The Binding of Palonosetron and Other Antiemetic Drugs to the Serotonin 5-HT3 Receptor.

Inaccurately perceived as niche drugs, antiemetics are key elements of cancer treatment alleviating the most dreaded side effect of chemotherapy. Serotonin 5-HT3 receptor antagonists are the most commonly prescribed class of drugs to control chemotherapy-induced nausea and vomiting. These antagonists have been clinically successful drugs since the 1980s, yet our understanding of how they operate at the molecular level has been hampered by the difficulty of obtaining structures of drug-receptor complexes. Here, we report the cryoelectron microscopy structure of the palonosetron-bound 5-HT3 receptor. We investigate the binding of palonosetron, granisetron, dolasetron, ondansetron, and cilansetron using molecular dynamics, covering the whole set of antagonists used in clinical practice. The structural and computational results yield detailed atomic insight into the binding modes of the drugs. In light of our data, we establish a comprehensive framework underlying the inhibition mechanism by the -setron drug family.

Natural Negative Allosteric Modulators of 5-HT3 Receptors.

Chemotherapy-induced nausea and vomiting (CINV) remain the most common and devastating side-effects associated with cancer chemotherapy. In recent decades, several lines of research emphasize the importance of 5-hydroxytryptamine3 (5-HT3; serotonin) receptors in the pathogenesis and treatment of CINV. 5-HT3 receptors are members of ligand-gated ion channels that mediate the rapid and transient membrane-depolarizing effect of 5-HT in the central and peripheral nervous system. These receptors play important roles in nausea and vomiting, as well as regulation of peristalsis and pain transmission. The development of antagonists for 5-HT3 receptor dramatically improved the treatment of CINV in cancer patients. In fact, the most common use of 5-HT3 receptor antagonists to date is the treatment of nausea and vomiting. In recent years, there has been an increasing tendency to use natural plant products as important therapeutic entities in the treatment of various diseases. In this article, we examined the results of earlier studies on the actions of natural compounds on the functional properties of 5-HT3 receptors. It is likely that these natural modulators of 5-HT3 receptors can be employed as lead structures for the synthesis of therapeutic agents for treating CINV in future clinical studies.

Compatibility and Stability of VARUBI (Rolapitant) Injectable Emulsion Admixed with Intravenous Granisetron Hydrochloride.

Prophylaxis or therapy with a combination of a neurokinin 1 (NK-1) receptor antagonist (RA), a 5-hydroxytryptamine- 3 (5-HT3) RA, and dexamethasone is recommended by international antiemesis guidelines for the prevention of chemotherapy-induced nausea and vomiting for patients receiving highly emetogenic chemotherapy and for select patients receiving moderately emetogenic chemotherapy. VARUBI (rolapitant) is a substance P/NK-1 RA that was recently approved by the U.S. Food and Drug Administration as an injectable emulsion in combination with other antiemetic agents in adults for the prevention of delayed nausea and vomiting associated with initial and repeat courses of emetogenic cancer chemotherapy, including, but not limited to, highly emetogenic chemotherapy. Granisetron Hydrochloride Injection USP is one of the 5-HT3 RAs indicated for the prevention of nausea and/or vomiting associated with initial and repeat courses of emetogenic cancer therapy, including high-dose cisplatin. Herein, we describe the physical and chemical compatibility and stability of VARUBI (rolapitant) injectable emulsion (166.5 mg/92.5 mL [1.8 mg/mL], equivalent to 185 mg of rolapitant hydrochloride) admixed with Granisetron Hydrochloride Injection USP (1.0 mg/mL, equivalent to 1.12 mg/mL hydrochloride). Binary admixtures of VARUBI injectable emulsion and Granisetron Hydrochloride Injection USP were prepared and stored in VARUBI ready-to-use glass vials and in four types of commonly used intravenous administration (tubing) sets. Evaluation of the physical and chemical compatibility and stability of the admixtures in the VARUBI ready-to-use vials stored at room temperature (20°C to 25°C) under fluorescent light and under refrigeration (2°C to 8°C protected from light) was conducted at 0, 1, 6, 24, and 48 hours, and that of the admixtures in the intravenous tubing sets was evaluated at 0, 2, and 6 hours of storage at 20°C to 25°C. Physical stability was evaluated by visual examination of the container contents under normal room light, and measurement of turbidity, globule size, and particulate matter. Chemical stability was assessed by measuring the pH of the admixture and determining drug concentrations (potency) and impurity levels by high-performance liquid chromatographic analysis. The pH, turbidity, globule size, and particulate matter of all samples remained within narrow and acceptable ranges at all study time points, indicating that combining the two formulations into a binary admixture is physically and chemically compatible and stable. VARUBI injectable emulsion admixed with Granisetron Hydrochloride Injection USP demonstrated compatibility and stability in a ready-to-use glass vial for at least 24 hours at room temperature and 48 hours under refrigeration, as well as in the four intravenous tubing sets for at least 6 hours at 20°C to 25°C. No decrease of drug concentration (or potency) of any admixed components occurred in the samples stored at the two conditions and time periods studied based on high-performance liquid chromatographic analysis. The levels of impurities stayed below the safety limits set by International Conference on Harmonisation during the study period.

