Loss of HCN2 in Dorsal Hippocampus of Young Adult Mice Induces Specific Apoptosis of the CA1 Pyramidal Neuron Layer

Neurons inevitably rely on a proper repertoire and distribution of membrane-bound ion-conducting channels. Among these proteins, the family of hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels possesses unique properties giving rise to the corresponding Ih-current that contributes to various aspects of neural signaling. In mammals, four genes (hcn1-4) encode subunits of HCN channels. These subunits can assemble as hetero- or homotetrameric ion-conducting channels. In order to elaborate on the specific role of the HCN2 subunit in shaping electrical properties of neurons, we applied an Adeno-associated virus (AAV)-mediated, RNAi-based knock-down strategy of hcn2 gene expression both in vitro and in vivo. Electrophysiological measurements showed that HCN2 subunit knock-down resulted in specific yet anticipated changes in Ih-current properties in primary hippocampal neurons and, in addition, corroborated that the HCN2 subunit participates in postsynaptic signal integration. To further address the role of the HCN2 subunit in vivo, we injected recombinant (r)AAVs into the dorsal hippocampus of young adult male mice. Behavioral and biochemical analyses were conducted to assess the contribution of HCN2-containing channels in shaping hippocampal network properties. Surprisingly, knock-down of hcn2 expression resulted in a severe degeneration of the CA1 pyramidal cell layer, which did not occur in mice injected with control rAAV constructs. This finding might pinpoint to a vital and yet unknown contribution of HCN2 channels in establishing or maintaining the proper function of CA1 pyramidal neurons of the dorsal hippocampus

Positron emission tomography imaging in diffuse intrinsic pontine gliomaINM

In pediatric patients with brain tumors, both the monitoring of brain tumor therapy and evaluation of treatment response is of paramount importance (1). In particular, the early identification of non-response allows the termination of an ineffective therapy to avoid possible side effects (e.g., bone marrow depression, nausea, fatigue, allergies, and polyneuropathy) and therefore to maintain or even improve life-quality. Furthermore, the early identification of non-response allows an earlier treatment change. For example, in the event of chemotherapy failure, negative side effects can be avoided and an earlier switch to another chemotherapeutic agent is possible before bone marrow reserves are exhausted. Moreover, identification of treatment failure may help reduce costs. To date, this is highly relevant because the expense of newer systemic treatment options (e.g., immunotherapy and targeted therapy options such as tyrosine kinase inhibitors, BRAF inhibitors, and MEK inhibitors) is considerably higher than conventional alkylating chemotherapy

O‑(2‑[18F]‑fluoroethyl)-L‑tyrosine (FET) in neurooncology: A review of experimental results

In recent years, PET using radiolabelled amino acids has gained considerable interest as an additional tool besides MRI to improve the diagnosis of cerebral gliomas and brain metastases. A very successful tracer in this field is O-(2-[18F]fluoroethyl)-L-tyrosine (FET) which in recent years has replaced short-lived tracers such as [11C]-methyl-L-methionine in many neuro-oncological centers in Western Europe. FET can be produced with high efficiency and distributed in a satellite concept like 2- [18F]fluoro-2-deoxy-D-glucose. Many clinical studies have demonstrated that FET PET provides important diagnostic information regarding the delineation of cerebral gliomas for therapy planning, an improved differentiation of tumor recurrence from treatment-related changes and sensitive treatment monitoring. In parallel, a considerable number of experimental studies have investigated the uptake mechanisms of FET on the cellular level and the behavior of the tracer in various benign lesions in order to clarify the specificity of FET uptake for tumor tissue. Further studies have explored the effects of treatment related tissue alterations on tracer uptake such as surgery, radiation and drug therapy. Finally, the role of blood-brain barrier integrity for FET uptake which presents an important aspect for PET tracers targeting neoplastic lesions in the brain has been investigated in several studies. Based on a literature research regarding experimental FET studies and corresponding clinical applications this article summarizes the knowledge on the uptake behavior of FET, which has been collected in more than 30 experimental studies during the last two decades and discusses the role of these results in the clinical context

Reproducibility of O-(2-[F-18]fluoroethyl)-L-tyrosine kinetics in brain tumors and influence of dexamethasone therapy: A PET study in rat gliomas

