Genetically engineered myeloid cells rebalance the core immune suppression program in metastasis.

Metastasis is the leading cause of cancer-related deaths, and greater knowledge of the metastatic microenvironment is necessary to effectively target this process. Microenvironmental changes occur at distant sites prior to clinically detectable metastatic disease; however, the key niche regulatory signals during metastatic progression remain poorly characterized. Here, we identify a core immune suppression gene signature in pre-metastatic niche formation that is expressed predominantly by myeloid cells. We target this immune suppression program by utilizing genetically engineered myeloid cells (GEMys) to deliver IL-12 to modulate the metastatic microenvironment. Our data demonstrate that IL12-GEMy treatment reverses immune suppression in the pre-metastatic niche by activating antigen presentation and T cell activation, resulting in reduced metastatic and primary tumor burden and improved survival of tumor-bearing mice. We demonstrate that IL12-GEMys can functionally modulate the core program of immune suppression in the pre-metastatic niche to successfully rebalance the dysregulated metastatic microenvironment in cancer.

Single centre observational study evaluating the impact of introducing High Flow Nasal Cannula outside of Paediatric Critical Care Unit.

AIM: To evaluate the impact of High Flow Nasal Cannula (HFNC) introduction outside of Paediatric Critical Care Units (PCCU), on PCCU admissions and intubation rates. Secondarily, to identify escalation predictors. METHODS: Retrospective observational study with matched PCCU admissions and intubation rates, 2-years before (Group 1) and 2-years after (Group 2) HFNC introduction outside of PCCU. Within Group 2, we compared those admitted to PCCU (escalation) and those who did not (non-escalation). Observations, change in observations and time to starting HFNC were analysed. RESULTS: Pre- and post-introduction comparison: Of 980 admissions in Group 1, 55 were admitted to PCCU, whereas of 1209 admission in Group 2, there were 85 admissions, P = 0.188. Group 1 had 25 intubations compared to 23 in Group 2, P = 0.309. Over twice as many children had some form of respiratory support in Group 2. Post-introduction: 104 children commenced HFNC, 72% for bronchiolitis. Median age was 4 months in the non-escalation group and 6.5 months in the escalation group, P = 0.663. Thirty-eight children escalated to PCCU: 33 required CPAP/BiPAP, 4 were intubated with 1 remaining on HFNC. Comparisons of age, gender, comorbidities, observations, change in observations and time to starting HFNC showed no significant escalation predictors. CONCLUSIONS: This study identified no statistically significant predictors of escalation. There was an observed increase in PCCU admissions with decreased intubations. The resource implications of this therapy are significant and further studies should examine cost effectiveness of HFNC use outside of PCCU.

The Binding of BF-227-Like Benzoxazoles to Human α-Synuclein and Amyloid ß Peptide Fibrils.

Development of an α-synuclein (α-Syn) positron emission tomography agent for the diagnosis and evaluation of Parkinson disease therapy is a key goal of neurodegenerative disease research. BF-227 has been described as an α-Syn binder and hence was employed as a lead to generate a library of α-Syn-binding compounds. [3H]BF-227 bound to α-Syn and amyloid ß peptide (Aß) fibrils with affinities (KD) of 46.0 nM and 15.7 nM, respectively. Affinities of BF-227-like compounds (expressed as Ki) for α-Syn and Aß fibrils were determined, along with 5 reference compounds (flutafuranol, flutemetamol, florbetapir, BF-227, and PiB). Selectivity for α-Syn binding, defined as the Ki(Aß)/Ki(α-Syn) ratio, was 0.23 for BF-227. A similar or lower ratio was measured for analogues decorated with alkyl or oxyethylene chains attached to the oxygen at the 6 position of BF-227, suggesting a lack of involvement of the side chain in fibril binding. BF-227-like iodobenzoxazoles had lower affinities and poor α-Syn selectivity. However, BF-227-like fluorobenzoxazoles had improved α-Syn selectively having Ki(Aß)/Ki(α-Syn) ranging from 2.2 to 5.1 with appreciable fibril affinity, although not sufficient to warrant further investigation. Compounds based on fluorobenzoxazoles might offer an approach to obtaining an α-Syn imaging agent with an appropriate affinity and selectivity.

