PEIGel: A biocompatible and injectable scaffold with innate immune adjuvanticity for synergized local immunotherapy.

Intratumoral immunotherapeutic hydrogel administration is emerging as an effective method for inducing a durable and robust antitumor immune response. However, scaffold hydrogels that can synergize with the loaded drugs, thus potentiating therapeutic efficacy, are limited. Here, we report a ternary hydrogel composed of polyvinyl alcohol (PVA), polyethylenimine (PEI)‒a cationic polymer with potential immunoactivation effects, and magnesium ions‒a stimulator of the adaptive immune response, which exhibits an intrinsic immunomodulation function of reversing the immunologically "cold" phenotype of a murine breast tumor to a "hot" phenotype by upregulating PD-L1 expression and promoting M1-like macrophage polarization. PEI hydrogel (PEIGel) encapsulating an immune checkpoint blockade (ICB) inhibitor‒anti-PD-L1 antibody (α-PDL1) exhibits synergistic effects resulting in elimination of primary tumors and remote metastases and prevention of tumor relapse after surgical resection. A preliminary mechanistic study revealed a probably hidden role of PEI in modulating the polyamine metabolism/catabolism of tumors to potentiate the immune adjuvant effect. These results deepen our understanding of the innate immune activation function of PEI and pave the way for harnessing PEI as an immune adjuvant for ICB therapy.

Quantitative Radionuclide Imaging Analysis of Enhanced Drug Delivery Induced by Photoimmunotherapy.

Photoimmunotherapy (PIT) is an upcoming potential cancer treatment modality, the effect of which is improved in combination with chemotherapy. PIT causes a super-enhanced permeability and retention (SUPR) effect. Here, we quantitatively evaluated the SUPR effect using radiolabeled drugs of varying molecular weights (18F-5FU, 111In-DTPA, 99mTc-HSA-D, and 111In-IgG) to determine the appropriate drug size. PIT was conducted with an indocyanine green-labeled anti-HER2 antibody and an 808 nm laser irradiation. Mice were subcutaneously inoculated with HER2-positive cells in both hindlimbs. The tumor on one side was treated with PIT, and the contralateral side was not treated. The differences between tumor accumulations were evaluated using positron emission tomography or single-photon emission computed tomography. Imaging studies found increased tumor accumulation of agents after PIT. PIT-treated tumors showed significantly increased uptake of 18F-5FU (p < 0.001) and 99mTc-HSA-D (p < 0.001). A tendency toward increased accumulation of 111In-DTPA and 111In-IgG was observed. These findings suggest that some low- and medium-molecular-weight agents are promising candidates for combined PIT, as are macromolecules; hence, administration after PIT could enhance their efficacy. Our findings encourage further preclinical and clinical studies to develop a combination therapy of PIT with conventional anticancer drugs.

Radiotheranostic Agent 64Cu-cyclam-RAFT-c(-RGDfK-)4 for Management of Peritoneal Metastasis in Ovarian Cancer.

PURPOSE: Ovarian cancer peritoneal metastases (OCPMs) are a pathophysiologically heterogeneous group of tumors that are rarely curable. αVß3 integrin (αVß3) is overexpressed on tumoral neovessels and frequently on ovarian cancer cells. Here, using two clinically relevant αVß3-positive OCPM mouse models, we studied the theranostic potential of an αVß3-specific radiopeptide, 64Cu-cyclam-RAFT-c(-RGDfK-)4 (64Cu-RaftRGD), and its intra- and intertumoral distribution in relation to the tumor microenvironment. EXPERIMENTAL DESIGN: αVß3-expressing peritoneal and subcutaneous models of ovarian carcinoma (IGR-OV1 and NIH:OVCAR-3) were established in nude mice. 64Cu-RaftRGD was administered either intravenously or intraperitoneally. We performed intratumoral distribution (ITD) studies, PET/CT imaging and quantification, biodistribution assay and radiation dosimetry, and therapeutic efficacy and toxicity studies. RESULTS: Intraperitoneal administration was an efficient route for targeting 64Cu-RaftRGD to OCPMs with excellent tumor penetration. Using the fluorescence surrogate, Cy5.5-RaftRGD, in our unique high-resolution multifluorescence analysis, we found that the ITD of 64Cu-RaftRGD was spatially distinct from, but complementary to, that of hypoxia. 64Cu-RaftRGD-based PET enabled clear visualization of multiple OCPM deposits and ascites and biodistribution analysis demonstrated an inverse correlation between tumor uptake and tumor size (1.2-17.2 mm). 64Cu-RaftRGD at a radiotherapeutic dose (148 MBq/0.357 nmol) showed antitumor activities by inhibiting tumor cell proliferation and inducing apoptosis, with negligible toxicity. CONCLUSIONS: Collectively, these results demonstrate the all-in-one potential of 64Cu-RaftRGD for imaging guided radiotherapy of OCPM by targeting both tumoral neovessels and cancerous cells. On the basis of the ITD finding, we propose that pairing αVß3- and hypoxia-targeted radiotherapies could improve therapeutic efficacy by overcoming the heterogeneity of ITD encountered with single-agent treatments.

