Suppression of a cancer stem-like phenotype mediated by alpha-lipoic acid in human lung cancer cells through down-regulation of β-catenin and Oct-4.

Abstract

Cancer stem cells (CSCs) that possess the ability of self-renewal and multi-potency have been shown to drive tumor progression and metastasis. The majority of recent studies has focused on potential molecules targeting CSCs so as to develop novel strategies for efficient cancer treatment or protection. Here, we show how alpha-lipoic acid (LA), an endogenous mitochondrial anti-oxidant, affects the CSC-like phenotypes of human non-small cell lung cancer-derived H23, H292 and H460 cells. CSC-like phenotypes were verified by anchorage-independent growth, three-dimensional (3D) spheroid formation and the expression of CSC markers. Enriched CSC populations were used to confirm the effects of LA. Protein ubiquitination and degradation were assessed using immunoprecipitation. We found that treatment with LA reduced the CSC-like phenotype, as indicated by a decreased expression of known CSC markers (CD133, CD44, ALDH1A1, Oct-4 and Nanog) in H460 cells. In addition, we found that LA reduced the CSC-related abilities of anchorage-independent growth and 3D spheroid formation, and suppressed factors related to epithelial-mesenchymal transition, such as E-cadherin, Vimentin, Slug and Snail. Mechanistically, we found that LA suppresses CSC through depletion of the cellular stemness proteins β-catenin and Oct-4 via decreasing the level of active (phosphorylated) Akt. This resulted in the induction of GSK3β-dependent β-catenin ubiquitin-proteasomal degradation and a decrease in the stabilized (phosphorylated) form of Oct-4. The effects of LA on the CSC-like phenotypes were confirmed in CSC enriched H460, H292 and H23non-small cell lung cancer-derived cells. Our data are indicative for a novel regulatory role and underlying mechanism of LA in the negative regulation of a CSC-like phenotype in non-small cell lung cancer-derived cells.