% isolated radiochemical yield and in >98% radiochemical and chemical purity. The molar activity of the final product was determined to be >148 GBq/µmol (>4 Ci/µmol).