PEGylation of Truncated Streptokinase Leads to Formulation of a Useful Drug with Ameliorated Attributes.

Streptokinase (SK) remains a favored thrombolytic agent in the developing world as compared to the nearly 10-fold more expensive human tissue-plasminogen activator (tPA) for the dissolution of pathological fibrin clots in myocardial infarction. However, unlike the latter, SK induces systemic activation of plasmin which results in a greater risk of hemorrhage. Being of bacterial origin, it elicits generation of unwanted antibody and has a relatively short half-life in vivo that needs to be addressed to make it more efficacious clinically. In order to address these lacunae, in the present study we have incorporated cysteine residues specifically at the N- and C-termini of partially truncated SK and these were then PEGylated successfully. Some of the obtained derivatives displayed enhanced plasmin resistance, longer half-life (upto several hours), improved fibrin clot-specificity and reduced immune-reactivity as compared to the native SK (nSK). This paves the way for devising next-generation SK-based thrombolytic agent/s that besides being fibrin clot-specific are endowed with an improved efficacy by virtue of an extended in vivo half-life.

Site-Specific Thiol-mediated PEGylation of Streptokinase Leads to Improved Properties with Clinical Potential.

Streptokinase (SK) is an efficient thrombolytic agent that dissolves fibrin blood clots with clinical efficiency comparable to the high priced drug, tissue plasminogen activator (tPA). However, being of bacterial origin, its major drawbacks are its potentially high antigenicity, and relatively short circulating half-life (approximately 10-15 min). In the present investigation, an attempt has been made to address both these shortcomings by site-specific pegylation, and to obtain longer lasting thrombolytics, which are consistent with clinical requirements. Therefore, we employed available three-dimensional structural information on SK to carry out site-specific cysteine incorporation at 'optimal' surfaceexposed sites within all the three domains in streptokinase followed by pegylation with 20KDa PEG groups, and screening for biologically active variants. Interestingly, some of these SK PEG-conjugates exhibited considerably subdued immunereactivity along with enhanced in-vitro proteolytic stability profiles and extended circulating in-vivo half-lives (2 to 20-fold compared to that of native unconjugated SK) depending upon location and number of PEG-groups per molecule obtained in homogeneous form. The obtained results are a promising approach for favorably modulating immune-reactivity and half-life by cysteine- specific PEGylation of SK to achieve therapeutic attributes desirable for the treatment of different circulatory disorders, such as ischemic stroke, myocardial infarction and pulmonary embolism.