The 5-hydroxytryptamine receptor antagonists as antiemetics: preclinical evaluation and mechanism of action

Evaluation of Antiemetic Therapy for Hepatic Arterial Infusion Chemotherapy with Oxaliplatin, Fluorouracil, and Leucovorin

Purpose

Our aim was to compare the antiemetic efficacy of the triple combination of aprepitant, dolasetron and dexamethasone with the combination of dolasetron and dexamethasone for chemotherapy-induced nausea and vomiting (CINV) in hepatocellular carcinoma (HCC) patients receiving hepatic arterial infusion chemotherapy (HAIC) with oxaliplatin, fluorouracil and leucovorin (FOLFOX).

Patients and Methods

This was a retrospective study. In the dolasetron plus dexamethasone group (D group), the patients received dolasetron (100 mg, i.v., on day 1) and dexamethasone (10 mg, i.v., on day 1) 30 min before starting administration of chemotherapeutic drugs. In the aprepitant plus dolasetron and dexamethasone group (AD group), the patients received dolasetron and dexamethasone as described above, and aprepitant (125 mg, p.o.) on day 1 followed by 80 mg on days 2 and 3. The primary endpoint was the complete response rate (CR, defined as no emetic episodes and no rescue medication use) during the first cycle of hepatic arterial infusion chemotherapy.

Results

Between January 2018 and August 2019, 302 eligible patients were included: 197 in AD group and 105 in D group. Patients in AD group had significantly higher complete response rates than those in D group during the first cycle (85.8% vs 71.4%, P = 0.003) and all cycles (73.6% vs 49.5%, P<0.001). Patients in AD group had lower rescue therapy (1.5% vs 26.7%, P<0.001) and lower incidence of disruption related to chemotherapy-induced nausea and vomiting (0.5% vs 6.7%, P = 0.002) than patients in D group.

Conclusion

Aprepitant, dolasetron plus dexamethasone is more effective to prevent chemotherapy-induced nausea and vomiting in hepatocellular carcinoma patients treated with FOLFOX-HAIC therapy than dolasetron plus dexamethasone.

Cannabinoid 2 (CB2) receptor agonism reduces lithium chloride-induced vomiting in Suncus murinus and nausea-induced conditioned gaping in rats

We aimed to investigate the potential anti-emetic and anti-nausea properties of targeting the cannabinoid 2 (CB2) receptor. We investigated the effect of the selective CB2 agonist, HU-308, on lithium chloride- (LiCl) induced vomiting in Suncus murinus (S. murinus) and conditioned gaping (nausea-induced behaviour) in rats. Additionally, we determined whether these effects could be prevented by pretreatment with AM630 (a selective CB2 receptor antagonist/inverse agonist). In S. murinus, HU-308 (2.5, 5mg/kg, i.p.) reduced, but did not completely block, LiCl-induced vomiting; an effect that was prevented with AM630. In rats, HU-308 (5mg/kg, i.p.) suppressed, but did not completely block, LiCl-induced conditioned gaping to a flavour; an effect that was prevented by AM630. These findings are the first to demonstrate the ability of a selective CB2 receptor agonist to reduce nausea in animal models, indicating that targeting the CB2 receptor may be an effective strategy, devoid of psychoactive effects, for managing toxin-induced nausea and vomiting.

Endocannabinoid Mechanisms Influencing Nausea

One of the first recognized medical uses of Δ(9)-tetrahydrocannabinol was treatment of chemotherapy-induced nausea and vomiting. Although vomiting is well controlled with the currently available non-cannabinoid antiemetics, nausea continues to be a distressing side effect of chemotherapy and other disorders. Indeed, when nausea becomes conditionally elicited by the cues associated with chemotherapy treatment, known as anticipatory nausea (AN), currently available antiemetics are largely ineffective. Considerable evidence demonstrates that the endocannabinoid system regulates nausea in humans and other animals. In this review, we describe recent evidence suggesting that cannabinoids and manipulations that enhance the functioning of the natural endocannabinoid system are promising treatments for both acute nausea and AN.

Pharmacogenetics and individualizing drug treatment during pregnancy

Pharmacogenetics as a tool to aid clinicians implement individualized pharmacotherapy is utilized in some areas of medicine. Pharmacogenetics in pregnancy is still a developing field. However, there are several areas of obstetric therapeutics where data are emerging that give glimpses into future therapeutic possibilities. These include opioid pain management, antihypertensive therapy, antidepressant medications, preterm labor tocolytics, antenatal corticosteroids and drugs for nausea and vomiting of pregnancy, to name a few. More data are needed to populate the therapeutic models and to truly determine if pharmacogenetics will aid in individualizing pharmacotherapy in pregnancy. The objective of this review is to summarize current data and highlight research needs.

Regulation of nausea and vomiting by cannabinoids and the endocannabinoid system

Nausea and vomiting (emesis) are important elements in defensive or protective responses that animals use to avoid ingestion or digestion of potentially harmful substances. However, these neurally-mediated responses are at times manifested as symptoms of disease and they are frequently observed as side-effects of a variety of medications, notably those used to treat cancer. Cannabis has long been known to limit or prevent nausea and vomiting from a variety of causes. This has led to extensive investigations that have revealed an important role for cannabinoids and their receptors in the regulation of nausea and emesis. With the discovery of the endocannabinoid system, novel ways to regulate both nausea and vomiting have been discovered that involve the production of endogenous cannabinoids acting centrally. Here we review recent progress in understanding the regulation of nausea and vomiting by cannabinoids and the endocannabinoid system, and we discuss the potential to utilize the endocannabinoid system in the treatment of these frequently debilitating conditions.

