Differential chromatin accessibility and transcriptional dynamics define breast cancer subtypes and their lineages

Breast cancer is a heterogeneous disease, and treatment is guided by biomarker profiles representing distinct molecular subtypes. Breast cancer arises from the breast ductal epithelium, and experimental data suggests breast cancer subtypes have different cells of origin within that lineage. The precise cells of origin for each subtype and the transcriptional networks that characterize these tumor-normal lineages are not established. In this work, we applied bulk, single-cell (sc), and single-nucleus (sn) multi-omic techniques as well as spatial transcriptomics and multiplex imaging on 61 samples from 37 breast cancer patients to show characteristic links in gene expression and chromatin accessibility between breast cancer subtypes and their putative cells of origin. We applied the PAM50 subtyping algorithm in tandem with bulk RNA-seq and snRNA-seq to reliably subtype even low-purity tumor samples and confirm promoter accessibility using snATAC. Trajectory analysis of chromatin accessibility and differentially accessible motifs clearly connected progenitor populations with breast cancer subtypes supporting the cell of origin for basal-like and luminal A and B tumors. Regulatory network analysis of transcription factors underscored the importance of BHLHE40 in luminal breast cancer and luminal mature cells, and KLF5 in basal-like tumors and luminal progenitor cells. Furthermore, we identify key genes defining the basal-like ( PRKCA , SOX6 , RGS6 , KCNQ3 ) and luminal A/B ( FAM155A , LRP1B ) lineages, with expression in both precursor and cancer cells and further upregulation in tumors. Exhausted CTLA4-expressing CD8+ T cells were enriched in basal-like breast cancer, suggesting altered means of immune dysfunction among breast cancer subtypes. We used spatial transcriptomics and multiplex imaging to provide spatial detail for key markers of benign and malignant cell types and immune cell colocation. These findings demonstrate analysis of paired transcription and chromatin accessibility at the single cell level is a powerful tool for investigating breast cancer lineage development and highlight transcriptional networks that define basal and luminal breast cancer lineages.

Single-cell profiling of human dura and meningioma reveals cellular meningeal landscape and insights into meningioma immune response

BACKGROUND

Recent investigations of the meninges have highlighted the importance of the dura layer in central nervous system immune surveillance beyond a purely structural role. However, our understanding of the meninges largely stems from the use of pre-clinical models rather than human samples.

METHODS

Single-cell RNA sequencing of seven non-tumor-associated human dura samples and six primary meningioma tumor samples (4 matched and 2 non-matched) was performed. Cell type identities, gene expression profiles, and T cell receptor expression were analyzed. Copy number variant (CNV) analysis was performed to identify putative tumor cells and analyze intratumoral CNV heterogeneity. Immunohistochemistry and imaging mass cytometry was performed on selected samples to validate protein expression and reveal spatial localization of select protein markers.

RESULTS

In this study, we use single-cell RNA sequencing to perform the first characterization of both non-tumor-associated human dura and primary meningioma samples. First, we reveal a complex immune microenvironment in human dura that is transcriptionally distinct from that of meningioma. In addition, we characterize a functionally diverse and heterogenous landscape of non-immune cells including endothelial cells and fibroblasts. Through imaging mass cytometry, we highlight the spatial relationship among immune cell types and vasculature in non-tumor-associated dura. Utilizing T cell receptor sequencing, we show significant TCR overlap between matched dura and meningioma samples. Finally, we report copy number variant heterogeneity within our meningioma samples.

CONCLUSIONS

Our comprehensive investigation of both the immune and non-immune cellular landscapes of human dura and meningioma at single-cell resolution builds upon previously published data in murine models and provides new insight into previously uncharacterized roles of human dura.

