49
and lacks fibrin-binding domain. Though lower in specificity, it has a higher plasma
half-life of around 11–14 min, which makes it better for bolus infusion treatment,
and reteplase is much cheaper than tPA (Ali et al. 2014). Intracranial haemorrhage
or bleeding problems are associated with reteplase treatment, similar to alteplase.
2.2.1.4 Tenecteplase
Tenecteplase is another recombinant mutant of tissue-type plasminogen activator
(tPA) with multiple point mutations. It comprises 527 amino acids. Mutations
include Asp103Thr, Glu117Asn and 4 alanine substitutions (Lys296Ala, His297Ala,
Arg298Ala and Arg299Ala). These mutations increase half-life, resistance to plasminogen activator inhibitor 1 (80-fold) and fibrin specificity (14-fold) (Smalling
1996). The longer half-life makes it suitable for bolus administration. Also fewer
bleeding complications were observed for tenecteplase treatment compared to
alteplase. Tenectplase was approved by the USFDA in 2000 for the treatment of
myocardial infarction. It is commercially available as TNKase (Fig. 2.2).
2.2.1.5 Urokinase Plasminogen Activator
Urokinase is another plasminogen activator used for treating cardiovascular diseases. An enzyme urokinase (UK) with a molecular weight of 54 kDa was isolated
from urine which converts plasminogen to plasmin while situated inside thrombus
and thus makes it protected against circulating antiplasmins. Also the absence of
urokinase inhibitors in plasma makes it readily available at the site of action. UK
has a prolonged half-life of about 15 min (Ali et al. 2014). Urokinase is a serine
protease, and a heterodimer with polypeptide chains of 20 kDa and 34 kDa. It is
secreted as a precursor molecule pro-urokinase, which is single chain and can be
activated to two-chain urokinase by plasmin or kallikrein (Bernik 1973). Prourokinase (pro-UK) is effective for around 24 h after administration while urokinase gets inactivated within a few hours. Upon intravenous administration pro-UK
attained complete fibrinolysis within 1.5 h while urokinase took 3 h for lysis. Prourokinase (pro-UK) is preferred over urokinase due to its improved selectivity
towards fibrin and superior half-life over the latter (Zamarron et al. 1984).
Recombinant pro-urokinase can be produced either in Escherichia coli or in mammalian cells. Prolyse is a recombinant pro-urokinase (rpro-UK) produced in the
Fig. 2.2 Crystal structure
of tissue-type plasminogen
activator in complex with
plasminogen activators
inhibitor-1. Tissue-type
plasminogen activator in
green colour and
plasminogen activators
inhibitor-1 blue colour
(pdb id: 5BRR)
2 Therapeutic Enzymes
and lacks fibrin-binding domain. Though lower in specificity, it has a higher plasma
half-life of around 11–14 min, which makes it better for bolus infusion treatment,
and reteplase is much cheaper than tPA (Ali et al. 2014). Intracranial haemorrhage
or bleeding problems are associated with reteplase treatment, similar to alteplase.
2.2.1.4 Tenecteplase
Tenecteplase is another recombinant mutant of tissue-type plasminogen activator
(tPA) with multiple point mutations. It comprises 527 amino acids. Mutations
include Asp103Thr, Glu117Asn and 4 alanine substitutions (Lys296Ala, His297Ala,
Arg298Ala and Arg299Ala). These mutations increase half-life, resistance to plasminogen activator inhibitor 1 (80-fold) and fibrin specificity (14-fold) (Smalling
1996). The longer half-life makes it suitable for bolus administration. Also fewer
bleeding complications were observed for tenecteplase treatment compared to
alteplase. Tenectplase was approved by the USFDA in 2000 for the treatment of
myocardial infarction. It is commercially available as TNKase (Fig. 2.2).
2.2.1.5 Urokinase Plasminogen Activator
Urokinase is another plasminogen activator used for treating cardiovascular diseases. An enzyme urokinase (UK) with a molecular weight of 54 kDa was isolated
from urine which converts plasminogen to plasmin while situated inside thrombus
and thus makes it protected against circulating antiplasmins. Also the absence of
urokinase inhibitors in plasma makes it readily available at the site of action. UK
has a prolonged half-life of about 15 min (Ali et al. 2014). Urokinase is a serine
protease, and a heterodimer with polypeptide chains of 20 kDa and 34 kDa. It is
secreted as a precursor molecule pro-urokinase, which is single chain and can be
activated to two-chain urokinase by plasmin or kallikrein (Bernik 1973). Prourokinase (pro-UK) is effective for around 24 h after administration while urokinase gets inactivated within a few hours. Upon intravenous administration pro-UK
attained complete fibrinolysis within 1.5 h while urokinase took 3 h for lysis. Prourokinase (pro-UK) is preferred over urokinase due to its improved selectivity
towards fibrin and superior half-life over the latter (Zamarron et al. 1984).
Recombinant pro-urokinase can be produced either in Escherichia coli or in mammalian cells. Prolyse is a recombinant pro-urokinase (rpro-UK) produced in the
Fig. 2.2 Crystal structure
of tissue-type plasminogen
activator in complex with
plasminogen activators
inhibitor-1. Tissue-type
plasminogen activator in
green colour and
plasminogen activators
inhibitor-1 blue colour
(pdb id: 5BRR)
2 Therapeutic Enzymes