Pharmacogenetic predictors of nausea and vomiting of pregnancy severity and response to antiemetic therapy: a pilot study

Background

Nausea and vomiting of pregnancy (NVP) is a common condition. The objective of this study was to evaluate the association between response to antiemetics in the treatment of NVP and genetic polymorphisms in the serotonin receptor subunit genes HTR3A and HTR3B.

Methods

Pregnant women ≥18 years of age with NVP starting antiemetic therapy with promethazine, prochlorperazine, metoclopramide, or ondansetron at ≤ 16 weeks gestational age were eligible. The study recruited 29 women with complete data and sampling who returned for their one week follow-up and were genotyped for HTR3A and HTR3B polymorphisms. Severity of NVP was captured (using Pregnancy Unique Quantification of Emesis (PUQE) and Quality of Life (QOL) tools) upon enrollment and after one week of antiemetic therapy. These measures were correlated with pharmacogenetic variability.

Results

Subjects with genotype associated with high serotonin affinity of the 5-HT_3B receptor (rs1176744, CC) required more antiemetic medications (p < 0.001) than other subjects. Those with genotypes associated with increased expression of the 5-HT_3A receptor subunit (rs1062613, CT or TT) had worse final PUQE scores (p = 0.01) than other subjects while rs3782025 variants carriers had significantly better initial (p = 0.02) and final (p = 0.02) PUQE scores than other subjects.

Conclusions

HTR3B and HTR3A gene variants may contribute to variability in response to antiemetic therapy for NVP.

Gingerol inhibits cisplatin-induced vomiting by down regulating 5-hydroxytryptamine, dopamine and substance P expression in minks

OBJECTIVE

To investigate the antiemetic effect of gingerol and its multi-targets effective mechanism on 5-hydroxytryptamine (5-HT), dopamine (DA) and substance P (SP). The antiemetic effect of gingerol was investigated on a vomiting model of mink induced by cisplatin (7.5 mg . kg(-1), i.p.) in 6 h observation. The levels of 5-HT, DA and distribution of substance P in the area postrema and ileum were measured by high performance liquid chromatography (HPLC) and immunohistochemistry respectively. The frequency of cisplatin induced retching and vomiting was significantly reduced by pretreatment with gingerol in a dose-dependent manner (P<0.05). Cisplatin produced a significant increase in 5-HT and DA levels in the area postrema and ileum of minks (P<0.05), and this increase was significantly inhibited by gingerol in a dose-dependent manner (P<0.05). Substance P-immunoreactive was mainly situated in the mucosa and submucosa of ileum as well as in the neurons of area postrema, and gingerol markedly suppressed the increase immunoreactivity of substance P induced by cisplatin in a dose-dependent manner (P<0.05). Gingerol has good activity against cisplatin-induced emesis in minks possibly by inhibiting central or peripheral increase of 5-HT, DA and substance P.

The antiemetic effect of a novel tropisetron patch in anticancer agents-induced kaolin pica model using rats

The efficacy of a novel transdermal patch containing tropisetron, a 5-hydroxytryptamine 3 (5-HT(3)) receptor antagonist, against emesis induced by anticancer agents were evaluated, in comparison with the effect of traditional tropisetron injection, in rats. The antiemetic effects were assessed via the inhibitory activity on the anticancer agent-induced kaolin-consuming behavior, a pica model representing vomiting in emesis-resistant rodents. The tropisetron patch (10mg/patch, 3.5cm(2)) was attached on the shaved back area of rats. Eight h later, each anticancer agent, cisplatin (10mg/kg, i.v.), cyclophosphamide (200mg/kg, i.p.) or doxorubicin (8mg/kg, i.v.), was administered, and thereafter, daily kaolin consumption was measured for 3 days. In comparison, the effect of daily injection of tropisetron (2mg/kg, i.v.), given 10min, 24 and 48h after the anticancer agent administration, was also evaluated. Kaolin intake greatly increased to 21, 17 and 10 folds of control ingestion on the first day after administration with the anticancer agents, cisplatin, cyclophosphamide and doxorubicin, respectively, and then gradually decreased to near control level on day 3. Such anticancer agent-induced increases in the kaolin consumption were remarkably attenuated by the attachment of tropisetron patch, resulting in the reduction to half levels, which is comparable to the efficacy of daily tropisetron injection. In particular, the blood concentration of tropisetron following patch attachment reached a maximum level of 30-40ng/ml in 12h and exhibited a plateau until detachment of the patch, in contrast to a rapid elimination with a half-life of 2.21h after injection of the drug. Taken together, it is suggested that the novel tropisetron patch could be a promising regimen for the relief of emesis, based on the long-term antiemetic effects on the diverse anticancer agents and the convenience to use the transdermal delivery system for the cancer patients who have difficulty in taking drugs due to surgical operation or gastrointestinal dysfunction.

Comparative Clinical Study of the Anti-Emetic Effects of Oral Ramosetron and Injected Granisetron in Patients With Malignant Glioma Undergoing ACNU Chemotherapy

The effectiveness of ramosetron tablets and granisetron injection was compared for reducing the frequency of nausea, vomiting, and anorexia in patients with malignant glioma undergoing ACNU chemotherapy. Patients with malignant glioma to be treated with ACNU chemotherapy were randomly assigned to receive oral ramosetron (20 patients) or intravenous granisetron (19 patients) prior to ACNU injection. Gastrointestinal toxicity within 48 hours of ACNU injection was compared to that in patients who had received ACNU chemotherapy with dopamine D2 receptor-blocker as a historical control group. Within 24 hours of the administration of ACNU, 15 of the 20 patients treated with ramosetron and 16 of the 19 treated with granisetron were nausea-free, and 14 of the former and 14 of the latter regained their normal appetite. There was no significant difference in the anti-emetic effects. Ten of the 17 controls experienced no vomiting within 6 hours of the injection of ACNU, five were nausea-free within 24 hours, and two retained their normal appetite within 24 hours. Oral ramosetron has the same anti-anorectic and anti-emetic effects as intravenous granisetron. Ramosetron tablets are less expensive and are easy to take, so should be on the list of first-choice anti-emetic drugs for patients treated with ACNU chemotherapy.