Recent developments and knowledge in pseudocereals including technological aspects

Amaranth, buckwheat, quinoa, and less known, canihua are the most important pseudocereals. Their high nutritional value is well recognized and they are increasingly used for the development of a wide range of starch-based foods, which has been fostered by intensified research data performed in recent years. In addition to health driven motivations, also environmental aspects like the ongoing climate change are an important stimulus to increase agricultural biodiversity again. As pseudocereals are botanically classified as dicotyledonous plants their chemical, physical and processing properties differ significantly from the monocotyledonous cereals. Most important factors that need to be addressed for processing is their smaller seed kernel size, their specific starch structure and granule architecture, their gluten-free protein, but also their dietary fibre and secondary plant metabolites composition. This review gives a condensed overview of the recent developments and gained knowledge with special attention to the technological and food processing aspects of these pseudocereals.

Distinct peripheral inflammatory profiles distinguish COVID-19 from influenza infection, with limited contributions from cytokine storm

We developed a prospective observational cohort of COVID-19 and influenza patients to assess the quality and magnitude of their immune responses at the cellular and protein levels. Although COVID-19 patients exhibited equivalent lymphocyte counts compared to influenza patients, they had fewer monocytes and lower surface HLA-class II expression on select monocyte populations compared to influenza patients and healthy controls. Decreased HLA-DR on intermediate monocytes was a significant predictor of COVID-19 disease severity. Protein cytokine levels were measured in two distinct COVID-19 cohorts, composed of 73 and 89 patients, revealing multiple inflammatory phenotypes. Only four percent of patients (7 of 162) exhibited a distinct Cytokine Storm Syndrome (CSS) phenotype. Furthermore, COVID-19 patients generally exhibited lower cytokine levels than influenza patients. Upregulation of a few innate inflammatory mediators, including IL-6, GCSF, IL-1RA, and MCP1, predicted death from acute respiratory failure among COVID-19 patients but were not statistically higher than those of influenza patients. Single-cell transcriptional profiling of 2 healthy controls as well as 3 COVID-19 and 3 influenza subjects with respiratory failure was concordant with the profound suppression in type I and type II interferon signaling in COVID-19 patients across multiple cell types. In contrast, COVID-19 cells were enriched for alterations in metabolic, stress, and apoptotic pathways. When considered across the spectrum of peripheral innate and adaptive immune profiles, the immune pathologies underlying severe influenza and COVID-19 are substantially distinct, with COVID-19 patients generally less inflamed than those with influenza.

Treatment of an aggressive orthotopic murine glioblastoma model with combination checkpoint blockade and a multivalent neoantigen vaccine

BACKGROUND

Although clinical trials testing immunotherapies in glioblastoma (GBM) have yielded mixed results, new strategies targeting tumor-specific somatic coding mutations, termed "neoantigens," represent promising therapeutic approaches. We characterized the microenvironment and neoantigen landscape of the aggressive CT2A GBM model in order to develop a platform to test combination checkpoint blockade and neoantigen vaccination.

METHODS

Flow cytometric analysis was performed on intracranial CT2A and GL261 tumor-infiltrating lymphocytes (TILs). Whole-exome DNA and RNA sequencing of the CT2A murine GBM was employed to identify expressed, somatic mutations. Predicted neoantigens were identified using the pVAC-seq software suite, and top-ranking candidates were screened for reactivity by interferon-gamma enzyme linked immunospot assays. Survival analysis was performed comparing neoantigen vaccination, anti-programmed cell death ligand 1 (αPD-L1), or combination therapy.

RESULTS

Compared with the GL261 model, CT2A exhibited immunologic features consistent with human GBM including reduced αPD-L1 sensitivity and hypofunctional TILs. Of the 29 CT2A neoantigens screened, we identified neoantigen-specific CD8+ T-cell responses in the intracranial TIL and draining lymph nodes to two H2-Kb restricted (Epb4H471L and Pomgnt1R497L) and one H2-Db restricted neoantigen (Plin2G332R). Survival analysis showed that therapeutic neoantigen vaccination with Epb4H471L, Pomgnt1R497L, and Plin2G332R, in combination with αPD-L1 treatment was superior to αPD-L1 alone.

