Prolonged inhibition of 5-HT₃ receptors by palonosetron results from surface receptor inhibition rather than inducing receptor internalization

Palonosetron for prevention of delayed chemotherapy-induced nausea and vomiting in pediatric patients: a meta-analysis

PURPOSE

Chemotherapy-induced nausea and vomiting (CINV) are common adverse events in patients undergoing emetogenic chemotherapy. Palonosetron, a second-generation 5-hydroxytryptamine-3 receptor antagonist (5-HT3 RA), has demonstrated non-inferiority to first-generation 5-HT3 RAs for CINV in pediatric patients. Although palonosetron has a long half-life and prolonged antiemetic action, its efficacy against delayed CINV in pediatric patients is not well understood. Therefore, this meta-analysis of randomized controlled trials (RCTs) aimed to evaluate the efficacy of palonosetron for delayed CINV in pediatric patients.

METHODS

A literature search of MEDLINE/PubMed, Embase, Cochrane Library, and Web of Science databases was performed. A meta-analysis was performed using forest plots, and risk ratios (RRs) and 95% confidence intervals (CIs) were calculated. A funnel plot was constructed to explore publication bias.

RESULTS

The literature search retrieved 842 records, of which 23 full-text articles were assessed, including six RCTs. Meta-analysis of four RCTs that reported on the complete response (CR: defined as no emesis and no rescue medication) rate for delayed CINV revealed that palonosetron was statistically superior to first-generation 5-HT3 RAs (RR = 1.21 [95% CI 1.09-1.35]; p < 0.01). Although the number of studies included was small, no publication bias was observed in the funnel plots. In addition, the CR rate for overall and acute CINV was also significantly higher for palonosetron (RR = 1.25 [95% CI 1.01-1.54]; p = 0.04 and RR = 1.06 [95% CI 1.01-1.12]; p = 0.03, respectively).

CONCLUSION

Palonosetron is effective in the prophylaxis of delayed CINV in pediatric patients.

Effects of Palonosetron on Nausea and Vomiting Induced by Multiple-Day Chemotherapy: A Retrospective Study

Patients who undergo multiple-day chemotherapy sessions experience hard-to-treat nausea and vomiting. Currently, there is no effective standard treatment for this condition. This study compared the preventive effect of first-generation 5-hydroxytryptamine 3 receptor antagonists (5-HT₃ RAs) and second-generation 5-HT₃ RAs palonosetron in multiple-day chemotherapy-induced nausea and vomiting. The design of this study was a retrospective case-control study of patients who received a five-day cisplatin-based chemotherapy and were treated with aprepitant, dexamethasone, granisetron, and ramosetron or palonosetron. The patients were divided into two groups: patients given granisetron and ramosetron (the first-generation group), and those given palonosetron (palonosetron group). The percentage of patients with a complete response or total control was assessed. They were divided into three phases: 0-216 h (overall phase), 0-120 h (remedial phase), and 120-216 h (after phase). The remedial phase was further divided into 0-24 h (early phase) and 24-120 h (later phase). Moreover, the nutritional status of each patient was assessed by noting the patients' total calorie-intake per day and total parenteral nutrition. First-generation 5-HT₃ RAs and palonosetron were used for treatment in 18 and 28 patients, respectively. The complete response rate and caloric oral intake of the later phase were higher in the palonosetron group than in the first-generation group. We conclude that palonosetron treatment was more effective than first-generation 5-HT₃ RAs in controlling multiple-day chemotherapy-induced nausea and vomiting.

Pharmacokinetics and safety evaluation of oral Palonosetron in Chinese healthy volunteers: A phase 1, open-label, randomized, cross-over study

PURPOSE

Palonosetron hydrochloride is a specific 5-HT3 receptor antagonist, used to prevent chemotherapy-induced nausea and vomiting (CINV), and is a known chemical entity currently registered in the oral and IV forms in several countries worldwide.

METHODS

Single-center, single-dose, 3-treatment, open-label, randomized, 3-period, phase-I cross-over study, conducted in 18 individuals (16 males and 2 females). The primary objective was to assess the pharmacokinetic profile of Palonosetron 0.25, 0.5 and 0.75mg, after a single, oral administration in Chinese male and female healthy volunteers.

