DOPAMINE ANTAGONISTS FOR NAUSEA AND VOMITING: SPECIAL CONSIDERATIONS

Male and female rats exhibit comparable gaping behavior but activate brain regions differently during expression of conditioned nausea

Twenty-five to fifty percent of patients undergoing chemotherapy will develop anticipatory nausea and vomiting (ANV), in which symptoms occur in anticipation of treatment. ANV is triggered by environmental cues and shows little response to traditional antiemetic therapy, suggesting that unique neural pathways mediate this response. Understanding the underlying neural mechanisms of this disorder is critical to the development of novel therapeutic interventions. The purpose of the present study was to identify brain areas activated during ANV and characterize sex differences in both the behavior and the brain areas activated during ANV. We used a rat model of ANV by pairing a novel context with the emetic drug lithium chloride (LiCl) to produce conditioned nausea behaviors in the LiCl-paired environment. We quantitated gaping, an analog of human vomiting, after acute or repeated LiCl in a unique environment. To identify brain regions associated with gaping, we measured c-fos activation by immunochemical staining after these same treatments. We found that acute LiCl activated multiple brain regions including the supraoptic nucleus of the hypothalamus, central nucleus of the amygdala, nucleus of the solitary tract and area postrema, none of which were activated during ANV. ANV activated c-fos expression in the frontal cortex, insula and paraventricular nucleus of the hypothalamus of males but not females. These data suggest that therapies such as ondansetron which target the area postrema are not effective in ANV because it is not activated during the ANV response. Further studies aimed at characterizing the neural circuits and cell types that are activated in the conditioned nausea response will help identify novel therapeutic targets for the treatment of this condition, improving both quality of life and outcomes for patients undergoing chemotherapy.

Preclinical Evaluation of the Effects of Trazpiroben (TAK-906), a Novel, Potent Dopamine D2/D3 Receptor Antagonist for the Management of Gastroparesis

Current therapies for gastroparesis, metoclopramide and domperidone, carry risks of extrapyramidal symptoms and life-threatening cardiac arrhythmias. Trazpiroben, a novel, potent dopamine D₂/D₃ receptor antagonist, has low brain permeation and very low affinity for human ether-à-go-go-related gene (hERG) channel inhibition, potentially improving on safety profiles of existing therapies. Trazpiroben demonstrated the following receptor affinities: high for D₂ and D_3, moderate for D₄ and minimal for D₁ and D₅ It demonstrated moderate affinity for adrenergic alpha 1B (α_1B) and 5-hydroxytryptamine 2A (5HT_2A) receptors and low potential for off-target adverse events (AEs). Trazpiroben potently inhibited dopamine-activated D_2L receptor activation of cognate G-proteins in human embryonic kidney 293 cell membranes and was a neutral D_2L receptor antagonist. In vivo, trazpiroben dose-dependently increased prolactin release in orally dosed rat (0.1-1mg/kg). Additionally, multiple oral doses in the rat (100mg/kg) and dog (50mg/kg) for 3 days produced robust plasma exposures and prolactin increases in both species. Trazpiroben inhibited retching/vomiting in the dog with apomorphine-induced emesis with a potency (0.1-1mg/kg) like that of trazpiroben-mediated prolactin increases in rat. Oral trazpiroben (1, 10, and 30mg/kg) did not affect rat rotarod performance, suggesting low brain penetration. Trazpiroben concentrations were low in cerebrospinal fluid versus plasma following multiple oral doses for 4 days in rat and dog. Trazpiroben weakly inhibited the hERG channel current (concentration causing half-maximal inhibition of control-specific binding of 15.6µM), indicating little potential for disrupting cardiac rhythm. Overall, trazpiroben is a potent D₂/D₃ receptor antagonist designed to avoid serious potential AEs associated with current gastroparesis therapies. Significance Statement Trazpiroben is a novel, potent dopamine D₂/D₃ selective receptor antagonist designed to avoid adverse effects associated with the current pharmacological therapies, metoclopramide and domperidone. Pre-clinical studies have demonstrated low brain penetration and weak affinity for the hERG channel, indicating that trazpiroben is not expected to be associated with central nervous system or cardiovascular safety issues. With these pharmacological properties, trazpiroben may represent a viable new treatment option for gastroparesis due to a potentially improved safety profile relative to existing therapies.

Repurposing the Antiemetic Metoclopramide as an Antiviral Against Dengue Virus Infection in Neuronal Cells

Dengue virus (DENV) is transmitted by Aedes mosquitoes to humans and is a threat worldwide. No effective new drugs have been used for anti-dengue treatment, and repurposing drugs is an alternative approach to treat this condition. Dopamine 2 receptor (D2R) is a host receptor positively associated with DENV infection. Metoclopramide (MCP), a D2R antagonist clinically used to control vomiting and nausea in patients with DENV infection, was putatively examined for inhibition of DENV infection by targeting D2R. In the mouse neural cell line Neuro-2a with D2R expression, a plaque assay demonstrated the antiviral efficacy of MCP treatment. However, in the cell line BHK-21, which did not express D2R, MCP treatment caused no further inhibition of DENV infection. Either MCP treatment or exogenous administration of a neutralizing D2R antibody blocked DENV binding. Treatment with MCP also reduced DENV dsRNA replication and DENV-induced neuronal cell cytotoxicity in vitro. An in vivo study demonstrated the antiviral effect of MCP against DENV-induced CNS neuropathy and mortality. These results showed that repurposing the D2R-targeting antiemetic MCP is a potential therapeutic strategy against DENV infection.