There has been much interest in targeting intracellular redox pathways as a therapeutic approach for
cancer. Given recent data to suggest that the redox status of extracellular
protein thiol groups (i.e. exofacial
thiols) effects cell behavior, we hypothesized that redox active anti-
cancer agents would modulate exofacial
protein thiols.
METHODOLOGY/PRINCIPAL FINDINGS: To test this hypothesis, we used the
sesquiterpene lactone parthenolide, a known anti-
cancer agent. Using flow cytometry, and western blotting to label free
thiols with Alexa Fluor 633 C(5)
maleimide dye and N-(biotinoyl)-N-(iodoacetyl) ethylendiamine (BIAM), respectively, we show that
parthenolide decreases the level of free exofacial
thiols on Granta mantle
lymphoma cells. In addition, we used immuno-precipitation techniques to identify the central redox regulator
thioredoxin, as one of the
surface protein thiol targets modified by
parthenolide. To examine the functional role of
parthenolide induced
surface protein thiol modification, we pretreated Granta cells with cell impermeable
glutathione (GSH), prior to exposure to
parthenolide, and showed that GSH pretreatment; (a) inhibited the interaction of
parthenolide with exofacial
thiols; (b) inhibited
parthenolide mediated activation of JNK and inhibition of NFkappaB, two well established mechanisms of
parthenolide activity and; (c) blocked the cytotoxic activity of
parthenolide. That GSH had no effect on the
parthenolide induced generation of intracellular
reactive oxygen species supports the fact that GSH had no effect on intracellular redox. Together these data support the likelihood that GSH inhibits the effect of
parthenolide on JNK, NFkappaB and cell death through its direct inhibition of
parthenolide's modulation of exofacial
thiols.
CONCLUSIONS/SIGNIFICANCE: Based on these data, we postulate that one component of
parthenolide's anti-
lymphoma activity derives from its ability to modify the redox state of critical exofacial
thiols. Further, we propose that
cancer cell exofacial
thiols may be important and novel targets for
therapy.