Optimized TELIP, an Echogenic Liposomal Nano-Carrier Loaded with Alteplase for Preclinical Studies

Background: Pharmacological treatment under conditions of slow fibrinolysis/thrombolysis requires the targeted delivery of plasminogen-activating activity. Echogenic liposomal formulations (regular TELIP) of single-chain tissue plasminogen activator (sctPA), while possessing high affinity to fibrin, contain free/loosely bound sctPA. We hypothesized that removal of free sctPA, which competes with liposomes and plasmin for fibrin, enhances unique features of the TELIP. Methods: Optimized and regular TELIP were assessed for the distribution of active sctPA (loosely bound, tightly bound, encapsulated), stability, binding to fibrin, initiating fibrinolysis in vitro and ex vivo using a battery of biochemical methods. Results: One milligram of the regular TELIP consists of 2.0–5.0 × 10⁹ echogenic liposomes (700–900 nm diameter). Non-specifically bound sctPA readily dissociates at the physiological ionic strength and pH. While up to 60% of sctPA in the regular TELIP is loosely bound with 6–15% encapsulated, and the rest is tightly bound to the liposomes; in the optimized TELIP, more than 80% of active sctPA is tightly bound with up to 40% of encapsulated. The latter is protected from high-molecular-weight ligands and could be released by an ultrasound pulse. Optimized TELIP shows low competition with plasmin for fibrin and effectively supports fibrinolysis in vitro and ex vivo. The optimized TELIP with maximal load of sctPA 3% (w/w) retains integrity at 37 °C for 5 h in vitro and up to 2 h ex vivo. Conclusions: The optimized TELIP is stable in vitro and ex vivo, does not interfere with fibrinolysis and retains a high level of encapsulated sctPA delivered precisely to the thrombus/fibrin clot.