Exploiting a Water Network to Achieve Enthalpy-driven, Bromodomain-selective BET Inhibitors

Shadrick WR, et al., 26(1):25-36, Bioorg Med Chem, 2018

The Bromodomain and Extra-Terminal domain family (BET) of proteins are potential therapeutic targets in a wide range of diseases including oncology, auto-immune disease, heart failure, and male contraception. The BET family of proteins comprises of BRD2, BRD3, BRD4, and BRDT, which are distinguished by the presence of two tandem bromodomains (BD1 and BD2). All BRDs have four alpha-helices that are tethered together by two loop regions (ZA and BC) of variable length and sequence. Described herein is the design and synthesis of a congeneric series 2- and 3-heteroaryl substituted tetrahydroquinolines (THQs) in order to exploit various water networks in the ZA channel of bromodomains to achieve enthalpy-driven, bromodomain-selective BET inhibitors. Binding affinity of each compound to both BRD2 bromodomains (BRD2-BD1 and BRD2-BD2) was investigated by Surface Plasmon Resonance (SPR) using a Pall ForteBio Pioneer instrument equipped with a HisCap sensor chip. The HisCap sensor surface was activated with nickel ions. Poly-His tagged BRD2 constructs were immobilized onto sensor chip surface by capture-coupling, a hybrid method of capture and amine coupling chemistry. Each compound was prepared in running buffer as a 3-fold dilution series and were injected in duplicate at each concentration. The SPR data obtained were processed and globally fitted to a 1:1 binding model. The kinetic rate constants (ka and kd) and the equilibrium dissociation constants (KD) were determined for all binding interactions. Overall results of this investigation suggest that the optimization of BD2-selective compounds has great implications for the development of promising clinical candidates.

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