Identification of functional synergism between monoclonal antibodies. Application to the enhancement of plasminogen activator inhibitor-1 neutralizing effects.

The serpin plasminogen activator inhibitor-1 (PAI-1), an important risk factor for thrombotic disease can be neutralized by distinct mechanisms. We hypothesized that the combination of two compounds, with PAI-1 neutralizing properties based on different mechanisms, may result in a synergistic effect. Therefore, seven monoclonal antibodies with PAI-1 neutralizing properties were pairwise evaluated for the possible presence of synergistic or antagonistic effects. Out of 21 combinations, three particular combinations, i.e. MA-33H1/MA-33B8, MA-33B8/MA-7D4B7, and MA-7D4B7/MA-33H1 exhibited strong synergistic effects in comparison with their properties when evaluated individually. The observed synergism resulted in a maximum enhancement between 2- and 5-fold (P < 0.05, vs. theoretically expected effect calculated based on additive effects). Strikingly, synergism was only observed between monoclonal antibodies directed against different epitopes and with different molecular mechanisms of PAI-1 neutralization. This phenomenon of synergism opens new perspectives in the design of therapeutic or preventive strategies aimed at enhancing endogenous fibrinolysis through modulation of PAI-1 activity.