Zfp281 and Zfp148 control CD4+ T cell thymic development and TH2 functions.

How CD4+ lineage gene expression is initiated in differentiating thymocytes remains poorly understood. Here, we show that the paralog transcription factors Zfp281 and Zfp148 control both this process and cytokine expression by T helper cell type 2 (TH2) effector cells. Genetic, single-cell, and spatial transcriptomic analyses showed that these factors promote the intrathymic CD4+ T cell differentiation of class II major histocompatibility complex (MHC II)-restricted thymocytes, including expression of the CD4+ lineage-committing factor Thpok. In peripheral T cells, Zfp281 and Zfp148 promoted chromatin opening at and expression of TH2 cytokine genes but not of the TH2 lineage-determining transcription factor Gata3. We found that Zfp281 interacts with Gata3 and is recruited to Gata3 genomic binding sites at loci encoding Thpok and TH2 cytokines. Thus, Zfp148 and Zfp281 collaborate with Gata3 to promote CD4+ T cell development and TH2 cell responses.

In vivo tracking of [89Zr]Zr-labeled engineered extracellular vesicles by PET reveals organ-specific biodistribution based upon the route of administration.

Extracellular vesicles (EVs) have garnered increasing interest as delivery vehicles for multiple classes of therapeutics based on their role as mediators in an important, natural intercellular communication system. We recently described a platform to allow the design, production and in vivo study of human EVs with specific properties (drug or tropism modifiers). This article seeks to compare and expand upon historical biodistribution and kinetic data by comparing systemically and compartmentally administered labeled engineered EVs using in vivo and ex vivo techniques. METHODS: EVs were surface-labeled to high radiochemical purity and specific activity with 89Zirconium deferoxamine ([89Zr]Zr-DFO) and/or cy7-scrambled antisense oligonucleotide (Cy7-ExoASOscr), or luminally loaded with GFP for in vivo tracking in rodents and non-human primates (NHPs). Positron Emission Tomography (PET) and subsequent immunohistochemistry (IHC) and autoradiography (ARG) cross-validation enabled assessment of the anatomical and cellular distribution of labeled EVs both spatially and temporally. RESULTS: Over time, systemic administration of engineered EVs distributed preferentially to the liver and spleen (Intravenous, IV), gastrointestinal tract and lymph nodes (Intraperitoneal, IP) and local/regional lymph nodes (Subcutaneous, SC). Immunostaining of dissected organs displaying PET signal revealed co-localization of an EV marker (PTGFRN) with a subset of macrophage markers (CD206, F4/80, IBA1). Compartmental dosing into NHP cerebrospinal fluid (CSF) resulted in a heterogenous distribution of labeled EVs depending upon whether the route was intrathecal (ITH), intracisterna magna (ICM) or intracerebroventricular (ICV), compared to the homogeneous distribution observed in rodents. Thus anatomically, ITH administration in NHP revealed meningeal distribution along the neuraxis to the base of the skull. In contrast ICM and ICV dosing resulted in meningeal distribution around the skull and to the cervical and thoracic spinal column. Further characterization using IHC shows uptake in a subset of meningeal macrophages. CONCLUSIONS: The present studies provide a comprehensive assessment of the fate of robustly and reproducibly labeled engineered EVs across several mammalian species. The in vivo distribution was observed to be both spatially and temporally dependent upon the route of administration providing insight into potential targeting opportunities for engineered EVs carrying a therapeutic payload.

Exosome-mediated genetic reprogramming of tumor-associated macrophages by exoASO-STAT6 leads to potent monotherapy antitumor activity.