Pharmacological aspects of anticancer drug-induced emesis with emphasis on serotonin release and vagal nerve activity

Cytotoxic drug-induced nausea and vomiting are the side effects most feared by cancer patients. Emesis is an instinctive defense reaction caused by the somatoautonomic nerve reflex, which is integrated in the medulla oblongata. Emesis caused by cytotoxic drugs such as cisplatin is associated with an increase in the concentration of 5-hydroxytryptamine (5-HT) in the intestine and the brainstem. It is proposed that cytotoxic drugs evoke 5-HT release from the enterochromaffin (EC) cells in the intestinal mucosa and that the released 5-HT stimulates the 5-HT receptors on the adjacent vagal afferent nerves. The depolarization of the vagal afferent nerves stimulates the vomiting center in the brainstem and eventually induces a vomiting reflex. 5-HT released from EC cells seems to mediate the cisplatin-induced emesis sensitive to 5-HT(3) receptor antagonists. The release of 5-HT from the EC cells, however, is regulated by polymodal mechanisms on autoreceptors or heteroreceptors. The precise role of 5-HT on the occurrence of vomiting has not been fully elucidated. The present review aims to describe the role of 5-HT in anticancer drug-induced emesis from the viewpoint of 5-HT release and afferent vagus nerve activity. Various methods for predicting emesis are also evaluated.

Management of postoperative nausea and vomiting in ambulatory surgery

The management of PONV has improved significantly over the years but remains a frequent occurrence in postoperative patients. Evaluation of individual patient risk and the consideration for prophylactic antiemetic in high-risk populations should reduce these unpleasant symptoms and help direct appropriate clinical strategies. Treatment following failure of prophylactic antiemetic therapy requires knowledge of previously used antiemetics and the time of their administration.

Clinical evaluation of Ramosetron injections in the treatment of cisplatin-induced nausea and vomiting

A phase III, double-blind, placebo-controlled study was performed to examine the safety and efficacy of ramosetron in cancer patients with cisplatin-induced nausea/vomiting. Patients were divided into two groups: group R received 0.3 mg ramosetron intravenously and group P received placebo. Eighty-eight patients were enrolled, 44 in each group; 84 (43 in group R, 41 in group P) were included in the clinical efficacy analysis and 86 (44 in group R, 42 in group P) in the safety analysis. Ramosetron was significantly more clinically effective than placebo against nausea, vomiting and anorexia; 65.1% of patients in group R experienced no vomiting in the first 6 h of observation compared with 7.3% of those receiving placebo. No serious adverse reactions or significant differences in safety were observed between the groups. Based on these results, ramosetron injection is effective in the treatment of cisplatin-induced nausea/vomiting and its clinical usefulness is demonstrated here.

An orally active, water-soluble neurokinin-1 receptor antagonist suitable for both intravenous and oral clinical administration

1-(5-[[(2R,3S)-2-([(1R)-1-[3,5-Bis(trifluoromethyl)phenyl]ethyl]oxy)-3-(4-fluorophenyl)morpholin-4-yl]methyl]-2H-1,2,3-triazol-4-yl)-N,N-dimethylmethanamine hydrochloride 3 is a high affinity, orally active, h-NK(1) receptor antagonist with a long central duration of action and a solubility in water of >100 mg/mL. The construction of the 5-dimethylaminomethyl 1,2,3-triazol-4-yl unit, which incorporates the solubilizing group of 3, was accomplished by thermal rearrangement of a propargylic azide in the presence of dimethylamine. Compound 3 is highly effective in pre-clinical tests that are relevant to clinical efficacy in emesis and depression.

Mucoadhesive suppositories of ramosetron hydrochloride utilizing Carbopol

Suppositories are the preferable dosage form for patients at home or experiencing nausea. Serotonin (5-HT(3))-receptor antagonists are used to treat vomiting in intravenous or oral administration but not suppository form. Ramosetron hydrochloride (RAM) is a new 5-HT(3) antagonist which effectively inhibits vomiting, and we prepared RAM suppositories using Witepsol((R)) H-15 (H-15) containing Carbopol((R)) 934P (CP). The viscosity of suppository base and RAM release properties from suppositories were examined. Plasma RAM concentrations after administration of suppositories to rabbits were estimated and irritation of rectal tissues were observed. Antiemetic effects of suppositories were studied using ferrets. The base viscosity increased with addition of CP. Suppositories containing CP exhibited better absorption in rabbits compared to H-15 suppositories, correlated with release behavior. Suppositories containing 2% CP had 2.5 times larger AUC(0-24 h) than H-15 suppositories, and the MRT was prolonged by 5.8 h compared with i.v. administration. 10% CP suppositories administered to rabbits for 5 days did not irritate the tissues. Antiemetic studies indicated that 2% CP suppository of RAM might have the same effect as i.v. administration. These results suggest that RAM suppositories containing CP are safe and useful in once-a-day dosage form for treatment of chemotherapy-induced nausea.

