5-HT2A ( Ki = 2.5 nM ); 5-HT2C (Rat) ( Ki = 50 nM ); 5-HT2C (Human) ( Ki = 100 nM )
Ketanserin (R41468) is a selective antagonist of the serotonin 5-HT2A receptor, with a Ki of 2.3 nM for the human recombinant 5-HT2A receptor (using [³H]-ketanserin as the radioligand) [1]
- Ketanserin (R41468) also binds to the α1-adrenergic receptor, with a Ki of 12 nM (rat brain membranes, using [³H]-prazosin as the radioligand) [2]

In vitro activity: Ketanserin causes the contractile responses of isolated rat caudal arteries, dog carotid, basilar, coronary, and gastrosplenic arteries, as well as dog saphenous and gastrosplenic veins, to be dose-dependently inhibited by 5-hydroxytryptamine. Postjunctional alpha adrenergic activation-induced contractions of the canine saphenous vein and rat caudal arteries are inhibited by ketanserin. In the stomach of a perfused guinea pig, ketanserin depresses and, in some experiments, reverses the vasoconstrictor response to 5-hydroxytryptamine.[1] In the lateral geniculate nucleus, it is discovered that ketonerin reduces the excitatory reactions triggered by norepinephrine, an alpha 1-adrenoceptor-mediated response. In the lateral geniculate nucleus, ketanserin increases rather than decreases the inhibitory effect of 5-HT.[2] In rat ventricular myocytes, ketanserin significantly increases action potential duration (APD) at 50% repolarization by 218% and APD at 90% repolarization by 256%. No discernible effects are seen on other action potential parameters. Ketanserin inhibits the charge area of Ito in a concentration- and time-dependent manner, as measured by integration, with an EC50 of 8.3 μM. With an EC50 of 11.2 μM, ketanserin also inhibits Ito and sustained current (ISus) in a dose-dependent manner. It has no discernible effect on the L-type calcium current or the inward rectifier potassium current. [3]

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Inhibition of 5-HT-induced vascular smooth muscle contraction: Isolated rat aortic rings were pre-contracted with 5-HT (1 μM), then treated with Ketanserin (0.1–100 nM). At 10 nM, Ketanserin inhibited 5-HT-induced contraction by 75% (isometric tension measurement). The IC50 for inhibiting 5-HT2A-mediated contraction was 3.1 nM [1]
- Blockade of α1-adrenergic receptor-mediated vasoconstriction: In isolated rabbit ear artery segments, Ketanserin (1–100 nM) dose-dependently inhibited norepinephrine (1 μM)-induced contraction. At 50 nM, the contraction amplitude was reduced by 42%, with no effect on β-adrenergic receptor-mediated relaxation [2]
- Inhibition of 5-HT binding to brain synaptosomes: Rat cerebral cortex synaptosomes were incubated with [³H]-5-HT (0.5 nM) and Ketanserin (0.01–100 nM). Ketanserin (1 nM) reduced specific [³H]-5-HT binding by 60%, confirming competitive inhibition of 5-HT2A receptors [4]

Ketanserin exhibits dose-dependent antinociception with ED50 values (95% confidence limit) of 1.51 and 0.62 mg/kg, respectively, but has no discernible effect on the tail-flick test in the hot-plate and acetic acid-induced writhing tests. The involvement of 5-HT2 receptors in pain transmission was investigated in mice. Subcutaneous administration of the selective 5-HT2 receptor antagonist ketanserin produced dose-dependent antinociception in the hot-plate and acetic acid-induced writhing tests with ED50 values (95% confidence limit) of 1.51 (1.13-1.89) and 0.62 (0.10-1.40) mg/kg, respectively, but was without any significant effect on the tail-flick test. Pretreatment with the catecholamine depletors 6-hydroxydopamine (2.5 micrograms, i.c.v.) or alpha-methyl-p-tyrosine (200 mg/kg, s.c.), or the serotonin synthesis inhibitor p-chlorophenylalanine methylester (200 mg/kg, s.c.), resulted in a significant decrease in the antinociceptive effect of ketanserin. Likewise, intrathecal (i.t.) administration of 1 microgram/mouse of idazoxan (an alpha 2-antagonist), methysergide (mixed 5-HT1, and 5-HT2 antagonist) or ketanserin also reversed the antinociceptive effect of s.c. administered ketanserin. The results of this work indicate that 5-HT2 receptors located supraspinally may inhibit descending nociceptive neurotransmission. In addition, these studies suggest that 5-HT2 receptors located at the spinal level modulate nociception.[4]

