Effects of CP-99, 994, a tachykinin NK(1) receptor antagonist, on abdominal afferent vagal activity in ferrets: evidence for involvement of NK(1) and 5-HT(3) receptors

Review article: An analysis of the pharmacological rationale for selecting drugs to inhibit vomiting or increase gastric emptying during treatment of gastroparesis

BACKGROUND

Drugs which can inhibit nausea/vomiting and/or increase gastric emptying are used to treat gastroparesis, mostly 'off-label'. Within each category, they act at different targets and modulate different physiological mechanisms.

AIMS

Address the questions: In gastroparesis, why should blocking one pathway causing vomiting, be more appropriate than another? Why might increasing gastric emptying via one mechanism be more appropriate than another?

METHODS

Drugs used clinically were identified via consensus opinions and reviews, excluding the poorly characterised. Their pharmacology was defined, mapped to mechanisms influencing vomiting and gastric emptying, and rationale developed for therapeutic use.

RESULTS

Vomiting: Rationale for 5-HT₃ , D₂ , H₁ or muscarinic antagonists, and mirtazapine, amitriptyline, nortriptyline, are poor. Arguments for inhibiting central consequences of vagal afferent transmission by NK₁ antagonism are complicated by doubts over effects on nausea. Gastric emptying: Confusion emerges because of side-effects of drugs increasing gastric emptying: Metoclopramide (5-HT₄ agonist, D₂ and 5-HT₃ antagonist; also blocks some emetic stimuli and causes tardive dyskinesia) and Erythromycin (high-efficacy motilin agonist, requiring low doses to minimise side-effects). Limited trials with selective 5-HT₄ agonists indicate variable efficacy.

CONCLUSIONS

Several drug classes inhibiting vomiting have no scientific rationale. NK₁ antagonism has rationale but complicated by limited efficacy against nausea. Studies must resolve variable efficacy of selective 5-HT₄ agonists and apparent superiority over motilin agonists. Overall, lack of robust activity indicates a need for novel approaches targeting nausea (e.g., modulating gastric pacemaker or vagal activity, use of receptor agonists or new targets such as GDF15) and objective assessments of nausea.

Ferric Citrate Hydrate Has Little Impact on Hyperplasia of Enterochromaffin Cells in the Rat Small Intestine Compared to Sodium Ferrous Citrate

INTRODUCTION

The most detrimental factor preventing the use of oral iron in the treatment of iron deficiency anemia is gastrointestinal side effects accompanied by nausea and vomiting. Anorexia is a known secondary effect of nausea and vomiting. The important gastrointestinal signaling molecule 5-hydroxytryptamine (5-HT) is critically involved in not only physiological function but also nausea and vomiting. The present study was designed to compare the effects of the administration of sodium ferrous citrate (SF) and ferric citrate hydrate (FC) to rats on anorexia and hyperplasia of enterochromaffin cells, which mainly synthesize and store 5-HT.

METHODS

Rats received either SF (3 or 30 mg/kg/day) or FC (30 mg/kg/day) orally for 4 days. Food and water intakes were measured every 24 h during the study. At 96 h after the first administration of the oral iron preparation, the duodenal and jejunal tissues were collected for analysis. Enterochromaffin cells were detected by immunohistochemical analysis.

RESULTS

Administration of 3 mg/kg SF had no effect on anorexia but led to increased hyperplasia of enterochromaffin cells in the duodenum (p < 0.1). Administration of 30 mg/kg SF significantly decreased food and water intakes and significantly increased hyperplasia of enterochromaffin cells in the duodenum and jejunum. Alternatively, administration of 30 mg/kg FC had no significant effect on food and water intakes or hyperplasia of enterochromaffin cells.

CONCLUSION

The lower impact on the hyperplasia of enterochromaffin cells of FC compared to SF may contribute to the maintenance of rats' physical condition.

Effectiveness of Naldemedine Compared with Magnesium Oxide in Preventing Opioid-Induced Constipation: A Randomized Controlled Trial

Simple Summary

Opioids are used in cancer pain management, however, their continuous use may not be tolerable owing to adverse effects such as constipation, sleepiness, nausea, and respiratory depression. Opioid-induced constipation reduces the quality of life of patients, and osmotic laxatives are conventionally recommended for preventing opioid-induced constipation. Recently, naldemedine, a peripherally acting μ-opioid receptor antagonist, can be used to safely and effectively treat opioid-induced constipation based on its etiological mechanism, without affecting central analgesia. In this study, we compared the effectiveness of magnesium oxide with that of naldemedine in preventing opioid-induced constipation. Naldemedine significantly prevented deterioration in the quality of defecation (the Japanese Patient Assessment of Constipation Quality of Life and complete spontaneous bowel movement) and reduced gastrointestinal adverse effects, mainly nausea, compared with magnesium oxide during 12-week administration.

Abstract

Opioid-induced constipation (OIC) may occur in patients receiving opioid treatment, decreasing their quality of life (QOL). We compared the effectiveness of magnesium oxide (MgO) with that of naldemedine (NAL) in preventing OIC. This proof-of-concept, randomized controlled trial (registration number UMIN000031891) involved 120 patients with cancer scheduled to receive opioid therapy. The patients were randomly assigned and stratified by age and sex to receive MgO (500 mg, thrice daily) or NAL (0.2 mg, once daily) for 12 weeks. The change in the average Japanese version of Patient Assessment of Constipation QOL (JPAC-QOL) from baseline to 2 weeks was assessed as the primary endpoint. The other endpoints were spontaneous bowel movements (SBMs) and complete SBMs (CSBMs). Deterioration in the mean JPAC-QOL was significantly lower in the NAL group than in the MgO group after 2 weeks. There were fewer adverse events in the NAL group than in the MgO group. Neither significant differences in the change in SBMs between the groups nor serious adverse events/deaths were observed. The CSBM rate was higher in the NAL group than in the MgO group at 2 and 12 weeks. In conclusion, NAL significantly prevented deterioration in constipation-specific QOL and CSBM rate compared with MgO.

Research Progress on the Antiemetic Effect of Traditional Chinese Medicine Against Chemotherapy-Induced Nausea and Vomiting: A Review

Chemotherapy-induced nausea and vomiting (CINV), a common side effect in antineoplastic treatment, dramatically decreases the quality of life as well as the compliance of cancer patients. Although numerous antiemetic agents have been used for CINV treatment, its adverse reactions as well as its inadequate control toward delayed emesis still limit its clinical usage. Traditional Chinese medicine (TCM), with more than 3,000 years of practical history in Asia, has been successfully applied to mitigate chemotherapy-induced side effects. Growing attention is drawn to the antiemetic effect of TCM against CINV due to its promising therapeutic property and higher safety recently. In this review, we summarize the classic antiemetic TCM-based treatment and its mechanisms, so as to provide a theoretical basis for further investigations of TCM against CINV in the future.

Evaluation of clinical outcomes and efficacy of palonosetron and granisetron in combination with dexamethasone in Egyptian patients receiving highly emetogenic chemotherapy

BACKGROUND

Chemotherapy-induced nausea and vomiting (CINV) is considered one of the most serious adverse events affecting chemotherapy-receiving cancer patients. It dramatically affects their food intake, nutritional status and more importantly their quality of life. We can observe CINV in highly emetogenic chemotherapy (HEC) such as adriamycin-cyclophosphamide combination (AC) in breast cancer patients and cisplatin-based regimens in other cancer types. This study aimed to evaluate the antiemetic efficacy of palonosetron (PALO) over granisetron (GRA) in combination with dexamethasone for multiple highly emetogenic chemotherapy drugs (HEC), especially in chemotherapy regimens in Egyptian breast cancer patients and cisplatin-based regimens in other diseases.

