Abstract PO2-27-06: ANXA9 facilitates the exocrine secretion of S100A4 and promotes pleural metastasis in breast cancer

Abstract Metastasis to distant organs stands as the primary contributor to mortality in cases of breast cancer. While localized breast cancer boasts a 5-year survival rate of roughly 99%, this figure drastically declines to approximately 26% for patients afflicted with distant metastasis. Regrettably, the current therapeutic landscape lacks efficacious and targeted interventions for the treatment of metastatic breast cancer. Our investigation has revealed a significant upregulation of S100A4 in metastatic breast cancer tissues, with notably high expression observed in the malignant pleural effusion of patients in advanced stages of the disease. Upon acceptance of the effective treatment, the expression of S100A4 in malignant pleural effusion decreased, along with a decrease in several cytokines, including IL-6, IL-8, CCL2, and CCL5. The breast cancer cellular models demonstrated that ANXA9 has the ability to regulate the excretion of S100A4 from cells into the surrounding medium. Similarly, the mice model of pleural metastasis indicated that the downregulation of ANXA9 (sh-ANXA9) resulted in decreased levels of S100A4 and cytokines IL-6, IL-8, CCL2, and CCL5 in the mice's hydrothorax. Additionally, our findings suggest that ANXA9 regulates the excretion of S100A4 through phosphorylation of ANXA9. The cellular membrane harbored phosphorylated ANXA9, which exhibited two phosphorylation sites. Upon mutation of these sites, the level of ANXA9 phosphorylation decreased, leading to a reduction in the exocrine release of ANXA9 from cells into the medium. Our research further revealed the significant involvement of ANXA9 in facilitating the progression of breast cancer, thereby suggesting that therapeutic interventions targeting ANXA9 could prove efficacious in treating metastatic breast cancer. This work was supported by Shanghai Sailing Program to Dengfeng Li (No. 20YF1437800), grant from the National Natural Science Foundation of China to Dengfeng li (No. 82103454) and grant from the National Natural Science Foundation of China to Lin Fang (No. 82073204). Citation Format: Xiqian Zhou, Dengfeng Li, Lin Fang, Junyong Zhao. ANXA9 facilitates the exocrine secretion of S100A4 and promotes pleural metastasis in breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-27-06.