RESULTS

After administration of a single oral dose of 0.25mg, 0.5mg, or 0.75mg palonosetron in Chinese male and female healthy subjects, plasma palonosetron concentrations reached maximum values (C_max) of 673 ± 151 pg/mL, 1330 ± 258 pg/mL, and 1990 ± 490 pg/mL, respectively, at 3-5 h (t_max). The plasma elimination half-life for 0.25, 0.5 and 0.75 mg of palonosetron was 41.8±9.72 hours, 44.6±8.59 hours and 42.3±8.51 hours, respectively. Single oral doses of 0.25mg, 0.5mg, or 0.75mg palonosetron were safe and well tolerated among all the 18 subjects involved.

CONCLUSIONS

The PK of palonosetron was found to be linear in the dose range of 0.25 to 0.75 mg. Oral palonosetron in doses up to 0.75 mg was well tolerated in healthy Chinese subjects. The PK and safety data obtained from this study were similar to previous phase I studies with IV palonosetron.

Structure, Function and Physiology of 5-Hydroxytryptamine Receptors Subtype 3

5-hydroxytryptamine receptor subtype 3 (5-HT₃R) is a pentameric ligand-gated ion channel (pLGIC) involved in neuronal signaling. It is best known for its prominent role in gut-CNS signaling though there is growing interest in its other functions, particularly in modulating non-serotonergic synaptic activity. Recent advances in structural biology have provided mechanistic understanding of 5-HT₃R function and present new opportunities for the field. This chapter gives a broad overview of 5-HT₃R from a physiological and structural perspective and then discusses the specific details of ion permeation, ligand binding and allosteric coupling between these two events. Biochemical evidence is summarized and placed within a physiological context. This perspective underscores the progress that has been made as well as outstanding challenges and opportunities for future 5-HT₃R research.

Prevention and Treatment of Postoperative Nausea and Vomiting (PONV): A Review of Current Recommendations and Emerging Therapies

Postoperative nausea and vomiting is one of the most frequent adverse events after surgery and anesthesia. It is distressing for the patient and can lead to other postoperative complications. Management of PONV involves a framework of risk assessment, multimodal risk reduction, and prophylactic measures, as well as prompt rescue treatment. There has been a significant paradigm shift in the approach towards PONV prevention. There have also been several emerging therapeutic options for PONV prophylaxis and treatment. In this review, we will discuss the up-to-date PONV management guidelines and highlight novel therapeutic options which have emerged in the last few years.

Potential roles of 5-HT3 receptor (5-HT3R) antagonists in modulating the effects of nicotine

5-HT₃R antagonists such as ondansetron, granisetron and tropisetron have been clinically used to treat nausea and vomiting in chemotherapy patients. However, current study and research revealed novel potentials of these ligands in other diseases like inflammation, Alzheimer's, and drug abuse. Towards utilising these drugs as anti-smoking agents to treat nicotine dependence problem, there are conflicting reports regarding the potential of these ligands in modulating the effects of nicotine in both human and animal behavioural studies. This is complicated by the heterogeneity of 5-HT₃R itself, cross regulation between nicotinic acetylcholinergic receptor (nAChR) and distinct pharmacological profiles of 5-HT₃R antagonists. This review gathered existing studies conducted investigating the potential of "-setron" class of 5-HT₃R antagonists in modulating nicotine effects. We proposed that the mechanism where 5-HT₃R antagonists mediate the effects of nicotine could be attributed by both direct at 5-HT₃R and indirect mechanism in nicotine addiction downstream regulation. The indirect mechanism mediated by the 5-HT₃R antagonist could be through α7 nAChR, 5-HT_1B receptor (5-HT_1BR), 5-HT_1C receptor (5-HT_1CR), calcineurin activity, p38 MAPK level, PPAR-γ and NF-κβ. Our review suggested that future studies should focus on newer 5-HT₃R antagonist with superior pharmacological profile or the one with multitarget action rather than high selectivity at single receptor.

