High-Throughput Assay Development for Cystine-Glutamate Antiporter (xc-) Highlights Faster Cystine Uptake than Glutamate Release in Glioma Cells

Ajit G. Thomas, Brain Science Institute, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, United States of America.
Rita Sattler, Brain Science Institute, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, United States of America; Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, United States of America.
Karen Tendyke, Next Generation Systems CFU, Eisai Inc., Andover, MA, 01810, United States of America.
Kara A. Loiacono, Next Generation Systems CFU, Eisai Inc., Andover, MA, 01810, United States of America.
Hans Hansen, Next Generation Systems CFU, Eisai Inc., Andover, MA, 01810, United States of America.
Vishal Sahni, Neuroscience and General Medicine PCU, Eisai Inc., Andover, MA, 01810, United States of America.
Yutaka Hashizume, Neuroscience and General Medicine PCU, Eisai Inc., Andover, MA, 01810, United States of America.
Camilo Rojas, Brain Science Institute, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, United States of America; Department of Comparative Medicine and Molecular Pathobiology, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, United States of America.
Barbara S. Slusher, Brain Science Institute, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, United States of America; Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, United States of America; Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, United States of America; Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, United States of America.

Document Type

Article

Abstract

The cystine-glutamate antiporter (system xc-) is a Na+-independent amino acid transporter that exchanges extracellular cystine for intracellular glutamate. It is thought to play a critical role in cellular redox processes through regulation of intracellular glutathione synthesis via cystine uptake. In gliomas, system xc- expression is universally up-regulated while that of glutamate transporters down-regulated, leading to a progressive accumulation of extracellular glutamate and excitotoxic cell death of the surrounding non-tumorous tissue. Additionally, up-regulation of system xc- in activated microglia has been implicated in the pathogenesis of several neurodegenerative disorders mediated by excess glutamate. Consequently, system xc- is a new drug target for brain cancer and neuroinflammatory diseases associated with excess extracellular glutamate. Unfortunately no potent and selective small molecule system xc- inhibitors exist and to our knowledge, no high throughput screening (HTS) assay has been developed to identify new scaffolds for inhibitor design. To develop such an assay, various neuronal and non-neuronal human cells were evaluated as sources of system xc-. Human glioma cells were chosen based on their high system xc- activity. Using these cells, [14C]-cystine uptake and cystine-induced glutamate release assays were characterized and optimized with respect to cystine and protein concentrations and time of incubation. A pilot screen of the LOPAC/NINDS libraries using glutamate release demonstrated that the logistics of the assay were in place but unfortunately, did not yield meaningful pharmacophores. A larger, HTS campaign using the 384-well cystine-induced glutamate release as primary assay and the 96-well 14C-cystine uptake as confirmatory assay is currently underway. Unexpectedly, we observed that the rate of cystine uptake was significantly faster than the rate of glutamate release in human glioma cells. This was in contrast to the same rates of cystine uptake and glutamate release previously reported in normal human fibroblast cells.

Medical Subject Headings

Amino Acid Transport System y+ (genetics, metabolism); Benzoates (pharmacology); Brain Neoplasms (genetics, metabolism); Cell Line, Tumor; Cystine (metabolism, pharmacology); Databases, Chemical; Gene Expression Regulation, Neoplastic (drug effects); Glioma (genetics, metabolism); Glutamic Acid (metabolism); Glycine (analogs & derivatives, pharmacology); High-Throughput Screening Assays (methods); Humans; Inhibitory Concentration 50; Models, Biological; RNA, Messenger (genetics, metabolism); Sulfasalazine (pharmacology); Time Factors

Publication Date

1-1-2015

Publication Title

PloS one

E-ISSN

1932-6203

Volume

10

Issue

8

First Page

e0127785

PubMed ID

26252954

Digital Object Identifier (DOI)

10.1371/journal.pone.0127785

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