Enhancement of Radiation Response in Breast Cancer Stem Cells by Inhibition of Thioredoxin- and Glutathione-Dependent Metabolism

Abstract

The current study determined if depletion of glutathione (GSH) and inhibition of thioredoxin reductase (TR) activity could enhance radiation responses in human breast cancer stem cells by a mechanism involving thiol dependent oxidative stress. Buthionine sulfoximine (BSO), a GSH synthesis inhibitor; sulfasalazine (SSZ), an inhibitor of xc- cysteine/glutamate antiporter; auranofin (Au), a thioredoxin reductase inhibitor; or 2AAPA, a GSH-reductase inhibitor, were used to inhibit GSH- and thioredoxin (Trx)-metabolism. Clonogenic survival, Matrigel assays, flow cytometry cancer stem cell assays (CD44+CD24-ESA+ or ALDH1), and human tumor xenograft models were used to determine the antitumor activity of drug and radiation combinations. Combined inhibition of GSH and Trx-metabolism enhanced cancer cell clonogenic killing and radiation responses in human breast and pancreatic cancer cells via a mechanism that could be inhibited by N-acetylcysteine (NAC). Au, BSO, and radiation also significantly decreased breast cancer cell migration and invasion in a thiol dependent fashion that could be inhibited by NAC. In addition pre-treating cells with Au sensitized breast cancer stem cell populations to radiation in vitro as determined by CD44+CD24-ESA+ or ALDH1. Combined administration of Au and BSO, given prior to radiation significantly increased the survival of mice with human breast cancer xenografts as well as decreasing the number of ALDH1 positive cancer stem cells. These results indicate that combined inhibition of GSH- and Trx-dependent thiol metabolism using pharmacologically relevant agents can enhance responses of human breast cancer stem cells to radiation both in vitro and in vivo.

Auranofin radiosensitizes tumor cells through targeting thioredoxin reductase and resulting overproduction of reactive oxygen species

“…The combination AF plus BSO showed a preferential radiosensitizing effect in hypoxic tumor cells, which featured an impaired radioresponse in the TMCS, our model of metabolic hypoxia. In mice, their simultaneous administration enhanced radioresponse in EMT6 and 4T1 mammary carcinomas, in line with a very recent report in a MDA-MB-231 breast cancer model [20]. We concluded that the combination of AF and BSO could be a promising radiosensitizing strategy justified in view of them being ready-to-use pharmaceuticals for clinical evaluation.…”

“…Along with improved radiation responses, AF sensitized breast cancer stem cells, and in combination with BSO decreased cell migration and invasion [20]. Of note, inhibition of TrxR by curcumin and 1, 2, 5-selenadiazole showed a comparable array of antitumor effects including radiosensitization [32, 45–47], while the disruption of GSH pathways by genistein and gadolinium (III) texaphyrin resulted in ROS-mediated radiosensitization [48, 49].…”

TRIAP1 knockdown sensitizes non‐small cell lung cancer to ionizing radiation by disrupting redox homeostasis

“…TXN1 overexpression in NSCLC is indicative of a more aggressive tumor phenotype, which in turn is associated with bad prognostic features and a poorer outcome . Inhibiting the expression and function of TXN1 has been shown to increase the radiosensitivity of various cancer types …”

D-penicillamine combined with inhibitors of hydroperoxide metabolism enhances lung and breast cancer cell responses to radiation and carboplatin via H 2 O 2 -mediated oxidative stress

“…One such difference is alterations in oxidative metabolism that have been noted in cancer versus normal cells [4, 31, 32] as well as cancer stem cells [33]. We have recently published data demonstrating that disruption of redox balance radiosensitizes breast cancer stem cells [34]. Cancer cells appear to demonstrate both increased steady state levels of ROS (O 2 •- and H 2 O 2 ) and abnormal metabolism of transition metals when compared to normal cells [4, 35].…”