PATIENTS AND METHODS

An open-label randomized trial was carried out, including 115 patients receiving at least four cycles of highly emetogenic chemotherapy regimens. All patients received dexamethasone in combination with the 5-HT3 receptor antagonist. We recorded patients' clinical and biochemical characteristics and withdraw blood samples to monitor serum substance P and serotonin in correlation with chemotherapy-induced nausea and vomiting (CINV). We use the MASCC antiemetic tool in the acute phase (0-24 hr) and delayed phase (24-120 h) to evaluate patient outcomes in both stages after each chemotherapy cycle.

RESULTS

In (PALO) group, only 7.84% of patients showed acute vomiting, and 11.76% showed acute nausea, whereas 43.75% of patients showed acute vomiting and 89.06% showed acute nausea in (GRA) group (P < 0.0001). For delayed CINV, 23.53% of patients showed delayed vomiting, and 47.06% showed delayed nausea in the (PALO) group, while 82.81% of patients showed delayed emesis, and 92.19% showed delayed nausea in (GRA) group (P < 0.0001). The study showed that PALO is a cost-effective choice when compared to GRA in CINV prevention as 45.10% of patients in (PALO) required additional rescue medications (Domperidone 10 mg orally three times per day plus Trimebutine 200 mg orally three times per week both for 5 days), while 95.24% in the (GRA) group used the same medications. Adverse events of both antiemetic drugs (PALO and GRA) include headaches and constipation and QTc prolongation reports, mostly mild to moderate, with relatively low rates among the two groups.

CONCLUSION

Palonosetron, combined with dexamethasone, is more effective than granisetron and dexamethasone combination against both acute and delayed emesis induced by highly emetogenic chemotherapy (HEC) cisplatin-based protocols and the combination of cyclophosphamide and anthracyclines (AC). Medical team members should make more efforts, especially clinical pharmacy personnel, to monitor medications' effectiveness and help the medical team achieve a suitable and reliable care plan.

Low-dose olanzapine, sedation and chemotherapy-induced nausea and vomiting: a prospective randomized controlled study

Aims: Comparison of efficacy, safety and sedation between two doses of olanzapine in the control of chemotherapy-induced nausea and vomiting (CINV). Patients & methods: A prospective, randomized, double-blind, controlled study was conducted, enrolling 68 patients receiving a single-day cycle of high and moderately emetogenic chemotherapy. Patients received either of olanzapine 5 mg or 10 mg from day 1 through 3 in addition to ondansetron and dexamethasone. Control of CINV, nausea, sedation, quality of life (QoL) and adverse events were compared. Results: Nausea, emesis control and improvement of QoL were similar in both groups. Sedation severity was 133% higher with 10 mg olanzapine. Conclusions: Lower dose olanzapine is effective to control CINV with significantly reduced sedation.

Severity of constipation related to palonosetron during first-line chemotherapy: a retrospective observational study

PURPOSE

Palonosetron, a long-acting 5-HT₃ receptor antagonist, is an effective antiemetic agent for chemotherapy-induced nausea and vomiting; however, it sometimes causes severe constipation. The aim of the present study was to evaluate the severity of palonosetron-related constipation.

METHODS

We retrospectively analyzed the incidence and severity of constipation after intravenous administration of 0.75-mg palonosetron in 150 chemotherapy-naïve patients who received first-line chemotherapy at Saga University Hospital. Constipation was classified into grades 1-5 according to the Common Terminology Criteria for Adverse Events version 5.0. Multiple logistic regression analysis was performed to identify factors associated with palonosetron-related worsening of constipation to grade 2 or higher.

RESULTS

Palonosetron significantly increased the incidence and severity of constipation (incidence: before vs. after palonosetron, 35.4% vs. 74.0%, p < 0.0001, and severity: before vs. after palonosetron, 26.7% and 8.7% in grades 1 and 2, respectively, vs. 46.7%, 23.3%, and 4.0% in grades 1, 2, and 3, respectively, p < 0.0001). Despite the use of laxatives, 4.0% of patients had grade 3 constipation requiring manual evacuation. Combination treatment with aprepitant (odds ratio (OR), 10.9; 95% confidence interval (CI), 1.3-90.0; p = 0.026) and older age (OR, 1.25; 95% CI, 1.01-1.57; p = 0.039) were factors associated with the severity of constipation.

CONCLUSION

Constipation was more severe in patients receiving combination treatment with aprepitant than in those treated with palonosetron alone. Older age was also associated with increased risk of severe palonosetron-related constipation. Identification of risk factors can help target risk-based laxative therapy.

An Integrated In Silico and In Vivo Approach to Identify Protective Effects of Palonosetron in Cisplatin-Induced Nephrotoxicity

Cisplatin is widely used to treat various types of cancers, but it is often limited by nephrotoxicity. Here, we employed an integrated in silico and in vivo approach to identify potential treatments for cisplatin-induced nephrotoxicity (CIN). Using publicly available mouse kidney and human kidney organoid transcriptome datasets, we first identified a 208-gene expression signature for CIN and then used the bioinformatics database Cmap and Lincs Unified Environment (CLUE) to identify drugs expected to counter the expression signature for CIN. We also searched the adverse event database, Food and Drug Administration. Adverse Event Reporting System (FAERS), to identify drugs that reduce the reporting odds ratio of developing cisplatin-induced acute kidney injury. Palonosetron, a serotonin type 3 receptor (5-hydroxytryptamine receptor 3 (5-HT3R)) antagonist, was identified by both CLUE and FAERS analyses. Notably, clinical data from 103 patients treated with cisplatin for head and neck cancer revealed that palonosetron was superior to ramosetron in suppressing cisplatin-induced increases in serum creatinine and blood urea nitrogen levels. Moreover, palonosetron significantly increased the survival rate of zebrafish exposed to cisplatin but not to other 5-HT3R antagonists. These results not only suggest that palonosetron can suppress CIN but also support the use of in silico and in vivo approaches in drug repositioning studies.

A History of Drug Discovery for Treatment of Nausea and Vomiting and the Implications for Future Research

The origins of the major classes of current anti-emetics are examined. Serendipity is a recurrent theme in discovery of their anti-emetic properties and repurposing from one indication to another is a continuing trend. Notably, the discoveries have occurred against a background of company mergers and changing anti-emetic requirements. Major drug classes include: (i) Muscarinic receptor antagonists-originated from historical accounts of plant extracts containing atropine and hyoscine with development stimulated by the need to prevent sea-sickness among soldiers during beach landings; (ii) Histamine receptor antagonists-searching for replacements for the anti-malaria drug quinine, in short supply because of wartime shipping blockade, facilitated the discovery of histamine (H1) antagonists (e.g., dimenhydrinate), followed by serendipitous discovery of anti-emetic activity against motion sickness in a patient undergoing treatment for urticaria; (iii) Phenothiazines and dopamine receptor antagonists-investigations of their pharmacology as "sedatives" (e.g., chlorpromazine) implicated dopamine receptors in emesis, leading to development of selective dopamine (D2) receptor antagonists (e.g., domperidone with poor ability to penetrate the blood-brain barrier) as anti-emetics in chemotherapy and surgery; (iv) Metoclopramide and selective 5-hydroxytryptamine3(5-HT3) receptor antagonists-metoclopramide was initially assumed to act only via D2 receptor antagonism but subsequently its gastric motility stimulant effect (proposed to contribute to the anti-emetic action) was shown to be due to 5-hydroxytryptamine4 receptor agonism. Pre-clinical studies showed that anti-emetic efficacy against the newly-introduced, highly emetic, chemotherapeutic agent cisplatin was due to antagonism at 5-HT3 receptors. The latter led to identification of selective 5-HT3 receptor antagonists (e.g., granisetron), a major breakthrough in treatment of chemotherapy-induced emesis; (v) Neurokinin1receptor antagonists-antagonists of the actions of substance P were developed as analgesics but pre-clinical studies identified broad-spectrum anti-emetic effects; clinical studies showed particular efficacy in the delayed phase of chemotherapy-induced emesis. Finally, the repurposing of different drugs for treatment of nausea and vomiting is examined, particularly during palliative care, and also the challenges in identifying novel anti-emetic drugs, particularly for treatment of nausea as compared to vomiting. We consider the lessons from the past for the future and ask why there has not been a major breakthrough in the last 20 years.