Effectiveness of checkpoint immunotherapy in cancer can be undermined by immunosuppressive tumor-associated macrophages (TAMs) with an M2 phenotype. Reprogramming TAMs toward a proinflammatory M1 phenotype is a novel approach to induce antitumor immunity. The M2 phenotype is controlled by key transcription factors such as signal transducer and activator of transcription 6 (STAT6), which have been "undruggable" selectively in TAMs. We describe an engineered exosome therapeutic candidate delivering an antisense oligonucleotide (ASO) targeting STAT6 (exoASO-STAT6), which selectively silences STAT6 expression in TAMs. In syngeneic models of colorectal cancer and hepatocellular carcinoma, exoASO-STAT6 monotherapy results in >90% tumor growth inhibition and 50 to 80% complete remissions. Administration of exoASO-STAT6 leads to induction of nitric oxide synthase 2 (NOS2), an M1 macrophage marker, resulting in remodeling of the tumor microenvironment and generation of a CD8 T cell-mediated adaptive immune response. Collectively, exoASO-STAT6 represents the first platform targeting transcription factors in TAMs in a highly selective manner.

Synthesis, characterization, and monkey PET studies of [¹8F]MK-1312, a PET tracer for quantification of mGluR1 receptor occupancy by MK-5435.

Two moderately lipophilic, high affinity ligands for metabotropic glutamate receptor subtype 1 (mGluR1) were radiolabeled with a positron-emitting radioisotope and evaluated in rhesus monkey as potential PET tracers. Both ligands were radiolabeled with fluorine-18 via nucleophilic displacement of the corresponding 2-chloropyridine precursor with [¹8F]potassium fluoride. [¹8F]MK-1312 was found to have a suitable signal for quantification of mGluR1 receptors in nonhuman primates and was more thoroughly characterized. In vitro autoradiographic studies with [¹8F]MK-1312 in rhesus monkey and human brain tissue slices revealed an uptake distribution consistent with the known distribution of mGluR1, with the highest uptake in the cerebellum, moderate uptake in the hippocampus, thalamus, and cortical regions, and lowest uptake in the caudate and putamen. In vitro saturation binding studies in rhesus monkey and human cerebellum homogenates confirmed that [¹8F]MK-1312 binds to a single site with a B(max) /K(d) ratio of 132 and 98, respectively. PET studies in rhesus monkey with [¹8F]MK-1312 showed high brain uptake and a regional distribution consistent with in vitro autoradiography results. Blockade of [¹8F]MK-1312 uptake with mGluR1 allosteric antagonist MK-5435 dose-dependently reduced tracer uptake in all regions of gray matter to a similarly low level of tracer uptake. This revealed a large specific signal useful for determination of mGluR1 receptor occupancy in rhesus monkey. Taken together, these results are promising for clinical PET studies with [¹8F]MK-1312 to determine mGluR1 occupancy of MK-5435.

The synthesis and preclinical evaluation in rhesus monkey of [¹8F]MK-6577 and [¹¹C]CMPyPB glycine transporter 1 positron emission tomography radiotracers.

Two positron emission tomography radiotracers for the glycine transporter 1 (GlyT1) are reported here. Each radiotracer is a propylsulfonamide-containing benzamide and was labeled with either carbon-11 or fluorine-18. [¹¹C]CMPyPB was synthesized by the alkylation of a 3-hydroxypyridine precursor using [¹¹C]MeI, and [¹8F]MK-6577 was synthesized by a nucleophilic aromatic substitution reaction using a 2-chloropyridine precursor. Each tracer shows good uptake into rhesus monkey brain with the expected distribution of highest uptake in the pons, thalamus, and cerebellum and lower uptake in the striatum and gray matter of the frontal cortex. In vivo blockade and chase studies of [¹8F]MK-6577 showed a large specific signal and reversible binding. In vitro autoradiographic studies with [¹8F]MK-6577 showed a large specific signal in both rhesus monkey and human brain slices and a distribution consistent with the in vivo results and those reported in the literature. In vivo metabolism studies in rhesus monkeys demonstrated that only more-polar metabolites are formed for each tracer. Of these two tracers, [¹8F]MK-6577 was more extensively characterized and is a promising clinical positron emission tomography tracer for imaging GlyT1 and for measuring GlyT1 occupancy of therapeutic compounds.

In Vitro Evaluation of [3H]CPPC as a Tool Radioligand for CSF-1R.

