In vitro activity: Mivebresib (formerly known as ABBV-075) is a novel potent bromodomain (BRD) inhibitor that is being tested in a Phase I study for the treatment of solid tumors. As a potent BET inhibitor (bromodomain (BRD)-containing proteind), Mivebresib has potential antineoplastic activity. It binds bromodomains of BRD2/4/T with similar affinities (Ki of 1-2.2 nM) and highly selective for 18 bromodomain proteins tested (Kd> 1 μM; more than 600-fold selectivity vs. BRD4), but exhibits roughly 10-fold weaker potency towards BRD3 (Ki of 12.2 nM) and has moderate activity towards CREBBP (Kd = 87 μM; 54-fold selectivity vs. BRD4). In addition, potent inhibition of the BET (bromodomain and extra-terminal) family with ABBV-075 is a highly efficacious therapy in pre-clinical models of prostate cancer. The single-digit to low nanomolar anti-proliferative IC50s and potent in vivo tumor growth inhibition of ABBV-075 is mediated in part via inhibition of androgen receptor (AR)-dependent transcription.

Kinase Assay: Mivebresib is a potent and orally available bromodomain and extraterminal domain (BET) bromodomain inhibitor. Mivebresib binds to BRD4 with a Kiof 1.5 nM. It binds bromodomains of BRD2/4/T with similar affinities (Ki of 1-2.2 nM) and highly selective for 18 bromodomain proteins tested (Kd> 1 μM; more than 600-fold selectivity vs. BRD4), but exhibits roughly 10-fold weaker potency towards BRD3 (Ki of 12.2 nM) and has moderate activity towards CREBBP (Kd = 87 μM; 54-fold selectivity vs. BRD4).

Cell Assay: Mivebresib inhibit DHT-stimulated transcription of AR target genes without significant effect on AR protein expression. In addition to blocking the transcription activation downstream of AR, Mivebresib is also a potent inhibitor of MYC and the TMPRSS2-ETS fusion proteins