Inhibition of Walker-256 Tumor Growth by Combining Microbubble-Enhanced Ultrasound and Endostar

Low-intensity focused ultrasound targeted microbubble destruction reduces tumor blood supply and sensitizes anti-PD-L1 immunotherapy

Immune checkpoint blockade (ICB) typified by anti-PD-1/PD-L1 antibodies as a revolutionary treatment for solid malignancies has been limited to a subset of patients due to poor immunogenicity and inadequate T cell infiltration. Unfortunately, no effective strategies combined with ICB therapy are available to overcome low therapeutic efficiency and severe side effects. Ultrasound-targeted microbubble destruction (UTMD) is an effective and safe technique holding the promise to decrease tumor blood perfusion and activate anti-tumor immune response based on the cavitation effect. Herein, we demonstrated a novel combinatorial therapeutic modality combining low-intensity focused ultrasound-targeted microbubble destruction (LIFU-TMD) with PD-L1 blockade. LIFU-TMD caused the rupture of abnormal blood vessels to deplete tumor blood perfusion and induced the tumor microenvironment (TME) transformation to sensitize anti-PD-L1 immunotherapy, which markedly inhibited 4T1 breast cancer's growth in mice. We discovered immunogenic cell death (ICD) in a portion of cells induced by the cavitation effect from LIFU-TMD, characterized by the increased expression of calreticulin (CRT) on the tumor cell surface. Additionally, flow cytometry revealed substantially higher levels of dendritic cells (DCs) and CD8⁺ T cells in draining lymph nodes and tumor tissue, as induced by pro-inflammatory molecules like IL-12 and TNF-α. These suggest that LIFU-TMD as a simple, effective, and safe treatment option provides a clinically translatable strategy for enhancing ICB therapy.

Ultrasound-Targeted Microbubble Destruction: Modulation in the Tumor Microenvironment and Application in Tumor Immunotherapy

Tumor immunotherapy has shown strong therapeutic potential for stimulating or reconstructing the immune system to control and kill tumor cells. It is a promising and effective anti-cancer treatment besides surgery, radiotherapy and chemotherapy. Presently, some immunotherapy methods have been approved for clinical application, and numerous others have demonstrated promising in vitro results and have entered clinical trial stages. Although immunotherapy has exhibited encouraging results in various cancer types, however, a large proportion of patients are limited from these benefits due to specific characteristics of the tumor microenvironment such as hypoxia, tumor vascular malformation and immune escape, and current limitations of immunotherapy such as off-target toxicity, insufficient drug penetration and accumulation and immune cell dysfunction. Ultrasound-target microbubble destruction (UTMD) treatment can help reduce immunotherapy-related adverse events. Using the ultrasonic cavitation effect of microstreaming, microjets and free radicals, UTMD can cause a series of changes in vascular endothelial cells, such as enhancing endothelial cells’ permeability, increasing intracellular calcium levels, regulating gene expression, and stimulating nitric oxide synthase activities. These effects have been shown to promote drug penetration, enhance blood perfusion, increase drug delivery and induce tumor cell death. UTMD, in combination with immunotherapy, has been used to treat melanoma, non-small cell lung cancer, bladder cancer, and ovarian cancer. In this review, we summarized the effects of UTMD on tumor angiogenesis and immune microenvironment, and discussed the application and progress of UTMD in tumor immunotherapy.