Liposomes are microscopic vesicles containing an aqueous core surrounded by a lipid bilayer, enabling lipophilic and hydrophilic drugs to be encapsulated. Due to this characteristic, they have been used as transporters of substances to treat or diagnose diseases, including radiopharmaceuticals.

This work aims to prepare liposome from phosphatidylserine, encapsulate 99mTc- MDP inside it, and compare murine 4T1 breast cell tumor uptake for 99mTc-MDP and 99mTc-MDP-liposome.

Liposome was prepared by adding 90 mg of phosphatidylserine in a chloroform/methanol solution at a concentration of (9:1). The solvents were evaporated in a desiccator until the lipids formed a film at the bottom of the vial. The radiopharmaceutical 99mTc-MDP was obtained from the reconstitution of a lyophilized kit with a 99mTcO4- solution, according to radiolabeling instructions. The liposome was reconstituted with saline and 99mTc-MDP was added; the solution was sonicated for 10 min. The purification and encapsulation of percentage were done by size exclusion filtration in an Amicon® 10 kD filter, including two water washes. Murine 4T1 breast cancer cells were grown in RPMI-1640 culture medium supplemented with 10% fetal bovine serum, under 37°C in a humidified atmosphere with 5% CO2 and seed at 5 × 104 cell/well and stood overnight in culture conditions. 99mTc-MDP and 99mTc-MDP-liposome were added to wells, in triplicate, and stood in culture conditions for 15, 30, 60 and 120 min. Culture medium was removed, cells were washed twice with PBS, the cells were detached from the wells, and radioactivity was measured in a gamma counter. The cell internalization percentage was determined by dividing cells counts by a standard sample.

The 99mTc-MDP encapsulation in the liposome reached an average of 68 ± 26% (n = 3), determined by size exclusion filtration. In vitro tumor cells uptake for 99mTc-MDP fluctuated between 0.2% during interval time. On the other hand, 99mTc-MDP-liposome tumor cells uptake had 0.7% ± 0.1% (15 min), 0.8 ± 0.2% (30 min) 0.9 ± 0.2% (60 min) and 1.2 ± 0,4 (120 min).

The experiments demonstrated the feasibility of liposome production and their use for encapsulate 99mTc-MDP radiopharmaceutical. Loaded 99mTc-MDP-liposome had significantly high tumor uptake compared to 99mTc-MDP alone, demonstrating the effectivity of the phosphatidylserine liposome in delivering radiopharmaceuticals in tumor cells.