Abstract
The xc− cystine/glutamate antiporter has been implicated in GSH-based chemoresistance because it mediates cellular uptake of cystine/cysteine for sustenance of intracellular GSH levels. Celastrol, isolated from a Chinese medicinal herb, is a novel heat shock protein 90 (Hsp90) inhibitor with potent anticancer activity against glioma in vitro and in vivo. In search of correlations between growth-inhibitory potency of celastrol in NCI-60 cell lines and microarray expression profiles of most known transporters, we found that expression of SLC7A11, the gene encoding the light chain subunit of xc−, showed a strong negative correlation with celastrol activity. This novel gene-drug correlation was validated. In celastrol-resistant glioma cells that highly expressed SLC7A11, sensitivity to celastrol was consistently increased via treatment with xc− inhibitors, including glutamate, (S)-4-carboxyphenylglycine, sulfasalazine, and SLC7A11 small interfering RNA. The GSH synthesis inhibitor, buthionine sulfoximine, also increased celastrol sensitivity, whereas the GSH booster, N-acetylcysteine, suppressed its cytotoxicity. Furthermore, the glioma cell lines were dependent on xc−-mediated cystine uptake for viability, because cystine omission from the culture medium resulted in cell death and treatment with sulfasalazine depleted GSH levels and inhibited their growth. Combined treatment of glioma cells with sulfasalazine and celastrol led to chemosensitization, as suggested by increased celastrol-induced cell cycle arrest, apoptosis, and down-regulation of the Hsp90 client protein, epidermal growth factor receptor. These results indicate that the xc− transporter provides a useful target for glioma therapy. xc− inhibitors such as sulfasalazine, a Food and Drug Administration-approved drug, may be effective both as an anticancer drug and as an agent for sensitizing gliomas to celastrol.
Footnotes
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.109.162248.
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ABBREVIATIONS:
- EGFR
- epidermal growth factor receptor
- Hsp90
- heat shock protein 90
- NF-κB
- nuclear factor κB
- GA
- geldanamycin
- DTP
- Developmental Therapeutics Program
- NCI
- National Cancer Institute
- SRB
- sulforhodamine B
- 4-S-CPG
- (S)-4-carboxyphenylglycine
- SASP
- sulfasalazine
- MTS
- 3-(4,5-dimethylthiazol-2-yl)-5-(3 carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium
- BSO
- buthionine sulfoximine
- NAC
- N-acetylcysteine
- siRNA
- small interfering RNA
- RT-PCR
- reverse transcription-polymerase chain reaction
- PI
- propidium iodide
- FACS
- fluorescence-activated cell-sorting analysis
- MDR1
- multidrug resistance 1
- MRP1
- multidrug resistance protein 1
- SASP
- salicylazosulfapyridine
- β-ME
- β-mercaptoethanol
- CI
- combination index
- NSC 270057
- hydroxypristimerin
- NSC 684506
- 22-hydroxytingenone.
- Received October 1, 2009.
- Accepted December 8, 2009.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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