Serotonin receptor antagonists in prophylaxis of acute and delayed emesis induced by moderately emetogenic, single-day chemotherapy: a randomized study

In this randomized study, the efficacy of a single dose of three serotonin antagonists were compared in prophylaxis of acute and delayed vomiting induced by moderately emetogenic, single-day chemotherapy in chemotherapy-naïve patients. A total of 54 patients were entered. Eighteen patients received ondansetron, 17 received tropisetron, and 19 received granisetron. Antiemetics were administered as 15-minute intravenous infusion before chemotherapy. Complete control of acute vomiting was achieved in 38.8% with ondansetron, 58.8% with tropisetron, and 73.7% with granisetron. Major response rates were 83.3%, 82.3%, and 89.5%, respectively. For the delayed control of emesis, complete control of delayed vomiting was achieved in 38.8% with ondansetron, 52.9% with tropisetron, and 73.7% with granisetron. The major response rates were 71.8%, 70.5%, and 100%, respectively. The adverse effects were rare and mild in all groups. The authors conclude that there may be clinically important differences among serotonin antagonists used for chemotherapy-induced emesis.

GR205171 blocks apomorphine and amphetamine-induced conditioned taste aversions

The tachykinin NK1 receptor antagonist, GR205171 ([2-methoxy-5-(5-trifluoromethyl-tetrazol-1-yl)-benzyl]-(2S-phenyl -piperidin-3S-yl)-amine), is a potent inhibitor of emesis induced by a wide variety of emetogens. This is in contrast to 5-HT3 (5-hydroxytryptamine3) receptor antagonists, such as ondansetron, which have a more restricted antiemetic profile. The present study evaluated the efficacy of GR205171, in comparison with ondansetron to block the acquisition of a conditioned taste aversion induced by either apomorphine (0.25 mg kg(-1) s.c.) or by amphetamine (0.5 mg kg(-1) s.c.) in rats. Pretreatment with GR205171 (0.1-1.0 mg kg(-1) s.c.) and ondansetron (0.001-0.1 mg kg(-1) s.c.) produced a dose-dependent blockade of conditioned taste aversions evoked by apomorphine. In contrast, the acquisition of conditioned taste aversions induced by amphetamine was inhibited by GR205171 (0.3-0.5 mg kg(-1) s.c.), but only attenuated by ondansetron (0.001-0.1 mg kg(-1) s.c.). These results suggest that tachykinin NK1 receptor antagonists may have potential in the treatment of drug-induced conditioned aversive behaviour and nausea.

Absolute bioavailability and electroencephalographic effects of conventional and extended-release formulations of venlafaxine in healthy subjects

Venlafaxine is currently marketed for treatment of depressive disorders as a conventional tablet formulation with a twice or three times daily dosage regimen. The absolute bioavailability of the conventional (CF) and extended-release (XR) formulations and their effects on electroencephalograms (EEG) and on a visual analog scale (VAS) for nausea were assessed in a randomized, double-blind, four-way crossover, placebo-controlled study of 16 healthy young men who were given either a single oral dose of 50 mg of CF venlafaxine, 75 mg of XR venlafaxine, or an intravenous dose of 10 mg of venlafaxine, or a placebo at 1-week intervals. The absolute bioavailability of venlafaxine was between 40% and 45% and was similar for both the CF and XR formulations. Venlafaxine produced central effects of a desipramine-like antidepressant. Regardless of formulation tested, the main EEG changes were an increase in fast beta (20-30 Hz) energy, which was more pronounced over the frontotemporal regions and extended within the full beta range (16-40 Hz). Maximum effect was reached at 6 hours for the CF and reached a plateau from 10 to 24 hours for the XR formulation. A dose-proportional increase in central activity, expressed as area under the effect curve (AUE) of the beta band, was observed between the CF (50 mg) and XR (75 mg) formulations. Compared with the CF tablet, the XR formulation also produced a much less intense maximum effect and a decrease of 63% in the AUE of nausea normalized by dose. The XR formulation has the same absolute bioavailability and the same central activity as assessed by EEG, but produced less intensive nausea than CF venlafaxine. The present findings suggest that a once-daily dosage regimen should be sufficient. This was confirmed by several clinical trials in depressive patients.

A comparative study of intravenous granisetron versus intravenous and oral ondansetron in the prevention of nausea and vomiting associated with moderately emetogenic chemotherapy

We conducted a prospective, randomized, open, single-center, parallel group study comparing the anti-emetic efficacy and toxicity of granisetron with that of ondansetron in patients receiving moderately emetogenic chemotherapy. From December 1994 to May 1995, patients who were to receive moderately emetogenic chemotherapy for the first time or who had not received chemotherapy (80 to 100 mg/m2 of cisplatin or 40 mg/m2 of doxorubicin) within 4 weeks previously were enrolled in this study. The following anti-emetic regimens were used: 3 mg of granisetron were given intravenously before chemotherapy for a single dose; 8 mg of ondansetron were given intravenously before chemotherapy and then every 8 hours for a total of 3 doses, plus 8 mg of an oral maintenance dose every 12 hours for 5 consecutive days. We evaluated 97 patients (48 received granisetron and 49 received ondansetron). In the first 24 hours after chemotherapy, complete and major responses were achieved in 76.6% of the patients receiving granisetron and in 72.9% of patients receiving ondansetron (p = 0.9033). Additionally, there was no difference in the control of delayed nausea and vomiting between the two groups (51.1% versus 54.2%, p = 0.9200), and there were no significant adverse effects or toxicities. We have concluded that a single dose of granisetron is as effective in prophylaxis of emesis induced by moderately emetogenic chemotherapy as a triple dose of ondansetron plus oral maintenance.

