Thioredoxin reductase 1 knockdown enhances selenazolidine cytotoxicity in human lung cancer cells via mitochondrial dysfunction

Abstract

Thioredoxin reductase (TR1) is a selenoprotein that is involved in cellular redox status control and deoxyribonucleotide biosynthesis. Many cancers, including lung, overexpress TR1, making it a potential cancer therapy target. Previous work has shown that TR1 knockdown enhances the sensitivity of cancer cells to anticancer treatments, as well as certain selenocompounds. However, it is unknown if TR1 knockdown produces similar effect on the sensitivity of human lung cancer cells. To further elucidate the role of TR1 in the mechanism of selenocompounds in lung cancer, a lentiviral microRNA delivery system to knockdown TR1 expression in A549 human lung adenocarcinoma cells was utilized. Cell viability was assessed after 48 hr treatment with the selenocysteine prodrug selenazolidines 2-butylselenazolidine-4(R)-carboxylic acid (BSCA) and 2-cyclohexylselenazolidine-4-(R)-carboxylic acid (ChSCA), selenocystine (SECY), methylseleninic acid (MSA), 1,4-phenylenebis(methylene)selenocyanate (p-XSC), and selenomethionine (SEM). TR1 knockdown increased the cytotoxicity of BSCA, ChSCA, and SECY but did not sensitize cells to MSA, SEM, or p-XSC. GSH and TR1 depletion together decreased cell viability, while no change was observed with GSH depletion alone. Reactive oxygen species generation was induced only in TR1 knockdown cells treated with the selenazolidines or SECY. These three compounds also decreased total intracellular glutathione levels and oxidized thioredoxin, but in a TR1 independent manner. TR1 knockdown increased selenazolidine and SECY-induced mitochondrial membrane depolarization, as well as DNA strand breaks and AIF translocation from the mitochondria. These results indicate the ability of TR1 to modulate the cytotoxic effects of BSCA, ChSCA and SECY in human lung cancer cells through mitochondrial dysfunction.

Thioredoxin reductase 1 deficiency enhances selenite toxicity in cancer cells via a thioredoxin-independent mechanism

“…The latter selenium form may react with reduced glutathione to form GS-Se-SG that was proposed to be the major form of entry of selenocompounds into selenium metabolism [9, 53]. Furthermore, it was recently reported that other selenocompounds such as 2-butylselenazolidine-4(R)-carboxylic acid, 2-cyclohexylselenazolidine-4(R)-carboxylic acid and selenocystine were much more toxic to TR1-deficient cells [54], and BSO, which is known to inhibit GSH synthesis, has been shown to inhibit tumor growth in TR1 knockout mice and to cause cell death in TR1-deficient cultured cells [54, 55]. The involvement of Trx1, however, in these studies was not investigated.…”

Major differences among chemopreventive organoselenocompounds in the sustained elevation of cytoprotective genes

“…Glutathione concentrations were determined after 2 hr treatments using the GSH-Glo kit as previously described (27). Reduced glutathione was directly measured.…”

Selenium-Based Drug Design

“…Accordingly, Poerschke and Moos [73] extended the earlier work of Roberts by utilizing a lentiviral microRNA delivery system to knockdown thioredoxin reductase expression in human lung adenocarcinoma cells and then examining the cytotoxic activities of the selenazolidine prodrugs, 2-butylselenazolidine-4(R)-carboxylic acid and 2-cyclohexylselenazolidine-4-(R)carboxylic acid. They found that thioredoxin reductase knockdown increased the cytotoxicity of selenazolidines in these adenocarcinoma cells via a mechanism involving mitochondrial dysfunction and caspase-independent activation of the apoptosis-inducing factor.…”