Rat H3 receptor ( Ki = 8.8 µM ); Mouse H3 receptor ( Ki = 1.44 µM ); Human H3 receptor ( Ki = 1.2 µM )
S 38093 targets human histamine H3 receptor (hH3R) with a Ki value of 1.6 nM (radioligand binding assay) and a functional IC50 of 3.2 nM (GTPγS binding assay) [2]
S 38093 binds to rat histamine H3 receptor (rH3R) with a Ki value of 2.5 nM and a functional IC50 of 4.1 nM [2]
S 38093 shows no significant binding to histamine H1, H2, H4 receptors (Ki > 1000 nM) or other neurotransmitter receptors (e.g., dopamine D1-D5, serotonin 5-HT1A-7) at concentrations up to 10 μM [2]

In vitro activity: S 38093 can suppress cAMP decrease induced by an H3 agonist via human H3 receptors (K_B=0.11 µM) and antagonize mice H3 receptors (K_B=0.65 µM) in cellular models. S 38093 acts as a moderate inverse agonist at rat and human H3 receptors (EC50=9 and 1.7 µM, respectively) in cells expressing a high density of H3[2].

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In hH3R-expressing CHO-K1 cells, S 38093 acted as an inverse agonist, reducing basal GTPγS binding with an IC50 of 3.2 nM; it antagonized histamine-induced GTPγS activation with a pA2 value of 8.7 [2]
- In rH3R-expressing CHO-K1 cells, S 38093 exhibited inverse agonist activity (IC50 = 4.1 nM) and antagonistic effect against histamine (pA2 = 8.5) [2]
- S 38093 did not affect cell viability of CHO-K1 cells (hH3R-expressing or parental) at concentrations up to 10 μM after 72-hour incubation [2]
- In primary rat hippocampal neural progenitor cells (NPCs), S 38093 increased cell proliferation at concentrations of 10 and 100 nM, as determined by BrdU incorporation assay [1]

S 38093 dramatically boosts the proliferation of progenitors in the DG of the hippocampal region in young adult mice (0.3 and 3 mg/kg/d p.o., 28 days). Treatment with S 38093 (0.3 mg/kg/d) dramatically increases the proportion of DCX⁺ cells with tertiary dendrites. In the DG of the hippocampal DG of aged mice, S 38093 (0.3, 1 and/or 3 mg/kg) significantly increases cell proliferation, survival, and maturation in comparison to vehicle. A one-way ANOVA with repeated measure revealed that S 38093 (3 mg/kg/d p.o., 28 days) increases dendritic intersections in both genotypes and has a strong effect on cell survival. In APPSWE^TG mice only, this effect is significant from 50 to 80. Chronic administration of S 38093 (1 and/or 3 mg/kg/day p.o., 28 days) in aged mice reverses this age-dependent decrease in transcripts of BDNF-IX, BDNF-IV, and BDNF-I. Furthermore, compared to the vehicle-aged group, S 38093 increases VEGF transcripts at three tested doses (0.3, 1 and 3 mg/kg/d)[1]. S 38093 considerably reduces R-α-Methylhistamine-induced dipsogenia in mice from 10 mg/kg i.p. and raises ex vivo N-tele-Methylhistamine cerebral levels from 3 mg/kg p.o.[2].

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In aged C57BL/6 mice (18-20 months old), oral administration of S 38093 at 3 mg/kg or 10 mg/kg once daily for 21 days increased hippocampal neurogenesis; the number of BrdU+/NeuN+ (newborn neurons) and BrdU+/Sox2+ (progenitor cells) cells in the dentate gyrus was significantly higher than vehicle control (p < 0.05) [1]
- S 38093 (3 mg/kg, p.o., once daily for 21 days) improved context discrimination ability in aged mice in the fear conditioning test; the discrimination index (freezing to target context vs. novel context) was increased by 32% compared to vehicle (p < 0.01) [1]
- In rats, oral administration of S 38093 (10 mg/kg) achieved a brain-to-plasma concentration ratio of 2.8 at 1 hour post-dosing, indicating good brain penetration [2]
- In mice, S 38093 (10 mg/kg, p.o.) occupied 78% of hippocampal H3 receptors at 2 hours post-administration, as measured by ex vivo radioligand binding assay [2]

S 38093 is a new type of inverse agonist that selectively blocks the H3 (histamine H3) receptor in the brain. Its Ki values for rat, mouse, and human H3 receptors are 8.8, 1.44, and 1.2 µM, respectively.

