Abstract PO1-24-02: Enhancement of TGF-β Receptor Inhibitor Efficacy through CD44 Suppression in Claudin-low Breast Cancer

Abstract Introduction: Claudin-low breast cancer is mostly classified as triple-negative breast cancer and is known to possess cancer stem cell properties with high expression of epithelial-to-mesenchymal transition (EMT) markers. However, specific therapeutic targets for this subtype have not yet been identified. While reports suggest that inhibition of EMT using EMT inhibitors can suppress cell and tumor proliferation, monotherapy may not be sufficient. The expression of CD44, a surface marker of cancer stem cells, has been reported to be involved in multiple signaling pathways, promoting cancer growth and invasion. In this study, we focus on CD44 and the TGF-β receptor, which is involved in EMT, to investigate the effect of inhibiting TGF-β receptor through CD44 inhibition in Claudin-low breast cancer and validate its potential as an effective treatment. Methods: SUM159 and MDA-MB-231 cell lines were used as Claudin-low breast cancer cell models. CD44 knockdown cells were established to examine the effects of TGF-β receptor inhibition and downstream signaling. Results: CD44 knockdown did not affect the expression of TGF-β receptor. Both SUM159 and MDA-MB-231 cells showed comparable cell growth inhibition through CD44 knockdown and TGF-β receptor inhibition, with enhanced effects observed in CD44 knockdown cells in response to TGF-β receptor inhibition. Furthermore, CD44 knockdown combined with TGF-β receptor inhibition significantly reduced the expression of Smad2/3. Conclusion: In Claudin-low breast cancer cells, CD44 knockdown enhances the effectiveness of TGF-β receptor inhibition and significantly influences the expression level of Smad2/3. Citation Format: Ryoichi Matsunuma, Sae Imada, Shoko Sato, Ryosuke Hayami, Michiko Tsuneizumi. Enhancement of TGF-β Receptor Inhibitor Efficacy through CD44 Suppression in Claudin-low 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 PO1-24-02.