Cathepsin B (CTSB), identified as a promising RA biomarker, was inhibited by CA-074-methyl ester (CA-074Me), reducing RA-FLS proliferation and migration through lipid ROS, as well as ferrous ion accumulation, and decreasing levels of FTH1, SLC7A11, and GPX4, ultimately leading to ferroptosis [66]. Here, CTSB is linked to rheumatoid arthritis.