Structure-guided optimization of small molecule c-Abl activators.

c-Abl kinase is maintained in its normal inactive state in the cell through an assembled, compact conformation. We describe two chemical series that bind to the myristoyl site of the c-Abl kinase domain and stimulate c-Abl activation. We hypothesize that these molecules activate c-Abl either by blocking the C-terminal helix from adopting a bent conformation that is critical for the formation of the autoinhibited conformation or by simply providing no stabilizing interactions to the bent conformation of this helix. Structure-based molecular modeling guided the optimization of binding and activation of c-Abl of these two chemical series and led to the discovery of c-Abl activators with nanomolar potency. The small molecule c-Abl activators reported herein could be used as molecular tools to investigate the biological functions of c-Abl and therapeutic implications of its activation.

Discovery and Development of TMPRSS6 Inhibitors Modulating Hepcidin Levels in Human Hepatocytes.

Iron overload disorders are characterized by the body's inability to regulate iron absorption and its storage which can lead to organ failures. Accumulated evidence has revealed that hepcidin, the master regulator of iron homeostasis, is negatively modulated by TMPRSS6 (matriptase-2), a liver-specific type II transmembrane serine protease (TTSP). Here, we report that treatment with a peptidomimetic inhibitor affecting TMPRSS6 activity increases hepcidin production in hepatic cells. Moreover, similar effects were observed when using non-peptidic inhibitors obtained through optimization of hits from high-throughput screening. Using HepG2 cells and human primary hepatocytes, we show that TMPRSS6 inhibitors block TMPRSS6-dependent hemojuvelin cleavage and increase HAMP expression and levels of secreted hepcidin.

Identification and Optimization of Novel Small c-Abl Kinase Activators Using Fragment and HTS Methodologies.

Abelson kinase (c-Abl) is a ubiquitously expressed, nonreceptor tyrosine kinase which plays a key role in cell differentiation and survival. It was hypothesized that transient activation of c-Abl kinase via displacement of the N-terminal autoinhibitory "myristoyl latch", may lead to an increased hematopoietic stem cell differentiation. This would increase the numbers of circulating neutrophils and so be an effective treatment for chemotherapy-induced neutropenia. This paper describes the discovery and optimization of a thiazole series of novel small molecule c-Abl activators, initially identified by a high throughput screening. Subsequently, a scaffold-hop, which exploited the improved physicochemical properties of a dihydropyrazole analogue, identified through fragment screening, delivered potent, soluble, cell-active c-Abl activators, which demonstrated the intracellular activation of c-Abl in vivo.

2-phenyl-4-piperazinylbenzimidazoles: orally active inhibitors of the gonadotropin releasing hormone (GnRH) receptor.

Antagonism of the gonadotropin releasing hormone (GnRH) receptor has shown positive clinical results in numerous reproductive tissue disorders such as endometriosis, prostate cancer and others. Traditional therapy has been limited to peptide agonists and antagonists. Recently, small molecule GnRH antagonists have emerged as potentially new treatments. This article describes the discovery of 2-phenyl-4-piperazinylbenzimidazoles as small molecule GnRH antagonists with nanomolar potency in in vitro binding and functional assays, excellent bioavailability (rat %F>70) and demonstrated oral activity in a rat model having shown significant serum leuteinizing hormone (LH) suppression.

Assay development and high-throughput screening of small molecular c-Abl kinase activators.

A 2-step kinase assay was developed and used in a high-throughput screen (HTS) of more than 1 million compounds in an effort to identify c-Abl tyrosine kinase activators. This assay employed a 2-step phosphorylation reaction: in the first step, purified recombinant c-Abl was activated by incubating with compound in the presence of adenosine triphosphate (ATP). In the second step, the TAMRA-labeled IMAP Abltide substrate was added to allow phosphorylation of the substrate to occur. The assay was calibrated such that inactive c-Abl protein was activated by ATP alone to a degree that it not only demonstrated a measurable c-Abl activity but also maintained a robust assay window for screening. The screen resulted in 8624 primary hits with >30% response. Further analysis showed that 1024 had EC(50) <10 µM with a max % response of >50%. These hits were structurally and chemically diverse with possibly different mechanisms for activating c-Abl. In addition, selective hits were shown to be cell permeable and were able to induce c-Abl activation as determined by In-Cell Western (ICW) analysis of HEK-MSRII cells transduced with BacMam virus expressing full-length c-Abl.

Discovery and characterization of a cell-permeable, small-molecule c-Abl kinase activator that binds to the myristoyl binding site.

c-Abl kinase activity is regulated by a unique mechanism involving the formation of an autoinhibited conformation in which the N-terminal myristoyl group binds intramolecularly to the myristoyl binding site on the kinase domain and induces the bending of the αI helix that creates a docking surface for the SH2 domain. Here, we report a small-molecule c-Abl activator, DPH, that displays potent enzymatic and cellular activity in stimulating c-Abl activation. Structural analyses indicate that DPH binds to the myristoyl binding site and prevents the formation of the bent conformation of the αI helix through steric hindrance, a mode of action distinct from the previously identified allosteric c-Abl inhibitor, GNF-2, that also binds to the myristoyl binding site. DPH represents the first cell-permeable, small-molecule tool compound for c-Abl activation.