Intracellular emetic signaling evoked by the L-type Ca2+ channel agonist FPL64176 in the least shrew (Cryptotis parva)

Ca²⁺ plays a major role in maintaining cellular homeostasis and regulates processes including apoptotic cell death and side-effects of cancer chemotherapy including vomiting. Currently we explored the emetic mechanisms of FPL64176, an L-type Ca²⁺ channel (LTCC) agonist with maximal emetogenic effect at its 10 mg/kg dose. FPL64176 evoked c-Fos immunoreactivity in shrew brainstem sections containing the vomit-associated nuclei, nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus. FPL64176 also increased phosphorylation of proteins ERK1/2, PKCα/βII and Akt in the brainstem. Moreover, their corresponding inhibitors (PD98059, GF 109203X and LY294002, respectively) reduced FPL64176-evoked vomiting. A 30 min subcutaneous (s.c.) pretreatment with the LTCC antagonist nifedipine (10 mg/kg) abolished FPL64176-elicited vomiting, c-Fos expression, and emetic effector phosphorylation. Ryanodine receptors (RyRs) and inositol trisphosphate receptors (IP₃Rs) mediate intracellular Ca²⁺ release from the sarcoplasmic/endoplasmic reticulum. The RyR antagonist dantrolene (i.p.), or a combination of low doses of nifedipine and dantrolene, but not the IP₃R antagonist 2-APB, significantly attenuated FPL64176-induced vomiting. The serotonin type 3 receptor (5-HT₃R) antagonist palonosetron (s.c.), the neurokinin 1 receptor (NK₁R) antagonist netupitant (i.p.) or a combination of non-effective doses of netupitant and palonosetron showed antiemetic potential against FPL64176-evoked vomiting. Serotonin (5-HT) and substance P immunostaining revealed FPL64176-induced emesis was accompanied by an increase in 5-HT but not SP-immunoreactivity in the dorsomedial subdivision of the NTS. These findings demonstrate that Ca²⁺ mobilization through LTCCs and RyRs, and subsequent emetic effector phosphorylation and 5-HT release play important roles in FPL64176-induced emesis which can be prevented by 5-HT₃R and NK₁R antagonists.

Tropisetron attenuates lipopolysaccharide induced neuroinflammation by inhibiting NF-κB and SP/NK1R signaling pathway

Tropisetron, an antagonist of serotonin type 3 receptors (5-HT₃Rs), has been investigated in colonic inflammatory process. Since substance P/neurokinin 1 receptor (SP/NK1R) signaling pathway plays a key role in several sensory neuronal inflammatory. We evaluated the anti-inflammatory activity of tropisetron in mice cerebral cortex, and discovered that it was a potential inhibitor in LPS-mediated neuron inflammation through SP/NK1R signaling pathway. We found that tropisetron significantly reduced the increased number of iba-1 positive microglia, down-regulated the gene transcription and protein expression of IL-1β,IL-6 and TNF-α in LPS stimulated cerebral cortex. To characterize the inhibitory mechanism of tropisetron at the SP response in inflammation, we further examined the effect of tropisetron on NF-κB and SP/NK1R signaling pathway in the process of mice cerebral cortex inflammation. We found that tropisetron inhibited the gene transcription and protein expression of NF-κB, SP, NK1R via inhibiting 5-HT₃R activity. These findings might provide new insights into the anti-inflammatory activities of 5-HT₃R inhibitor tropisetron, which would be the interaction of serotonin receptor signaling and SP/NK1R pathway. These might highlight their potential to design novel therapeutic strategies to manage inflammatory diseases.

NK1R/5-HT1AR interaction is related to the regulation of melanogenesis

Substance P (SP) is a candidate mediator along the brain-skin axis and can mimic the effects of stress to regulate melanogenesis. Previously, we and others have found that the regulation of SP for pigmentary function was mediated by neurokinin 1 receptor (NK1R). Emerging evidence has accumulated that psychologic stress can induce dysfunction in the cutaneous serotonin 5-hydroxytryptamine (5-HT)-5-HT1A/1B receptor system, thereby resulting in skin hypopigmentation. Moreover, NK1R and 5-HTR (except 5-HT3) belong to GPCR. The present study aimed at assessing the possible existence of NK1R-5-HTR interactions and related melanogenic functions. Western blot and PCR detection revealed that SP reduced expression of 5-HT1A receptor via the NK1 receptor. Biochemical analyses showed that NK1R and 5-HT1AR could colocalize and interact in a cell and in the skin. When the N terminus of the NK1R protein was removed NK1R surface targeting was prevented, the interaction between NK1R-5-HT1AR decreased, and the depigmentation caused by SP and WAY100635 could be rescued. Importantly, pharmaceutical coadministration of NK1R agonist (SP) and 5-HT1A antagonist (WAY100635) enhanced the NK1-5-HT1A receptor coimmunoprecipitation along with the depigmentary response. SP and WAY100635 cooperation elicited activation of a signaling cascade (the extracellular, regulated protein kinase p-JNK signaling pathway) and inhibition of p70S6K1 phosphorylation and greatly reduced melanin production in vitro and in vivo in mice and zebrafish. Moreover, the SP-induced depigmentation response did not be occur in 5-htr1aa^+/- zebrafish embryos. Taken together, the results of our systemic study increases our knowledge of the roles of NK1R and 5-HT1AR in melanogenesis and provides possible, novel therapeutic strategies for treatment of skin hypo/hyperpigmentation.-Wu, H., Zhao, Y., Huang, Q., Cai, M., Pan, Q., Fu, M., An, X., Xia, Z., Liu, M., Jin, Y., He, L., Shang, J. NK1R/5-HT1AR interaction is related to the regulation of melanogenesis.

The anti-asthmatic drug pranlukast suppresses the delayed-phase vomiting and reverses intracellular indices of emesis evoked by cisplatin in the least shrew (Cryptotis parva)

The introduction of second generation serotonin 5-HT₃ receptor (5-HT₃) antagonist palonosetron combined with long-acting substance P neurokinin NK₁ receptor (NK₁) antagonists (e.g. netupitant) has substantially improved antiemetic therapy against early- and delayed-phases of emesis caused by highly emetogenic chemotherapeutics such as cisplatin. However, the improved efficacy comes at a cost that many patients cannot afford. We introduce a new class of antiemetic, the antiasthmatic leukotriene CysLT1 receptor antagonist pranlukast for the suppression of cisplatin-evoked vomiting. Pranlukast (10mg/kg) by itself significantly reduced the mean frequency of vomits (70%) and fully protected least shrews from vomiting (46%) during the delayed-phase of cisplatin (10mg/kg)-evoked vomiting. Although, pranlukast tended to substantially reduce both the mean frequency of vomits and the number of shrews vomiting during the early-phase, these reductions failed to attain significance. When combined with a first (tropisetron)- or a second (palonosetron)-generation 5-HT₃ receptor antagonist, pranlukast potentiated their antiemetic efficacy during both phases of vomiting. In addition, pranlukast by itself prevented several intracellular signal markers of cisplatin-evoked delayed-vomiting such as phosphorylation of ERK1/2 and PKA. When pranlukast was combined with either palonosetron or tropisetron, these combinations suppressed the evoked phosphorylation of: i) ERK1/2 during both acute- and delayed-phase, ii) PKCα/β at the peak acute-phase, and iii) PKA at the peak delayed-phase. The current and our published findings suggest that overall behavioral and intracellular signaling effects of pranlukast via blockade of CysLT1 receptors generally appear to be similar to the NK₁ receptor antagonist netupitant with some differences.

