Curcumin analogue FLLL32 induces ferroptosis by targeting the STAT3-GPX4/SLC40A1 axis in colorectal cancer

FLLL32 is a curcumin analogue with reported anti-tumor activity, mainly through inhibition of signal transducer and activator of transcription 3 (STAT3) signaling and induction of apoptosis. However, whether FLLL32 regulates ferroptosis in colorectal cancer (CRC) and the underlying mechanism remain unclear. Here, using a patient-derived CRC organoid screening platform, we identified FLLL32 as a potent anti-CRC compound. FLLL32 suppressed CRC organoid growth, inhibited CRC cell proliferation and migration in vitro, and inhibited xenograft tumor growth in vivo. In parallel, FLLL32 induced ferroptosis-associated iron accumulation, reactive oxygen species (ROS) production, lipid peroxidation, mitochondrial morphological and functional abnormalities. The ferroptosis inhibitor Ferrostatin-1 markedly restored FLLL32-impaired cell viability and reduced ROS, whereas the apoptosis inhibitor Z-VAD-FMK showed weaker protection. These findings suggest that ferroptosis is a major contributor to FLLL32-induced cell death, although apoptotic features are also present. Mechanistically, FLLL32 interacted with STAT3, and Glu638 and Met726 contributed to the FLLL32-STAT3 interaction. FLLL32 also suppressed STAT3 Tyr705 phosphorylation and nuclear signaling, thereby disrupting pSTAT3-mediated transcriptional regulation of glutathione peroxidase 4 (GPX4) and solute carrier family 40 member 1 (SLC40A1), weakening lipid peroxide detoxification and cellular iron efflux, promoting intracellular iron accumulation, and enhancing ferroptosis in CRC cells. These findings define a STAT3-GPX4/SLC40A1-dependent mechanism underlying the anti-CRC activity of FLLL32 and support further investigation of STAT3-associated ferroptosis regulation as a potential therapeutic vulnerability in CRC.