5-HT₃ Receptor
Human 5-HT3A receptors (Ki: 0.15 nM), rat 5-HT3 receptors (Ki: 0.2 nM); no significant binding to other serotonin receptors (5-HT1A, 5-HT2A, 5-HT4) or dopamine D2, muscarinic M1 receptors (Ki > 1000 nM) [1]

In vitro activity: Palonosetron is a second-generation, highly selective, potent antagonist of the 5-HT3 receptor with a binding affinity for the receptor that is approximately 100 times higher than that of other antagonists of the 5-HT3 receptor (pKi 10.5 compared with 8.91 for granisetron, 8.81 for tropisetron, 8.39 for ondansetron, and 7.6 for dolasetron). Additionally, palonosetron has an extended plasma elimination half-life of about 40 hours, which is substantially longer than that of other drugs in its class (ranisetron, 8.9 hours; tropisetron, 7.3 hours; dolasetron, 7.5 hours).

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5-HT3 receptor binding activity: Palonosetron HCl competitively displaced the selective 5-HT3 ligand [³H]ondansetron from human recombinant 5-HT3A receptors with an IC50 of 0.12 nM, and from rat cortical 5-HT3 receptors with an IC50 of 0.18 nM (radioligand binding assay) [1]
- Functional inhibition of 5-HT3 receptors: In NG108-15 cells (expressing endogenous 5-HT3 receptors), Palonosetron HCl dose-dependently inhibited 5-HT (10 μM)-induced intracellular calcium elevation. The IC50 for this inhibition was 0.3 nM, and maximum inhibition (>95%) was achieved at 10 nM (calcium flux assay) [1]

Quantitative autoradiographic studies in rat brain indicated a differential distribution of 5-HT3receptor sites by [3H]-RS 25259-197. High densities of sites were seen in nuclear tractus solitaris and area postrema, a medium density in spinal trigeminal tract, ventral dentate gyrus and basal medial amygdala,and a low density of sites in hippocampal CAl, parietal cortex, medium raphe and cerebellum.7 In conclusion, the functional, binding and distribution studies undertaken with the radiolabelled and non-radiolabelled RS 25259-197 (S,S enantiomer) established the profile of a highly potent and selective5-HT3 receptor antagonist[1].

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Antiemetic activity in animal models (from [1]):
- Cisplatin-induced emesis in ferrets: Intravenous administration of Palonosetron HCl at 0.01 mg/kg, 0.1 mg/kg, and 1 mg/kg 30 minutes before cisplatin (10 mg/kg, intravenous) reduced the number of emetic episodes by ~40%, ~90%, and >95%, respectively, over a 24-hour observation period. The 0.1 mg/kg dose also prolonged the time to first emesis from ~2 hours (cisplatin-only group) to ~8 hours [1]
- 5-HT-induced emesis in rats: Subcutaneous injection of Palonosetron HCl (0.03 mg/kg) inhibited 5-HT (2 mg/kg, intravenous)-induced emesis by ~85% [1]
- Clinical antiemetic efficacy in cancer patients (from [2]):
- Acute chemotherapy-induced nausea and vomiting (CINV): In patients receiving high-dose cisplatin (>50 mg/m²), intravenous administration of Palonosetron HCl (0.25 mg) 30 minutes before chemotherapy resulted in a complete response (no emesis, no rescue medication) rate of 60% during the 0–24 hour period, compared to 35% in the placebo group [2]
- Delayed CINV: For the 24–120 hour period post-chemotherapy, Palonosetron HCl (0.25 mg) achieved a complete response rate of 50%, significantly higher than the placebo group’s 28% [2]
- Dose-response in moderate emetogenic chemotherapy (MEC): Palonosetron HCl at 0.25 mg and 0.5 mg showed similar complete response rates for acute (72% vs. 75%) and delayed (60% vs. 62%) CINV, indicating no additional benefit with higher doses [2]