CONCLUSIONS

We identified endogenous neoantigen specific CD8+ T cells within an αPD-L1 resistant murine GBM and show that neoantigen vaccination significantly augments survival benefit in combination with αPD-L1 treatment. These observations provide important preclinical correlates for GBM immunotherapy trials and support further investigation into the effects of multimodal immunotherapeutic interventions on antiglioma immunity.

KEY POINTS

1. Neoantigen vaccines combined with checkpoint blockade may be promising treatments.2. CT2A tumors exhibit features of human GBM microenvironments.3. Differential scanning fluorimetry assays may complement in silico neoantigen prediction tools.

Differential diagnosis of auditory hallucinations in teenagers. Assessment and difficulties: Case report of a 13 year old patient

Introduction

Learning from a case of a 13 year old patient with auditory hallucinations for 2 months, admitted to the hospital due to suicidal ideation. Her mother had been diagnosed with Lupus and OCD. Her mood had been low for several months, probable mild intellectual disability.

Objectives

Learn how to assess auditory hallucinations and possible new onset psychotic symptoms in teenagers. Learn about different levels of care involved. Discuss differential diagnosis and future directions and treatment.

Methods

Description of the case. Differential diagnosis: Obsessive compulsive disorder, Major depressive disorder with Psychotic features, schizophrenia spectrum disorder, epilepsy or other neurologic disease, autoimmune disease, post-traumatic stress disorder… Tests and consults conducted by Neurology team Psychopharmacology description.

Results

Differential diagnosis: Obsessive compulsive disorder, Major depressive disorder with Psychotic features, schizophrenia spectrum disorder, epilepsy, autoimmune diseases like Lupus, post-traumatic stress disorder etc. Video EEG: normal. Brain MRI: normal Blood work unremarkable with positive ANA (titer 1:80). Work up, including lumbar puncture with autoimmune encephalitis and MS panels was negative. Psychopharmacology: Fluoxetine up to 40mg, and Aripiprazol up to 20mg without a good response. Possible sexual trauma was disclosed in a second hospitalization, months later.

Conclusions

Recommendation of assessing new onset of psychotic symptoms in detail to get a good diagnosis. Psychotic symptoms in young teenagers may occur as part of different presentations and it is important to provide a good follow up of the patient in order to provide the most accurate treatment.

Conflict of interest

Alicia Koplowitz Foundation

Distinct inflammatory profiles distinguish COVID-19 from influenza with limited contributions from cytokine storm

We pursued a study of immune responses in coronavirus disease 2019 (COVID-19) and influenza patients. Compared to patients with influenza, patients with COVID-19 exhibited largely equivalent lymphocyte counts, fewer monocytes, and lower surface human leukocyte antigen (HLA)-class II expression on selected monocyte populations. Furthermore, decreased HLA-DR on intermediate monocytes predicted severe COVID-19 disease. In contrast to prevailing assumptions, very few (7 of 168) patients with COVID-19 exhibited cytokine profiles indicative of cytokine storm syndrome. After controlling for multiple factors including age and sample time point, patients with COVID-19 exhibited lower cytokine levels than patients with influenza. Up-regulation of IL-6, G-CSF, IL-1RA, and MCP1 predicted death in patients with COVID-19 but were not statistically higher than patients with influenza. Single-cell transcriptional profiling revealed profound suppression of interferon signaling among patients with COVID-19. When considered across the spectrum of peripheral immune profiles, patients with COVID-19 are less inflamed than patients with influenza.

Detection of neoantigen-specific T cells following a personalized vaccine in a patient with glioblastoma

Neoantigens represent promising targets for personalized cancer vaccine strategies. However, the feasibility of this approach in lower mutational burden tumors like glioblastoma (GBM) remains unknown. We have previously reported the use of an immunogenomics pipeline to identify candidate neoantigens in preclinical models of GBM. Here, we report the application of the same immunogenomics pipeline to identify candidate neoantigens and guide screening for neoantigen-specific T cell responses in a patient with GBM treated with a personalized synthetic long peptide vaccine following autologous tumor lysate DC vaccination. Following vaccination, reactivity to three HLA class I- and five HLA class II-restricted candidate neoantigens were detected by IFN-γ ELISPOT in peripheral blood. A similar pattern of reactivity was observed among isolated post-treatment tumor-infiltrating lymphocytes. Genomic analysis of pre- and post-treatment GBM reflected clonal remodeling. These data demonstrate the feasibility and translational potential of a therapeutic neoantigen-based vaccine approach in patients with primary CNS tumors.

