A novel inhibitor of class IIa histone deacetylases attenuates collagen‐induced arthritis

Abstract Background and Purpose Most inhibitors of histone deacetylases (HDACs) are not selective and are cytotoxic. Some have anti‐inflammatory activity in disease models, but cytotoxicity prevents long‐term uses in non‐fatal diseases. Inhibitors selective for class IIa HDACs are much less cytotoxic and may have applications in management of chronic inflammatory diseases. Experimental Approach LL87 is a novel HDAC inhibitor examined here for HDAC enzyme selectivity. It was also investigated in macrophages for cytotoxicity and for inhibition of lipopolysaccharide (LPS)‐stimulated cytokine secretion. In a rat model of collagen‐induced arthritis, LL87 was investigated for effects on joint inflammation in Dark Agouti rats. Histological, immunohistochemical, micro‐computed tomography and molecular analyses characterise developing arthritis and anti‐inflammatory efficacy. Key Results LL87 was significantly more inhibitory against class IIa than class I or IIb HDAC enzymes. In macrophages, LL87 was not cytotoxic and reduced both LPS‐induced secretion of pro‐inflammatory cytokines, and IL6‐induced class IIa HDAC activity. In rats, LL87 attenuated paw swelling and clinical signs of arthritis, reducing collagen loss and histological damage in ankle joints. LL87 decreased immune cell infiltration, especially pro‐inflammatory macrophages and osteoclasts, into synovial joints and significantly reduced expression of pro‐inflammatory cytokines and tissue‐degrading proteases. Conclusion and Implications A novel inhibitor of class IIa HDACs has been shown to have an anti‐inflammatory and anti‐arthritic profile distinct from current therapies. It is efficacious in reducing macrophage infiltration and joint inflammation in a chronic model of rat arthritis.