3.9. In Vivo Photothermal Treatment for Tumor Ablation

Female nude mice 8–10-weeks old with an average weight of 20 g were purchased from Xiamen University Laboratory Animal Center. The whole animal experiments were completed in the Animal Center and followed the Chinese National Institutes of Health guidelines for care and use of laboratory animals.

An MCF-7 tumor model was built by subcutaneous injection of 100 μL of MCF-7 cells (5 × 10⁶ cells) into the right back of nude mice. Once the average volume of the tumors reached approximately 200 mm³, the mice were randomly divided into 4 groups with 5 mice in each group. The four group mice were intravenously injected with 100 μL of PBS, PDA-PEG and PDA-150PY-PEG only once and treated with: (1) PBS only; (2) PBS with 808 nm laser; (3) PDA-PEG NPs with 808 nm laser; and (4) PDA-150PY-PEG NPs with 808 nm laser. The injection dosage of PDA and PDA-150PY NPs was both 300 μg. After 12 h post-injection, the tumor site of each mouse was irradiated by 808 nm laser at a power density of 1.5 W/cm² for 10 min per day and continuous irradiation for 4 days. On the first day of laser irradiation treatment, the in vivo thermal imaging was performed simultaneously using an IR thermal camera. The tumor volumes were measured daily, and the body weight was weighed the next day. The tumor volume was calculated according to the formula: Volume (mm³) = Length (mm) × Width² (mm²)/2.

After 2 days of photothermal treatment, a mouse was randomly selected from each group for dissection. Heart, liver, spleen, lung, kidney and tumor tissue were collected and fixed with fixative. The fixed tissue specimens were further stained with hematoxylin and eosin (H&E) and examined by light-field microscope.