Delayed and fractional use of enzymatic debridement with nexobrid for extensive burn injury: a case report

Selective enzymatic debridement is increasingly being used in cases of burn wounds. However, until now the use of Nexobrid has been limited to 15% of total body surface area (TBSA) and immediate use on admission day. A 61-year-old Caucasian male suffered a severe burn injury that affected 95% TBSA. After surgical escharotomy and tracheotomy on admission day, we successfully performed a fractional enzymatic debridement of 54% of the TBSA in three different sessions within four days. This case report reveals that a delayed and fractional application of Nexobrid to more than 15% TBSA is possible.

Quantitative [18F]Fluorodopa/PET and Histology of Fetal Mesencephalic Dopaminergic Grafts to the Striatum of MPTP-Poisoned Minipigs

The functional restoration of the dopamine innervation of striatum in MPTP-poisoned Göttingen minipigs was assessed for 6 months following grafting of fetal pig mesencephalic neurons. Pigs were assigned to a normal control group and a MPTP-poisoned group, members of which received no further treatment, or which received bilateral grafts to the striatum of tissue blocks harvested from E28 fetal pig mesencephalon with and without immunosuppressive treatment after grafting, or with additional co-grafting with immortalized rat neural cells transfected to produce GDNF. In the baseline condition, and again at 3 and 6 months postsurgery, all animals were subjected to quantitative [18F]fluorodopa PET scans and testing for motor impairment. At the end of 6 months, tyrosine hydroxylase (TH)-containing neurons were counted in the grafts by stereological methods. The MPTP poisoning persistently reduced the magnitude of k3D, the relative activity of DOPA decarboxylase in striatum, by 60%. Grafting restored the rate of [18F]fluorodopa decarboxylation to the normal range, and normalized the scores in motor function. The biochemical and functional recovery was associated with survival of approximately 100,000 TH-positive graft neurons in each hemisphere. Immunosuppression did not impart a greater recovery of [18F]fluorodopa uptake, nor were the number of TH-positive graft neurons or the volumes of the grafts increased in the immunosuppressed group. Contrary to expectation, co-grafting of transfected GDNF-expressing HiB5 cells, a rat-derived neural cell line, tended to impair the survival of the grafts with the lowest values for graft volumes, TH-positive cell numbers, behavioral scores, and relative DOPA decarboxylase activity. From the results we conclude that pig ventral mesencephalic allografts can restore functional dopamine innervation in adult MPTP-lesioned minipigs.

Faculty professional development in emergent pedagogies for instructional innovation in dental education

Innovative pedagogies have significantly impacted health professions' education, dental education included. In this context, faculty, defined in this study as instructor in higher education, has been increasingly required to hone their instructional skills. The purpose of this exploratory study was to share the design, implementation and preliminary outcomes of two programmes to enhance dental faculty's instructional skills, the Teaching and Learning Seminar Series and the Course Director Orientation. Data sources included faculty and student surveys developed and administered by the researchers; data extracted from the learning management system; reports from the learning analytics tool; and classroom observations. Participants' satisfaction, self-reported learning, instructional behavioural change, and impact on student learning behaviours and institutional practice were assessed borrowing from Kirkpatrick's 4-level model of evaluation of professional development effectiveness. Initial findings showed that faculty in both programmes reported positive learning experiences. Participants reported that the programmes motivated them to improve instructional practice and improved their knowledge of instructional innovation. Some faculty reported implementation of new instructional strategies and tools, which helped create an active and interactive learning environment that was welcomed by their students. The study contributes to literature and best practice in health sciences faculty development in pedagogy and may guide other dental schools in designing professional development programmes.