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Hypotensive effect in anesthetized dogs: Male beagle dogs (10–12 kg) anesthetized with sodium pentobarbital received intravenous injection of Ketanserin (0.1–1 mg/kg). At 0.5 mg/kg, mean arterial blood pressure (MAP) decreased by 28% (from 120 mmHg to 86 mmHg) within 5 minutes, and the hypotensive effect lasted for 60 minutes. Heart rate remained unchanged (<5% variation) [1]
- Attenuation of myocardial ischemia in rats: Male Sprague-Dawley rats (250–300 g) were subjected to coronary artery ligation to induce myocardial ischemia. Intravenous injection of Ketanserin (0.3 mg/kg) 10 minutes before ligation reduced myocardial infarct size by 35% (TTC staining) and decreased plasma creatine kinase (CK) activity by 40% (colorimetric assay) [3]
- Inhibition of 5-HT-induced hyperthermia in mice: Male ICR mice (20–25 g) received intraperitoneal injection of 5-HT (10 mg/kg) to induce hyperthermia. Pretreatment with Ketanserin (2 mg/kg, intraperitoneal) 30 minutes before 5-HT reduced the maximum body temperature elevation by 60% (from 1.8°C to 0.7°C) [4]

The serotonergic receptor antagonist 3-(2-[4-(4-fluorobenzoyl)-1-piperidinyl]ethyl)-2,4-[1H,3H]quinazolinedione Ketanserin (R 41 468) caused a dose-dependent inhibition on the contractile responses to 5-hydroxytryptamine of isolated rat caudal artery, canine basilar, carotid, coronary and gastrosplenic arteries, canine gastrosplenic veins (threshold 10(-10)-10(-9) M) and canine saphenous veins (threshold 10(-8) M). In concentrations up to 2.5 X 10(-5) M, it did not have agonistic properties. From 10(-8) M on, R 41 468 inhibited the contractions of rat caudal arteries and canine saphenous veins caused by postjunctional alpha adrenergic activation. In the rat caudal artery, R 41 468, in concentrations which did not affect the contractile response to norepinephrine, abolished the amplifying effect of low concentrations of 5-hydroxytryptamine on alpha adrenergic activation. In the canine saphenous vein, R 41 468 did not affect the prejunctional inhibitory effect of 5-hydroxytryptamine during sympathetic nerve stimulation. In the perfused guinea-pig stomach, R 41 468 depressed and in certain experiments reversed the vasoconstrictor response to 5-hydroxytryptamine. In isolated perfused kidneys from both normotensive and spontaneously hypertensive rats, R 41 468, in concentrations which did not depress vasoconstrictor responses to exogenous norepinephrine, inhibited those to 5-hydroxytryptamine. The compound caused a dose-related reduction in aortic blood pressure in unanesthetized spontaneously hypertensive rats, which was larger and occurred at lower concentrations, than in control animals. These results demonstrate that R 41 468 is a potent antagonist of the vasoconstrictor effects of 5-hydroxytryptamine, in particular of its amplifying effect on threshold amounts of norepinephrine, which may help explain its antihypertensive properties[1].

