In vitro activity: Unlike previously described monovalent inhibitors, AZD5153 ligates two bromodomains in BRD4 simultaneously. AZD5153 treatment markedly affects transcriptional programs of MYC, E2F, and mTOR. Of note, mTOR pathway modulation is associated with cell line sensitivity to AZD5153. AZD5153 potently disrupts BRD4 foci in U2OS cells with an IC50 value of 1.7 nmol/L. AZD5153 efficiently downregulates MYC protein levels across the cell line panel irrespective of their sensitivity to AZD5153. AML, MM, and DLBCL cell lines are highly sensitive to AZD5153.

Kinase Assay: AZD-5153 HNT salt, the 6-Hydroxy-2-naphthoic acid salt form of AZD5153, is a potent, selective, and orally available BET/BRD4 (bromodomain and extraterminal) bromodomain inhibitor with pKi of 8.3 for BRD4 and possesses a bivalent binding mode. Unlike previously described monovalent inhibitors, AZD5153 ligates two bromodomains in BRD4 simultaneously. AZD5153 treatment markedly affects transcriptional programs of MYC, E2F, and mTOR. Of note, mTOR pathway modulation is associated with cell line sensitivity to AZD5153.

Cell Assay: Apoptosis was analyzed by flow cytometry using CellEvent Caspase 3/7 Green detection reagent. MV-4-11, MM.1S, and K562 cells were pretreated with AZD5153 or I-BET762 for 48 hours in culture media. Cells were collected and stained with 5 μmol/L final concentration of CellEvent for 30 minutes at 37°C. Flow cytometry was done on a BD Fortessa using the Blue laser and FITC filter set.