Marriage of black phosphorus and Cu2+ as effective photothermal agents for PET-guided combination cancer therapy.

The use of photothermal agents (PTAs) in cancer photothermal therapy (PTT) has shown promising results in clinical studies. The rapid degradation of PTAs may address safety concerns but usually limits the photothermal stability required for efficacious treatment. Conversely, PTAs with high photothermal stability usually degrade slowly. The solutions that address the balance between the high photothermal stability and rapid degradation of PTAs are rare. Here, we report that the inherent Cu2+-capturing ability of black phosphorus (BP) can accelerate the degradation of BP, while also enhancing photothermal stability. The incorporation of Cu2+ into BP@Cu nanostructures further enables chemodynamic therapy (CDT)-enhanced PTT. Moreover, by employing 64Cu2+, positron emission tomography (PET) imaging can be achieved for in vivo real-time and quantitative tracking. Therefore, our study not only introduces an "ideal" PTA that bypasses the limitations of PTAs, but also provides the proof-of-concept application of BP-based materials in PET-guided, CDT-enhanced combination cancer therapy.

64Cu-Intraperitoneal Radioimmunotherapy: A Novel Approach for Adjuvant Treatment in a Clinically Relevant Preclinical Model of Pancreatic Cancer.

Pancreatic cancer (PC) has a very poor prognosis. Surgery is the primary treatment for patients with resectable PC; however, local recurrence, hepatic metastasis, and peritoneal dissemination often occur even after extensive surgery. Adjuvant chemotherapy, typically with gemcitabine, has been used clinically but with only a modest survival benefit. To achieve a better outcome, we investigated the efficacy of 64Cu-intraperitoneal radioimmunotherapy (ipRIT) with 64Cu-labeled antiepidermal growth factor receptor antibody cetuximab as an adjuvant treatment after PC surgery using an orthotopic xenografted mouse model. Methods: The efficacy of adjuvant 64Cu-ipRIT was investigated in a human PC mouse model harboring orthotopic xenografts of xPA-1-DC cells. To reproduce the clinical situation, PC xenografts were surgically resected when pancreatic tumors were readily visible but not metastatic tumors. Increasing doses of 64Cu-cetuximab were intraperitoneally injected, and the mice were monitored for toxicity to determine the safe therapeutic dose. For adjuvant 64Cu-ipRIT, the day after tumor resection, the mice were intraperitoneally administered 22.2 MBq of 64Cu-PCTA-cetuximab and the survival was compared with that in surgery-only controls. For comparison, adjuvant chemotherapy with gemcitabine was also examined using the same model. Results: The mouse model not only developed primary tumors in the pancreas but also subsequently reproduced local recurrence, hepatic metastasis, and peritoneal dissemination after surgery, which is similar to the manifestations that occur with human PC. Adjuvant 64Cu-ipRIT with 64Cu-labeled cetuximab after surgery effectively suppressed local recurrence, hepatic metastasis, and peritoneal dissemination in this model. Significant improvement of the survival with minimal toxicity was achieved by adjuvant 64Cu-ipRIT compared with that in control mice that underwent surgery only. Adjuvant chemotherapy with gemcitabine nominally prolonged the survival, but the effect was not statistically significant. Conclusion:64Cu-ipRIT with cetuximab can be an effective adjuvant therapy after PC surgery.

