Comparative effects of PEG-containing liposomal formulations on in vivo pharmacokinetics of streptokinase

Abstract

Streptokinase (SK) is an effective thrombolytic agent, but it has a short half-life due to its rapid elimination from the body. In this study, we prepared and evaluated polyethyleneglycol (PEG)-based liposomal formulations (PEG-liposomes) containing SK with a view toward prolonging its circulatory half-life. SK-bearing liposomes (SK-liposomes) were prepared using freeze-thaw method after film hydration and extrusion techniques, composed of phosphatidylcholine [egg phosphatidylcholine (EPC), dipalmitoyl PC, or distearoyl PC], cholesterol and cholesterol-3-sulfate with or without PEG. Their physicochemical properties were characterized by the measurement of size and zeta potential and incorporation efficiency. SK-liposomal formulations were applied to rats through a femoral vein via intravenous administration to compare the effects of liposomal delivery and PEG on the half-life of SK in blood. Free SK was used as a control. SK activities in plasma were measured to estimate the amidolytic activity of SK-plasminogen complex after rupturing liposomes with Triton X-100. Pharmacokinetic parameters were obtained from SK activity-time profiles. The SK-liposomes had a homogenous distribution of negatively charged nanoparticles at the range of 10-33% of the incorporation efficiencies of SK. Among the SK-liposomes, SK-EPC- and SK-EPC/PEG-liposomes had injectable diameters (<200 nm). SK was administered as free SK, SK-EPC-liposomes, or SK-EPC/PEG-liposomes for in vivo study. SK-EPC/PEG-liposomes had significantly greater the t(1/2), AUC(∞) and MRT values of SK than SK alone or SK-EPC-liposomes. These findings suggest that PEG-liposomal incorporation of SK enhances thrombolytic activity in vivo, and that such liposomes can be utilized to enhance the pharmacokinetic profiles of other therapeutic proteins with a short biological half-life.

The evolution of recombinant thrombolytics: Current status and future directions

“…188 A PEGylated liposomal formulation of streptokinase was also found to enhance its systemic circulation. 189 The PEGylated t-PA loaded liposomes had an enhanced half-life of 141 min. Further, attachment of the peptide sequence, i.e CQQHHLGGAKQAGDV of the fibrinogen g chain that binds to the GPIIb/ IIIa integrin expressed on activated platelets caused a 35% increase in clot lysis and 4.3-fold less fibrinogenolysis.…”