Objectives: Previous studies have shown that uptake kinetics of O-(2-[18F]fluoroethyl)-L-tyrosine (FET) in brain tumors correlates with the grade of malignancy. This study investigates the reproducibility of FET kinetics in rat gliomas and the influence of the commonly used dexamethasone (Dex) therapy.Methods: Tumor cells were implanted in the striatum of 31 Fischer rats (15 rats with 9L gliosarcoma; 16 with F98 glioma). Dynamic FET PET (0-60 min post injection, p.i.) was performed after 10 days of tumor growth (baseline) and 48 h later (control) using animal PET (Inveon). Group 1 (n= 8 for 9L; n=10 for F98) received no treatment and group 2 (n= 7 for 9L; n=6 for F98) was injected with 8 mg/kg Dex intraperitoneal after baseline PET plus 4 mg/kg Dex 24 h and 1 h before control PET. Tumor to brain ratios (TBR) (18-60 min p.i.) and the slope of a linear fit of the time activity curve (15 to 60 min p.i.) were determined.Results: The two tumor models showed different FET kinetics (9L slope: +0.17 ± 0.12 SUV/h; F98 slope: +0.76 ± 0.09 SUV/h; p < 0.001) and different TBR (9L: 1.87 ± 0.07; F98: 1.98 ± 0.07; p = 0.005). Both models showed no significant changes of slope in both groups. In all untreated gliomas, TBR slightly increased (9L: 1.87 ± 0.07 vs. 1.95 ± 0.08, p < 0.001; F98: 1.98 ± 0.07 vs. 2.04 ± 0.06, p = 0.002) from baseline to control scan, while the TBR in all Dex treated gliomas decreased (9L: 1.86 ± 0.03 vs. 1.65 ± 0.08, p < 0.001; F98: 1.99 ± 0.10 vs. 1.89 ± 0.15, p = 0.025). This decrease is due to enhanced FET accumulation in normal brain tissue after Dex treatment.Conclusions: FET kinetics in cerebral gliomas show high reproducibility and little interference with Dex therapy. Thus, changes of FET kinetics may be considered reliable indicators of biological reactions occurring in brain tumors during radio/chemotherapy

Influence of Dexamethasone on O-(2-[18F]-Fluoroethyl)-l-Tyrosine Uptake in the Human Brain and Quantification of Tumor Uptake

PurposeO-(2-[18F]fluoroethyl)-l-tyrosine ([18F]FET) is an established positron emission tomography (PET) tracer for brain tumor imaging. This study explores the influence of dexamethasone therapy on [18F]FET uptake in the normal brain and its influence on the maximum and mean tumor-to-brain ratio (TBR).Procedures[18F]FET PET scans of 160 brain tumor patients were evaluated (80 dexamethasone treated, 80 untreated; each group with 40 men/40 women). The standardized uptake value of [18F]FET uptake in the normal brain (SUVbrain) in the different groups was compared. Nine patients were examined repeatedly with and without dexamethasone therapy.ResultsSUVbrain of [18F]FET uptake was significantly higher in dexamethasone-treated patients than in untreated patients (SUVbrain 1.33 ± 0.1 versus 1.06 ± 0.16 in male and 1.45 ± 0.25 versus 1.31 ± 0.28 in female patients). Similar results were observed in patients with serial PET scans. Furthermore, compared to men, a significantly higher SUVbrain was found in women, both with and without dexamethasone treatment. There were no significant differences between the different groups for TBRmax and TBRmean, which could have been masked by the high standard deviation. In a patient with a stable brain metastasis investigated twice with and without dexamethasone, the TBRmax and the biological tumor volume (BTV) decreased considerably after dexamethasone due to an increased SUVbrain.ConclusionDexamethasone treatment appears to increase the [18F]FET uptake in the normal brain. An effect on TBRmax, TBRmean, and BTV cannot be excluded which should be considered especially for treatment monitoring and the estimation of BTV using [18F]FET PET

Reproducibility of O-(2-18^{18}F-fluoroethyl)-L-tyrosine uptake kinetics in brain tumors and influence of corticoid therapy: an experimental study in rat gliomas

PurposePositron emission tomography (PET) using O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET) is a well-established method for the diagnostics of brain tumors. This study investigates reproducibility of 18F-FET uptake kinetics in rat gliomas and the influence of the frequently used dexamethasone (Dex) therapy.MethodsF98 glioma or 9L gliosarcoma cells were implanted into the striatum of 31 Fischer rats. After 10–11 days of tumor growth, the animals underwent dynamic PET after injection of 18F-FET (baseline). Thereafter, animals were divided into a control group and a group receiving Dex injections, and all animals were reinvestigated 2 days later. Tumor-to-brain ratios (TBR) of 18F-FET uptake (18–61 min p.i.) and the slope of the time-activity-curves (TAC) (18–61 min p.i.) were evaluated using a Volume-of-Interest (VOI) analysis. Data were analyzed by two-way repeated measures ANOVA and reproducibility by the intraclass correlation coefficient (ICC).ResultsThe slope of the tumor TACs showed high reproducibility with an ICC of 0.93. A systematic increase of the TBR in the repeated scans was noted (3.7 ± 2.8 %; p < 0.01), and appeared to be related to tumor growth as indicated by a significant correlation of TBR and tumor volume (r = 0.77; p < 0.0001). After correction for tumor growth TBR showed high longitudinal stability with an ICC of 0.84. Dex treatment induced a significant decrease of the TBR (−8.2 ± 6.1 %; p < 0.03), but did not influence the slope of the tumor TAC.ConclusionTBR of 18F-FET uptake and tracer kinetics in brain tumors showed high longitudinal stability. Dex therapy may induce a minor decrease of the TBR; this needs further investigation