Development of 2-(2-(3-(4-([18F]Fluoromethoxy- d2)phenyl)-7-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione for Positron-Emission-Tomography Imaging of Phosphodiesterase 10A in the Brain.

Phosphodiesterase 10A (PDE10A) is a newly identified therapeutic target for central-nervous-system disorders. 2-(2-(3-(4-([18F]Fluoroethoxy)phenyl)-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione ([18F]MNI-659, [18F]5) is a useful positron-emission-tomography (PET) ligand for imaging of PDE10A in the human brain. However, the radiolabeled metabolite of [18F]5 can accumulate in the brain. In this study, using [18F]5 as a lead compound, we designed four new 18F-labeled ligands ([18F]6-9) to find one more suitable than [18F]5. Of these, 2-(2-(3-(4-([18F]fluoromethoxy- d2)phenyl)-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione ([18F]9) exhibited high in vitro binding affinity ( Ki = 2.9 nM) to PDE10A and suitable lipophilicity (log D = 2.2). In PET studies, the binding potential (BPND) of [18F]9 (5.8) to PDE10A in the striatum of rat brains was significantly higher than that of [18F]5 (4.6). Furthermore, metabolite analysis showed much lower levels of contamination with radiolabeled metabolites in the brains of rats given [18F]9 than in those given [18F]5. In conclusion, [18F]9 is a useful PET ligand for PDE10A imaging in brain.

Change in the Binding of [11C]BU99008 to Imidazoline I2 Receptor Using Brain PET in Zucker Rats.

PURPOSE: The imdazoline I2 receptor (I2R) has been found in the feeding centers of the brain, such as the hypothalamus, and certain I2R ligands have been reported to stimulate food intake. Thus, it has been proposed that I2R may play a role in feeding control. [11C]BU99008 was developed as a positron emission tomography (PET) tracer for imaging of I2R. [11C]BU99008 displayed relatively high brain penetration and specific binding by brain PET studies in preclinical studies. Here, we evaluated a pathological condition caused by obesity related to I2R function by quantitative PET study using [11C]BU99008. PROCEDURES: PET scans were acquired in the Zucker (ZUC) lean and fatty rats, radioactivity and metabolites of plasma were measured, and the kinetic parameters were estimated. RESULTS: Radioactivity levels after the injection of [11C]BU99008 in the hypothalamus of both ZUC lean and fatty rats were highly accumulated, and then gradually decreased until 60 min after the injection. The accumulated radioactivity from 30 to 60 min after the injection in the hypothalamus of the ZUC fatty rats was 1.3 times greater than that of lean rats. The volume of distribution (VT) estimated by Logan graphical analysis in the hypothalamus of the ZUC fatty rats was 1.8 times greater than that in the ZUC lean rats. In metabolite analysis, the percentages of the unchanged form in the plasma of the ZUC fatty rats at 60 min after the injection (5.0 %) was significantly lower than that of lean rats (9.1 %). CONCLUSIONS: By PET imaging using [11C]BU99008, we demonstrated that the accumulated radioactivity and estimated VT value in the feeding center of ZUC lean rats was lower than that in fatty rats. PET studies using [11C]BU99008 may contribute to elucidate a pathological condition caused by obesity related to I2R function.

Integrated treatment using intraperitoneal radioimmunotherapy and positron emission tomography-guided surgery with 64Cu-labeled cetuximab to treat early- and late-phase peritoneal dissemination in human gastrointestinal cancer xenografts.

