Abstract
1254
Objectives: Radionuclide 177Lu (t1/2: 6.65 days, Emax: 0.497 MeV) is considered as a promising candidate to benefit nanotechnology-mediated combination therapy of cancer. However, broad applications of various reported nanosystems were impeded because of their suboptimal tumor targeting efficiency and sequestration in the reticuloendothelial system. Our goal is to rationally integrate tumor targeting of nanocarrier with multi-modal imaging to guide high-efficacy delivery of 177Lu and combinatorial therapy.
Methods: A novel theranostic nanoplatform nanostructured porphyrin-polyethylene glycol mesh (denoted as PPNs) with dual tumor- and mitochondria-targeting properties was synthesized by conjugating meso-tetra(4-carboxyphenyl)-porphyrin (denoted as mTCPP) with 8-arm-amine-polyethylene glycol (aPEG). The mTCPP in the PPNs acted as a theranostic component based on its photodynamic therapy (PDT) properties and fluorescence imaging. In vivo biodistribution of PPNs with approximately 1 nm, 10 nm, and 50 nm in diameter was investigated by positron emission tomography (PET) imaging after labeling with 64Cu (via coordination with mTCPP in PPNs). The chelation of 177Lu was dependent on the entire nanostructure. In vitro anticancer efficiency was evaluated by MTT assay. After staining with various dyes, confocal imaging was utilized to analyze the reactive oxygen species (ROS) level, the morphology of cell nucleus and mitochondria, and the localization of PPNs in cells. In vivo combination treatment of PDT and radionuclide therapy (RT) was carried out to achieve synergistic inhibition of the tumor growth. RESULTS: The size of obtained PPNs was readily controlled by modulating the reaction time of mTCPP and aPEG. The maximum tumor accumulation (15.6 %ID/g, 72 h p.i.; n = 3) and excellent tumor-to-muscle ratio (16.6, 72 h p.i.; n = 3) was achieved for 64Cu-PPNs-10nm based on non-invasive PET imaging, which was much higher than that of 64Cu-PPNs-1nm and 64Cu-PPNs-50nm. Confocal imaging confirmed the cellular uptake of PPNs-10nm. After staining with various dyes for visualizing subcellular organelles, a time-dependent co-localization of PPNs in mitochondria was observed, likely due to the charge interaction. Combination of 177Lu-PPNs and 660 nm laser irradiation greatly increased ROS level in cells and also induced significant mitochondrial fragmentation and cell nucleus condensation. In vitro assessment confirmed efficient mitochondrial uptake of 177Lu-PPNs which greatly enhanced the efficacies of RT and/or PDT. Taking advantage of strong fluorescence and radiolabel ability of PPNs, multimodal imaging revealed excellent tumor uptake efficiency of PPNs due to the enhanced permeability and retention (EPR) effect after intravenous injection. In vivo fluorescence signals and gamma camera images in both groups, 177Lu-PPNs-10nm alone and co-treatment of 177Lu-PPNs-10nm with laser, were strong and lasted up to 14 days. Remarkably, synergistic inhibition of tumor growth was achieved by the co-treatment of 177Lu-PPNs-10nm and laser (i.e. RT + PDT). CONCLUSION: A facile method was developed to construct nanotheranostic agents with controllable biodistribution in vivo and subcellular organelle targeting in vitro by complexing mTCPP with aPEG. Efficient tumor and mitochondria targeting, evidenced by multimodality imaging, enhanced the co-treatment efficacy of therapeutic radionuclide 177Lu and PDT.