Endogenous Neoantigen-Specific CD8 T Cells Identified in Two Glioblastoma Models Using a Cancer Immunogenomics Approach

The "cancer immunogenomics" paradigm has facilitated the search for tumor-specific antigens over the last 4 years by applying comprehensive cancer genomics to tumor antigen discovery. We applied this methodology to identify tumor-specific "neoantigens" in the C57BL/6-derived GL261 and VM/Dk-derived SMA-560 tumor models. Following DNA whole-exome and RNA sequencing, high-affinity candidate neoepitopes were predicted and screened for immunogenicity by ELISPOT and tetramer analyses. GL261 and SMA-560 harbored 4,932 and 2,171 nonsynonymous exome mutations, respectively, of which less than half were expressed. To establish the immunogenicities of H-2K^b and H-2D^b candidate neoantigens, we assessed the ability of the epitopes predicted in silico to be the highest affinity binders to activate tumor-infiltrating T cells harvested from GL261 and SMA-560 tumors. Using IFNγ ELISPOT, we confirmed H-2D^b-restricted Imp3_D81N (GL261) and Odc1_Q129L (SMA-560) along with H-2K^b-restricted E2f8_K272R (SMA-560) as endogenous tumor-specific neoantigens that are functionally immunogenic. Furthermore, neoantigen-specific T cells to Imp3_D81N and Odc1_Q129L were detected within intracranial tumors as well as cervical draining lymph nodes by tetramer analysis. By establishing the immunogenicities of predicted high-affinity neoepitopes in these models, we extend the immunogenomics-based neoantigen discovery pipeline to glioblastoma models and provide a tractable system to further study the mechanism of action of T cell-activating immunotherapeutic approaches in preclinical models of glioblastoma. Cancer Immunol Res; 4(12); 1007-15. ©2016 AACR.

Discovery of τ Neutrino Appearance in the CNGS Neutrino Beam with the OPERA Experiment

The OPERA experiment was designed to search for ν_{μ}→ν_{τ} oscillations in appearance mode, i.e., by detecting the τ leptons produced in charged current ν_{τ} interactions. The experiment took data from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of the ν_{μ}→ν_{τ} appearance, achieved with four candidate events in a subsample of the data, was previously reported. In this Letter, a fifth ν_{τ} candidate event, found in an enlarged data sample, is described. Together with a further reduction of the expected background, the candidate events detected so far allow us to assess the discovery of ν_{μ}→ν_{τ} oscillations in appearance mode with a significance larger than 5σ.

Affinity maturation of antibodies requires integrity of the adult thymus

The generation of B-cell responses to proteins requires a functional thymus to produce CD4(+) T cells which helps in the activation and differentiation of B cells. Because the mature T-cell repertoire has abundant cells with the helper phenotype, one might predict that in mature individuals, the generation of B-cell memory would proceed independently of the thymus. Contrary to that prediction, we show here that the removal of the thymus after the establishment of the T-cell compartment or sham surgery without removal of the thymus impairs the affinity maturation of antibodies. Because removal or manipulation of the thymus did not decrease the frequency of mutation of the Ig variable heavy chain exons encoding antigen-specific antibodies, we conclude that the thymus controls affinity maturation of antibodies in the mature individual by facilitating the selection of B cells with high-affinity antibodies.