Peritoneal dissemination is a common cause of death from gastrointestinal cancers and is difficult to treat using current therapeutic options, particularly late-phase disease. Here, we investigated the feasibility of integrated therapy using 64Cu-intraperitoneal radioimmunotherapy (ipRIT), alone or in combination with positron emission tomography (PET)-guided surgery using a theranostic agent (64Cu-labeled anti-epidermal growth factor receptor antibody cetuximab) to treat early- and late-phase peritoneal dissemination in mouse models. In this study, we utilized the OpenPET system, which has open space for conducting surgery while monitoring objects at high resolution in real time, as a novel approach to make PET-guided surgery feasible. 64Cu-ipRIT with cetuximab inhibited tumor growth and prolonged survival with little toxicity in mice with early-phase peritoneal dissemination of small lesions. For late-phase peritoneal dissemination, a combination of 64Cu-ipRIT for down-staging and subsequent OpenPET-guided surgery for resecting large tumor masses effectively prolonged survival. OpenPET clearly detected tumors (≥3 mm in size) behind other organs in the peritoneal cavity and was useful for confirming the presence or absence of residual tumors during an operation. These findings suggest that integrated 64Cu therapy can serve as a novel treatment strategy for peritoneal dissemination.

Kinetics and metabolism of apocynin in the mouse brain assessed with positron-emission tomography.

BACKGROUND: Apocynin is a constituent of the medicinal herb Picrorhiza kurroa. It is an inhibitor of nicotinamide adenine dinucleotide phosphate oxidase. This compound shows potential anti-inflammatory and antioxidant effects and has been tested as a neuroprotectant in many animal models of brain disease. In such studies, understanding the brain kinetics of apocynin would be important for interpreting its in vivo efficacy; however, little has been reported on the kinetics of apocynin in the brain. PURPOSE: The purpose of this study is to investigate the kinetics and metabolism of apocynin in the brain of mice. STUDY DESIGN: The kinetics and metabolism of apocynin were examined using [11C]apocynin and positron-emission tomography (PET). METHODS: In vivo PET scanning was performed in mice for 20min after intraperitoneal administration of an apocynin solution containing [11C]apocynin. Metabolites in the brain were analyzed using high-performance liquid chromatography. The doses of apocynin used ranged from <1.5 µg/kg (tracer dose) to 100mg/kg. RESULTS: Brain radioactivity during the period of 0 to 20min after administration was negligible at the tracer dose and extremely low at the dose of 10mg/kg. Moderate radioactivity was observed in the brain a few minutes after administration at the doses of 25 and 50mg/kg and rapidly decreased thereafter. At a dose of 100mg/kg, [11C]apocynin resulted in a high uptake of radioactivity followed by a gradual washout. In contrast to the brain, a clear dose-dependent increase in radioactivity was not observed in the blood. The fraction of the unchanged form in the brain decreased with time, and the degree of the reduction depended on apocynin doses: apocynin was rapidly metabolized in the brain at lower doses, whereas it was slowly decomposed at higher doses. On the basis of these data, the maximum apocynin concentrations in the brain were calculated to be 10 µM (10mg/kg), 49 µM (25mg/kg), 150 µM (50mg/kg), and 380 µM (100mg/kg). A metabolite observed in the brain was found to be apocynin glucuronide but not diapocynin, an active metabolite. CONCLUSION: These results would be useful for an evaluation of the potential efficacy of apocynin as a neuroprotective agent.

18F-FEDAC as a Targeting Agent for Activated Macrophages in DBA/1 Mice with Collagen-Induced Arthritis: Comparison with 18F-FDG.