Compatibility and Stability of VARUBI (Rolapitant) Injectable Emulsion Admixed with Intravenous Palonosetron Hydrochloride Injection and Dexamethasone Sodium Phosphate Injection.

Prophylaxis or therapy with a combination of a neurokinin 1 (NK-1) receptor antagonist (RA), a 5-hydroxytryptamine-3 (5-HT3) RA, and dexamethasone is recommended by international antiemesis guidelines for the prevention of chemotherapy-induced nausea and vomiting for patients receiving highly emetogenic chemotherapy and for selected patients receiving moderately emetogenic chemotherapy. VARUBI (rolapitant) is a substance P/NK-1 RA that was recently approved by the U.S. Food and Drug Administration as an injectable emulsion in combination with other antiemetic agents in adults for the prevention of delayed nausea and vomiting associated with initial and repeat courses of emetogenic cancer chemotherapy, including, but not limited to, highly emetogenic chemotherapy. Palonosetron is one of the 5-HT3 RAs indicated for the prevention of nausea and/or vomiting associated with initial and repeat courses of emetogenic cancer therapy, including high-dose cisplatin. Herein, we describe the physical and chemical compatibility and stability of VARUBI injectable emulsion (166.5 mg/92.5 mL [1.8 mg/mL, free base], equivalent to 185 mg of rolapitant hydrochloride) admixed with palonosetron injection 0.25 mg free base in 5 mL (equivalent to 0.28 mg hydrochloride salt) and with either 5 mL (20 mg) or 2.5 mL (10 mg) of dexamethasone sodium phosphate. Admixtures were prepared and stored in VARUBI injectable emulsion ready-to-use glass vials as supplied by the rolapitant manufacturer and in four types of commonly used intravenous administration (tubing) sets. Assessment of the physical and chemical compatibility and stability of the admixtures in the VARUBI ready-to-use vials stored at room temperature (20°C to 25°C) under fluorescent light and under refrigeration (2°C to 8°C protected from light) was conducted at 0, 1, 6, 24, and 48 hours, and that of the admixtures in the intravenous tubing sets was evaluated at 0, 2, and 6 hours of storage at 20°C to 25°C. Physical stability was evaluated by visual examination of the container contents under normal room light, and measurement of turbidity, globule size, and particulate matter. Chemical stability was assessed by measuring the pH of the admixture and determining drug concentrations (potency) and impurity levels by high-performance liquid chromatographic analysis. All samples were physically and chemically compatible throughout the study duration. The pH, turbidity, globule size, and particulate matter of the admixture stayed within narrow and acceptable ranges. VARUBI injectable emulsion admixed with intravenous palonosetron and dexamethasone was chemically and physically stable in the ready-to-use glass vials for at least 24 hours at room temperature and 48 hours under refrigeration, as well as in the four selected intravenous tubing sets for at least 6 hours at room temperature. No decrease of drug concentration (or potency) of any admixed components occurred in the samples stored at the two temperature ranges and time periods studied as measured by high-performance liquid chromatographic analysis.