Defective B cell memory and autoantibodies in subjects of cardiac transplantation in infancy (169.27)

Aberrant functions of T cells and B cells may impair B cell memory and are thought to allow development of autoantibodies. Rarely, B cell memory defects and/or autoimmunity can be traced to specific mutations; however, in most cases which properties of T cells and B cells cause deficient B cell responses and/or autoimmunity are unclear. To answer these questions we studied child recipients of cardiac transplantation during infancy who, owing to removal of the thymus and T cell depletion at the time of surgery, have a greatly reduced T cell receptor repertoire diversity. We found these children to have impaired memory IgG antibody responses to polypeptide vaccines compared to controls, even though they appeared to mount IgM responses. These results suggest that the defective T cell compartment in recipients of cardiac transplantation in infancy impairs B cell memory and/or isotype class- switching. Remarkably, despite these defects and despite ongoing treatment with immunosuppressive drugs, 6 of the 9 subjects studied produced anti-ssDNA and rheumatoid factor antibodies as early as of 2 years of age. These findings suggest that the diversity of T cells and/or the availability of recent thymic emigrants are needed to generate B cell memory and prevent autoimmunity.

Neutrophil Dysfunction in Guanosine 3′,5′-Cyclic Monophosphate-Dependent Protein Kinase I-Deficient Mice

The regulation of neutrophil functions by Type I cGMP-dependent protein kinase (cGKI) was investigated in wild-type (WT) and cGKI-deficient (cGKI-/-) mice. We demonstrate that murine neutrophils expressed cGKIalpha. Similar to the regulation of Ca2+ by cGKI in other cells, there was a cGMP-dependent decrease in Ca2+ transients in response to C5a in WT, but not cGKI-/- bone marrow neutrophils. In vitro chemotaxis of bone marrow neutrophils to C5a or IL-8 was significantly greater in cGKI-/- than in WT. Enhanced chemotaxis was also observed with cGKI-/- peritoneal exudate neutrophils (PE-N). In vivo chemotaxis with an arachidonic acid-induced inflammatory ear model revealed an increase in both ear weight and myeloperoxidase (MPO) activity in ear punches of cGKI-/- vs WT mice. These changes were attributable to enhanced vascular permeability and increased neutrophil infiltration. The total extractable content of MPO, but not lysozyme, was significantly greater in cGKI-/- than in WT PE-N. Furthermore, the percentage of MPO released in response to fMLP from cGKI-/- (69%) was greater than that from WT PE-N (36%). PMA failed to induce MPO release from PE-N of either genotype. In contrast, fMLP and PMA released equivalent amounts of lysozyme from PE-N. However, the percentage released was less in cGKI-/- (approximately 60%) than in WT (approximately 90%) PE-N. Superoxide release (maximum velocity) revealed no genotype differences in responses to PMA or fMLP stimulation. In summary, these results show that cGKIalpha down-regulates Ca2+ transients and chemotaxis in murine neutrophils. The regulatory influences of cGKIalpha on the secretagogue responses are complex, depending on the granule subtype.

PET evaluation of the uptake of N-[11C]methyl CP-643,051, an NK1 receptor antagonist, in the living porcine brain

Antagonists of neurokinin receptors such as CP-643,051 are presently under investigation as potential antidepressants, but little is known about the brain uptake and distribution of these agents. We developed a method for the efficient N-[11C]methylation of CP-122,721, yielding the NK1 antagonist N-[11C]methyl CP-643,051. The brain uptake and distribution of N-[11C]methyl CP-643,051 were studied by positron emission tomography (PET) in the anaesthetized pig, first in a baseline condition, and again after displacement of specific binding with the NK1 receptor antagonist L-732,138 (0.6 mg/kg, i.v.). In order to validate this displacement procedure, we tested the effects of L-732,138 on cerebral blood flow (CBF) in one pig. We found that N-[11C]methyl CP-643,051 had a distribution volume close to 3 ml g(-1), and a binding potential (pB) of 0.3 in the pig striatum; this binding was displaceable by the L-732,138 pre-treatment, which evoked a small (10-20%) global increase in CBF. We conclude that of N-[11C]methyl CP-643,051 may serve as a lead structure for the development of PET NK-1 ligands of higher specific binding in vivo.