In vitro and in vivo predictors of the anti-emetic activity of tachykinin NK1 receptor antagonists

The ability of tachykinin NK1 receptor antagonists to inhibit GR73632 (D-Ala-[L-Pro9,Me-Leu8]substance P-(7-11))-induced foot tapping in gerbils was employed as an indirect measure of brain penetration and this was compared with their ability to prevent acute emesis induced by cisplatin in ferrets. (+)-GR203040 ((2S,3S and 2R,3R)-2-methoxy-5-tetrazol-1-yl-benzyl-(2-phenyl-piperidin- 3-yl)-amine), CP-99,994 ((2S,3S)-cis-3-(2-methoxybenzylamino)-2-phenyl piperidine) dihydrochloride), and L-742,694 (2-(S)-(3,5-bis(trifluoromethyl)benzyloxy)-3-(S)-phenyl-4-(5-(3-oxo-1,2, 4-triazolo)methylmorpholine) potently inhibited GR73632-induced foot tapping (ID50 < or = 0.85 mg/kg), and acute retching induced by cisplatin (ID50 < or = 0.18 mg/kg). RPR100893 ((3aS,4S,7aS)-7,7-diphenyl-4-(2-methoxyphenyl)-2-[(S)-2-(2-m ethoxyphenyl)proprionyl] perhydroisoindol-4-ol) was not a potent antagonist of retching (ID50 4.1 mg/kg) or foot tapping (ID50 > 10 mg/kg). High doses (3-10 mg/kg) of CGP49823 ((2R,4S)-2-benzyl-1-(3,5-dimethylbenzoyl)-N-[(4-quinolinyl)methyl] -4-piperineamine) dihydrochloride), FK888 (N2-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl)carbonyl-L-propyl]-N-methy l-N-phenylmethyl-L-3-(2-naphthyl)-alaninamide), and LY303870 ((R)-1-[N-(2-methoxybenzyl)acetylamino]-3-(1H-indol-3-yl)-2-[N-(2-(4-(pi peridinyl)piperidin-1-yl)acetyl)amino]propane) were required to inhibit foot tapping; these agents were not anti-emetic in this dose range. SR140333 ((S)-1-[2-[3-(3,4-dichlorphenyl)-1 (3-isopropoxyphenylacetyl)piperidin-3-yl] ethyl]-4-phenyl-1 azaniabicyclo [2.2.2]octane; 3-10 mg/kg) failed to inhibit foot tapping or emesis. Affinities for the human and ferret tachykinin NK1 receptor were highly correlated (r = 0.93, P = 0.0008). Inhibition of foot tapping in gerbils, but not NK1 receptor binding affinity, predicted anti-emetic activity in ferrets (r = 0.75, P < 0.01). These findings confirm that the anti-emetic activity of tachykinin NK1 receptor antagonists is dependent on brain penetration.

Physiology of chemotherapy-induced emesis and antiemetic therapy. Predictive models for evaluation of new compounds

The physiology of emesis has been studied for several hundred years, focusing on the different centres involved and the mechanics of expulsion. The vomiting centre receives inputs from various emetic detectors such as the gut, the vestibular labyrinths and the chemoreceptor trigger zone. Emesis is a common disabling effect in motion sickness, postoperative conditions and in radio- and chemotherapy. Our current understanding of the mechanisms has been provided mainly by the recent introduction of serotonin 5-HT3 receptor antagonists into therapeutic use. Nevertheless, despite the considerable advances made in the understanding of the different pathways involved in emesis, there are number of areas that still require experimental investigation. Different animal and human models are available to study the physiology of emesis and to evaluate the antiemetic activity of new compounds, but they need to be predictors of clinical situations.

An overview of randomised studies comparing 5-HT3 receptor antagonists to conventional anti-emetics in the prophylaxis of acute chemotherapy-induced vomiting

Ten years after it was demonstrated in the ferret that cisplatin-induced emesis could be blocked by the selective 5-HT3 receptor antagonist MDL 72222, 5-HT3 receptor antagonists have become routine anti-emetic agents for chemotherapy-induced emesis. However, although in association with highly emetogenic, mainly cisplatin-containing regimens, the use of these agents is well justified, the net benefit of 5-HT3 receptor antagonists in association with moderately emetogenic regimens has not been that well clarified. Here, we present an overview of 30 randomised studies comparing 5-HT3 antagonists with the conventional anti-emetics in the prophylaxis of acute vomiting induced by cytotoxic chemotherapy. A meta-analysis showed that 5-HT3 antagonists reduce the risk of acute vomiting in comparison to conventional anti-emetics both with cisplatin treatments (15 trials; odds ratio 0.60; 95% confidence interval 0.51-0.70) and with moderately emetogenic treatments (11 trials; odds ratio 0.47; 95% confidence interval 0.39-0.58). The risk of acute vomiting seems to be further reduced when 5-HT3 antagonists are combined with dexamethasone.

