Shiga toxins from enterohemorrhagic Escherichia coli and anti-GB3 antibody as novel agents against triple negative breast cancer

Abstract

Shiga toxins (Stx) are potent bacterial exotoxins and the main virulence factor of enterohemorrhagic Escherichia coli. Stx have ribotoxic activity in eukaryotic target cells of the mammalian host by recognizing its globotriaosylceramide receptor (Gb3), which results in rapid protein synthesis inhibition and cell death. Our aim was to study the potential of Stx1, Stx2, and an anti-Gb3 antibody as novel cytotoxic agents against triple negative breast cancer (TNBC) cells. The expression of Gb3 and Stx uptake was analyzed by immunofluorescence (IF) in TNBC MDA-MB-231 and non-tumorigenic mammary epithelial cells NMuMG, using VERO cells as a positive control. Results showed that MDA-MB-231 tumor cells express the Gb3 receptor as much as VERO cells. In addition, MDA-MB-231 ‒but not mammary epithelial cells NMuMG‒ can incorporate Stx2. Cell viability was evaluated through MTT assays, finding that MDA-MB-231 cell viability was reduced by Stx1, Stx2, and anti-Gb3 treatments, while NMuMG cell viability remained unaltered. Both Stx1 and Stx2 reduced proliferation and migration in MDA-MB-231 cells, assessed through BrdU incorporation and the wound healing assay, respectively. The expression levels of LC3 as an autophagy marker increased with Stx1, Stx2, and anti-Gb3 treatments. In all assays, the presence of PPMP, an inhibitor that reduces Gb3 synthesis, blocked the effects produced by Stx. Finally, Stx treatment increased total and nuclear TAR-DNA-binding protein-43 protein expression. These findings suggest that Stx1 and Stx2 are potential new therapeutic agents in TNBC.