Determining the Oncological and Immunological Effects of Histotripsy for Tumor Ablation
Histotripsy is an emerging non-invasive, non-thermal, image-guided cancer ablation modality that has recently been approved for its first clinical trial in the United States (NCT04573881). Histotripsy utilizes focused ultrasound to generate acoustic cavitation within a tumor to mechanically fractionate targeted tissues. While pre-clinical work has demonstrated the feasibility of applying histotripsy to solid tumors including primary liver and renal tumors, there is still a need to investigate the potential of histotripsy to treat additional malignancies. In investigating the potential for treating other malignancies there are two avenues that need to be considered: 1) the feasibility for treating tissues with more complex stromal structures and 2) the ability of histotripsy to modulate the tumor microenvironment. To determine the safety and feasibility of additional applications of histotripsy, we conducted dose studies ex vivo on human tumors and human liver to establish dosimetry metrics for applying histotripsy to more fibrotic tumors such as cholangiocarcinoma while sparing nearby critical structures, such as bile ducts and blood vessels. Learning the safety dose-margins from the excised tissues, we performed an in vivo study using mice bearing patient-derived xenograft cholangiocarcinoma tumors. With this model, we were able to demonstrate our ability ablate the stiff cholangiocarcinoma tumors without causing any debilitating off- target damage. To gain a more robust understanding of the effects of histotripsy ablation on potentially difficult to treat tumors, we developed a porcine xenograft tumor model and utilized veterinary cancer patients. These studies have helped established protocols for utilizing histotripsy with ultrasound guidance to treat tumors that are more difficult to treat and can withstand mechanical ablation, including pancreatic adenocarcinoma, osteosarcomas, and soft tissue sarcomas. Pigs share many similarities with human anatomy and physiology, making them an ideal model organism for testing new medical devices and regimes for treating new targets. Using pigs, we were able to establish a procedure to utilize histotripsy to target the pancreas in vivo without causing any lasting or major side effects, such as off-target damage or pancreatitis. One limitation to the porcine model and veterinary patients, is the limitation of gaining rapid insight into the immunological effects of histotripsy. Established cancer mouse models offer the opportunity to rapidly test many organisms with an intact immune system. We used these mice to study pancreatic adenocarcinoma to determine the immune response after histotripsy ablation. For these tumors the general response was an increase in immune cell infiltration post-treatment and a shift in the tumor microenvironment to a more anti-tumor environment. The results of this dissertation provide insight into establishing protocols for treating new types of tumors with histotripsy and immunological effects that lay groundwork for improving future co-therapeutic treatment planning. Future work will aim to translate histotripsy into clinical applications and determining co-therapies that can help control metastasis.