2.1. Materials
IR780 was purchased from Sigma-Aldrich (St Louis, MO, USA). The mouse colon cancer cell line (CT-26) was purchased from Shanghai Institute of Cell Biology (Shanghai, China). DAPI was purchased from Beyotime Institute of Biotechnology (Shanghai, China). The rabbit CD47 antibody were obtained from Cell Signaling Technology. All other reagents were from Nanjing Wanqing Chemical Glassware Instrument unless otherwise stated.
2.2. RBC membrane derivation
RBC membranes were obtained from nature RBCs following previously published protocols with modifications.[19] Briefly, whole blood was withdrawn from Balb/c mice and was centrifuged at 2000 rpm for 10 min at 4 °C to collect the erythrocytes, which were continually washed with ice cold 1×PBS for three times. Then, the washed RBCs subjected into a hypotonic treatment with 0.25×PBS in ice bath for 20 min, and subsequently centrifuged at 8000 rpm for 15 min to remove the released hemoglobin. Finally, the obtained RBC membranes were washed with 1×PBS twice and were centrifuged at 12,000 rpm for 10 min to get the RBC membrane.
2.3. Preparation of IR780@RBC and IR780@rRBC
IR780@RBC was prepared by an ultrasonic method. Briefly, the obtained RBC ghosts (1 mL whole blood) were sonicated for 10 min in a bath sonicator (50 kHz, 100W). The resulting vesicles were subsequently extruded serially through 400-nm and then 220-nm polycarbonate porous membranes. Then the resulted RBC-Membrane-Derived Vesicles were mixed with IR780 ethanol solution (1 mg/mL) and sonicated again for 5 min. Then the final product IR780@RBC was obtained by extruding through 220 nm polycarbonate porous membranes to remove free dye and dialyzing against water to remove ethanol.
IR780@rRBC was prepared by a film dispersion method.[20] In brief, the dehydrated lipids (1 mL whole blood) and 1 mg IR780 were dissolved in 5 mL of ethanol and the organic solvent was evaporated under vacuum at 37 ℃. The dried lipid film was then hydrated with 2 mL of endogenous proteins solution (1 mL whole blood) at 37 ℃ for 30 min and sonicated at 100W for 5 min. Then the final product IR780@rRBC was obtained by extruding through 220 nm polycarbonate porous membranes to remove free dye. Endogenous proteins and dehydrated lipids were isolated and purified from RBC ghosts using an organic solvent method similarly with the purification method from human plasma sample.[21, 22] Briefly, the obtained RBC ghosts were dissolved in PBS buffer (pH 5~6) and delipidated by adding equal volume of ethanol. After centrifugation, the supernatant was mixed with equal volume of ethanol and centrifuged again. The final supernatant, which contained endogenous proteins and dehydrated lipids, was concentrated by polyethylene glycol (MW: 20,000) and dialyzed against PBS buffer, followed by precipitating dehydrated lipids with cold ethanol.
SDS-PAGE was used to confirm the protein integrity of RBC membranes in IR780@RBC and IR780@rRBC nanoparticles. Western blotting was conducted to assess the presence of CD47 protein. The amount of the IR780 in IR780@RBC and IR780@rRBC was determined by UV–vis absorption spectra according to standard curve. IR780 encapsulation efficiency was calculated as follows:
2.4. Characterization and stability of IR780@rRBC
Structure was examined using a transmission electron microscope (TEM, H-600, Hitachi, Japan). Particle size was determined by dynamic light scattering (DLS, Brookhaven, USA). Absorption spectra were recorded by UV−vis spectro-photometer. The stability was evaluated by measuring the changed diameter in PBS buffer and serum at room temperature for up to 96 h. Long term stability was evaluated by measuring size of NPs before lyophilizing in 10 wt% sucrose solution and after resuspension. The amount of IR780 released from the IR780@RBC and IR780@rRBC in PBS buffer was studied using the dialysis method.
