Visualizing Cancer-Originating Acetate Uptake Through MCT1 in Reactive Astrocytes in the Glioblastoma Tumor Microenvironment.

BACKGROUND: Reactive astrogliosis is a hallmark of various brain pathologies, including neurodegenerative diseases and glioblastomas. However, the specific intermediate metabolites contributing to reactive astrogliosis remain unknown. This study investigated how glioblastomas induce reactive astrogliosis in the neighboring microenvironment and explores 11C-acetate PET as an imaging technique for detecting reactive astrogliosis. METHODS: Through in vitro, mouse models, and human tissue experiments, we examined the association between elevated 11C-acetate uptake and reactive astrogliosis in gliomas. We explored acetate from glioblastoma cells, which triggers reactive astrogliosis in neighboring astrocytes by upregulating MAO-B and MCT1 expression. We evaluated the presence of cancer stem cells in the reactive astrogliosis region of glioblastomas and assessed the correlation between the volume of 11C-acetate uptake beyond MRI and prognosis. RESULTS: Elevated 11C-acetate uptake is associated with reactive astrogliosis and astrocytic MCT1 in the periphery of glioblastomas in human tissues and mouse models. Glioblastoma cells exhibit increased acetate production as a result of glucose metabolism, with subsequent secretion of acetate. Acetate derived from glioblastoma cells induces reactive astrogliosis in neighboring astrocytes by increasing the expression of MAO-B and MCT1. We found cancer stem cells within the reactive astrogliosis at the tumor periphery. Consequently, a larger volume of 11C-acetate uptake beyond contrast-enhanced MRI was associated with worse prognosis. CONCLUSION: Our results highlight the role of acetate derived from glioblastoma cells in inducing reactive astrogliosis and underscore the potential value of 11C-acetate PET as an imaging technique for detecting reactive astrogliosis, offering important implications for the diagnosis and treatment of glioblastomas.

Visualizing reactive astrocyte-neuron interaction in Alzheimer's disease using 11C-acetate and 18F-FDG.

Reactive astrogliosis is a hallmark of Alzheimer's disease (AD). However, a clinically validated neuroimaging probe to visualize the reactive astrogliosis is yet to be discovered. Here, we show that PET imaging with 11C-acetate and 18F-fluorodeoxyglucose (18F-FDG) functionally visualizes the reactive astrocyte-mediated neuronal hypometabolism in the brains with neuroinflammation and AD. To investigate the alterations of acetate and glucose metabolism in the diseased brains and their impact on the AD pathology, we adopted multifaceted approaches including microPET imaging, autoradiography, immunohistochemistry, metabolomics, and electrophysiology. Two AD rodent models, APP/PS1 and 5xFAD transgenic mice, one adenovirus-induced rat model of reactive astrogliosis, and post-mortem human brain tissues were used in this study. We further curated a proof-of-concept human study that included 11C-acetate and 18F-FDG PET imaging analyses along with neuropsychological assessments from 11 AD patients and 10 healthy control subjects. We demonstrate that reactive astrocytes excessively absorb acetate through elevated monocarboxylate transporter-1 (MCT1) in rodent models of both reactive astrogliosis and AD. The elevated acetate uptake is associated with reactive astrogliosis and boosts the aberrant astrocytic GABA synthesis when amyloid-ß is present. The excessive astrocytic GABA subsequently suppresses neuronal activity, which could lead to glucose uptake through decreased glucose transporter-3 in the diseased brains. We further demonstrate that 11C-acetate uptake was significantly increased in the entorhinal cortex, hippocampus and temporo-parietal neocortex of the AD patients compared to the healthy controls, while 18F-FDG uptake was significantly reduced in the same regions. Additionally, we discover a strong correlation between the patients' cognitive function and the PET signals of both 11C-acetate and 18F-FDG. We demonstrate the potential value of PET imaging with 11C-acetate and 18F-FDG by visualizing reactive astrogliosis and the associated neuronal glucose hypometablosim for AD patients. Our findings further suggest that the acetate-boosted reactive astrocyte-neuron interaction could contribute to the cognitive decline in AD.

Preclinical Evaluation of a Companion Diagnostic Radiopharmaceutical, [18F]PSMA-1007, in a Subcutaneous Prostate Cancer Xenograft Mouse Model.

