Bromodomain (BD) and extra-terminal domain containing proteins (BET) are chromatin adapters that bind acetylated histone marks via two tandem BDs, BD1 and BD2, to regulate gene transcription. BET proteins are involved in transcriptional reprogramming in response to inflammatory stimuli. BET BD inhibitors (BETis) that are nonselective for BD1 or BD2 have recognized anti-inflammatory properties in vitro and counter pathology in models of inflammation or autoimmune disease. Although both BD1 and BD2 bind acetylated histone residues, they may independently regulate the expression of BET-sensitive genes. Here we characterized the ability of RVX-297, a novel orally active BETi with selectivity for BD2, to modulate inflammatory processes in vitro, in vivo, and ex vivo. RVX-297 suppressed inflammatory gene expression in multiple immune cell types in culture. Mechanistically, RVX-297 displaced BET proteins from the promoters of sensitive genes and disrupted recruitment of active RNA polymerase II, a property shared with pan-BETis that nonselectively bind BET BDs. In the lipopolysaccharide model of inflammation, RVX-297 reduced proinflammatory mediators assessed in splenic gene expression and serum proteins. RVX-297 also countered pathology in three rodent models of polyarthritis: rat and mouse collagen-induced arthritis, and mouse collagen antibody–induced arthritis. Further, RVX-297 prevented murine experimental autoimmune encephalomyelitis (a model of human multiple sclerosis) disease development when administered prophylactically and reduced hallmarks of pathology when administered therapeutically. We show for the first time that a BD2-selective BETi maintains anti-inflammatory properties and is effective in preclinical models of acute inflammation and autoimmunity.

Background/Objectives: Obesity can cause metabolic disorders and hepatic steatosis. Continuous hepatic influx of dietary lipids leads to adaptive metabolic changes, including increased fatty acid oxidation (FAO) and ketogenesis. However, these adaptations are not enough to counter the detrimental accumulation of lipids, resulting in hepatic steatosis. Apabetalone is a clinical-stage Bromodomain and Extra-Terminal domain inhibitor (BETi) that attenuated the increase in hepatic fibrosis score (FS) and reduced the rate of ischemic major adverse cardiovascular events and hospitalizations for heart failure in a subgroup of patients having a high likelihood of Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) in the phase 3 clinical trial, BETonMACE. Methods: To analyze apabetalone’s effects on lipid and ketone metabolism, RNA seq, Oil Red staining and triglyceride quantification were performed in livers from a mouse model of diabetes-induced obesity and ketones were measured in plasma. Results: Mice fed a high-fat diet (HFD) were obese and demonstrated liver steatosis. Apabetalone treatment maintained the beneficial metabolic adaptation induced by HFD (increased FAO) and decreased hepatic triglycerides and lipid droplets. This inhibition of lipid anabolism redirected substrates to FAO and ketogenesis, resulting in increased plasma ketones, showing for the first time the role of BETi in ketogenesis. In the heart, apabetalone treatment reduced cardiac oxidative stress and plasma NT-proBNP levels. Conclusions: Apabetalone improves hepatic lipid handling, favoring ketogenesis. As ketones have demonstrated beneficial effects on cardiac function, increased ketones induced by apabetalone may not only contribute to the observed attenuation of FS in patients, but also a reduction in cardiac events among patients with high likelihood of MASLD, as well as in the overall trial population.