Drugs Repurposed as Antiferroptosis Agents Suppress Organ Damage, Including AKI, by Functioning as Lipid Peroxyl Radical Scavengers
Authors: Mishima Eikan , Sato Emiko , Ito Junya , Yamada Ken-ichi , Suzuki Chitose , Oikawa Yoshitsugu , Matsuhashi Tetsuro , Kikuchi Koichi , Toyohara Takafumi , Suzuki Takehiro , Ito Sadayoshi , Nakagawa Kiyotaka , Abe Takaaki 
Published: November 2019

Significance Statement
Ferroptosis, cell death mediated by free radical reactions and driven by oxidative degradation of lipids, is a therapeutic target because of its role in organ injuries, including AKI. However, the ferroptosis-causing radicals targeted by ferroptosis suppressors have not been unequivocally identified. Certain cytochrome P450 substrate drugs are known to prevent lipid peroxidation via obscure mechanisms. The authors screened cytochrome P450 substrate drugs, identifying a diverse group of drugs with antiferroptotic properties, including promethazine and rifampicin. The antiferroptotic effect of these drugs was linked to their scavenging activity against lipid peroxyl radicals. Elevated lipid peroxyl radical levels were associated with ferroptosis onset, whereas radical scavenging by the drugs suppressed ferroptosis-related pathologic changes in different renal cell types and ameliorated organ injuries (including AKI) in mice, suggesting therapeutic potential for such repurposed drugs.

Background
Ferroptosis, nonapoptotic cell death mediated by free radical reactions and driven by the oxidative degradation of lipids, is a therapeutic target because of its role in organ damage, including AKI. Ferroptosis-causing radicals that are targeted by ferroptosis suppressors have not been unequivocally identified. Because certain cytochrome P450 substrate drugs can prevent lipid peroxidation via obscure mechanisms, we evaluated their antiferroptotic potential and used them to identify ferroptosis-causing radicals.

Methods
Using a cell-based assay, we screened cytochrome P450 substrate compounds to identify drugs with antiferroptotic activity and investigated the underlying mechanism. To evaluate radical-scavenging activity, we used electron paramagnetic resonance–spin trapping methods and a fluorescence probe for lipid radicals, NBD-Pen, that we had developed. We then assessed the therapeutic potency of these drugs in mouse models of cisplatin-induced AKI and LPS/galactosamine-induced liver injury.

Results
We identified various US Food and Drug Administration–approved drugs and hormones that have antiferroptotic properties, including rifampicin, promethazine, omeprazole, indole-3-carbinol, carvedilol, propranolol, estradiol, and thyroid hormones. The antiferroptotic drug effects were closely associated with the scavenging of lipid peroxyl radicals but not significantly related to interactions with other radicals. The elevated lipid peroxyl radical levels were associated with ferroptosis onset, and known ferroptosis suppressors, such as ferrostatin-1, also functioned as lipid peroxyl radical scavengers. The drugs exerted antiferroptotic activities in various cell types, including tubules, podocytes, and renal fibroblasts. Moreover, in mice, the drugs ameliorated AKI and liver injury, with suppression of tissue lipid peroxidation and decreased cell death.

Conclusions
Although elevated lipid peroxyl radical levels can trigger ferroptosis onset, some drugs that scavenge lipid peroxyl radicals can help control ferroptosis-related disorders, including AKI.