Yuting Xiang,1,2,* Li Tang,1,* Hua Pang,3 Han Xu,1,2 Yiman He,1,2 Yuyue Feng,3 Linjun Ju,3 Liang Zhang,1 Dong Wang1 

1Department of Ultrasound, The First Affiliated Hospital of Chongqing Medical University, Chongqing, People’s Republic of China; 2Chongqing Key Laboratory of Ultrasound Molecular Imaging, Chongqing Medical University, Chongqing, People’s Republic of China; 3Department of Nuclear Medicine, The First Affiliated Hospital of Chongqing Medical University, Chongqing, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Liang Zhang; Dong Wang, Department of Ultrasound, The First Affiliated Hospital of Chongqing Medical University, 1 Youyi Road, Yuzhong District, Chongqing, 400042, People’s Republic of China, Email zhangliang338@cqmu.edu.cn; wang57554@163.com

Background: The inadequate perfusion, frequently resulting from abnormal vascular configuration, gives rise to tumor hypoxia. The presence of this condition hinders the effective delivery of therapeutic drugs and the infiltration of immune cells into the tumor, thereby compromising the efficacy of treatments against tumors. The objective of this study is to exploit the thermal effect of ultrasound (US) in order to induce localized temperature elevation within the tumor, thereby facilitating vasodilation, augmenting drug delivery, and enhancing immune cell infiltration.
Methods: The selection of US parameters was based on intratumor temperature elevation and their impact on cell viability. Vasodilation and hypoxia improvement were investigated using enzyme-linked immunosorbent assay (ELISA) and immunofluorescence examination. The distribution and accumulation of commercial pegylated liposomal doxorubicin (PLD) and PD-L1 antibody (anti-PD-L1) in the tumor were analyzed through frozen section analysis, ELISA, and in vivo fluorescence imaging. The evaluation of tumor immune microenvironment was conducted using flow cytometry (FCM). The efficacy of US-enhanced chemotherapy in combination with immunotherapy was investigated by monitoring tumor growth and survival rate after various treatments.
Results: The US irradiation condition of 0.8 W/cm2 for 10 min effectively elevated the tumor temperature to approximately 40 °C without causing any cellular or tissue damage, and sufficiently induced vasodilation, thereby enhancing the distribution and delivery of PLD and anti-PD-L1 in US-treated tumors. Moreover, it effectively mitigated tumor hypoxia while significantly increasing M1-phenotype tumor-associated macrophages (TAMs) and CD8+ T cells, as well as decreasing M2-phenotype TAMs. By incorporating US irradiation, the therapeutic efficacy of PLD and anti-PD-L1 was substantially boosted, leading to effective suppression of tumor growth and prolonged survival in mice.
Conclusion: The application of US (0.8 W/cm2 for 10 min) can effectively induce vasodilation and enhance the delivery of PLD and anti-PD-L1 into tumors, thereby reshaping the immunosuppressive tumor microenvironment and optimizing therapeutic outcomes.

Keywords: ultrasound, thermal effect, vasodilatation, drug delivery, tumor microenvironment