Role of 5-hydroxytryptamine3 (5-HT3) antagonists in the prevention of emesis caused by anticancer therapy

Most anticancer drugs are cytotoxic and produce various side-effects, among which nausea and vomiting are almost ubiquitous and usually extremely distressing to the patient. Cancer chemotherapy elicits two main phases of vomiting: an intense, acute phase of vomiting that occurs almost immediately following anti-cancer therapy and a milder, delayed phase of nausea and vomiting of longer duration. The mechanisms underlying the induction of nausea and vomiting after cancer chemotherapy are poorly understood but may be mediated by serotonin (5-hydroxytryptamine or 5-HT), particularly in the acute phase. Serotonin activates 5-HT3 receptors, which function as ligand-gated ion channels located either in the periphery and/or in the central nervous system to produce emesis, among other effects. The peripheral 5-HT3 receptors may be pharmacologically distinct from the central 5-HT3 receptors and may exhibit some association with GTP-binding proteins. In addition, different populations may exist as distinct subtypes of the same receptor. The 5-HT3 receptor antagonist ondansetron (GR 38032F) is effective in preventing the emesis induced by cytotoxic agents currently used in the treatment of many forms of cancer. Ondansetron has, comparatively, a much higher efficacy in the treatment of acute emesis following cancer chemotherapy than it does in the delayed phase, suggesting that the late phase of emesis may be mediated by other distinct mechanisms.

Compounds possessing 5-HT3 receptor antagonistic activity inhibit intestinal propulsion in mice

The role of 5-HT3 receptors in the control of intestinal propulsive activity was investigated in mice by a simple method in which the time taken for excretion of the head of an orally administered non-absorbable marker (whole gut transit time) was measured. Selective 5-HT3 receptor antagonists ramosetron (YM060) at 0.01-0.3 mg/kg s. c. and ondansetron at 0.1-1 mg/kg s.c. dose-dependently prolonged the whole gut transit time. Prokinetic benzamides, such as renzapride (0.3-10 mg/kg s.c.), zacopride (0.01-0.3 mg/kg s.c.) and cisapride (0.1-3 mg/kg s.c.), which have been reported to possess 5-HT3 receptor blocking properties, also dose-dependently prolonged it. These results indicate that activation of 5-HT3 receptors seems to be one factor that underlies the physiological control of intestinal propulsive activity in mice. In contrast to their beneficial therapeutic effects on gastroduodenal dysmotility, prokinetic benzamides, at least those which have 5-HT3 receptor antagonistic activity, may be unsuitable in the treatment of impaired lower intestinal propulsive activity.

5-HT3 receptor blocking properties of the antiparkinsonian agent, talipexole

1. Talipexole showed moderate displacement activity of 3H-GR 65630 binding to 5-HT3 receptors in both rat cortical and intestinal membrane fractions with Ki values of 0.35 microM and 0.22 microM, respectively. 2. Bromocriptine failed to displace the binding activity in either experimental system even at a concentration of 10 microM. 3. Both talipexole and tropisetron were found to significantly inhibit 5-HT3 receptor-mediated effects of 5-HT in isolated guinea-pig ileum or atrium; however, the effect of talipexole was weaker than that of tropisetron. 4. Bromocriptine, in contrast, had no antagonistic effects on 5-HT3 receptor-mediated activity in guinea-pig ileum or atrium. 5. It was concluded that talipexole might act as an antagonist on 5-HT3 receptors in both brain and intestinal tissues.

Tachykinin NK1 receptor antagonists act centrally to inhibit emesis induced by the chemotherapeutic agent cisplatin in ferrets

These studies have compared the pharmacological profile of two non-peptide human type neurokinin1 (hNK1) receptor selective antagonists, L-741,671 and a quaternised compound L-743,310. In radioligand binding studies L-741,671 and L-743,310 had high affinity for ferret and cloned hNK1 receptors [Ki (nM) ferret 0.7 and 0.1; human 0.03 and 0.06, respectively] but low affinity for rodent NK1 receptors [Ki (nM) 64 and 17, respectively] suggesting that ferret receptors have hNK1-like binding pharmacology. Studies in vivo showed that L-741,671 and L-743,310 had equivalent functional activity in the periphery (ID50s of 1.6 and 2 micrograms/kg i.v., respectively) as measured by inhibition of plasma protein extravasation evoked in the oesophagus of guinea pigs by resiniferatoxin (7 nmol/kg i.v.). Using an in situ brain perfusion technique in anaesthetised rats, L-741,671 was shown to be much more brain penetrant than the quaternary compound L-743,310 which had an entry rate similar to the poorly brain penetrant plasma marker inulin. These compounds thus provided an opportunity to compare the anti-emetic effects of equi-active hNK1 receptor antagonists with and without brain penetration to central NK1 receptor sites. When tested against cisplatin-induced emesis in ferrets, L-741,671 (0.3, 1 and 3 mg/kg i.v.) produced marked dose-dependent inhibition of retching and vomiting but L-743,310 was inactive at 3 and 10 micrograms/kg i.v. In contrast, direct central injection of L-741,671 and L-743,310 (30 micrograms) into the vicinity of the nucleus tractus solitarius or L-743,310 (200 micrograms) intracisternally was shown to inhibit retching and vomiting induced by i.v. cisplatin. L-741,671 and L-743,310 had equivalent functional activity, at the same dose, against cisplatin-induced emesis when injected centrally. These observations indicated that had L-743,310 penetrated into the brain after systemic administration it would have been active in the cisplatin-induced emesis assay and so show that brain penetration is essential for the anti-emetic action of systemically administered NK1 receptor antagonists.

The interaction of dexamethasone with ondansetron on drug-induced emesis in the ferret

The potential of dexamethasone (0.5-20 mg/kg i.p.) to antagonize the emesis induced by cisplatin (10 mg/kg i.v.), apomorphine (0.25 mg/kg s.c.), morphine (0.5 mg/kg s.c.) and copper sulphate (100 mg/kg intragastric) was investigated alone and in combination with ondansetron in the ferret. There was a trend for dexamethasone 0.1-5 mg/kg to reduce cisplatin-induced emesis and for 0.05-2.5 mg/kg to delay the onset of apomorphine-induced emesis but doses of dexamethasone up to 20 mg/kg were without effect to modify morphine- or copper sulphate-induced emesis. The combination of dexamethasone 2.5 mg/kg with ondansetron 0.1 mg/kg did not have additive effects to reduce cisplatin-induced emesis but did reduce significantly the total numbers of episodes recorded. Ondansetron 1 mg/kg was without effect to modify apomorphine-, morphine- or copper sulphate-induced emesis but the combination pretreatment of ondansetron 1 mg/kg with dexamethasone 2.5 and 5 mg/kg reduced significantly apomorphine-induced retching. Data are discussed in terms of the antiemetic effectiveness of dexamethasone to antagonize chemotherapy-induced emesis in man.

