Our paper is the result of a fruitful collaboration between the research group led by Fernanda Laezza at the University of Texas Medical Branch (USA) and the HTS Screening Core at Texas A&M Houston, led by Dr. Clifford Stephan. The Laezza lab studies cellular and molecular mechanisms by which the voltage-gated Na+ (Nav) channel is regulated by cellular signaling pathways through protein:protein interactions, including the fibroblast growth factor 14 (FGF14), an accessory protein that controls biophysical properties and functional activity of the channel and has been linked to a variety of CNS disorders.
Voltage-gated Na+ channels underlie the electrical communication between neurons in the brain, and conditions that change the properties of these channels, such as how often they open or close, can give rise to neuropsychiatric disorders. In previous studies we showed that the Nav1.6 complex is regulated by serine/threonine kinases such as GSK3, but we have recently become interested in whether this complex could be subject to tyrosine kinase regulation. In the CNS, tyrosine kinases are a central node of homeostatic plasticity; as the underlying mechanisms of how homeostatic plasticity are not completely understood, we reasoned that tyrosine kinase pathways may affect neuronal excitability through regulation of the Nav channel and FGF14.
So, we sought to develop an assay that would enable us to investigate how the FGF14:Nav1.6 complex is regulated by kinase signaling pathways, and to determine whether known drugs that target these pathways might affect this complex. Assay development for an in-cell assay can be a very long road, starting from creating a stable cell line all the way through plate miniaturization (96- to 384-well plates) and parameter optimization (volumes, reagents, concentrations), not to mention troubleshooting when things go wrong (and they do). That said, our assay optimization process paid off – we screened a small chemical library of FDA-approved cancer drugs to assess the reproducibility and robustness of our assay, but as a side product it also produced some very interesting results. When we explored the top scoring compounds, or “hits,” from this test library and found that many of them had effects that could be realistic to the true biology in the CNS based off of existing data, we had to follow up with them.
Figure 1. Overview of our in-cell screening platform and initial results, as well as potential mechanisms for how lestaurtinib may affect neuronal excitability.
The top validated hit lestaurtinib, a tyrosine kinase inhibitor that targets JAK2, FLT3, and Trk receptors, is the most potent inhibitor (IC50 = 0.95 μM) of the FGF14:Nav1.6 interaction that we have identified to date. There are currently 14 ongoing or completed clinical trials using lestaurtinib for the treatment of various cancers including myelofibrosis, leukemia, prostate cancer, and neuroblastoma. These results indicate that this FDA-approved drug might be of interest for CNS activity in diseases characterized by dysfunction of Trk receptor signaling. Our results suggest not only that tyrosine kinases do in fact play a key role in controlling the Nav channel complex, but also that lestaurtinib could potentially be repurposed toward channelopathies and other CNS diseases characterized by dysfunction of neuronal excitability mediated by Nav channels.
Overall, the results we present show that lestaurtinib, as well as other drugs that are already FDA-approved and show blood-brain barrier permeability, may have a significant impact on the interaction between FGF14 and Nav1.6, which could result in changes in neuronal excitability in vivo. These exciting results have propelled us onward as we proceed through the next stages of our campaign, with the intent of using our newly optimized assay for larger, more comprehensive CNS drug discovery studies and uncovering key neuronal signaling pathways.
Paul A. Wadsworth & Fernanda Laezza
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