Background: Previous studies have reported that tumor debris and inflammation made by high-intensity focused ultrasound (HIFU) therapy induced the antitumor immune response, however, HIFU as a monotherapy is still not potent enough to eradicate tumors and treat distant metastasis. We have reported that mechanical HIFU (M-HIFU), that will mechanically destroy tumor cells/tissues through acoustic cavitation, induced stronger antitumor immune response compared to conventional thermal HIFU (T-HIFU) that will cause thermal ablation of tumors. In the present study, we established an immune based combination therapy of M-HIFU and immune checkpoint blockade to enhance systemic antitumor immune response and treated distant/metastatic tumors in murine breast cancer models.

Methods and Results: HER2 oncogene-dependent murine breast cancer cell line, MM3MG-HER2, was established in our lab. In mice with bilateral implantation of MM3MG-HER2 tumors, M-HIFU monotherapy induced stronger HER2-specific cellular response and inhibited the growth of HIFU-untreated distant tumors as well as HIFU treated-tumors, more potently than T-HIFU. Flow cytometry and immunohistochemical analysis of tumor microenvironment revealed significantly stronger accumulation of activated T cell and NK cells in M-HIFU-treated tumors. On the other hand, M-HIFU induced stronger expression of programmed death-ligand 1 (PD-L1) on various immune cells in both sides of tumors than T-HIFU therapy or no treatment control. Based on these findings, we investigated the combination therapy of M-HIFU and PD-1/PD-L1 axis blockades, and found significantly enhanced tumor-specific cellular immune response compared to each monotherapy, which resulted in improved therapeutic effect against distant tumors as well as HIFU treated-tumors. Furthermore, immune cell depletion studies demonstrated that both CD8+ T cells and NK cells played an essential role for the antitumor efficacy in this combinatory therapy against both HIFU-treated tumors and untreated distant tumors.

Conclusion: this study provides strong rational evidence that M-HIFU combined with PD-1/PD-L1 axis blockades could be a promising treatment strategy against advanced breast cancer with metastatic lesion.

Citation Format: Shinya Abe, Takuya Osada, Kensuke Kaneko, Pei Zhong, Herbert K. Lyerly. A novel combination therapy of high intensity focused ultrasound and PDL1 blockades against advanced breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4071.