LIBX-A401: A Novel Selective Inhibitor of Acyl-CoA Synthetase Long Chain Family Member 4 (ACSL4) and Its Binding Mode

Acyl-coenzyme A synthetase long-chain family member 4 (ACSL4), a pivotal enzyme in lipid metabolism, has emerged as a therapeutic target for ferroptosis-related conditions and cancer. However, its reference inhibitor, rosiglitazone, has off-target activity on peroxisome proliferator-activated receptor gamma (PPARγ), a key regulator of lipid homeostasis. Here, the discovery of LIBX-A401, a potent ACSL4 inhibitor derived from rosiglitazone devoid of PPARγ activity, is reported. Its binding to ACSL4 is ATP-dependent, stabilizing the C-terminal domain and altering the fatty acid gate region, as shown by Hydrogen-Deuterium Exchange Mass Spectrometry. Photoaffinity labeling identified A329 within the fatty acid binding site, while molecular dynamics and mutagenesis highlighted Q302 as critical for LIBX-A401 binding. LIBX-A401 exhibits anti-ferroptotic properties in cells, supported by target engagement. These findings establish LIBX-A401 as a valuable tool to study ACSL4 in ferroptosis and cancer, while its elucidated binding mode paves the way for the rational design of improved inhibitors.