Background/Purpose: BET (Bromodomain and Extra-Terminal) proteins have recently emerged as a key epigenetic regulator of genes at the transcriptional level and inhibition of their binding to select histone peptide sequences bearing acetylated lysines can suppress the production of some inflammatory cytokines. Here we determine the activity of a novel, orally bioavailable BET inhibitor, RVX-297, in an animal model of rheumatoid arthritis.

Methods: Binding of RVX-297 to purified bromodomains (BDs) was measured by competition with a tetra-acetylated peptide derived from the amino terminus of histone 4 using fluorescence resonance energy transfer (FRET) and by thermal denaturation of BDs. The effect of RVX-297 on inflammatory mediators in cellular assays was measured by quantitative RT-PCR.  RVX-297 was dosed by oral gavage in the rat collagen-induced arthritis (CIA) model, an experimental model of polyarthritis that has been widely used for preclinical evaluation of anti-arthritic agents.

Results: RVX-297 selectively binds to BET bromodomains (e.g. IC₅₀s = 0.82 and 0.012mM for BRD4 BD1 and BD2, respectively), but not to other BDs tested.  In vitro, RVX-297 dose dependently inhibited LPS-induced IL-6 in mouse bone marrow-derived macrophages, (IC50 = 0.3 mM) and T-cell receptor-induced IL-17 mRNA expression in human PBMCs (IC50 of 3.7 mM).  Furthermore, in human primary synovial fibroblasts taken from patients with rheumatoid arthritis, RVX-297 inhibited TNFa-induced MMP1, MMP3, RANKL, VCAM-1 and IL-6 expression, all of which have been associated with diseased tissue. These observations suggested that RVX-297 might also show activity in an autoimmune disease model for rheumatoid arthritis.

Following administration of collagen, the rat collagen-induced arthritis model develops a measurable polyarticular inflammation, progressive destruction of cartilage and bone destruction in association with pannus formation.  Therapeutic oral administration of RVX-297 from the onset of established arthritis significantly reduced the progression of disease severity in a dose-dependent manner (25 to 75 mg/kg b.i.d.). On day 7 of arthritis, RVX-297 (75 mg/kg b.i.d.) inhibited the increase in ankle diameter by 92% relative to disease controls. To further characterize the pharmacodynamic effects, histopathology of the ankle and knee joints was evaluated. At 50 mg/kg and 75 mg/kg, b.i.d., RVX-297 reduced the histopathology parameters in the in the ankle by 64% and in the knee by 86 – 94%.The expression of the inflammatory mediators IL-1b, MMP3, MMP13, RANKL, VCAM-1 and IL-6 were all reduced in the ankle joint at the mRNA or protein level.

Conclusion: These results demonstrate that the BET inhibitor RVX-297 significantly decreases clinical signs of disease in a rat model of rheumatoid arthritis, reflecting a decrease in production of a number of cytokine and inflammatory mediators. Therefore, BET inhibitors offer promise for the treatment of rheumatoid arthritis and other autoimmune diseases.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/oral-administration-of-a-novel-small-molecule-bet-bromodomain-inhibitor-rvx-297-reduces-disease-severity-in-a-rat-collagen-induced-arthritis-model/