A-9758 inhibits human, mouse, dog and rat RORγ transactivation (IC50s: 38 nM, 20 nM, 25 nM and 64 nM). A-9758 displays a cofactor profile in recruiting co-repressors (NCoR1: EC50=60 nM, NCoR2: EC50=43 nM) and derecruiting co-activators (NCoA1: IC50=110 nM, PGC1α: IC50=49 nM). A-9758 inhibits TCR-mediated IL-17A secretion with an IC50 of 100 and 38 nM for human CD4+ T cells and in vitro differentiated mouse Th17 cells, respectively. A-9758 attenuates the differentiation of RORγt expressing Th17 cells and/or their effector function.