Microglia play a role in several central nervous system (CNS) diseases and are a highly sought target for positron emission tomography (PET) imaging and therapeutic intervention. 5-Cyano-N-(4-(4-[11C]methylpiperazin-1-yl)-2-(piperidin-1-yl)phenyl)furan-2-carboxamide ([11C]CPPC) is a radiopharmaceutical designed to selectively target microglia via macrophage colony stimulating factor-1 receptor (CSF-1R) in the CNS. Herein, we report the first preclinical evaluation of [3H]CPPC using radioligand binding methods for the evaluation of putative CSF-1R inhibitors in rodent models of neuroinflammation. The distribution of [3H]CPPC by autoradiography did not align with 18 kDa translocator protein (TSPO) distribution using [3H]PBR28 and IBA-1 staining for microglia. In the CNS, [3H]CPPC had considerable nonspecific binding, as indicated by a low displacement of the tritiated ligand by unlabeled CPPC and the known CSF1R inhibitors BLZ-945 and PLX3397. Spleen was identified as a tissue that provided an adequate signal-to-noise ratio to enable screening with [3H]CPPC and a library of 20 novel PLX3397 derivatives. However, unlabeled CPPC lacked selectivity and showed off-target binding to a substantial number of kinase targets (204 out of 403 tested) at a concentration relevant to in vitro radioligand binding assays (10 µM). These findings suggest that, while [3H]CPPC may have utility as a radioligand tool for the evaluation of peripheral targets and screening of CSF-1R inhibitors, it may have limited utility as an in vivo CNS imaging probe on the basis of the current evaluation.

Preclinical In Vitro and In Vivo Characterization of Synaptic Vesicle 2A-Targeting Compounds Amenable to F-18 Labeling as Potential PET Radioligands for Imaging of Synapse Integrity.

PURPOSE: Current synaptic vesicle 2A (SV2A) positron emission tomography (PET) imaging agents include the nanomolar affinity probes [11C]UCB-J and [18F]UCB-H derived from the anti-epileptic drug levitaracetam (Keppra®). An industry-utilized "de-risking" approach was used to carry out initial pharmacological characterization and to assess potential next-generation candidates amenable to F-18 radiolabeling for preliminary evaluation. PROCEDURES: Radioligand binding methods were employed in mammalian brain homogenates to determine the SV2A affinity (Kd) and maximal binding capacity (Bmax) of [3H]UCB-J. Novel leads were then screened to identify compounds minimally with comparable binding affinities with UCB-J in order to select a F-18-labeled candidate for subsequent in vivo assessment in rat. In parallel, mammalian brain tissue section autoradiography was performed to assess specific SV2A distribution. RESULTS: [3H]UCB-J bound with high affinity to a single population of sites in the rat brain (Kd = 2.6 ± 0.25 nM; Bmax = 810 ± 25 fmol/mg protein) and control human cortex (Kd = 2.9 ± 0.54 nM; Bmax = 10,000 ± 640 fmol/mg protein). Distribution of specific SV2A binding was shown to be homogeneous throughout the rodent brain and primarily in gray matter regions of rodent and human brain sections. Analog screening identified MNI-1038, MNI-1126/SDM-8, and SDM-2 as having comparable binding affinities with the currently available PET ligands. Subsequent [18F]MNI-1126/[18F]SDM-8 dynamic micro-PET imaging in rats revealed in vivo uptake and accumulation in the brain with favorable kinetics. Chase studies using 30 mg/kg levetiracetam confirmed that in vivo brain uptake of [18F]MNI-1126/[18F]SDM-8 was reversible. CONCLUSIONS: Taken together, these data suggest [18F]MNI-1126/[18F]SDM-8 (since renamed as [18F]SynVesT-1) characterized via an in vitro screening cascade provided a measurable in vivo SV2A specific signal in the rodent brain. This tracer as well as the close analog [18F]SDM-2 (since renamed as [18F]SynVesT-2) is currently undergoing further evaluation in preclinical and clinical studies.

Esophageal extracellular matrix hydrogel mitigates metaplastic change in a dog model of Barrett's esophagus.

