Folate receptor-targeted fluorescent paramagnetic bimodal liposomes for tumor imaging.

RATIONALE AND OBJECTIVE: Receptor-targeted delivery of imaging and therapeutic agents can lead to enhanced efficacy for both. Multimodality imaging offers unique advantages over traditional single modality imaging. Tumor marker folate receptor (FR)-targeted fluorescent paramagnetic bimodal liposomes were synthesized to co-deliver paramagnetic and fluorescence agents for magnetic resonance (MR) and optical bimodal imaging contrast enhancement.

MATERIALS AND METHODS: Fluorescent and paramagnetic bimodal liposomes were synthesized with a mean diameter of 136 nm and a low polydispersity index. The liposomes incorporated folate-PEG(3350)-CHEMS for FR targeting, Gd(III)[N,N-Bis-stearylamidomethyl-N'-amidomethyl]diethylenetriamine tetraacetic acid (Gd-DTPA-BSA) for MR contrast, and calcein for fluorescence. To determine the specificity and efficiency of delivery, the liposomes were evaluated in FR-positive KB and HeLa cells and FR-negative A549 cells, which were analyzed by fluorescence microscopy, magnetic resonance imaging (MRI), and flow cytometry (FCM).

RESULTS: FR-specific and efficient cellular uptake of the FR-targeted bimodal liposomes was confirmed by fluorescence microscopy and by FCM. The mean fluorescence intensity (MFI) of KB cells treated with FR-targeted liposomes was 45× that of cells treated with nontargeted liposomes, and 18× that of cells treated with FR-targeted liposomes and excess folic acid (FA). The MFI of HeLa cells treated with targeted liposomes was 33× that of nontargeted liposomes, and was 16× that of the mixture of targeted liposomes and free FA. In contrast, the MFI of A549 cells treated with FR-targeted liposomes was nearly the same as those treated with nontargeted liposomes. The T(1)-weighted MR images of HeLa and KB cells incubated with FR-targeted liposomes had much higher signal intensity than those treated with nontargeted liposomes or free Gd-DTPA. Furthermore, the FR-targeting effect could be blocked by excess free FA.

CONCLUSION: FR-targeted fluorescent paramagnetic bimodal liposomes provided a novel platform for bimodal tumor imaging and theranostic delivery.