Sulfasalazine inhibits the growth of primary brain tumors independent of nuclear factor‐κB

Abstract

Nuclear factor‐κB (NF‐κB) is a pleiotropic transcription factor that generally enhances cellular resistance to apoptotic cell death. It has been shown to be constitutively active in some cancers and is being pursued as potential anticancer target. Sulfasalazine which is used clinically to treat Crohn’s disease has emerged as a potential inhibitor of NF‐κB and has shown promising results in two pre‐clinical studies to target primary brain tumors, gliomas. Once digested, sulfasalazine is cleaved into sulfapyridine and 5‐aminosalicylic acid (5‐ASA; mesalamine) by colonic bacteria, and the latter, too, is reported to suppress NF‐κB activity. We now show that glioma cells obtained from patient biopsies or glioma cell lines do not show significant constitutive NF‐κB activation, unless exposed to inflammatory cytokines. This does not change when gliomas are implanted into the cerebrum of severe combined immundeficient mice. Nevertheless, sulfasalazine but not its cleaved form 5‐ASA caused a dose‐dependent inhibition of glioma growth. This effect was entirely attributable to the inhibition of cystine uptake via the system xc− cystine–glutamate transporter. It could be mimicked by S‐4‐carboxy‐phenylglycine (S‐4‐CPG) a more specific system xc− inhibitor, and lentiviral expression of a constitutively active form of IκB kinase b was unable to overcome the growth retarding effects of sulfasalazine or S‐4‐CPG. Both drugs inhibited cystine uptake causing a chronic depletion of intracellular GSH and consequently compromised cellular redox defense which stymied tumor growth. This data suggests that system xc− is a promising therapeutic target in gliomas and possibly other cancers and that it can be pharmacologically inhibited by Sulfasalazine, an FDA‐approved drug.

Dissection of mitogenic and neurodegenerative actions of cystine and glutamate in malignant gliomas

“…As to potential glioma therapy, system X c À emerges as a promising target (Chung et al, 2005;Savaskan et al, 2008;Chung and Sontheimer, 2009;Pham et al, 2010). Both components of system X c À (xCT and CD98) have shown to be transcriptionally upregulated in glioma specimens and interference with system X c À may disrupt two major pathophysiological properties of glioma cells: (1) the ability to induce neurodegeneration and (2) the ability to incorporate high levels of cystine required for rapid proliferation.…”

“…Both components of system X c À (xCT and CD98) have shown to be transcriptionally upregulated in glioma specimens and interference with system X c À may disrupt two major pathophysiological properties of glioma cells: (1) the ability to induce neurodegeneration and (2) the ability to incorporate high levels of cystine required for rapid proliferation. Although glioma cells appear to be highly dependent on system X c À -mediated cystine incorporation required for glutathione production and thus the scavenging of reactive oxygen species (Chung et al, 2005;Chung and Sontheimer, 2009;Pham et al, 2010), normal cells might be less vulnerable. This notion is supported by genetic deletion studies, that is, xCT-deficient mice are healthy in appearance and fertile (Sato et al, 2005;Shih et al, 2006;Liu et al, 2007).…”

Glutathione depletion causes a JNK and p38MAPK-mediated increase in expression of cystathionine-γ-lyase and upregulation of the transsulfuration pathway in C6 glioma cells

“…The requirement for cysteine is furnished via the x c -exchanger, which, as recorded in the case of gliomas, releases glutamate that damages surrounding neurones, thus providing space for tumour growth (Sontheimer, 2008). Consequently, blockade of the exchanger is viewed as a potential target for cancer therapy (Lo et al, 2008;Savaskan et al, 2008;Chung and Sontheimer, 2009) and has proven successful in experimental models as a means of limiting glutamate release. However, other recent evidence indicates that methionine uptake in gliomas is high and correlates positively with tumour viability (Kato et al, 2008), thus questioning the potential effectiveness of blockade of the x c -exchanger as a means of limiting GSH synthesis and tumour cell survival.…”

The transsulfuration pathway: a source of cysteine for glutathione in astrocytes

“…The requirement for cysteine is furnished via the x c -exchanger, which, as recorded in the case of gliomas, releases glutamate that damages surrounding neurones, thus providing space for tumour growth (Sontheimer, 2008). Consequently, blockade of the exchanger is viewed as a potential target for cancer therapy (Chung and Sontheimer, 2009;Lo et al, 2008;Savaskan et al, 2008) and has proven successful in experimental models as a means of limiting glutamate release. However, other evidence indicates that methionine uptake in gliomas is high and correlates positively with tumour viability (Kato et al, 2008), which may indicate a greater dependence on transsulfuration in these cells than in normal astrocytes.…”