Pharmacological Vitamin C-induced high H2O2 generation mediates apoptotic cell death by caspase 3/7 activation in breast cancer tumor spheroids

BACKGROUND: Pharmacological vitamin C (Vit-C), or high-dose Vit-C has recently gained attention as a potential cancer therapeutic. However, the anticancer activity of Vit-C has not been investigated in realistic 3D models of human cancers, especially with respect to breast cancer (BC), and its potential benefits remain under debate. Herein, we investigate the activity and mechanism of action of pharmacological Vit-C on two BC tumor spheroids.

METHODS: We developed two distinct types of BC tumor spheroids from MDA-MB-231 and MCF-7 cells. The spheroids underwent treatment with a range of concentrations of pharmacological Vit-C (1, 5, 10, 15, and 20 mM). Assessments were conducted to determine the cell viability, H2O2 levels, glutathione-to-glutathione disulfide (GSH/GSSG) ratios, and apoptosis. Both flow cytometry analyses of Annexin V/PI staining and caspase3/7 activity assay were used to check apoptosis.

RESULTS: We showed that Vit-C induced dose-dependent cell death in both types of tumor spheroids, primarily driven by elevated H2O2 production and a concomitant oxidative stress imbalance induced by the GSH depletion. The high levels of H2O2 generated by Vit-C triggered the apoptosis of spheroids. In MCF-7 spheroids, Vit-C-induced H2O2 production was higher, with a more pronounced decrease in the GSH/GSSG ratio, indicating greater susceptibility to oxidative stress-induced cell death. However, MDA-MB-231 spheroids exhibited a more severe cytotoxic response.

CONCLUSIONS: This study reveals that Vit-C induces oxidative stress-mediated cell death in both non-aggressive and aggressive BC spheroids. Unlike traditional in vitro studies, this work provides novel insights into the response of two BC tumor subtypes to Vit-C, demonstrating its potential as a targeted common therapy for BC.