Galanin-3 receptor
GALR3 (galanin‑3 receptor) – no binding affinity or potency values provided in this reference. [2]
GalR3 (galanin-3 receptor). HT-2157 is a highly selective competitive antagonist for the galanin-3 receptor, with negligible affinity for GalR1 and GalR2 (Ki >10,000 nM for both subtypes). It binds with high affinity to membranes from cells expressing the human Gal3 receptor. The compound modulates galaninergic signaling pathways involved in anxiety, depression, and ethanol consumption.

HT-2157 (SNAP 37889) is highly selective for Gal₃ over the Gal₁ and Gal₂ subtypes (Ki>10,000 nM for each subtype; n=46 of each subtype), and binds with high affinity to membranes from transiently transfected LMTK^- cells expressing the human Gal₃ receptor (Ki=17.44±0.01 nM; n>100). When tested for the antagonism of galanin-evoked inhibition of adenylyl cyclase, HT-2157 (0.1-10 μM) produces concentration-dependent rightward shifts of the concentration-effect curve to galanin[1].

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HT-2157 binds with high affinity to human GALR3 (Ki = 17.44 nM) and shows >100‑fold selectivity over GALR1 and GALR2, as well as over a broad panel of G‑protein‑coupled receptors, ion channels, enzymes, and transporters (including MAO‑A, MAO‑B, SERT, NET, DAT). [1]
HT-2157 (0.1–10 μM) produces concentration‑dependent rightward shifts of the galanin concentration‑effect curve in an adenylyl cyclase assay using HEK‑293 cells transiently transfected with GALR3 and Gα2; Schild regression slope is 0.92 (not different from unity), and constrained slope yields pKb = 7.54 (Kb = 29 nM). [1]
SNAP 398299 (a water‑soluble analog of HT-2157) binds to human GALR3 with Ki = 5.33 nM and shows >1,000‑fold selectivity over GALR1 and GALR2. [1]
In whole‑cell patch‑clamp recordings from rat dorsal raphe nucleus (DRN) slices, pre‑incubation with SNAP 398299 (1 μM, 3–5 min) significantly attenuates galanin‑evoked outward currents by 53.8% (from 28 pA to 12.8 pA); the effect is reversible upon washout. [1]
In vitro, HT-2157 binds to the human Gal3 receptor with a Ki of 17.44±0.01 nM in LMTK- cells expressing the receptor. It shows >570-fold selectivity for GalR3 over GalR1 and GalR2. The compound is highly selective for Gal3 over Gal1 and Gal2 subtypes. These binding characteristics make HT-2157 a valuable tool for studying GalR3 function in CNS research.

In rats who prefer alcohol, the galanin-3 receptor antagonist HT-2157 (SNAP 37889) decreases operant responding for ethanol. In the iP (alcohol-preferring) rat, the novel selective GALR3 antagonist HT-2157 is used to decrease anxiety-like behavior and voluntary ethanol consumption. In either the light-dark or elevated plus maze paradigms, male intraperitoneal rats treated with HT-2157 at a dose of 30 mg/kg (i.p.) do not exhibit changes in anxiety-like behavior or altered locomotor activity. Operant responding for solutions containing ethanol, sucrose, and saccharin is decreased when HT-2157 (30 mg/kg, i.p.) is administered. The current study's overall findings demonstrate that HT-2157 (30 mg/kg, i.p.) is useful in lowering operant responding to ethanol[2].
HT-2157 (30 mg/kg, i.p.) did not significantly alter locomotor activity (number of moves, move time, distance moved) in the iP rat over a 60‑min session when compared to vehicle, although a transient reduction was observed at the 5‑ and 10‑min intervals; pre‑treatment time was set to 60 min for subsequent experiments to avoid early sedative effects. [2]
HT-2157 (30 mg/kg, i.p., 60 min pre‑treatment) had no significant effect on anxiety‑like behavior in the elevated plus maze (open arm entries, time in open arms) or the light‑dark test (time spent in light vs. dark side) compared to vehicle. [2]
HT-2157 (30 mg/kg, i.p.) significantly reduced operant responding for 10% (v/v) ethanol by 44% in iP rats during a 20‑min fixed‑ratio 3 (FR3) session, with a significant decrease observed at the first 5‑min interval; water responding was unchanged. [2]
HT-2157 (30 mg/kg, i.p.) also significantly reduced operant responding for 5% (w/v) sucrose by 40% and for 0.1% (w/v) saccharin by 54% in iP rats under the same FR3 schedule, with no effect on water responding. [2]
In vivo, HT-2157 (30 mg/kg, i.p.) reduces operant responding for ethanol in alcohol-preferring (iP) rats. The compound decreases anxiety-like behavior and voluntary ethanol consumption in iP rats. Acute administration of SNAP 37889 (HT-2157) or its more soluble analog SNAP 398299 enhances social interaction in rats. HT-2157 elevates cortical serotonin (5-HT) levels by 746% at 10 mg/kg p.o. and reduces forced swim test immobility, demonstrating anxiolytic and antidepressant-like effects without sedation at behaviorally active doses.

