A quantitative high-throughput screen for modulators of IL-6 signaling: a model for interrogating biological networks using chemical libraries.

Small molecule modulators are critical for dissecting and understanding signaling pathways at the molecular level. Interleukin 6 (IL-6) is a cytokine that signals via the JAK-STAT pathway and is implicated in cancer and inflammation. To identify modulators of this pathway, we screened a chemical collection against an IL-6 responsive cell line stably expressing a beta-lactamase reporter gene fused to a sis-inducible element (SIE-bla cells). This assay was optimized for a 1536-well microplate format and screened against 11 693 small molecules using quantitative high-throughput screening (qHTS), a method that assays a chemical library at multiple concentrations to generate titration-response profiles for each compound. The qHTS recovered 564 actives with well-fit curves that clustered into 32 distinct chemical series of 13 activators and 19 inhibitors. A retrospective analysis of the qHTS data indicated that single concentration data at 1.5 and 7.7 microM scored 35 and 71% of qHTS actives, respectively, as inactive and were therefore false negatives. Following counter screens to identify fluorescent and non-selective series, we found four activator and one inhibitor series that modulated SIE-bla cells but did not show similar activity in reporter gene assays induced by EGF and hypoxia. Small molecules within these series will make useful tool compounds to investigate IL-6 signaling mediated by JAK-STAT activation.