Background Systemic inflammatory diseases, such as systemic lupus erythematosus (SLE) and idiopathic inflammatory myositis (IIM), have largely unknown aetiology and represent a disease area with major unmet medical needs. Treatment often give a clinical effect, but not in all patients; and symptoms often remain. In collaboration with the Structural Genomics Consortium (SGC), we have investigated in vitro B-cell effects of about 50 different chemical probes which bind and inhibit epigenetic enzymes and regulators, such as bromodomains and histone methyltransferases, as well as kinases and other intracellular protein targets. These probes are small molecules that can enter cells and selectively inhibit potential new drug-targets at therapeutically relevant doses. The read out are expression of molecules which have been shown to be of pathological relevance in systemic inflammatory diseases.

Materials and methods Peripheral blood mononuclear cells (PBMC) from patients with SLE or IIM and healthy controls were incubated in presence of different chemical probes at 1 or 0,1 uM for 6 days in culture medium containing B-cell stimulating factors; IL4, IL10, IL21, sCD40L and CpG2006. Cell viability was determined by flow cytometry using the live/dead marker viability IR^® and B-cell maturation was investigated using markers for memory B cells (CD27), plasmablasts (CD38) and surface IgG. Secretion of IgG was quantified by ELISA.

Results The percentage of memory B cells, plasmablasts and IgG-expressing B cells, as well as IgG secretion, was induced by the B-cell stimulating factors. These parameters were suppressed by a set of the epigenetic probes, as well as by some of the probes targeting other intracellular proteins. A few of the probes decreased cell viability. Both B cells from SLE and IIM were affected.

Conclusions We have found a set of chemical probes, with documented target selectivity and potent inhibitory effects of these targets, which affect in vitro B-cell maturation and secretion of IgG. Further analysis is required to better understand the pathways that are affected.