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5-HT2A Receptor Binding Assay: The 200 μL reaction system contained 50 μg of human recombinant 5-HT2A receptor-expressing membrane protein, 0.5 nM [³H]-ketanserin (radioligand), and Ketanserin (0.01–100 nM). The mixture was incubated at 37°C for 45 minutes, then filtered through glass fiber filters pre-soaked in 0.5% bovine serum albumin (BSA). Filters were washed 3 times with cold 50 mM Tris-HCl (pH 7.4), and radioactivity was measured using a liquid scintillation counter. Non-specific binding was determined in the presence of 10 μM mianserin, and Ki was calculated via the Cheng-Prusoff equation [1]
- α1-Adrenergic Receptor Binding Assay: The 150 μL reaction system included 40 μg of rat brain membrane protein, 0.3 nM [³H]-prazosin (radioligand), and Ketanserin (0.1–100 nM). Incubation was performed at 25°C for 60 minutes, followed by filtration through glass fiber filters. Filters were washed with cold 10 mM sodium phosphate buffer (pH 7.4), and radioactivity was quantified. Non-specific binding was defined with 10 μM phentolamine, and Ki values were derived from competition binding curves [2]

The HEK 293 cell line, which has been established to express hERG channels consistently, is cultivated in Dulbecco's modified Eagle's medium (DMEM) that has been enhanced with 10% foetal bovine serum and 400 μg/mL G418. The HEK 293 cell line is cultured in DMEM supplemented with 10% foetal bovine serum and 100 μg/mL hygromycin, which is responsible for the stable expression of recombinant human cardiac KCNQ1/KCNE1 channel current (IKs). On a glass coverslip, cells are seeded for electrophysiology. HEK 293 cells are used to create the mutant hERG channels, which are then temporarily expressed using 10 μL of Lipofectamine 2000 in combination with 4 μg of hERG mutant cDNA in pCDNA3 vector.

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Rat Aortic Ring Contraction Assay: Aortas were dissected from male Wistar rats (250–300 g) and cut into 3 mm rings. Rings were mounted in organ baths containing Krebs-Henseleit buffer (37°C, 95% O₂/5% CO₂) and equilibrated for 60 minutes under a resting tension of 2 g. After pre-contraction with 1 μM 5-HT (stable contraction achieved), Ketanserin (0.1–100 nM) was added cumulatively. Changes in tension were recorded using isometric transducers, and the percentage inhibition of contraction was calculated relative to the 5-HT-induced maximum contraction [1]
- Rat Cerebral Cortex Synaptosome Binding Assay: Cerebral cortices were homogenized from male Sprague-Dawley rats (180–220 g) in 0.32 M sucrose buffer. Homogenates were centrifuged at 1000×g for 10 minutes, and the supernatant was centrifuged at 12,000×g for 20 minutes to obtain synaptosomes. Synaptosomes (50 μg protein) were incubated with 0.5 nM [³H]-5-HT and Ketanserin (0.01–100 nM) at 37°C for 30 minutes. The reaction was terminated by adding cold buffer, and samples were filtered through glass fiber filters. Radioactivity was measured, and specific binding was calculated by subtracting non-specific binding (in presence of 10 μM unlabeled 5-HT) [4]

Rat: A total of 180–220 g male Sprague-Dawley rats, 2 months old, free of specific pathogens, are used. The following six groups are created at random from the rats: 10-OH-DPAT 5-HT_1A receptor agonist PS group (DPAT-PS group, n = 30); 5-HT_1A receptor antagonist (MDL73005) PS group (MDL-PS group, n = 30); 5-HT_2A receptor agonist (DOI) PS group (DOI-PS group, n = 30); 5-HT_2A receptor antagonist (Ketanserin) PS group (Ketan-PS group, n = 30); the solvent control no-stress group (0.9% physiological saline group, CON group); and the PS only group (PS group, n = 30). The six subgroups (n=5 each) comprising the DPAT-PS, MDL-PS, DOI-PS, Ketan-PS, and PS groups are further separated based on the amount of time that elapses between the stress and analysis: immediately following the stress, as well as 0.5, 1, 2, 6, and 24 hours after the stress. The five members of the CON group eat normally. Ketanserin, diluted in 0.9% physiological saline, is injected intraperitoneally at a dose of 5 mg/kg one hour prior to each stress exposure for the Ketan-PS group.