Several radiolabeled prostate-specific membrane antigen (PSMA)-targeted agents have been developed for detecting prostate cancer, using positron emission tomography imaging and targeted radionuclide therapy. Among them, [18F]PSMA-1007 has several advantages, including a comparatively long half-life, delayed renal excretion, and compatible structure with α-/ß-particle emitter-labeled therapeutics. This study aimed to characterize the preclinical pharmacokinetics and internal radiation dosimetry of [18F]PSMA-1007, as well as its repeatability and specificity for target binding using prostate tumor-bearing mice. In PSMA-positive tumor-bearing mice, the kidney showed the greatest accumulation of [18F]PSMA-1007. The distribution in the tumor attained its peak concentration of 2.8%ID/g at 112 min after intravenous injection. The absorbed doses in the tumor and salivary glands were 0.079 ± 0.010 Gy/MBq and 0.036 ± 0.006 Gy/MBq, respectively. The variance of the net influx (Ki) of [18F]PSMA-1007 to the tumor was minimal between scans performed in the same animals (within-subject coefficient of variation = 7.57%). [18F]PSMA-1007 uptake in the tumor was specifically decreased by 32% in Ki after treatment with a PSMA inhibitor 2-(phosphonomethyl)-pentanedioic acid (2-PMPA). In the present study, we investigated the in vivo preclinical characteristics of [18F]PSMA-1007. Our data from [18F]PSMA-1007 PET/computed tomography (CT) studies in a subcutaneous prostate cancer xenograft mouse model supports clinical therapeutic strategies that use paired therapeutic radiopharmaceuticals (such as [177Lu]Lu-PSMA-617), especially strategies with a quantitative radiation dose estimate for target lesions while minimizing radiation-induced toxicity to off-target tissues.

11 C-Acetate PET/CT Detects Reactive Astrogliosis Helping Glioma Classification.

PURPOSE: 11 C-acetate ( 11 C-ACE) uptake on PET/CT was recently discovered to represent reactive astrocytes in the tumor microenvironment. This study aimed at evaluating the role of 11 C-ACE PET/CT as an imaging biomarker of reactive astrogliosis in characterizing different types of gliomas. METHODS: In this prospective study, a total of 182 patients underwent 11 C-ACE PET/CT before surgery. The ratio of SUV max of a glioma to the SUV mean of the contralateral choroid plexus ( 11 C-ACE TCR) on PET/CT was calculated. 11 C-ACE TCRs were compared with the World Health Organization grades and isocitrate dehydrogenase 1 ( IDH1 ) mutation status. Grade 2 was considered low-grade tumor, and grades 3 and 4 were considered high-grade tumors. RESULTS: The median 11 C-ACE TCR was significantly higher in IDH1 wild-type (wt) tumors (n = 91) than in IDH1 -mutant (mt) tumors (n = 91) (2.38 vs 1.30, P < 0.001). Of the 91 IDH1 -mt tumors, there were no differences in the median 11 C-ACE TCRs between oligodendrogliomas (ODs) and astrocytic tumors (1.40 vs 1.20, P > 0.05). In grading low- versus high-grade gliomas, the receiver operating characteristic curve analyses showed a higher area under the curve (0.951) in IDH1 -wt tumors than in IDH1 -mt tumors (0.783, P = 0.002). Grade 2 ODs were well differentiated from high-grade gliomas. The 11 C-ACE TCR of grade 3 ODs was significantly lower than that of IDH1 -wt glioblastomas. CONCLUSIONS: High 11 C-ACE uptake is associated with high-grade IDH1 -wt tumors, thus facilitating differentiation from high-grade IDH1-mt and low-grade gliomas. In particular, low 11 C-ACE uptake in ODs is advantageous in overcoming the limitation of radiolabeled amino acid tracers.

Extracellular Citrate Treatment Induces HIF1α Degradation and Inhibits the Growth of Low-Glycolytic Hepatocellular Carcinoma under Hypoxia.

HCC is well known for low glycolysis in the tumors, whereas hypoxia induces glycolytic phenotype and tumor progression. This study was conducted to evaluate the expression of SLCs in human HCCs and investigated whether extracellular nutrient administration related to SLCs in low-glycolytic HCC can prevent hypoxic tumor progression. SLCs expression was screened according to the level of glycolysis in HCCs. Then, whether extracellular nutrient treatment can affect hypoxic tumor progression, as well as the mechanisms, were evaluated in an in vitro cell line and an in vivo animal model. Low-glycolytic HCCs showed high SLC13A5/NaCT and SLC16A1/MCT1 but low SLC2A1/GLUT1 and HIF1α/HIF1α expression. Especially, high SLC13A5 expression was significantly associated with good overall survival in the Cancer Genome Atlas (TCGA) database. In HepG2 cells with the highest NaCT expression, extracellular citrate treatment upon hypoxia induced HIF1α degradation, which led to reduced glycolysis and cellular proliferation. Finally, in HepG2-animal models, the citrate-treated group showed smaller tumor with less hypoxic areas than the vehicle-treated group. In patients with HCC, SLC13A5/NaCT is an important SLC, which is associated with low glycolysis and good prognosis. Extracellular citrate treatment induced the failure of metabolic adaptation to hypoxia and tumor growth inhibition, which can be a potential therapeutic strategy in HCCs.

Glucose Loading Enhances the Value of 18F-FDG PET/CT for the Characterization and Delineation of Cerebral Gliomas.

