New role of phenothiazine derivatives as peripherally acting CB1 receptor antagonizing anti-obesity agents

Abstract

Developing peripherally active cannabinoid 1 (CB1) receptor antagonists is a novel therapeutic approach for the management of obesity. An unusual phenothiazine scaffold containing CB1R antagonizing hit was identified by adopting virtual screening work flow. The hit so identified was further modified by introducing polar functional groups into it to enhance the polar surface area and decrease the hydrophobicity of the resulting molecules. CB1 receptor antagonistic activity for the designed compounds was computed by the previously established pharmacophore and three dimensional quantitative structure-activity relationship models. Docking studies of these designed compounds confirmed the existence of favourable interactions within the active site of the CB1 receptor. The designed compounds were synthesized and evaluated for their CB1 receptor antagonistic activity. Parallel artificial membrane permeability assay was performed to evaluate their potential to permeate into the central nervous system wherein it was observed that the compounds did not possess the propensity to cross the blood brain barrier and would be devoid of central nervous system side effects. In pharmacological evaluation, the synthesized compounds (23, 25, 27 and 34) showed significant decrease in food intake suggesting their potential application in the management of obesity through CB1 receptor antagonist activity.

Figure 1

Chemical structures of some known centrally and peripherally acting CB1 receptor antagonists (1–4).

Figure 2

(a) Virtual screening flowchart and chemical structure of hit V11 (5), (b) Pharmacophore model (AHRR) aligned to hit V11 (5), (c) Binding mode of hit V11 (5) in the active site of CB1 receptor (red dotted line represents hydrogen bond).

Figure 3

Synthetic pathway for compounds (5, 22–36). Reagents and conditions: (a) NaOC₂H₅, EtOH, rt; (b) triethylamine, DCM, reflux; (c) K₂CO₃, DMF, rt.

Figure 4

Synthetic pathway for compounds (42–49). Reagents and conditions: (a) NaH, DMSO, THF, 0 °C; (b) K₂CO₃, DMF, rt.

Figure 5

Hypophagic response of the test compounds in twenty four hour fasted rats. Among the tested compounds, 23, 25, 27 and 34 (10 mg/kg, p.o.) showed significant hypophagic activity alone (A) and also suppressed the hyperphagic effect of WIN-55212-2 (2 mg/kg, i.p.) (B) revealing their CB1 receptor antagonist potential. Data expressed as mean ± SEM (n = 6). **p < 0.01, *p < 0.05 vs. vehicle-treated control group (A). ^#p < 0.01 vs. vehicle-treated control group. ***p < 0.001 vs. WIN-55212-2-treated group (B). One-way ANOVA, Bonferroni post hoc test.

Figure 6

Mapping of (a) the highest fitness score compound (26) and (b) the lowest fitness score compound (32) on the best pharmacophoric model (AHRR).

Figure 7

Binding interactions of (a) active compound (25), and (b) less active compound (47) in the active site of CB1 receptor (red dotted line represents hydrogen bond).