SR 1555 is a novel RORγ-specific synthetic ligand [1].

Retinoic acid receptor-related nuclear receptor (ROR) belongs to the nuclear receptor superfamily, a group of structurally related, ligand-dependent transcription factors. RORs function as key regulators of many physiological processes that occur during embryonic development and in the adult [2]. RORγ plays a dominant role in T cell differentiation, particularly in the development of TH17 cells, which are implicated in autoimmune diseases such as multiple sclerosis and rheumatoid arthritis [3].

In vitro: In a GAL4-NR chimeric co-transfection assay, SR1555 was devoid of LXR, FXR, and RORα activity, but it dose-dependently repressed the activity at RORγ with an IC50 of ≈ 1.5 μM. In competitive radioligand binding assays, SR1555 bound to RORγ with an IC50 of 1 μM. SR1555 specifically targeted RORγ and inhibited its transcriptional activity leading to suppression of IL-17 gene expression. EL4 cells treated SR1555 (10 μM) for 24 h inhibited Il17a gene expression by greater than 70%, demonstrating that SR1555 could inhibit the expression of this TH17 mediated cytokine [1]. SR1555 not only inhibited TH17 cell development and function but also increased the frequency of T regulatory cells [1].

References:
[1] Solt L A, Kumar N, He Y, et al. Identification of a selective RORγ ligand that suppresses Th17 cells and stimulates T regulatory cells[J]. ACS chemical biology, 2012, 7(9): 1515-1519.
[2] Jetten A M, Ueda E. The ROR nuclear orphan receptor subfamily: critical regulators of multiple biological processes[J]. Progress in nucleic acid research and molecular biology, 2001, 69: 205-247.
[3] Ivanov I I, McKenzie B S, Zhou L, et al. The orphan nuclear receptor RORγt directs the differentiation program of proinflammatory IL-17+ T helper cells[J]. Cell, 2006, 126(6): 1121-1133.