Measurements were performed in a commercially available LTSL formulation (Thermodox®, Celsion, Columbia, MD). The fluorescence intensity of a solution of DOX-loaded liposomes is low due to DOX’s self-quenching. Upon DOX release from a liposome, the fluorescence intensity of a liposome solution is increased. DOX-release experiments were performed by adding a liposome suspension (10 μL, 2 mg/mL DOX) to 750 μL human plasma (plasma collected with apheresis, whole blood treated with 1:12 ACD – anticoagulant citrate dextrose solution A). Prior to adding liposomes, plasma was equilibrated to a predetermined temperature (25°, 37°–47°C) in 1 mL total volume cuvette (1 cm path length) for at least 5 min. The change in fluorescence intensity due to DOX release from the liposomes was monitored with a Cary Eclipse spectrofluorometer equipped with a Peltier temperature controller and Eclipse Kinetic Software (Varian, CA) for 60 s at various temperatures. 15 μL of 25% (wt/wt) Triton X-100 was added at the end of the 60 s to lyse the liposomes and induce maximum release of DOX from the liposome. Excitation and emission wave-lengths were set at 498 nm (5 nm slit width) and 593 nm (10 nm slit width), respectively. The amount of DOX released after time t was calculated according to Equation 1 :
where It represents the intensity at time t. Io is the fluorescence intensity at 25°C and Imax is the intensity after the addition of Triton. The experiment was repeated three separate times in different plasma samples and data are reported as the mean (n = 3).
where It represents the intensity at time t. Io is the fluorescence intensity at 25°C and Imax is the intensity after the addition of Triton. The experiment was repeated three separate times in different plasma samples and data are reported as the mean (n = 3).