Arghya Kusum Dhar

Antidepressant-like activity of 2-(4-phenylpiperazin-1-yl)-1, 8-naphthyridine-3-carboxylic acid (7a), a 5-HT3 receptor antagonist in behaviour based rodent models: Evidence for the involvement of serotonergic system

The present study was designed to investigate the putative antidepressant-like activity of 7a, a 5-HT₃ receptor antagonist, (although indirect evidence of 5-HT3 antagonism) with an optimal log P (3.35) and pA₂ value (7.6) greater than ondansetron (pA₂--6.6) using behavioural tests battery of depression. Acute treatment of 7a (0.5-2 mg/kg, i.p.) in mice produced antidepressant-like effects in forced swim test (FST) and tail suspension test (TST) without affecting the baseline locomotion in actophotometer test in mice. Moreover, the combination of a sub-effective dose of 7a (0.25 mg/kg, i.p.) and fluoxetine (5 mg/kg, i.p.) produced an anti-immobility effect in mouse FST. Pretreatment of mice with p-chlorophenylalanine methyl ester (PCPA; 100 mg/kg, i.p., an inhibitor of serotonin (5-HT) synthesis, for 4 consecutive days) and 1-(m-Chlorophenyl)-biguanide (mCPBG, 10 mg/kg, i.p., a 5-HT₃ receptor agonist) prevented the anti-immobility effects of 7a (2 mg/kg, i.p.) in the mouse FST. In addition, 7a (0.5-2 mg/kg, i.p.) treatment also potentiated the 5-hydroxytryptophan (5-HTP) and pargyline induced head twitch response in mice. Furthermore, sub-chronic treatment (14 days) with 7a (0.5-2 mg/kg, i.p.) and paroxetine (10 mg/kg, i.p.) significantly attenuated the behavioural anomalies induced by bilateral olfactory bulbectomy in rats in a modified open field paradigm. These results suggest that the antidepressant-like action of 7a may be mediated by an interaction with the serotonergic system and this molecule should be further investigated as an alternative therapeutic approach for the treatment of depression.

Design, Synthesis and Evaluation of Antidepressant Activity of Novel 2-Methoxy 1, 8 Naphthyridine 3-Carboxamides as 5-HT3 Receptor Antagonists

A series of novel 1,8‐naphthyridine‐3‐carboxamides as 5‐HT3 receptor antagonists were synthesized with an intention to explore the antidepressant activity of these compounds. The title carboxamides were designed using ligand‐based approach keeping in consideration the structural requirement of the pharmacophore of 5‐HT3 receptor antagonists. The compounds were synthesized using appropriate synthetic route from the starting material nicotinamide. 5‐HT3 receptor antagonism of all the compounds, which was denoted in the form of pA2 value, was determined in longitudinal muscle myenteric plexus preparation from guinea‐pig ileum against 5‐HT3 agonist, 2‐methyl‐5‐HT. Compound 8g (2‐methoxy‐1, 8‐naphthyridin‐3‐yl) (2‐methoxy phenyl piperazine‐1‐yl) methanone was identified as the most active compound, which expressed a pA2 value of 7.67. The antidepressant activity of all the compounds was examined in mice model of forced swim test (FST); importantly, none of the compounds was found to cause any significant changes in the locomotor activity of mice at the tested dose levels. In FST, the compounds with considerably higher pA2 value exhibited promising antidepressant‐like activity, whereas compounds with lower pA2 value did not show antidepressant‐like activity as compared to the control group.

Ligand-based design, synthesis, and pharmacological evaluation of 3-Methoxyquinoxalin-2-carboxamides as structurally novel serotonin type-3 receptor antagonists.

Employing a ligand‐based approach, 3‐methoxyquinoxalin‐2‐carboxamides were designed as serotonin type‐3 (5‐HT3) receptor antagonists and synthesized from the starting material o‐phenylenediamine in a sequence of reactions. The structures of the synthesized compounds were confirmed by spectral data. These carboxamides were investigated for their 5‐HT3 receptor antagonisms in longitudinal muscle myenteric plexus preparations from guinea‐pig ileum against a standard 5‐HT3 agonist, 2‐methy‐5‐HT, and their antagonism activities are expressed as pA2 values. Compounds 6a (pA2: 7.2), 6e (pA2: 7.0), 6f (pA2: 7.5), 6g (pA2: 7.5), 6n (pA2: 7.0), and 6o (pA2: 7.2) exhibited antagonism greater than that of the standard 5‐HT3 antagonist, ondansetron (pA2: 6.9).

Neuropharmacological evaluation of a novel 5-HT3 receptor antagonist (6g) on chronic unpredictable mild stress-induced changes in behavioural and brain oxidative stress parameters in mice.