Comparative investigation of the anti-emetic effects of granisetron and palonosetron during the treatment of acute myeloid leukemia

Chemotherapy-induced nausea and vomiting has a considerable negative impact on the quality of life of patients with cancer. Unfortunately, there has been little progress in the development of supportive therapies for the anti-emetic treatment of patients with hematopoietic tumors. This lack of supportive treatments motivated the present retrospective comparison between two groups of anti-emetic drugs. The current study aimed to compare granisetron and palonosetron in order to determine which is more effective, based on cases of patients undergoing remission induction therapy and consolidation therapy for the treatment of acute myeloid leukemia. Granisetron or palonosetron were administered in Japanese-approved dosages (3 mg granisetron once per day for 5 or 7 days, or one administration of 0.75 mg palonosetron). Patients were randomly selected, and their clinical information was acquired from medical records. The data represent the doctors' and nurses' records. The results demonstrated that palonosetron treatment (in which the drug was administered alone or in combination with aprepitant) was more effective than granisetron treatment for the complete control of acute vomiting. Therefore, in the treatment of hematopoietic malignancies, palonosetron is an effective regimen to be administered alongside more than 5 continuous days of anti-cancer agents. Furthermore, the combination of palonosetron and aprepitant was found to be the optimal combination. In conclusion, palonosetron is superior to granisetron for the prevention of nausea and vomiting induced by chemotherapy for hematological cancers. In Japan, the standard dose of palonosetron is 0.75 mg; a dose of 0.25 mg of palonosetron must be compared with 0.75 mg in future studies.

Higher dose of palonosetron versus lower dose of palonosetron plus droperidol to prevent postoperative nausea and vomiting after eye enucleation and orbital hydroxyapatite implant surgery: a randomized, double-blind trial

Objective

Postoperative nausea and vomiting (PONV) is commonly observed after eye enucleation and orbital hydroxyapatite implant surgery. This prospective, randomized, double-blind trial was conducted to investigate the hypothesis that compared with monotherapy using a higher dose of palonosetron, using a lower dose of palonosetron in combination with droperidol could reduce the incidence of PONV and achieve similar prophylaxis against PONV after the aforementioned surgery.

Patients and methods

A total of 129 patients who were in the American Society of Anesthesiologists Classes I and II, aged between 18 and 70 years, and scheduled for eye enucleation and orbital hydroxyapatite implant surgery, were enrolled in this study. They were randomized into three groups: Group P2.5 (2.5 μg/kg palonosetron), Group P7.5 (7.5 μg/kg palonosetron), and Group P+D (2.5 μg/kg palonosetron and 15 μg/kg droperidol). Patients received the different antiemetic regimens intravenously 5 min before surgery. The severity of nausea and vomiting and the complete response (CR) rate during a 72-h postoperative period were assessed.

Results

All patients completed the trial. The nausea score of Group P2.5 was significantly higher than those of the other two groups at 0–4 h and 24–48 h (P<0.05). Vomiting scores among all groups were similar during all intervals (P>0.05). Compared with Group P2.5, the CR rate was significantly improved at all intervals in Group P+D, except at 4–72 h, and was also elevated at 24–72 h in Group P7.5 (P<0.05). Fewer patients in Group P2.5 did not experience any nausea or vomiting throughout the study (49%) compared with those in Group P7.5 (67%) and Group P+D (81%; P<0.01).

Conclusion

Combining low-dose palonosetron with droperidol potentiated prophylaxis for PONV and achieved a similar prophylactic effect as that with a higher dose of palonosetron.

Palonosetron-5-HT3 Receptor Interactions As Shown by a Binding Protein Cocrystal Structure

Palonosetron is a potent 5-HT₃ receptor antagonist and an effective therapeutic agent against emesis. Here we identify the molecular determinants of compound recognition in the receptor binding site by obtaining a high resolution structure of palonosetron bound to an engineered acetylcholine binding protein that mimics the 5-HT₃ receptor binding site, termed 5-HTBP, and by examining the potency of palonosetron in a range of 5-HT₃ receptors with mutated binding site residues. The structural data indicate that palonosetron forms a tight and effective wedge in the binding pocket, made possible by its rigid tricyclic ring structure and its interactions with binding site residues; it adopts a binding pose that is distinct from the related antiemetics granisetron and tropisetron. The functional data show many residues previously shown to interact with agonists and antagonists in the binding site are important for palonosetron binding, and indicate those of particular importance are W183 (a cation-π interaction and a hydrogen bond) and Y153 (a hydrogen bond). This information, and the availability of the structure of palonosetron bound to 5-HTBP, should aid the development of novel and more efficacious drugs that act via 5-HT₃ receptors.

