Abstract 4201: Immune priming with low intensity focused ultrasound and radiation therapy in murine breast cancer
Authors: Schumacher Michelle M. , Chavez Claudia Gutierrez , Singh Saurabh , Karunakaran Chandra , Pandey Sanjay , Kumar Mayank , Gonzales Rodney Macedo , Guha Chandan 
Published: June 2022

Abstract
Introduction: Our long-term goal is to use focal therapy, such as radiation therapy (RT) and ultrasound, to induce stress and engineer the tumor microenvironment (TME) to drive a systemic anti-tumoral immunity, while achieving primary tumor control. Current RT-induced systemic anti-tumoral immunity is dampened by defective tumor antigen presentation resulting in immune escape, an immunosuppressive TME, and the presence of anergic T cells in the immune privileged tumor draining lymph nodes. We have previously developed a proprietary non-ablative low intensity focused ultrasound (LOFU) therapy that induces unfolded protein response (UPR) and endoplasmic reticulum (ER) stress in LOFU-treated cells and reverses T cell anergy in draining lymph nodes in a mouse model of metastatic melanoma. To further extend our findings to other solid tumors, we hypothesized that a combination of acoustic stress and immune priming by non-ablative LOFU, followed by ablative RT will promote the release of heat shock proteins and other damage-associated molecular pattern (DAMP) factors along with tumor-associated antigens for launching a systemic anti-tumor response in a murine breast cancer (TSA).
Methods: TSA cells and palpable orthotopic mammary tumors in BALB/c thymic and athymic nude mice were treated with varying parameters of multi-frequency LOFU and RT (8-10 Gy/fraction), over 1-3 consecutive days. Cell surface immunomodulation of TSA cells and tumor infiltrating immune cell populations were analyzed with flow cytometry and tumor volumes were recorded to calculate growth delay along with survival.
Results: LOFU-treated TSA cells exhibited an increase in cell surface chaperones, BiP/GRP78, calreticulin, HSP70 and HSP90 at 24 hours post treatment. Furthermore, there was increased secretion of HMGB1, an immunomodulatory DAMP activator for dendritic cells. LOFU+RT-treated tumors had higher numbers of GP70 tetramer-positive CD8+ T cells by day 10 with higher levels of Ki67+ and GzB+ markers. In a dual tumor abscopal model, we observed significantly lower average tumor volumes of both the primary treated, and secondary untreated tumors, 35 days post treatment. There was a trend towards better tumor control and survival in mice with tumors treated with LOFU+RT, when compared to RT alone. Parallel studies in athymic immunodeficient mice failed to regress tumors treated with LOFU+RT.
Conclusions: LOFU + RT poses to be a promising combination therapy not only for elimination of primary tumor tissue but also the induction of a tumor-specific immune response. Further optimization of LOFU parameters is underway to maximize the immunogenic effects of LOFU+RT for combination therapy with immunotherapy.
Citation Format: Michelle M. Schumacher, Claudia Gutierrez Chavez, Saurabh Singh, Chandra Karunakaran, Sanjay Pandey, Mayank Kumar, Rodney Macedo Gonzales, Chandan Guha. Immune priming with low intensity focused ultrasound and radiation therapy in murine breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4201.