Among AP‐1 inhibitors, T‐5224 is a lead compound that specifically inhibits the binding of AP‐1 to regulatory regions of target genes, such as inflammation‐related genes,36, 37 and is currently under phase II clinical trials for patients with rheumatoid arthritis and other inflammatory diseases after the absence of serious side effects was confirmed in phase I trials (JapicCTI‐101359).38 This evidence concerns the gene JUN and rheumatoid arthritis.