GSK046 (iBET-BD2)

GSK046 shows an excellent level of selectivity for the BET family with no measurable activity for non-BET bromodomains. GSK046 is tested in an LPS-stimulated peripheral blood mononuclear cell (PBMC) cellular assay. After stimulation, these immune cells release a range of cytokines and chemokines, including monocyte chemoattractant protein 1 (MCP-1/CCL2). GSK046 also inhibits MCP-1 production (pIC50 = 7.5) with a minimal drop-off from the biochemical BRD4 BD2 potency observed.^[2]

The metabolic stability of GSK046 is tested in male Wistar Han rat, male Beagle dog and mixed gender pooled human hepatocytes. Suspensions of cryopreserved hepatocytes from each species are used. Incubations are performed at a test or control compound concentration of 0.5 μM at 37 °C, at a cell density of 0.5 million viable cells/mL. Control incubations are also performed in lysed cells to reveal any non-enzymatic degradation. For Rat and Human incubation samples (50 μL) are removed from the incubation mixture at 0, 5, 10, 20, 40 and 60 min. For Dog incubation samples (50 μL) are removed from the incubation mixture at 0, 10, 20, 40, 60 and 120 min. The samples are added to methanol, containing internal standard, (100 μL) to stop the reaction. Following protein precipitation, the compound remaining in the supernatants is measured using specific LC-MS/MS methods as a ratio to the internal standard in the absence of a calibration curve. Peak area ratios (Compound to IS) are fitted to an unweighted logarithmic decline in substrate. Using the first order rate constant, clearance is calculated by adjustment for protein concentration, volume of the incubation and hepatic scaling factor.

GSK046 has suitable physicochemical and pharmacokinetic properties to be utilized in vivo, and it has also been demonstrated that a highly selective BD2 inhibitor retains the ability to potently inhibit MCP-1 cytokine release in a cellular and whole blood context. GSK046 proves useful for further biological profiling. GSK046 is efficacious in a broad range of inflammatory pathologies and selective BD2 inhibition may be a useful new therapeutic strategy for immunoinflammatory diseases.^[2]