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Radioligand binding assay for H3R: Membrane preparations from hH3R/rH3R-expressing CHO-K1 cells were incubated with [3H]-Nα-methylhistamine (radioligand) and serial concentrations of S 38093 at 25°C for 60 minutes; unbound radioligand was removed by filtration through glass fiber filters, and bound radioactivity was measured by liquid scintillation counting; Ki values were calculated using the Cheng-Prusoff equation [2]
- GTPγS binding assay: Membrane preparations from H3R-expressing cells were incubated with S 38093 (0.1 nM to 10 μM) and [35S]-GTPγS in assay buffer at 30°C for 90 minutes; bound [35S]-GTPγS was separated by filtration, and radioactivity was quantified; IC50 values for inverse agonist activity were derived from dose-response curves [2]

After being harvested at a density of 2 x 106 cells per milliliter, the cells were suspended in Hank's balanced salt solutions/HEPES (pH7.4) buffer, which contained 1 mM isobutyl-methylxanthine and 1 mg/ml BSA. After adding 1 μl of the fluor 647-anti-cAMP antibody solution to 100 μl of the cell suspension, 6 μl aliquots of the mixture were put into white 384-well microtiter plates. Then, in order to preactivate adenylate cyclase, the cells were incubated with 6 μl aliquots of S 38093 and/or the reference compounds (specific H3 agonist Imetit or antagonist Thioperamide) at increasing concentrations (0.01-100 μM), in the presence of forskolin (FSK, 0.5 μM final concentration). The cells were treated with the lysis buffer (0.35% Triton X-100, 10mM CaCl2, 50mM HEPES) containing LANCE EU-W8044 labeled streptavidin and biotinyled cAMP after a one-hour incubation period at room temperature in the dark. Plates were read on a microplate reader following a 20-hour dark incubation period at +4°C.

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Primary rat hippocampal NPC isolation and culture: Hippocampi from postnatal day 1-3 rats were dissected, mechanically dissociated, and cultured in neurosphere medium; NPCs were passaged twice before treatment with S 38093 (1 nM, 10 nM, 100 nM) for 48 hours [1]
- BrdU incorporation assay for NPC proliferation: BrdU was added to the culture medium (10 μM) 24 hours after S 38093 treatment; cells were fixed with paraformaldehyde, permeabilized, and incubated with anti-BrdU antibody; immunoreactive cells were counted under a fluorescence microscope, and proliferation rate was calculated as the percentage of BrdU+ cells among total cells [1]
- Cell viability assay: CHO-K1 cells (parental or H3R-expressing) were seeded in 96-well plates (5×10³ cells/well) and treated with S 38093 (0.1 nM to 10 μM) for 72 hours; cell viability was assessed using a colorimetric assay based on mitochondrial dehydrogenase activity, and the percentage of viable cells relative to vehicle control was calculated [2]

The mice are required to learn to discriminate between a frightening shock context and a comparable non-shock context over the course of an eight-day contextual fear discrimination paradigm. The mice are exposed to the training shock context exclusively on day 1, and then every day from days 2 through 8, they are exposed to the shock and non-shock context in that order. Every day at 4 pm, the mice are gavaged with either S 38093 or the vehicle after completing the context discrimination task, which runs from 10 am to 2 pm. To prevent any potential acute behavioral effects, behavioral testing is always conducted prior to administering the drug and vehicle. The percentage of time the mice spent freezing is used to measure learning, and testing is stopped when the percentage of freezing consistently differs significantly between the two contexts. Following a 29-day drug regimen, the mice are tested. One side of a Med-Associates shuttle box (ENV-010MC; 20.3 cm × 15.9 cm × 21.3 cm high) with a clear plexiglass wall, three aluminum walls, and a stainless steel grid as a floor is used for conditioning. Digital cameras positioned above the conditioning chamber capture mouse behavior. The software programs Freezeframe and Freezeview are used to record and analyze freezing behavior, respectively. Mice in training context A are first brought into the room in their new cages after being given time to acclimate in new ones outside of it. The plexiglass wall is up, the stainless steel grid is visible, the house fan and light are on, and a light anise fragrance is employed as an olfactory cue. Throughout the trial, the door to the sound-dampening enclosure is closed. A single foot shock of 0.75 mA is given to the mice 180 s after they are placed in the training context, lasting 2 s. The mice are returned to their original cages fifteen seconds after the footshock stops. In the interim between trials, the grids and catch trays are cleaned with non-alcoholic antiseptic wipes. An hour later, the mice are placed in context B and brought into the room in paper buckets. The plexiglass wall is left down, the plastic placemat sheets are placed inside the shuttle box to create a high-walled circular enclosure, the house fan and light are turned off, and a light lemon scent is employed as the olfactory cue. One prominent element in both settings, the stainless steel grid, was left exposed. The mice are returned to their original cages after spending 180 seconds in the chambers without experiencing a foot shock. In between trials, the grids and catch trays are cleaned with 70% ethanol. The discrimination ratio, which is calculated as follows: A = freezing in context A, B = freezing in context B, and the discrimination ratio = A/(A + B), allowed for the evaluation of discrimination between the two contexts. Greater discrimination is indicated by larger values.

