7-Dehydrocholesterol is an endogenous suppressor of ferroptosis.

Ferroptosis is a form of cell death that has received considerable attention not only as a means to eradicate defined tumour entities but also because it provides unforeseen insights into the metabolic adaptation that tumours exploit to counteract phospholipid oxidation1,2. Here, we identify proferroptotic activity of 7-dehydrocholesterol reductase (DHCR7) and an unexpected prosurvival function of its substrate, 7-dehydrocholesterol (7-DHC). Although previous studies suggested that high concentrations of 7-DHC are cytotoxic to developing neurons by favouring lipid peroxidation3, we now show that 7-DHC accumulation confers a robust prosurvival function in cancer cells. Because of its far superior reactivity towards peroxyl radicals, 7-DHC effectively shields (phospho)lipids from autoxidation and subsequent fragmentation. We provide validation in neuroblastoma and Burkitt's lymphoma xenografts where we demonstrate that the accumulation of 7-DHC is capable of inducing a shift towards a ferroptosis-resistant state in these tumours ultimately resulting in a more aggressive phenotype. Conclusively, our findings provide compelling evidence of a yet-unrecognized antiferroptotic activity of 7-DHC as a cell-intrinsic mechanism that could be exploited by cancer cells to escape ferroptosis.

Intrinsic and Extrinsic Limitations to the Design and Optimization of Inhibitors of Lipid Peroxidation and Associated Cell Death.

The archetype inhibitors of ferroptosis, ferrostatin-1 and liproxstatin-1, were identified via high-throughput screening of compound libraries for cytoprotective activity. These compounds have been shown to inhibit ferroptosis by suppressing propagation of lipid peroxidation, the radical chain reaction that drives cell death. Herein, we present the first rational design and optimization of ferroptosis inhibitors targeting this mechanism of action. Engaging the most potent radical-trapping antioxidant (RTA) scaffold known (phenoxazine, PNX), and its less reactive chalcogen cousin (phenothiazine, PTZ), we explored structure-reactivity-potency relationships to elucidate the intrinsic and extrinsic limitations of this approach. The results delineate the roles of inherent RTA activity, H-bonding interactions with phospholipid headgroups, and lipid solubility in determining activity/potency. We show that modifications which increase inherent RTA activity beyond that of the parent compounds do not substantially improve RTA kinetics in phospholipids or potency in cells, while modifications that decrease intrinsic RTA activity lead to corresponding erosions to both. The apparent "plateau" of RTA activity in phospholipid bilayers (kinh ∼ 2 × 105 M-1 s-1) and cell potency (EC50 ∼ 4 nM) may be the result of diffusion-controlled reactivity between the RTA and lipid-peroxyl radicals and/or the potential limitations on RTA turnover/regeneration by endogenous reductants. The metabolic stability of selected derivatives was assessed to identify a candidate for in vivo experimentation as a proof-of-concept. This PNX-derivative demonstrated stability in mouse liver microsomes comparable to liproxstatin-1 and was successfully used to suppress acute renal failure in mice brought on by tissue-specific inactivation of the ferroptosis regulator GPX4.

Targeting Ferroptosis: New Hope for As-Yet-Incurable Diseases.

Attaining control over life and death decisions facilitates the identification of new therapeutic strategies for diseases affected by early cell loss or resistance to cell death. In this context, ferroptosis, a prevailing form of non-apoptotic cell death marked by the iron-dependent oxidative destruction of lipid bilayers and metabolic aberrations, has attracted overwhelming interest among basic researchers and clinicians due to its relevance for a number of degenerative diseases, such as neurodegeneration, ischemia/reperfusion injury (IRI), and organ failure, as well as therapy-resistant tumors. As the ferroptotic death pathway offers various druggable nodes, it is anticipated that the preclinical and clinical development of ferroptosis modulators will unleash unprecedented opportunities for the treatment of as-yet-incurable diseases.