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Anesthetized Dog Blood Pressure Model: Male beagle dogs (10–12 kg) were anesthetized with sodium pentobarbital (30 mg/kg, intravenous). A femoral artery catheter was inserted to measure mean arterial blood pressure (MAP) via a pressure transducer, and a femoral vein catheter was used for drug administration. Dogs were randomized into 4 groups (n=4/group) receiving intravenous Ketanserin at 0.1, 0.3, 0.5, or 1 mg/kg (dissolved in 0.9% saline). MAP was recorded every 5 minutes for 2 hours, and heart rate was monitored simultaneously [1]
- Rat Myocardial Ischemia Model: Male Sprague-Dawley rats (250–300 g) were anesthetized with isoflurane (2–3% in O₂). A left thoracotomy was performed to expose the heart, and the left anterior descending coronary artery (LAD) was ligated with 6-0 silk suture. Rats were randomized into 2 groups (n=6/group):
1. Ischemia control: Intravenous injection of 0.9% saline (10 mL/kg) 10 minutes before LAD ligation;
2. Ketanserin-treated: Intravenous injection of Ketanserin (0.3 mg/kg, dissolved in 0.9% saline) 10 minutes before LAD ligation.
After 24 hours of ligation, rats were euthanized, hearts were excised for TTC staining (infarct size measurement), and blood was collected for CK activity detection [3]
- Mouse 5-HT-Induced Hyperthermia Model: Male ICR mice (20–25 g) were housed under controlled conditions (22±2°C, 12-hour light/dark cycle) and acclimated for 3 days. Mice were randomized into 3 groups (n=8/group):
1. Normal control: Intraperitoneal injection of 0.9% saline (10 mL/kg);
2. 5-HT-only: Intraperitoneal injection of 5-HT (10 mg/kg, dissolved in saline);
3. Ketanserin+5-HT: Intraperitoneal injection of Ketanserin (2 mg/kg, dissolved in 0.1% DMSO+saline) 30 minutes before 5-HT.
Body temperature was measured using a rectal probe every 30 minutes for 2 hours [4]

Plasma protein binding: Ketoseri was 95% bound to human plasma (ultrafiltration, plasma concentration range: 0.1–10 μg/mL) [2] - Elimination half-life: In anesthetized dogs, the elimination half-life (t1/2) after intravenous injection of ketoseri (0.5 mg/kg) was 1.8 hours (plasma concentration determined by high performance liquid chromatography) [1] - Tissue distribution: In rats, the brain/plasma concentration ratio was 0.8 1 hour after intravenous injection of ketoseri (0.3 mg/kg), and the drug accumulation was highest in the adrenal glands and kidneys ([³H]-ketoseri radiometric detection) [2]

Acute in vivo toxicity: The LD50 of ketoserin administered intraperitoneally to male ICR mice was 85 mg/kg. Mice with doses >60 mg/kg showed ataxia and respiratory depression and died within 24 hours [1]
- Subacute toxicity: In rats, intravenous administration of ketoserin (0.5 mg/kg) daily for 14 days did not show significant changes in serum ALT, AST, BUN, or creatinine levels. Histopathological examination of the liver, kidneys, and heart showed no tissue damage [2]

[1]. J Pharmacol Exp Ther . 1981 Jul;218(1):217-30.

[2]. Neuropharmacology . 1985 Apr;24(4):265-73.

[3]. Circ Res . 1994 Oct;75(4):711-21.

[4]. Brain Res . 1991 Mar 15;543(2):335-40.

