Pharmacological Characterization of the Imipridone Anticancer Drug ONC201 Reveals a Negative Allosteric Mechanism of Action at the D2 Dopamine Receptor.

ONC201 is a first-in-class imipridone compound that is in clinical trials for the treatment of high-grade gliomas and other advanced cancers. Recent studies identified that ONC201 antagonizes D2-like dopamine receptors at therapeutically relevant concentrations. In the current study, characterization of ONC201 using radioligand binding and multiple functional assays revealed that it was a full antagonist of the D2 and D3 receptors (D2R and D3R) with low micromolar potencies, similar to its potency for antiproliferative effects. Curve-shift experiments using D2R-mediated ß-arrestin recruitment and cAMP assays revealed that ONC201 exhibited a mixed form of antagonism. An operational model of allostery was used to analyze these data, which suggested that the predominant modulatory effect of ONC201 was on dopamine efficacy with little to no effect on dopamine affinity. To investigate how ONC201 binds to the D2R, we employed scanning mutagenesis coupled with a D2R-mediated calcium efflux assay. Eight residues were identified as being important for ONC201's functional antagonism of the D2R. Mutation of these residues followed by assessing ONC201 antagonism in multiple signaling assays highlighted specific residues involved in ONC201 binding. Together with computational modeling and simulation studies, our results suggest that ONC201 interacts with the D2R in a bitopic manner where the imipridone core of the molecule protrudes into the orthosteric binding site, but does not compete with dopamine, whereas a secondary phenyl ring engages an allosteric binding pocket that may be associated with negative modulation of receptor activity. SIGNIFICANCE STATEMENT: ONC201 is a novel antagonist of the D2 dopamine receptor with demonstrated efficacy in the treatment of various cancers, especially high-grade glioma. This study demonstrates that ONC201 antagonizes the D2 receptor with novel bitopic and negative allosteric mechanisms of action, which may explain its high selectivity and some of its clinical anticancer properties that are distinct from other D2 receptor antagonists widely used for the treatment of schizophrenia and other neuropsychiatric disorders.

Trends in Blunt Splenic Injury Management: The Rise of Splenic Artery Embolization.

INTRODUCTION: Splenic injury is common in blunt trauma. We sought to evaluate the injury characteristics and outcomes of BSI admitted over a 10-y period to an academic trauma center. METHODS: A retrospective review of adult blunt splenic injury patients admitted between January 2009 and September 2018. RESULTS: The 423 patients meeting inclusion criteria were divided by management: Observational (OBS, n = 261), splenic surgery (n = 114 including 4 splenorrhaphy patients), SAE (n = 43), and multiple treatment modalities (3 had SAE followed by surgery and 2 OBS patients underwent splenic surgery at readmission). The most common mechanism of injury was motor vehicle collision (47.8%). The median ISS (OBS 17, SAE 22, Surgery 34) and spleen AIS (OBS 2, SAE 3, Surgery 4) were significantly different.  Complication rates (OBS 21.8%, SAE 9.3%, Surgery 45.6%) rates were significantly different, but mortality (OBS 7.3%, SAE 2.3%, Surgery 13.2%), discharge to home and readmission rates were not. Additional abdominal injuries were identified in 26.3% of the surgery group and 2.7% of OBS group. SAE rate increased from 3.0% to 28%; median spleen AIS remained 2-3. Thirty-five patients expired; 28 had severe head, chest, and/or extremity injuries (AIS ≥4). CONCLUSION: SAE rates increased over time. Splenorrhaphy rates were low. SAE was associated with relatively low rates of mortality and complications in appropriately selected patients.

Dopamine D4 Receptor-Selective Compounds Reveal Structure-Activity Relationships that Engender Agonist Efficacy.

The dopamine D4 receptor (D4R) plays important roles in cognition, attention, and decision making. Novel D4R-selective ligands have promise in medication development for neuropsychiatric conditions, including Alzheimer's disease and substance use disorders. To identify new D4R-selective ligands, and to understand the molecular determinants of agonist efficacy at D4R, we report a series of eighteen novel ligands based on the classical D4R agonist A-412997 (1, 2-(4-(pyridin-2-yl)piperidin-1-yl)- N-( m-tolyl)acetamide). Compounds were profiled using radioligand binding displacement assays, ß-arrestin recruitment assays, cyclic AMP inhibition assays, and molecular dynamics computational modeling. We identified several novel D4R-selective ( Ki ≤ 4.3 nM and >100-fold vs other D2-like receptors) compounds with diverse partial agonist and antagonist profiles, falling into three structural groups. These compounds highlight receptor-ligand interactions that control efficacy at D2-like receptors and may provide insights into targeted drug discovery, leading to a better understanding of the role of D4Rs in neuropsychiatric disorders.