Bioisosteric approach to the discovery of imidazo[1,2-a]pyrazines as potent Aurora kinase inhibitors.

Our continued effort toward the development of the imidazo[1,2-a]pyrazine scaffold as Aurora kinase inhibitors is described. Bioisosteric approach was applied to optimize the 8-position of the core. Several new potent Aurora A/B dual inhibitors, such as 25k and 25l, were identified.

Discovery of orally bioavailable imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors.

We report a series of potent imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors. Optimization of the solvent accessible 8-position led to improvements in both oral bioavailability and off-target kinase inhibition. Compound 25 demonstrates anti-tumor activity in an A2780 ovarian tumor xenograft model.

ProBDNF induces neuronal apoptosis via activation of a receptor complex of p75NTR and sortilin.

Brain-derived neurotrophic factor (BDNF) is best characterized for critical roles in neuronal survival, differentiation, and synaptic modulation mediated by the TrkB receptor tyrosine kinase. Developmentally regulated death signaling by BDNF has also been demonstrated via activation of p75NTR. Because recent studies suggest that proNGF, the precursor form of NGF, is more active than mature NGF in inducing apoptosis after binding to p75NTR and a coreceptor, sortilin, we asked whether the precursor of BDNF (proBDNF) is also a proapoptotic ligand in the nervous system. proBDNF is secreted by cultured neurons, and recombinant proBDNF binds to sortilin. In sympathetic neurons coexpressing sortilin and p75NTR, we found that proBDNF is an apoptotic ligand that induces death at subnanomolar concentrations. In contrast, mature BDNF, but not proBDNF, is effective in inducing TrkB phosphorylation. proBDNF effects are dependent on cellular coexpression of both p75NTR and sortilin, because neurons deficient in p75NTR are resistant to proBDNF-induced apoptosis, and competitive antagonists of sortilin block sympathetic neuron death. Moreover, addition of preformed complexes of soluble sortilin and proBDNF failed to induce apoptosis of cells coexpressing both sortilin and p75NTR, suggesting that interaction of proBDNF with both receptors on the cell surface is required to initiate cell death. Together with our past findings, these data suggest that the neurotrophin family is capable of modulating diverse biological processes via differential processing of the proneurotrophins.

SCH 1473759, a novel Aurora inhibitor, demonstrates enhanced anti-tumor activity in combination with taxanes and KSP inhibitors.

PURPOSE: Aurora kinases are required for orderly progression of cells through mitosis, and inhibition of these kinases by siRNA or small molecule inhibitors results in cell death. We previously reported the synthesis of SCH 1473759, a novel sub-nanomolar Aurora A/B inhibitor. METHODS: We utilized SCH 1473759 and a panel of tumor cell lines and xenograft models to gain knowledge about optimal dosing schedule and chemotherapeutic combinations for Aurora A/B inhibitors. RESULTS: SCH 1473759 was active against a large panel of tumor cell lines from different tissue origin and genetic backgrounds. Asynchronous cells required 24-h exposure to SCH 1473759 for maximal induction of >4 N DNA content and inhibition of cell growth. However, following taxane- or KSP inhibitor-induced mitotic arrest, less than 4-h exposure induced >4 N DNA content. This finding correlated with the ability of SCH 1473759 to accelerate exit from mitosis in response to taxane- and KSP inhibitor-induced arrest. We tested various dosing schedules in vivo and demonstrated SCH 1473759 dose- and schedule-dependent anti-tumor activity in four human tumor xenograft models. Further, the efficacy was enhanced in combination with taxanes and found to be most efficacious when SCH 1473759 was dosed 12-h post-taxane treatment. CONCLUSIONS: SCH 1473759 demonstrated potent mechanism-based activity, and activity was shown to be enhanced in combination with taxanes and KSP inhibitors. This information may be useful for optimizing the clinical efficacy of Aurora inhibitors.

Aurora kinase inhibitors based on the imidazo[1,2-a]pyrazine core: fluorine and deuterium incorporation improve oral absorption and exposure.

Aurora kinases are cell cycle regulated serine/threonine kinases that have been linked to cancer. Compound 1 was identified as a potent Aurora inhibitor but lacked oral bioavailability. Optimization of 1 led to the discovery of a series of fluoroamine and deuterated analogues, exemplified by compound 25, with an improved pharmacokinetic profile. We found that blocking oxidative metabolism at the benzylic position and decreasing the basicity of the amine are important to obtaining compounds with good biological profiles and oral bioavailability.

SCH 2047069, a novel oral kinesin spindle protein inhibitor, shows single-agent antitumor activity and enhances the efficacy of chemotherapeutics.

Kinesin spindle protein (KSP) is a mitotic kinesin required for the formation of the bipolar mitotic spindle, and inhibition of this motor protein results in mitotic arrest and cell death. KSP inhibitors show preclinical antitumor activity and are currently undergoing testing in clinical trials. These agents have been dosed intravenously using various dosing schedules. We sought to identify a KSP inhibitor that could be delivered orally and thus provide convenience of dosing as well as the ability to achieve more continuous exposure via the use of dose-dense administration. We discovered SCH 2047069, a potent KSP inhibitor with oral bioavailability across species and the ability to cross the blood-brain barrier. The compound induces mitotic arrest characterized by a monaster spindle and is associated with an increase in histone H3 and mitotic protein monoclonal 2 phosphorylation both in vitro and in vivo. SCH 2047069 showed antitumor activity in a variety of preclinical models as a single agent and in combination with paclitaxel, gemcitabine, or vincristine.

Discovery of a Potent, Injectable Inhibitor of Aurora Kinases Based on the Imidazo-[1,2-a]-Pyrazine Core.

The imidazo-[1,2-a]-pyrazine (1) is a dual inhibitor of Aurora kinases A and B with modest cell potency (IC50 = 250 nM) and low solubility (5 µM). Lead optimization guided by the binding mode led to the acyclic amino alcohol 12k (SCH 1473759), which is a picomolar inhibitor of Aurora kinases (TdF K d Aur A = 0.02 nM and Aur B = 0.03 nM) with improved cell potency (phos-HH3 inhibition IC50 = 25 nM) and intrinsic aqueous solubility (11.4 mM). It also demonstrated efficacy and target engagement in human tumor xenograft mouse models.