2.5. Cytotoxicity
The cytotoxicity of IR780@rRBC NPs in CT-26 cells was measured according to a standard MTT assay at different incubation time. Briefly, the cells were seeded in 96-well plates (1×104 cells per well) and cultured until reaching ∼80% confluence. Then, the culture medium was replaced with a fresh medium containing different concentration of IR780, IR780@RBC or IR780@rRBC NPs, after incubation for 2 h, 8 h or 24 h, the cell viability was measured by MTT assay at 490 nm.
2.6. Macrophage cell uptake studies of IR780@rRBC NPs
To compare the stealth functionality of IR780, IR780@RBC and IR780@rRBC NPs, mouse macrophage cell line RAW264.7 was chosen for cell uptake studies. Simply, the cells were seeded into 6-well plates (2×105 cells per well) in DMEM with 10% FBS and 1% penicillin and streptomycin. After cells were reaching ∼60% confluence, they were washed by PBS and replaced with fresh complete cell culture medium containing IR780, IR780@RBC or IR780@rRBC NPs for 1 h. Then, cells were washed with PBS and fixed with 4% paraformaldehyde for 30 min. After fixation, cells were washed with PBS and stained with DAPI for 10 min. Finally, cells were washed with PBS again and imaged by confocal microscopy.
2.7. In vivo pharmacokinetics studies
Six-week-old female balb/c mice were used in compliance with protocol approved by the Institutional Animal Care and Use Committee of Nantong University. For pharmacokinetics studies, fifteen male mice were randomly divided into free IR780, IR780@RBC and IR780@rRBC NPs groups (n=5). The above formulations were administered via intravenous injection with the IR780 dose of 1.4 mg/kg. At different time points (0, 15 min, and 1, 2, 4, 8, 12, 24, 48, 72, 96 h), blood samples were collected by retro-orbital bleeding. The content of IR780 in the serum samples was measured using a Varioskan Flash Spectral Scanning multimode plate reader (Thermo Fisher Scientific, Waltham, MA, USA).
2.8. In vivo biodistribution and PTT therapeutic efficacy studies
For pharmacokinetics studies, 1×107 CT-26 cells were subcutaneously injected into the right flank of each mouse. Two weeks later, the developed tumor was excised and cut into ∼1 mm3 pieces. The pieces of tumors were implanted into the right flank to establish subcutaneous tumors for the biodistribution and therapeutic studies.
Nine mice bearing xenograft tumor were used and divided into three groups (n = 3 per group) and were given a single dose of IR780@rRBC NPs (0.3 mg/kg IR780) by intravenous injection. Whole-body fluorescence imaging was performed using IVIS Lumina imaging system (Xenogen Co., USA) with excitation/emission set to 745/808 nm. Fluorescence images were acquired in anesthetized animals at different time points (12 h, 24 h and 48 h). IVIS Living Imaging Software was used for the analysis of the amount of IR780 in tissues.
Therapeutic study started when the tumors reached ∼200 mm3.The mice were divided into groups (n = 6 per group) and treated with (i) PBS, (ii) IR780 + NIR laser, (iii) IR780@RBC + NIR laser, (iv) IR780@rRNC NPs, (v) IR780@rRNC NPs +NIR laser. All samples were administered via Intravenous injection (1.4 mg/kg IR780). The day of administration was designated as day 0. After 24 h, the tumors were exposed to the NIR laser irradiation (1 W/cm2) for 3 min. Treatment administrations and laser irradiation were repeated on days 2 and 3. Tumor sizes and mouse body weights were recorded every other day. Tumor volume (V) was calculated as V = d2 × D/2, where D and d are the longest and shortest diameter of the tumor, respectively.
2.9. Statistical analysis
Statistical assessment was conducted by two-sided Student’s t test for two groups and one-way ANOVA analysis of variance for multiple groups (P < 0.05 was considered statistically significant). All analyses were performed with SPSS 19.0 for Windows.