Activated macrophages have been known to play pivotal roles in the pathogenesis of rheumatoid arthritis (RA). 18F-FEDAC (N-benzyl-N-methyl-2-[7,8-dihydro-7-(2-18F-fluoroethyl)-8-oxo-2-phenyl-9H-purin-9-yl]acetamide) is a radiolabeled ligand for the 18-kDa translocator protein (TSPO), which is abundant in activated macrophages. We evaluated the feasibility of using 18F-FEDAC in a murine RA model. Methods: RAW 264.7 mouse macrophages were activated by lipopolysaccharide. TSPO expression levels in activated and inactivated macrophages were measured by quantitative polymerase chain reaction and Western blotting. The cellular uptake and specific binding of 18F-FEDAC were measured using a γ-counter. For the in vivo study, collagen-induced arthritis (CIA) was developed in DBA/1 mice, and the clinical score for arthritis was measured regularly. 18F-FEDAC and 18F-FDG PET images were acquired on days 23 and 37 after the first immunization. Histologic examinations were performed to evaluate macrophages and TSPO expression. Results: We found increased TSPO messenger RNA and protein expression in activated macrophages. Uptake of 18F-FEDAC in activated macrophages was higher than that in nonactivated cells and was successfully blocked by the competitor, PK11195. In CIA mice, joint swelling was apparent on day 26 after the first immunization, and the condition worsened by day 37. 18F-FEDAC uptake by arthritic joints increased early on (day 23), whereas 18F-FDG uptake did not. However, 18F-FDG uptake by arthritic joints markedly increased at later stages (day 37) to a higher level than 18F-FEDAC uptake. The 18F-FEDAC uptake correlated weakly with summed severity score (P = 0.019, r = 0.313), whereas the 18F-FDG uptake correlated strongly with summed severity score (P < 0.001, r = 0.897). Histologic sections of arthritic joints demonstrated an influx of macrophages compared with that in normal joints. Conclusion:18F-FEDAC enabled the visualization of active inflammation sites in arthritic joints in a CIA model by targeting TSPO expression in activated macrophages. The results suggest the potential usefulness of 18F-FEDAC imaging in the early phase of RA.

Norepinephrine Transporter in Major Depressive Disorder: A PET Study.

OBJECTIVE: The norepinephrine transporter has been suggested to play a crucial role in major depressive disorder. However, norepinephrine transporter availability in major depressive disorder and its role with clinical symptoms are not known. The authors tested norepinephrine transporter availability in patients with major depressive disorder with the aim to identify any associations between test results and clinical symptoms. METHOD: The present research was a cross-sectional study in which 19 patients with major depressive disorder and 19 age- and sex-matched healthy comparison subjects underwent positron emission tomography scanning to evaluate the norepinephrine transporter availability measured by the radioligand (S,S)-[18F]FMeNER-D2. Norepinephrine transporter availability in the thalamus and its subregions was quantified in terms of nondisplaceable binding potential (BPND). The authors also analyzed the association between norepinephrine transporter availability and clinical symptoms. RESULTS: Compared with healthy subjects, patients with major depressive disorder showed 29.0% higher BPND values in the thalamus and, in particular, 28.2% higher values in the thalamic subregion anatomically connected to the prefrontal cortex. Elevated norepinephrine transporter availability in the thalamus in patients was positively correlated with attention, as measured by the Trail Making Test, part A. CONCLUSIONS: These findings revealed altered norepinephrine transmission in patients with major depressive disorder, suggesting that this alteration could be related to attention in this patient population.

A useful PET probe [11C]BU99008 with ultra-high specific radioactivity for small animal PET imaging of I2-imidazoline receptors in the hypothalamus.

INTRODUCTION: A positron emission tomography (PET) probe with ultra-high specific radioactivity (SA) enables measuring high receptor specific binding in brain regions by avoiding mass effect of the PET probe itself. It has been reported that PET probe with ultra-high SA can detect small change caused by endogenous or exogenous ligand. Recently, Kealey et al. developed [11C]BU99008, a more potent PET probe for I2-imidazoline receptors (I2Rs) imaging, with a conventional SA (mean 76GBq/µmol) showed higher specific binding in the brain. Here, to detect small change of specific binding for I2Rs caused by endogenous or exogenous ligand in an extremely small region, such as hypothalamus in the brain, we synthesized and evaluated [11C]BU99008 with ultra-high SA as a useful PET probe for small-animal PET imaging of I2Rs. METHODS: [11C]BU99008 was prepared by [11C]methylation of N-desmethyl precursor with [11C]methyl iodide. Biodistribution, metabolite analysis, and brain PET studies were conducted in rats. RESULTS: [11C]BU99008 with ultra-high SA in the range of 5400-16,600GBq/µmol were successfully synthesized (n=7), and had appropriate radioactivity for in vivo study. In the biodistribution study, the mean radioactivity levels in all investigated tissues except for the kidney did not show significant difference between [11C]BU99008 with ultra-high SA and that with conventional SA. In the metabolite analysis, the percentage of unchanged [11C]BU99008 at 30min after the injection of probes with ultra-high and conventional SA was similar in rat brain and plasma. In the PET study of rats' brain, radioactivity level (AUC30-60 min) in the hypothalamus of rats injected with [11C]BU99008 with ultra-high SA (64 [SUV ∙ min]) was significantly higher than that observed for that with conventional SA (50 [SUV ∙ min]). The specific binding of [11C]BU99008 with ultra-high SA (86% of total binding) for I2R was higher than that of conventional SA (76% of total binding). CONCLUSION: A PET study using [11C]BU99008 with ultra-high SA would thus contribute to the detection of small changes in or small regions with I2R expression and hence may be useful in elucidating new functions of I2R.