The ¹²⁵I-galanin displacement assay is used to determine the binding affinities for HT-2157 (SNAP 37889) and SNAP 398299 at the human Gal₁, Gal₂, and Gal₃ receptors. Furthermore, is examined for binding in a wide panel of cross-reactivity components, such as ion channels, transporters, enzymes, and G-protein-coupled receptors. The ability of HT-2157 to antagonize functional responses to galanin is examined in modified HEK-293 cells (PEAK^rapid cells) transiently cotransfected with the Gal₃ receptor and Gα_z by measuring the inhibition of adenylyl cyclase activity[1].

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Receptor binding assay: binding affinities at human GALR1, GALR2, and GALR3 were determined using a 125I‑galanin displacement assay on membranes from transiently transfected LMTK‑cells. Non‑specific binding was defined with 1 μM galanin. Selectivity was assessed against a broad panel of GPCRs, ion channels, enzymes, and transporters (NovaScreen). [1]
Adenylyl cyclase functional assay: modified HEK‑293 cells (PEAKrapid cells) were transiently co‑transfected with human GALR3 and Gα2. Cells were incubated with varying concentrations of galanin in the presence or absence of HT-2157 (0.1–10 μM). Inhibition of forskolin‑stimulated cAMP accumulation was measured. Schild analysis was performed to determine pKb and slope. [1]
Whole‑cell patch‑clamp recording: DRN neurons from rat brain slices (300 μm) were recorded in whole‑cell configuration at −70 mV. Galanin (1 μM) was applied via micropipette to evoke outward currents. SNAP 398299 (1 μM) was pre‑incubated for 3–5 min before co‑application. Current amplitudes were measured before, during, and after antagonist washout. [1]
The receptor binding assay for HT-2157 typically involves membranes prepared from LMTK- cells transiently transfected with the human Gal3 receptor. Radioligand binding studies are performed using a suitable radiolabeled galanin ligand (e.g., ¹²⁵I-galanin) incubated with varying concentrations of HT-2157. Nonspecific binding is determined in the presence of excess unlabeled galanin. The Ki value is calculated from competition binding curves using the Cheng-Prusoff equation. For selectivity profiling, similar assays are performed using membranes expressing Gal1 and Gal2 receptors.

Cell-based assays for HT-2157 involve LMTK- cells transiently transfected with human GalR3, GalR1, or GalR2 receptors. Functional antagonism is assessed using second messenger assays, such as measuring inhibition of forskolin-stimulated cAMP accumulation, as galanin receptors are typically Gi-coupled. Cells are pre-incubated with varying concentrations of HT-2157, followed by stimulation with a GalR3 agonist (e.g., galanin). cAMP levels are measured using ELISA or homogeneous time-resolved fluorescence (HTRF) assays. IC50 values for antagonism are calculated from dose-response curves.

Rats: The effect of HT-2157 on locomotor activity is examined using adult male iP rats (n=12; 418-467 g). To make sure that any future changes in anxiety or ethanol consumption are not the result of the drug's sedative properties, locomotor activity is tested. The rats undergo three consecutive days of 60-minute sessions to acclimate to the locomotor cells (26 x 26 x 40 cm). Rats are split into two even groups and given a single injection of either HT-2157 (30 mg/kg, i.p.) or vehicle (1 ml/kg, i.p.) 30 min before they were placed in the locomotor cells for a 60-minute session in order to minimize the effect of habituation during the treatment phase. The treatments are switched around the next day, giving each rat treatment with both the vehicle and the SNAP 37889 compound. The TruScan 2.0 program automatically records movements in terms of the total distance traveled (cm), the number of moves, and the move time (s).

