Phase 1 Trial of Mutant proUK, M5, and Its Inhibitor, C1-inhibitor

Mutant proUK, M5, was specifically designed to improve the plasma stability of single-chain proUK by reducing its intrinsic catalytic activity and allowing it to retain its proenzyme form until it encounters a thrombus. As an additional consequence of the mutation, its two-chain enzymatic form (tcM5) is sensitive to inhibition by C1-inhibitor (C1INH) a relatively abundant plasma inhibitor. While it has a negligible effect on urokinase (UK), C1INH inhibits tcM5 irreversibly, preventing non-specific plasminogen activation, responsible for bleeding complications. The effect of endogenous C1INH can be augmented by the addition of exogenous C1INH. In vitro studies in rats and dogs indicated that adding C1INH to plasma prior to clot lysis by M5 prevented bleeding, fibrinogenolysis and plasminogen depletion but did not affect the rate of fibrinolysis. In a recent pilot rat stroke study, at similarly effective doses, M5, preceded by C1INH adjunctive therapy, was equivalent to tPA alone but caused significantly less ICH, was much more effective than tPA preceded by adjunctive C1INH, and was the only group with a significant functional improvement at 24h. Dose restrictions which limit efficacy of tPA-based thrombolysis are expected to be circumvented by M5 preceded by adjunctive C1INH. C1INH is a commercially available plasma derived product with a well-established safety and efficacy profile and is currently indicated and available for routine prophylaxis of hereditary angioedema (HAE).