Comparison of the antiemetic effects of a 5-HT1A agonist, LY228729, and 5-HT3 antagonists in the pigeon

Vomiting may be induced by a variety of agents such as drugs, oncolytics, and provocative motion, as well as being conditioned to occur to environmental stimuli. Such emesis has recently been shown to be blocked by agonists at the 5-HT1A subtype of serotonin receptor. The antiemetic effects of LY228729 [(-)-4-(dipropylamine)-1,3,4,5-tetrahydrobenz-(c,d)indole-6- carboxamide], a 5-HT1A receptor agonist, were tested and compared to the antiemetic effects of the 5-HT3 receptor antagonists ondansetron, tropisetron, and MDL 72222 (3-tropanyl-3,5-dichlorobenzoate). The emetic stimuli tested are known to be blocked by 5-HT3 antagonists in species other than the pigeon. In the pigeon, LY228729 totally abolished vomiting induced by fully emetic doses of cisplatin (10 mg/kg), ipecac (3 ml/kg), emetine (10 mg/kg), and a 5-HT3 agonist, m-(chlorophenyl)-biguanide (1.25 mg/kg). MDL 72222 blocked ipecac-induced vomiting in a dose-related manner and was partially effective in attenuating cisplatin-induced emesis. Ondansetron and tropisetron were partially effective in blocking emetine- and mCPBG-induced vomiting. Ondansetron exhibited an intrinsic emetic response that could not be blocked by MDL 7222, but which was eliminated by LY228729. It was concluded that 5-HT1A agonists are more effective in the pigeon than are 5-HT3 antagonists against these types of emetic stimuli. These results broaden the range of emetic stimuli that are blocked by 5-HT1A agonists in the pigeon.

Progress in reducing nausea and emesis. Comparisons of ondansetron (Zofran), granisetron (Kytril), and tropisetron (Navoban)

BACKGROUND

Nausea and vomiting are the most distressing side effects associated with the administration of chemotherapy for neoplastic diseases. Nausea, in particular, often had been ignored in studies of chemotherapy side effects. Recently, progress has been made in the control of chemotherapy-induced nausea and vomiting, due, in part, to a better understanding of the physiologic mechanisms involved.

METHODS

This paper reviews recent advances in the control of emesis, focusing on pharmacologic treatments.

RESULTS

The efficacy and safety of the serotonin (5-HT3) receptor antagonists granisetron, ondansetron, and tropisetron in the control of acute and delayed emesis and emesis induced by repeat-cycle chemotherapy are summarized. Although differences in study design and definitions of response criteria have made it difficult to compare the studies that have evaluated these three agents, the overall body of literature supports several clinical findings.

CONCLUSIONS

(1) The 5HT3 antiemetic agents have been shown to be clinically more effective in the control of nausea and emesis than previously used agents. (2) No one of the three has demonstrated consistently greater efficacy. (3) Efficacy appears to be more pronounced for cisplatin-containing regimens than for moderate or less emetogenic chemotherapy regimens. (4) Effectiveness of the 5HT3 agents appears to be less for delayed nausea and emesis than for acute symptoms. Potential control of anticipatory nausea and emesis has not been investigated. (5) Control over nausea appears to be significantly less than control over emesis. In the studies in which it has been measured, nausea control remains incomplete for approximately half the patients given 5HT3 agents. (6) The efficacy of the agents appears to diminish across repeated days and, perhaps, across repeated chemotherapy cycles. (7) The addition of a steroid such as dexamethasone increases the efficacy of both 5HT3 and other antiemetic agents. This effect also seems to apply to delayed nausea and emesis.

The interaction of RS 25259-197, a potent and selective antagonist, with 5-HT3 receptors, in vitro

