Description and Background

M5 is a single site mutant of prourokinase (proUK) engineered in order to make the distinct fibrinolytic paradigm of proUK available at therapeutic doses. 

This single point mutation of proUK overcomes the instability of proUK in plasma at therapeutic concentrations, at which proUK is converted to UK, a non-specific plasminogen activator.  The mechanism of action of proUK and M5 is different and has several advantages over the mechanism of action of tPA. 

The advantages inherent in the proUK paradigm of fibrinolysis over that of tPA include:

• Stability: proUK is a proenzyme, inert when infused until it reaches an intravascular thrombus
• Specificity: proUK preferentially targets intravascular clots rather than hemostatic fibrin clots
• Safety: proUK is not thrombogenic, associated with low rate of reocclusion, and less bleeding
• Delivery: M5's stability enables IV delivery, making intra-arterial infusions unnecessary

Making proUK more suitable for therapeutic thrombolysis

Structure-function studies and site-directed mutagenesis were used to design and develop a mutant which was more stable in plasma and better adapted for therapeutic purposes than native proUK Eventually, a single amino acid (out of the 411 in proUK) substitution mutant was selected because of its promising properties.

The proUK experience greatly simplifies the production, pharmacokinetics, toxicology and clinical development of M5, which is 99.8% equivalent to proUK.