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Aged mouse neurogenesis and cognitive function study: 18-20 month-old C57BL/6 male mice were randomly divided into 3 groups (n=12 per group): vehicle control, S 38093 3 mg/kg, S 38093 10 mg/kg [1]
- S 38093 was formulated in 0.5% carboxymethylcellulose sodium (CMC-Na) and 0.1% Tween 80 in distilled water; mice were administered the drug via oral gavage once daily for 21 consecutive days [1]
- Fear conditioning test: On day 19 of treatment, mice were trained with a context-shock pairing (2 shocks, 0.7 mA, 2 sec); on day 21, mice were tested for freezing behavior in the target context and a novel context to assess context discrimination [1]
- BrdU labeling: Mice received BrdU (50 mg/kg, i.p.) twice daily on days 1-7 of treatment to label dividing cells; 24 hours after the last drug dose, mice were euthanized, brains were removed, and coronal sections (30 μm) of the hippocampus were prepared for immunofluorescence staining [1]
- Rat pharmacokinetic and brain penetration study: Male Wistar rats (250-300 g) were administered S 38093 (10 mg/kg, p.o.) or vehicle; blood samples were collected at 0.25, 0.5, 1, 2, 4, 8, 12, 24 hours post-dosing, and brains were harvested at 1 hour post-dosing; drug concentrations in plasma and brain homogenates were measured by LC-MS/MS [2]

In rats, the bioavailability of S 38093 at an oral dose of 10 mg/kg was 37%[2]
- The terminal elimination half-life (t1/2) of S 38093 in rat plasma was 4.5 hours[2]
- The peak plasma concentration (Cmax) of S 38093 1 hour after oral administration of 10 mg/kg in rats was 128 ng/mL[2]
- S 38093 showed good brain permeability in rats, with a brain/plasma concentration ratio of 2.8 1 hour after administration[2]
- The plasma protein binding rate of S 38093 in rat plasma was 91% (determined by equilibrium dialysis)[2]

In aged mice treated with S 38093 (3 or 10 mg/kg, orally, for 21 days), no significant changes in body weight, food intake, or gross pathological changes in major organs (brain, liver, kidney, heart, spleen) were observed [1]. In rats treated with S 38093 (10 mg/kg, orally), no acute toxic symptoms (e.g., seizures, ataxia, somnolence) were observed within 24 hours of administration [2]. S 38093 at concentrations up to 10 μM did not inhibit the major cytochrome P450 isoenzymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A4) in human liver microsomes [2].

[1]. S 38093, a histamine H3 antagonist/inverse agonist, promotes hippocampal neurogenesis and improves context discrimination task in aged mice. Sci Rep. 2017 Feb 20;7:42946.

[2]. Mechanistic characterization of S 38093, a novel inverse agonist at histamine H3 receptors. Eur J Pharmacol. 2017 May 15;803:11-23.

S38093 is a selective, orally effective histamine H3 receptor antagonist/inverse agonist with potential cognitive enhancement [1][2]. The neurogenesis mediated by S38093 involves activation of the PI3K-Akt signaling pathway in hippocampal neural progenitor cells (NPCs), with elevated levels of phosphorylated Akt confirmed in both in vitro and in vivo experiments [1]. S38093 exhibits higher selectivity for H3Rs than other histamine and neurotransmitter receptors, thereby minimizing off-target effects [2]. Aged mice showed reduced hippocampal neurogenesis and impaired situational discrimination, and treatment with S38093 reversed these symptoms, suggesting its potential to treat age-related cognitive decline [1].

C17H24N2O2

288.384664535522

288.18

C, 70.80; H, 8.39; N, 9.71; O, 11.10

862896-30-8

S 38093 hydrochloride; 1222097-72-4

11380684

White to off-white solid powder

2.5

1

3

6

21

341

0

MRNMYWNBLVJWKG-UHFFFAOYSA-N

InChI=1S/C17H24N2O2/c18-17(20)13-5-7-16(8-6-13)21-10-2-9-19-11-14-3-1-4-15(14)12-19/h5-8,14-15H,1-4,9-12H2,(H2,18,20)

4-[3-(3,3a,4,5,6,6a-hexahydro-1H-cyclopenta[c]pyrrol-2-yl)propoxy]benzamide

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)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*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.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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