Gd-encapsulating Anti-HER2 Immunoliposomes for MR Monitoring of Targeted Drug Delivery

Purpose The goal of this study was to characterize the distribution of HER2 receptor targeted immunoliposomes in a mouse model of human breast cancer and compare this to non-targeted sterically stabilized liposomes. Introduction Liposomes are currently being investigated as a means of improving delivery of chemotherapeutic agents to tumors. Sterically stabilized liposomes have been studied because they remain in the bloodstream longer than conventional liposomes, which are quickly cleared.by the reticuloendothelial svstem. Imaroved tarnetinn mav be achieved by conjugating lidosomes 4th &tibodies specific for certain tumor cell receptors. It has been demonstrated in multiple HER2-overexpressing human breast tumor xenograft models, that treatment with doxorubicin-loaded anti-HER2 immunoliposomes (ILs) produces significantly increased antitumor cytotoxicity and significantly less systemic toxicity than free doxorubicin’. We have previously utilized MR to characterize the uptake of -different compositions and doses of stericallv stabilized linosomes. The nurnose of this study is to characterize and compare (targeted) antiHER2 lipsomes with non-targeted liposomes. We are ultimately interested in developing magnetic resonance (MR) methods utilizing gadolinium (Gd) encapsulating anti-HER2 liposomes to monitor chemotherapy treatment. Methods Stericallv stabilized POPC/Chol/PEG-PE liposomes (3:2:0.3 molar ratio) encapsulating GdDTPA-BMA were prepared by the freeze thaw method then extruded. The mean diameter determined by dynamic light scattering was 90 * 30 nm. A portion of these liposomes were conjugated with SF, a&-HER2 antibody -as previously described’. Nude mice imnlanted with 17B estradiol pellets were implanted in the shoulder region with 2 x 10’ cells from the human breast tumor line BT474M1+6, which overexpresses HER2. For imaging studies, mice were anesthetized with an intra-peritoneal injection of 0.05 ml/kg ketamine/xylazine. The mice were imaged at 21-28 days post-implantation when tumors had reached a diameter of 1-2 cm. Mice were injected retro-orbitally with either non-targeted (n=2) or anti-HER2 targeted (n=2) liposomes (0.1 or 0.05 mmol/kg GdDTPA-BMA, respectively). Images were acquired immediately after administration of lioosomes to verify blood pool enhancement and at 8-16, 24, and 44 hrs post-injection. Imaging experiments were performed on a 1.5 T GE Siana clinical scanner using the conventional Medical Advances wrist coil. Anima& were imaged in pairs in a customized holder. An axial image was obtained for tumor localization. followed bv a coronal Tl-weighted high resolution 3DFGRE image over the whole timor (TR= 22 ms, TE=4.2 ms, FOV-8 x 8 cm, imaging matrix 512 x 256. slice thickness 0.7 mm. 2 resolution 157 X 157 X 700 microns). NEX. image -