Aim: The aim of the study was to evaluate a novel 5 HT3 receptor antagonist (6g) on chronic stress induced changes in behavioural and brain oxidative stress parameter in mice. A complicated relationship exists among stressful stimuli, bodys reaction to stress and the onset of clinical depression. Chronic unpredictable stressors can produce a situation similar to human depression, and such animal models can be used for the preclinical evaluation of antidepressants. Materials and Methods: In the present study, a novel and potential 5-HT3 receptor antagonist (4-benzylpiperazin-1-yl)(3-methoxyquinoxalin-2-yl) methanone (6g) with good Log P (3.08) value and pA2(7.5) values, synthesized in our laboratory was investigated to study the effects on chronic unpredictable mild stress (CUMS)-induced behavioural and biochemical alterations in mice. Mice were subjected to different stress paradigms daily for a period of 28 days to induce depressive-like behaviour. Results: The results showed that CUMS caused depression-like behaviour in mice, as indicated by the significant (P < 0.05) decrease in sucrose consumption and locomotor activity and increase in immobility the forced swim test. In addition, it was found that lipid peroxidation and nitrite levels were significantly (P < 0.05) increased, whereas glutathione levels, superoxide dismutase and catalase activities decreased in brain tissue of CUMS-treated mice. ‘6g’ (1 and 2 mg/kg, p.o., 21 days) and fluoxetine treatment (20 mg/kg, p.o., 21 days) significantly (P < 0.05) reversed the CUMS-induced behavioural (increased immobility period, reduced sucrose preference and decreased locomotor activity) and biochemical (increased lipid peroxidation; decreased glutathione levels, superoxide dismutase and catalase activities). However fluoxetine treatment (20 mg/kg, p.o., 21 days) significantly decreased the nitrite level in the brain while ‘6g’ (1 and 2 mg/kg, p.o., 21 days) did not show significant (P < 0.05) effect on the nitrite levels in brain. Conclusion: Compound ‘6g’ exerted antidepressant-like effects in behavioural despair paradigm in chronically stressed mice by restoring antioxidant mechanisms.

2-(4-substituted piperazin-1-yl)-1,8-naphthyridine-3-carboxylic acids: novel 5-HT3 receptor antagonists with anxiolytic-like activity in rodent behavioral models.

The aim of this study was to investigate the anxiolytic potential of a series of novel carboxylic acid based 1,8 naphthyridines as 5-HT3 receptor antagonists. The pA2 values of all the compounds were determined against agonist 2-methyl-5-hydroxytryptamine in longitudinal muscle myenteric plexus preparations from guinea pig ileum. Compounds with higher pA2 values, particularly those greater than ondansetron, a standard 5-HT3 receptor antagonist, and optimal log P values were screened in mice by using behavioral tests such as a light-dark (L/D) aversion test, elevated plus maze (EPM) test, and an open field test (OFT). In the L/D test, compounds 7a, 7b, 7d, 7e, and 7i (2 mg/kg body mass, intraperitoneal) significantly (P < 0.05) increased the latency time to leave the light compartment, total time spent in the light compartment, and the number of transitions between the light and dark compartments. Compounds 7a, 7d, 7f, 7h, and 7i (2 mg/kg, i.p.) significantly (P < 0.05) increased the time spent in the open arms and the number of entries into the open arms in the EPM test. In addition, compounds 7a, 7d, 7e, 7f, and 7h (2 mg/kg, i.p.) significantly (P < 0.05) increased the ambulation scores and the frequency of rearing in the OFT.

Design, Synthesis, and Pharmacological Evaluation of Novel 2‐(4‐substituted piperazin‐1‐yl)1, 8 Naphthyridine 3‐Carboxylic Acids as 5‐HT3 Receptor Antagonists for the Management of Depression

1, 8‐naphthyridine‐3‐carboxylic acid analogs were synthesized and found to possess potential 5‐HT3 receptor antagonism as well as antidepressant‐like activity. Initially, 5‐HT3 receptor antagonism of all the compounds was determined in the form of pA2 value against agonist 2‐methyl 5‐HT in longitudinal muscle–myenteric plexus preparation from guinea‐pig ileum. Among all the compounds tested, compound 7a demonstrated most promising pA2 value of 7.6. Subsequently, all the compounds were evaluated for antidepressant activity using forced swim test and tail suspension test in mice. Compounds 7a, 7d, 7f, 7h, and 7i exhibited significant (p < 0.05) antidepressant‐like activity as compound to vehicle‐treated group. Importantly, none of the tested compound affected locomotor activity of mice at tested dose levels.

Piperazine analogs of naphthyridine-3-carboxamides and indole-2-carboxamides: novel 5-HT3 receptor antagonists with antidepressant-like activity.

Series of piperazine analogs of naphthyridine‐3‐carboxamides and indole‐2‐carboxamides were designed using a ligand‐based approach with consideration of the pharmacophoric requirements for 5‐HT3 receptor antagonists. The title carboxamides were synthesized using appropriate synthetic routes. Initially, the 5‐HT3 receptor antagonistic activity of all the compounds was determined on isolated guinea pig ileum tissue against the 5‐HT3 agonist, 2‐methyl‐5‐hydroxytryptamine, which was denoted in the form of pA2 values. The structure–activity relationship regarding the influence of the aromatic part and basic moiety as features in the 5‐HT3 pharmacophore was derived. Among all the compounds screened, the piperazine derivatives of indole‐2‐carboxamide 13i and naphthyridine‐3‐carboxamide 8h exhibited prominent 5‐HT3 receptor antagonism with pA2 values of 7.5 and 7.3, respectively. Subsequent investigation of the antidepressant activities of selected compounds in the mouse forced swim test (FST) led to the identification of the piperazine analogs of indole‐2‐carboxamide 13i and naphthyridine‐3‐carboxamide 8h as the most promising compounds. Both 13i and 8h demonstrated significant reduction in the duration of immobility as compared to the control. Importantly, none of the tested compounds affected the baseline locomotion of mice at the tested dose levels.