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Animal protocol for locomotor activity: adult male iP rats (n=12, 418‑467 g) were habituated to locomotor activity monitors for 60 min daily for 3 days. On test days, rats received a single intraperitoneal (i.p.) injection of HT-2157 (30 mg/kg) or vehicle (5% DMSO and 1% hydroxypropyl‑methyl cellulose in saline; 1 ml/kg) 30 min before a 60‑min session. Treatments were reversed the next day. Movements (number of moves, move time, distance) were recorded automatically. [2]
Animal protocol for elevated plus maze: adult male iP rats (n=24, 313‑480 g) received a single i.p. injection of HT-2157 (30 mg/kg) or vehicle 60 min before being placed in the central square of the maze. Number of entries and time spent in open and closed arms were recorded for 5 min. [2]
Animal protocol for light‑dark test: same cohort of rats received HT-2157 (30 mg/kg, i.p.) or vehicle 60 min before being placed in the dark half of a chamber divided into light and dark halves; total time and entries into each side were recorded for 10 min. [2]
Animal protocol for operant self‑administration of ethanol: a separate cohort of male iP rats (n=12, 368‑401 g) was trained using a sucrose‑fade protocol over 9 days to respond for 10% (v/v) ethanol on an FR3 schedule (20‑min daily sessions). Once stable baseline was achieved, rats received vehicle (1 ml/kg, i.p.) on Wednesdays and HT-2157 (30 mg/kg, i.p.) on Thursdays, with no‑injection days on Monday, Tuesday, and Friday. Drug or vehicle was given 60 min before the session. Lever presses for ethanol and water were recorded. [2]
Animal protocol for operant self‑administration of sucrose: the same cohort of rats was retrained with 5% (w/v) sucrose instead of ethanol using the same FR3 schedule (20‑min sessions). After stable responding, vehicle and HT-2157 (30 mg/kg, i.p.) were administered as described. [2]
Animal protocol for operant self‑administration of saccharin: a different cohort of male iP rats (n=12, 306‑361 g) was trained to respond for 0.1% (w/v) saccharin on an FR3 schedule (20‑min sessions). Following stable responding, vehicle and HT-2157 (30 mg/kg, i.p.) were given 60 min pre‑session as above. [2]
Male alcohol-preferring (iP) rats are used for in vivo efficacy studies. HT-2157 is administered intraperitoneally at a dose of 30 mg/kg. For operant responding studies, rats are trained to self-administer ethanol in operant conditioning chambers. After stabilization of responding, HT-2157 or vehicle is administered, and operant responding for ethanol is measured. For anxiety-like behavior assessment, elevated plus maze or social interaction tests are performed after compound administration. For microdialysis studies, probes are implanted in the rat frontal cortex to measure extracellular 5-HT levels following HT-2157 administration.

HT-2157 is a small molecule with favorable CNS penetration properties. It has a molecular weight of 366.3 g/mol and is soluble in DMSO. Pharmacokinetic studies in rats show that the compound is orally bioavailable, with detectable brain exposure after oral administration. HT-2157 elevates cortical 5-HT levels at 10 mg/kg p.o., indicating good central nervous system penetration. The compound was progressed to clinical evaluation, suggesting acceptable pharmacokinetic properties in humans.

No specific toxicity data reported; however, HT-2157 (30 mg/kg, i.p.) did not cause significant sedation or adverse effects on body weight throughout the study. A transient reduction in locomotor activity was noted at 5‑10 min post‑injection, but overall session totals were not different from vehicle. [2]
HT-2157 was evaluated in Phase 1/2 clinical trials (NCT01413932) for major depressive disorder. Preclinical safety studies demonstrated that the compound was well-tolerated at behaviorally active doses, with no sedation observed. However, safety concerns reportedly halted further development. The compound showed no significant toxicity at doses effective for reducing anxiety-like behavior and ethanol consumption in rat models. Further detailed toxicology data are limited as development was discontinued.

[1]. Anxiolytic- and antidepressant-like profiles of the galanin-3 receptor (Gal3) antagonists SNAP 37889 and SNAP 398299. Proc Natl Acad Sci U S A. 2005 Nov 29;102(48):17489-94.

[2]. The galanin-3 receptor antagonist, SNAP 37889, reduces operant responding for ethanol in alcohol-preferring rats. Regul Pept. 2011 Jan 17;166(1-3):59-67.

HT-2157 is a selective GALR3 antagonist that reduced operant responding for ethanol, sucrose, and saccharin in iP rats without affecting water intake, suggesting a general reduction in reward‑seeking behavior rather than a specific effect on ethanol. The effect was not due to sedation or anxiolysis at the tested dose. The mechanism may involve blockade of GALR3 in hypothalamic regions (e.g., PVN) that modulate consummatory behavior and noradrenergic transmission. These findings support further investigation of GALR3 antagonism for the treatment of alcohol use disorders and eating disorders. [2]
HT-2157 (SNAP 37889) is a selective GalR3 antagonist developed for CNS research and potential therapeutic applications in psychiatric disorders. The compound was investigated for major depressive disorder in a Phase 1/2 clinical trial (NCT01413932). It has been used as a pharmacological tool to study the role of galanin-3 receptors in anxiety, depression, and alcohol addiction. HT-2157 is an indolone-derived small molecule with high selectivity for GalR3 over GalR1 and GalR2, making it the definitive GalR3-selective antagonist for research applications. Development was reportedly halted due to safety concerns.

C21H13F3N2O

366.34

366.098

C, 68.85; H, 3.58; F, 15.56; N, 7.65; O, 4.37

303149-14-6

1471834

Yellow to orange solid powder

5.569

0

5

2

27

583

0

O=C1N(C2=CC=CC=C2)C3=C(C=CC=C3)/C1=N/C4=CC=CC(C(F)(F)F)=C4

TXCGMRVPXUBHAL-UHFFFAOYSA-N

InChI=1S/C21H13F3N2O/c22-21(23,24)14-7-6-8-15(13-14)25-19-17-11-4-5-12-18(17)26(20(19)27)16-9-2-1-3-10-16/h1-13H

1-phenyl-3-[3-(trifluoromethyl)phenyl]iminoindol-2-one

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.

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: ≥ 2.5 mg/mL (6.82 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 25.0 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: ≥ 2.5 mg/mL (6.82 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 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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