Pre-Clinical Investigation of Histotripsy for Non-Invasive Ablation of Liver Cancer

Abstract

Liver cancer, including hepatocellular carcinoma (HCC) is one of the top ten causes of cancer related deaths worldwide and in the United States. The liver is also a frequent site for metastases originating from colorectal cancer, pancreatic cancer, melanoma, lung cancer and breast cancer. Depending on the location, severity and staging of liver cancer, multiple treatment options are currently available including surgical resection, liver transplantation, chemotherapy, radiation therapy, targeted drug therapy, immunotherapies, and ablation techniques including radiofrequency ablation (RFA), microwave ablation (MWA), cryoablation, high intensity focused ultrasound (HIFU), yet the prognosis of HCC remains poor with five-year survival rates reported at only 18% in the US. Even after treatment, the high prevalence of tumor recurrence and metastasis highlights the clinical need for improving outcomes of liver cancer. Histotripsy is a novel non-invasive, non-ionizing, and non-thermal ablation technique that mechanically destroys target tissue by controlled acoustic cavitation. High pressure (focal peak negative pressure P- >30MPa), microsecond-length ultrasound pulses cause endogenous nanometer-scale gas nuclei in the target tissue to rapidly expand and collapse, generating high mechanical stress and strain to disrupt the cellular structure into an acellular homogenate. This dissertation presents histotripsy as a therapeutic ultrasound technology for effective treatment of liver cancer and other solid tumors. The first study evaluated the safety and feasibility and survival benefits of histotripsy for in vivo tumor ablation. Results showed that non-invasive histotripsy ablation reduced local tumor progression of subcutaneous human-derived HCC tumor and improved survival outcomes in immunocompromised mice. This study also characterized the radiological features correlating to the histotripsy tumor response. The second study evaluated the safety, feasibility, and tumor volume reduction effects of histotripsy for liver cancer ablation in an orthotopic, immune-competent in vivo rat HCC model. For the first time, it was demonstrated that complete as well as partial histotripsy ablation of tumors can result in complete tumor regression with no recurrence. The third study evaluated the effects of partial histotripsy tumor ablation on tumor response, risk of metastases and immune infiltration in an orthotopic, immunocompetent, metastatic rodent hepatocellular carcinoma (HCC) model. Results showed that histotripsy significantly improved survival outcomes with no increased risk of metastasis compared to controls and demonstrated that augmented tumor immune infiltration may have contributed to the eventual regression even with partial treatment of tumors. The fourth study evaluated the anti-tumor immune response generated by histotripsy ablation of subcutaneous murine melanoma and HCC tumors. Histotripsy stimulated potent local intratumoral infiltration of innate and adaptive immune cell populations, promoted abscopal immune responses at untreated tumor sites and inhibited growth of pulmonary metastases. Histotripsy was capable of releasing tumor antigens with retained immunogenicity and was able to amplify the efficacy of checkpoint inhibition immunotherapy. The fifth study compared the tumor response and survival outcomes with single and repeat histotripsy treatment in human-derived and mouse HCC murine models. One week after the initial histotripsy treatment, animals received a repeat histotripsy treatment. Results showed that both histotripsy groups significantly improved survival outcomes over control. Overall, this dissertation demonstrated the potential of histotripsy for successful non-invasive tumor ablation, reduction of local tumor burden and prevention of metastasis. Future studies will continue to investigate the safety, efficacy, and biological effects of histotripsy for potential translation to clinic.