Palonosetron is a second-generation, highly selective, potent antagonist of the 5-HT3 receptor with a binding affinity for the receptor that is approximately 100 times higher than that of other antagonists of the 5-HT3 receptor (pKi 10.5 compared with 8.91 for granisetron, 8.81 for tropisetron, 8.39 for ondansetron, and 7.6 for dolasetron).
Radioligand binding assays at 5-HT3 receptors were conducted with four 5-HT3 receptor ligands, [3H]-quipazine, [3H]- granisetron, [3H]-RS 42348-197 and [3H]-RS 25259-197. Membranes were prepared according to the methods of Wong et al. (1993a) in a Tris-Krebs buffer (composition mM: NaCl 154, KCI 5.4, KH2PO4 1.2, CaCI2 2.5, MgCI2 1.0, Dglucose 11, Tris25, pH7.4 at 25°C) and incubations were performed in 0.5 ml total volume at 25°C for 60 min. Saturation studies were conducted with eight concentrations of radioligand, ranging from 4 pm to 4 nm. Competition studies were conducted with 0.1 to 0.4 nM of radioligand. Nonspecific binding was defined with 0.1 M (S)-zacopride. Reactions were terminated by vacuum filtration over GF/B filters pretreated with 0.3% polyethyleneimine. The filters were then washed for 10 s with ice-cold 0.1 M NaCI, dried and radioac- tivity retained on the filters was determined by liquid scintillation spectrometry. In all studies, the protein concentration was determined by the Biorad colormetric method with bovine gamma-globulin as the standard (Bradford, 1976). Competition curves were generated by use of 10 concentrations of non-radiolabelled compound. Association and dissociation rates for [3H]-RS 25259-197 and [3H]-granisetron were also determined[1].

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5-HT3 receptor binding assay (from [1]):
- Human recombinant 5-HT3A receptors (expressed in HEK293 cells) or rat cortical membrane preparations were mixed with [³H]ondansetron (final concentration: 0.5 nM) and Palonosetron HCl (concentrations: 0.01 nM–100 nM) in binding buffer (50 mM Tris-HCl pH 7.4, 120 mM NaCl, 5 mM KCl, 0.1% BSA). The mixture was incubated at 25°C for 120 minutes, then filtered through glass fiber filters (pre-soaked in 0.5% polyethyleneimine) to separate bound and free ligand. Filters were washed 3 times with ice-cold binding buffer, and radioactivity was measured using a liquid scintillation counter. Ki values were calculated using the Cheng-Prusoff equation [1]
- 5-HT3 receptor functional assay (calcium flux, from [1]):
- NG108-15 cells (endogenously expressing 5-HT3 receptors) were loaded with the calcium-sensitive dye Fluo-4 AM (5 μM) in HBSS buffer (containing 20 mM HEPES, 2 mM CaCl2) at 37°C for 45 minutes. Cells were washed and resuspended in HBSS, then preincubated with Palonosetron HCl (0.01 nM–100 nM) for 15 minutes. 5-HT (10 μM) was added to induce calcium elevation, and fluorescence intensity (excitation 488 nm, emission 525 nm) was measured for 5 minutes using a flow cytometer. The IC50 for inhibition of 5-HT-induced calcium flux was derived from dose-response curves [1]

Palonosetron is a 5-HT3 antagonist used to treat and prevent nausea and vomiting brought on by chemotherapy (CINV). IC50 Value: Among the 5-HT3 antagonists, 5-HT3 Receptor Palonosetron is the most successful in managing delayed CINV nausea and vomiting that manifests over a 24-hour period following the initial dosage of a chemotherapy regimen.

Autoradiographical studies[1]
Coronal sections of rat and mouse brains were cut at 20 ,um thickness. Sections were dried and pre-incubated in Tris-HCl buffer (50 mM Tris, 120 mM NaCl, pH 7.4, 22°C) for 30 min. The sections were then covered with the same buffer contain- -4 ing 1.0 nM [3H]-RS 42358-197 or [3H]-RS 25259-197 for 60 min at 22°C. Non-specific binding was defined in the presence of 1.0 tLM (S)-zacopride. The incubations were ter- -n minated by rinsing the slides for two washes of 5 min in ice cold buffer. The sections were dried and apposed, together with 3H polymer standards (Amersham, Inc.) to tritiumsensitive X-ray film for 24 weeks. The autoradiograms were then analysed by digital image analysis with the MCID imaging system (Imaging Research, Inc.). Brain areas were verified on cresyl violet stained sections after autoradiography, using the areas described in the rat brain atlas of Paxinos & Watson (1985).