Synthesis and Pharmacological Evaluation of [11C]Granisetron and [18F]Fluoropalonosetron as PET Probes for 5-HT3 Receptor Imaging

Serotonin-gated ionotropic 5-HT₃ receptors are the major pharmacological targets for antiemetic compounds. Furthermore, they have become a focus for the treatment of irritable bowel syndrome (IBS) and there is some evidence that pharmacological modulation of 5-HT₃ receptors might alleviate symptoms of other neurological disorders. Highly selective, high-affinity antagonists, such as granisetron (Kytril) and palonosetron (Aloxi), belong to a family of drugs (the "setrons") that are well established for clinical use. To enable us to better understand the actions of these drugs in vivo, we report the synthesis of 8-fluoropalonosetron (15) that has a binding affinity (K_i = 0.26 ± 0.05 nM) similar to the parent drug (K_i = 0.21 ± 0.03 nM). We radiolabeled 15 by nucleophilic ¹⁸F-fluorination of an unsymmetrical diaryliodonium palonosetron precursor and achieved the radiosynthesis of 1-(methyl-¹¹C)-N-granisetron ([¹¹C]2) through N-alkylation with [¹¹C]CH₃I, respectively. Both compounds [¹⁸F]15 (chemical and radiochemical purity >95%, specific activity 41 GBq/μmol) and [¹¹C]2 (chemical and radiochemical purity ≥99%, specific activity 170 GBq/μmol) were evaluated for their utility as positron emission tomography (PET) probes. Using mouse and rat brain slices, in vitro autoradiography with both [¹⁸F]15 and [¹¹C]2 revealed a heterogeneous and displaceable binding in cortical and hippocampal regions that are known to express 5-HT₃ receptors at significant levels. Subsequent PET experiments suggested that [¹⁸F]15 and [¹¹C]2 are of limited utility for the PET imaging of brain 5-HT₃ receptors in vivo.

In silico investigation into the interactions between murine 5-HT3 receptor and the principle active compounds of ginger (Zingiber officinale)

Gingerols and shogaols are the primary non-volatile actives within ginger (Zingiber officinale). These compounds have demonstrated in vitro to exert 5-HT3 receptor antagonism which could benefit chemotherapy-induced nausea and vomiting (CINV). The site and mechanism of action by which these compounds interact with the 5-HT3 receptor is not fully understood although research indicates they may bind to a currently unidentified allosteric binding site. Using in silico techniques, such as molecular docking and GRID analysis, we have characterized the recently available murine 5-HT3 receptor by identifying sites of strong interaction with particular functional groups at both the orthogonal (serotonin) site and a proposed allosteric binding site situated at the interface between the transmembrane region and the extracellular domain. These were assessed concurrently with the top-scoring poses of the docked ligands and included key active gingerols, shogaols and dehydroshogaols as well as competitive antagonists (e.g. setron class of pharmacologically active drugs), serotonin and its structural analogues, curcumin and capsaicin, non-competitive antagonists and decoys. Unexpectedly, we found that the ginger compounds and their structural analogs generally outscored other ligands at both sites. Our results correlated well with previous site-directed mutagenesis studies in identifying key binding site residues. We have identified new residues important for binding the ginger compounds. Overall, the results suggest that the ginger compounds and their structural analogues possess a high binding affinity to both sites. Notwithstanding the limitations of such theoretical analyses, these results suggest that the ginger compounds could act both competitively or non-competitively as has been shown for palonosetron and other modulators of CYS loop receptors.