Superagonist, Full Agonist, Partial Agonist, and Antagonist Actions of Arylguanidines at 5-Hydroxytryptamine-3 (5-HT3) Subunit A Receptors.

Introduction of minor variations to the substitution pattern of arylguanidine 5-hydroxytryptamine-3 (5-HT3) receptor ligands resulted in a broad spectrum of functionally-active ligands from antagonist to superagonist. For example, (i) introduction of an additional Cl-substituent(s) to our lead full agonist N-(3-chlorophenyl)guanidine (mCPG, 2; efficacy % = 106) yielded superagonists 7-9 (efficacy % = 186, 139, and 129, respectively), (ii) a positional isomer of 2, p-Cl analog 11, displayed partial agonist actions (efficacy % = 12), and (iii) replacing the halogen atom at the meta or para position with an electron donating OCH3 group or a stronger electron withdrawing (i.e., CF3) group resulted in antagonists 13-16. We posit based on combined mutagenesis, crystallographic, and computational analyses that for the 5-HT3 receptor, the arylguanidines that are better able to simultaneously engage the primary and complementary subunits, thus keeping them in close proximity, have greater agonist character while those that are deficient in this ability are antagonists.

Effects of ramosetron oral disintegrating tablets on gastric emptying: crossover study using the 13C-acetic acid breath test.

BACKGROUND/AIMS: Ramosetron is a new selective 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist that reportedly has more potent antiemetic effects than other 5-HT3 receptor antagonists. The aim of this study was to determine the effect of ramosetron pretreatment on gastric emptying using the 13C-acetic acid breath test. METHODOLOGY: Ten healthy male and female volunteers participated in this randomized, twoway crossover study. After they had fasted overnight, the subjects were randomly assigned to receive 0.1 mg ramosetron 1 hour before ingestion of a test meal (200 kcal per 200 mL, containing 100 mg 13C acetate) or to receive the test meal alone. Under both conditions, breath samples were collected for 150 min following ingestion of the meal. Statistical comparison of the parameters between the two test conditions was performed. RESULTS: No significant differences in the calculated parameters, including T 1/2, T lag, GEC or ß and κ, were observed between the two test conditions. CONCLUSIONS: The present study revealed that 0.1 mg ramosetron had no significant effect on the rate of gastric emptying. Thus, our results suggest that ramosetron can be administered safely, without gastrointestinal adverse effects, even to terminal cancer patients with delayed or accelerated gastric emptying abnormality.

Compatibility of intravenous fosaprepitant with intravenous 5-HT3 antagonists and corticosteroids.

PURPOSE: Fosaprepitant dimeglumine for injection is the water-soluble phosphorylated prodrug of the neurokinin-1 receptor antagonist aprepitant. Both agents are approved (in combination with a 5-HT3 antagonist and a corticosteroid) for prevention of chemotherapy-induced nausea and vomiting. Because fosaprepitant is likely to be combined and stored in the same intravenous (IV) bag with 5-HT3 antagonists and corticosteroids, the in vitro compatibility of fosaprepitant with these agents and other IV diluents was assessed. METHODS: Fosaprepitant (1 mg/mL in 0.9 % sodium chloride injection solution) was combined in binary or tertiary fashion with therapeutic-dose preparations of a 5-HT3 antagonist (ondansetron, granisetron, palonosetron, or tropisetron) and/or a corticosteroid (dexamethasone sodium phosphate or methylprednisolone sodium succinate). For diluent compatibility assessment, fosaprepitant was also prepared 1 mg/mL in 0.9 % sodium chloride injection solution, water for injection, or 5 % dextrose injection solution. After 24-h storage under ambient conditions, samples were assayed for degradation. RESULTS: Fosaprepitant demonstrated compatibility when combined in the same IV infusion bag with common 5-HT3 antagonists and corticosteroids for storage and IV coadministration, with the exception of palonosetron (incompatible under all experimental conditions) and tropisetron (incompatible unless combined with a corticosteroid). No incompatibility was observed between fosaprepitant and any of the 3 diluents tested. CONCLUSIONS: Use of fosaprepitant in combination with other antiemetics may provide a flexible option for administration of antiemetics to patients receiving moderately or highly emetogenic chemotherapy.

