Mitigation of off-target adrenergic binding and effects on cardiovascular function in the discovery of novel ribosomal S6 kinase 2 inhibitors.

We previously reported the discovery of a novel ribosomal S6 kinase 2 (RSK2) inhibitor, (R)-5-Methyl-1-oxo-2,3,4,5-tetrahydro-1H-[1,4]diazepino[1,2-a] indole-8-carboxylic acid [1-(3-dimethylamino-propyl)-1H-benzoimidazol-2-yl]-amide (BIX 02565), with high potency (IC(50) = 1.1 nM) targeted for the treatment of heart failure. In the present study, we report that despite nanomolar potency at the target, BIX 02565 elicits off-target binding at multiple adrenergic receptor subtypes that are important in the control of vascular tone and cardiac function. To elucidate in vivo the functional consequence of receptor binding, we characterized the cardiovascular (CV) profile of the compound in an anesthetized rat CV screen and telemetry-instrumented conscious rats. Infusion of BIX 02565 (1, 3, and 10 mg/kg) in the rat CV screen resulted in a precipitous decrease in both mean arterial pressure (MAP; to -65 ± 6 mm Hg below baseline) and heart rate (-93 ± 13 beats/min). In telemetry-instrumented rats, BIX 02565 (30, 100, and 300 mg/kg p.o. QD for 4 days) elicited concentration-dependent decreases in MAP after each dose (to -39 ± 4 mm Hg on day 4 at T(max)); analysis by Demming regression demonstrated strong correlation independent of route of administration and influence of anesthesia. Because of pronounced off-target effects of BIX 02565 on cardiovascular function, a high-throughput selectivity screen at adrenergic α(1A) and α(2A) was performed for 30 additional RSK2 inhibitors in a novel chemical series; a wide range of adrenergic binding was achieved (0-92% inhibition), allowing for differentiation within the series. Eleven lead compounds with differential binding were advanced to the rat CV screen for in vivo profiling. This led to the identification of potent RSK2 inhibitors (cellular IC(50) <0.14 nM) without relevant α(1A) and α(2A) inhibition and no adverse cardiovascular effects in vivo.

5-Aminomethylbenzimidazoles as potent ITK antagonists.

Benzamide 1 demonstrated good potency as a selective ITK inhibitor, however the amide moiety was found to be hydrolytically labile in vivo, resulting in low oral exposure and the generation of mutagenic aromatic amine metabolites. Replacing the benzamide with a benzylamine linker not only addressed the toxicity issue, but also improved the cellular and functional potency as well as the drug-like properties. SAR studies around the benzylamines and the identification of 10n and 10o as excellent tools for proof-of-concept studies are described.

Discovery of potent inhibitors of interleukin-2 inducible T-cell kinase (ITK) through structure-based drug design.

Interleukin-2 inducible T-cell kinase (ITK) is a member of the Tec kinase family and is involved with T-cell activation and proliferation. Due to its critical role in acting as a modulator of T-cells, ITK inhibitors could provide a novel route to anti-inflammatory therapy. This work describes the discovery of ITK inhibitors through structure-based design where high-resolution crystal structural information was used to optimize interactions within the kinase specificity pocket of the enzyme to improve both potency and selectivity.

2-Aminobenzimidazoles as potent ITK antagonists: trans-stilbene-like moieties targeting the kinase specificity pocket.

Based on the information from molecular modeling and X-ray crystal structures, the kinase specificity pocket of ITK could be occupied upon extension of the right-hand-side of the 2-benzimidazole core of the inhibitors. 2-Aminobenzimidazoles with a trans-stilbene-like extension were designed and synthesized as novel ITK antagonists. Significant improvement on binding affinity and cellular activity were obtained through the trans-stilbene-like antagonists. Several compounds showed inhibitory activity in an IL-2 functional assay.

Identification of pharmacological inhibitors of the MEK5/ERK5 pathway.

We have identified two novel MEK5 inhibitors, BIX02188 and BIX02189, which inhibited catalytic function of purified, MEK5 enzyme. The MEK5 inhibitors blocked phosphorylation of ERK5, without affecting phosphorylation of ERK1/2 in sorbitol-stimulated HeLa cells. The compounds also inhibited transcriptional activation of MEF2C, a downstream substrate of the MEK5/ERK5 signaling cascade, in a cellular trans-reporter assay system. These inhibitors offer novel pharmacological tools to better characterize the role of the MEK5/ERK5 pathway in various biological systems.