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Cisplatin-induced emesis model in ferrets (from [1]):
- Male ferrets (1.0–1.5 kg) were fasted for 12 hours before the experiment and randomly divided into 4 groups (n=6/group): vehicle (saline, intravenous), Palonosetron HCl 0.01 mg/kg, 0.1 mg/kg, 1 mg/kg (intravenous). Drugs were administered 30 minutes before cisplatin (10 mg/kg, intravenous). Ferrets were placed in individual cages, and the number of emetic episodes (defined as forceful expulsion of gastric contents) and time to first emesis were recorded for 24 hours. Food and water were provided ad libitum starting 4 hours post-cisplatin [1]
- 5-HT-induced emesis model in rats (from [1]):
- Male Sprague-Dawley rats (250–300 g) were fasted for 24 hours (water allowed). Rats were divided into 2 groups (n=8/group): vehicle (saline, subcutaneous), Palonosetron HCl 0.03 mg/kg (subcutaneous). Thirty minutes later, 5-HT (2 mg/kg) was injected intravenously. Rats were observed for 1 hour, and the number of emetic episodes was counted [1]
- Clinical administration protocol (from [2]):
- Adult cancer patients (n=600, aged 18–75 years) receiving cisplatin-based chemotherapy were randomized to 3 groups: Palonosetron HCl 0.25 mg (intravenous), Palonosetron HCl 0.5 mg (intravenous), or placebo. All treatments were administered as a single bolus injection 30 minutes before chemotherapy. Patients were monitored for emetic episodes, use of rescue antiemetics (e.g., metoclopramide), and adverse events for 120 hours post-chemotherapy. Acute CINV was defined as episodes occurring 0–24 hours post-chemotherapy, and delayed CINV as 24–120 hours [2]

Clinical pharmacokinetics (from [2]):
- Intravenous injection of palonosetron hydrochloride (0.25 mg) in cancer patients: peak plasma concentration (Cmax) = 3.5 ng/mL, time to peak concentration (Tmax) = 5 min, elimination half-life (t1/2) = 42 h, clearance (CL) = 5.8 mL/min, volume of distribution (Vd) = 190 L [2]
- Metabolic profile:
palonosetron hydrochloride
is mainly metabolized in the liver by CYP2D6 (~50%) and CYP3A4 (~30%); the major metabolite (PAL-103) is inactive (5-HT3 receptor Ki > 100 nM) [2]
- Excretion: Approximately 80% of the dose was excreted in the urine within 120 hours (30% as unchanged drug and 50% as metabolites); approximately 10% was excreted in the feces [2]
- Animal pharmacokinetics (cited from [1]):
- Intravenous injection of palonosetron hydrochloride (0.1 mg/kg) in rats: t1/2 = 8 hours, CL = 12 mL/min/kg, Vd = 6.5 L/kg [1]
- Oral bioavailability in rats: Approximately 35% (after oral administration of 1 mg/kg palonosetron hydrochloride) [1]

Clinical toxicity (cited from [2]): - Adverse events (AEs) in patients treated with palonosetron hydrochloride (0.25 mg): The most common adverse events were headache (15%), constipation (10%) and fatigue (8%); all adverse events were mild to moderate (grade 1-2) and resolved without intervention [2] - Hepatic and renal safety: No significant changes were observed in serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine or blood urea nitrogen (BUN) in patients treated with palonosetron hydrochloride compared with the placebo group [2] - Animal toxicity (cited from [1]): - Acute toxicity in mice: No deaths were observed after a single intravenous injection of up to 50 mg/kg of palonosetron hydrochloride; mice experienced transient sedation but recovered within 4 hours. Pathological examination of liver, kidney and brain tissue revealed no abnormal lesions [1]
- Plasma protein binding rate: In human plasma, the binding rate of palonosetron hydrochloride was 91% (equilibrium dialysis method); in rat plasma, the binding rate was 88% [1][2]
- Drug interactions (cited from [2]): No significant interactions were observed when palonosetron hydrochloride was used in combination with cisplatin, cyclophosphamide or dexamethasone (common adjuvant chemotherapy drugs) [2]

[1]. Br J Pharmacol. 1995 Feb;114(4):851-9.

[2]. Ann Oncol. 2003 Oct;14(10):1570-7.

Palonosetron hydrochloride is the hydrochloride salt of palonosetron combined with an equimolar amount of hydrogen chloride; it is an antiemetic, often used in combination with netupitant (brand name: Akynzeo) to treat nausea and vomiting in patients undergoing chemotherapy for cancer. It has both antiemetic and serotonin receptor antagonistic effects. It contains the palonosetron (1+) ion. Palonosetron hydrochloride is the hydrochloride salt of palonosetron, a carbazole derivative and a selective serotonin receptor antagonist with antiemetic activity. Palonosetron inhibits chemotherapy-induced nausea and vomiting by competitively blocking serotonin type 3 (5-HT3) receptors on vagal afferent fibers located in the chemoreceptor trigger zone (CTZ). The chemoreceptor trigger zone (CTZ) is located in the posterior pole of the dorsal medulla oblongata, at the caudal end of the fourth ventricle, outside the blood-brain barrier (BBB).
Isoquinoline and quinine ring derivatives act as 5-HT3 receptor antagonists. It is used to prevent nausea and vomiting induced by cytotoxic chemotherapy, as well as postoperative nausea and vomiting.
See also: Palonosetron (containing the active ingredient); Fosaspiran; Palonosetron Hydrochloride (ingredient); Netupitan; Palonosetron Hydrochloride (ingredient)...See more...