Comparison between the antiemetic effects of palonosetron and granisetron in breast cancer patients treated with anthracycline-based regimens

Chemotherapy-induced nausea and vomiting is a serious adverse side-effect of anthracycline-based chemotherapy regimens, in patients with breast cancer. A combination of three drugs, 5-hydroxytryptamine (5-HT₃) receptor antagonist, aprepitant and dexamethasone, is recommended for antiemetic therapy. Palonosetron (PALO), a novel 5-HT₃ receptor antagonist has been identified to be effective against delayed nausea and vomiting. In this study, the results of PALO for patients who received anthracycline-based chemotherapy were compared with that of granisetron (GRA) using a crossover study design. This study evaluated the efficacy of antiemetics in the first cycle of chemotherapy, as well as the second and third cycles. A total of 21 patients and 19 patients were assigned to PALO and GRA treatment groups during the first cycle of chemotherapy, respectively. The patients switched to the other antiemetic drug for the second chemotherapy cycle (PALO followed by GRA or GRA followed by PALO). The patients could select PALO or GRA antiemetics for the third cycle, according to their preference. A total of 21 patients selected PALO and 18 patients selected GRA in the third cycle, and one patient was withdrawn from the study as their third cycle questionnaire was not obtained. No significant differences between PALO and GRA were identified in first and second cycles. However, during the third cycle, a significant difference was observed in acute-phase complete control of emetic events between the PALO and GRA groups, which was defined as no emetic episode, no additional antiemetic treatment and no more than mild nausea, between PALO and GRA. These results demonstrated that changing antiemetics may affect the efficacy of antiemetics. This study indicates that alteration of antiemetic regimens, including drug combination and order, may improve the efficacy of antiemetic treatment.

5-Hydroxytryptamine (5-HT) cellular sequestration during chronic exposure delays 5-HT3 receptor resensitization due to its subsequent release

The serotonergic synapse is dynamically regulated by serotonin (5-hydroxytryptamine (5-HT)) with elevated levels leading to the down-regulation of the serotonin transporter and a variety of 5-HT receptors, including the 5-HT type-3 (5-HT₃) receptors. We report that recombinantly expressed 5-HT₃ receptor binding sites are reduced by chronic exposure to 5-HT (IC₅₀ of 154.0 ± 45.7 μm, t_½ = 28.6 min). This is confirmed for 5-HT₃ receptor-induced contractions in the guinea pig ileum, which are down-regulated after chronic, but not acute, exposure to 5-HT. The loss of receptor function does not involve endocytosis, and surface receptor levels are unaltered. The rate and extent of down-regulation is potentiated by serotonin transporter function (IC₅₀ of 2.3 ± 1.0 μm, t_½ = 3.4 min). Interestingly, the level of 5-HT uptake correlates with the extent of down-regulation. Using TX-114 extraction, we find that accumulated 5-HT remains soluble and not membrane-bound. This cytoplasmically sequestered 5-HT is readily releasable from both COS-7 cells and the guinea pig ileum. Moreover, the 5-HT level released is sufficient to prevent recovery from receptor desensitization in the guinea pig ileum. Together, these findings suggest the existence of a novel mechanism of down-regulation where the chronic release of sequestered 5-HT prolongs receptor desensitization.

Evaluation of the ability of continuous palonosetron infusion, using a patient-controlled analgesia device, to reduce postoperative nausea and vomiting

BACKGROUND

The efficacy of palonosetron in preventing postoperative nausea and vomiting (PONV), as well as chemotherapy-induced nausea and vomiting, has already been demonstrated in multiple clinical studies. The purpose of this study was to determine whether continuous infusion of palonosetron following single injection could reduce PONV to a greater extent than single injection only of palonosetron.

METHODS

In total, 132 women were enrolled in the study. All subjects were over the age of 20 years and were scheduled to undergo gynecologic laparoscopic surgery. Patients were randomly allocated into two groups. In both groups, patients received 0.075 mg of palonosetron intravenously, immediately before induction of anesthesia. In the continuous palonosetron infusion group, 0.075 mg (1.5 ml) of palonosetron was added to the patient-controlled analgesia device. In the single-injection palonosetron group, 1.5 ml of normal saline was added.

RESULTS

The incidence of PONV 24 hours postoperatively was significantly lower in the continuous palonosetron infusion group than the single-injection palonosetron group (31.8 vs. 56.1%, P = 0.009).

CONCLUSIONS

Continuous palonosetron infusion, following single injection, reduces the incidence of PONV compared with single injection only.

