2.9. In vivo antitumor efficacy

Mice harboring 4T1 tumors were randomly divided into six groups with five mice per group and were injected through the tail vein with saline, HTCP-Au/shNC, HTCP-Au/shNC-808, HTCP-Au/shNC/DOX, HTCP-Au/shPD-L1, and HTCP-Au/shPD-L1/DOX-808 (15 mg/kg HTCP-Au, 5 mg/kg shPD-L1, or shNC, 6 mg/kg DOX) every 6 days. For the mice of the HTCP-Au/shNC-808 and HTCP-Au/shPD-L1/DOX-808 groups, the tumor was irradiated for 30 s with near-infrared (NIR; 1.5 W/cm²), 5 h after the first injection, and every 3 d thereafter. The tumor volume and body weight were monitored every 2 d On Day 13 after injection, the mice were sacrificed, and their tumor tissues were excised and weighed to calculate tumor inhibition rates. In addition, the tumor tissues were dewaxed, stained, dehydrated, rendered transparent, and sealed for histopathological and immunohistochemical analyses. The level of interferon gamma (IFN-γ) secretion was assayed using an enzyme-linked immunosorbent assay (ELISA) kit.