Design, synthesis, biological evaluation and histopathological studies of Pyridazine and Pyrazoline derivatives as potential anti-inflammatory agents

A series of novel pyridazinone and 2-pyrazoline derivatives were designed, synthesized, and screened for their in vitro COX-1 and COX-2 inhibitory properties using celecoxib and indomethacin as reference drugs. Compounds 4c and 4e were of particular interest as they exhibited the highest potency towards COX-2 enzyme with IC₅₀ values of 0.90 μM and 0.82 μM, respectively, which is comparable to celecoxib (IC₅₀ = 0.73 μM). Compounds 4c and 4e exhibited selectivity indices of 8.70 and 4.98, respectively, which are markedly higher than that of indomethacin (SI = 0.40), indicating a pronounced preference for COX-2 inhibition. Consequently, the in vivo anti-inflammatory activity of compounds 4c and 4e was tested using the rat paw edema model which showed a gradual decrease in percentage of edema to reach 9.91% and 13.89%, respectively, after 3 h. Notably, compound 4c showed anti-inflammatory activity comparable to that of indomethacin and celecoxib, which produced final percentage edema values of 8.99% and 9.07%, respectively in the third hour. Histopathological examination revealed that compounds 4c and 4e had milder gastric effects compared to indomethacin which showed severe pathological alterations and ulcerative lesions of gastric tissue. Moreover, compounds 4c and 4e decreased serum PGE2, IL-1β and TNF-α to lower levels than indomethacin. Molecular docking results supported the selectivity and potency of 4c and 4e highlighting their ability to occupy the secondary pocket of the COX-2 enzyme and establish interactions with its key Amino acids His90 and Arg513. Together, these findings suggest that compounds 4c and 4e are promising leads for the design of COX-2 inhibitors.