Formulation and in vivo evaluation of ondansetron orally disintegrating tablets using different superdisintegrants.

The aim of this study was to formulate cost effective taste-masked orally disintegrating tablets of ondansetron, a bitter drug using different superdisintegrants by a wet granulation technique. Microcrystalline cellulose (Avicel) as a diluent and disintegrant in addition to aspartame as a sweetener were used in all formulations. The prepared tablets were evaluated for weight variation, thickness, hardness, friability, drug content, water content, in vitro disintegration time and in vitro drug release. The tablets' hardness was maintained in the range of 2-3 kg and friability was <1% for all batches. All tablet formulations disintegrated rapidly in vitro within 5.83 to 33.0 sec. The optimized formulation containing 15% Polyplasdone XL-10 released more than 90% of drug within 5 min and the release was comparable to that of a commercial product. In human volunteers, optimized formulation was found to have a pleasant taste and mouth feel and they disintegrated in the oral cavity within 12 sec. The stability results were also satisfactory. A pharmacokinetic study with the optimized formulation was performed in comparison with a reference (Zofer MD 8®) and they were found to be bioequivalent. In conclusion, a cost effective ondansetron orally disintegrating tablet was successfully prepared with acceptable hardness, desirable taste and rapid disintegration in the oral cavity.

Enantioselective determination of ondansetron and 8-hydroxyondansetron in human plasma from recovered surgery patients by liquid chromatography-tandem mass spectrometry.

A liquid chromatographic-mass spectrometric assay with atmospheric pressure chemical ionization for quantification of ondansetron and its main metabolite 8-hydroxyondansetron in human plasma was presented. The enantiomeric separation was achieved on a Chiralcel OD-R column containing cellulose tris-(3,5-dimethylphenylcarbamate). The validation data were within the required limits. The assay was successfully applied to authentic plasma samples. Quantitative results from postoperative patients receiving ondansetron demonstrated a great interindividual variability in postoperative plasma drug concentrations, the metabolites were not detected in their unconjugated form. A wide variation in the S-(+)-/R-(-)-ondansetron concentration ratio between 0.14 and 7.18 is indicative for a stereoselective disposition or metabolism. In further studies CYP2D6 and CYP3A4 genotype dependent metabolism of ondansetron enantiomers as well as of co-administered drugs and clinical efficacy of the medication should be tested.

5-HT3 antagonists under development.

IMPORTANCE OF THE FIELD: The main therapeutic area of 5-HT(3) receptor antagonists is the treatment of chemotherapy-induced nausea and vomiting (CINV), which is the most common and distressing side effects of anticancer treatment. The second major clinical application of 5-HT(3) receptor antagonists is in the treatment of irritable bowel syndrome (IBS). 5-HT(3) antagonists have been widely used and found to decrease gut transit, increase fluid absorption and reduce pain. The uses of 5-HT(3) antagonists are expending to treatment of CNS diseases such as anxiety and sleep disorders as antipsychotics and so on. AREAS COVERED IN THIS REVIEW: The structures, in vitro activities, in vivo effects and some clinical data on 5-HT(3) receptor antagonists under development. WHAT THE READER WILL GAIN: Future research directions in 5-HT(3) antagonists based on the clinical trial data of the pipeline molecules. TAKE HOME MESSAGE: Most drug candidates in clinical trials were discovered in the early 1990s and their patent expiry is imminent. Acquiring intellectual properties of novel 5-HT(3) receptor antagonists with improved efficacies would provide a bright future. Particularly, as the current 5-HT(3) receptor antagonists are classified into only three representative structural families (one third are zacopride-like benzamides and the others are ondansteron-like tricyclic compounds and dolansetron-like bicyclic compounds), structurally diverse compound libraries need to be extensively investigated for identification of novel 5-HT(3) receptor antagonists.