AM251

Biological Activity

AM251 is a selective cannabinoid 1 (CB1) receptor antagonist with an IC50 of 8 nM. AM251 also acts as a potent GPR55 agonist with an EC50 of 39 nM. AM251 block the inhibitory effects of endocannabinoids and synthetic cannabinoid agonists on transmitter release through an action at presynaptic cannabinoid 1 receptors in brain.

I. Cell Applications
AM251 (10⁻⁶ M, once daily for 3 days) in neonatal rat hippocampal mixed cell cultures antagonizes endocannabinoid signaling and inhibits olfactory ensheathing glia-conditioned medium-induced increase in oligodendroglial process branching complexity, used to study the role of CB1 receptors in oligodendrocyte development.
AM251 (100 nM, co-incubated with 1 µM WIN55212-2 for 2 h) in U2OS-CB1-EGFP redistribution assays antagonizes CB1 receptor internalization with an IC₅₀ of approximately 45 nM, used for CB1 receptor antagonist activity screening.
AM251 (10 µM, 48 h) on human and mouse islet β-cells promotes β-cell proliferation and reduces apoptosis, used to study the regulatory role of the endocannabinoid system in pancreatic function.
AM251 (1 µM, incubation for at least 5 min) on isolated rat dorsal raphe nucleus 5-HT neurons inhibits the firing rate of approximately 50% of recorded neurons; this inhibitory effect is blocked by the GABA_A receptor antagonist picrotoxin, suggesting that CB1 receptors regulate 5-HT neuronal activity via the GABAergic system.

II. In Vivo Applications (Mouse)
AM251 (30 mg/kg; oral gavage; once daily for 7 days) in high-fat diet-induced obese (DIO) C57BL/6 mice significantly reduces food intake and body weight; microCT confirms significant decreases in inguinal subcutaneous, mesenteric, retroperitoneal, and epididymal adipose tissue mass; the anorectic effect attenuates by day 4, but body weight reduction persists throughout the study period.
AM251 (10 mg/kg; intraperitoneal injection; once daily for 4 weeks) in high-fat diet-induced obese C57BL/6 mice rapidly and persistently reduces body weight and decreases inflammatory M1-type adipose tissue macrophage infiltration; mechanistically, it upregulates miR-30e-5p and downregulates its target gene DLL4, inhibiting the DLL4-Notch signaling pathway, thereby suppressing Th1 cell polarization and adipocyte energy storage.
AM251 (1 mg/kg; intraperitoneal injection; once daily for 3 days) in cranial irradiation (9 Gy) C57BL/6 mice, administered starting 30 min post-irradiation, improves cognitive dysfunction at 4 and 12 weeks post-irradiation (novel object recognition and object-in-place tests), and alleviates anxiety- and depressive-like behaviors (elevated plus maze and forced swim tests); the mechanism involves increased hippocampal neurogenesis (1.7-fold increase in DCX⁺ neurons, 2.5-fold increase in BrdU⁺/NeuN⁺ mature neurons) and reduced HMGB1 inflammatory marker expression.

III. In Vivo Applications (Rat)
AM251 (3 mg/kg; intraperitoneal injection; once daily for 6 weeks) in high-fat diet (21% fat)-induced obese SD rats reduces body weight gain (vehicle 655.9 g vs. AM251 607.2 g), significantly decreases epididymal, peri-renal, and brown fat pad weights, reduces plasma leptin, glucagon, ghrelin, and GLP-1 levels, but increases PAI-1 and various pro- and anti-inflammatory cytokine levels; does not induce white adipose tissue "browning" (no change in UCP1 mRNA), suggesting that its weight-loss mechanism is independent of adipose tissue browning.
AM251 (1 mg/kg; intraperitoneal injection; once daily, or 5 mg/kg; once every 5 days) in SD rats produces sustained reductions in food intake and body weight without tolerance; a single 5 mg/kg dose significantly reduces food intake for up to 4 days without inducing conditioned taste aversion (CTA); the central CB1 receptor antagonism disappears after 48 h, suggesting that the sustained anorexic effect is not dependent on persistent central receptor blockade.
AM251 (1 mg/kg; intraperitoneal injection; once daily for 14 weeks) in streptozotocin-induced type 1 diabetic mice significantly reduces albuminuria (by ~50%), an effect independent of body weight, blood glucose, HbA1c, and systolic blood pressure changes, suggesting that CB1 receptor blockade can directly improve glomerular permeability in diabetic nephropathy.

Reference:
https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2023.1134130/full
https://www.icrs.com/assets/docs/previoussymposia/ICRS.2002.symposium.pdf
https://pmc.ncbi.nlm.nih.gov/articles/PMC6523050/
https://pmc.ncbi.nlm.nih.gov/articles/PMC8273551/
https://pmc.ncbi.nlm.nih.gov/articles/PMC9569643/
https://pmc.ncbi.nlm.nih.gov/articles/PMC1615836/
https://pmc.ncbi.nlm.nih.gov/articles/PMC2844813/
https://pubmed.ncbi.nlm.nih.gov/31134094/

Chemical Information

Molecular Weight	555.24
Formula	C22H21Cl2IN4O
CAS Number	183232-66-8
Solubility (25°C)	DMSO 25 mg/mL
Storage	Powder          -20°C   3 years ;  4°C   2 years In solvent       -80°C   6 months ;  -20°C   1 month

References

[1] Ins B Correia-S, et al. AM251, a cannabinoid receptor 1 antagonist, prevents human fibroblasts differentiation and collagen deposition induced by TGF-β - An in vitro study

[2] Inmaculada Ruz-Maldonado, et al. The cannabinoid ligands SR141716A and AM251 enhance human and mouse islet function via GPR55-independent signalling

[3] Tomoyo Yoshinaga, et al. AM251 Suppresses Epithelial-Mesenchymal Transition of Renal Tubular Epithelial Cells

[4] Sara Carpi, et al. AM251 induces apoptosis and G2/M cell cycle arrest in A375 human melanoma cells

[5] Izabela Bialuk, et al. AM251, cannabinoids receptors ligand, improves recognition memory in rats