Exploring a potential palonosetron allosteric binding site in the 5-HT(3) receptor

Palonosetron (Aloxi) is a potent second generation 5-HT(3) receptor antagonist whose mechanism of action is not yet fully understood. Palonosetron acts at the 5-HT(3) receptor binding site but recent computational studies indicated other possible sites of action in the extracellular domain. To test this hypothesis we mutated a series of residues in the 5-HT3A receptor subunit (Tyr(73), Phe(130), Ser(163), and Asp(165)) and in the 5-HT3B receptor subunit (His(73), Phe(130), Glu(170), and Tyr(143)) that were previously predicted by in silico docking studies to interact with palonosetron. Homomeric (5-HT(3)A) and heteromeric (5-HT(3)AB) receptors were then expressed in HEK293 cells to determine the potency of palonosetron using both fluorimetric and radioligand methods to test function and ligand binding, respectively. The data show that the substitutions have little or no effect on palonosetron inhibition of 5-HT-evoked responses or binding. In contrast, substitutions in the orthosteric binding site abolish palonosetron binding. Overall, the data support a binding site for palonosetron at the classic orthosteric binding pocket between two 5-HT3A receptor subunits but not at allosteric sites previously identified by in silico modelling and docking.

Palonosetron plus dexamethasone in highly emetogenic chemotherapy: pooled data from two Phase III trials

Aim: Data from two randomized trials were pooled to further characterize the effectiveness of palonosetron combined with dexamethasone in the setting of highly emetogenic chemotherapy. Patients & methods: The analysis included 1411 patients who were randomized to receive palonosetron or ondansetron/granisetron intravenously on day 1 plus either 1-day or 3-day dexamethasone dosing. The primary end point was complete response (no vomiting and no rescue antiemetics over days 1–5) in cycle one. Data across the studies were analyzed by the Mantel–Haenszel method. Results: The vast majority of patients received either cisplatin (62%) or anthracycline plus cyclophosphamide (34%). The palonosetron regimen provided a 12 percentage-point improvement in the rate of overall complete response compared with the control regimen (49.2 vs 37.3%; odds ratio: 1.65; 95% CI: 1.33–2.04; p < 0.0001). The frequency of no delayed nausea at all daily periods was consistently higher in the palonosetron group. Conclusion: The current analysis confirmed that palonosetron plus dexamethasone improved control of highly emetogenic chemotherapy-induced nausea and vomiting throughout 5 days postchemotherapy to a significantly greater extent than the combination including older 5-HT3 antagonists.

Agonists and antagonists induce different palonosetron dissociation rates in 5-HT₃A and 5-HT₃AB receptors

Palonosetron is a potent 5-HT₃ receptor antagonist with a unique structure and some unusual properties. Here we explore the properties of palonosetron at heterologously expressed 5-HT₃A and 5-HT₃AB receptors. We used receptors expressed in HEK293 cells, and functionally analysed them using a membrane potential sensitive dye in a Flexstation, which revealed IC₅₀s of 0.24 nM and 0.18 nM for 5-HT₃A and 5-HT₃AB receptors respectively. Radioligand binding studies with [³H]palonosetron revealed similar K_ds: 0.34 nM for 5-HT₃A and 0.15 nM for 5-HT₃AB receptors. Kinetic studies showed palonosetron association and dissociation rates were slightly faster in 5-HT₃AB than 5-HT₃A receptors, and for both subtypes dissociation rates were ligand-dependent, with antagonists causing more rapid dissociation than agonists. Similar ligand effects were not observed for [³H]granisetron dissociation studies. These data support previous studies which show palonosetron has actions distinct to other 5-HT₃ receptor antagonists, and the slow rates observed for agonist induced dissociation (t_1/2 > 10 h) could at least partly explain the long duration of palonosetron effects in vivo.

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Palonosetron IC₅₀s and K_ds for 5-HT₃A and 5-HT₃AB receptors in HEK293 cells are similar.

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Palonosetron association and dissociation rates are slower at 5-HT₃A than 5-HT₃AB receptors.

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Agonist-induced palonosetron dissociation rates are slower than those for antagonists in both 5-HT₃A and 5-HT₃AB receptors.

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Agonist- and antagonist-induced granisetron dissociation rates are similar in both 5-HT₃A and 5-HT₃AB receptors.

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Palonosetron and granisetron have distinct actions.