Abstract PS4-03-25: Targeting Pro-Metastatic Stress Kinase Networks in Triple-Negative Breast Cancer Using Patient-Derived Models

Abstract Background: Metastatic triple-negative breast cancer (mTNBC) is one of the most challenging forms of breast cancer to treat due to profound heterogeneity and drug resistance. There have been very limited advancements in approval of targeted treatment regimens that are not chemotherapy-based for mTNBC in the past decade. Kinases are tractable therapeutic targets, but while kinase inhibitors have improved outcomes in many metastatic solid tumors including other breast cancer subtypes, they have not improved patient outcomes in TNBC clinical trials. We posit this is because we do not leverage understanding of complex kinase signaling networks and how we utilize kinase inhibitors in TNBC is not optimized. Further, high doses of kinase inhibitors to achieve cytotoxicity have unacceptable side effects for patients limiting real-world use. Chronic stress states such as those initiated by hypoxia, poor nutrient delivery and higher metabolic demands promote pro-metastatic transcriptional programs in TNBC. Our preclinical research and secondary analyses from clinical trial data reveal stress kinase signaling networks, and not individual pathways, drives TNBC metastatic transformation. Our central hypothesis is the RKIP/BACH1 signaling axis is a regulator of the chronic stress response to suppress TNBC metastasis and can be leveraged to produce biomarkers for risk stratification and a novel combination regimens. Methods: Prior work showed activation of the physiologic metastasis suppressor RKIP effectively reduced TNBC metastasis in cell line models through inhibition of stress MAPK networks (p38, JNK, ERK1/2, MLK) resulting in decreased transcription of the pro-metastatic transcription factor BACH1. We utilized mass spectrometry-based techniques with a kinase inhibitor system (MIB-MS) to characterize the activity of kinase signaling networks in heavily treated mTNBC organoids and examined kinase networks prominent in BACH1-high TNBC from publicly available phosphoproteomics datasets. We utilize live/dead, proliferation assays and transwell invasion assays to test efficacy of our stress kinase inhibitor regimen. Results: We show that combinations of 3 kinase inhibitors used in early phase clinical trials (Ralimetinib (p38), JNK-in-8 (JNK) or FDA approved (Trametinib (MEK & ERK1/2)) inhibit stress kinase networks, pro-motility gene expression and TNBC cell invasion. Low dose inhibition of multiple kinase nodes of networks, rather than single kinase nodes, more effectively reduces oncogenic signaling output and prevents compensatory signaling activation and potentiates suppression of organoid tumor initiating capacity when used in combination with chemotherapy. Using patient-derived organoids that recapitulate heterogeneous mTNBC molecular characteristics we successfully generated stable BACH1-knockout organoids which will be used to further identify BACH1-dependent critical kinase networks. Conclusions: Inhibition of these stress kinase networks should enable effective reprogramming of metastatic or high-risk cancers to more benign states and make tumors more susceptible to approved anti-proliferative therapies such as chemotherapy or immunotherapy while limiting toxicities from kinase inhibitors using a low-dose, multi-drug combination approach. Citation Format: M. Matossian, M. Bungert, C. Nguyen, G. Yerradoddi, M. East, D. Okumu, R. Nanda, G. Johnson, M. Rosner. Targeting Pro-Metastatic Stress Kinase Networks in Triple-Negative Breast Cancer Using Patient-Derived Models [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-03-25.