Chronic inflammatory gastric reflux alters the esophageal microenvironment and induces metaplastic transformation of the epithelium, a precancerous condition termed Barrett's esophagus (BE). The microenvironmental niche, which includes the extracellular matrix (ECM), substantially influences cell phenotype. ECM harvested from normal porcine esophageal mucosa (eECM) was formulated as a mucoadhesive hydrogel, and shown to largely retain basement membrane and matrix-cell adhesion proteins. Dogs with BE were treated orally with eECM hydrogel and omeprazole (n = 6) or omeprazole alone (n = 2) for 30 days. eECM treatment resolved esophagitis, reverted metaplasia to a normal, squamous epithelium in four of six animals, and downregulated the pro-inflammatory tumor necrosis factor-α+ cell infiltrate compared to control animals. The metaplastic tissue in control animals (n = 2) did not regress. The results suggest that in vivo alteration of the microenvironment with a site-appropriate, mucoadhesive ECM hydrogel can mitigate the inflammatory and metaplastic response in a dog model of BE.

Inverse agonist histamine H3 receptor PET tracers labelled with carbon-11 or fluorine-18.

Two histamine H3 receptor (H3R) inverse agonist PET tracers have been synthesized and characterized in preclinical studies. Each tracer has high affinity for the histamine H3 receptor, has suitable lipophilicity, and neither is a substrate for the P-glycoprotein efflux pump. A common phenolic precursor was used to synthesize each tracer with high specific activity and radiochemical purity by an alkylation reaction using either [(11)C]MeI or [(18)F]FCD(2)Br. Autoradiographic studies in rhesus monkey and human brain slices showed that each tracer had a widespread distribution with high binding densities in frontal cortex, globus pallidus and striatum, and lower uptake in cerebellum. The specificity of this expression pattern was demonstrated by the blockade of the autoradiographic signal by either the H3R agonist R-alpha-methylhistamine or a histamine H3R inverse agonist. In vivo PET imaging studies in rhesus monkey showed rapid uptake of each tracer into the brain with the same distribution seen in the autoradiographic studies. Each tracer could be blocked by pretreatment with a histamine H3R inverse agonist giving a good specific signal. Comparison of the in vitro metabolism of each compound showed slower metabolism in human liver microsomes than in rhesus monkey liver microsomes, with each compound having a similar clearance rate in humans. The in vivo metabolism of 1b in rhesus monkey showed that at 60 min, approximately 35% of the circulating counts were due to the parent. These tracers are very promising candidates as clinical PET tracers to both study the histamine H3R system and measure receptor occupancy of H3R therapeutic compounds.

Reversal of warfarin-coagulopathy: How to improve plasma transfusion practice in a community hospital setting?

BACKGROUND: Plasma is often given inappropriately to reverse warfarin-induced coagulopathy, wasting health-care resources and exposing the patients to transfusion-associated risks. AIMS: The clinical practice at our institution was evaluated in order to reduce the number of unnecessary plasma transfusions. MATERIALS AND METHODS: Retrospective audit of plasma transfusions was done (July 2014 to June 2015). DESIGN: To improve the clinical practice, a two-prong strategy was implemented: (1) in-service was given to clinicians on the warfarin-reversal guidelines and (2) for a 30-day period, plasma orders were placed on the approval list of the Transfusion Medicine Service. RESULTS: Of the 729 units of plasma, 189 (26% of total) were given for the reversal of warfarin-induced coagulopathy. The medical charts of these patients were reviewed: 46 units of plasma (~25%) were given inappropriately (e.g., patients with minimally elevated international normalized ratio, no evidence of bleeding, and no surgery within 24 h). To check the effectiveness of our intervention, two audits of plasma transfusions were done. During the first audit (January 1-February 29, 2016), 24 patients received plasma to reverse warfarin-coagulopathy. Medical chart review revealed that the vast majority of plasma orders (96.66%) followed the guidelines. A second audit was carried out a year later (January 1-March 31, 2017): during this 3-month period, 47 patients were transfused with plasma for warfarin reversal with a 94% adherence to the guidelines. CONCLUSION: We conclude that plasma transfusion practices may be improved by a combination of education and active enforcement of warfarin reversal guidelines.

Extracellular Matrix Degradation Products Downregulate Neoplastic Esophageal Cell Phenotype.

