Gemcitabine treatment of rat soft tissue sarcoma with phosphatidyldiglycerol-based thermosensitive liposomes.

PURPOSE: The pyrimidine analogue gemcitabine (dFdC) is frequently used in the treatment of patients with solid tumors. However, after i.v. application dFdC is rapidly inactivated by metabolization. Here, the potential of thermosensitive liposomes based on 1,2-dipalmitoyl-sn-glycero-3-phosphodiglycerol (DPPG2-TSL) were investigated as carrier and targeting system for delivery of dFdC in combination with local hyperthermia (HT). METHODS: DPPG2-TSL were prepared by the lipid film hydration and extrusion method and characterized by dynamic light scattering, thin layer chromatography, phosphate assay and HPLC. In vivo experiments were performed in Brown Norway rats with a syngeneic soft tissue sarcoma. Local HT treatment was performed by light exposure. RESULTS: DPPG2-TSL were stable at 37°C in serum and showed a temperature dependent dFdC release >40°C. Plasma half-life of dFdC was strongly increased from 0.07 h (non-liposomal) to 0.53 h (liposomal, vesicle size 105 nm) or 2.59 h (liposomal, 129 nm). Therapy of BN175 tumors with dFdC encapsulated in DPPG2-TSL + HT showed significant improvement in tumor growth delay compared to non-liposomal dFdC without HT (p < 0.05), non-liposomal dFdC with HT (p < 0.01), and liposomal dFdC without HT (p < 0.05), respectively. CONCLUSIONS: Gemcitabine encapsulated in DPPG2-TSL in combination with local HT is a promising tool for the treatment of solid tumors. Therefore, these encouraging results ask for further investigation and evaluation.

Size of thermosensitive liposomes influences content release.

Thermosensitive liposomes (TSL) in combination with regional hyperthermia represent a powerful tool for tumor specific drug delivery. The objective of this study was to investigate the influence of vesicle size on the biophysical properties of TSL. TSL were composed of DPPC/DSPC/1,2-dipalmitoyl-sn-glycero-3-phosphoglyceroglycerol (DPPG(2)) 50:20:30 (mol/mol) (DPPG(2)-TSL) and DPPC/P-Lyso-PC/DSPE-PEG2000 90:10:4 (mol/mol) (PEG/Lyso-TSL) with encapsulated fluorescent dye carboxyfluorescein, anticancer drug doxorubicin or magnetic resonance contrast agent gadodiamide. Extrusion was performed with polycarbonate filters of distinct pore size to obtain TSL with different diameters (50 to 200nm). Phase transition temperature (T(m)) of the bilayer forming phospholipids was not influenced by vesicle size in the tested range. However, vesicle size had a major impact on in vitro content release properties of TSL in the investigated temperature range between 30 and 45°C. Generally, vesicle size was inversely related to content release properties with increased content release rates for decreased vesicle sizes. Size dependency of content release properties varied between all tested formulations and DPPG(2)-TSL were generally less affected by size changes in the range of 100 to 150nm as compared to PEG/Lyso-TSL. Independent from gadodiamide release, vesicle size influenced the signal intensity of DPPG(2)-TSL also at temperatures below T(m) due to improved water exchange for smaller vesicles. Liposomes around 100nm in size are routinely used in vivo, hence a quality control for TSL preparations is required prior to use. Even small changes in size or a wider size distribution might affect stability and release properties and thus yield in decreased efficacy or unwanted side effects of drug loaded TSL during in vivo applications.