HDAC6-IN-34 (compound 21) is an oral active and selective HDAC6 inhibitor with the IC₅₀ of 18 nM. HDAC6-IN-34 increases the acetylation level of tubulin without affecting histone acetylation in cutaneous T-cell lymphoma cells and inhibits TNF-α secretion in LPS (HY-D1056)-stimulated macrophage cells. HDAC6-IN-34 shows excellent anti-arthritic efficacy in rat^[1].