Ketoserin belongs to the quinazoline class of compounds, with the structure quinazoline-2,4(1H,3H)-dione, substituted at the 3-position with 2-[4-(p-fluorobenzoyl)piperidin-1-yl]ethyl. It possesses various pharmacological activities, including α-adrenergic antagonist, serotonergic antagonist, antihypertensive agent, cardiovascular agent, and EC 3.4.21.26 (prolyl oligopeptidase) inhibitor. Ketoserin belongs to the quinazoline, piperidine, organofluorine, and aromatic ketone classes. It is the conjugate base of ketoserin(1+). Ketoserin has been investigated for the treatment of septic shock, severe sepsis, and diabetic foot ulcers. Ketoserin is a quinazoline derivative and a 5-hydroxytryptamine (5-HT) receptor subtype 2 (5-HTR2) antagonist, with potential antihypertensive and antiplatelet activities. After administration, ketoserin binds to 5-HT2 and inhibits its mediated signal transduction, thereby inhibiting serotonin-dependent vasoconstriction and platelet activation. It is a selective serotonin receptor antagonist with a weak adrenergic receptor blocking effect. This drug effectively lowers blood pressure in patients with essential hypertension and inhibits platelet aggregation. It is well-tolerated and particularly effective in elderly patients. See also: Ketoserin tartrate (note moved to). Mechanism of Action: Ketoserin (R41468) exerts its main pharmacological action by competitively antagonizing the 5-HT2A receptor, inhibiting 5-HT-mediated vasoconstriction, platelet aggregation, and neuroexcitation responses. Its weak α1-adrenergic receptor antagonism contributes to its hypotensive effect in vivo [1,2]. - Therapeutic Potential: Ketoserin was initially developed for the treatment of hypertension, particularly essential hypertension. In preclinical models (e.g., anesthetized dogs), ketoserin lowers blood pressure without causing significant tachycardia and has a protective effect against myocardial ischemia in rats [1,3]
- Chemical properties:ketoserin (R41468) is soluble in DMSO (20 mg/mL) and slightly soluble in water (1 mg/mL). It is stable for 48 hours at 4°C in aqueous solution at pH 6.0–8.0 [2]

C22H22FN3O3

395.43

395.164

C, 66.82; H, 5.61; F, 4.80; N, 10.63; O, 12.14

74050-98-9

Ketanserin tartrate; 83846-83-7

3822

White to off-white solid powder

1.3±0.1 g/cm3

227-235°C

1.593

3.21

1

5

5

29

627

0

FC1C([H])=C([H])C(=C([H])C=1[H])C(C1([H])C([H])([H])C([H])([H])N(C([H])([H])C([H])([H])N2C(N([H])C3=C([H])C([H])=C([H])C([H])=C3C2=O)=O)C([H])([H])C1([H])[H])=O

FPCCSQOGAWCVBH-UHFFFAOYSA-

InChI=1S/C22H22FN3O3/c23-17-7-5-15(6-8-17)20(27)16-9-11-25(12-10-16)13-14-26-21(28)18-3-1-2-4-19(18)24-22(26)29/h1-8,16H,9-14H2,(H,24,29)

3-[2-[4-(4-fluorobenzoyl)piperidin-1-yl]ethyl]-1H-quinazoline-2,4-dione

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

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: ≥ 1.67 mg/mL (4.22 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 16.7 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: ≥ 1.67 mg/mL (4.22 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 16.7 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: ≥ 1.67 mg/mL (4.22 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 16.7 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: ≥ 0.5 mg/mL (1.26 mM) (saturation unknown) in 10% DMF 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
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 5: 4%DMSO + 40%PEG300 + 4%Tween 80 + 52%ddH2O: 1.0mg/ml (2.53mM)

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Solubility in Formulation 6: 6.25 mg/mL (15.81 mM) in 50% PEG300 50% Saline (add these co-solvents sequentially from left to right, and one by one), suspension solution; with ultrasonication.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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