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      Dendrimer-conjugated glutaminase inhibitor selectively targets microglial glutaminase in a mouse model of Rett syndrome

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          Abstract

          Background: Elevated glutamate production and release from glial cells is a common feature of many CNS disorders. Inhibitors of glutaminase (GLS), the enzyme responsible for converting glutamine to glutamate have been developed to target glutamate overproduction. However, many GLS inhibitors have poor aqueous solubility, are unable to cross the blood brain barrier, or demonstrate significant toxicity when given systemically, precluding translation. Enhanced aqueous solubility and systemic therapy targeted to activated glia may address this challenge. Here we examine the impact of microglial-targeted GLS inhibition in a mouse model of Rett syndrome (RTT), a developmental disorder with no viable therapies, manifesting profound central nervous system effects, in which elevated glutamatergic tone, upregulation of microglial GLS, oxidative stress and neuroimmune dysregulation are key features.

          Methods: To enable this, we conjugated a potent glutaminase inhibitor, N-(5-{2-[2-(5-amino-[1,3,4]thiadiazol-2-yl)-ethylsulfanyl]-ethyl}-[1,3,4]thiadiazol-2-yl)-2-phenyl-acetamide (JHU29) to a generation 4 hydroxyl PAMAM dendrimer (D-JHU29). We then examined the effect of D-JHU29 in organotypic slice culture on glutamate release. We also examined GLS activity in microglial and non-microglial cells, and neurobehavioral phenotype after systemic administration of D-JHU29 in a mouse model of RTT.

          Results: We report successful conjugation of JHU29 to dendrimer resulting in enhanced water solubility compared to free JHU29. D-JHU29 reduced the excessive glutamate release observed in tissue culture slices in a clinically relevant Mecp2-knockout (KO) RTT mouse. Microglia isolated from Mecp2-KO mice demonstrated upregulation of GLS activity that normalized to wild-type levels following systemic treatment with D-JHU29. Neurobehavioral assessments in D-JHU29 treated Mecp2-KO mice revealed selective improvements in mobility.

          Conclusion: These findings demonstrate that glutaminase inhibitors conjugated to dendrimers are a viable mechanism to selectively inhibit microglial GLS to reduce glutamate production and improve mobility in a mouse model of RTT, with broader implications for selectively targeting this pathway in other neurodegenerative disorders.

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          Antitumor activity of the glutaminase inhibitor CB-839 in triple-negative breast cancer.

          Glutamine serves as an important source of energy and building blocks for many tumor cells. The first step in glutamine utilization is its conversion to glutamate by the mitochondrial enzyme glutaminase. CB-839 is a potent, selective, and orally bioavailable inhibitor of both splice variants of glutaminase (KGA and GAC). CB-839 had antiproliferative activity in a triple-negative breast cancer (TNBC) cell line, HCC-1806, that was associated with a marked decrease in glutamine consumption, glutamate production, oxygen consumption, and the steady-state levels of glutathione and several tricarboxylic acid cycle intermediates. In contrast, no antiproliferative activity was observed in an estrogen receptor-positive cell line, T47D, and only modest effects on glutamine consumption and downstream metabolites were observed. Across a panel of breast cancer cell lines, GAC protein expression and glutaminase activity were elevated in the majority of TNBC cell lines relative to receptor positive cells. Furthermore, the TNBC subtype displayed the greatest sensitivity to CB-839 treatment and this sensitivity was correlated with (i) dependence on extracellular glutamine for growth, (ii) intracellular glutamate and glutamine levels, and (iii) GAC (but not KGA) expression, a potential biomarker for sensitivity. CB-839 displayed significant antitumor activity in two xenograft models: as a single agent in a patient-derived TNBC model and in a basal like HER2(+) cell line model, JIMT-1, both as a single agent and in combination with paclitaxel. Together, these data provide a strong rationale for the clinical investigation of CB-839 as a targeted therapeutic in patients with TNBC and other glutamine-dependent tumors.
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            Tumor Necrosis Factor Alpha: A Link between Neuroinflammation and Excitotoxicity

            Tumor necrosis factor alpha (TNF- α ) is a proinflammatory cytokine that exerts both homeostatic and pathophysiological roles in the central nervous system. In pathological conditions, microglia release large amounts of TNF- α ; this de novo production of TNF- α is an important component of the so-called neuroinflammatory response that is associated with several neurological disorders. In addition, TNF- α can potentiate glutamate-mediated cytotoxicity by two complementary mechanisms: indirectly, by inhibiting glutamate transport on astrocytes, and directly, by rapidly triggering the surface expression of Ca+2 permeable-AMPA receptors and NMDA receptors, while decreasing inhibitory GABAA receptors on neurons. Thus, the net effect of TNF- α is to alter the balance of excitation and inhibition resulting in a higher synaptic excitatory/inhibitory ratio. This review summarizes the current knowledge of the cellular and molecular mechanisms by which TNF- α links the neuroinflammatory and excitotoxic processes that occur in several neurodegenerative diseases, but with a special emphasis on amyotrophic lateral sclerosis (ALS). As microglial activation and upregulation of TNF- α expression is a common feature of several CNS diseases, as well as chronic opioid exposure and neuropathic pain, modulating TNF- α signaling may represent a valuable target for intervention.
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              Targeted inhibition of tumor-specific glutaminase diminishes cell-autonomous tumorigenesis.

