Preparation of Radiolabeled Europium loaded Nanoparticle for in vivo Imaging and Gamma Ray Induced Photodynamic Therapy

4 Objectives: Photodynamic therapy (PDT) elicits anti-tumor effect utilizing a photosensitizer (PS) and a light which can activate PS to produce reactive oxygen species (ROS). The poor penetration depth of the light is the major limitation of PDT. γ ray induced luminescence can be used as a light source for PDT to overcome the limitation, based on the high tissue penetration ability of γ ray. Herein, we developed radiolabeled europium embedded liposome nanoparticle (Eu-Lipo), which has an ability of radioluminescence, for in vivo imaging and γ ray induced PDT. Methods: The Eu-Lipo was synthesized by a self-assembly method using phosphatidylcholine (PC) derivatives and tip sonication. Eu3+ ions were chelated to diethylenetriaminepentaacetic acid (DTPA) (Eu-DTPA). Rose Bengal (RB), victoria blue-BO (VBBO), and chlorin e6 (Ce6) was chosen for PSs. Eu-DTPA and PSs were embedded into the hydrophilic core part of the structure during the self-assembly method. Eu-Lipo was further modified by using NOTA and PEG5k for radiolabeling and long circulation in vivo. The radioluminescence effect of Eu-Lipo was tested by mixing with 99mTc. ROS generation test was demonstrated with different kinds of PSs loaded Eu-Lipos with 99mTc. Eu-Lipo was labeled with 64Cu (64Cu-Eu-Lipo). 64Cu-Eu-Lipo was injected intravenously to mouse tumor models and the PET images were acquired at 0, 1, 4, 24, and 48 hours after the injection (Fig. 1). Results: The hydrodynamic size of self-assembled Eu-Lipo was about 80 nm. And Eu-Lipo had a high stability for 7 days in the physiological conditions including phosphate buffered solution (PBS), cell media, and human serum (Fig. 2). We found that the Eu-Lipo emitted radioluminescence at red visible light in the presence of 99mTc. The intensity of radioluminescence was increased according to the amount of Eu and the radioactivity of 99mTc (Fig. 3a). Eu-Lipo showed an ability of ROS production by 99mTc. Among Eu-Lipo with different PSs, VBBO loaded Eu-Lipo (Eu/VBBO lipo) showed the largest increment of ROS production by 99mTc, which was about 8-fold higher than Eu-Lipo (Fig. 3b). In PET imaging, both Eu-Lipo and Eu/VBBO lipo showed high blood pool uptakes until 4 hours (~30 %ID/g) and substantial tumor uptakes after 24 hours (~15 %ID/g) (Fig. 4). Conclusions: Eu-lipo demonstrated abilities of producing radioluminescence at red visible spectrum region and ROS production under γ ray irradiation. Furthermore, the Eu-lipo showed an efficient tumor passive targeting with a favorable circulation property. Based upon these abilities, Eu-Lipo could be successfully utilized for γ ray induced PDT for deep seated tumors. $$graphic_31E7C7DA-E142-44D4-B52F-03111B369869$$ $$graphic_6DBFFAEC-2139-4B8C-9E98-233BD26BB538$$ $$graphic_9DEB6849-952D-4D75-AEEF-9A3D9FEA06CB$$ $$graphic_306BF84D-A996-47DA-BAC8-FDA38D326AE2$$