Nausea: current knowledge of mechanisms, measurement and clinical impact

Nausea is a subjective sensation, which often acts as a signal that emesis is imminent. It is a widespread problem that occurs as a clinical sign of disease or as an adverse effect of a drug therapy or surgical procedure. The mechanisms of nausea are complex and the neural pathways are currently poorly understood. This review summarises the current knowledge of nausea mechanisms, the available animal models for nausea research and the anti-nausea properties of commercially available anti-emetic drugs. The review also presents subjective assessment and scoring of nausea. A better understanding of the underlying mechanisms of nausea might reveal potential clinically useful biomarkers for objective measurement of nausea in species of veterinary interest.

Synergistic effect of 5-hydroxytryptamine 3 and neurokinin 1 receptor antagonism in rodent models of somatic and visceral pain

Synergistic activity has been observed between serotonergic 5-hydroxytryptamine 3 (5-HT3) and tachykinergic neurokinin 1 (NK1) receptor-mediated responses. This study investigated the efficacy of a 5-HT3 antagonist, palonosetron, and a NK1 antagonist, netupitant, alone or in combination in rodent models of somatic and visceral colonic hypersensitivity. In a rat model of experimental neuropathic pain, somatic hypersensitivity was quantified by the number of ipsilateral paw withdrawals to a von Frey filament (6g). Electrophysiologic responses were recorded in the dorsal horn neurons after mechanical or thermal stimuli. Acute colonic hypersensitivity was induced experimentally in rats by infusing dilute acetic acid (0.6%) directly into the colon. Colonic sensitivity was assessed by a visceromotor behavioral response quantified as the number of abdominal contractions in response to graded isobaric pressures (0-60 mm Hg) of colorectal distension. Palonosetron or netupitant was administered alone or in combination via oral gavage. When dosed alone, both significantly reduced somatic sensitivity, decreased the evoked response of spinal dorsal horn neurons to mechanical or thermal stimulation, and caused significant (P < 0.05) inhibition of colonic hypersensitivity in a dose-dependent manner. The combined administration of palonosetron and netupitant at doses that were ineffective alone significantly reduced both somatic and visceral sensitivity and decreased the evoked response of spinal dorsal horn neurons to mechanical or thermal stimulation. In summary, the combination of palonosetron with a NK1 receptor antagonist showed synergistic analgesic activity in rodent models of somatic and visceral hypersensitivity, and may prove to be a useful therapeutic approach to treat pain associated with irritable bowel syndrome.

Netupitant and palonosetron trigger NK1 receptor internalization in NG108-15 cells

Current therapy for chemotherapy-induced nausea and vomiting includes the use of both 5-HT₃ and NK₁ receptor antagonists. Acute emesis has largely been alleviated with the use of 5-HT₃ receptor antagonists, while an improvement in preventing delayed emesis has been achieved with NK₁ receptor antagonists. Delayed emesis, however, remains a problem with a significant portion of cancer patients receiving highly emetogenic chemotherapy. Like other drugs in its class, palonosetron, a 5-HT₃ receptor antagonist, has shown efficacy against acute emesis. However, palonosetron has also shown consistent improvement in the suppression of delayed emesis. Since both 5-HT₃ and NK₁ receptor antagonists are often simultaneously administered to patients, the question remains if palonosetron’s effect on delayed emesis would remain distinct when co-administered with an NK₁ receptor antagonist. Recent mechanistic studies using NG108-15 cells have shown that palonosetron and netupitant, an NK₁ receptor antagonist currently in phase 3 clinical trials, exhibited synergistic effects when inhibiting the substance P response. The present studies showed that both netupitant and palonosetron-induced NK₁ receptor internalization in NG108-15 cells and that when used together receptor internalization was additive. Palonosetron-induced NK₁ receptor internalization was dependent on the presence of the 5-HT₃ receptor. Results provide a possible explanation for palonosetron’s enhancement of the inhibition of the SP response and suggest that the effect of palonosetron and NK₁ receptor antagonists on prevention of delayed emesis could be additive.

Current pharmacotherapy for chemotherapy-induced nausea and vomiting in cancer patients

INTRODUCTION

Nausea and vomiting are two of the most frequent and troubling side effects patients experience during chemotherapy, interfering with compliance with cancer therapies and quality of life. While newly available treatments have improved our ability to manage nausea and vomiting, anticipatory and delayed nausea and vomiting are still major problems for patients receiving chemotherapy. Many cancer patients consider delaying future chemotherapy cycles and some contemplate stopping chemotherapy altogether because of their fear of experiencing further nausea and vomiting.

AREAS COVERED

The purpose of this article is to provide an overview of the pathopsychophysiology of chemotherapy-induced nausea and vomiting (CINV), the recommended guidelines for treatment, and current agents in late-stage clinical trials, and future research needs to address the continued challenges of treatment-related nausea and vomiting.

EXPERT OPINION

Despite advances in pharmaceutical and behavioral therapies, and the provision of standard clinical guidelines for effectively managing CINV, patients continue to experience it. Moreover, control of nausea, acute and delayed, and anticipatory nausea and vomiting remains an important, unmet need among cancer patients. It is critical to focus attention on better understanding the mechanisms underlying nausea, anticipatory symptoms and delayed symptoms.

Palonosetron for the prevention of chemotherapy-induced nausea and vomiting

Chemotherapy-induced nausea and vomiting (CINV) remains both a feared side effect of cancer treatment and a focus of many supportive care initiatives/guidelines. The class of medications known as serotonin receptor antagonists (5-HT3RAs) are integral in the prevention of CINV from both moderately and highly emetogenic chemotherapy. Palonosetron (ALOXI(®)), a second-generation 5-HT3RA, has a higher affinity for the 5-HT3 receptor, has a longer half-life and has unique interactions with the 5-HT3 receptor compared with the current first-generation 5-HT3RA such as ondansetron, granisetron, dolasetron and tropisetron. This may allow palonosetron an advantage in control of CINV. This review article examines the available evidence, the pharmacokinetics and the safety and tolerability of palonosetron in the prevention of CINV.

Recent advances in pharmacotherapy of chemotherapy-induced nausea and vomiting

Nausea and vomiting remain among the most feared side effects of chemotherapy for cancer patients. Significant progress has been made in the last 15 years in developing more effective and better-tolerated measures to minimize chemotherapy-induced nausea and vomiting (CINV). During the 1990s, the selective 5-hydroxytryptamine receptor antagonists were first introduced for the treatment of CINV, and resulted in more effective and better tolerated treatment of CINV. Despite recent progress, however, a significant number of patients still develop CINV, particularly during the 2-5-day period (delayed emesis) following chemotherapy. There is evidence that this may be an underappreciated problem on the part of some caregivers. Recently, two new antiemetics, aprepitant, the first member of the neurokinin-1 antagonists, and palonosetron, a second-generation 5-hydroxytryptamine receptor antagonist, received regulatory approval in the U.S. Both represent useful additions to the therapeutic armamentarium for the management of CINV.

Pathology of emesis: its autonomic basis

Vagal and non-vagal pathways as well as several brainstem nuclei participate in vomiting in response to different emetic stimuli. Autonomic pathways involved in nausea are less well understood. Numerous gastrointestinal disorders with prominent nausea and vomiting including gastroparesis, cyclic vomiting syndrome, and motion sickness have associated autonomic nervous system dysfunction. Autonomic disturbances are also seen with non-gastrointestinal diseases with gut manifestations such as migraine headaches, orthostatic intolerance, and familial dysautonomia. Stimulation of emetic pathways involves activation of a range of receptor subtypes. Agents acting on these receptors form the basis for antiemetic therapies. Chemotherapy-induced nausea and vomiting, a prevalent and severe consequence of anticancer treatment, is preventable in many instances by agents acting on the autonomic nervous system. Likewise, non-medication therapies may act in part via modulation of some of these same autonomic pathways.

