13 Utilizing Non-Invasive Focused Ultrasound to Improve Immunotherapy for Triple Negative Breast Cancer

Checkpoint inhibitor immunotherapy is an emerging treatment option which has shown to be incredibly successful across multiple cancer types and stages. It functionally serves to block certain cell membrane proteins on immune cells and facilitate their efforts towards killing off tumor cells. In contrast to chemotherapy and radiotherapy, immunotherapy targets specific cell populations, minimizing systemic toxicity. In the clinical setting of breast cancer however, response rates for patients are modest at best. This can be explained by inadequate infiltration and communication between critical immune cells such as T lymphocytes, natural killer cells, and dendritic cells. Hormone receptive/HER2 negative breast tumors also have vasculature and stromal barriers contributing to the overall poor response. Therefore, significant interest exists in reshaping the tumor microenvironment while administering an immunotherapeutic in the landscape of breast cancer. Of the different combination therapies possible with immunotherapy, few are as unique as focused ultrasound. Magnetic resonance guided focused ultrasound (MRgFUS) is a non-invasive surgery that uses sound waves to thermally damage tissues with high specificity. Like a magnifying glass converging rays from the sun, focused ultrasound concentrates ultrasound energy to a very small focal region. The amount of thermal damage induced at a focal spot can be monitored and determined using thermometry methods available to magnetic resonance imaging (MRI). It has been shown that MRgFUS exposure on the tumor microenvironment releases inflammatory factors necessary for a systemic immune response.

This process can also lead to recruitment of additional lymphocytes through partial destruction of the tumor and its boundaries. To investigate this, we designed a set of experiments to examine the efficacy of MRgFUS and checkpoint inhibitor immunotherapy in a pre-clinical breast cancer mouse model. In total, six treatment groups were planned for female mice with orthotopically implanted tumors. Four of these groups being treated with light or thorough ultrasound ablation with or without an immunotherapeutic. The other two groups being immunotherapeutic only and an untreated control. Mice were randomly enrolled into one of these groups when their tumors reached a certain size. We then harvested tumors two weeks after the beginning of treatment for immunohistochemistry and cellular composition analysis via flow cytometry. The hypothesized outcome being the combination (light or thorough ablation with immunotherapeutic) treatment would decrease tumor growth rate and increase the percentage of positive immune factors such as lymphocyte counts compared to the individual treatment controls alone. Our findings should be informative on whether the hypothesis is valid for our model and treatment plan. Additionally, we seek to compare how our results differ from the literature where the effects of focused ultrasound and immunotherapy are interrogated in other pre-clinical models. The long-term goal of this project aims to eventually compile enough significant evidence to justify a clinical trial in humans.