Tranexamic Acid-Encapsulating Thermosensitive Liposomes for Site-Specific Pharmaco-Laser Therapy of Port Wine Stains

Site-specific pharmaco-laser therapy (SSPLT) is a developmental stage treatment modality designed to non-invasively remove superficial vascular pathologies such as port wine stains (PWS) by combining conventional laser therapy with the prior administration of a prothrombotic and/or antifibrinolytic pharmaceutical-containing drug delivery system. For the antifibrinolytic SSPLT component, six different PEGylated thermosensitive liposomal formulations encapsulating tranexamic acid (TA), a potent antifibrinolytic lysine analogue, were characterized for drug:lipid ratio, encapsulation efficiency, size, endovesicular TA concentration (C TA), phase transition temperature (T m), and assayed for heat-induced TA release. Assays were developed for the quantification of liposomal TA and heat-induced TA release from two candidate formulations. The outcome parameters were then combined with a 3D histological reconstruction of a port wine stain biopsy to extrapolate in vivo posologies for SSPLT. The prime formulation, DPPC:DSPE-PEG2000 (96:4 molar ratio), had a drug:lipid molar ratio of 0.82, an encapsulation efficiency of 1.29%, a diameter of 155 nm, and a C TA of 214 mM. The peak TA release from this formulation (T m = 42.3 °C) comprised 96% within 2.5 min, whereas this was 94% in 2 min for DPPC:MPPC:DSPE-PEG2000 (86:10:4) liposomes (T m = 41.5 °C). Computational analysis revealed that < 400 DPPC:DSPE-PEG2000 (96:4 molar ratio) liposomes are needed to treat a PWS of 40 cm2, compared to a three-fold greater quantity of DPPC:MPPC:DSPE-PEG2000 (86:10:4) liposomes, indicating that, in light of the assayed parameters and endovascular laser-tissue interactions, the former formulation is most suitable for antifibrinolytic SSPLT. This was further confirmed with experiments involving ex vivo and in vivo liposome-platelet and liposome-red blood cell association as well as uptake and toxicity assays with cultured endothelial cells (HUVECs), macrophages (RAW 264.7), and hepatocytes (HepG2).