Artesunate, an anti-malarial drug, has been repurposed as an anticancer drug due to its induction of cell death via reactive oxygen species (ROS) production. However, the molecular mechanisms regulating cancer cell death and the resistance of cells to artesunate remain unclear. We investigated the molecular mechanisms behind the antitumor effects of artesunate and an approach to overcome artesunate resistance in head and neck cancer (HNC). The effects of artesunate and trigonelline were tested in different HNC cell lines, including three cisplatin-resistant HNC cell lines. The effects of these drugs as well as the inhibition of Keap1, Nrf2, and HO-1 were assessed by cell viability, cell death, glutathione (GSH) and ROS production, protein expression, and mouse tumor xenograft models. Artesunate selectively killed HNC cells but not normal cells. The artesunate sensitivity was relatively low in cisplatin-resistant HNC cells. Artesunate induced ferroptosis in HNC cells by decreasing cellular GSH levels and increasing lipid ROS levels. This effect was blocked by co-incubation with ferrostatin-1 and a trolox pretreatment. Artesunate activated the Nrf2-antioxidant response element (ARE) pathway in HNC cells, which contributed to ferroptosis resistance. The silencing of Keap1, a negative regulator of Nrf2, decreased artesunate sensitivity in HNC cells. Nrf2 genetic silencing or trigonelline reversed the ferroptosis resistance of Keap1-silenced and cisplatin-resistant HNC cells to artesunate in vitro and in vivo. Nrf2-ARE pathway activation contributes to the artesunate resistance of HNC cells, and inhibition of this pathway abolishes ferroptosis-resistant HNC. Our results show the effectiveness and molecular mechanism of artesunate treatment on head and neck cancer (HNC). Artesunate selectively killed HNC cells but not normal cells by inducing an iron-dependent, ROS-accumulated ferroptosis. However, this effect may be suboptimal in some cisplatin-resistant HNCs because of Nrf2-antioxidant response element (ARE) pathway activation. Inhibition of the Nrf2-ARE pathway increased artesunate sensitivity and reversed the ferroptosis resistance in resistant HNC cells.

SLC7A11 is a cell transmembrane protein composing the light chain of system xc⁻, transporting extracellular cystine into cells for cysteine production and GSH biosynthesis. SLC7A11 is a critical gateway for redox homeostasis by maintaining the cellular levels of GSH that counter cellular oxidative stress and suppress ferroptosis. SLC7A11 is overexpressed in various human cancers and regulates tumor development, proliferation, metastasis, microenvironment, and treatment resistance. Upregulation of SLC7A11 in cancers is needed to adapt to high oxidative stress microenvironments and maintain cellular redox homeostasis. High basal ROS levels and SLC7A11 dependences in cancer cells render them vulnerable to further oxidative stress. Therefore, cyst(e)ine depletion may be an effective new strategy for cancer treatment. However, the effectiveness of the SLC7A11 inhibitors or cyst(e)inase has been established in many preclinical studies but has not reached the stage of clinical trials for cancer patients. A better understanding of cysteine and SLC7A11 functions regulating and interacting with redox-active proteins and their substrates could be a promising strategy for cancer treatment. Therefore, this review intends to understand the role of cysteine in antioxidant and redox signaling, the regulators of cysteine bioavailability in cancer, the role of SLC7A11 linking cysteine redox signaling in cancer metabolism and targeting SLC7A11 for novel cancer therapeutics.

Ferroptosis is a newly defined form of cell death induced by iron-dependent accumulation of lethal lipid peroxidation. Ferroptosis represent a therapeutic strategy to suppress therapy-resistant cancer cells with more property of epithelial-mesenchymal transition (EMT). However, epigenetic reprogramming of EMT has been rarely studied in the context of ferroptosis susceptibility. Therefore, we examined the therapeutic potentiality of EMT epigenetic reprogramming in promoting ferroptosis in head and neck cancer (HNC) cells. The effects of ferroptosis inducers and EMT inhibition or induction were tested in HNC cell lines and mouse tumor xenograft models. These effects were analyzed concerning cell viability and death, lipid reactive oxygen species and iron production, labile iron pool, glutathione contents, NAD/NADH levels, and mRNA/protein expression. Cell density and the expression levels of E-cadherin, vimentin, and ZEB1 were associated with the different susceptibility to ferroptosis inducers. CDH1 silencing or ZEB1 overexpression increased the susceptibility to ferroptosis, whereas CDH overexpression or ZEB1 silencing decreased the susceptibility, in vitro and in vivo. Histone deacetylase SIRT1 gene silencing or pharmacological inhibition by EX-527 suppressed EMT and consequently decreased ferroptosis, whereas SIRT inducers, resveratrol and SRT1720, increased ferroptosis. MiR-200 family inhibitors induced EMT and increased ferroptosis susceptibility. In HNC cells with low expression of E-cadherin, the treatment of 5-azacitidine diminished the hypermethylation of CDH1, resulting in increased E-cadherin expression and decreased ferroptosis susceptibility. Our data suggest that epigenetic reprogramming of EMT contributes to promoting ferroptosis in HNC cells.