Oridonin induces ferroptosis by inhibiting gamma‐glutamyl cycle in TE1 cells

Abstract

Oridonin (Ori) is a natural tetracyclic diterpenoid active compound with excellent antitumor activity, but the mechanism of Ori on esophageal cancer cell, TE1, remains unclear. In this study, we examined the levels of intracellular iron, malondialdehyde, and reactive oxygen species after Ori treatment, while interfering with the effects of Ori with ferroptosis inhibitor, demonstrating that Ori's inhibition of TE1 cell proliferation is associated with ferroptosis. To understand the molecular mechanism of Ori, we performed UPLC–MS/MS metabolomics profiling on TE1 cells, which show that gamma‐glutamyl amino acids (gamma‐glutamylleucine, gamma‐glutamylvaline), 5‐oxoproline, glutamate, GSH, and GSSG are changed significantly after Ori treatment. Meanwhile, the activity of gamma‐glutamyl transpeptidase 1 (GGT1) decreased. This revealed that Ori inhibited the gamma‐glutamyl cycle in TE1 cells. Furthermore, we found that Ori can covalently bind to cysteine to form the conjugate oridonin‐cysteine (Ori‐Cys), resulting in the inhibition of glutathione synthesis, which is consistent with the decrease in the enzymatic activity of glutamate cysteine ligase catalytic subunit (GCLC). Eventually, the value of intracellular GSH/GSSG was reduced, and the enzymatic activity of the glutathione peroxidase 4 (GPX4) was significantly decreased. In conclusion, our experiments indicated that Ori can inhibit the gamma‐glutamyl cycle, thereby inducing ferroptosis to exert anti‐cancer activity.

Understanding the role of cysteine in ferroptosis: progress & paradoxes

“…To obtain this cysteine, GSH must be catabolized. GSH export and extracellular catabolism via the gamma-glutamyl cycle does contribute to intracellular cysteine pools [72], and disruption of the key enzyme gamma-glutamyl transpeptidase 1 (GGT1) may be sufficient to induce ferroptosis [73]. However, this is likely to be only useful in the short-term.…”

Cysteine as a Multifaceted Player in Kidney, the Cysteine-Related Thiolome and Its Implications for Precision Medicine

“…Under such conditions, GPX4 might employ alternative reducing molecules, like cysteine and its metabolite CoA [165,175]. Glutathione catabolism [176], compared to the RTP [177], may be a more efficient alternative source of cysteine to avoid ferroptosis, at least in short-term cysteine deprivation. The CoAdependent post-translational modification, named CoAlation [178], of glycolytic enzymes may boost NADPH synthesis via the PPP, affording protection from ferroptosis [179].…”

Medicinal Plants for the Treatment of Gastrointestinal Cancers From the Metabolomics Perspective

“…To investigate the underlying mechanism, a UPLC-MS/MS-based metabolomics analysis of TE1 cells was conducted. It was found that oridonin administration altered the levels of glutamate, 5-oxoproline, and gamma-glutamyl amino acids (gamma-glutamyl valine and gamma-glutamyl leucine), which could suppress the gamma-glutamyl cycle to induce ferroptosis to exert its anti-EC activity ( Zhang et al, 2021 ).…”