Inhibition of substance P-mediated responses in NG108-15 cells by netupitant and palonosetron exhibit synergistic effects

Netupitant is a potent and selective NK(1) receptor antagonist under development in combination with a fixed dose of palonosetron for the prevention of chemotherapy induced nausea and vomiting. Palonosetron is a 5-HT(3) receptor antagonist approved for both the prevention of acute and delayed chemotherapy induced nausea and vomiting after moderately emetogenic chemotherapy. Accumulating evidence suggests that substance P (SP), a ligand acting largely on tachykinin (NK(1)) receptors, is the dominant mediator of delayed emesis. Interestingly, palonosetron does not bind to the NK(1) receptor so that the mechanism behind palonosetron's unique efficacy against delayed emesis is not clear. Palonosetron exhibits a distinct ability among 5-HT(3) receptor antagonists to inhibit crosstalk between NK(1) and 5-HT(3) receptor signaling pathways. The objective of the current work was to determine if palonosetron's ability to inhibit receptor signaling crosstalk would influence netupitant's inhibition of the SP-mediated response when the two drugs are dosed together. We first studied the inhibition of SP-induced Ca(2+) mobilization in NG108-15 cells by palonosetron, ondansetron and granisetron. Unexpectedly, in the absence of serotonin, palonosetron inhibited the SP-mediated dose response 15-fold; ondansetron and granisetron had no effect. Netupitant also dose-dependently inhibited the SP response as expected from an NK1 receptor antagonist. Importantly, when both palonosetron and netupitant were present, they exhibited an enhanced inhibition of the SP response compared to either of the two antagonists alone. The results further confirm palonosetron's unique pharmacology among 5-HT(3) receptor antagonists and suggest that it can enhance the prevention of delayed emesis provided by NK(1) receptor antagonists.

Palonosetron: An Evidence-Based Choice in Prevention of Nausea and Vomiting Induced by Moderately Emetogenic Chemotherapy

Aims and background

In 2003, the second-generation, 5-HT3 receptor antagonist (5-HT3 RA) palonosetron was approved by the FDA for the prevention of nausea and vomiting associated with highly and moderately emetogenic chemotherapy. We reviewed the current knowledge on the role of palonosetron against acute and delayed emesis in patients with solid tumors undergoing single-day moderately emetogenic chemotherapy regimens.

Methods

A literature review in PubMed was performed to update currently available preclinical and clinical evidence on palonosetron, prioritizing randomized clinical trials.

Results

The distinct pharmacology of palonosetron provides a rationale behind the improved efficacy observed with the drug in prevention of delayed symptoms. This may be explained by allosteric binding properties and by palonosetron-triggered receptor internalization, which result in prolonged inhibition of the 5-HT3 receptor function. Very recent pharmacology experiments have also suggested that palonosetron would be able to differentially inhibit 5-HT3/neurokinin 1 (NK-1) receptor signaling cross-talk. In two recent meta-analyses, palonosetron was shown to be more effective than other available 5-HT3 RAs in preventing acute and delayed nausea and vomiting for both HEC and MEC. Recent findings also suggest that a single-day regimen of palonosetron plus dexamethasone (both drugs administered intravenously) may provide a reasonable therapeutic alternative to reduce the total dexamethasone dose administered in patients undergoing moderately emetogenic chemotherapy.

Conclusions

On the basis of accumulating data, the evidence-based international guidelines devised from the major organizations have been recently updated to recommend the use of palonosetron plus 3-day dexamethasone for the optimal prevention of nausea and vomiting due to moderately emetogenic chemotherapy. There is still a need to investigate the efficacy of palonosetron in combination with an NK-1 receptor antagonist and dexamethasone in well-designed randomized trials.

Pharmacological mechanisms of 5-HT₃ and tachykinin NK₁ receptor antagonism to prevent chemotherapy-induced nausea and vomiting

Nausea and vomiting are among the most common and distressing consequences of cytotoxic chemotherapies. Nausea and vomiting can be acute (0-24h) or delayed (24-72 h) after chemotherapy administration. The introduction of 5-HT(3) receptor antagonists in the 90s was a major advance in the prevention of acute emesis. These receptor antagonists exhibited similar control on acute emesis but had no effect on delayed emesis. These findings led to the hypothesis that serotonin plays a central role in the mechanism of acute emesis but a lesser role in the pathogenesis of delayed emesis. In contrast, delayed emesis has been largely associated with the activation of neurokinin 1 (NK(1)) receptors by substance P. However, in 2003, a new 5-HT(3) receptor antagonist was introduced into the market; unlike first generation 5-HT(3) receptor antagonists, palonosetron was found to be effective in preventing both acute and delayed chemotherapy induced nausea and vomiting. Recent mechanistic studies have shown that palonosetron, in contrast to first generation receptor antagonists, exhibits allosteric binding to the 5-HT(3) receptor, positive cooperativity, persistent inhibition of receptor function after the drug is removed and triggers 5-HT(3) receptor internalization. Further, in vitro and in vivo experiments have shown that palonosetron can inhibit substance P-mediated responses, presumably through its unique interactions with the 5-HT(3) receptor. It appears that the crossroads of acute and delayed emeses include interactions among the 5-HT(3) and NK(1) receptor neurotransmitter pathways and that inhibitions of these interactions lend the possibility of improved treatment that encompasses both acute and delayed emeses.

Inhibiting substance p pathway for prevention of chemotherapy-induced emesis: preclinical data, clinical trials of neurokinin-1 receptor antagonists

Neurokinin-1 (NK-1) receptor antagonists are a new class of antiemetic agents that have activity in controlling cisplatin-induced acute and delayed emesis. Preclinical data in animal models show that the NK-1 receptor antagonists have broad antiemetic activity. The NK-1 receptor antagonists have activity in controlling emesis induced by peripherally acting and centrally acting emetogens, suggesting a mechanism of action at multiple sites. The effects at central and peripheral sites to control acute and delayed emesis cannot be determined at this time based on available studies. When added to a standard regimen of a 5-hydroxytryptamine-3 (5- HT3) receptor antagonist and dexamethasone, the NK-1 receptor antagonists improve control of acute emesis. The NK-1 receptor antagonists improve delayed emesis compared with placebo, and when used in combination with dexamethasone, compared with dexamethasone alone. Acute and delayed nausea may also be improved by the NK-1 receptor antagonists when they are used in combination with a 5-HT3 receptor antagonist and dexamethasone prechemotherapy or with daily dosing for 5 days after chemotherapy. The current data suggest that the mechanism of action of the NK-1 receptor antagonists appears to be different from that of the 5-HT3 receptor antagonists. Future studies may consider using NK-1 receptor antagonists with moderately emetogenic chemotherapy as well as bone marrow transplantation.

Synergistic antiemetic interactions between serotonergic 5-HT3 and tachykininergic NK1-receptor antagonists in the least shrew (Cryptotis parva)

Significant electrophysiological and biochemical findings suggest that receptor cross-talk occurs between serotonergic 5-HT(3)- and tachykininergic NK(1)-receptors in which co-activation of either receptor by ineffective doses of their corresponding agonists (serotonin (5-HT) or substance P (SP), respectively) potentiates the activity of the other receptor to produce a response. In contrast, selective blockade of any one of these receptors attenuates the increase in abdominal vagal afferent activity caused by either 5-HT or SP. This interaction has important implications in chemotherapy-induced nausea and vomiting (CINV) since 5-HT(3)- and NK(1)-receptor antagonists are the major classes of antiemetics used in cancer patients receiving chemotherapy. The purpose of this study was to demonstrate whether the discussed interaction produces effects at the behavioral level in a vomit-competent species, the least shrew. Our results demonstrate that pretreatment with either a 5-HT(3) (tropisetron)- or an NK(1) (CP99,994)-receptor specific antagonist, attenuates vomiting caused by a selective agonist (2-methyl 5-HT or GR73632, respectively) of both emetic receptors. In addition, relative to each antagonist alone, their combined doses were 4-20 times more potent against vomiting caused by each emetogen. Moreover, combined sub-maximal doses of the agonists 2-methyl 5-HT and GR73632, produced 8-12 times greater number of vomits relative to each emetogen tested alone. However, due to large variability in vomiting caused by the combination doses, the differences failed to attain significance. The antiemetic dose-response curves of tropisetron against both emetogens were U-shaped probably because larger doses of this antagonist behave as a partial agonist. The data demonstrate that 5-HT(3)- and NK(1)-receptors cross-talk to produce vomiting, and that synergistic antiemetic effects occur when both corresponding antagonists are concurrently used against emesis caused by each specific emetogen.