1. A series of isoquinolines have been identified as 5-HT3 receptor antagonists. One of these, RS 25259-197 [(3aS)-2-[(S)-1-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro- 1- oxo-1H-benzo[de]isoquinoline-hydrochloride], has two chiral centres. The remaining three enantiomers are denoted as RS 25259-198 (R,R), RS 25233-197 (S,R) and RS 25233-198 (R,S). 2. At 5-HT3 receptors mediating contraction of guinea-pig isolated ileum, RS 25259-197 antagonized contractile responses to 5-HT in an unsurmountable fashion and the apparent affinity (pKB), estimated at 10 nM, was 8.8 +/- 0.2. In this tissue, the -log KB values for the other three enantiomers were 6.7 +/- 0.3 (R,R), 6.7 +/- 0.1 (S,R) and 7.4 +/- 0.1 (R,S), respectively. The apparent affinities of RS 25259-197 and RS 25259-198, RS 25233-197 and RS 25233-198 at 5-HT3 receptors in membranes from NG-108-15 cells were evaluated by a [3H]-quipazine binding assay. The -log Ki values were 10.5 +/- 0.2, 8.4 +/- 0.1, 8.6 +/- 0.1 and 9.5 +/- 0.1, respectively, with Hill coefficients not significantly different from unity. Thus, at these 5-HT3 receptors, the rank order of apparent affinities was (S,S) > (R,S) > (S,R) = (R,R). 3. RS 25259-197 displaced the binding of the selective 5-HT3 receptor ligand, [3H]-RS 42358-197, in membranes from NG-108-15 cells, rat cerebral cortex, rabbit ileal myenteric plexus and guinea-pig ileal myenteric plexus, with affinity (pKi) values of 10.1 +/- 0.1, 10.2 +/- 0.1, 10.1 +/- 0.1 and 8.3 +/- 0.2, respectively. In contrast, it exhibited low affinity (pKi <6.0) at 28 other receptors in binding assays, including adrenoceptors (alpha1A, alpha 1B, alpha2A, alpha 2B ,beta1, beta2), muscarinic (M1-M4), dopamine (D1, D2), opioid and other 5-HT(5-HTlA, 5-HTlD, 5-HT2C, 5-HT4) receptors.4. RS 25259-197 was tritium labelled (specific activity: 70 Ci mmol-1) and evaluated in pharmacological studies. Saturation studies with [3H]-RS 25259-197 in membranes from NG-108-15 and cloned homomeric a subunits of the 5-HT3 receptor from N1E-1 15 cells expressed in human kidney 293E1 cells,revealed an equilibrium dissociation constant (Kd) of 0.05 +/- 0.02 and 0.07 +/- 0.01 nM, and Bmax of610 +/- 60 and 1068 +/- 88 fmol mg-1, respectively. Competition studies in NG-108-15 cells indicated a pharmacological specificity entirely consistent with labelling a 5-HT3 receptor, i.e. RS 25259-197> granisetron> (S)-zacopride> tropisetron> (R)-zacopride> ondansetron> MDL 72222.5. In contrast to the majority of radioligands available to label 5-HT3 receptors, [3H]-RS 25259-197 labelled a high affinity site in hippocampus from human post-mortem tissue with an equilibrium dissociation constant (Kd) of 0.15 +/- 0.07 nM and density (BmaX) of 6.8 +/- 2.4 fmol mg-1 protein. Competition studies in this tissue indicated a pharmacological specificity consistent with labelling of a 5-HT3receptor.6. Quantitative autoradiographic studies in rat brain indicated a differential distribution of 5-HT3receptor sites by [3H]-RS 25259-197. High densities of sites were seen in nuclear tractus solitaris and area postrema, a medium density in spinal trigeminal tract, ventral dentate gyrus and basal medial amygdala,and a low density of sites in hippocampal CAl, parietal cortex, medium raphe and cerebellum.7 In conclusion, the functional, binding and distribution studies undertaken with the radiolabelled and non-radiolabelled RS 25259-197 (S,S enantiomer) established the profile of a highly potent and selective5-HT3 receptor antagonist.

The 5-HT3 antagonist ondansetron reduces gastrointestinal side effects induced by a specific serotonin re-uptake inhibitor in man

The selective serotonin re-uptake inhibitors (SSRIs) are increasingly being used to treat depression and anxiety disorders. Gastrointestinal (GI) symptoms are the main side effects, probably resulting from the stimulation of central or peripheral 5-HT receptors. The present double-blind, placebo-controlled study was undertaken to see if the GI side effects of fluvoxamine could be attenuated by the co-administration of the 5-HT(3) antagonist ondansetron. The results demonstrate that, in volunteers, a single 100 mg oral dose of fluvoxamine can produce GI symptoms. Co-administration of ondansetron significantly reduced peak nausea and GI side effects, compared with placebo.

Enantioselective inhibition of apomorphine-induced emesis in the ferret by the neurokinin1 receptor antagonist CP-99,994

These studies have examined the effects of the selective neurokinin1 (NK1) receptor antagonist CP-99,994 on the retching and vomiting response to apomorphine. CP-99,994 (1-3 mg/kg i.p.) attenuated retching and vomiting induced by apomorphine (0.25 mg/kg s.c.) with complete inhibition of retching and vomiting at the 3 mg/kg dose. In contrast CP-100,263 (3 mg/kg i.p.), the enantiomer of CP-99,994 with 1000-fold lower affinity for the NK1 receptor, was without effect.

Tropisetron. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential as an antiemetic

Tropisetron is a potent and selective serotonin 3 (5-hydroxytryptamine3; 5-HT3) receptor antagonist with antiemetic properties, probably mediated via antagonism of receptors both at peripheral sites and in the central nervous system. When compared with antiemetic regimens containing high-dose metoclopramide in a small number of studies, tropisetron was generally as effective at preventing acute and delayed vomiting induced by high-dose cisplatin (> or = 50 mg/m2). In these studies tropisetron completely prevented vomiting occurring in the first 24 hours after chemotherapy in 35 to 76% of patients. Tropisetron was superior to alizapride in preventing emesis induced by high-dose alkylating agents. The effectiveness of tropisetron in patients who had previously had partial control of emesis was improved by the addition of dexamethasone. Tropisetron appears to be well tolerated with the most frequently reported adverse effect being headache. Extrapyramidal effects, which can occur in 5 to 10% of patients receiving high-dose metoclopramide and which may limit its use, have been reported in only isolated cases with tropisetron. Thus, tropisetron is an effective, apparently well tolerated agent which can be administered once daily for the prevention of chemotherapy-induced nausea and vomiting. However, further clinical experience is needed to clarify the optimum role of tropisetron as an antiemetic agent, particularly with regard to other drugs in its class. Nonetheless, preliminary results indicate that tropisetron will be a useful alternative for use in controlling emesis induced by cytotoxic therapy.