5-HT3 Receptor Antagonists. 3. Quinoline Derivatives Which May Be Effective in the Therapy of Irritable Bowel Syndrome

Article abstract of DOI:10.1021/jm00074a009

A series of quinolinecarboxylic acid derivatives has been previously described as a new class of 5-HT₃ receptor antagonists due to deviation of a carbonyl moiety from the plane of an aromatic ring in their minimum-energy conformations.These derivatives were evaluated in a wrap-restraint stress-induced defecation model in rats.Reference compounds, ondansetron (1), granisetron (2), and YM060 (4), potently inhibited a stress-induced increase in stools excreted from fed rats (ID50 = 0.27, 0.12, and 0.0052 mg/kg, po, respectively).However, quinoline derivatives exhibited different activities depending on structural class. 4-Hydroxyquinoline-3-carboxylic acid derivatives 5 and 6a possess high affinity for the 5-HT₃ receptor (K_i = 6.1 and 1.5 nM, respectively) and exhibit potent activity in the Bezold-Jarisch (B-J) reflex test (ED50 = 0.0017 and 0.00010 mg/kg, iv, respectively), but they did not effectively inhibit the increase in fecal pellet output at the dose of 1 mg/kg, po.On the other hand, most of 1-substituted 2-oxoquinoline-4-carboxylates 10 showed less potent activity in the B-J reflex test than 1 or 2 but inhibited restraint stress-induced defecation more potently than 1 or 2.The ID50 value of endo-8-methyl-8-azabicyclo<3.2.1>oct-3-yl 1-isobutyl-2-oxo-1,2-dihydro-4-quinolinecarboxylate 10e was 0.013 mg/kg, po.With respect to the selected compounds 6a and 10e, effects on 5-HT- and thyrotropin-releasing hormone (TRH)-induced defecation, castor oil-induced diarrhea and wrap-restraint stress-induced colonic propulsion in rats were examined.These 5-HT₃ receptor antagonists did not effectively inhibit castor oil-induced diarrhea, which has been reported not to be mediated via the 5-HT₃ receptor.Although 10e showed 800-fold decreased potency compared with 4 in the B-J refles test, 10e exhibited activity as potent as 4 in 5-HT- and TRH-induced defecation assays; 10e exhibited 7-fold increased potency compared with 4 in wrap-restraint stress-induced colonic propulsions.From these results, 10e appears to interact selectively with 5-HT₃ receptors in the gastrointestinal system and might be effective in the therapy of irritable bowel syndrome (IBS).