[CAS NO. 1365888-06-7]  Brilanestrant (GDC-0810)

In cell-free radio-ligand competitive binding assays, GDC-0810 binds both ERα and ERβ with low nanomolar affinity. GDC-0810 has little to no inhibition against CYP1A2, CYP2D6, or CYP3A4 (IC50 > 20 μM), modest inhibitory effect on CYP2C9 and CYP2C19 (IC50 = 2.2 and 3.3 μM respectively), and potent inhibition of CYP2C8 (IC50 of <0.1 μM). Selectivity of GDC-0810 over other nuclear hormone receptors is also found to be good. In transcriptional reporter assays for the mineralocorticoid (MR), progesterone-A (PR-A), progesterone (PR-B), and glucocorticoid (GR) receptors, GDC-0810 has minimal activity (IC50 > 1 μM). While in binding assays, GDC-0810 displays little activity toward the androgen receptor (AR; IC50 > 4 μM) and GR (IC50 = 0.99 μM). GDC-0810-mediated ERα depletion is dependent on the 26S proteasome. GDC-0810 antagonizes ERα ligand binding domain mutants in vitro and in vivo. In cell-free E2 competitive binding assays that was used to determine the binding of GDC-0810 to ER.WT, ER.Y537S and ER.D538G ligand binding domains, GDC-0810 retains its ability to potently displace E2 from the ligand binding domain, albeit with a slightly increased IC50 (WT: 2.6 nM vs. ER.Y537S: 5.5 nM and ER.D538G: 5.4 nM). GDC-0810 can compete the PGC1α co-activator peptide off the mutated ligand binding domain, implying that GDC-0810 is capable of driving an 'active' to 'inactive' conformational shift of mutant ER, though with a ~five-seven fold reduction in biochemical potency compared to wild-type ER.