Histotripsy-induced vascular remodeling in the tumor microenvironment enhances local and off-target intratumoral drug delivery

Solid tumors are refractory to treatment because their poorly perfused microenvironment blocks immune cell infiltration and effective drug delivery. Histotripsy is a non-invasive focused ultrasound modality that generates cavitation microbubbles to mechanically disrupt solid tumors, reducing hypoxia and stimulating tumor-targeted adaptive immune responses. This study investigated whether post-histotripsy hypoxia reduction and cytotoxic immune cell infiltration are linked to tumor vascular normalization and enhanced perfusion.

Structural analysis of treated tumors and contralateral off-target tumors after partial histotripsy revealed significant vascular remodeling, enhanced vascular integrity, and decreased vascular leakage, all indicative of vascular normalization in multiple in vivo models of melanoma, hepatocellular carcinoma, and pancreatic adenocarcinoma. These effects appeared antigen-specific, because no remodeling was seen in contralateral off-target tumors of discordant pathology.

Mechanistically, CXCR3+CD8+ T cells helped mediate the vascular changes: genetic knockout of CD8 and pharmacological antagonism of CXCR3 impaired both remodeling and normalization. Histotripsy also produced significant changes in endothelial CXCR4 and Angiopoietin-1 and -2 expression, suggesting their potential involvement in promoting vascular normalization and remodeling.

The vascular remodeling was accompanied by enhanced tumor perfusion and increased intratumoral delivery of chemotherapeutic agents and therapeutic monoclonal antibodies. The findings suggest histotripsy not only creates a more favorable microenvironment for immunotherapy but also optimizes drug delivery into solid tumors, indicating that combining histotripsy with chemotherapy or immunotherapy may be a novel strategy to overcome limitations of conventional solid tumor therapies.