Therapeutic Ultrasound-Induced Antitumor Immune Response and Enhanced by Immunostimulant for Tumor Treatment

Abstract

To evaluate whether antitumor immunity is enhanced systemically by combining pulsed-wave ultrasound hyperthermia (pUSHT) and local injection of an immunostimulant, OK-432. BALB/c mice were inoculated CT26-luc-GFP tumors on both flanks as a bilateral tumor model. The treated-side tumor underwent a 10-day treatment with pUSHT and/or subcutaneous injection of OK-432. The untreated-side tumor was regarded as a non-visualized small tumor to assess the degree of anti-tumor immune response. In a rechallenge tumor model, a rechallenge tumor was implanted contralaterally after the treated-side tumor experienced a 5-day treatment and then surgically removed. This model was designed to evaluate the establishment of a long-term active tumor-specific immune memory for preventing tumor recurrence. The tumor growth rate and growth activity of both tumors (treated- and untreated-side) were significantly inhibited with the OK+pUSHT combination treatment. Systemic anti-tumor effect seemed to be prolonged. The results of IF and H&E staining showed that there was a remarkable increase of NK cell infiltration in the tumor center and an earlier necrosis area for the combination treatment. Survival rates significantly increased for the OK+pUSHT group. In the rechallenge test, the volume of all reimplanted tumors decreased and then disappeared as compared with the control group. Combining pUSHT with local injection of immunostimulant OK-432 may lead to indirectly activation of systemic antitumor immunity.