Polydopamine Nanoparticles as a Versatile Molecular Loading Platform to Enable Imaging-guided Cancer Combination Therapy

Abstract

Cancer combination therapy to treat tumors with different therapeutic approaches can efficiently improve treatment efficacy and reduce side effects. Herein, we develop a theranostic nano-platform based on polydopamine (PDA) nanoparticles, which then are exploited as a versatile carrier to allow simultaneous loading of indocyanine green (ICG), doxorubicin (DOX) and manganese ions (PDA-ICG-PEG/DOX(Mn)), to enable imaging-guided chemo & photothermal cancer therapy. In this system, ICG acts as a photothermal agent, which shows red-shifted near-infrared (NIR) absorbance and enhanced photostability compared with free ICG. DOX, a model chemotherapy drug, is then loaded onto the surface of PDA-ICG-PEG with high efficiency. With Mn(2+) ions intrinsically chelated, PDA-ICG-PEG/DOX(Mn) is able to offer contrast under T1-weighted magnetic resonance (MR) imaging. In a mouse tumor model, the MR imaging-guided combined chemo- & photothermal therapy achieves a remarkable synergistic therapeutic effect compared with the respective single treatment modality. This work demonstrates that PDA nanoparticles could serve as a versatile molecular loading platform for MR imaging guided combined chemo- & photothermal therapy with minimal side effects, showing great potential for cancer theranostics.

Keywords: Combination therapy; Indocyanine green; Magnetic resonance imaging.; Nano-Drug delivery system; Polydopamine.

Figure 1

Preparation and characterization of PDA-ICG-PEG.(a) A scheme showing the synthesis of PDA-ICG-PEG nanoparticles, as well as the followed drug loading and metal ion chelating. (b) A TEM image of PDA-ICG-PEG nanoparticles. (c) Dynamic light scattering (DLS) data of PDA and PDA-ICG-PEG nanoparticles in aqueous solutions. (d) UV-Vis-NIR spectra of PDA and PDA-ICG-PEG. Insert: a photo of PDA-ICG-PEG in different solutions: water (1), NaCl (2) and PBS (3). e) Temperature changes of water, PDA and PDA-ICG-PEG at same PDA concentrations (0.014 mg/ml) under irradiation by the 808-nm laser (0.8 W/cm²). (f) Temperature changes of PDA-ICG-PEG and free ICG solutions with the same ICG concentration under irradiation of the 808-nm laser with the power density of 0.8 W/cm² for 5 cycles (3 min of irradiation for each cycle).Insert: Photos of free ICG and PDA-ICG-PEG solutions before (left) and after (right) laser irradiation.

Figure 2

Drug loading and release.(a) UV-Vis-NIR spectra of DOX loaded PDA-ICG-PEG with different feeding ratios of DOX to PDA. (b) Quantification of DOX loading at different DOX : PDA ratios.(c) DOX release from PDA-ICG-PEG-DOX nanoparticles in buffers at the different pH values. (d) NIR-triggered release of DOX from PDA-ICG-PEG-DOX nanoparticles. The samples were irradiated with an NIR laser (0.8 W/cm²) for 5 min at different time points as indicated by the arrows. Error bars were based on at least triplicated measurements.

Figure 3

In vitro combination therapy.(a) Relative viabilities of 4T1 cells and HeLa cells after being incubated with various concentrations of PDA-ICG-PEG for 24 h. (b) Relative viabilities of 4T1 cells after being incubated with free DOX or PDA-ICG-PEG/DOX at various concentrations for 24 h. (c) Confocal fluorescence images of 4T1 cells incubated with PDA-ICG-PEG/DOX (or free DOX) with/without laser irradiation (808 nm, 0.8 W/cm², 20 min). (d) Relative viabilities of 4T1 cells after being incubated with DOX, PDA-ICG-PEG, PDA-ICG-PEG/DOX with/without laser irradiation at different power density for 20 min. The cell viability test was conducted after further incubation for 24 h. The data are shown as mean ±standard deviation (SD) with at least triplicated measurements.

Figure 4

MR imaging.(a) T1 and T2 weighted MR images of PDA-ICG-PEG/DOX(Mn) with various Mn²⁺ concentrations. (b&c) The T1 relaxation rates (b) and T2 relaxation rates (c) of PDA-ICG-PEG/DOX(Mn) aqueous solutions with different Mn²⁺ concentrations. The longitudinal relaxivity (r1) and transverse relaxivity (r2) were determined to be 14.15 mM^-1 S^-1 and 39.2 mM^-1 S^-1, respectively. (d) In vivo T1-weighted MR images of mouse taken before injection (upper) and 24 h post i.v. injection (bottom) with PDA-ICG-PEG/DOX(Mn). A brightening effect could be observed in the tumor region. (e) T1-weighted MR signals in the tumor before injection and 24 h post i.v. injection with PDA-ICG-PEG/DOX(Mn).

Figure 5

In vivo combination therapy.(a) IR thermal images of 4T1 tumor-bear mice with/without the NIR laser irradiation (808 nm, 0.5 W/cm², 20 min) after i.v. injection with PBS, free DOX, PDA-ICG-PEG, PDA-ICG-PEG/DOX for 24 h at the same PDA and DOX concentrations. (b) Temperature changes of tumor-bearing mice monitored by the IR thermal camera in different groups during laser irradiation as indicated in (a). (c) Tumor growth curves of different groups of mice (5 mice for each group) after various treatments indicated in (a). (d) H&E stained slices of tumors collected from mice one day after various treatments indicated. Note: (1), (2), (3), (4), (5) were used to represent, PDA-ICG-PEG/DOX (1),PBS (plus Laser) (2),free DOX (plus Laser)(3), PDA-ICG-PEG (plus Laser) (4), and PDA-ICG-PEG/DOX (plus Laser) (5).