Radionuclide Imaging-Guided Chemo-Radioisotope Synergistic Therapy Using a 131I-Labeled Polydopamine Multifunctional Nanocarrier

Abstract

Development of biocompatible nanomaterials with multiple functionalities for combination of radiotherapy and chemotherapy has attracted tremendous attention in cancer treatment. Herein, poly(ethylene glycol) (PEG) modified polydopamine (PDA) nanoparticles were successfully developed as a favorable biocompatible nanoplatform for co-loading antitumor drugs and radionuclides to achieve imaging-guided combined radio-chemotherapy. It is demonstrated that PEGylated PDA nanoparticles can effectively load two different drugs including sanguinarine (SAN) and metformin (MET), as well as radionuclides ¹³¹I in one system. The loaded SAN and MET could inhibit tumor growth via inducing cell apoptosis and relieving tumor hypoxia, while labeling PDA-PEG with ¹³¹I enables in vivo radionuclide imaging and radioisotope therapy. As revealed by the therapeutic efficacy both in cell and animal levels, the multifunctional PDA nanoparticles (¹³¹I-PDA-PEG-SAN-MET) can effectively repress the growth of cancer cells in a synergistic manner without significant toxic side effects, exhibiting superior treatment outcome than the respective monotherapy. Therefore, this study provides a promising polymer-based platform to realize imaging-guided radioisotope/chemotherapy combination cancer treatment in future clinical application.

Keywords: PDA nanoparticles; metformin; radionuclide imaging; sanguinarine; synergistic therapy.

Figure 1

Schematic Illustration of the PDA-Based Nanoparticles for Combined Chemo-Radiotherapy Dopamine hydrochloride was polymerized under vigorous stirring and functionalized with PEG. The PDA-PEG was then labeled with radionuclide ¹³¹I, as well as small molecular drugs SAN and MET. The obtained ¹³¹I-PDA-PEG-SAN-MET nanoparticles could be used as multifunctional therapeutic agents for radionuclide imaging guided combination therapy.

Figure 2

Preparation and Characterization of PDA Nanoparticles (A) Transmission electron microscopy (TEM) images of PDA nanoparticles. (B) Size distribution of PDA, PDA-PEG, and PDA-PEG-SAN-MET in water measured by dynamic light scattering (DLS). (C) The stability of PDA and PDA-PEG in H₂O, PBS, 1640 medium and fetal bovine serum (FBS). (D) UV-vis–NIR spectra of PDA, PDA-PEG, and PDA-PEG-SAN-MET.

Figure 3

Drug Loading and Radiolabeling on PDA-PEG (A and B) Quantification of SAN (A) or MET (B) loading at different feeding amounts of SAN or MET. (C and D) Release of SAN (C) or MET (D) from PDA-PEG nanoparticles at pH 5.3 or pH 7.4, respectively. (E) The radiostability of ¹³¹I-PDA-PEG after incubation in PBS or serum.

Figure 4

The Cellular Uptake, In Vitro Chemotherapy, and Radioisotope Therapy Efficacy of Nanoparticles (A) Confocal fluorescence imaging of 4T1 cells that were incubated with Cy5.5-labeled PDA-PEG-SAN-MET for 6 hr. (B) The relative cellular viabilities of 4T1 cells after incubation with different concentrations of PDA-PEG for 24 hr. (C) The relative cellular viabilities of 4T1 cells after incubation with different concentrations of free SAN, PDA-PEG-SAN and PDA-PEG-SAN-MET for 24 hr. (D) The relative cellular viabilities of 4T1 cells after being incubated with different concentrations of free ¹³¹I and ¹³¹I-PDA-PEG (0.10, 0.20, 0.41, 0.83, and 1.65 μg/mL PDA-PEG) for 24 hr. (E) The relative cellular viabilities of 4T1 cells after being incubated with different concentrations of ¹³¹I-PDA-PEG, PDA-PEG-SAN-MET and ¹³¹I-PDA-PEG-SAN-MET (0.10, 0.20, 0.41, 0.83, and 1.65 μg/ml PDA-PEG) for 24 hr. All data are shown as mean ± SD of three independent experiments.

Figure 5

Cell Apoptosis Induced by PDA-PEG-SAN Nanoparticles The 4T1 cells were treated with different concentrations (0, 3, 4 μM of SAN and 0, 1.24, 1.65 μg/mL PDA-PEG) of PDA-PEG-SAN nanoparticles for 24 hr. (A) The cells stained with FITC-Annexin V/PI kit were collected for flow cytometry analysis. (B) The quantification of the flow cytometry from three independent experiments. The apoptotic cells were determined by the percentage of Annexin V (+)/PI (−) cells. (C) Caspase-3 activity from the cells that were treated the same as (A). The cells were incubated with Ac-DEVD-pNA, a substrate for caspase-3. Then the released fluorescence products were measured using a caspase-3 activity assay kit. All data are shown as mean ± SD of three independent experiments.

Figure 6

In Vivo Imaging and Biodistribution of ¹³¹I Labeled PDA-PEG (A) Gamma imaging of mice bearing 4T1 tumors after i.v. injection of free ¹³¹I (200 μCi) or ¹³¹I-PDA-PEG (10 mg/kg of PDA-PEG, 200 μCi of ¹³¹I) at different time point. (B) The blood circulation curve of ¹³¹I-PDA-PEG-SAN-MET nanoparticles (200 μCi of ¹³¹I, 10 mg/kg of PDA-PEG) that were i.v. injected into tumor bearing mice. (C) The biodistribution of the same dose of ¹³¹I-PDA-PEG-SAN-MET measured at 24 hr post injection into tumor bearing mice.

Figure 7

In Vivo Combination Radio-Chemotherapy Based on ¹³¹I-PDA-PEG-SAN-MET Nanoparticles (A) Tumor growth curves of 4T1 tumor bearing mice (n = 5) treated with different groups at day 0, 4, 8, and 12. Doses for each injection per mouse: 200 μCi of ¹³¹I, 10 mg/kg of PDA-PEG, 4 mg/kg of SAN, 8 mg/kg of MET. The tumor volumes were normalized to their initial sizes, which were set as 1. (B) The weight curves of mice after various treatments during the period of observation lasted for 14 days. (C) Representative immunofluorescence images of tumor slices collected from mice 24 hr post injection of control or ¹³¹I-PDA-PEG-SAN-MET. The cell nuclei, blood vessels, and hypoxia areas were stained with DAPI (blue), anti-CD31 antibody (red), and anti-pimonidazole antibody (green), respectively.