              Glutaminase (GLS), which converts glutamine to glutamate, plays a key role in cancer cell metabolism, growth, and proliferation. GLS is being explored as a cancer therapeutic target, but whether GLS inhibitors affect cancer cell-autonomous growth or the host microenvironment or have off-target effects is unknown. Here, we report that loss of one copy of Gls blunted tumor progression in an immune-competent MYC-mediated mouse model of hepatocellular carcinoma. Compared with results in untreated animals with MYC-induced hepatocellular carcinoma, administration of the GLS-specific inhibitor bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES) prolonged survival without any apparent toxicities. BPTES also inhibited growth of a MYC-dependent human B cell lymphoma cell line (P493) by blocking DNA replication, leading to cell death and fragmentation. In mice harboring P493 tumor xenografts, BPTES treatment inhibited tumor cell growth; however, P493 xenografts expressing a BPTES-resistant GLS mutant (GLS-K325A) or overexpressing GLS were not affected by BPTES treatment. Moreover, a customized Vivo-Morpholino that targets human GLS mRNA markedly inhibited P493 xenograft growth without affecting mouse Gls expression. Conversely, a Vivo-Morpholino directed at mouse Gls had no antitumor activity in vivo. Collectively, our studies demonstrate that GLS is required for tumorigenesis and support small molecule and genetic inhibition of GLS as potential approaches for targeting the tumor cell-autonomous dependence on GLS for cancer therapy.
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                Author and article information

                Journal
                Theranostics
                Theranostics
                thno
                Theranostics
                Ivyspring International Publisher (Sydney )
                1838-7640
                2020
                27 April 2020
                : 10
                : 13
                : 5736-5748
                Affiliations
                [1 ]Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore MD, 21205
                [2 ]Center for Nanomedicine, Department of Ophthalmology, Wilmer Eye Institute Johns Hopkins University School of Medicine, Baltimore MD, 21231
                [3 ]Johns Hopkins Drug Discovery, Johns Hopkins University School of Medicine, Baltimore MD, 21205
                [4 ]Department of Neurology, Johns Hopkins University School of Medicine, Baltimore MD, 21205
                [5 ]Hugo W. Moser Research Institute at Kennedy Krieger Inc., Baltimore MD, 21205
                [6 ]Kennedy Krieger Institute - Johns Hopkins University for Cerebral Palsy Research Excellence, Baltimore, MD 21287
                [7 ]Departments of Chemical and Biomolecular Engineering, and Materials Science and Engineering, Johns Hopkins University, Baltimore MD, 21218
                Author notes
                ✉ Corresponding authors: Rangaramanujam M. Kannan, Professor of Ophthalmology, Center for Nanomedicine at the Wilmer Eye Institute, 400 North Broadway, Baltimore, Maryland 21231, USA. Tel.: +1 443-287-8634; Fax: +1 443-287-8635; e-mail: krangar1@ 123456jhmi.edu . Sujatha Kannan, MD. Mailing address: Department of Anesthesiology and Critical Care Medicine, Charlotte Bloomberg Children's Center 6318D, 1800 Orleans Street Baltimore, MD, 21287. Tel: 410- 955-6412; E-mail: skannan3@ 123456jhmi.edu

                Competing Interests: RMK and SK are co-founders and have a financial interest in Ashvattha Therapeutics LLC, Orpheris Inc., and RiniSight; three start-ups translating dendrimer drug delivery platform. The conflict of interest is managed by the Johns Hopkins University.

                Article
                thnov10p5736
                10.7150/thno.41714
                7254984
                32483415
                0829f68f-581d-49bc-9fb3-5d3f63ab3713
                © The author(s)

                This is an open access article distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/4.0/). See http://ivyspring.com/terms for full terms and conditions.

                History
                : 1 November 2019
                : 14 April 2020
                Categories
                Research Paper

                Molecular medicine
                pamam dendrimer,microglia,glutaminase,rett syndrome
                Molecular medicine
                pamam dendrimer, microglia, glutaminase, rett syndrome

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