IMPACT STATEMENT: Extracellular matrix (ECM) biomaterials were used to treat esophageal cancer patients after cancer resection and promoted regrowth of normal mucosa without recurrence of cancer. The present study investigates the mechanisms by which these materials were successful to prevent the cancerous phenotype. ECM downregulated neoplastic esophageal cell function (proliferation, metabolism), but normal esophageal epithelial cells were unaffected in vitro, and suggests a molecular basis (downregulation of PI3K-Akt, cell cycle) for the promising clinical results. The therapeutic effect appeared to be enhanced using homologous esophageal ECM. This study suggests that ECM can be further investigated to treat cancer patients after resection or in combination with targeted therapy.

Structural Basis for Achieving GSK-3ß Inhibition with High Potency, Selectivity, and Brain Exposure for Positron Emission Tomography Imaging and Drug Discovery.

Using structure-guided design, several cell based assays, and microdosed positron emission tomography (PET) imaging, we identified a series of highly potent, selective, and brain-penetrant oxazole-4-carboxamide-based inhibitors of glycogen synthase kinase-3 (GSK-3). An isotopologue of our first-generation lead, [3H]PF-367, demonstrates selective and specific target engagement in vitro, irrespective of the activation state. We discovered substantial ubiquitous GSK-3-specific radioligand binding in Tg2576 Alzheimer's disease (AD), suggesting application for these compounds in AD diagnosis and identified [11C]OCM-44 as our lead GSK-3 radiotracer, with optimized brain uptake by PET imaging in nonhuman primates. GSK-3ß-isozyme selectivity was assessed to reveal OCM-51, the most potent (IC50 = 0.030 nM) and selective (>10-fold GSK-3ß/GSK-3α) GSK-3ß inhibitor known to date. Inhibition of CRMP2T514 and tau phosphorylation, as well as favorable therapeutic window against WNT/ß-catenin signaling activation, was observed in cells.

Species differences in mGluR5 binding sites in mammalian central nervous system determined using in vitro binding with [18F]F-PEB.

Binding of [18F]3-fluoro-5-[(pyridin-3-yl)ethynyl]benzonitrile ([18F]F-PEB) was evaluated in membranes and tissue sections prepared from rat, rhesus and human brain. Saturation equilibrium binding experiments with frozen brain cortex and caudate-putamen membranes of young adult rhesus and human and with cortex and striatum from rat yielded data indicative of specific high-affinity binding (KD=0.1-0.15 nM, n> or =3) to a saturable site previously shown to be metabotropic glutamate receptor 5 (mGluR5; Patel S, Ndubizu O, Hamill T, Chaudhary A, Burns HD, Hargreaves RJ, Gibson RE. Screening cascade and development of potential positron emission tomography radiotracers for mGluR5: in vitro and in vivo characterization. Mol Imaging Biol 2005;7:314-323). High-affinity binding of [18F]F-PEB was also detected in cerebellum membranes from rat, rhesus and human. The density of binding sites (Bmax) measured using [18F]F-PEB followed the rank order cortex approximately caudate-putamen/striatum>cerebellum for all three species, with the cerebellum Bmax being significantly lower than that observed in the other regions. Receptor autoradiography studies in tissue sections confirmed that the regional distribution of [18F]F-PEB in mammalian central nervous system is consistent with that of mGluR5 and that a small but specific mGluR5 signal is observed in rhesus and human cerebellum. A small and quantifiable specific signal could also be observed in rat cerebellum using this radiotracer. Immunohistochemical analysis in brain sections revealed a rank order of staining in rhesus and human brain of cortex approximately caudate-putamen>cerebellum. Rat brain immunohistochemistry followed the same rank order, although the staining in the cerebellum was significantly lower. Using a "no-wash" wipe assay, the development of a specific signal within 20 min of incubation of tissue brain sections (>60% in the cortex and striatum; 36-49% in the cerebellum) from all three species confirmed previous in vivo data from rat and rhesus monkey that [18F]PEB is likely to provide a useful in vivo signal using positron emission tomography (PET). This study provides the first quantitative demonstration and direct comparison of a PET tracer candidate identifying mGluR5 binding sites in mammalian cerebellum, which subsequently raises questions in terms of using the cerebellum as a null tissue in PET imaging studies in the laboratory and the clinic.

