SUN-019 The Selective Progesterone Receptor Modulator Ulipristal Acetate Blocks Glucocorticoid Receptor Transactivation

Progesterone is a crucial regulator of the female reproductive system, but also contributes to the pathogenesis of certain gynecological diseases. As such, selective progesterone receptor modulators (SPRMs) have shown potential for the treatment of such diseases. The SPRM Ulipristal acetate (UPA) offers a much-needed therapeutic option for the clinical management of uterine fibroids. Although UPA initially passed safety evaluations in Europe, post-marketing analysis identified cases of liver injury and hepatic failure, leading to temporary restrictions on UPA use. The structural analysis predicted low glucocorticoid receptor (GR) antagonist properties of UPA, however the anti-glucocorticoid activity of Ulipristal has been demonstrated on reporter constructs in HeLa cells. To determine whether UPA can alter the activity of endogenous GR in various relevant cell types, immortalized human uterine fibroid cells (UtLM) and hepatocytes (HepG2) were treated with the synthetic glucocorticoid dexamethasone and/or UPA. Co-treatment of 100 nM UPA with dexamethasone reduced glucocorticoid-induced expression of PER1, FKBP5, and GILZ in HepG2 and UtLM cells by 30-55%. At 1μM, UPA completely blocked glucocorticoid regulation of these genes in both cell lines. As a comparison, the extent of glucocorticoid inhibition by UPA was comparable to the known PR and GR antagonist RU 486. To discover whether the anti-glucocorticoid activity of UPA was mediated by PR, we knocked down PR expression by siRNA and found that the inhibitory activity of UPA does not require PR, suggesting a direct effect on GR. To determine the mechanism by which UPA inhibits GR activity, we evaluated hallmarks of GR transactivation. As hormone-dependent phosphorylation at S211 is associated with transcriptionally active GR, we evaluated p211 status in response to dexamethasone treatment with and without UPA. In the presence of UPA, dexamethasone-mediated phosphorylation at 211 was significantly diminished. Furthermore, dexamethasone-dependent nuclear translocation of GR was reduced by approximately 70% in both cell lines. Reduced activation of GR resulted in diminished GR recruitment to known regulatory regions in the GILZ promoter in the presence of UPA. We next evaluated the effect of UPA on glucocorticoid-mediated transcription in primary cells. Co-treatment of dexamethasone with UPA blunted glucocorticoid responsiveness in primary human uterine fibroid tissue cultured ex vivo. To determine whether UPA could inhibit endogenous glucocorticoid signaling, mice were treated with vehicle or 2 mg/kg UPA and various tissues were isolated for gene expression analysis. UPA inhibited basal expression of Per1, Fkbp5, and Gilz in the uterus and liver, and lung but not the spleen. These studies suggest that UPA selectively regulates GR activity, which is an important consideration for its use as a long-term therapeutic agent.