HDAC9 and rheumatoid arthritis: CKD-506, an HDAC6 inhibitor, Reduced the production of IL-6 and TNF-α by activated PBMCs from RA patients; inhibited the production of IL-8, IL-6, MMP-1, and MMP-3 by activated FLS; inhibited the severity of arthritis in a murine model of AIA.456 Interestingly, these studies could not show an association between the use of these HDAC inhibitors and the deacetylation of H3 and H4.