Bromodomain protein 4 (BRD4), a member of the bromodomain and extra-terminal domain (BET) protein family, binds to acetylated histone tails via its two bromodomains BD1 and BD2. It forms a complex with the positive transcription elongation factor b which controls phosphorylation of RNA polymerase II, ultimately leading to stimulation of transcription elongation. An essential role of BRD4 in cell proliferation and cancer growth has been reported in several recent studies.

The benzodiazepine JQ-1 is a strong antagonist of the binding of BRD4 to acetylated histone tails and has been used to elucidate the functions of the BET protein family members. JQ-1 is active in vivo in several therapeutic models but reveals a poor pharmacokinetic profile with high clearance and low oral bioavailability in animal studies. We investigated the benzodiazepine core of JQ-1 with the aim of optimization of oral bioavailability. Several possible core variations were identified that kept overall cellular activity but increased metabolic stability. The benzazepine BAY6356 was selected as a potent BET inhibitor with an improved overall pharmacokinetic profile and oral bioavailability between 60 and 100% in mouse, rat and dog. The strong antiproliferative activity observed in vitro in acute myeloid leukemia (AML) and multiple myeloma (MM) cell lines was confirmed in vivo in the MOLM-13 (AML) and MOLP-8 (MM) tumor models implanted in SCID mice. Daily oral treatment at the Maximal Tolerated Dose of 30 mg/kg led to strong tumor reduction in MOLM-13 (17% T/C on day 13 post tumor implantation) and in MOLP-8 (4% T/C on day 19 post tumor implantation) xenografts (T/C≤ 40% = active, T/C≤10% = highly active, according to NCI criteria). In the MOLM-13 model, c-Myc down-regulation was shown in vivo. Furthermore, for a same total dose, intermittent dosing every other day or twice a week in the MOLP-8 model proved to be as active as daily dosing, demonstrating exposure-driven efficacy. These favorable preclinical data support the evaluation of BAY6356 for further development.

Citation Format: Norbert Schmees, Bernard Haendler, Pascale Lejeune, Antje Stresemann, Roland Neuhaus, Stephan Siegel, Amaury Ernesto Fernandez-Montalvan, Hilmar Weinmann, Volker Gekeler. New benzazepine BET-inhibitors with improved oral bioavailability. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4749. doi:10.1158/1538-7445.AM2014-4749