PET evaluation of a tetracyclic, atypical antidepressant, [N-methyl-11C]mianserin, in the living porcine brain

We synthesized [N-methyl-11C]mianserin by alkylation of N-desmethyl mianserin with [11C]methyl iodide followed by HPLC purification. We used PET for determining the regional cerebral pharmacokinetics of the radiotracer in anesthetized swine. [N-methyl-11C]Mianserin entered most brain regions readily (range of K1 values: 0.66-1.13), reaching highest levels in the basal ganglia and thalamus. The binding potential of [N-methyl-11C]mianserin was relatively low (range: 0.07-0.50), but regional differences were nonetheless observed, with highest values in the temporal cortex and lowest values in the brainstem. These PET findings, which are the first ones for a tetracyclic, antidepressant drug, show that [N-methyl-11C]mianserin has only a limited degree of regional specificity of binding in the living brain.

Positron emission tomography of hepatic first-pass metabolism of ammonia in pig

Hepatic first-pass metabolism plays a key role in metabolic regulation and drug metabolism. Metabolic processes can be quantified in vivo by positron emission tomography scanning (PET). We wished to develop a PET technique to measure hepatic first-pass metabolism of ammonia. Seven anaesthetised pigs were given positron-labelled ammonia, (13)NH(3), into the portal vein and into the vena cava as successive 2-min infusions followed by 22-min dynamic liver scanning. Vena cava infusion data were used to account for recirculation of tracer and metabolites following the portal vein infusion. The scan data were analysed by a model of sinusoidal zonation of ammonia metabolism with periportal urea formation and perivenous formation of glutamine. The hepatic extraction fraction of (13)NH(3) was 0.73+/-0.16 (mean+/-SD, n=7 pigs). Values of clearance of ammonia to urea and to glutamine were obtained, as were rate constants for washout of these two metabolites. Overall, the modelling showed half of the ammonia uptake to be converted to urea and half to glutamine. The washout rate constant for glutamine was about one-tenth of that for urea. We conclude that hepatic first-pass metabolism of ammonia was successfully assessed by PET.

Metabolites of (18)F-FDG and 3-O-(11)C-methylglucose in pig liver

PET uses (18)F-FDG widely to estimate glucose metabolism in vivo. Dynamic PET data are evaluated by kinetic models of the metabolic pathways. Knowledge of the metabolites of FDG is of critical importance for the interpretation of kinetic PET studies. The purpose of this study was to determine the metabolic pathways of FDG and 3-O-(11)C-methylglucose (MG) in liver tissue in vivo. It is usually assumed that MG is not metabolized and FDG is converted to (18)F-FDG-6-phosphate (FDG-6-P).

METHODS

The study was performed on 6 anesthetized 40-kg pigs that were given the 2 tracers intravenously. The content of metabolites was determined in successive liver tissue biopsies. Freeze-clamped liver tissue samples were subjected to extraction by acetonitrile at -5 degrees C to -10 degrees C, and extracts were analyzed by radio-high-performance liquid chromatography (radio-HPLC). The findings were identified by means of radio-HLPC measurements of the products of in vitro enzymatic reactions.

RESULTS

The applied extraction technique provided almost quantitative recovery of the radioactivity from tissue. After MG injection, only MG was detectable in the liver tissue; no labeled metabolites were found. After FDG injection, 2 metabolites were identified, FDG-6-P and 2-(18)F-fluoro-2-deoxy-6-phosphogluconate (FD-6-PG1). The tissue content of FDG increased rapidly, and, after 5 min, only FDG was identified; hereafter, the fraction of FDG decreased to approximately 40% of the tissue radioactivity after 180 min. After 20 min, FDG-6-P was found in each of the pigs and it increased throughout the measurement period of 180 min, with a somewhat slower rise at late time points. FD-6-PG1 began to appear in the liver tissue after 45 min and increased throughout the 180-min experiment, with the increase somewhat slower than that of FDG-6-P. After 180 min, approximately 40% of the metabolites was attributed to FD-6-PG1. The content of other metabolites was <2%, even after 180 min.

CONCLUSION

After the FDG injection, not only FDG-6-P but also FD-6-PG1 were formed in the liver. Any possible incorporation of FDG into glycogen was of minor importance.