Safety evaluation of aprepitant for the prevention of chemotherapy-induced nausea and vomiting

INTRODUCTION

Aprepitant is the only neurokinin (NK(1)) receptor antagonist (RA) approved for prevention of chemotherapy-induced nausea and vomiting (CINV). Aprepitant is co-administered with a 5-HT(3) RA and a corticosteroid. Although aprepitant is safe, in most clinical settings potential drug-drug interactions need to be considered before prescription.

AREAS COVERED

This article thoroughly reviews aprepitant and, in particular, clinically relevant safety aspects of the drug. The literature review was performed using Medline with the following search terms: adverse events, aprepitant, chemotherapy, CYP3A4, MK-0869, neurokinin(1) receptor antagonist, safety and tolerability.

EXPERT OPINION

The recommended antiemetic regimen of aprepitant, a 5-HT(3) RA and a corticosteroid is safe. The combination of aprepitant, a 5-HT(3) RA and dexamethasone is now the gold standard of antiemetic treatment in prevention of CINV induced by HEC, or by the combination of an anthracycline and cyclophosphamide. The intravenous formulation of aprepitant used as a single dose is expected to be of benefit to cancer patients.

Mechanisms of Broad-Spectrum Antiemetic Efficacy of Cannabinoids against Chemotherapy-Induced Acute and Delayed Vomiting

Chemotherapy-induced nausea and vomiting (CINV) is a complex pathophysiological condition and consists of two phases. The conventional CINV neurotransmitter hypothesis suggests that the immediate phase is mainly due to release of serotonin (5-HT) from the enterochromaffin cells in the gastrointestinal tract (GIT), while the delayed phase is a consequence of release of substance P (SP) in the brainstem. However, more recent findings argue against this simplistic neurotransmitter and anatomical view of CINV. Revision of the hypothesis advocates a more complex, differential and overlapping involvement of several emetic neurotransmitters/modulators (e.g. dopamine, serotonin, substance P, prostaglandins and related arachidonic acid derived metabolites) in both phases of emesis occurring concomitantly in the brainstem and in the GIT enteric nervous system (ENS) [1]. No single antiemetic is currently available to completely prevent both phases of CINV. The standard antiemetic regimens include a 5-HT₃ antagonist plus dexamethasone for the prevention of acute emetic phase, combined with an NK₁ receptor antagonist (e.g. aprepitant) for the delayed phase. Although NK₁ antagonists behave in animals as broad-spectrum antiemetics against different emetogens including cisplatin-induced acute and delayed vomiting, by themselves they are not very effective against CINV in cancer patients. Cannabinoids such as D⁸-THC also behave as broad-spectrum antiemetics against diverse emetic stimuli as well as being effective against both phases of CINV in animals and patients. Potential side effects may limit the clinical utility of direct-acting cannabinoid agonists which could be avoided by the use of corresponding indirect-acting agonists. Cannabinoids (both phyto-derived and synthetic) behave as agonist antiemetics via the activation of cannabinoid CB₁ receptors in both the brainstem and the ENS emetic loci. An endocannabinoid antiemetic tone may exist since inverse CB₁ agonists (but not the corresponding silent antagonists) cause nausea and vomiting.

The antiemetic 5-HT3 receptor antagonist Palonosetron inhibits substance P-mediated responses in vitro and in vivo

Palonosetron is the only 5-HT(3) receptor antagonist approved for the treatment of delayed chemotherapy-induced nausea and vomiting (CINV) in moderately emetogenic chemotherapy. Accumulating evidence suggests that substance P (SP), the endogenous ligand acting preferentially on neurokinin-1 (NK-1) receptors, not serotonin (5-HT), is the dominant mediator of delayed emesis. However, palonosetron does not bind to the NK-1 receptor. Recent data have revealed cross-talk between the NK-1 and 5HT(3) receptor signaling pathways; we postulated that if palonosetron differentially inhibited NK-1/5-HT(3) cross-talk, it could help explain its efficacy profile in delayed emesis. Consequently, we evaluated the effect of palonosetron, granisetron, and ondansetron on SP-induced responses in vitro and in vivo. NG108-15 cells were preincubated with palonosetron, granisetron, or ondansetron; antagonists were removed and the effect on serotonin enhancement of SP-induced calcium release was measured. In the absence of antagonist, serotonin enhanced SP-induced calcium-ion release. After preincubation with palonosetron, but not ondansetron or granisetron, the serotonin enhancement of the SP response was inhibited. Rats were treated with cisplatin and either palonosetron, granisetron, or ondansetron. At various times after dosing, single neuronal recordings from nodose ganglia were collected after stimulation with SP; nodose ganglia neuronal responses to SP were enhanced when the animals were pretreated with cisplatin. Palonosetron, but not ondansetron or granisetron, dose-dependently inhibited the cisplatin-induced SP enhancement. The results are consistent with previous data showing that palonosetron exhibits distinct pharmacology versus the older 5-HT(3) receptor antagonists and provide a rationale for the efficacy observed with palonosetron in delayed CINV in the clinic.

Ablation of least shrew central neurokinin NK1 receptors reduces GR73632-induced vomiting

The neurocircuitry mediating the emetic reflex is still incompletely understood, and a key question is the degree to which central and/or peripheral components contribute to the overall vomiting mechanism. Having previously found a significant peripheral component in neurokinin NK-receptor mediated emesis, the authors undertook this study to examine the putative central component. Adult least shrews were injected intracerebroventricularly (icv) with saline or the blood-brain barrier impermeable toxin, stable substance P-saporin (SSP-SAP), which ablates cells expressing NK receptors. After 3 days, shrews were challenged intraperitoneally with the emetogenic NK agonist GR73632 at different doses, and vomiting and scratching behaviors were quantified. Ablation of NK1-bearing cells was verified immunohistochemically. Although SSP-SAP injection reduced emesis at GR73632 doses of 2.5 and 5 mg/kg, no injections completely eliminated emesis. These data demonstrate that there is both a major central nervous system component and a minor peripheral nervous system component to tachykinin-mediated vomiting. Side effects of the current generation of antiemetics could potentially be reduced by improving bioavailability of the drugs in the more potent central nervous system compartment while reducing bioavailability in the less potent peripheral compartment.

Antiemetic control: toward a new standard of care for emetogenic chemotherapy

Chemotherapy-induced nausea and vomiting (CINV) is associated with a significant deterioration in quality of life. The emetogenicity of the chemotherapeutic agents, repeated chemotherapy cycles, and patient risk factors significantly influence CINV. 5-hydroxytryptamine-3 (5-HT(3)) receptor antagonists plus dexamethasone have significantly improved the control of acute CINV, but delayed CINV remains a significant clinical problem. Two new agents, palonosetron and aprepitant, have been approved for the prevention of both acute and delayed CINV. Palonosetron is a second-generation 5-HT(3) receptor antagonist with a longer half-life and a higher binding affinity than first-generation 5-HT(3) receptor antagonists. Aprepitant is the first agent available in the new drug class of neurokinin-1 (NK-1) receptor antagonists. Casopitant is another NK-1 receptor antagonist that is under review by the FDA after recent completion of Phase III clinical trials. The introduction of these new agents has generated revised antiemetic guidelines for the prevention of CINV. Future studies may consider the use of palonosetron, aprepitant and casopitant with other antiemetic agents (olanzapine, gabapentin, cannabinoids) in moderately and highly emetogenic chemotherapy, as well as in the clinical settings of multiple-day chemotherapy and bone marrow transplantation.

