Discovery of RNA Editing Inhibitors for Neurological Disorders

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 389; p. 535
• Main Authors: Sodhi, Monsheel, Buck, Tristram G., Nwabuisi-Heath, Evelyn, Broni, Emmanuel, Bebla, Kristeen, Miller, Whelton
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.06.2024
• ISSN: 0022-3565
• DOI: 10.1124/jpet.535.128001

Abstract ID 128001 Poster Board 535 Suicide is an escalating medical problem that is strongly associated with depression and similar mood disorders. Suicide occurs every 14 minutes in the United States. A growing body of data indicates that RNA editing is increased in the brains of patients with MDD who die by suicide. This RNA editing process is catalyzed by enzymes called Adenosine Deaminases Acting on RNAs or ‘ADARs’, and our previous work reveals increased expression of one of these enzymes, ADAR1, in the dorsolateral prefrontal cortex (DLPFC) of MDD suicide (MDD-S) subjects. ADAR-mediated RNA editing in the mammalian brain has a profound effect on glutamatergic and serotoninergic transmission, which are both implicated in the pathophysiology of depression. We now present the results of analyses of ADAR expression and RNA editing in the DLPFC in a large cohort of postmortem MDD subjects. ADAR activity was measured by analyzing the levels of RNA editing of the AMPA receptor subunit, GluA2. GluA2 RNA editing was increased in major depressive suicide cases (n = 48) compared with controls (F1,72=12.26, p=0.001). GluA2 editing was correlated with ADAR2 but not ADAR1 expression in the control subjects (Pearson coefficient=0.67, n = 34, p < 0.00002). Our results indicate that the GluA2 subunit of the AMPA receptor, which gates the AMPA receptor ion channel, has greater levels of RNA editing at the R/G site in major depression and in major depressive subjects who died by suicide. Preclinical studies in rodents reveal that mice with reduced expression and activity of ADAR2 exhibit behaviors similar to mice that are treated with antidepressant drugs. These data indicate that RNA editing may be a novel target for the development of antidepressant drugs. We have applied two strategies to identify small molecules: in silico molecular docking of a compound library to ADAR2 catalytic and RNA binding sites, complemented by high throughput screening (HTS) of compound libraries. The in silico analysis applied consensus scoring to rank potential ADAR2 inhibitors after performing molecular docking with AutoDock Vina and Glide (Maestro), using a library of 35,161 compounds obtained from traditional Chinese medicine. A total of 47 compounds were predicted to have strong binding affinities for the human ADAR2 protein with insignificant levels of toxicity. Molecular dynamics (MD) simulations, including the molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) procedure, also emphasized the binding of these shortlisted compounds. In a complementary analysis we performed a preliminary HTS screen using an in vitro assay of ADAR2 activity that we have developed. The assay had a Z score>0.5. Using this assay, we identified 20 compounds that inhibit ADAR2 from the Prestwick library (1200 compounds) of FDA approved drugs. Some of these compounds also passed an in silico screen using molecular docking methods. In conclusion, very few compounds have been discovered that inhibit RNA editing. Screening chemical libraries will provide novel molecular probes for mechanistic investigations of this process in cell culture. Furthermore, these compounds will be critical for future investigations in animal models that recapitulate some features of behavioral dysfunction identified in suicides with MDD. Moreover, modulation of the RNA editing of glutamate receptors is a novel alternative to directly targeting of AMPA glutamate receptors for the treatment of mood disorders.