Temperature-dependence of radical-trapping activity of phenoxazine, phenothiazine and their aza-analogues clarifies the way forward for new antioxidant design

Poon, Jia‐fei; Farmer, Luke A.; Haidasz, Evan A.; Pratt, Derek A.

doi:10.1039/d1sc02976b

Cited by 10 publications

(19 citation statements)

References 35 publications

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“…For example, the reactivity of the aromatic amine phenothiazine drops from k inh = 8 × 10 6 M –1 s –1 in PhCl to 5.8 × 10 4 M –1 s –1 in liposomal egg phosphatidylcholinewith the latter being strikingly similar to what is measured for the Cu and Ni complexes under the same conditions (2–5 × 10 4 M –1 s –1 except the poorly soluble CuATSM 2 ). Phenothiazine is a good basis of comparison since it has a similar N–H BDE to that predicted for the peroxyl addition adducts (78.7 vs 77.8 kcal/mol by CBS-QB3, see the Supporting Information) and a similar H-bond acidity (α 2 H = 0.38 vs 0.36 measured for NiATSM, vide supra ). Thus, while HAT is expected to be faster than the initial radical addition in weak or non-H-bonding solvents (such as THF/PhCl), radical addition may be faster than HAT in phospholipids.…”

Section: Discussionmentioning

confidence: 90%

Radical-Trapping Antioxidant Activity of Copper and Nickel Bis(Thiosemicarbazone) Complexes Underlies Their Potency as Inhibitors of Ferroptotic Cell Death

2021

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Herein we demonstrate that copper(II)-diacetylbis(N 4 -methylthiosemicarbazone)(CuATSM), clinical candidate for the treatment of ALS and Parkinson's disease, is a highly potent radical-trapping antioxidant (RTA) and inhibitor of (phospho)lipid peroxidation. In THF autoxidations, CuATSM reacts with THF-derived peroxyl radicals with k inh = 2.2 × 10 6 M −1 s −1 roughly 10-fold greater than α-tocopherol (α-TOH), Nature's best RTA. Mechanistic studies reveal no H/D kinetic isotope effects and a lack of rate-suppressing effects from Hbonding interactions, implying a different mechanism from α-TOH and other canonical RTAs, which react by H-atom transfer (HAT). Similar reactivity was observed for the corresponding Ni 2+ complex and complexes of both Cu 2+ and Ni 2+ with other bis(thiosemicarbazone) ligands. Computations corroborate the experimental finding that rate-limiting HAT cannot account for the observed RTA activity and instead suggest that the reversible addition of a peroxyl radical to the bis(thiosemicarbazone) ligand is responsible. Subsequent HAT or combination with another peroxyl radical drives the reaction forward, such that a maximum of four radicals are trapped per molecule of CuATSM. This sequence is supported by spectroscopic and mass spectrometric experiments on isolated intermediates. Importantly, the RTA activity of CuATSM (and its analogues) translates from organic solution to phospholipid bilayers, thereby accounting for its (their) ability to inhibit ferroptosis. Experiments in mouse embryonic fibroblasts and hippocampal cells reveal that lipophilicity as well as inherent RTA activity contribute to the potency of ferroptosis rescue, and that one compound (CuATSP) is almost 20-fold more potent than CuATSM and among the most potent ferroptosis inhibitors reported to date.

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Section: Discussionmentioning

confidence: 90%

Radical-Trapping Antioxidant Activity of Copper and Nickel Bis(Thiosemicarbazone) Complexes Underlies Their Potency as Inhibitors of Ferroptotic Cell Death

2021

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“…The two correlations have similar slopes, but are vertically offset by roughly one order of magnitude because of the greater inherent reactivity of PNX compared to PTZ − a fact underpinned by their N-H BDEs (76.1 kcal/mol for the former vs 78.2 kcal/mol for the latter). 40,41,56 Plotting the corresponding k inh lip values versus ∑σ p + leads to poorer correlations with much larger slopes and a convergence in the reactivity of the PNX and PTZ derivatives (Figure 6C). Indeed, because of the very strong Hbond basicity of the phosphodiester moiety, a LFER for RTA activity in phospholipids must account not only for how electronics change the intrinsic reactivity but also the engagement of the RTA in H-bonds (Figure 6D).…”

Section: ■ Discussionmentioning

confidence: 99%

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

Farmer

Poon

et al. 2022

J. Am. Chem. Soc.

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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 (k inh ∼ 2 × 10 5 M −1 s −1 ) and cell potency (EC 50 ∼ 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.

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“…Lipoxygenases inhibitors with radical trapping can function as terminators of the radical chain reactions of lipid autoxidation to inhibit ferroptosis ( Poon et al, 2021 ). For LOX inhibitors that lack radical trapping ability, those targeting 15-LOX-1, exhibit a degree of anti-ferroptosis activity ( Kagan et al, 2017 ).…”

Section: Therapeutic Applicationmentioning

confidence: 99%

Ferroptosis: Underlying mechanism and the crosstalk with other modes of neuronal death after intracerebral hemorrhage

Cao

Xiao²,

Liu³

et al. 2023

Front. Cell. Neurosci.

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Intracerebral hemorrhage (ICH) is a serious cerebrovascular disease with high rates of morbidity, mortality, and disability. Optimal treatment of ICH is a major clinical challenge, as the underlying mechanisms remain unclear. Ferroptosis, a newly identified form of non-apoptotic programmed cell death, is characterized by the iron-induced accumulation of lipid reactive oxygen species (ROS), leading to intracellular oxidative stress. Lipid ROS causes damage to nucleic acids, proteins, and cell membranes, eventually resulting in ferroptosis. In the past 10 years, ferroptosis has resulted in plenty of discoveries and breakthroughs in cancer, neurodegeneration, and other diseases. Some studies have also reported that ferroptosis does occur after ICH in vitro and in vivo and contribute to neuronal death. However, the studies on ferroptosis following ICH are still in the preliminary stage. In this review, we will summarize the current evidence on the mechanism underlying ferroptosis after ICH. And review the traditional modes of neuronal death to identify the crosstalk with ferroptosis in ICH, including apoptosis, necroptosis, and autophagy. Additionally, we also aim to explore the promising therapeutic application of ferroptosis in cell death-based ICH.

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Temperature-dependence of radical-trapping activity of phenoxazine, phenothiazine and their aza-analogues clarifies the way forward for new antioxidant design

Abstract: The prediction and/or rationalization of diarylamine radical-trapping antioxidant (RTA) activity at the elevated temperatures where they are most useful presents a significant challenge, precluding the development of new technology. Whilst...

Cited by 10 publications

References 35 publications

Radical-Trapping Antioxidant Activity of Copper and Nickel Bis(Thiosemicarbazone) Complexes Underlies Their Potency as Inhibitors of Ferroptotic Cell Death

Radical-Trapping Antioxidant Activity of Copper and Nickel Bis(Thiosemicarbazone) Complexes Underlies Their Potency as Inhibitors of Ferroptotic Cell Death

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

Ferroptosis: Underlying mechanism and the crosstalk with other modes of neuronal death after intracerebral hemorrhage

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