Regorafenib as a potential adjuvant chemotherapy agent in disseminated small colon cancer: Drug selection outcome of a novel screening system using nanoimprinting 3-dimensional culture with HCT116-RFP cells.

Colon cancer is one of the leading causes of cancer death worldwide. Adjuvant chemotherapy following primary surgical treatment is suggested to be beneficial in eradicating invisible disseminated small tumors in colon cancer; however, an effective drug remains to be developed. Recently, we reported a novel drug screening system using a nanoimprinting 3-dimensional (3D) culture that creates multicellular spheroids, which simulate in vivo conditions and, thereby, predict effective drugs in vivo. This study aimed to perform drug selection using our recently developed 3D culture system in a human colon cancer HCT116 cell line stably expressing red fluorescent protein (HCT116-RFP), to determine the most effective agent in a selection of clinically used antitumor agents for colon cancer. In addition, we confirmed the efficacy of the selected drug regorafenib, in vivo using a mouse model of disseminated small tumors. HCT116-RFP cells were cultured using a nanoimprinting 3D culture and in vitro drug selection was performed with 8 clinically used drugs [bevacizumab, capecitabine, cetuximab, 5-fluorouracil (5-FU), irinotecan, oxaliplatin, panitumumab and regorafenib]. An in vivo study was performed in mice bearing HCT116-RFP intraperitoneally disseminated small tumors using 3'-[18F]-fluoro-3'-deoxythymidine-positron emission tomography and fluorescence microscopy imaging to evaluate the therapeutic effects. Regorafenib was determined to be the most effective drug in the 3D culture, and significantly inhibited tumor growth in vivo, compared to the untreated control and 5-FU-treated group. The drug 5-FU is commonly used in colon cancer treatment and was used as a reference. Our results demonstrate that regorafenib is a potentially efficacious adjuvant chemotherapeutic agent for the treatment of disseminated small colon cancer and, therefore, warrants further preclinical and clinical studies.

Norepinephrine transporter occupancy by nortriptyline in patients with depression: a positron emission tomography study with (S,S)-[¹8F]FMeNER-D2.

Norepinephrine transporter (NET) plays important roles in the treatment of various neuropsychiatric disorders, such as depression and attention deficit hyperactivity disorder (ADHD). Nortriptyline is a NET-selective tricyclic antidepressant (TCAs) that has been widely used for the treatment of depression. Previous positron emission tomography (PET) studies have reported over 80% serotonin transporter occupancy with clinical doses of selective serotonin reuptake inhibitors (SSRIs), but there has been no report of NET occupancy in patients treated with relatively NET-selective antidepressants. In the present study, we used PET and (S,S)-[18¹8F]FMeNER-D2 to investigate NET occupancies in the thalamus in 10 patients with major depressive disorder taking various doses of nortriptyline, who were considered to be responders to the treatment. Reference data for the calculation of occupancy were derived from age-matched healthy controls. The result showed approximately 50-70% NET occupancies in the brain as a result of the administration of 75-200 mg/d of nortriptyline. The estimated effective dose (ED50) and concentration (EC50) required to induce 50% occupancy was 65.9 mg/d and 79.8 ng/ml, respectively. Furthermore, as the minimum therapeutic level of plasma nortriptyline for the treatment of depression has been reported to be 70 ng/ml, our data indicate that this plasma nortriptyline concentration corresponds to approximately 50% NET occupancy measured with PET, suggesting that more than 50% of central NET occupancy would be appropriate for the nortriptyline treatment of patients with depression.