Advancing Drug Discovery and Development Using Molecular Imaging (ADDMI): an Interest Group of the World Molecular Imaging Society and an Inaugural Session on Positron Emission Tomography (PET).

Multi-modality molecular imaging techniques have expanded the role of imaging biomarkers in the pharmaceutical industry and are beginning to streamline the drug discovery and development process. The World Molecular Imaging Society (WMIS) serves as a forum for discussing innovative and exploratory multi-modal, interdisciplinary molecular imaging research with a mission of bridging the gap between pathology and in vivo imaging. To formalize the role of the WMIS in pharmaceutical research efforts, members of the society have formed an interest group entitled Advancing Drug Discovery and Development using Molecular Imaging (ADDMI). The ADDMI interest group launched their efforts at the 2016 World Molecular Imaging Congress by hosting a session of invited lectures on translational positron emission tomography (PET) imaging in the central nervous system. This article provides a synopsis of those lectures and frames the role of translational imaging biomarker strategies in the drug discovery and development process.

Extracardiac manifestations of atrial myxomas.

Primary cardiac tumors are extremely rare and constitute only about 5% of all cardiac tumors. Cardiac myxomas are noncancerous primary tumors of the heart and constitute about of 50% of all primary heart tumors. Left-sided atrial myxomas are more common than right-sided atrial myxomas. Atrial myxomas can lead to a triad of complications. The most common symptoms are associated with obstruction due to the size and location of the tumor. The next most common symptoms are associated with pulmonary and systemic embolization. Patients may also present with constitutional symptoms. Diagnosis is made via means of transesophageal echocardiography and magnetic resonance imaging. Early diagnosis and surgical resection remain the treatment of choice to prevent complications. Patients usually have a good prognosis after resection.

Screening cascade and development of potential Positron Emission Tomography radiotracers for mGluR5: in vitro and in vivo characterization.

PURPOSE: Use of mGluR5 receptor radiotracers to determine whether an in vitro binding assay is able to predict how good a radiotracer is likely to be in imaging receptor in the central nervous system (CNS) via positron emission tomography (PET). PROCEDURES: Saturation and equilibrium competition studies in rat and rhesus membranes were used to determine receptor concentrations and tracer affinities. In addition, specific binding of metabotropic receptor subtype 5 (mGluR5) radioligands in rhesus and rat brain sections was determined using a "no-wash protocol," and the in vivo binding signal in rats was determined using micro-PET. RESULTS: Affinity values were determined for a series of mGluR5 antagonists (1-5) and ranged from 0.1 to 11 nM in rat. A previously reported "no-wash protocol" was then employed to determine specific binding in tissue sections following a 20-min incubation, and the regional distribution of these mGluR5 radiotracers determined in rat brain via autoradiography. The analogs 1b, 2b, 3b, and 4b, but not 5b, displayed good signal-to-noise ratios under these conditions with high density of binding in caudate, cortex, and hippocampus and lower density in cerebellum. With this information it was predicted that 1c, 2c, 3b, and 4b would display measurable signal-to-noise ratios in vivo, and that the larger in vitro signals for 3b and 4b would translate to 3b and 4b yielding the best in vivo signals. These predictions were investigated using micro-PET imaging in rat. Compound 1c showed a rapid wash-in and rapid wash-out profile in rat brain. Compound 2c showed similar signal-to-noise ratio as 1b, but slower washout. Compounds 3b and 4b showed the best signal-to-noise ratio in vivo, while 5b did not provide a significant signal, as predicted. In vivo occupancy estimates for 2-methyl-6-(phenylethynyl)-pyridine (MPEP) following intravenous administration were determined using radiolabeled compounds 1c, 2c, and 3b; they were essentially the same and were on the order of 1 mg kg(-1) (ID(50)). CONCLUSIONS: An in vitro screen of several mGluR5 tracers was used to rapidly predict whether radiolabeled mGluR5 analogs would be useful as PET radiotracers. Results provided an extension to previously reported data. Two of the four radiotracers with the best in vitro "no-wash" results also showed the best potential as measured noninvasively using micro-PET.