Efficacy and safety of zuranolone co-initiated with an antidepressant in adults with major depressive disorder: results from the phase 3 CORAL study.

Major depressive disorder (MDD) is a mental health disorder that can cause disability and functional impairment that standard-of-care (SOC) antidepressant therapies (ADTs) can take weeks to treat. Zuranolone is a neuroactive steroid and positive allosteric modulator of synaptic and extrasynaptic γ-aminobutyric acid (GABA) type A receptors approved as an oral, once-daily, 14-day treatment course in adults with postpartum depression and under investigation in adults with MDD. The phase 3 CORAL Study (NCT04476030) evaluated the efficacy and safety of zuranolone 50 mg co-initiated with SOC ADT (zuranolone+ADT) vs placebo co-initiated with SOC ADT (placebo+ADT) in adults with MDD. Patients were randomized 1:1 to once-daily, blinded zuranolone+ADT or placebo+ADT for 14 days, then continued open-label SOC ADT for 28 more days. The primary endpoint was change from baseline (CFB) in the 17-item Hamilton Rating Scale for Depression (HAMD-17) total score at Day 3. Among 425 patients in the full analysis set, CFB in HAMD-17 total score at Day 3 was significantly improved with zuranolone+ADT vs placebo+ADT (least squares mean [standard error], -8.9 [0.39] vs -7.0 [0.38]; p = 0.0004). The majority of patients receiving zuranolone+ADT that experienced treatment-emergent adverse events (TEAEs) reported mild or moderate events. The most common TEAEs present in ≥10% of patients in either zuranolone+ADT or placebo+ADT groups were somnolence, dizziness, headache, and nausea. These results demonstrate that zuranolone+ADT provided more rapid improvement in depressive symptoms compared with placebo+ADT in patients with MDD, with a safety profile consistent with previous studies. Clinical trial registration: ClinicalTrials.gov identifier: NCT04476030.

RGS9-2 modulates D2 dopamine receptor-mediated Ca2+ channel inhibition in rat striatal cholinergic interneurons.

Regulator of G protein signaling (RGS) proteins negatively regulate receptor-mediated second messenger responses by enhancing the GTPase activity of Galpha subunits. We describe a receptor-specific role for an RGS protein at the level of an individual brain neuron. RGS9-2 and Gbeta(5) mRNA and protein complexes were detected in striatal cholinergic and gamma-aminobutyric acidergic neurons. Dialysis of cholinergic neurons with RGS9 constructs enhanced basal Ca(2+) channel currents and reduced D(2) dopamine receptor modulation of Cav2.2 channels. These constructs did not alter M(2) muscarinic receptor modulation of Cav2.2 currents in the same neuron. The noncatalytic DEP-GGL domain of RGS9 antagonized endogenous RGS9-2 activity, enhancing D(2) receptor modulation of Ca(2+) currents. In vitro, RGS9 constructs accelerated GTPase activity, in agreement with electrophysiological measurements, and did so more effectively at Go than Gi. These results implicate RGS9-2 as a specific regulator of dopamine receptor-mediated signaling in the striatum and identify a role for GAP activity modulation by the DEP-GGL domain.

Insights into G protein structure, function, and regulation.

In multicellular organisms from Caenorhabditis elegans to Homo sapiens, the maintenance of homeostasis is dependent on the continual flow and processing of information through a complex network of cells. Moreover, in order for the organism to respond to an ever-changing environment, intercellular signals must be transduced, amplified, and ultimately converted to the appropriate physiological response. The resolution of the molecular events underlying signal response and integration forms the basis of the signal transduction field of research. An evolutionarily highly conserved group of molecules known as heterotrimeric guanine nucleotide-binding proteins (G proteins) are key determinants of the specificity and temporal characteristics of many signaling processes and are the topic of this review. Numerous hormones, neurotransmitters, chemokines, local mediators, and sensory stimuli exert their effects on cells by binding to heptahelical membrane receptors coupled to heterotrimeric G proteins. These highly specialized transducers can modulate the activity of multiple signaling pathways leading to diverse biological responses. In vivo, specific combinations of G alpha- and G beta gamma-subunits are likely required for connecting individual receptors to signaling pathways. The structural determinants of receptor-G protein-effector specificity are not completely understood and, in addition to involving interaction domains of these primary acting proteins, also require the participation of scaffolding and regulatory proteins.

Closely related G-protein-coupled receptors use multiple and distinct domains on G-protein alpha-subunits for selective coupling.

The molecular basis of selectivity in G-protein receptor coupling has been explored by comparing the abilities of G-protein heterotrimers containing chimeric Galpha subunits, comprised of various regions of Gi1alpha, Gtalpha, and Gqalpha, to stabilize the high affinity agonist binding state of serotonin, adenosine, and muscarinic receptors. The data indicate that multiple and distinct determinants of selectivity exist for individual receptors. While the A1 adenosine receptor does not distinguish between Gi1alpha and Gtalpha sequences, the 5-HT1A and 5-HT1B serotonin and M2 muscarinic receptors can couple with Gi1 but not Gt. It is possible to distinguish domains that eliminate coupling and are defined as "critical," from those that impair coupling and are defined as "important." Domains within the N terminus, alpha4-helix, and alpha4-helix-alpha4/beta6-loop of Gi1alpha are involved in 5-HT and M2 receptor interactions. Chimeric Gi1alpha/Gqalpha subunits verify the critical role of the Galpha C terminus in receptor coupling, however, the individual receptors differ in the C-terminal amino acids required for coupling. Furthermore, the EC50 for interactions with Gi1 differ among the individual receptors. These results suggest that coupling selectivity ultimately involves subtle and cooperative interactions among various domains on both the G-protein and the associated receptor as well as the G-protein concentration.

Dissecting receptor-G protein specificity using G alpha chimeras.

In conclusion, by taking advantage of the overall sequence homology and structural similarity of G alpha subunits, functional chimeric G alpha subunits can be generated and used as tools for the identification of sequence-specific factors that mediate receptor: G protein specificity. The [35S]GTP gamma S binding assay and the affinity shift activity assay are two sensitive biochemical approaches that can be used to assess receptor: G protein coupling in vitro. These in vitro assays limit confounding influences from cellular proteins and allow for the strict control of receptor: G protein ratios.