Casopitant: a novel NK(1)-receptor antagonist in the prevention of chemotherapy-induced nausea and vomiting

Chemotherapy-induced nausea and vomiting (CINV) are among the most feared and distressing symptoms experienced by patients with cancer. The knowledge of the pathogenesis and neuropharmacology of CINV has expanded enormously over the last decades, the most significant discoveries being the role of 5-hydroxytryptamine (5-HT)(3)- and neurokinin (NK)(1) receptors in the emetic reflex arch. This has led to the development of two new classes of antiemetics acting as highly selective antagonists at one of these receptors. These drugs have had a huge impact in the protection from chemotherapy-induced vomiting, whereas the effect on nausea seems to be limited. The first NK(1) receptor antagonist, aprepitant, became clinically available in 2003, and casopitant, the second in this class of antiemetics, has now completed phase III trials. This review delineates the properties and clinical use of casopitant in the prevention of CINV.

Utilization of the least shrew as a rapid and selective screening model for the antiemetic potential and brain penetration of substance P and NK1 receptor antagonists

Substance P (SP) is thought to play a cardinal role in emesis via the activation of central tachykinin NK1 receptors during the delayed phase of vomiting produced by chemotherapeutics. Although the existing supportive evidence is significant, due to lack of an appropriate animal model, the evidence is indirect. As yet, no study has confirmed that emesis produced by SP or a selective NK1 receptor agonist is sensitive to brain penetrating antagonists of either NK1, NK2, or NK3 receptors. The goals of this investigation were to demonstrate: 1) whether intraperitoneal (i.p.) administration of either SP, a brain penetrating (GR73632) or non-penetrating (e.g. SarMet-SP) NK1 receptor agonist, an NK2 receptor agonist (GR64349), or an NK3 receptor agonist (Pro7-NKB), would induce vomiting and/or scratching in the least shrew (Cryptotis parva) in a dose-dependent manner; and whether these effects are sensitive to the above selective receptor antagonists; 2) whether an exogenous emetic dose of SP (50 mg/kg, i.p.) can penetrate into the shrew brain stem and frontal cortex; 3) whether GR73632 (2.5 mg/kg, i.p.)-induced activation of NK1 receptors increases Fos-measured neuronal activity in the neurons of both brain stem emetic nuclei and the enteric nervous system of the gut; and 4) whether selective ablation of peripheral NK1 receptors can affect emesis produced by GR73632. The results clearly demonstrated that while SP produced vomiting only, GR73632 caused both emesis and scratching behavior dose-dependently in shrews, and these effects were sensitive to NK1-, but not NK2- or NK3-receptor antagonists. Neither the selective, non-penetrating NK1 receptor agonists, nor the selective NK2- or NK3-receptor agonists, caused a significant dose-dependent behavioral effect. An emetic dose of SP selectively and rapidly penetrated the brain stem but not the frontal cortex. Systemic GR73632 increased Fos expression in the enteric nerve plexi, the medial subnucleus of nucleus tractus solitarius, and the dorsal motor nucleus of the vagus, but not the area postrema. Ablation of peripheral NK1 receptors attenuated the ability of GR73632 to induce a maximal frequency of emesis and shifted its percent animals vomiting dose-response curve to the right. The NK1-ablated shrews exhibited scratching behavior after systemic GR73632-injection. These results, for the first time, affirm a cardinal role for central NK1 receptors in SP-induced vomiting, and a facilitatory role for gastrointestinal NK1 receptors. In addition, these data support the validation of the least shrew as a specific and rapid behavioral animal model to screen concomitantly both the CNS penetration and the antiemetic potential of tachykinin NK1 receptor antagonists.

Fosaprepitant (MK-0517): a neurokinin-1 receptor antagonist for the prevention of chemotherapy-induced nausea and vomiting

Chemotherapy-induced nausea and vomiting (CINV) is a distressing and common adverse event associated with cancer treatment. Updated anti-emetic guidelines were published in 2007 by the National Comprehensive Cancer Network and in 2006 by the American Society of Clinical Oncology, which have included the use of the new and more effective anti-emetic agents (5-hydroxytryptamine-3 [5-HT(3)] receptor antagonists and neurokinin-1 [NK-1] receptor antagonists). Aprepitant is a selective NK-1 receptor antagonist approved as part of combination therapy with a corticosteroid and a 5-HT(3) receptor antagonist for the prevention of acute and delayed CINV. Fosaprepitant (also known as MK-0517 and L-758,298) is a water-soluble phosphoryl prodrug for aprepitant, which, when administered intravenously, is converted to aprepitant within 30 min after intravenous administration via the action of ubiquitous phosphatases. Because fosaprepitant is rapidly converted to the active form (aprepitant), it is expected to provide the same aprepitant exposure in terms of AUC, and a correspondingly similar anti-emetic effect. Clinical studies have suggested that fosaprepitant could be appropriate as an intravenous alternative to the aprepitant oral capsule. In a study in healthy subjects, fosaprepitant was well tolerated up to 150 mg (1 mg/ml), and fosaprepitant 115 mg was bioequivalent in its AUC to aprepitant 125 mg. Fosaprepitant 115 mg has been submitted for FDA approval as an alternative on day 1 of a 3-day oral aprepitant regimen, with oral aprepitant administered on days 2 and 3. Fosaprepitant may be a useful parenteral alternative to oral aprepitant. Further study is needed to clarify the use of fosaprepitant for the prevention of CINV, and to clarify optimal dosing regimens that may be appropriate substitutes for oral aprepitant.

New approaches to chemotherapy-induced nausea and vomiting: from neuropharmacology to clinical investigations

Nausea and vomiting are considered to be among the most distressing consequences of cytotoxic chemotherapies. Currently, there are several novel 5-HT(3) receptor antagonists for the treatment of chemotherapy-induced nausea and vomiting (CINV), including ondansetron, granisetron, and dolasetron. These agents provide significant improvement in the management of acute emesis but are ineffective at preventing delayed emesis. In 2003, a new 5-HT(3) receptor antagonist, palonosetron HCL (Aloxi), was introduced to the U.S. market. Palonosetron was found to be effective in preventing delayed CINV. Indeed, palonosetron was the first and only 5-HT(3) receptor antagonist approved by the FDA for the prevention of both acute and delayed CINV. More recently, studies on the role of substance P in the emetic process led to the development of aprepitant (Emend) for the prevention of delayed emesis in combination with 5-HT(3) receptor antagonists. Despite these major advances, CINV remains uncontrolled in some patients. Current efforts are focused on treating refractory emesis and include both the clinical evaluation of compounds marketed for other indications and the preclinical evaluation of novel molecules targeting other transmitters in the emetic pathway. Ongoing work in pharmacogenomics has postulated several candidate genes that could be involved in emetic sensitivity and responsiveness to antiemetic therapy. Investigations into the pharmacogenomics of CINV may someday be able to aid in the identification of high risk patients and patients unlikely to respond to conventional therapies.

Interactions of metoclopramide and ergotamine with human 5-HT(3A) receptors and human 5-HT reuptake carriers

The actions of metoclopramide and ergotamine, drugs which are used as a combined migraine medication, on human (h)5-HT3A receptors and 5-HT reuptake carriers, stably expressed in HEK-293 cells, were studied with patch-clamp- and ([3H]5-HT)-uptake techniques. At clinical concentrations, metoclopramide inhibited peak and integrated currents through h5-HT3A receptors concentration-dependently (IC50 = 0.064 and 0.076 microM, respectively) when it was applied in equilibrium (60 s before and during 5-HT (30 microM) exposure). The onset and offset time constants of metoclopramide action were 1.3 and 2.1 s, respectively. The potency of metoclopramide when exclusively applied during the agonist pulse decreased more than 200-fold (IC50 = 19.0 microM, peak current suppression). Metoclopramide (0.10 microM) did not alter the EC50 of 5-HT-induced peak currents. In contrast to the lack of competitive interaction between metoclopramide and 5-HT in this functional assay, metoclopramide inhibited specific [3H]GR65630 binding to human h5-HT3A receptors in a surmountable manner. This seeming discrepancy between functional studies and radioligand binding experiments may be accounted for by (1) the slow kinetics of inhibition of peak currents by metoclopramide compared with the fast onset and offset kinetics of 5-HT-induced currents and (2) the low efficacy of metoclopramide in inhibiting radioligand binding (e.g. only 20% binding inhibition compared to 79% peak current suppression by 200 nM metoclopramide). At low concentrations (1-10 nM), ergotamine had no effect on 5-HT (30 microM)-induced peak currents. Above clinical concentrations, ergotamine (>3 microM) inhibited them. When both drugs were applied together (0.10 microM metoclopramide +0.001 to 0.01 microM ergotamine), an inhibition of both, peak and integrated current responses was observed. Neither metoclopramide (< or =30 microM) nor ergotamine (< or =30 microM) had an effect on the 5-HT reuptake carrier as they did not alter the citalopram-sensitive [3H]5-HT uptake.