Radiosynthesis and evaluation of [11C]YM-202074 as a PET ligand for imaging the metabotropic glutamate receptor type 1.

INTRODUCTION: Developing positron emission tomography (PET) ligands for imaging metabotropic glutamate receptor type 1 (mGluR1) is important for studying its role in the central nervous system. N-cyclohexyl-6-{[N-(2-methoxyethyl)-N-methylamino]methyl}-N-methylthiazolo[3,2-a]benzimidazole-2-carboxamide (YM-202074) exhibited high binding affinity for mGluR1 (K(i)=4.8 nM), and selectivity over other mGluRs in vitro. The purpose of this study was to label YM-202074 with carbon-11 and to evaluate in vitro and in vivo characteristics of [(11)C]YM-202074 as a PET ligand for mGluR1 in rodents. METHODS: [(11)C]YM-202074 was synthesized by N-[(11)C]methylation of its desmethyl precursor with [(11)C]methyl iodide. The in vitro and in vivo brain regional distributions were determined in rats using autoradiography and PET, respectively. RESULTS: [(11)C]YM-202074 (262-630 MBq, n=5) was obtained with radiochemical purity of >98% and specific activity of 27-52 GBq/mumol at the end of synthesis, starting from [(11)C]CO(2) of 19.3-21.5 GBq. In vitro autoradiographic results showed that the high specific binding of [(11)C]YM-202074 for mGluR1 was presented in the cerebellum, thalamus and hippocampus, which are known as mGluR1-rich regions. In ex vivo autoradiography and PET studies, the radioligand was specifically distributed in the cerebellum, although the uptake was low. Furthermore, the regional distribution was fairly uniform in the whole brain by pretreatment with JNJ16259685 (a mGluR1 antagonist). However, radiometabolite(s) was detected in the brain. CONCLUSIONS: From these results, especially considering the low brain uptake and the influx of radiometabolite(s) into brain, [(11)C]YM-202074 may not be a useful PET ligand for in vivo imaging of mGluR1 in the brain.

Synthesis and evaluation of 3-(4-chlorobenzyl)-8-[11C]methoxy-1,2,3,4-tetrahydrochromeno[3,4-c]pyridin-5-one: a PET tracer for imaging sigma(1) receptors.

3-(4-Chlorobenzyl)-8-methoxy-1,2,3,4-tetrahydrochromeno[3,4-c]pyridin-5-one (1), a putative dopamine D(4) receptor antagonist (k(i) = 8.7 nM), was labeled by positron-emitter (11C) and its pharmacological evaluation was carried out with in vitro quantitative autoradiography and positron emission tomography (PET). 11C-Methylation of a corresponding desmethyl precursor (2) with [11C]CH(3)I gave [11C]1 with >or=98% of radiochemical purity after HPLC purification and 67-90 GBq/micromol of specific activity at the end of synthesis. The in vitro autoradiography using rat brain sections demonstrated that [11C]1 shows no specific binding to the D(4) receptors, but a high specific binding to sigma(1) receptors (IC(50) = 105 nM). In the PET study with monkey brain, [11C]1 was highly taken up by the brain and trapped in the brain for at least 90 min. The distribution pattern of radioactivity in the brain was striatum > thalamus > frontal cortex > cerebellum, which was same as the result of in vitro autoradiography. Pre-treatment with non-radioactive 1 (1 mg/kg) produced a significant reduction of radioactivity in all the regions including the cerebellum. Pre-treatment with (+)pentazocine (1 mg/kg), a selective sigma(1) receptor agonist, also reduced the radioactivity in the same regions to a similar extent. These results indicate that [11C]1 may have some specific binding to the sigma(1) receptors, which is consistent with the result of in vitro autoradiography.