Mechanisms of ferroptosis

Abstract

Ferroptosis is a non-apoptotic form of cell death that can be triggered by small molecules or conditions that inhibit glutathione biosynthesis or the glutathione-dependent antioxidant enzyme glutathione peroxidase 4 (GPX4). This lethal process is defined by the iron-dependent accumulation of lipid reactive oxygen species and depletion of plasma membrane polyunsaturated fatty acids. Cancer cells with high level RAS-RAF-MEK pathway activity or p53 expression may be sensitized to this process. Conversely, a number of small molecule inhibitors of ferroptosis have been identified, including ferrostatin-1 and liproxstatin-1, which can block pathological cell death events in brain, kidney and other tissues. Recent work has identified a number of genes required for ferroptosis, including those involved in lipid and amino acid metabolism. Outstanding questions include the relationship between ferroptosis and other forms of cell death, and whether activation or inhibition of ferroptosis can be exploited to achieve desirable therapeutic ends.

Keywords: Cancer; Cell death; Erastin; Ferrostatin-1; Glutathione; Glutathione peroxidase 4; Iron; Polyunsaturated fatty acid; RAS; Reactive oxygen species; Sorafenib.

Fig. 1

Overview of the ferroptosis pathway. In many cells, cystine (Cys₂) import via system $x_{\text{c}}^{-}$ is required for glutathione synthesis, and the function of glutathione peroxidase 4 (GPX4). GPX4 activity prevents the accumulation of lipid ROS that are lethal to the cell. Treatment blocks cystine uptake, ultimately depleting the cell of glutathione and inhibiting the function of GPX4. Direct inhibition of the rate-limiting glutathione synthetic enzyme glutamate-cysteine ligase (GCL) using buthionine-(S,R)-sulfoximine (BSO) can also lead to the same iron- and ROS-dependent ferroptotic phenotype. Other small molecule inducers of ferroptosis are indicated in red, while suppressors of ferroptosis are in blue. GCL Glutamate cysteine ligase, GSS glutathione synthetase, Cys cysteine, Glu glutamate, Gly glycine, Gln glutamine. α-KG alpha-ketoglutarate, GPNA l-g-glutamyl-p-nitroanilide, AOA amino oxyacetate, BHA butylated hydroxyanisole, BHT butylated hydroxytoluene, DFO deferoxamine, 2,2-BP 2,2-bipyridyl, CPX ciclopirox

Fig. 2

Structure of small molecule ferroptosis inducers. a molecules that inhibit the function of system $x_{\text{c}}^{-}$. b Molecules that inhibit the function of glutathione peroxidase 4 (GPX4). ML162 is also known as DPI7

Fig. 3

The relationship between iron, diatomic oxygen (O₂), PUFAs and glutathione (GSH). Iron (Fe²⁺), O₂ and PUFAs are each, individually, required for cell growth and survival (green arrows). GSH is also required for cell growth and proliferation, as well as to prevent the combination of Fe²⁺, O₂ and PUFAs from triggering ferroptosis