Abstract B032: Novel immunotherapy approach for metastatic triple-negative breast cancer

Abstract Currently, there are no curative therapies for metastatic triple-negative breast cancer (TNBC), which accounts for 10–15% of all breast cancers and has a higher rate of early recurrences. Durable responses to therapy of metastatic breast cancer are enhanced when an anti-tumor immune response is activated. However, not all patients treated with immunotherapies demonstrate durable responses. Therefore, it is essential to develop novel treatment regimens that are less toxic and more effective. We suggest that it is possible to immunize patients against their own TNBC metastases by using Focused Ultrasound (FUS) therapy to augment tumor antigen release. FUS is an emerging non-invasive, non-toxic treatment modality for localized treatment of cancers. Damaged tumor cells have been shown to release endogenous danger signals, which could stimulate an immune response, implying that the patient’s dying cancer cells serve as a therapeutic vaccine that stimulates an anti-tumor immune response. We hypothesize that FUS will augment tumor antigen release and danger signals to mediate the rejection of both FUS-treated and untreated tumors. We believe that this approach will increase the percentage of patients who will respond to immunotherapies by stimulating a TNBC-specific immune response. However, the optimum parameters to simulate this response are mostly unknown. Therefore, we conducted experiments to compare different FUS parameters with biological responses. Female Balb/c mice were inoculated orthotopically (1 or 2 mammary glands) with 4T1 cancer cells. When tumors became palpable, 1 mammary tumor received FUS treatments using a 1.14 MHz transducer (FUS Instruments, Canada). FUS was applied either in pulsed (44 W), or in continuous mode (20W). Following FUS treatment, necrosis, apoptosis, cytokines, gene expression, temperature, tumor growth, and metastasis were measured. We observed an increase in both necrosis (H&E) and apoptosis (Caspase-3) with FUS treatment when compared to untreated tumors. Next, we evaluated high mobility group box 1 (HMGB1) protein release in 4T1 cells in vitro to assess changes likely to result in signaling related to immunogenic cell death (ICD). We found that thermal dosing was capable of eliciting ICD, as indicated by the release of HMGB1, with an effect that peaked near 60°C. Our experiments also showed that there is a decrease in the size of secondary tumors as well as lung metastases in FUS-treated animals when compared to the controls (abscopal effect). The volcanic plots and heat maps showed that there are differences in gene expression between the control and FUS-treated groups. Serum Luminex analysis showed several cytokines (e.g., GM-CSF, MIP-1, IL-1a, IL-6, G-CSF) vital for immune responses changed in the FUS-treated group. These data suggest that FUS leads to increased immune responses and a decrease in the tumor size and the number of metastases. This paradigm shift has the potential to open treatment for metastatic TNBC. Citation Format: Paul Griffin, Riya Jain, Sean Le, Kyle Rajapakse, Wilson Miller, Kumari Andarawewa. Novel immunotherapy approach for metastatic triple-negative breast cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr B032.