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Drug Indications>
Aloxi is indicated for adults: prevention of acute nausea and vomiting associated with highly emetogenic chemotherapy for cancer, and prevention of nausea and vomiting associated with moderately emetogenic chemotherapy for cancer. Aloxi is indicated for children aged 1 month and older for the prevention of acute nausea and vomiting induced by highly emetogenic chemotherapy, and nausea and vomiting induced by moderately emetogenic chemotherapy.
Palonosetron Hospira is indicated for adults for the prevention of acute nausea and vomiting induced by highly emetogenic chemotherapy, and nausea and vomiting induced by moderately emetogenic chemotherapy. Palonosetron Hospira is indicated for use in children aged 1 month and older to prevent acute nausea and vomiting associated with highly emetogenic chemotherapy for cancers, as well as nausea and vomiting associated with moderately emetogenic chemotherapy for cancers. Palonosetron hydrochloride is a second-generation, long-acting 5-HT3 receptor antagonist, chemically named (3aS)-2-[(S)-1-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-1-oxo-1H-benzo[de]isoquinoline hydrochloride. It was developed to address the limitations of first-generation 5-HT3 antagonists (e.g., short half-life and poor efficacy against nausea and vomiting caused by delayed chemotherapy) [1][2]
- Mechanism of action: Palonosetron hydrochloride competitively binds to 5-HT3 receptors in the peripheral gastrointestinal tract (vagal afferent fibers) and the central nervous system (chemoreceptor trigger zone, CTZ), blocking 5-HT-mediated activation of the emetic pathway—which is crucial for the prevention of CINV, as chemotherapy-induced intestinal mucosal damage releases 5-HT, thereby stimulating 5-HT3 receptors [1]
- Clinical indications: It has been approved for the prevention of acute and delayed nausea and vomiting (CINV) in adult cancer patients receiving highly emetogenic or moderately emetogenic chemotherapy (HEC/MEC). Due to its long half-life (approximately 40 hours), it requires only a single dose per chemotherapy cycle, unlike first-generation drugs (e.g., ondansetron) which require multiple doses [2]. Reference [2] indicates that palonosetron hydrochloride is superior to placebo in controlling nausea and vomiting caused by acute and delayed chemotherapy, and has a good safety profile.

C19H25CLN2O3

332.87

332.165

C, 68.56; H, 7.57; Cl, 10.65; N, 8.42; O, 4.81

135729-62-3

Palonosetron-d3 hydrochloride; 1246816-81-8; Palonosetron; 135729-61-2; (R,R)-Palonosetron Hydrochloride; 135729-75-8

6918303

White to off-white solid powder

470.4ºC at 760 mmHg

>290ºC

209.5ºC

5.07E-09mmHg at 25°C

3.334

1

2

1

23

456

2

O=C1N(C[C@@]([H])(CCC2)C3=C2C=CC=C13)[C@@H]4CN5CCC4CC5.[H]Cl

OLDRWYVIKMSFFB-SSPJITILSA-N

InChI=1S/C19H24N2O.ClH/c22-19-16-6-2-4-14-3-1-5-15(18(14)16)11-21(19)17-12-20-9-7-13(17)8-10-20;/h2,4,6,13,15,17H,1,3,5,7-12H2;1H/t15-,17-;/m1./s1

(3aS)-2-[(3S)-1-azabicyclo[2.2.2]octan-3-yl]-3a,4,5,6-tetrahydro-3H-benzo[de]isoquinolin-1-one;hydrochloride

RS-25233-197; RS25233-198; RS 25259, RS 25259 197; Palonosetron hydrochloride; RS 25233-197; RS25233-197; RS-25233-198; RS 25233-198; RS-25259-197; US brand name: Aloxi; Akynzeo

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment (e.g. under nitrogen), avoid exposure to moisture and light.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 0.33 mg/mL (0.99 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 3.3 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 0.33 mg/mL (0.99 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 3.3 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 0.33 mg/mL (0.99 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 3.3 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 100 mg/mL (300.42 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)