306 | Nature | Vol 578 | 13 February 2020
Article
Selective inhibition of the BD2
bromodomain of BET proteins in prostate
cancer
Emily J. Faivre^1 , Keith F. McDaniel^1 , Daniel H. Albert^1 , Srinivasa R. Mantena^2 , Joshua P. Plotnik^1 ,
Denise Wilcox^1 , Lu Zhang^1 , Mai H. Bui^1 , George S. Sheppard^1 , Le Wang^1 , Vasudha Sehgal^1 ,
Xiaoyu Lin^1 , Xiaoli Huang^1 , Xin Lu^1 , Tamar Uziel^1 , Paul Hessler^1 , Lloyd T. Lam^1 , Richard J. Bellin^1 ,
Gaurav Mehta^1 , Steve Fidanze^1 , John K. Pratt^1 , Dachun Liu^1 , Lisa A. Hasvold^1 , Chaohong Sun^1 ,
Sanjay C. Panchal^1 , John J. Nicolette^2 , Stacey L. Fossey^2 , Chang H. Park^1 ,
Kenton Longenecker^1 , Lance Bigelow^1 , Maricel Torrent^1 , Saul H. Rosenberg^1 , Warren M. Kati^1 &
Yu Shen^1 *Proteins of the bromodomain and extra-terminal (BET) domain family are epigenetic
readers that bind acetylated histones through their bromodomains to regulate gene
transcription. Dual-bromodomain BET inhibitors (DbBi) that bind with similar
affinities to the first (BD1) and second (BD2) bromodomains of BRD2, BRD3, BRD4 and
BRDt have displayed modest clinical activity in monotherapy cancer trials. A reduced
number of thrombocytes in the blood (thrombocytopenia) as well as symptoms of
gastrointestinal toxicity are dose-limiting adverse events for some types of DbBi^1 –^5.
Given that similar haematological and gastrointestinal defects were observed after
genetic silencing of Brd4 in mice^6 , the platelet and gastrointestinal toxicities may
represent on-target activities associated with BET inhibition. The two individual
bromodomains in BET family proteins may have distinct functions^7 –^9 and different
cellular phenotypes after pharmacological inhibition of one or both bromodomains
have been reported^10 ,^11 , suggesting that selectively targeting one of the
bromodomains may result in a different efficacy and tolerability profile compared
with DbBi. Available compounds that are selective to individual domains lack
sufficient potency and the pharmacokinetics properties that are required for in vivo
efficacy and tolerability assessment^10 –^13. Here we carried out a medicinal chemistry
campaign that led to the discovery of ABBV-744, a highly potent and selective inhibitor
of the BD2 domain of BET family proteins with drug-like properties. In contrast to the
broad range of cell growth inhibition induced by DbBi, the antiproliferative activity of
ABBV-744 was largely, but not exclusively, restricted to cell lines of acute myeloid
leukaemia and prostate cancer that expressed the full-length androgen receptor (AR).
ABBV-744 retained robust activity in prostate cancer xenografts, and showed fewer
platelet and gastrointestinal toxicities than the DbBi ABBV-075^14. Analyses of RNA
expression and chromatin immunoprecipitation followed by sequencing revealed
that ABBV-744 displaced BRD4 from AR-containing super-enhancers and inhibited
AR-dependent transcription, with less impact on global transcription compared with
ABBV-075. These results underscore the potential value of selectively targeting the
BD2 domain of BET family proteins for cancer therapy.Analysis of historical time-resolved fluorescence resonance energy
transfer (TR-FRET) data from approximately 2,500 compounds from
our DbBi program identified ethyl amide 1 , with a modest 17× selectivity
for the BD2 of BRD4 compared with the BD1 of BRD4. Although activity
against the BD2 of BRD4 for compound 1 (1.2 nM) was not improved
compared with the DbBi ABBV-075 (1.3 nM), activity against the BD1 of
BRD4 was reduced compared with ABBV-075 (22 nM for 1 , 2.8 nM for
ABBV-075). Replacement of the 2,4-difluorophenyl moiety of 1 with a
2,6-dimethylphenyl ether further impaired BD1 activity, resulting in the
110× BD2-selective pyrrolopyridone 2 (124 nM and 1.1 nM for BD1 andhttps://doi.org/10.1038/s41586-020-1930-8
Received: 26 July 2018
Accepted: 25 November 2019
Published online: 22 January 2020
(^1) Oncology Discovery, AbbVie, North Chicago, IL, USA. (^2) Preclinical Safety, Development Sciences, AbbVie, North Chicago, IL, USA. *e-mail: [email protected]