Influence of Bevacizumab on Blood Brain Barrier Permeability and O-(2-F-18-Fluoroethyl)-L-Tyrosine Uptake in Rat Gliomas

Restoration of the blood-brain barrier (BBB) after antiangiogenic therapy of gliomas with bevacizumab may result in a decrease in contrast enhancement on MRI despite tumor progression. This so-called pseudoresponse is difficult to differentiate from a true tumor response with conventional MRI. Initial patient studies have indicated that PET using O-(2-F-18-fluoroethyl)-L-tyrosine (F-18-FET) may be helpful for solving this diagnostic problem. This study was performed to investigate the effects of bevacizumab on BBB permeability and F-18-FET uptake in a human xenograft model. Methods: Human U87 glioblastoma cells were implanted into the striatum of immunodeficient RNU rats. F-18-FET PET scans and ex vivo autoradiography were performed in animals receiving a single high dose of bevacizumab (45 mg/kg 2 d before PET; n = 9) or in animals receiving 2 lower doses (10 mg/kg 9 and 2 d before PET; n = 10) to evaluate short-term and long-term effects on the BBB, respectively, and in control animals without bevacizumab treatment (n = 8). Time-activity curves, slope, and tumor-to-brain ratios of F-18-FET uptake (18-61 min after injection) were evaluated using a volume-of-interest analysis. After PET scanning, Evans blue dye (EBD) was injected into animals, and cryosections of the brains were evaluated by autoradiography, by histology, and for EBD fluorescence to assess BBB permeability. Results: Compared with the control, short-term bevacizumab therapy resulted in a trend toward BBB restoration (P = 0.055) and long-term therapy resulted in a significant decrease (P = 0.004) in BBB permeability, as assessed by EBD fluorescence. In contrast, no significant differences in tumor-to brain ratios or slope of F-18-FET uptake were observed in PET and autoradiography (P > 0.05). Conclusion: F-18-FET uptake in glioblastomas seems to be largely independent of BBB permeability and reflects the viability of tumor tissue during antiangiogenic therapy more reliably than contrast-enhanced MRI

High uptake of 68Ga-PSMA and 18F-DCFPyL in the peritumoral area of rat gliomas due to activated astrocytes

BackgroundRecent studies reported on high uptake of the PSMA ligands [68Ga]HBED-CC (68Ga-PSMA) and 18F-DCFPyL in cerebral gliomas. This study explores the regional uptake and cellular targets of 68Ga-PSMA and 18F-DCFPyL in three different rat glioma models.MethodsF98, 9 L, or U87 rat gliomas were implanted into the brains of 38 rats. After 13 days of tumor growth, 68Ga-PSMA (n = 21) or 18F-DCFPyL (n = 17) was injected intravenously, and animals were sacrificed 40 min later. Five animals for each tracer and tumor model were additionally investigated by micro-PET at 20–40 min post injection. Cryosections of the tumor bearing brains were analyzed by ex vivo autoradiography and immunofluorescence staining for blood vessels, microglia, astrocytes, and presence of PSMA. Blood-brain barrier (BBB) permeability was tested by coinjection of Evans blue dye (EBD). 68Ga-PSMA uptake after restoration of BBB integrity by treatment with dexamethasone (Dex) was evaluated in four animals with U87 gliomas. Competition experiments using the PSMA-receptor inhibitor 2-(phosphonomethyl)pentane-1,5-dioic acid (PMPA) were performed for both tracers in two animals each.ResultsAutoradiography demonstrated a strong 68Ga-PSMA and 18F-DCFPyL binding in the peritumoral area and moderate binding in the center of the tumors. PMPA administration led to complete inhibition of 68Ga-PSMA and 18F-DCFPyL binding in the peritumoral region. Restoration of BBB by Dex treatment reduced EBD extravasation but 68Ga-PSMA binding remained unchanged. Expression of activated microglia (CD11b) was low in the intra- and peritumoral area but GFAP staining revealed strong activation of astrocytes in congruency to the tracer binding in the peritumoral area. All tumors were visualized in micro PET, showing a lower tumor/brain contrast with 68Ga-PSMA than with 18F-DCFPyL.ConclusionsHigh uptake of 68Ga-PSMA and 18F-DCFPyL in the peritumoral area of all glioma models is presumably caused by activated astrocytes. This may represent a limitation for the clinical application of PSMA ligands in gliomas