Signals for nausea and emesis: Implications for models of upper gastrointestinal diseases

Nausea and vomiting are amongst the most common symptoms encountered in medicine as either symptoms of diseases or side effects of treatments. In a more biological setting they are also important components of an organism's defences against ingested toxins. Identification of treatments for nausea and vomiting and reduction of emetic liability of new therapies has largely relied on the use of animal models, and although such models have proven invaluable in identification of the anti-emetic effects of both 5-hydroxytryptamine(3) and neurokinin(1) receptor antagonists selection of appropriate models is still a matter of debate. The present paper focuses on a number of controversial issues and gaps in our knowledge in the study of the physiology of nausea and vomiting including: The choice of species for the study of emesis and the underlying behavioural (e.g. neophobia), anatomical (e.g. elongated, narrow abdominal oesophagus with reduced ability to shorten) and physiological (e.g. brainstem circuitry) mechanisms that explain the lack of a vomiting reflex in certain species (e.g. rats); The choice of response to measure (emesis[retching and vomiting], conditioned flavour avoidance or aversion, ingestion of clay[pica], plasma hormone levels[e.g. vasopressin], gastric dysrhythmias) and the relationship of these responses to those observed in humans and especially to the sensation of nausea; The stimulus coding of nausea and emesis by abdominal visceral afferents and especially the vagus-how do the afferents encode information for normal postprandial sensations, nausea and finally vomiting?; Understanding the central processing of signals for nausea and vomiting is particularly problematic in the light of observations that vomiting is more readily amenable to pharmacological treatment than is nausea, despite the assumption that nausea represents "low" intensity activation of pathways that can evoke vomiting when stimulated more intensely.

Emerging drugs for chemotherapy-induced emesis

Chemotherapy-induced nausea and vomiting (CINV) is associated with a significant deterioration in quality of life. The emetogenicity of the chemotherapeutic agents, repeated chemotherapy cycles and patient risk factors (female gender, younger age, no alcohol consumption, history of motion sickness) are the major risk factors for CINV. The use of 5-hydroxytryptamine-3 (5-HT3) receptor antagonists plus dexamethasone has significantly improved the control of acute CINV, but delayed nausea and vomiting remains a significant clinical problem. Two new agents, palonosetron and aprepitant, have recently been approved for the prevention of both acute and delayed CINV. Palonosetron is a 5-HT3 receptor antagonist with a longer half-life and a higher binding affinity than first-generation 5-HT3 receptor antagonists. Aprepitant is the first agent available in the new drug class of neurokinin-1 receptor (NK-1) antagonists. There are a number of 5-HT3 receptor antagonists and NK-1 receptor antagonists currently in Phase II and III clinical trials. Revised antiemetic guidelines for the prevention of CINV are reviewed. Future studies may consider the use of palonosetron and aprepitant with current and other new agents (olanzapine, gabapentin) in moderately and highly emetogenic chemotherapy, as well as in the clinical settings of multiple-day chemotherapy and bone marrow transplantation.

Effects of tramadol and O-demethyl-tramadol on human 5-HT reuptake carriers and human 5-HT3A receptors: A possible mechanism for tramadol-induced early emesis

([3H]5-HT)-uptake and patch-clamp techniques were used to study the actions of (+) and (-) tramadol and the active metabolites of tramadol, (+) and (-) O-demethyl-tramadol on the human serotonin (5-HT) transporter and the human 5-HT3A receptor, stably expressed in HEK-293 cells. The (+) and (-) enantiomers of tramadol suppressed the human 5-HT transporter concentration-dependently (IC50=1.0 and 0.8 microM, respectively), resulting in 97% and 87% transport inhibition at their respective initial plasma concentrations (9.5 microM). The (+) and (-) enantiomers of the active tramadol metabolite were less potent than tramadol in inhibiting the human 5-HT transporter (IC50=15 and 44 microM, respectively), resulting in 19.2% and 4.8% transport inhibition at their highest plasma concentrations (2.5 microM). In contrast to their potent suppression of the 5-HT transporter, both, (+) and (-) tramadol inhibited 5-HT (30 microM)-induced currents only at substantially higher concentrations (IC50=199 and 251 microM, respectively), resulting in only 6% and 4% inhibition at the initial maximum plasma concentration. A similar low potent inhibition of human 5-HT(3A) receptors was found for (+) and (-) O-demethyl-tramadol (IC50=158 and 63 microM, respectively). In conclusion, at clinical plasma concentrations tramadol potently suppresses the human 5-HT transporter, whereas it has only a slight effect on the human 5-HT3A receptor. The results are compatible with a possible mechanism for tramadol-induced early emesis involving the serotonergic system.

Serotonin and Anticancer Drug-induced Emesis

Cytotoxic drug-induced nausea and vomiting are the side effects most feared by cancer patients. Emesis is an instinctive defense reaction caused by the somato-autonomic nerve reflex, which is integrated in the medulla oblongata. Emesis caused by anticancer drugs is associated with an increase in the concentration of serotonin (5-HT) (5-HT) in the intestinal mucosa and brainstem. 5-HT released from the enterochromaffin (EC) cells, which synthesize and secrete 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 appears to mediate the cisplatin-induced emesis sensitive to 5-HT(3) receptor antagonists. The precise role of 5-HT in the occurrence of vomiting has not been fully elucidated. The present review describes the role of 5-HT in anticancer drug-induced emesis from the viewpoint of 5-HT release and afferent vagal nerve activity. Various models and methods for predicting emesis are also evaluated.

Neurokinin NK1 and NK3 receptors as targets for drugs to treat gastrointestinal motility disorders and pain

NK1 and NK3 receptors do not appear to play significant roles in normal GI functions, but both may be involved in defensive or pathological processes. NK1 receptor antagonists are antiemetic, operating via vagal sensory and motor systems, so there is a need to study their effects on other gastro-vagal functions thought to play roles in functional bowel disorders. Interactions between NK1 receptors and enteric nonadrenergic, noncholinergic motorneurones suggest a need to explore the role of this receptor in disrupted colonic motility. NK1 receptor antagonism does not exert consistent analgesic activity in humans, but similar studies have not been carried out against pain of GI origin, where NK1 receptors may have additional influences on mucosal inflammatory or "irritant" processes. NK3 receptors mediate certain disruptions of intestinal motility. The activity may be driven by tachykinins released from intrinsic primary afferent neurones (IPANs), which induce slow EPSP activity in connecting IPANs and hence, a degree of hypersensitivity within the enteric nervous system. The same process is also proposed to increase C-fibre sensitivity, either indirectly or directly. Thus, NK3 receptor antagonists inhibit intestinal nociception via a "peripheral" mechanism that may be intestine-specific. Studies with talnetant and other selective NK3 receptor antagonists are, therefore, revealing an exciting and novel pathway by which pathological changes in intestinal motility and nociception can be induced, suggesting a role for NK3 receptor antagonism in irritable bowel syndrome.

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.