Discovery of a selective and biologically active low-molecular weight antagonist of human interleukin-1ß

Human interleukin-1 ss (hIL-1 ss) is a pro-inflammatory cytokine involved inmany diseases. While hIL-1 ss directed antibodies have shown clinical benefit, an orally available low-molecular weight antagonist is still elusive, limiting the applications of hIL-1 ss-directed therapies. Here we describe the discovery of a lowmolecular weight hIL-1 ss antagonist that blocks the interaction with the IL-1R1 receptor. Starting from a low affinity fragment-based screening hit 1, structurebased optimization resulted in a compound (S)-2 that binds and antagonizes hIL-1 ss with single-digit micromolar activity in biophysical, biochemical, and cellular assays. X-ray analysis reveals an allostericmode of action that involves a hitherto unknown binding site in hIL-1 ss encompassing two loops involved in hIL-1R1/hIL-1 ss interactions. We show that residues of this binding site are part of a conformationally excited state of the mature cytokine. The compound antagonizes hIL-1 ss function in cells, including primary human fibroblasts, demonstrating the relevance of this discovery for future development of hIL1 ss directed therapeutics.