Photosensitizer-loaded biomimetic platform for multimodal imaging-guided synergistic phototherapy

Abstract

Photodynamic therapy (PDT) has attracted much attention as a strategy for tumor therapy. However, the insolubility and poor tumor-targeting ability of most photosensitizers (PSs) hinder PDT from further development. Therefore, it is necessary to explore new carriers with good water solubility and biocompatibility to deliver PSs to tumors. Melanin nanoparticles are novel biomimetic nanocarriers with excellent biocompatibility, loading capacity, photothermal therapy (PTT) and magnetic resonance (MR)/photoacoustic (PA) imaging properties. Here we designed polydopamine melanin nanoparticles (PDMNs) as a delivery platform for the photosensitizer Chlorin e6 (PDMN-Ce6) and realized its application as a theranostic agent for tumor therapy. The PDMN-Ce6 exhibited excellent biocompatibility, good water solubility and high loading capability (35.2 wt%) for Ce6. Compared with the free Ce6, PDMN-Ce6 showed higher cellular internalization and superior synergistic phototherapy effects in an in vitro study. An in vivo study indicated that the accumulation of PDMN-Ce6 at tumor sites was 2.8-fold higher than that of free Ce6 at 24 h post-injection, which was beneficial for MR/PA imaging. Moreover, the synergetic therapy significantly inhibited tumor growth, causing tumor necrosis and tumor angiogenesis suppression. These results suggest that our biomimetic and biocompatible platform could improve the delivery of Ce6 to tumors and realize multimodal imaging-guided tumor synergetic phototherapy.

Scheme 1. Schematic illustration of the synthesis and application of the biomimetic platform PDMN–Ce6 for MRI/PAI-guided synergistic phototherapy.

Fig. 1. (a) TEM image of PDMN; scale bar: 100 nm. (b) UV-Vis spectra of Ce6, PDMN and PDMN–Ce6 from 300 to 1000 nm. (c) FT-IR spectra of Ce6, PDMN and PDMN–Ce6. (d) The hydrodynamic diameters of PDMN and PDMN–Ce6. (e) The loading capacity of Ce6 on the PDMN. (f) The hydrodynamic diameters of PDMN–Ce6 in PBS or FBS for 15 days.

Fig. 2. (a) SOSG fluorescence intensity (FI) at 530 nm in H₂O, PDMN, PDMN–Ce6, PDMN + Ce6 and Ce6 under laser irradiation (660 nm, 1 W cm⁻², 5 min). (b) Thermal images and (c) temperature curves of H₂O, Ce6, PDMN and PDMN–Ce6 at the same proportional concentrations under irradiation (660 nm laser, 1 W cm⁻², 5 min). (d) Photostability of PDMN–Ce6 over five cycles of irradiation with a 660 nm laser at 1 W cm⁻² for 5 min and cooling for 7 min.

Fig. 3. (a) MRI images and plot of PDMN–Ce6 at different concentrations. (b) PAI images and plot of PDMN–Ce6 at different concentrations. The images from 1 to 5 correspond to the concentrations of 0, 0.1, 0.5, 1 and 4 mg mL⁻¹, respectively.

Fig. 4. (a) The degree of cellular uptake of PDMN–Ce6 and Ce6 (equal proportional concentrations) after incubation for 4 h, 8 h and 24 h. (b) The degree of cellular uptake of different concentrations of PDMN–Ce6 after 24 h. (c) Detection of the cellular internalization pathway by treatment of the cells with different cell inhibitors or culture at 4 °C.

Fig. 5. (a) Relative cell viability of MCF 10A and (b) SKBR-3 cells after incubation with PDMN or PDMN–Ce6 at different concentrations without irradiation. (c) Relative cell viability of SKBR-3 cells after incubation with PDMN, PDMN–Ce6 or Ce6 at different concentrations under irradiation (660 nm, 1 W cm⁻², 5 min). Asterisk * indicates p < 0.05; asterisks ** indicates p < 0.01.

Fig. 6. (a) The biodistribution of PDMN–Ce6 and Ce6 at time points 1 h, 4 h, 8 h and 24 h after intravenous injection. The images were captured by the animal optical imaging system. (b) Relative fluorescence intensities at different time points of the main tissues of mice injected with PDMN–Ce6. (c) Relative fluorescence intensities at different time points of the main tissues of mice injected with Ce6. (d) MRI of mice before and 24 h after intravenous injection of PDMN–Ce6. (e) PAI of mice before and 24 h after intravenous injection of PDMN–Ce6. The red circles indicate the locations of the tumors.

Fig. 7. (a) Representative thermal images of tumor-bearing mice after laser irradiation for 5 min (660 nm, 1 W cm⁻²). (b) The tumor temperatures during the period of irradiation (660 nm, 1 W cm⁻², 5 min) in mice treated with PBS, Ce6, PDMN and PDMN–Ce6 at a time point 24 h after injection. (c) Tumor growth curves of tumor-bearing mice after treatment. The tumor volumes were normalized to their initial sizes (asterisks indicate p < 0.05).

Fig. 8. (a) H&E and IHC staining of tumors from each mice group after treatment; scale bars: 100 μm. (b) The microvessel density (MVD) of tumors in the different mice groups after treatment.

Fig. 9. The blood biochemical indicator analysis after intravenous injection of mice with PBS, Ce6, PDMN or PDMN–Ce6; data were obtained for (a) ALT, AST, ALP and (b) BUN and SCr. (c) The hemolytic reaction of RBCs after incubation with different concentrations of PDMN–Ce6. (d) The changes of body weight for mice in each group after treatment.