Pharmacological studies on proglumetacin maleate, a new non-steroidal anti-inflammatory drug (4). Mode of action on anti-inflammatory activity

The possible mechanism of the anti-inflammatory activity of proglumetacin maleate (PGM), a new indomethacin (IND) derivative interacting with arachidonic acid (AA) metabolism, was investigated to elucidate the contributions of PGM itself and its two major metabolites, desproglumideproglumetacin maleate (DPP) and IND. PGM caused much less inhibition of PGE2 formation by sheep seminal vesicle microsomes (IC50 = 310 microM) and TXB2 formation by a washed rabbit platelet suspension (IC50 = 6.3 microM) than IND. DPP also caused less inhibition of cyclooxygenase than IND. Moreover, PGM had less effect on sodium arachidonate (SAA)-induced rat platelet aggregation ex vivo and AA-induced sudden death in rabbits than IND. These results show that PGM has anti-inflammatory activity after its conversion to the active metabolite IND. However, the inhibitory effects of PGM and DPP were as strong as that of IND on SAA- or collagen-induced rabbit platelet aggregation in vitro. These activities are considered to be associated with platelet membrane interaction. Moreover, unlike IND, PGM (IC50 = 1.5 microM) and DPP (IC50 = 16.3 microM) strongly inhibited 5-HETE formation by the cytosol of guinea pig polymorphonuclear leukocytes. This unique activity of PGM on 5-lipoxygenase may contribute to its anti-inflammatory activity.