This study aimed to assess how to enhance the value of 18F-Fluorodeoxyglucose (FDG) PET/CTs for glioma grading and better delineation of the tumor boundary by glucose loading. In mouse models of brain tumor using U87MG cells, 18F-FDG-PET images were obtained after fasting and after glucose loading. There was a significant difference in the tumor-to-normal cortex-uptake ratio (TNR) between the fasting and glucose-loading scans. 14C-2-Deoxy-D-glucose (14C-DG) uptake was measured in vitro using U87MG, U373MG and primary neurons cultured with different concentrations of glucose. The tumor-to-neuron ratio of 14C-DG uptake increased with up to 10 mM of glucose. Finally, 10 low-grade and 17 high-grade glioma patients underwent fasting and glucose loading 18F-FDG PET/CT and the TNR was compared between scans. The effect of glucose loading was significant in high-grade but not in low-grade gliomas. The receiver operating characteristic curve analyses with a cut-off TNR of 0.81 showed a higher area under the curve after glucose loading than fasting for differentiating low-grade versus high-grade gliomas. In addition, the glucose loading PET/CT was more useful than the fasting PET/CT for the discrimination of oligodendrogliomas from IDH-wildtype glioblastomas. Glucose loading resulted in a greater reduction in 18F-FDG uptake in the normal cortex than in tumors, which increases the usefulness of 18F-FDG PET/CT for grading.

Modulation of SIRT3 expression through CDK4/6 enhances the anti-cancer effect of sorafenib in hepatocellular carcinoma cells.

BACKGROUND: Hepatocellular carcinoma (HCC) is the leading cause of cancer-related deaths worldwide. The only drug currently approved for clinical use in the treatment of advanced HCC is sorafenib. However, many patients with HCC show reduced sensitivity to sorafenib during treatment. SIRT3, a member of the mammalian sirtuin family, is a tumor suppressor in certain tumor types. However, only few studies have investigated the effects of SIRT3 on tumor prognosis and sorafenib sensitivity in patients with HCC. Here, we aimed to investigate the correlation between SIRT3 expression and glucose metabolism and proliferation in HCC and discover effective compounds that increase endogenous SIRT3 modulation effect of sorafenib. METHODS: To determine the correlation between SIRT3 and glucose related proteins, immunostaining was performed with liver cancer tissue using various antibodies. To investigate whether the expression of SIRT3 in HCC is related to the resistance to sorafenib, we treated sorafenib after the modulation of SIRT3 levels in HCC cell lines (overexpression in Huh7, knockdown in HepG2). We also employed PD0332991 to modulate the SIRT3 expression in HCC cell and conducted functional assays. RESULTS: SIRT3 expression was downregulated in high glycolytic and proliferative HCC cells of human patients, xenograft model and HCC cell lines. Moreover, SIRT3 expression was downregulated after sorafenib treatment, resulting in reduced drug sensitivity in HCC cell lines. To enhance the anti-tumor effect of sorafenib, we employed PD0332991 (CDK4/6-Rb inhibitor) based on the correlation between SIRT3 and phosphorylated retinoblastoma protein in HCC. Notably, combined treatment with sorafenib and PD0332991 showed an enhancement of the anti-tumor effect in HCC cells. CONCLUSIONS: Our data suggest that the modulation of SIRT3 by CDK4/6 inhibition might be useful for HCC therapy together with sorafenib, which, unfortunately, has limited efficacy and whose use is often associated with drug resistance.

The critical role of glucose deprivation in epithelial-mesenchymal transition in hepatocellular carcinoma under hypoxia.

Imaging with 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is used to determine sites of abnormal glucose metabolism to predict high tumor grade, metastasis, and poor patient survival. However, not all tumors with increased 18F-FDG uptake show aggressive tumor biology, as evident from the moderate correlation between metastasis and high FDG uptake. We hypothesized that metastasis is likely attributable to the complexity and heterogeneity of the cancer microenvironment. To identify the cancer microenvironment that induces the epithelial-mesenchymal transition (EMT) process, tumor areas of patients with HCC were analyzed by immunostaining. Our data demonstrated the induction of EMT process in HCC cells with low proliferation under hypoxic conditions. To validate our finding, among HCC cell lines, HepG2 cells with highly increased expression of HIF1α under hypoxia were employed in vitro and in vivo. Major changes in EMT-associated protein expression, such as the up-regulation of N-cadherin and snail/slug are associated with decreased proliferation-related protein (PCNA) caused by glucose deprivation under hypoxia. Indeed, PCNA knockdown-HepG2 cells under hypoxia showed the induction of more EMT process compare to the control. Thus, HCC cells with low proliferative potential under glucose-deprived and hypoxic conditions show high probability for induced EMT process and promote cell invasion. This study investigates reasons as to why an EMT process cannot fully be predicted. Our observations indicate that rather than analyzing a single factor, an integrated analysis of hypoxia with low glucose metabolism and low cell proliferation might be helpful to predict the potential impact on induction of EMT process and promotion of cell invasion.