Small Molecule Inhibitors of Hsp90 Potently Affect Inflammatory Disease Pathways and Exhibit Activity in Models of Rheumatoid Arthritis

Objective. To evaluate the ability of SNX-7081, a novel small molecule inhibitor of Hsp90, to block components of inflammation, including cytokine production, protein kinase activity, and angiogenic signaling. A close analog was evaluated in preclinical in vivo models of rheumatoid arthritis (RA). Methods. SNX-7081 binding to Hsp90 was characterized in Jurkat cells and RA synovial fibroblasts (RASFs). Inhibition of NF-kappa B nuclear translocation was evaluated in cellular systems, using lipopolysaccharide (LPS), tumor necrosis factor alpha, or interleukin-1 beta stimulation. Suppression of cytokine production in THP-1. cells, human umbilical vein endothelial cells, and RASFs was studied. Disruption of MAPK signaling cascades by SNX-7081 following growth factor stimulation was assessed. SNX-7081 was tested in 2 relevant angiogenesis assays: platelet-derived growth factor activation of fibroblasts and LPS-induced nitric oxide (NO) release in J774 macrophages. A close analog, SNX-4414, was evaluated in rat collagen-induced arthritis and adjuvant-induced arthritis, following oral treatment. Results. SNX-7081. showed strong binding affinity to Hsp90 and expected induction of Hsp70. NF-kappa B nuclear translocation was blocked by SNX-7081 at nanomolar concentrations, and cytokine production was potently inhibited. Growth factor activation of ERK and JNK signaling was significantly reduced by SNX-7081. NO production was also sharply inhibited. In animal models, SNX-4414 fully inhibited paw swelling and improved body weight. Scores for inflammation, pannus formation, cartilage damage, and bone resorption returned to normal. Conclusion. The present results demonstrate that a small molecule Hsp90 inhibitor can impact inflammatory disease processes. The strong in vivo efficacy observed with SNX-4414 provides preclinical validation for consideration of Hsp90 inhibitors in the treatment of RA.