Abstract
Sonodynamic therapy (SDT) uses a combination of sonosensitizers and low‑intensity therapeutic ultrasound to destroy tumor cells. However, its effects on the tumor microenvironment, particularly on the immune state, remain unknown. The purpose of the present study was to examine the capacity and potency of the antitumor immunity induced by SDT. In the present study, sonosensitizer, 5‑aminolevulinic acid (5‑ALA), and/or ultrasound (US) were used to treat mouse B16F10 melanoma xenograft (1.0 MHz, 0.8 W/cm2, 10% duty cycle) and human umbilical vein endothelial cells (HUVECs; 0.87 MHz, 0.6 W/cm2, 60% duty cycle). Various immune cells, and proteins associated with the immunoregulation such as forkhead Box P3 (Foxp3), cytotoxic T‑lymphocyte associated protein 4 (CTLA‑4), and CD80 were detected by immunofluorescence staining and western blotting. The effect of SDT on blood vessels which were located in the central and peripheral area of tumor tissues was observed by transmission electron microscopy, immunohistochemical and immunofluorescence staining. The effect of SDT on intercellular adhesion molecule‑1 (ICAM‑1) expression on HUVECs was detected by western blotting and reverse transcription‑semi‑quantitative polymerase chain reaction. The results revealed that SDT inhibited tumor growth and improved outcomes. The mean inhibition rate of tumor volume in the US + ALA group was 43.8% and median survival was 45 days in US + ALA group vs. 27.5 days in the control group. SDT increased the number of CD45+ cells, in particular CD8+ and CD68+ cells and upregulated the expression of CD80 in the tumor tissues. The expression levels of Foxp3 and CTLA‑4 were downregulated following SDT. The endothelial cells of tumor central were damaged, but the lumen area of the tumor peripheral vessels (TPVs) and the expression of ICAM‑1 on HUVECs were increased after SDT. The results indicated that SDT improved the outcomes of melanoma‑loading mice, increased the infiltration of CD8+ T cells and downregulates the expression of Foxp3 and CTLA‑4 in mouse melanoma tissues. Furthermore, SDT increased the lumen area of TPVs in murine xenograft and the expression of ICAM‑1 on HUVECs, which may be beneficial to the transendothelial migration of immune cells and the anti‑tumor immune response.